2020 Vol. 45, No. 9
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2020, 45(9): 3436-3450.
doi: 10.3799/dqkx.2020.242
Abstract:
The Hongqiyingzi Group in the Chongli area is located in the northern margin of the North China Craton. The rock association, structural characteristics and formation age of the Hongqiyingzi Group in the Chongli area are of great significance to study the tectonic evolution of the North China Craton from late Neoarchean to early Paleoproterozoic. In this paper, based on field, petrography, geochemistry, zircon U-Pb geochronology and Hf isotope analysis of these mafic rocks from the Hongqiyingzi Group in Chongli area, we study the origin and genesis of these rocks and discuss their tectonic implications on the late Neoarchean to early Paleoproterozoic crustal evolution of the North China Craton. The mafic rocks of the Hongqiyingzi Group are mainly composed of amphibolite and clinopyroxene amphibolite. The mafic rocks have a relatively wide range of geochemical compositions including SiO2 (40.17%－51.53%), Na2O (1.52%－3.47%) and K2O (0.43%－1.23%). These rocks have relatively high values of CaO (9.15%－12.68%), MgO (5.90%－13.36%) and Al2O3 (9.81%－20.92%), and are characterized by enrichment of large ion lithophile elements such as Ba, U, K, and Sr, depletion of high field strength elements such as Th, Nb, Ta, and Ti and flat heavy rare earth elements patterns. The LA-ICP-MS zircon U-Pb dating shows that the magmatic zircon of amphibolite was formed at 2 477±23 Ma, with the upper intercept age of 2 468±29 Ma, representing its formation age. The Hf isotopic analyses of amphibolite show that the εHf(t) values are negative (－5.2－0). The one-stage (TDM1) and two-stage Hf model ages (TDM2) are 2 673－2 783 Ma and 2 880－3 074 Ma, respectively, indicating that they were originated from recycling of the Archean crustal materials. In addition, the εHf(t) values of zircons suggest that a crustal accretion event occurred in the Neoarchean in the Chongli area. The geochemical characteristics indicate that these rocks were formed in an arc-related tectonic environment. Based on the research of other areas in the North China Craton, we suggest that a magmatic event related with arc environment may have occurred in the late Neoarchean to early Paleoproterozoic in the Chongli area.
The Hongqiyingzi Group in the Chongli area is located in the northern margin of the North China Craton. The rock association, structural characteristics and formation age of the Hongqiyingzi Group in the Chongli area are of great significance to study the tectonic evolution of the North China Craton from late Neoarchean to early Paleoproterozoic. In this paper, based on field, petrography, geochemistry, zircon U-Pb geochronology and Hf isotope analysis of these mafic rocks from the Hongqiyingzi Group in Chongli area, we study the origin and genesis of these rocks and discuss their tectonic implications on the late Neoarchean to early Paleoproterozoic crustal evolution of the North China Craton. The mafic rocks of the Hongqiyingzi Group are mainly composed of amphibolite and clinopyroxene amphibolite. The mafic rocks have a relatively wide range of geochemical compositions including SiO2 (40.17%－51.53%), Na2O (1.52%－3.47%) and K2O (0.43%－1.23%). These rocks have relatively high values of CaO (9.15%－12.68%), MgO (5.90%－13.36%) and Al2O3 (9.81%－20.92%), and are characterized by enrichment of large ion lithophile elements such as Ba, U, K, and Sr, depletion of high field strength elements such as Th, Nb, Ta, and Ti and flat heavy rare earth elements patterns. The LA-ICP-MS zircon U-Pb dating shows that the magmatic zircon of amphibolite was formed at 2 477±23 Ma, with the upper intercept age of 2 468±29 Ma, representing its formation age. The Hf isotopic analyses of amphibolite show that the εHf(t) values are negative (－5.2－0). The one-stage (TDM1) and two-stage Hf model ages (TDM2) are 2 673－2 783 Ma and 2 880－3 074 Ma, respectively, indicating that they were originated from recycling of the Archean crustal materials. In addition, the εHf(t) values of zircons suggest that a crustal accretion event occurred in the Neoarchean in the Chongli area. The geochemical characteristics indicate that these rocks were formed in an arc-related tectonic environment. Based on the research of other areas in the North China Craton, we suggest that a magmatic event related with arc environment may have occurred in the late Neoarchean to early Paleoproterozoic in the Chongli area.
2020, 45(9): 3451-3460.
doi: 10.3799/dqkx.2020.130
Abstract:
Resulting from an integration of geological survey and information technology, the Digital geological survey system (DGSS) can acquire throughout data for geological survey and field mapping, which is the characteristics of Big Data. At present, geological information has entered into data-driven times of Big Data application. In order to analyze, study and apply Big Data better, this paper introduces the work process of establishing spatial database and the contents of database based on DGSS, discusses the importance of establishing geological map spatial database and its key role of updating database in medium-small map, by extracting and applying different thematic maps and mapping 1:500 000 scale geological map of Ulanhot using data-driven technology.
Resulting from an integration of geological survey and information technology, the Digital geological survey system (DGSS) can acquire throughout data for geological survey and field mapping, which is the characteristics of Big Data. At present, geological information has entered into data-driven times of Big Data application. In order to analyze, study and apply Big Data better, this paper introduces the work process of establishing spatial database and the contents of database based on DGSS, discusses the importance of establishing geological map spatial database and its key role of updating database in medium-small map, by extracting and applying different thematic maps and mapping 1:500 000 scale geological map of Ulanhot using data-driven technology.
2020, 45(9): 3461-3474.
doi: 10.3799/dqkx.2019.052
Abstract:
It is generally accepted that the Jiangnan Orogenic Belt was formed by the amalgamation of the Yangtze and Cathaysian blocks during the Neoproterozoic period. However, the time of the amalgamation and its tectonic properties are still controversial. Comprehensive understanding of the formation mechanism of the Jiangnan Orogenic Belt is a prerequisite for exploring the Precambrian geological evolution, and also an important factor for in-depth analysis of the Phanerozoic geological nature in South China. The mineral composition and geochemical characteristics of sedimentary rocks can be used as a good indicator for the source of sediments and the tectonic setting of their formation. However, previous studies have been focused on the geochemistry-geochronology of magmatic rocks or the geochronology of clastic zircons in the strata, and the tracing of sediments is seldom reported. According to our integrated study on petrology, geochemistry, and zircon geochronology on the Xiaomuping Formation and Huanghudong Formation of Lengjiaxi Group from Pingjiang area, it is shown that (1) whole rock samples have high SiO2 (58.82%－70.62%) and Al2O3(13.35%－20.99%) contents, and high A/CN (3.8－12.4), K2O/Na2O (0.95－3.20), La/Sc (2.0－2.7) and Th/Sc (0.84－0.86) ratios, but low CaO, MgO and Na2O contents (0.19%－2.85%, 1.43%－2.13% and 1.44%－2.27%, respectively) and Co/Th (0.83－5.30) ratio; (2) these samples are enriched in LREE and have significant negative Eu anomaly, which is similar to those of the PAAS. (3) The maximum age peak of detrital zircon collection is 856 Ma and 861 Ma; Hence, we propose that the sedimentary rocks of the Lengjiaxi Group from the Jiangnan Orogen are derived from intermediate-felsic magmatic sources in an active continental margin setting at 860－830 Ma, and then experienced rapid erosion and relatively weak weathering processes.
It is generally accepted that the Jiangnan Orogenic Belt was formed by the amalgamation of the Yangtze and Cathaysian blocks during the Neoproterozoic period. However, the time of the amalgamation and its tectonic properties are still controversial. Comprehensive understanding of the formation mechanism of the Jiangnan Orogenic Belt is a prerequisite for exploring the Precambrian geological evolution, and also an important factor for in-depth analysis of the Phanerozoic geological nature in South China. The mineral composition and geochemical characteristics of sedimentary rocks can be used as a good indicator for the source of sediments and the tectonic setting of their formation. However, previous studies have been focused on the geochemistry-geochronology of magmatic rocks or the geochronology of clastic zircons in the strata, and the tracing of sediments is seldom reported. According to our integrated study on petrology, geochemistry, and zircon geochronology on the Xiaomuping Formation and Huanghudong Formation of Lengjiaxi Group from Pingjiang area, it is shown that (1) whole rock samples have high SiO2 (58.82%－70.62%) and Al2O3(13.35%－20.99%) contents, and high A/CN (3.8－12.4), K2O/Na2O (0.95－3.20), La/Sc (2.0－2.7) and Th/Sc (0.84－0.86) ratios, but low CaO, MgO and Na2O contents (0.19%－2.85%, 1.43%－2.13% and 1.44%－2.27%, respectively) and Co/Th (0.83－5.30) ratio; (2) these samples are enriched in LREE and have significant negative Eu anomaly, which is similar to those of the PAAS. (3) The maximum age peak of detrital zircon collection is 856 Ma and 861 Ma; Hence, we propose that the sedimentary rocks of the Lengjiaxi Group from the Jiangnan Orogen are derived from intermediate-felsic magmatic sources in an active continental margin setting at 860－830 Ma, and then experienced rapid erosion and relatively weak weathering processes.
2020, 45(9): 3475-3486.
doi: 10.3799/dqkx.2019.228
Abstract:
The Yueyawan Cu-Ni deposit is a newly discovered magmatic Cu-Ni sulfide deposit in Kalatage area of East Tianshan Mountain. In order to restrict the metallogenic age of the Yueyawan Cu-Ni deposit, LA-ICP-MS U-Pb and Re-Os isotopic dating had been conducted for zircons and pyrrhotite from the ore-forming olivine gabbro, respectively. The 206Pb/238U ages of zircons range from 255 Ma to 292 Ma, and yield an average weighted age of 274±2.4 Ma, which represents the diagenetic age of olivine gabbro. The isochron age of the Re-Os isotopic dating of pyrrhotite is 271.9±9.5 Ma, which represents the age of Cu-Ni mineralization. The initial 187Os/188Os ratio is 0.279 6±0.008 9, and γOs value is 117-126, indicating that crustal materials had been involved into the sulfide mineralization. The diagenesis and metallogenesis of mafic magma in Yueyawan occurred in Early Permian, contemporary with the typical Cu-Ni sulfide deposits in Huangshan-Tulaergen area of East Tianshan Mountain.
