2015 Vol. 40, No. 1
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2015, 40(1): 1-16.
doi: 10.3799/dqkx.2015.001
Abstract:
Combined with field investigation and ore-forming geological conditions of the Kaerqueka copper polymetallic deposit, the geochemical characteristics of the deposit are summarized, the origin of the ore-forming materials is ascertained, and the rock-forming and ore-forming mechanisms are discussed according to the S, Pb isotopes as well as chemical analysis, including major element analysis, trace element analysis. Results of typical magmatic rocks, wall rocks and ores show that the magmatic rocks which were derived from deep and affected by crustal contamination during intrusion are intermediate acidity comagmatic rocks and belong to the high-K calc-alkaline series. All REE distribution patterns of different geologic bodies incline to the right and LREE-rich, indicating that the magmatic rock, skarn and ore belong to the same metallogenic system. The geochemistry of trace elements shows that the granites of the deposit occurred in volcanic arc environment. The δ34SCDT values of ore minerals lie between those of magmatic rock and country rock sulfur, with a range of 4.4‰ to 11.0‰, which indicates various metallogenic material sources. The Th/U values of lead isotope in ore minerals range from 3.46 to 3.69 and the μ values range from 9.46 to 9.52 (< 9.58), which fall between the values of crust and primitive mantle and indicate that the ore lead is characterized by both deep-sourced and crust-sourced origins. The tracer analysis regarding the characteristic parameters, lead composition model and Δβ-Δγ diagram show that the ore lead is mainly crust-derived and mixed with minor mantle-derived lead and affected by magmatism. The geochemical characteristics of Kaerqueka deposit suggest that the ore-forming materials mainly originated from magma with minor strata substance. The complicated evolution of magmatic rock is revealed by the porphyry-type copper-molybdenum mineralization in magmatic rock, the skarn-type lead-zinc mineralization following the contact of carbonate rock and the late low-medium hydrothermal vein-type gold mineralization, which indicates the Kaerqueka deposit is a polygenetic compound deposit.
Combined with field investigation and ore-forming geological conditions of the Kaerqueka copper polymetallic deposit, the geochemical characteristics of the deposit are summarized, the origin of the ore-forming materials is ascertained, and the rock-forming and ore-forming mechanisms are discussed according to the S, Pb isotopes as well as chemical analysis, including major element analysis, trace element analysis. Results of typical magmatic rocks, wall rocks and ores show that the magmatic rocks which were derived from deep and affected by crustal contamination during intrusion are intermediate acidity comagmatic rocks and belong to the high-K calc-alkaline series. All REE distribution patterns of different geologic bodies incline to the right and LREE-rich, indicating that the magmatic rock, skarn and ore belong to the same metallogenic system. The geochemistry of trace elements shows that the granites of the deposit occurred in volcanic arc environment. The δ34SCDT values of ore minerals lie between those of magmatic rock and country rock sulfur, with a range of 4.4‰ to 11.0‰, which indicates various metallogenic material sources. The Th/U values of lead isotope in ore minerals range from 3.46 to 3.69 and the μ values range from 9.46 to 9.52 (< 9.58), which fall between the values of crust and primitive mantle and indicate that the ore lead is characterized by both deep-sourced and crust-sourced origins. The tracer analysis regarding the characteristic parameters, lead composition model and Δβ-Δγ diagram show that the ore lead is mainly crust-derived and mixed with minor mantle-derived lead and affected by magmatism. The geochemical characteristics of Kaerqueka deposit suggest that the ore-forming materials mainly originated from magma with minor strata substance. The complicated evolution of magmatic rock is revealed by the porphyry-type copper-molybdenum mineralization in magmatic rock, the skarn-type lead-zinc mineralization following the contact of carbonate rock and the late low-medium hydrothermal vein-type gold mineralization, which indicates the Kaerqueka deposit is a polygenetic compound deposit.
2015, 40(1): 17-33.
doi: 10.3799/dqkx.2015.002
Abstract:
In this paper, we present laser ablation (MC)-ICP-MS U-Pb dating and Hf isotopic compositions of zircons from two representative granitoid samples collected from Shedong W-Mo deposit in the southern edge of the Dayaoshan. Highly precise U-Pb results indicate that zircons from Sheshan biotite granodiorite (SD256) and granodiorite-(porphyry) (SD190) which emplaced in the Pingtoubei quartz sandstone yields weighted mean 206Pb/238U age of 438.7±3.0 Ma (MSWD=0.22) and 438.1±2.6 Ma (MSWD=0.28), respectively. And the zircons crystallized in the Kwangsian granites yield 176Hf/177Hf ratios of 0.282 406 to 0.282 518, εHf(438 Ma) values ranging from -3.7 to 0 and Hf model ages (TDM2) of 1 226 to 1 417 Ma. Our U-Pb and Hf isotopic data can be interpreted as the crystallization time of granites, and indicate that it was formed in the ~438 Ma (Caledonian) and may have been formed by reworking of Mesoproterozoic juvenile crust (1.2-1.4 Ga) closely related to partial melting. Together with other published geochronological data, it is proposed that the late Early Paleozoic granites predominantly have a similar formation age and exhibit a planar-shaped distribution, rather than a north-east-striking-distribution pattern in the hinterland of the South China. Moreover, the Caledonian tectonic-magmatic-metallogenic movement may be the one of key reasons for the large-scale magmatism and metal mineralization in the following tectonic episodes, such as Indosinian and Yanshanian in the South China.
