2018 Vol. 43, No. 7
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2018, 43(7): 2195-2205.
doi: 10.3799/dqkx.2018.538
Abstract:
Very abundant bivalves have been found from the Dongchong Formation, Yunkai area, Western Guangdong Province. The bivalve fauna consists of Praenucula cf. sharpei Babin and Gutierrez-Marco, P. sp., Homilodonta regularis (Portlock), Similodonta similis (Ulrich), S. cf. cerys Cope, S. sp., Trigonoconcha acuta Sanchez, Concavodonta sp., Arcodonta sp., Sthenodonta cf. eastii (Tata), S. sp., Nuculites cf. cylindricus (Portlock), N. sp., Phestia sp., Cardiolaria? sp., Inaequidens cf. davisi Pojeta and Gilbert-Tomlinson, I. sp., Mytilarca? sp., Cyrtodonta sp., Modiolopsis spp., Carminodonta sp., Famatinodonta sp. and several un-named new genera, being featured by small individual size, high abundance and diversity, palaeotaxodont assuming absolute superiority. Several Middle Ordovician trilobites and brachiopods occurred together with the bivalves. That fauna offers new data of Middle Ordovician bivalves, and will be helpful for better understanding of the early evolution of bivalves as well as the stratigraphic subdivision and correlations of Ordovician strata in the research area.
Very abundant bivalves have been found from the Dongchong Formation, Yunkai area, Western Guangdong Province. The bivalve fauna consists of Praenucula cf. sharpei Babin and Gutierrez-Marco, P. sp., Homilodonta regularis (Portlock), Similodonta similis (Ulrich), S. cf. cerys Cope, S. sp., Trigonoconcha acuta Sanchez, Concavodonta sp., Arcodonta sp., Sthenodonta cf. eastii (Tata), S. sp., Nuculites cf. cylindricus (Portlock), N. sp., Phestia sp., Cardiolaria? sp., Inaequidens cf. davisi Pojeta and Gilbert-Tomlinson, I. sp., Mytilarca? sp., Cyrtodonta sp., Modiolopsis spp., Carminodonta sp., Famatinodonta sp. and several un-named new genera, being featured by small individual size, high abundance and diversity, palaeotaxodont assuming absolute superiority. Several Middle Ordovician trilobites and brachiopods occurred together with the bivalves. That fauna offers new data of Middle Ordovician bivalves, and will be helpful for better understanding of the early evolution of bivalves as well as the stratigraphic subdivision and correlations of Ordovician strata in the research area.
2018, 43(7): 2206-2221.
doi: 10.3799/dqkx.2018.155
Abstract:
The Ediacaran Doushantuo Formation in Yangtze Gorges area is one of the most intensively investigated units for Ediacaran biological and environmental study in the world. However, the Doushantuo Formation was less investigated in the northern Huangling area than the southern one. The correlation of Doushantuo Formation between the two areas is still unclear. Four complete sections of the Doushantuo Formation, including two drill cores and two outcrop sections, are documented in this paper. The Doushantuo Formation in the northern Huangling area is subdivided into four members. Three sequence boundaries are recognized in the Doushantuo Formation, separately at the base of Member Ⅰ, the top of the second part of Member Ⅱ and the boundary between Member Ⅲ and Member Ⅳ. According to the lithostratigraphic and sequence stratigraphic studies, the Doushantuo Formation between the northern and southern Huangling areas can be well correlated. This study provides a firm base for the statigraphic study of the phosphate strata.
The Ediacaran Doushantuo Formation in Yangtze Gorges area is one of the most intensively investigated units for Ediacaran biological and environmental study in the world. However, the Doushantuo Formation was less investigated in the northern Huangling area than the southern one. The correlation of Doushantuo Formation between the two areas is still unclear. Four complete sections of the Doushantuo Formation, including two drill cores and two outcrop sections, are documented in this paper. The Doushantuo Formation in the northern Huangling area is subdivided into four members. Three sequence boundaries are recognized in the Doushantuo Formation, separately at the base of Member Ⅰ, the top of the second part of Member Ⅱ and the boundary between Member Ⅲ and Member Ⅳ. According to the lithostratigraphic and sequence stratigraphic studies, the Doushantuo Formation between the northern and southern Huangling areas can be well correlated. This study provides a firm base for the statigraphic study of the phosphate strata.