The Yueyawan Cu-Ni deposit is a newly discovered magmatic Cu-Ni sulfide deposit in Kalatage area of East Tianshan Mountain. In order to restrict the metallogenic age of the Yueyawan Cu-Ni deposit, LA-ICP-MS U-Pb and Re-Os isotopic dating had been conducted for zircons and pyrrhotite from the ore-forming olivine gabbro, respectively. The 206Pb/238U ages of zircons range from 255 Ma to 292 Ma, and yield an average weighted age of 274±2.4 Ma, which represents the diagenetic age of olivine gabbro. The isochron age of the Re-Os isotopic dating of pyrrhotite is 271.9±9.5 Ma, which represents the age of Cu-Ni mineralization. The initial 187Os/188Os ratio is 0.279 6±0.008 9, and γOs value is 117-126, indicating that crustal materials had been involved into the sulfide mineralization. The diagenesis and metallogenesis of mafic magma in Yueyawan occurred in Early Permian, contemporary with the typical Cu-Ni sulfide deposits in Huangshan-Tulaergen area of East Tianshan Mountain.
2020, 45(9): 3487-3501.
doi: 10.3799/dqkx.2019.229
Abstract:
Quartz overgrowth is a common and important cementation in sandstone reservoirs. On the basis of micro-observation on different oil saturation sandstone thin sections from the Es3 interval of the Central Anticlinal Belt in Dongying depression, the width and the content of quartz overgrowth were quantified and the temperature of fluid inclusions were measured. Then the characteristics of quartz overgrowth, the stage of quartz overgrowth and the possible source of silica required for quartz overgrowth were analyzed. The width and the content of quartz overgrowth vary significantly with a range 4－90 μm and 2.50－39 927.80 μm2, respectively. There are two main stages of secondary quartz overgrowth related to oil and gas filling in sandstone. Combined with burial-temperature histories, the two stages of quartz overgrowth are 15－6 Ma and 4－0 Ma, respectively. The dissolution of potash feldspar and the transformation of clay minerals in sandstone and mudstone layers of the Es3 interval are the main siliceous sources for the quartz overgrowth. The characteristics of quartz overgrowth in different oil saturation sandstone can be concluded into the similarity and difference: (1) The overall distribution of maximum width of quartz overgrowth and the area of each quartz overgrowth in different oil saturation sandstone are the same; (2) the width and the area of quartz overgrowth are generally different from each other. Porosity and permeability of sandstone, acidic water environment caused by hydrocarbon-bearing fluid filling and oil-water distribution characteristics are the main reasons for the similarity and difference of quartz overgrowth in sandstones with different oil saturation. And the quartz overgrowth can be regarded as trace marker of hydrocarbon-bearing fluid filling.
Quartz overgrowth is a common and important cementation in sandstone reservoirs. On the basis of micro-observation on different oil saturation sandstone thin sections from the Es3 interval of the Central Anticlinal Belt in Dongying depression, the width and the content of quartz overgrowth were quantified and the temperature of fluid inclusions were measured. Then the characteristics of quartz overgrowth, the stage of quartz overgrowth and the possible source of silica required for quartz overgrowth were analyzed. The width and the content of quartz overgrowth vary significantly with a range 4－90 μm and 2.50－39 927.80 μm2, respectively. There are two main stages of secondary quartz overgrowth related to oil and gas filling in sandstone. Combined with burial-temperature histories, the two stages of quartz overgrowth are 15－6 Ma and 4－0 Ma, respectively. The dissolution of potash feldspar and the transformation of clay minerals in sandstone and mudstone layers of the Es3 interval are the main siliceous sources for the quartz overgrowth. The characteristics of quartz overgrowth in different oil saturation sandstone can be concluded into the similarity and difference: (1) The overall distribution of maximum width of quartz overgrowth and the area of each quartz overgrowth in different oil saturation sandstone are the same; (2) the width and the area of quartz overgrowth are generally different from each other. Porosity and permeability of sandstone, acidic water environment caused by hydrocarbon-bearing fluid filling and oil-water distribution characteristics are the main reasons for the similarity and difference of quartz overgrowth in sandstones with different oil saturation. And the quartz overgrowth can be regarded as trace marker of hydrocarbon-bearing fluid filling.
2020, 45(9): 3502-3508.
doi: 10.3799/dqkx.2019.121
Abstract:
To solve the problem of drilling in severely cracked hard rock in deep high temperature and high pressure (HTHP) stratum of Well Songke-2, mechanical analysis and physical simulation experiment were used to clarify the factors affecting the thickness of the plugging layer in this study. The sealing effect of high-strength skeleton particles and HT deformable soften particles was verified through HTHP filtration test, and the on-site operation pressure was calculated and controlled. The self-locking mechanical model of the three-particle bridge group skeleton was established, and the anti-destructive ability formula of the single bridge group was derived. Compared with the blank formula, emulsified asphalt, oxidized asphalt and sulfonated asphalt can reduce the HTHP water loss volume by 56%, 44% and 48%, respectively. Particle size and strength, crack width and pressure difference have important influence on the thickness of the plugging layer. A quick blocking effect can be achieved by combining the rigid plugging agent with deformable plugging particles. Based on the above analysis and tests, the drilling pressure in the operation was effectively controlled in conjunction with the on-site technology, and the compaction and anti-collapse effect under moderate positive pressure difference was realized. With the techniques mentioned above, the fifth spud of Well Songke-2 was completed successfully with the open-hole section from 5 910 to 7 018 m.
To solve the problem of drilling in severely cracked hard rock in deep high temperature and high pressure (HTHP) stratum of Well Songke-2, mechanical analysis and physical simulation experiment were used to clarify the factors affecting the thickness of the plugging layer in this study. The sealing effect of high-strength skeleton particles and HT deformable soften particles was verified through HTHP filtration test, and the on-site operation pressure was calculated and controlled. The self-locking mechanical model of the three-particle bridge group skeleton was established, and the anti-destructive ability formula of the single bridge group was derived. Compared with the blank formula, emulsified asphalt, oxidized asphalt and sulfonated asphalt can reduce the HTHP water loss volume by 56%, 44% and 48%, respectively. Particle size and strength, crack width and pressure difference have important influence on the thickness of the plugging layer. A quick blocking effect can be achieved by combining the rigid plugging agent with deformable plugging particles. Based on the above analysis and tests, the drilling pressure in the operation was effectively controlled in conjunction with the on-site technology, and the compaction and anti-collapse effect under moderate positive pressure difference was realized. With the techniques mentioned above, the fifth spud of Well Songke-2 was completed successfully with the open-hole section from 5 910 to 7 018 m.
2020, 45(9): 3119-3160.
doi: 10.3799/dqkx.2020.121
Abstract:
The North China Craton (NCC) has a long-term formation and evolution history up to 3.8 Ga rock records, with 4.0-4.1 Ga zircons. This paper summarizes the Archean tectonothermal events of the Craton, mainly focusing on the timing of the events. The oldest metamorphic zircon ages are 3.71-3.75 Ga and 4.0 Ga identified for detrital or xenocrystic zircons from Paleozoic meta-volcano-sedimentary rock in western segment of the North Qinling Belt near the southern margin of the NCC. Paleoarchean (~3.3 Ga) tectonothermal event widely occurs in the Anshan area, resulting in formation of banded trondhjemite gneisses. Early Neoarchean-late Mesoarchean metamorphic zircon ages can be subdivided into two groups: 2.65-2.85 Ga and ~2.6 Ga. 2.65-2.85 Ga metamorphic zircon ages have been obtained in western Shandong, eastern Shandong and Lushan. It is difficult to determine the exact age of tectonothermal event because of strong overprinting of the late Neoarchean. However, late Mesoarchean to early Neoarchean tectonothermal event must have occurred in the NCC. Compared with the 2.65-2.85 Ga tectonothermal events, the ~2.6 Ga event was more clearly developed in the NCC, such as in eastern Shandong and Lushan, besides being widely identified in western Shandong. 2.6 Ga is a convenient time to set as the early Neoarchean-late Neoarchean boundary. The most important Archean tectonothermal events occurred at the late Neoarchean (2.49-2.53 Ga), which have been identified in every Archean basement area of the NCC. In general, its northern domain recorded higher-grade metamorpism than its southern domain probably due to the former exposuring deeper crustal level. In the NCC, metamorphic intensity and scope became stronger and larger with time going on, peaking at the end of the Noearchean, consistent with the Archean continental crust becoming larger in thickness and scale with time. In some areas where the late Paleoproterozoic tectonothermal event was well developed, some metamorphic zircons recorded the earlest Paleoproterozic and even younger ages (2.40-2.47 Ga). This may not mean the existence of these events, but is a result of strong overprinting of the late Paleoproterozoic events.