In this paper, we present laser ablation (MC)-ICP-MS U-Pb dating and Hf isotopic compositions of zircons from two representative granitoid samples collected from Shedong W-Mo deposit in the southern edge of the Dayaoshan. Highly precise U-Pb results indicate that zircons from Sheshan biotite granodiorite (SD256) and granodiorite-(porphyry) (SD190) which emplaced in the Pingtoubei quartz sandstone yields weighted mean 206Pb/238U age of 438.7±3.0 Ma (MSWD=0.22) and 438.1±2.6 Ma (MSWD=0.28), respectively. And the zircons crystallized in the Kwangsian granites yield 176Hf/177Hf ratios of 0.282 406 to 0.282 518, εHf(438 Ma) values ranging from -3.7 to 0 and Hf model ages (TDM2) of 1 226 to 1 417 Ma. Our U-Pb and Hf isotopic data can be interpreted as the crystallization time of granites, and indicate that it was formed in the ~438 Ma (Caledonian) and may have been formed by reworking of Mesoproterozoic juvenile crust (1.2-1.4 Ga) closely related to partial melting. Together with other published geochronological data, it is proposed that the late Early Paleozoic granites predominantly have a similar formation age and exhibit a planar-shaped distribution, rather than a north-east-striking-distribution pattern in the hinterland of the South China. Moreover, the Caledonian tectonic-magmatic-metallogenic movement may be the one of key reasons for the large-scale magmatism and metal mineralization in the following tectonic episodes, such as Indosinian and Yanshanian in the South China.
2015, 40(1): 34-48.
doi: 10.3799/dqkx.2015.003
Abstract:
Jiang Tso ophiolite, which belongs to the most eastern part of Qieli Lake ophiolite subzone, is located at the middle segment of the Bangonghu-Nujiang suture zone to the south of Pung Lake ophiolite. The rock association of Jiang Tso ophiolite is relatively complete and mainly composed of metamorphic peridotite, gabbro and diabase. Comparing with N-MORB, the major and trace elements of Jiang Tso ophiolite are characterized with high content in Mg and low contents in Ti, K, Na, P and the depletion of elements of Nb, Ta, Hf, and Th. In addition, it displays relative enrichment of Rb, Sr, and Ba. Geochemistry characteristics of the Jiang Tso ophiolite indicate it is of supra-subduction zone type ophiolite and formed in the spreading ridge of back arc basin. The zircon SHRIMP U-Pb weighted average ages of gabbro is 189.8±3.3 Ma (MSWD=0.97), which suggests that the extension time of Tethys oceanic basin in Jiang Tso region was consistent with the formation time of the Dongqiao oceanic basin in the middle part, and also corresponding to that of the oceanic basin in the western part, while later than the development of oceanic basin in the eastern part of the Bangonghu-Nujiang suture zone. From the geochronological data, it can be deduced that the development of the Bangonghu-Nujiang oceanic basin was characterized by being gradually later from east to west.
Jiang Tso ophiolite, which belongs to the most eastern part of Qieli Lake ophiolite subzone, is located at the middle segment of the Bangonghu-Nujiang suture zone to the south of Pung Lake ophiolite. The rock association of Jiang Tso ophiolite is relatively complete and mainly composed of metamorphic peridotite, gabbro and diabase. Comparing with N-MORB, the major and trace elements of Jiang Tso ophiolite are characterized with high content in Mg and low contents in Ti, K, Na, P and the depletion of elements of Nb, Ta, Hf, and Th. In addition, it displays relative enrichment of Rb, Sr, and Ba. Geochemistry characteristics of the Jiang Tso ophiolite indicate it is of supra-subduction zone type ophiolite and formed in the spreading ridge of back arc basin. The zircon SHRIMP U-Pb weighted average ages of gabbro is 189.8±3.3 Ma (MSWD=0.97), which suggests that the extension time of Tethys oceanic basin in Jiang Tso region was consistent with the formation time of the Dongqiao oceanic basin in the middle part, and also corresponding to that of the oceanic basin in the western part, while later than the development of oceanic basin in the eastern part of the Bangonghu-Nujiang suture zone. From the geochronological data, it can be deduced that the development of the Bangonghu-Nujiang oceanic basin was characterized by being gradually later from east to west.