The North China Craton (NCC) has a long-term formation and evolution history up to 3.8 Ga rock records, with 4.0-4.1 Ga zircons. This paper summarizes the Archean tectonothermal events of the Craton, mainly focusing on the timing of the events. The oldest metamorphic zircon ages are 3.71-3.75 Ga and 4.0 Ga identified for detrital or xenocrystic zircons from Paleozoic meta-volcano-sedimentary rock in western segment of the North Qinling Belt near the southern margin of the NCC. Paleoarchean (~3.3 Ga) tectonothermal event widely occurs in the Anshan area, resulting in formation of banded trondhjemite gneisses. Early Neoarchean-late Mesoarchean metamorphic zircon ages can be subdivided into two groups: 2.65-2.85 Ga and ~2.6 Ga. 2.65-2.85 Ga metamorphic zircon ages have been obtained in western Shandong, eastern Shandong and Lushan. It is difficult to determine the exact age of tectonothermal event because of strong overprinting of the late Neoarchean. However, late Mesoarchean to early Neoarchean tectonothermal event must have occurred in the NCC. Compared with the 2.65-2.85 Ga tectonothermal events, the ~2.6 Ga event was more clearly developed in the NCC, such as in eastern Shandong and Lushan, besides being widely identified in western Shandong. 2.6 Ga is a convenient time to set as the early Neoarchean-late Neoarchean boundary. The most important Archean tectonothermal events occurred at the late Neoarchean (2.49-2.53 Ga), which have been identified in every Archean basement area of the NCC. In general, its northern domain recorded higher-grade metamorpism than its southern domain probably due to the former exposuring deeper crustal level. In the NCC, metamorphic intensity and scope became stronger and larger with time going on, peaking at the end of the Noearchean, consistent with the Archean continental crust becoming larger in thickness and scale with time. In some areas where the late Paleoproterozoic tectonothermal event was well developed, some metamorphic zircons recorded the earlest Paleoproterozic and even younger ages (2.40-2.47 Ga). This may not mean the existence of these events, but is a result of strong overprinting of the late Paleoproterozoic events.
2020, 45(9): 3161-3178.
doi: 10.3799/dqkx.2020.254
Abstract:
The formation of the voluminous syenogranites of the late Neoarchean is an important mark of maturation and stabilization of continental crust, and play a vital role in understanding the formation and evolution of early continental crust. However, the formation age and genesis of the Yanzhuang syenogranite in the Sushui Complex in the southern margin of the North China Craton are not well defined, and the tectonic setting remains controversial. This paper presents the zircon U-Pb ages and Hf isotopes as well as whole rock element and Nd isotope compositions of the Yanzhuang syenogranites. SHRIMP dating of zircon from the granite yields an age of 2 515±7 Ma. The rocks are high in SiO2 (73.05%－74.85%) and K2O (4.46%－5.86%) and low in CaO (0.55%－0.98%), total FeO (0.73%－1.28%) and MgO (0.31%－0.52%), with K2O+Na2O and A/CNK at 8.32%－9.36% and 1.01－1.04, respectively. They show variations in REE contents (ΣREE=63.8×10-6－250.02×10-6), with relative enrichment of LREE to HREE ((La/Yb)N=25.44－92.87) and somewhat negative Eu anomaly (Eu/Eu*=0.47－0.79). The rocks are low in Sr and Ba, and high in Rb, Th and U, with depletion in Nb, Zr, Y, Yb, Cr, Co and Ni. Thus they have high Rb/Sr, Rb/Ba and Sr/Yb ratios and low Sm/Nd and Nd/Th ratios, and show the characteristics of highly fractionated I type granite. The Yanzhuang syenogranite has whole-rock εNd(t) values of -1.09－0.89 and magmatic zircon εHf(t) values of 2.85－3.66, with Hf model TDM2 ages of 2 258－2 883 Ma (mainly 2 600－2 883 Ma). Combined with early work, this study indicates that the Yanzhuang syenogranite shows the feature of syn-collision and post-collision granites formed by partial melting of juvenile crust in a tectonic transition setting from compression to extension, probably with addition of a small amount of mantle material. The formation of voluminous syenogranites in this period marks the termination of the Archean intense magmatism and the stabilization of the North China Craton at the end of the Neoarchean.
The formation of the voluminous syenogranites of the late Neoarchean is an important mark of maturation and stabilization of continental crust, and play a vital role in understanding the formation and evolution of early continental crust. However, the formation age and genesis of the Yanzhuang syenogranite in the Sushui Complex in the southern margin of the North China Craton are not well defined, and the tectonic setting remains controversial. This paper presents the zircon U-Pb ages and Hf isotopes as well as whole rock element and Nd isotope compositions of the Yanzhuang syenogranites. SHRIMP dating of zircon from the granite yields an age of 2 515±7 Ma. The rocks are high in SiO2 (73.05%－74.85%) and K2O (4.46%－5.86%) and low in CaO (0.55%－0.98%), total FeO (0.73%－1.28%) and MgO (0.31%－0.52%), with K2O+Na2O and A/CNK at 8.32%－9.36% and 1.01－1.04, respectively. They show variations in REE contents (ΣREE=63.8×10-6－250.02×10-6), with relative enrichment of LREE to HREE ((La/Yb)N=25.44－92.87) and somewhat negative Eu anomaly (Eu/Eu*=0.47－0.79). The rocks are low in Sr and Ba, and high in Rb, Th and U, with depletion in Nb, Zr, Y, Yb, Cr, Co and Ni. Thus they have high Rb/Sr, Rb/Ba and Sr/Yb ratios and low Sm/Nd and Nd/Th ratios, and show the characteristics of highly fractionated I type granite. The Yanzhuang syenogranite has whole-rock εNd(t) values of -1.09－0.89 and magmatic zircon εHf(t) values of 2.85－3.66, with Hf model TDM2 ages of 2 258－2 883 Ma (mainly 2 600－2 883 Ma). Combined with early work, this study indicates that the Yanzhuang syenogranite shows the feature of syn-collision and post-collision granites formed by partial melting of juvenile crust in a tectonic transition setting from compression to extension, probably with addition of a small amount of mantle material. The formation of voluminous syenogranites in this period marks the termination of the Archean intense magmatism and the stabilization of the North China Craton at the end of the Neoarchean.
2020, 45(9): 3179-3195.
doi: 10.3799/dqkx.2020.240
Abstract:
In this paper, we summarize the evolutionary history on Fuping Complex from the early Neoarchean to late Paleoproterozoic by comprehensive analyses of data collected on its geochemistry, zircon U-Pb dating, isotopic geochemistry and metamorphism. It is found that the protolith of ca. 2.7 Ga gneisses are tonalite with the geochemical features of TTG, and zircons in these gneisses show positive εHf(t) values of 5.44 to 7.50, with single stage model age (TDM) of 2 745-2 824 Ma, which indicates the intensive crustal growth in early Neoarchean in the Fuping Complex. The late Neoarchean gneisses yield the age of 2 543-2 484 Ma and are mainly composed of tonalite-trondjemite-granodiorite (TTG) besides some monzogranite. TTG gneisses have εNd(t) values ranging from -1.64 to +0.96, with single stage model age (TDM) of 2.76-3.04 Ga, and zircon εHf(t) of -1.9-+7.91, with single stage model age (THf1) and two stage model age (THf2) of 2 546-2 888 Ma and 2 548-3 119 Ma, respectively. Thus, these TTG are derived from partial melting of the early Neoarchean rocks with some addition of Mesoarchean crust. Gabbro coeval with TTG gneisses displays the features of island arc magma and ca. 2.5 Ga metamorphism in Neoarchean supracrustal rocks, suggesting that the Fuping Complex underwent subduction and arc-continent or continent-continent collision in late Neoarchean. 2.1-2.0 Ga granitoids widely occur in the Fuping Complex with the feartures of A-type granite and the simultaneous volcanic-sedimentary rocks formed intra-continental rift environment in middle Paleoproterozoic. Mafic granulite enclaves in the Fuping Complex yield metamorphic age of 1.89-1.85 Ga and show clockwise P-T paths, which represents closure of intra-continent rifts and cratonization of the North China Craton in late Paleoproterozoic.
In this paper, we summarize the evolutionary history on Fuping Complex from the early Neoarchean to late Paleoproterozoic by comprehensive analyses of data collected on its geochemistry, zircon U-Pb dating, isotopic geochemistry and metamorphism. It is found that the protolith of ca. 2.7 Ga gneisses are tonalite with the geochemical features of TTG, and zircons in these gneisses show positive εHf(t) values of 5.44 to 7.50, with single stage model age (TDM) of 2 745-2 824 Ma, which indicates the intensive crustal growth in early Neoarchean in the Fuping Complex. The late Neoarchean gneisses yield the age of 2 543-2 484 Ma and are mainly composed of tonalite-trondjemite-granodiorite (TTG) besides some monzogranite. TTG gneisses have εNd(t) values ranging from -1.64 to +0.96, with single stage model age (TDM) of 2.76-3.04 Ga, and zircon εHf(t) of -1.9-+7.91, with single stage model age (THf1) and two stage model age (THf2) of 2 546-2 888 Ma and 2 548-3 119 Ma, respectively. Thus, these TTG are derived from partial melting of the early Neoarchean rocks with some addition of Mesoarchean crust. Gabbro coeval with TTG gneisses displays the features of island arc magma and ca. 2.5 Ga metamorphism in Neoarchean supracrustal rocks, suggesting that the Fuping Complex underwent subduction and arc-continent or continent-continent collision in late Neoarchean. 2.1-2.0 Ga granitoids widely occur in the Fuping Complex with the feartures of A-type granite and the simultaneous volcanic-sedimentary rocks formed intra-continental rift environment in middle Paleoproterozoic. Mafic granulite enclaves in the Fuping Complex yield metamorphic age of 1.89-1.85 Ga and show clockwise P-T paths, which represents closure of intra-continent rifts and cratonization of the North China Craton in late Paleoproterozoic.
2020, 45(9): 3196-3216.
doi: 10.3799/dqkx.2020.228
Abstract:
The Jiaobei is a typical Precambrian metamorphic terrane in the North China Craton that records multiple high-grade metamorphic events. It is of great scientific significance to determine the nature, timing of each metamorphic event in order to further understand the geological evolution of the early Precambrian in the Jiaobei Terrane and even the North China Craton. A combined study of mineral inclusions, cathodoluminescence (CL) images, LA-ICP-MS U-Pb dating, and in-situ rare earth element (REE) compositions of zircons provides clear evidence on the timing of the metamorphism and partial melting in the Qixia garnet amphibolites and related granitic leucosomes. The zircons separated from garnet amphibolites (19LR53-1) can be subdivided into two distinct zircon domains: The late Neoarchean zircons are rounded in shape and black-luminescent in CL images, eighteen late Neoarchean zircons record a consistent 207Pb/206Pb age, ranging from 2 540±58 Ma to 2 439±54 Ma with a weighted average age of 2 498±25 Ma, which represents the late Neoarchean metamorphic timing of the garnet amphibolites. In contrast, the late Paleoproterozoic zircons usually have columnar crystals and relatively high (grey-off-white) cathodoluminescence in CL image. Fourteen late Paleoproterozoic zircons record a consistent 207Pb/206Pb age, ranging from 1 906±54 Ma to 1 821±60 Ma with a weighted average age of 1 865±30 Ma, which represents the retrogressive timing of garnet amphibolites during late Paleoproterozoic cratonization. The zircons in the granitic leucosomes (19LR53-2) have irregular crystal shapes and relatively weak (gray-black) cathodoluminescence in the CL image. Some of them contain felsic mineral inclusions, such as K-feldspar+plagiclase+quartz+apatite. Eighteen zircons from the granitic leucosomes record a consistent 207Pb/206Pb age, ranging from 2 521±48 Ma to 2 453±42 Ma with a weighted average age of 2 480±22 Ma. The age is interpretated as the late Neoarchean anatectic timing of the Jiaobei terrane, which, together with the published data, suggests that the Archean basement rocks of the Jiaobei terrane have not only experienced the high-grade metamorphism and crustal anatexis in the late Neoarchean, but also overprinted the high-grade metamorphism and crustal anatexis in the late Paleoproterozoic. They may be the geological responses of the two cratonizations of the North China Craton.
The Jiaobei is a typical Precambrian metamorphic terrane in the North China Craton that records multiple high-grade metamorphic events. It is of great scientific significance to determine the nature, timing of each metamorphic event in order to further understand the geological evolution of the early Precambrian in the Jiaobei Terrane and even the North China Craton. A combined study of mineral inclusions, cathodoluminescence (CL) images, LA-ICP-MS U-Pb dating, and in-situ rare earth element (REE) compositions of zircons provides clear evidence on the timing of the metamorphism and partial melting in the Qixia garnet amphibolites and related granitic leucosomes. The zircons separated from garnet amphibolites (19LR53-1) can be subdivided into two distinct zircon domains: The late Neoarchean zircons are rounded in shape and black-luminescent in CL images, eighteen late Neoarchean zircons record a consistent 207Pb/206Pb age, ranging from 2 540±58 Ma to 2 439±54 Ma with a weighted average age of 2 498±25 Ma, which represents the late Neoarchean metamorphic timing of the garnet amphibolites. In contrast, the late Paleoproterozoic zircons usually have columnar crystals and relatively high (grey-off-white) cathodoluminescence in CL image. Fourteen late Paleoproterozoic zircons record a consistent 207Pb/206Pb age, ranging from 1 906±54 Ma to 1 821±60 Ma with a weighted average age of 1 865±30 Ma, which represents the retrogressive timing of garnet amphibolites during late Paleoproterozoic cratonization. The zircons in the granitic leucosomes (19LR53-2) have irregular crystal shapes and relatively weak (gray-black) cathodoluminescence in the CL image. Some of them contain felsic mineral inclusions, such as K-feldspar+plagiclase+quartz+apatite. Eighteen zircons from the granitic leucosomes record a consistent 207Pb/206Pb age, ranging from 2 521±48 Ma to 2 453±42 Ma with a weighted average age of 2 480±22 Ma. The age is interpretated as the late Neoarchean anatectic timing of the Jiaobei terrane, which, together with the published data, suggests that the Archean basement rocks of the Jiaobei terrane have not only experienced the high-grade metamorphism and crustal anatexis in the late Neoarchean, but also overprinted the high-grade metamorphism and crustal anatexis in the late Paleoproterozoic. They may be the geological responses of the two cratonizations of the North China Craton.
2020, 45(9): 3217-3238.
doi: 10.3799/dqkx.2020.096
Abstract:
Precambrian orogenesis has always been a hot and challenging issue in the study of accretionary and collisional orogenic belts. In this paper, we study the volcanic-sedimentary rocks in the Paleoproterozoic Jiao-Liao-Ji orogenic belt at the Helan Town in the Liaodong Peninsula using methods of detailed mapping in the field and age dating indoors, and finally decipher the Paleoproterozoic evolution of this area in the eastern China Block of the North China Craton. Many syn-depositional structures such as asymmetric folds, isoclinal folds, and inter-bedding slip lineations were recognized and classified as syn-depositional structures based on our detailed field structural analysis of the volcanic rocks from the Li'eryu Formation, calcareous mudstones from the Gaojiayu Formation, and carbonates from the Dashiqiao Formation. We further classified these structures as D1-0, which formed in an extensional process at the early opening stage of the Liaoji back-arc basin. Based on detailed field mapping of the intrusive mafic rocks and its related eruption "pillow lava" in the Pushihe area of Helan Town, it was proposed that the eruption of the basic "pillow lava" indicates that the Liaoji back-arc basin turned into the maximum extension stage. Besides, a large number of thrust nappe structures and asymmetric fault-propagation folds were observed in the volcanic rocks of the Li'eryu Formation, the calcareous mudstones of the Gaojiayu Formation, and the carbonates of the Dashiqiao Formation in the Liaohe Group, and were defined as D1-1 or D1-2. These structures indicate the contraction of the Liaoji back-arc basin, also imply the beginning of the Paleoproterozoic orogenesis. Detrital zircon study of the Gaojiayu Formation indicates that the predominated provenance of the clastics was from a 2.5 Ga basement, and few of them were from the 2.17 Ga volcanic rocks. Combined with petro-geochemistry and geochronology data in our study area, it is concluded that the opening and closure of the Liaoji back-arc basin recorded a complete Paleoproterozoic orogenesis process and also indicated the plate tectonic initiation at the time.
Precambrian orogenesis has always been a hot and challenging issue in the study of accretionary and collisional orogenic belts. In this paper, we study the volcanic-sedimentary rocks in the Paleoproterozoic Jiao-Liao-Ji orogenic belt at the Helan Town in the Liaodong Peninsula using methods of detailed mapping in the field and age dating indoors, and finally decipher the Paleoproterozoic evolution of this area in the eastern China Block of the North China Craton. Many syn-depositional structures such as asymmetric folds, isoclinal folds, and inter-bedding slip lineations were recognized and classified as syn-depositional structures based on our detailed field structural analysis of the volcanic rocks from the Li'eryu Formation, calcareous mudstones from the Gaojiayu Formation, and carbonates from the Dashiqiao Formation. We further classified these structures as D1-0, which formed in an extensional process at the early opening stage of the Liaoji back-arc basin. Based on detailed field mapping of the intrusive mafic rocks and its related eruption "pillow lava" in the Pushihe area of Helan Town, it was proposed that the eruption of the basic "pillow lava" indicates that the Liaoji back-arc basin turned into the maximum extension stage. Besides, a large number of thrust nappe structures and asymmetric fault-propagation folds were observed in the volcanic rocks of the Li'eryu Formation, the calcareous mudstones of the Gaojiayu Formation, and the carbonates of the Dashiqiao Formation in the Liaohe Group, and were defined as D1-1 or D1-2. These structures indicate the contraction of the Liaoji back-arc basin, also imply the beginning of the Paleoproterozoic orogenesis. Detrital zircon study of the Gaojiayu Formation indicates that the predominated provenance of the clastics was from a 2.5 Ga basement, and few of them were from the 2.17 Ga volcanic rocks. Combined with petro-geochemistry and geochronology data in our study area, it is concluded that the opening and closure of the Liaoji back-arc basin recorded a complete Paleoproterozoic orogenesis process and also indicated the plate tectonic initiation at the time.
2020, 45(9): 3239-3257.
doi: 10.3799/dqkx.2020.125
Abstract:
Paleoproterozoic is an important orogenic tectonic evolution stage during the formation of the North China Craton. The mafic dyke swarms formed during this period provide important information to understanding the tectonic-magmatic process of rifting-subduction-collision-exhumation of the orogeny. This study reports the metamorphic mafic dykes (two-pyroxene granulite) widely distributed in the Neoarchean-Paleoproterozoic metamorphic base in the Tianzhen-Huai'an area. These dykes occur consistently with regional main tectonic foliation in the field and are mainly composed of clinopyroxene+orthopyroxene+plagioclase+amphibole. The metamorphic age of the mafic dyke is 1 820-1 834 Ma obtained by LA-MC-ICPMS zircon U-Pb isotope dating, which is consistent with the granulite facies metamorphic event in the study area. Based on the analyses of regional mafic dyke age data, we consider that the emplacement age is around 1.95-1.91 Ga. This study documents two types of metamorphic mafic dykes: high Mg low Ti type and low Mg high Ti type. They have experienced different degrees of fractional crystallization of olivine, clinopyroxene and plagioclase. Both types of mafic dykes show negative anomalies in high-field-strength elements (such as Nb, Ta, Ti, Zr, and Hf). According to the zircon Hf isotopic and the geochemical features, we suggest that the mafic dykes originated from a lithospheric mantle metasomatized by subduction fluids, or/and they were contaminated by the crust. Two episodes of metamorphosed mafic dykes are identified in the North China Craton: 2.16-2.04 Ga and 1.97-1.83 Ga. The early stage represents an intra-plate rifting process that occurred on the basis of the initial Craton; in contrast, the later period records transformation from subduction-collision to extensional setting, that is the collisional orogenic tectonic regime changed from horizontal compression to vertical uplift, and the tectonic transition time is roughly around 1.95-1.91 Ga.