2015, 40(1): 49-60.
doi: 10.3799/dqkx.2015.004
Abstract:
This paper presents LA-ICP-MS zircon U-Pb dating, geochemical and Hf isotopic data of the granodiorite from Miantian intrusion in Yanbian region, with the aim of constraining its petrogenesis and beginning time of subduction of the Paleo-Pacific plate beneath the Eurasian continent. The Miantian intrusion consists mainly of granodiorite with minor diorite. The LA-ICP-MS U-Pb dating results of zircons from the granodiorite indicate that the intrusion formed in the Early Jurassic (177±2 Ma, MSWD=1.13). Geochemically, these rocks fall into the calc-alkaline to high-K calc-alkaline series, with A/CNK ratios of 0.88-1.12, which are sub-aluminous granites, being of the characteristics of I type granitoids, enrichment in LILE (such as K, Ba, Rb), LREE, Th and U, relatively depleted in HFSE (such as Ta, Nb, Ti, P). The εHf(t) values of the granodiorite vary from ±8.72 to ±12.28, and two-stage model ages (TDM2) vary from 437 to 663 Ma. These characteristics suggest that the primary magma was derived from the remelting of juvenile crustal materials (Neoproterozoic to Early Paleozoic). It is concluded that granodiorite from Miantian intrusion formed in compressional structure setting similar to volcanic arc which could be related to the subduction of the Paleo-Pacific plate beneath the Eurasian continent.
This paper presents LA-ICP-MS zircon U-Pb dating, geochemical and Hf isotopic data of the granodiorite from Miantian intrusion in Yanbian region, with the aim of constraining its petrogenesis and beginning time of subduction of the Paleo-Pacific plate beneath the Eurasian continent. The Miantian intrusion consists mainly of granodiorite with minor diorite. The LA-ICP-MS U-Pb dating results of zircons from the granodiorite indicate that the intrusion formed in the Early Jurassic (177±2 Ma, MSWD=1.13). Geochemically, these rocks fall into the calc-alkaline to high-K calc-alkaline series, with A/CNK ratios of 0.88-1.12, which are sub-aluminous granites, being of the characteristics of I type granitoids, enrichment in LILE (such as K, Ba, Rb), LREE, Th and U, relatively depleted in HFSE (such as Ta, Nb, Ti, P). The εHf(t) values of the granodiorite vary from ±8.72 to ±12.28, and two-stage model ages (TDM2) vary from 437 to 663 Ma. These characteristics suggest that the primary magma was derived from the remelting of juvenile crustal materials (Neoproterozoic to Early Paleozoic). It is concluded that granodiorite from Miantian intrusion formed in compressional structure setting similar to volcanic arc which could be related to the subduction of the Paleo-Pacific plate beneath the Eurasian continent.
2015, 40(1): 61-76.
doi: 10.3799/dqkx.2015.005
Abstract:
Zircon U-Pb age, major and trace elements and Sr, Nd isotope compositions of the Riariqu quartz diorites from the south of the Ganzi-Litang suture zone, northeastern Qiangtang terrane are studied to decipher its petrogenesis and geodynamic significance. LA-ICP-MS zircon U-Pb dating yields an emplacement age of 218±1 Ma for the intrusion. Bulk-rock analyses show that these rocks belong to the calc-alkaline series, with SiO2 contents ranging from 53.02% to 62.06%. They are enriched in Al2O3 (15.84%-17.00%) and CaO (6.71%-8.94%), depleted in TiO2 (0.49%-1.01%) and P2O5 (0.04%-0.12%), defining their metaluminous characteristics. All samples have high concentrations of MgO (3.31%-5.66%), Cr (33.45×10-6-176.64×10-6) and Ni (13.34×10-6-43.62×10-6), and resultant high Mg# (50-62). These rocks are enriched in LREE and LILE, and depleted in HFSE with low REE contents (38.05×10-6-61.58×10-6). The (87Sr/86Sr)i ratios range from 0.706 8 to 0.707 9, and εNd(t) values vary from -5.5 to -1.6. The geochemical and Sr-Nd isotopic compositions of the Riariqu quartz diorites are similar to those of high-Mg dioritoids/sanukitoids. We contend that the Riariqu quartz diorites were derived from low-degree partial melting (10%-15%) of a phlogopite-bearing spinel lherzolite mantle, which was metasomatized by sediment-derived melts. Fractional crystallization of pyroxene and amphibole might also occur during the magma evolution. The geochemical characteristics indicate that the Riariqu quartz diorites are arc-related magmatic rocks, and were generated in a subduction-related tectonic setting. Combined with the ophiolites and continental marginal arc lavas in the study area, and the regional adakites in the Yidun terrane, it is suggested that the Riariqu quartz diorites might be generated during the southwestward subduction of Ganzi-Litang Paleo-Tethys Ocean in the Late Triassic.