Paleoproterozoic is an important orogenic tectonic evolution stage during the formation of the North China Craton. The mafic dyke swarms formed during this period provide important information to understanding the tectonic-magmatic process of rifting-subduction-collision-exhumation of the orogeny. This study reports the metamorphic mafic dykes (two-pyroxene granulite) widely distributed in the Neoarchean-Paleoproterozoic metamorphic base in the Tianzhen-Huai'an area. These dykes occur consistently with regional main tectonic foliation in the field and are mainly composed of clinopyroxene+orthopyroxene+plagioclase+amphibole. The metamorphic age of the mafic dyke is 1 820-1 834 Ma obtained by LA-MC-ICPMS zircon U-Pb isotope dating, which is consistent with the granulite facies metamorphic event in the study area. Based on the analyses of regional mafic dyke age data, we consider that the emplacement age is around 1.95-1.91 Ga. This study documents two types of metamorphic mafic dykes: high Mg low Ti type and low Mg high Ti type. They have experienced different degrees of fractional crystallization of olivine, clinopyroxene and plagioclase. Both types of mafic dykes show negative anomalies in high-field-strength elements (such as Nb, Ta, Ti, Zr, and Hf). According to the zircon Hf isotopic and the geochemical features, we suggest that the mafic dykes originated from a lithospheric mantle metasomatized by subduction fluids, or/and they were contaminated by the crust. Two episodes of metamorphosed mafic dykes are identified in the North China Craton: 2.16-2.04 Ga and 1.97-1.83 Ga. The early stage represents an intra-plate rifting process that occurred on the basis of the initial Craton; in contrast, the later period records transformation from subduction-collision to extensional setting, that is the collisional orogenic tectonic regime changed from horizontal compression to vertical uplift, and the tectonic transition time is roughly around 1.95-1.91 Ga.
2020, 45(9): 3258-3267.
doi: 10.3799/dqkx.2020.135
Abstract:
The petrogenesis of Paleoproterozoic remelting granite in Jining-Liangcheng area has been interpreted differently in academia. Geochronologic and geochemical studies of two types of remelting granite are presented in this paper. Zircon LA-MC-ICP-MS U-Pb isotopic dating reveals that the porphyritic charnockites emplaced at 1 954 Ma and were metamorphosed at 1 827 Ma, and the meta-leucogranites emplaced at 1 956 Ma. The porphyritic charnockites are characterized by low Si contents, high Fe and Mg contents, with negative Eu anomalies and relative depletion of Sr. The meta-leucogranites have high content of Si and low contents of Fe and Mg, strong depletion in high filed-strength elements (HFSE, such as Nb, Ta and Ti) and enrichment in large iron lithophile elements (LILE, such as K, Rb and Ba). Both two types of granite were generated in the same period, from the remelting associated with mantle-source magma underplating. The source magma of the porphyritic charnockites was mixed with certain amount of mantle contribution during remelting of meta-sediments of khondalite series, before fractional crystallization. And the source magma of the meta-leucogranites was generated mainly from remelting of meta-sediments of khondalite series, with limited influence of mantle contribution.
The petrogenesis of Paleoproterozoic remelting granite in Jining-Liangcheng area has been interpreted differently in academia. Geochronologic and geochemical studies of two types of remelting granite are presented in this paper. Zircon LA-MC-ICP-MS U-Pb isotopic dating reveals that the porphyritic charnockites emplaced at 1 954 Ma and were metamorphosed at 1 827 Ma, and the meta-leucogranites emplaced at 1 956 Ma. The porphyritic charnockites are characterized by low Si contents, high Fe and Mg contents, with negative Eu anomalies and relative depletion of Sr. The meta-leucogranites have high content of Si and low contents of Fe and Mg, strong depletion in high filed-strength elements (HFSE, such as Nb, Ta and Ti) and enrichment in large iron lithophile elements (LILE, such as K, Rb and Ba). Both two types of granite were generated in the same period, from the remelting associated with mantle-source magma underplating. The source magma of the porphyritic charnockites was mixed with certain amount of mantle contribution during remelting of meta-sediments of khondalite series, before fractional crystallization. And the source magma of the meta-leucogranites was generated mainly from remelting of meta-sediments of khondalite series, with limited influence of mantle contribution.
2020, 45(9): 3268-3281.
doi: 10.3799/dqkx.2020.140
Abstract:
The study on the formation age and petrogenetic mechanism of early Precambrian rocks in the southeast margin of Tarim block is relatively weak, which restricts the understanding of the formation and early evolution of continental crust. These geochemistry and zircon Hf isotope compositions show that primary magma of the quartz diorite gneiss was formed by partial melting of the lower crust meta-basalt with minor addition of mantle-derived materials. LA-ICP-MS zircon U-Pb dating results reveal that the diagenetic ages of the quartz diorite gneiss are 2 662±12 Ma and 2 676±15 Ma, indicating the Archean rock formation ages in the southeastern margin of Tarim were mainly concentrated in 2.55－2.70 Ga; corresponding metamorphic ages are 1 980±30 Ma and 1 828±20 Ma－2 087±29 Ma respectively, representing the geological record of magmatic-matamorphic events related to orogenic processes in the middle and late period of Paleoproterozoic in the southeastern margin of Tarim. Additionally, two-stage model ages(TDM2)of zircon for the quartz diorite gneiss in this study vary from 2 954 to 3 742 Ma, with peak ages clustering at ~3.24 Ga. Thus, combined with the available data, it is suggested that the ~3.2 Ga age represents the main period of continental crustal growth in the southeastern margin of Tarim, and subsequently crustal reconstruction occurred in 2.55－2.70 Ga. It is concluded that ancient crustal material recycling could be an important way of continental crustal evolution in the middle and late period of Neoarchean in this area.
The study on the formation age and petrogenetic mechanism of early Precambrian rocks in the southeast margin of Tarim block is relatively weak, which restricts the understanding of the formation and early evolution of continental crust. These geochemistry and zircon Hf isotope compositions show that primary magma of the quartz diorite gneiss was formed by partial melting of the lower crust meta-basalt with minor addition of mantle-derived materials. LA-ICP-MS zircon U-Pb dating results reveal that the diagenetic ages of the quartz diorite gneiss are 2 662±12 Ma and 2 676±15 Ma, indicating the Archean rock formation ages in the southeastern margin of Tarim were mainly concentrated in 2.55－2.70 Ga; corresponding metamorphic ages are 1 980±30 Ma and 1 828±20 Ma－2 087±29 Ma respectively, representing the geological record of magmatic-matamorphic events related to orogenic processes in the middle and late period of Paleoproterozoic in the southeastern margin of Tarim. Additionally, two-stage model ages(TDM2)of zircon for the quartz diorite gneiss in this study vary from 2 954 to 3 742 Ma, with peak ages clustering at ~3.24 Ga. Thus, combined with the available data, it is suggested that the ~3.2 Ga age represents the main period of continental crustal growth in the southeastern margin of Tarim, and subsequently crustal reconstruction occurred in 2.55－2.70 Ga. It is concluded that ancient crustal material recycling could be an important way of continental crustal evolution in the middle and late period of Neoarchean in this area.
2020, 45(9): 3282-3294.
doi: 10.3799/dqkx.2020.150
Abstract:
The formation age and evolution of the Liaohe Group in the Liao-Ji Paleoproterozoic structural belt have always been a research hotspot. Zircon LA-ICP-MS U-Pb geochronology of basic volcanic rocks intercalated in metamorphic sedimentary rocks of the Li'eryu Formation in Kuandian area is studied. Zircons from seven basic magmatic rocks are divided into magmatic zircons and metamorphic zircons. The dating results show two stages of 2 150－2 130 Ma and 2 050－2 020 Ma, representing the diagenetic age of the rocks. Combined with the acid volcanic rocks exposed in this area, it is considered that the formation age of the Liaohe Group in Kuandian area is at least 2.17－2.03 Ga. The metamorphic ages obtained from five amphibolites show that the metamorphism occurred after 1 900 Ma and lasted from 1 870 to 1 780 Ma, which can be further divided into three phases: 1 870－1 861 Ma, 1 845－1 842 Ma and 1 790－1 780 Ma. The peak period of metamorphism is ~1 850 Ma, which is the second strong metamorphic peak period of Paleoproterozoic in this area. The third stage is consistent with the metamorphic event of ~1 800 Ma. The age of meta diorite (D015) vein is 1 314±24 Ma and metamorphic age of amphibolite (D1465-1) is 1 290±21 Ma. This is the first time that Mesoproterozoic magma and metamorphism events have been identified in eastern Liaoning. Combined with 1 320－1 380 Ma magmatic activity in western Liaoning and northern Hebei, these events are considered as the response of North China Craton to the breakup process of Columbia supercontinent.
The formation age and evolution of the Liaohe Group in the Liao-Ji Paleoproterozoic structural belt have always been a research hotspot. Zircon LA-ICP-MS U-Pb geochronology of basic volcanic rocks intercalated in metamorphic sedimentary rocks of the Li'eryu Formation in Kuandian area is studied. Zircons from seven basic magmatic rocks are divided into magmatic zircons and metamorphic zircons. The dating results show two stages of 2 150－2 130 Ma and 2 050－2 020 Ma, representing the diagenetic age of the rocks. Combined with the acid volcanic rocks exposed in this area, it is considered that the formation age of the Liaohe Group in Kuandian area is at least 2.17－2.03 Ga. The metamorphic ages obtained from five amphibolites show that the metamorphism occurred after 1 900 Ma and lasted from 1 870 to 1 780 Ma, which can be further divided into three phases: 1 870－1 861 Ma, 1 845－1 842 Ma and 1 790－1 780 Ma. The peak period of metamorphism is ~1 850 Ma, which is the second strong metamorphic peak period of Paleoproterozoic in this area. The third stage is consistent with the metamorphic event of ~1 800 Ma. The age of meta diorite (D015) vein is 1 314±24 Ma and metamorphic age of amphibolite (D1465-1) is 1 290±21 Ma. This is the first time that Mesoproterozoic magma and metamorphism events have been identified in eastern Liaoning. Combined with 1 320－1 380 Ma magmatic activity in western Liaoning and northern Hebei, these events are considered as the response of North China Craton to the breakup process of Columbia supercontinent.
2020, 45(9): 3295-3312.
doi: 10.3799/dqkx.2020.182
Abstract:
The Yangtze Block preserves large quantities of Paleoproterozoic rocks which hold the evidence of the Columbia supercontinent cycle, however, its evolution from the assembly to break-up and relative location in the palaeosupercontinent, are still in dispute. In this study, we present an integrated dataset of whole-rock geochemistry, zircon U-Pb age and Lu-Hf isotope of the Mayuan and Baiyu granitoids in the Beiba area of the northwestern Yangtze Block. Zircon U-Pb dating reveals that the Mayuan granodiorite and the Baiyu K-feldspar granite were emplaced at ~2 090 Ma and ~1 760 Ma, respectively. Geochemically, the Mayuan granodiorite shows strongly peraluminous characteristics with depletion in Sr, Cr, Ni, enrichment in Y and Yb, relatively enriched in LREE and depleted in HFSE, and these features bear resemblance to those of cal-alkali granite; in addition, its zircon Lu-Hf isotopic analyses yield positive εHf(t) values of +0.91 to +2.59. The Baiyu K-feldspar granite is alkali-rich and enriched in Sr, low Al, Mg, Mn and P, with A/CNK of 0.96-1.04; the trace elements show enrichment in Th, Na, Ta, Zr, Hf and depletion in Sr, Eu, with high total REE concentration, high LREE/HREE ratio, and strongly negative Eu anomalies; moreover, the granite has high HFSEs (Zr+Nb+Ce+Y=797×10-6-1 495×10-6) and 10 000×Ga/Al ratios (3.30-3.73). Together with high zircon saturation temperatures (897-939 ℃) from the K-feldspar granite, they are classified as A-type granites with negative εHf(t) values from -13.58 to -10.29. Integrated with the analysis of trace elements and oxygen fugacity of zircon and previous research results, the Mayuan 2 090-2 080 Ma granitoids were likely to be generated by remelting of both juvenile and old crustal components within an arc-related setting; the Baiyu 1 790-1 760 Ma K-feldspar granite may be derived from partial melting of ancient crustal materials within the intracontinental rift setting. And they are likely to be the responses to the assembly and break-up of the Columbia supercontinent. Taking account of geophysical data and magmatic-metamorphic events, it is suggested that the Yangtze Block was spatially linked to Laurentia in the Columbia supercontinent.
The Yangtze Block preserves large quantities of Paleoproterozoic rocks which hold the evidence of the Columbia supercontinent cycle, however, its evolution from the assembly to break-up and relative location in the palaeosupercontinent, are still in dispute. In this study, we present an integrated dataset of whole-rock geochemistry, zircon U-Pb age and Lu-Hf isotope of the Mayuan and Baiyu granitoids in the Beiba area of the northwestern Yangtze Block. Zircon U-Pb dating reveals that the Mayuan granodiorite and the Baiyu K-feldspar granite were emplaced at ~2 090 Ma and ~1 760 Ma, respectively. Geochemically, the Mayuan granodiorite shows strongly peraluminous characteristics with depletion in Sr, Cr, Ni, enrichment in Y and Yb, relatively enriched in LREE and depleted in HFSE, and these features bear resemblance to those of cal-alkali granite; in addition, its zircon Lu-Hf isotopic analyses yield positive εHf(t) values of +0.91 to +2.59. The Baiyu K-feldspar granite is alkali-rich and enriched in Sr, low Al, Mg, Mn and P, with A/CNK of 0.96-1.04; the trace elements show enrichment in Th, Na, Ta, Zr, Hf and depletion in Sr, Eu, with high total REE concentration, high LREE/HREE ratio, and strongly negative Eu anomalies; moreover, the granite has high HFSEs (Zr+Nb+Ce+Y=797×10-6-1 495×10-6) and 10 000×Ga/Al ratios (3.30-3.73). Together with high zircon saturation temperatures (897-939 ℃) from the K-feldspar granite, they are classified as A-type granites with negative εHf(t) values from -13.58 to -10.29. Integrated with the analysis of trace elements and oxygen fugacity of zircon and previous research results, the Mayuan 2 090-2 080 Ma granitoids were likely to be generated by remelting of both juvenile and old crustal components within an arc-related setting; the Baiyu 1 790-1 760 Ma K-feldspar granite may be derived from partial melting of ancient crustal materials within the intracontinental rift setting. And they are likely to be the responses to the assembly and break-up of the Columbia supercontinent. Taking account of geophysical data and magmatic-metamorphic events, it is suggested that the Yangtze Block was spatially linked to Laurentia in the Columbia supercontinent.
2020, 45(9): 3313-3329.
doi: 10.3799/dqkx.2020.126
Abstract:
The Diebusige Complex, as the oldest metamorphic complex with the highest metamorphic grade from the Alxa Block, is an excellent object to investigate the formation, evolution, and tectonic affinity of the Alxa Block. This paper presents comprehensive studies on the biotite-plagioclase gneiss from the Diebusige Complex, including detailed field investigation, petrological observation and LA-ICP-MS zircon U-Pb dating. The detrital zircon U-Pb dating indicates that the ages of the detrital zircons from the biotite-plagioclase gneiss in the Diebusige Complex are between 2 177 and 2 010 Ma, with a peak age of ca. 2 050 Ma. Combined with the maximum metamorphic age of 1 969 Ma, it is proposed that the depositional timing of the biotite-plagioclase gneiss is 2 050~1 969 Ma. Comprehensive comparative analysis shows that the depositional timing and provenance of the biotite-plagioclase gneiss in the Diebusige Complex is highly consistent with the meta-sedimentary rocks from the Longshoushan Complex and the Khondalite Belt (especially the western part of the Khondalite Belt). In addition, metamorphic zircon U-Pb dating and REE analyses indicate that the metamorphic zircons of the biotite-plagioclase gneiss yield continuous ages of 1 969~1 811 Ma. Based on the similarities in the detrital zircon age patterns and metamorphic timing of the meta-sedimentary rocks from the Khondalite Belt in Paleoproterozoic, it is suggested that the Alxa Block should be the western part of the Khondalite Belt in Paleoproterozoic.
The Diebusige Complex, as the oldest metamorphic complex with the highest metamorphic grade from the Alxa Block, is an excellent object to investigate the formation, evolution, and tectonic affinity of the Alxa Block. This paper presents comprehensive studies on the biotite-plagioclase gneiss from the Diebusige Complex, including detailed field investigation, petrological observation and LA-ICP-MS zircon U-Pb dating. The detrital zircon U-Pb dating indicates that the ages of the detrital zircons from the biotite-plagioclase gneiss in the Diebusige Complex are between 2 177 and 2 010 Ma, with a peak age of ca. 2 050 Ma. Combined with the maximum metamorphic age of 1 969 Ma, it is proposed that the depositional timing of the biotite-plagioclase gneiss is 2 050~1 969 Ma. Comprehensive comparative analysis shows that the depositional timing and provenance of the biotite-plagioclase gneiss in the Diebusige Complex is highly consistent with the meta-sedimentary rocks from the Longshoushan Complex and the Khondalite Belt (especially the western part of the Khondalite Belt). In addition, metamorphic zircon U-Pb dating and REE analyses indicate that the metamorphic zircons of the biotite-plagioclase gneiss yield continuous ages of 1 969~1 811 Ma. Based on the similarities in the detrital zircon age patterns and metamorphic timing of the meta-sedimentary rocks from the Khondalite Belt in Paleoproterozoic, it is suggested that the Alxa Block should be the western part of the Khondalite Belt in Paleoproterozoic.
2020, 45(9): 3330-3340.
doi: 10.3799/dqkx.2020.132
Abstract:
This paper reports SHRIMP U-Pb dating results and MC-ICPMS Hf isotopes of zircons as well as whole-rock geochemical compositions on granitoidic rocks from the early Precambrian basement in the Xiaoqinling area, southern margin of the North China Craton. Two TTG gneiss samples have ~2.50 Ga and slightly younger ages for magmatic and metamorphic zircons, respectively, with magmatic zircons having εHf(t) values of 0.71 to 4.37. One granitic gneiss sample has a magmatic zircon age of ~2.30 Ga and εHf(t) values of -1.21 to 0.11. All samples have recorded late Paleoproterozoic metamorphic ages or the influence of the event. The rocks are similar in element composition, showing strong light to heavy REE differentiation and enrichment in LILE and depletion in Nb, P and Ti. Combined with early work, the identification of late Neoarchean TTG rocks and tectonothermal event support the conclusion that the southern margin of the North China Craton is similar in early Precambrian geological history to others all over the craton. However, the former shows its peculiarity in widespread developement of ~2.3 Ga magmatism.
This paper reports SHRIMP U-Pb dating results and MC-ICPMS Hf isotopes of zircons as well as whole-rock geochemical compositions on granitoidic rocks from the early Precambrian basement in the Xiaoqinling area, southern margin of the North China Craton. Two TTG gneiss samples have ~2.50 Ga and slightly younger ages for magmatic and metamorphic zircons, respectively, with magmatic zircons having εHf(t) values of 0.71 to 4.37. One granitic gneiss sample has a magmatic zircon age of ~2.30 Ga and εHf(t) values of -1.21 to 0.11. All samples have recorded late Paleoproterozoic metamorphic ages or the influence of the event. The rocks are similar in element composition, showing strong light to heavy REE differentiation and enrichment in LILE and depletion in Nb, P and Ti. Combined with early work, the identification of late Neoarchean TTG rocks and tectonothermal event support the conclusion that the southern margin of the North China Craton is similar in early Precambrian geological history to others all over the craton. However, the former shows its peculiarity in widespread developement of ~2.3 Ga magmatism.