Zircon U-Pb age, major and trace elements and Sr, Nd isotope compositions of the Riariqu quartz diorites from the south of the Ganzi-Litang suture zone, northeastern Qiangtang terrane are studied to decipher its petrogenesis and geodynamic significance. LA-ICP-MS zircon U-Pb dating yields an emplacement age of 218±1 Ma for the intrusion. Bulk-rock analyses show that these rocks belong to the calc-alkaline series, with SiO2 contents ranging from 53.02% to 62.06%. They are enriched in Al2O3 (15.84%-17.00%) and CaO (6.71%-8.94%), depleted in TiO2 (0.49%-1.01%) and P2O5 (0.04%-0.12%), defining their metaluminous characteristics. All samples have high concentrations of MgO (3.31%-5.66%), Cr (33.45×10-6-176.64×10-6) and Ni (13.34×10-6-43.62×10-6), and resultant high Mg# (50-62). These rocks are enriched in LREE and LILE, and depleted in HFSE with low REE contents (38.05×10-6-61.58×10-6). The (87Sr/86Sr)i ratios range from 0.706 8 to 0.707 9, and εNd(t) values vary from -5.5 to -1.6. The geochemical and Sr-Nd isotopic compositions of the Riariqu quartz diorites are similar to those of high-Mg dioritoids/sanukitoids. We contend that the Riariqu quartz diorites were derived from low-degree partial melting (10%-15%) of a phlogopite-bearing spinel lherzolite mantle, which was metasomatized by sediment-derived melts. Fractional crystallization of pyroxene and amphibole might also occur during the magma evolution. The geochemical characteristics indicate that the Riariqu quartz diorites are arc-related magmatic rocks, and were generated in a subduction-related tectonic setting. Combined with the ophiolites and continental marginal arc lavas in the study area, and the regional adakites in the Yidun terrane, it is suggested that the Riariqu quartz diorites might be generated during the southwestward subduction of Ganzi-Litang Paleo-Tethys Ocean in the Late Triassic.
2015, 40(1): 77-97.
doi: 10.3799/dqkx.2015.006
Abstract:
Located in the southern Bangong Co-Nujiang River suture zone, the Gaerqiong-Galale ore district is an important Cu-Au ore dense district with a large area of volcanics. This study firstly accurately determinates the ages of volcanics in different strata using U-Pb zircon geochronology method, then discusses the structural setting during formation combining the geochemistry characteristics. The results show that volcanic breccia age of Langjiu Group is 141.70±0.47 Ma (MSWD=0.43), rhyolite age of Duoai Group is 136.80±0.48 Ma (MSWD=0.79), formation age is early Early Cretaceous, being attributed to volcanism of Bangong-Nujiang southward subduction; volcanic breccias age of Duoai Group (GE volcanic breccias) is 85.20±0.53 Ma (MSWD=3.40), formation age is Late Cretaceous and does not belong to the Early Cretaceous Duoai Group, which was the volcanism product of Qiangtang landmass and Gangdese landmass converging after ocean basin demise and was later than the mineralization age (86.87±0.50 Ma) of the Gaerqiong Cu-Au deposit. Geochemical characteristics indicate that volcanics are enriched in LILE, e.g. Rb, Th, U and others, but depleted in Ta, Nb, Yb, Ti and other HFSE, and it exhibits arc volcanic rock characteristics. It is found that there was continuous volcanism from early to middle Early Cretaceous during Bangong-Nujiang southward subduction about 30 Ma (140-110 Ma); it was also accompanied by volcanism of Late Cretaceous during Qiangtang landmass and Gangdese landmass converging after ocean basin demise; the age of this volcanism is similar to that of rock mineralization in district, and they may belong to the same magma system.
Located in the southern Bangong Co-Nujiang River suture zone, the Gaerqiong-Galale ore district is an important Cu-Au ore dense district with a large area of volcanics. This study firstly accurately determinates the ages of volcanics in different strata using U-Pb zircon geochronology method, then discusses the structural setting during formation combining the geochemistry characteristics. The results show that volcanic breccia age of Langjiu Group is 141.70±0.47 Ma (MSWD=0.43), rhyolite age of Duoai Group is 136.80±0.48 Ma (MSWD=0.79), formation age is early Early Cretaceous, being attributed to volcanism of Bangong-Nujiang southward subduction; volcanic breccias age of Duoai Group (GE volcanic breccias) is 85.20±0.53 Ma (MSWD=3.40), formation age is Late Cretaceous and does not belong to the Early Cretaceous Duoai Group, which was the volcanism product of Qiangtang landmass and Gangdese landmass converging after ocean basin demise and was later than the mineralization age (86.87±0.50 Ma) of the Gaerqiong Cu-Au deposit. Geochemical characteristics indicate that volcanics are enriched in LILE, e.g. Rb, Th, U and others, but depleted in Ta, Nb, Yb, Ti and other HFSE, and it exhibits arc volcanic rock characteristics. It is found that there was continuous volcanism from early to middle Early Cretaceous during Bangong-Nujiang southward subduction about 30 Ma (140-110 Ma); it was also accompanied by volcanism of Late Cretaceous during Qiangtang landmass and Gangdese landmass converging after ocean basin demise; the age of this volcanism is similar to that of rock mineralization in district, and they may belong to the same magma system.
2015, 40(1): 98-114.
doi: 10.3799/dqkx.2015.007
Abstract:
To understand the genesis of Ma'anshan rock composed of early period pegmatite and megacryst porphyritic adamellite, medium period fine granite and late period granite porphyry dykes, intrusion epochs are confirmed using SHRIMP and LA-ICP-MS zircon U-Pb methods. The dating shows that the pegmatite porphyritic adamellite is 132.2±1.6 Ma (MSWD=1.9, n=11), the megacrysts porphyritic adamellite 127.7 ±1.2 Ma (MSWD=1.1, n=10), the fine-grained granite 128.3±1.1 Ma (MSWD=1.7, n=10) and the granite porphyry dykes 127.4±1.8 Ma (MSWD=0.77, n=11). Rock geochemistry shows that the rock from early to late has the characteristic of alkali series shoshonite series evolving to high potassium calc (during evolution), whereas the differentiation degree gradually increases. The porphyritic adamellites have the characteristics of high ΣREE content, obvious differentiation between light rare earth and heavy rare earth elements, with a strong negative Eu anomaly and weak rightward REE distribution patterns. It is enriched in elements of K, Th, U, Rb and weakly depleted in Ba, Sr, P, Nb, Ta, Ti. The fine-grained granite and granite porphyry dyke have the characteristics of lower ΣREE content, not obvious differentiation between light and heavy rare earth elements, with a strong negative Eu anomaly, and "V"-type REE distribution patterns. It is enriched in elements of K, Th, U, Rb, strongly depleted in Ba, Sr, P, Nb, Ti. Ma'anshan rock was formed by the function of partially molten magma emplacement successively crystallization differentiation and it is the product of intracontinental extension after the Early Cretaceous subduction orogeny in Northwest Zhejiang-South Anhui, with the characteristic of highly fractionated I-type granites.
To understand the genesis of Ma'anshan rock composed of early period pegmatite and megacryst porphyritic adamellite, medium period fine granite and late period granite porphyry dykes, intrusion epochs are confirmed using SHRIMP and LA-ICP-MS zircon U-Pb methods. The dating shows that the pegmatite porphyritic adamellite is 132.2±1.6 Ma (MSWD=1.9, n=11), the megacrysts porphyritic adamellite 127.7 ±1.2 Ma (MSWD=1.1, n=10), the fine-grained granite 128.3±1.1 Ma (MSWD=1.7, n=10) and the granite porphyry dykes 127.4±1.8 Ma (MSWD=0.77, n=11). Rock geochemistry shows that the rock from early to late has the characteristic of alkali series shoshonite series evolving to high potassium calc (during evolution), whereas the differentiation degree gradually increases. The porphyritic adamellites have the characteristics of high ΣREE content, obvious differentiation between light rare earth and heavy rare earth elements, with a strong negative Eu anomaly and weak rightward REE distribution patterns. It is enriched in elements of K, Th, U, Rb and weakly depleted in Ba, Sr, P, Nb, Ta, Ti. The fine-grained granite and granite porphyry dyke have the characteristics of lower ΣREE content, not obvious differentiation between light and heavy rare earth elements, with a strong negative Eu anomaly, and "V"-type REE distribution patterns. It is enriched in elements of K, Th, U, Rb, strongly depleted in Ba, Sr, P, Nb, Ti. Ma'anshan rock was formed by the function of partially molten magma emplacement successively crystallization differentiation and it is the product of intracontinental extension after the Early Cretaceous subduction orogeny in Northwest Zhejiang-South Anhui, with the characteristic of highly fractionated I-type granites.
2015, 40(1): 115-129.
doi: 10.3799/dqkx.2015.008
Abstract:
Shulan ductile shear zone represents a suit of mylonites with sinistral strike-slip characteristics and NNE gneissosity located in south-middle part of the Jiamusi-Yitong fault (called Jia-Yi fault in short). Systematic measurement of the finite strains of feldspar in mylonites indicates that the strain type is extension strain in L-S tectonites. Quartz C-axis EBSD fabric indicates that the quartz fabrics is mainly low-middle temperature prism-glide fabrics with slip system of {0001} < 110>. By calculation of micro structures and quartz C-axis fabrics, it is found that the shearing strain is 0.44; all kinematic vorticities are all more than 0.95, which indicates that the deformation is mainly simple shear. Mineral deformation behaviors, quartz C-axis EBSD fabrics, quartz grain size-frequency diagram and Kruhl thermometer demonstrate that the ductile shear zone was developed under a condition of low-grade greenschist facies, with deformation temperatures ranging from 400 to 500 ℃, and dislocation creep is the main deformation mechanism. The shapes of recrystallized quartz grains in mylonites with their jagged and indented boundaries are natural records of deformation conditions. Fractal analysis shows that the boundaries of recrystallized grains have statistically self-similarities with the numbers of fractal dimension from 1.195 to 1.220. The paleo-stress from dynamically recrystallized grain sizes of quartz are 24.35-27.59 MPa, representing the lower limit of the paleo-stress during mylonization. Together with temperature estimates and applying published flow laws, it is concluded that estimated strain rates on the order of 10-12.00 to 10-13.18 s-1, contrasting with regional strain rate of 10-13.00 to 10-15.00 s-1, indicate deformation of mylonite in Shulan ductile shear zone with low strain rates which are consistent with most other ductile zone, suggest the deformation is slow process. Taking into consideration of the regional tectonic setting of NE China, we suggest that the formation of the ductile shear zone with NNE trending might be related to moving direction changing of the Izanagi plate obliquely subducting under the Eurasia plate.