2020, 45(9): 3341-3352.
doi: 10.3799/dqkx.2020.107
Abstract:
Previous studies on the Neoarchean geology in western Shandong were mainly regional with few reports on the outcrop scale. Detailed field observation and SHRIMP U-Pb zircon dating are carried out in this study on rocks in a road cutting section in the Lihang area, western Shandong, where different types of rocks are very fresh and show complex and various relationships. Banded tonalitic gneiss and fine-grained tonalitic gneiss have magmatic zircon ages of 2.62 Ga and 2.63 Ga, respectively, which are considered to be the crystallization times of the rocks. Another banded tonalitic gneiss has similar magmatic and metamorphic zircon ages of ~2.57 Ga. More work is required to determine its geological meaning. A trondhjemitic dyke has a formation age of 2.60 Ga. A diorite dyke intruding banded tonalitic gneiss and trondhjemitic vein has magmatic and metamorphic zircon ages of 2.52 Ga and 2.51 Ga, respectively, with 2.66-2.69 Ga xenocrystic zircons. Combined with previous work, it is concluded that there are tonalitic gneisses of different ages (~2.7 Ga and ~2.6 Ga) in the Taishan area, which are difficult to be distinguished from each other in field. The geological records in this section may be an epitome of Neoarchean geological history of western Shandong but without ~2.7 Ga TTG record.
Previous studies on the Neoarchean geology in western Shandong were mainly regional with few reports on the outcrop scale. Detailed field observation and SHRIMP U-Pb zircon dating are carried out in this study on rocks in a road cutting section in the Lihang area, western Shandong, where different types of rocks are very fresh and show complex and various relationships. Banded tonalitic gneiss and fine-grained tonalitic gneiss have magmatic zircon ages of 2.62 Ga and 2.63 Ga, respectively, which are considered to be the crystallization times of the rocks. Another banded tonalitic gneiss has similar magmatic and metamorphic zircon ages of ~2.57 Ga. More work is required to determine its geological meaning. A trondhjemitic dyke has a formation age of 2.60 Ga. A diorite dyke intruding banded tonalitic gneiss and trondhjemitic vein has magmatic and metamorphic zircon ages of 2.52 Ga and 2.51 Ga, respectively, with 2.66-2.69 Ga xenocrystic zircons. Combined with previous work, it is concluded that there are tonalitic gneisses of different ages (~2.7 Ga and ~2.6 Ga) in the Taishan area, which are difficult to be distinguished from each other in field. The geological records in this section may be an epitome of Neoarchean geological history of western Shandong but without ~2.7 Ga TTG record.
2020, 45(9): 3353-3371.
doi: 10.3799/dqkx.2020.188
Abstract:
The Huai'an Complex in Northwest Hebei Province consists of meta-supracrustal rocks and metamorphic plutonic rocks. There are still some controversies about some issues such as the formation age of supracrustal rocks, the tectonic setting of Huai'an Complex and the relationship between Huai'an Complex and Khondalite belt. Some representative outcrops of the Huai'an Complex have been studied in detail by field investigation, petrology, zircon SHRIMP U-Pb dating, isotopic and elements geochemistry. All of the 4 samples yielded metamorphic ages of 1.86-1.81 Ga, which further supports the previous view that the Huai'an Complex suffered extensive late Paleoproterozoic metamorphism. The BIF-bearing supracrustal rock assemblage was intruded and enclaved by the meta-gabbro (HB1425) and gneissic tonalite (HB1426), which yielded the formation ages of ca. 2.5 Ga and 2.55 Ga, respectively. It suggests that the supracrustal rocks in this location are older than 2.55 Ga. Leptite (HB1431) and hypersthene garnet biotite plagioclase gneiss (Hy-Grt-Bt-Pl gneiss, HB1435) contain the oldest detrital zircons of 2.46 Ga and 2.51 Ga, respectively, probably together with some Paleoproterozoic zircons, indicating that the supracrustal rocks in the two localities are Paleoproterozoic. These results further confirm the development of two stage supracrustal rock assemblages in the Huai'an Complex. The whole rocks εNd(t), TDM1 and TDM2 of the meta-gabbro and gneissic tonalite are +2.19 to +3.06, 2.67 to 2.75 Ga and 2.67 to 2.69 Ga, respectively, indicating no widespread older continental crust material is involved in their source and the Neoarchean is the main period of continental crust growth in the Huai'an area. Some of the ~1.82 Ga metamorphic zircons in metagabbro yielded positive εHf(t) values up to +11.1. The most likely reason for the Hf isotope composition is the mantle addition during the Paleoproterozoic metamorphic event. The zircon O-isotope shows that there may be rocks with low δ18O in the area, and low δ18O fluid could modify the O-isotope of zircon during the Paleoproterozoic metamorphism. It is concluded that the Huai'an Complex has the similar double-layered crustal structure to the Khondalite Belt although it is different in the proportion of the late Noearchean and Paleoproterozoic rocks. The Huai'an Complex may represent the deeper crustal level of the Khondalite belt due to stronger exhumation.
The Huai'an Complex in Northwest Hebei Province consists of meta-supracrustal rocks and metamorphic plutonic rocks. There are still some controversies about some issues such as the formation age of supracrustal rocks, the tectonic setting of Huai'an Complex and the relationship between Huai'an Complex and Khondalite belt. Some representative outcrops of the Huai'an Complex have been studied in detail by field investigation, petrology, zircon SHRIMP U-Pb dating, isotopic and elements geochemistry. All of the 4 samples yielded metamorphic ages of 1.86-1.81 Ga, which further supports the previous view that the Huai'an Complex suffered extensive late Paleoproterozoic metamorphism. The BIF-bearing supracrustal rock assemblage was intruded and enclaved by the meta-gabbro (HB1425) and gneissic tonalite (HB1426), which yielded the formation ages of ca. 2.5 Ga and 2.55 Ga, respectively. It suggests that the supracrustal rocks in this location are older than 2.55 Ga. Leptite (HB1431) and hypersthene garnet biotite plagioclase gneiss (Hy-Grt-Bt-Pl gneiss, HB1435) contain the oldest detrital zircons of 2.46 Ga and 2.51 Ga, respectively, probably together with some Paleoproterozoic zircons, indicating that the supracrustal rocks in the two localities are Paleoproterozoic. These results further confirm the development of two stage supracrustal rock assemblages in the Huai'an Complex. The whole rocks εNd(t), TDM1 and TDM2 of the meta-gabbro and gneissic tonalite are +2.19 to +3.06, 2.67 to 2.75 Ga and 2.67 to 2.69 Ga, respectively, indicating no widespread older continental crust material is involved in their source and the Neoarchean is the main period of continental crust growth in the Huai'an area. Some of the ~1.82 Ga metamorphic zircons in metagabbro yielded positive εHf(t) values up to +11.1. The most likely reason for the Hf isotope composition is the mantle addition during the Paleoproterozoic metamorphic event. The zircon O-isotope shows that there may be rocks with low δ18O in the area, and low δ18O fluid could modify the O-isotope of zircon during the Paleoproterozoic metamorphism. It is concluded that the Huai'an Complex has the similar double-layered crustal structure to the Khondalite Belt although it is different in the proportion of the late Noearchean and Paleoproterozoic rocks. The Huai'an Complex may represent the deeper crustal level of the Khondalite belt due to stronger exhumation.
2020, 45(9): 3372-3385.
doi: 10.3799/dqkx.2020.237
Abstract:
A large number of ~2.3 Ga geologic bodies have been identified in the North China Craton (NCC) in global magmatic quiescence, which is vital for unveiling the Paleoproterozoic geological evolution on the NCC. This paper presents the whole rock geochemical data, zircon U-Pb ages and Hf isotopes of the Henglingguan monzogranite in Zhongtiao mountains area. LA-ICPMS dating of zircon from the Henglingguan monzogranite yields an age of 2 308±12 Ma. The Henglingguan monzogranite is high in SiO2, K2O, Al2O3 and alkali, and low in CaO, NaO and TiO2, with A/CNK concentrated between 1.0 and 1.1, which belongs to high-K calc-alkaline and metaluminous-peraluminous series. The monzogranite is high in total REE contents, showing strong fractionation of LREE and HREE and obvious negative Eu anomaly. As to the trace elements, the monzogranite shows enrichment in Nb, Ta, Zr, Hf, U and Rb, and depletion in V, Cr, Co and Ni, which is consistent with characteristics of I-type granite. Zircons in the Henglingguan monzogranite have εHf(t) values ranging from 0.52 to 6.24, with an average of 2.06, and Hf model TDM1 age of 2 419-2 642 Ma and TDM2 age of 2 438-2 738 Ma. The Henglingguan monzogranite shows the features of syn-collision granites originated from partial melting of the ~2.5 Ga ancient crust in collision environment, which shows the NCC was not quiet during the Paleoproterozoic global magmatic quiescence.
A large number of ~2.3 Ga geologic bodies have been identified in the North China Craton (NCC) in global magmatic quiescence, which is vital for unveiling the Paleoproterozoic geological evolution on the NCC. This paper presents the whole rock geochemical data, zircon U-Pb ages and Hf isotopes of the Henglingguan monzogranite in Zhongtiao mountains area. LA-ICPMS dating of zircon from the Henglingguan monzogranite yields an age of 2 308±12 Ma. The Henglingguan monzogranite is high in SiO2, K2O, Al2O3 and alkali, and low in CaO, NaO and TiO2, with A/CNK concentrated between 1.0 and 1.1, which belongs to high-K calc-alkaline and metaluminous-peraluminous series. The monzogranite is high in total REE contents, showing strong fractionation of LREE and HREE and obvious negative Eu anomaly. As to the trace elements, the monzogranite shows enrichment in Nb, Ta, Zr, Hf, U and Rb, and depletion in V, Cr, Co and Ni, which is consistent with characteristics of I-type granite. Zircons in the Henglingguan monzogranite have εHf(t) values ranging from 0.52 to 6.24, with an average of 2.06, and Hf model TDM1 age of 2 419-2 642 Ma and TDM2 age of 2 438-2 738 Ma. The Henglingguan monzogranite shows the features of syn-collision granites originated from partial melting of the ~2.5 Ga ancient crust in collision environment, which shows the NCC was not quiet during the Paleoproterozoic global magmatic quiescence.
2020, 45(9): 3386-3402.
doi: 10.3799/dqkx.2020.080
Abstract:
This paper presents a study of the mineral inclusions, U-Pb isotopes and trace elements of the metamorphic zircons from the granitic gneisses in the Dengkou area and the amphibolites in the Shetai area. The results show that the U-Pb age of one granite gneiss magmatic zircon in Dengkou area is 2 549±14 Ma, the age of metamorphic zircon is 1 874 ±26 Ma, and that of another granite gneiss metamorphic zircon is 1 877 ±25 Ma, and their REE patterns are generally left-leaning. On the other hand, the metamorphic zircons of the amphibolites in the Shetai area yield U-Pb ages of 1 924±25 Ma and 1 800±20 Ma in the south and 2 469±15 Ma in the north, respectively and they also show left-leaning REE patterns. Based on the rock assemblage, spatial distribution of the late Neoarchean and Paleoproterozoic metamorphic events, and the previous research results, we suggest that the north boundary of the Khondalite Belt in the Dengkou area more likely extends to the west, rather than the southwest as previously thought and the boundary in the Shetai area is distributed along the Wuchuan-Guyang-Shetai instead of along the Wuchuan-Guyang-Urad Houqi.
This paper presents a study of the mineral inclusions, U-Pb isotopes and trace elements of the metamorphic zircons from the granitic gneisses in the Dengkou area and the amphibolites in the Shetai area. The results show that the U-Pb age of one granite gneiss magmatic zircon in Dengkou area is 2 549±14 Ma, the age of metamorphic zircon is 1 874 ±26 Ma, and that of another granite gneiss metamorphic zircon is 1 877 ±25 Ma, and their REE patterns are generally left-leaning. On the other hand, the metamorphic zircons of the amphibolites in the Shetai area yield U-Pb ages of 1 924±25 Ma and 1 800±20 Ma in the south and 2 469±15 Ma in the north, respectively and they also show left-leaning REE patterns. Based on the rock assemblage, spatial distribution of the late Neoarchean and Paleoproterozoic metamorphic events, and the previous research results, we suggest that the north boundary of the Khondalite Belt in the Dengkou area more likely extends to the west, rather than the southwest as previously thought and the boundary in the Shetai area is distributed along the Wuchuan-Guyang-Shetai instead of along the Wuchuan-Guyang-Urad Houqi.
2020, 45(9): 3403-3419.
doi: 10.3799/dqkx.2020.086
Abstract:
Barrovian-type progressive metamorphism could lead to a new understanding of crustal thickening and orogenesis. We conduct a detailed field survey and indoor researches about the Barrovian metamorphic zone of the Lianshanguan-Qijiabao of the Benxi area, to understand better of field distribution and metamorphic characteristics of Barrovian metamorphic zone which is located at the Langzishan Formation of the North Liaohe Group in Liaodong Peninsula. The Barrovian metamorphic zone in the Langzishan Formation is divided into biotite zone, garnet zone, staurolite zone, kyanite zone from south to north, according to detailed field mapping. The analysis of petrography suggests kyanite-staurolite-garnet mica-schist of kyanite zone has three stages mineral assemblages:(1) Progressive metamorphic mineral assemblages (M1) are Pl+Qz+Ms+Bt+Ctd+Chl±Grt; (2) metamorphic peak (M2) is characterized by Ky+St+Grt+Bt+Ms+Qz+Pl+Ilm; (3) retrograde metamorphic stage mainly has trichoid sillimanite (M3-1) and chlorite and sericite around rims and cracks of porphyroblasts (M3-2). Phase equilibrium modeling shows metamorphic P-T of progressive metamorphic stage and peak stage of kyanite-staurolite-garnet mica-schist are respectively ~440 ℃/~3.7 kbar, ~670 ℃/~7.9 kbar, and the rock has a typical clockwise P-T path. The results of U-Pb geochronology of metamorphic zircons indicate kyanite-staurolite-garnet mica-schist has experienced peak metamorphism at ~1.96 Ga; these ages of U-Pb detrital zircons are scattered among 2 631-2 020 Ma, indicating the clastic sediments may be from an ancient Archean basement of ~2.5 Ga and magmatic rocks of 2.2-2.1 Ga. Combined with previous research data, the clockwise P-T-t path and thrusting nappe structure recorded by the Barrovian metamorphic zone of the Langzishan Formation represent Jiao-Liao-Ji belt has experienced crustal thickening produced by orogenesis around 1.96 Ga.
Barrovian-type progressive metamorphism could lead to a new understanding of crustal thickening and orogenesis. We conduct a detailed field survey and indoor researches about the Barrovian metamorphic zone of the Lianshanguan-Qijiabao of the Benxi area, to understand better of field distribution and metamorphic characteristics of Barrovian metamorphic zone which is located at the Langzishan Formation of the North Liaohe Group in Liaodong Peninsula. The Barrovian metamorphic zone in the Langzishan Formation is divided into biotite zone, garnet zone, staurolite zone, kyanite zone from south to north, according to detailed field mapping. The analysis of petrography suggests kyanite-staurolite-garnet mica-schist of kyanite zone has three stages mineral assemblages:(1) Progressive metamorphic mineral assemblages (M1) are Pl+Qz+Ms+Bt+Ctd+Chl±Grt; (2) metamorphic peak (M2) is characterized by Ky+St+Grt+Bt+Ms+Qz+Pl+Ilm; (3) retrograde metamorphic stage mainly has trichoid sillimanite (M3-1) and chlorite and sericite around rims and cracks of porphyroblasts (M3-2). Phase equilibrium modeling shows metamorphic P-T of progressive metamorphic stage and peak stage of kyanite-staurolite-garnet mica-schist are respectively ~440 ℃/~3.7 kbar, ~670 ℃/~7.9 kbar, and the rock has a typical clockwise P-T path. The results of U-Pb geochronology of metamorphic zircons indicate kyanite-staurolite-garnet mica-schist has experienced peak metamorphism at ~1.96 Ga; these ages of U-Pb detrital zircons are scattered among 2 631-2 020 Ma, indicating the clastic sediments may be from an ancient Archean basement of ~2.5 Ga and magmatic rocks of 2.2-2.1 Ga. Combined with previous research data, the clockwise P-T-t path and thrusting nappe structure recorded by the Barrovian metamorphic zone of the Langzishan Formation represent Jiao-Liao-Ji belt has experienced crustal thickening produced by orogenesis around 1.96 Ga.
2020, 45(9): 3420-3435.
doi: 10.3799/dqkx.2020.244
Abstract:
Many high-pressure metamorphic rocks or blocks from the North China Craton were recognized in the Sulu tectonic complex belt, providing many opportunities to investigate the mechanism of the involvement and exhumation of the materials from the upper subduction zone. In this paper, we present a study of petrology, mineral chemistry and phase equilibria modeling on the (garnet) plagioclase amphibolites in the Rushan area, and three metamorphic stages have been found in the rock: (1) The pre-peak stage with the mineral assemblage of garnet+quartz+plagioclase+amphibole+ilmenite; (2) the peak high-pressure stage with the diagnostic amphibolite-facies assemblage of garnet+clinopyroxene+plagioclase+amphibole+quartz+ilmenite; (3) the post-peak decompression stage represented by amphibole+plagioclase+garnet+ilmenite, and typical "white eye" textures can be observed. Phase equilibria modeling constrained the P-T conditions of the pre-peak, peak, and post-peak of 6.4－7.0 kbar/610－640 ℃, 9.3－10.0 kbar/700－730 ℃, 5.2－5.8 kbar/680－710 ℃, respectively. These P-T conditions indicate that the materials from the upper subduction zone have already subducted to ~30 km and 36－40 km, respectively. U-Pb dating of zircons show that the protolith age of the garnet plagioclase amphibolite is 1 734±24 Ma, and the metamorphic age of plagioclase amphibolite is 1 849±28 Ma (from Longjiaoshan reservoir), which all indicates a North China Plate origin. Our data, combined with those of previous studies, indicate that the Wuji garnet plagioclase amphibolites might have been involved in the subduction in Triassic and experienced metamorphism. Together with the "tectonic rock slices" from South China Block, a 80－100 km wide tectonic mélange zone is suggested between the North China Plate and the South China Block.
Many high-pressure metamorphic rocks or blocks from the North China Craton were recognized in the Sulu tectonic complex belt, providing many opportunities to investigate the mechanism of the involvement and exhumation of the materials from the upper subduction zone. In this paper, we present a study of petrology, mineral chemistry and phase equilibria modeling on the (garnet) plagioclase amphibolites in the Rushan area, and three metamorphic stages have been found in the rock: (1) The pre-peak stage with the mineral assemblage of garnet+quartz+plagioclase+amphibole+ilmenite; (2) the peak high-pressure stage with the diagnostic amphibolite-facies assemblage of garnet+clinopyroxene+plagioclase+amphibole+quartz+ilmenite; (3) the post-peak decompression stage represented by amphibole+plagioclase+garnet+ilmenite, and typical "white eye" textures can be observed. Phase equilibria modeling constrained the P-T conditions of the pre-peak, peak, and post-peak of 6.4－7.0 kbar/610－640 ℃, 9.3－10.0 kbar/700－730 ℃, 5.2－5.8 kbar/680－710 ℃, respectively. These P-T conditions indicate that the materials from the upper subduction zone have already subducted to ~30 km and 36－40 km, respectively. U-Pb dating of zircons show that the protolith age of the garnet plagioclase amphibolite is 1 734±24 Ma, and the metamorphic age of plagioclase amphibolite is 1 849±28 Ma (from Longjiaoshan reservoir), which all indicates a North China Plate origin. Our data, combined with those of previous studies, indicate that the Wuji garnet plagioclase amphibolites might have been involved in the subduction in Triassic and experienced metamorphism. Together with the "tectonic rock slices" from South China Block, a 80－100 km wide tectonic mélange zone is suggested between the North China Plate and the South China Block.