Shulan ductile shear zone represents a suit of mylonites with sinistral strike-slip characteristics and NNE gneissosity located in south-middle part of the Jiamusi-Yitong fault (called Jia-Yi fault in short). Systematic measurement of the finite strains of feldspar in mylonites indicates that the strain type is extension strain in L-S tectonites. Quartz C-axis EBSD fabric indicates that the quartz fabrics is mainly low-middle temperature prism-glide fabrics with slip system of {0001} < 110>. By calculation of micro structures and quartz C-axis fabrics, it is found that the shearing strain is 0.44; all kinematic vorticities are all more than 0.95, which indicates that the deformation is mainly simple shear. Mineral deformation behaviors, quartz C-axis EBSD fabrics, quartz grain size-frequency diagram and Kruhl thermometer demonstrate that the ductile shear zone was developed under a condition of low-grade greenschist facies, with deformation temperatures ranging from 400 to 500 ℃, and dislocation creep is the main deformation mechanism. The shapes of recrystallized quartz grains in mylonites with their jagged and indented boundaries are natural records of deformation conditions. Fractal analysis shows that the boundaries of recrystallized grains have statistically self-similarities with the numbers of fractal dimension from 1.195 to 1.220. The paleo-stress from dynamically recrystallized grain sizes of quartz are 24.35-27.59 MPa, representing the lower limit of the paleo-stress during mylonization. Together with temperature estimates and applying published flow laws, it is concluded that estimated strain rates on the order of 10-12.00 to 10-13.18 s-1, contrasting with regional strain rate of 10-13.00 to 10-15.00 s-1, indicate deformation of mylonite in Shulan ductile shear zone with low strain rates which are consistent with most other ductile zone, suggest the deformation is slow process. Taking into consideration of the regional tectonic setting of NE China, we suggest that the formation of the ductile shear zone with NNE trending might be related to moving direction changing of the Izanagi plate obliquely subducting under the Eurasia plate.
2015, 40(1): 130-144.
doi: 10.3799/dqkx.2015.009
Abstract:
The adamellite develops in Yanchangbeishan of Lenghu area in Qinghai, which is located in the west segment of the north margin of Qaidam. The samples have higher SiO2 (74.98%-76.92%) and K2O (4.44%-5.93%) contents, but lower MgO (0.04%-0.07%) and CaO (0.43%-0.69%) contents. The Rittmann indices of the rock range in 2.43-2.79, which shows that it belongs to high potassium calc-alkaline series. The alumina saturation average index is 1.01, which indicates that the adamellite belongs to peraluminous granites. Moreover, the samples are intensively depleted in HFSEs (Nb, Ta), with enriched LILEs (K, Rb, Ba, Pb), reflecting the characteristics of island-arc magma. LA-ICP-MS zircon U-Pb dating shows that the formation age of the rock is 252±3 Ma. The zircon Hf isotope analysis reveals that 176Hf/177Hf ratios, varying in 0.282 958 to 0.283 032, have high positive εHf(t) (8.75-14.50) and two-stage Hf model ages (averaged at 385 Ma). In the 176Hf/177Hf -εHf(t) discrimation diagrams, these zircons are plotted nearly on the depleted mantle evolution line. It can be concluded that the rock chiefly derived from the new basaltic lower crust which is originated from depleted mantle. Based on the regional geological background and the geochemical characteristics of the masses, we consider that Yanchangbeishan adamellite bears similar characteristics of its primary magma with mafic-ultramafic rocks of Devonian, which were supposed to be originated from partial melting of the young basaltic lower crust related to subduction of Zongwulong small oceanic basin from south. Thereby, it reveals that the north margin of Qaidam was in volcanic arc or active continental margin tectonic environment during Permian epoch.
The adamellite develops in Yanchangbeishan of Lenghu area in Qinghai, which is located in the west segment of the north margin of Qaidam. The samples have higher SiO2 (74.98%-76.92%) and K2O (4.44%-5.93%) contents, but lower MgO (0.04%-0.07%) and CaO (0.43%-0.69%) contents. The Rittmann indices of the rock range in 2.43-2.79, which shows that it belongs to high potassium calc-alkaline series. The alumina saturation average index is 1.01, which indicates that the adamellite belongs to peraluminous granites. Moreover, the samples are intensively depleted in HFSEs (Nb, Ta), with enriched LILEs (K, Rb, Ba, Pb), reflecting the characteristics of island-arc magma. LA-ICP-MS zircon U-Pb dating shows that the formation age of the rock is 252±3 Ma. The zircon Hf isotope analysis reveals that 176Hf/177Hf ratios, varying in 0.282 958 to 0.283 032, have high positive εHf(t) (8.75-14.50) and two-stage Hf model ages (averaged at 385 Ma). In the 176Hf/177Hf -εHf(t) discrimation diagrams, these zircons are plotted nearly on the depleted mantle evolution line. It can be concluded that the rock chiefly derived from the new basaltic lower crust which is originated from depleted mantle. Based on the regional geological background and the geochemical characteristics of the masses, we consider that Yanchangbeishan adamellite bears similar characteristics of its primary magma with mafic-ultramafic rocks of Devonian, which were supposed to be originated from partial melting of the young basaltic lower crust related to subduction of Zongwulong small oceanic basin from south. Thereby, it reveals that the north margin of Qaidam was in volcanic arc or active continental margin tectonic environment during Permian epoch.
2015, 40(1): 145-162.
doi: 10.3799/dqkx.2015.010
Abstract:
The Bairendaba-Weilasituo deposits are the two of the largest hydrothermal vein-type silver deposits at the southern Great Xing'an Range. This paper presents the studies of the fluid inclusions from wolframite, light sphalerite, quartz and fluorite and the sulfur isotope of sulfides. Results show that the homogenization temperatures and salinities decrease gradually from stages Ⅰ to Ⅲ in the Bairendaba deposit. During the mineralization periods of the Weilasituo deposit, fluid of stages Ⅰ and Ⅱ is featured with higher temperature and salinity. The stage Ⅲ has immiscible fluid, which is of medium temperature and salinity (homogenization temperature is 208 to 294 ℃, salinity is 4.65% to 12.39%), and the higher temperature and lower salinity (homogenization temperature is 333 to 406 ℃, salinity is 3.55% to 6.88%) respectively. The fluid of the stage Ⅳ is characterized by lower temperature and salinity. The gas phase compositions of the fluid inclusion show that ore-forming fluids are CO2-H2O-NaCl system in the two deposits. In the Bairendaba deposit, the temperature and salinity decreased from stagesⅠ to Ⅲ and H-O isotopes show that the earlier stage fluid is magmatic and the later stage fluid is meteoric water. In the Weilasituo deposit, H-O isotopes and fluid composition (CH4/C2H6 varies from 39.271% to 101.438%), showing that the fluid is magmatic. Sulfur isotopes demonstrate that the sulfur is from the deep source in Bairendaba-Weilasituo deposits. It is concluded that metallogenic mechanism of the Bairendaba deposit is the fluid mixing with different origins, metallogenic mechanism of the Weilasituo deposit is cooling and fluid immiscibility.
The Bairendaba-Weilasituo deposits are the two of the largest hydrothermal vein-type silver deposits at the southern Great Xing'an Range. This paper presents the studies of the fluid inclusions from wolframite, light sphalerite, quartz and fluorite and the sulfur isotope of sulfides. Results show that the homogenization temperatures and salinities decrease gradually from stages Ⅰ to Ⅲ in the Bairendaba deposit. During the mineralization periods of the Weilasituo deposit, fluid of stages Ⅰ and Ⅱ is featured with higher temperature and salinity. The stage Ⅲ has immiscible fluid, which is of medium temperature and salinity (homogenization temperature is 208 to 294 ℃, salinity is 4.65% to 12.39%), and the higher temperature and lower salinity (homogenization temperature is 333 to 406 ℃, salinity is 3.55% to 6.88%) respectively. The fluid of the stage Ⅳ is characterized by lower temperature and salinity. The gas phase compositions of the fluid inclusion show that ore-forming fluids are CO2-H2O-NaCl system in the two deposits. In the Bairendaba deposit, the temperature and salinity decreased from stagesⅠ to Ⅲ and H-O isotopes show that the earlier stage fluid is magmatic and the later stage fluid is meteoric water. In the Weilasituo deposit, H-O isotopes and fluid composition (CH4/C2H6 varies from 39.271% to 101.438%), showing that the fluid is magmatic. Sulfur isotopes demonstrate that the sulfur is from the deep source in Bairendaba-Weilasituo deposits. It is concluded that metallogenic mechanism of the Bairendaba deposit is the fluid mixing with different origins, metallogenic mechanism of the Weilasituo deposit is cooling and fluid immiscibility.
2015, 40(1): 163-168.
doi: 10.3799/dqkx.2015.011
Abstract:
The study on the tailings and their physical and chemical compositions can provide important scientific basis for the control of the mine environment and the proper utilization of tailings. The mineral and geochemical characteristics of the tailings of the skarn copper-iron deposits in the Tonglüshan copper deposit are studied in the paper, Hubei Province, and the heavy metals are extracted and separated by the dilute sulfuric acid.The results show that mineral compositions of the tailings have changed significantly after chemical mineral processing and the long-term physical and chemical weathering. The main form of copper mineral is copper oxide in the tailings, with heavy metals increasingly enriched from the top down. The enrichment of heavy metal elements peaks in the sixth horizon of the tailing pond. It is found that the copper in the tailing pond has potential recycle value.
The study on the tailings and their physical and chemical compositions can provide important scientific basis for the control of the mine environment and the proper utilization of tailings. The mineral and geochemical characteristics of the tailings of the skarn copper-iron deposits in the Tonglüshan copper deposit are studied in the paper, Hubei Province, and the heavy metals are extracted and separated by the dilute sulfuric acid.The results show that mineral compositions of the tailings have changed significantly after chemical mineral processing and the long-term physical and chemical weathering. The main form of copper mineral is copper oxide in the tailings, with heavy metals increasingly enriched from the top down. The enrichment of heavy metal elements peaks in the sixth horizon of the tailing pond. It is found that the copper in the tailing pond has potential recycle value.
2015, 40(1): 169-178.
doi: 10.3799/dqkx.2015.012
Abstract:
Based on the regional tectonic analysis of Beibu Gulf basin, in this paper, the tectonic activities of Fushan sag is studied, the dynamic formation mechanism of the sag is discussed, and the formation mechanism of double-layer structure in Paleogene strata of the eastern area is analyzed. It is regarded that Fushan sag was under the dual effect of sinistral strike-slip of Red River fault and clockwise rotation of Hainan uplift. During the deposition period of the third member of Liushagang Formation (Els3), intense horizontal extension occurred during the rotation and pull-apart of the sag, which provided dynamic source for the antithetic faults of the lower tectonic layer in the eastern area. The rapid uplift of Hainan uplift led to the formation of gravity slumping growth faults in the upper tectonic layer. In the Early Oligocene, the intrusive igneous rocks in the second member of Liushagang Formation (Els2) formed a natural barrier. Finally, there formed the double-layer structure. The forming process of the double-layer can be divided into five major stages as follows: rifting embryonic period, extending faulted period of the lower tectonic layer, development period of middle plastic layer, formation period of tectonic system, and finalizing period of double-layer structure.
Based on the regional tectonic analysis of Beibu Gulf basin, in this paper, the tectonic activities of Fushan sag is studied, the dynamic formation mechanism of the sag is discussed, and the formation mechanism of double-layer structure in Paleogene strata of the eastern area is analyzed. It is regarded that Fushan sag was under the dual effect of sinistral strike-slip of Red River fault and clockwise rotation of Hainan uplift. During the deposition period of the third member of Liushagang Formation (Els3), intense horizontal extension occurred during the rotation and pull-apart of the sag, which provided dynamic source for the antithetic faults of the lower tectonic layer in the eastern area. The rapid uplift of Hainan uplift led to the formation of gravity slumping growth faults in the upper tectonic layer. In the Early Oligocene, the intrusive igneous rocks in the second member of Liushagang Formation (Els2) formed a natural barrier. Finally, there formed the double-layer structure. The forming process of the double-layer can be divided into five major stages as follows: rifting embryonic period, extending faulted period of the lower tectonic layer, development period of middle plastic layer, formation period of tectonic system, and finalizing period of double-layer structure.
2015, 40(1): 179-188.
doi: 10.3799/dqkx.2015.013
Abstract:
Thermokarst lakes have greatly influenced landscapes in cold regions, and the thermal erosion of their lakeshores may induce ground instability that affects infrastructure. Our study area includes three sub-regions where thermokarst lakes have obviously extended: the Chumaerhe high plateau, Wudaoliang basin, and Beiluhe basin. Based on continual monitoring of four lakes, and sporadic observation of lake-bottom temperatures of many lakes using HOBO Sensors in 2009—2010, the thermal regime of lake bottoms and the relation between lake-bottom temperature and water depth are examined. The results show that in January, when ice cover was present, the lake-bottom temperatures at 90% of the lakes in Chumarhe high plateau were below 0 ℃, which is likely because of shallow depths and high salinity of lakes in the region. However, the lake-bottom temperature of most lakes in Wudaoliang and Beiluhe basins were above 0 ℃, except in some lakes shallower than the maximum ice thickness. In general, lake-bottom temperature in the three sub-regions increased with water depth during this period. When lakes were free of ice between June and October, the lake-bottom temperatures in the three sub-regions were all warm and the highest temperature was near 18 ℃. The seasonal increase in lake-bottom temperature in summer is more rapid in shallower lakes, and the temperatures were inversely related to water depth. The annual variation in lake-bottom temperature approximates a sinusoidal curve, with the coldest temperature occurring in January to February and the warmest in July to August.
Thermokarst lakes have greatly influenced landscapes in cold regions, and the thermal erosion of their lakeshores may induce ground instability that affects infrastructure. Our study area includes three sub-regions where thermokarst lakes have obviously extended: the Chumaerhe high plateau, Wudaoliang basin, and Beiluhe basin. Based on continual monitoring of four lakes, and sporadic observation of lake-bottom temperatures of many lakes using HOBO Sensors in 2009—2010, the thermal regime of lake bottoms and the relation between lake-bottom temperature and water depth are examined. The results show that in January, when ice cover was present, the lake-bottom temperatures at 90% of the lakes in Chumarhe high plateau were below 0 ℃, which is likely because of shallow depths and high salinity of lakes in the region. However, the lake-bottom temperature of most lakes in Wudaoliang and Beiluhe basins were above 0 ℃, except in some lakes shallower than the maximum ice thickness. In general, lake-bottom temperature in the three sub-regions increased with water depth during this period. When lakes were free of ice between June and October, the lake-bottom temperatures in the three sub-regions were all warm and the highest temperature was near 18 ℃. The seasonal increase in lake-bottom temperature in summer is more rapid in shallower lakes, and the temperatures were inversely related to water depth. The annual variation in lake-bottom temperature approximates a sinusoidal curve, with the coldest temperature occurring in January to February and the warmest in July to August.