2018, 43(7): 2222-2233.
doi: 10.3799/dqkx.2018.226
Abstract:
To date there are only a few studies on genetic potential of the Early Carboniferous shale in Guizhong depression, which severely restricts the unconventional oil and gas exploration (mainly shale gas) in this area. In this study, typical profile measurements and sampling analysis of the shale from the Early Carboniferous slope facies in Guizhong depression were conducted, and then the hydrocarbon generating potential of the shale was discussed from multiple perspectives, including the TOC content, rock pyrolysis, organic carbon isotope composition, n-alkane composition and the vitrinite reflectance of the shale. Combined with regional tectonic evolution history, three models of near source gas reservoirs, which are closely related to the shale from the Lower Carboniferous Yanguanian Stage, are summarized. The results show that, TOC values are ranging from 0.25% to 15.67%. The shales deposited before forced regressive are rich in organic matter, with TOC values greater than 2%. There are weak positive correlations between TOC value and chloroform bitumen "A", the hydrocarbon generating potential and the total hydrocarbon respectively. The type of the organic metter in the shales is mainly classified as kerogen type Ⅱ. The values of Ro are ranging from 1.72% to 2.78%, in the overmature stage. According to the lithologic characteristics and the present tectonic position of Guizhong depression, we suggest that the ramp structure zone in the middle of the depression is favorable for the formation of near source gas reservoirs, while the back thrust zone is poor. The thrust nappe structure zone in the edge of the depression is the near source gas accumulation zone with lithologic traps.
To date there are only a few studies on genetic potential of the Early Carboniferous shale in Guizhong depression, which severely restricts the unconventional oil and gas exploration (mainly shale gas) in this area. In this study, typical profile measurements and sampling analysis of the shale from the Early Carboniferous slope facies in Guizhong depression were conducted, and then the hydrocarbon generating potential of the shale was discussed from multiple perspectives, including the TOC content, rock pyrolysis, organic carbon isotope composition, n-alkane composition and the vitrinite reflectance of the shale. Combined with regional tectonic evolution history, three models of near source gas reservoirs, which are closely related to the shale from the Lower Carboniferous Yanguanian Stage, are summarized. The results show that, TOC values are ranging from 0.25% to 15.67%. The shales deposited before forced regressive are rich in organic matter, with TOC values greater than 2%. There are weak positive correlations between TOC value and chloroform bitumen "A", the hydrocarbon generating potential and the total hydrocarbon respectively. The type of the organic metter in the shales is mainly classified as kerogen type Ⅱ. The values of Ro are ranging from 1.72% to 2.78%, in the overmature stage. According to the lithologic characteristics and the present tectonic position of Guizhong depression, we suggest that the ramp structure zone in the middle of the depression is favorable for the formation of near source gas reservoirs, while the back thrust zone is poor. The thrust nappe structure zone in the edge of the depression is the near source gas accumulation zone with lithologic traps.
2018, 43(7): 2234-2248.
doi: 10.3799/dqkx.2018.591
Abstract:
The Devonian sedimentary strata, widely developed in the Qinling orogenic belt, are good vehicles to reveal the ocean-continent transition, tectonic attributes and tectonic settings of the Qinling orogenic belt in the Middle Paleozoic. This study presents new geochemical and zircon U-Pb isotopic data for the Devonian sedimentary rocks in Xichuan area. Geochemical data show that the Devonian clastic rocks are characterized by moderate compositional maturity, and a higher portion of sediment recycling, and are likely to have been derived predominantly from felsic igneous rocks within upper-continental-crust. The detrital zircon ages are mainly concentrated in Late Neoproterozoic-Paleozoic (0.40-0.63 Ga), Neoproterozoic (0.7-0.9 Ga) and Mesoproterozoic (1.0-1.6 Ga), with a small amount of ages in Paleoproterozoic and Middle-Late Archean. Comprehensive analysis suggests that the Devonian basin in Xichuan area has beea formed in passive continental margin, and its provenance may be mainly the uplift basement and tectonic highland of the South Qinling, not from the North Qinling. The subduction accretion event along the Shangdan Ocean probably did not affect the interior of South Qinling.
The Devonian sedimentary strata, widely developed in the Qinling orogenic belt, are good vehicles to reveal the ocean-continent transition, tectonic attributes and tectonic settings of the Qinling orogenic belt in the Middle Paleozoic. This study presents new geochemical and zircon U-Pb isotopic data for the Devonian sedimentary rocks in Xichuan area. Geochemical data show that the Devonian clastic rocks are characterized by moderate compositional maturity, and a higher portion of sediment recycling, and are likely to have been derived predominantly from felsic igneous rocks within upper-continental-crust. The detrital zircon ages are mainly concentrated in Late Neoproterozoic-Paleozoic (0.40-0.63 Ga), Neoproterozoic (0.7-0.9 Ga) and Mesoproterozoic (1.0-1.6 Ga), with a small amount of ages in Paleoproterozoic and Middle-Late Archean. Comprehensive analysis suggests that the Devonian basin in Xichuan area has beea formed in passive continental margin, and its provenance may be mainly the uplift basement and tectonic highland of the South Qinling, not from the North Qinling. The subduction accretion event along the Shangdan Ocean probably did not affect the interior of South Qinling.
2018, 43(7): 2249-2275.
doi: 10.3799/dqkx.2018.574
Abstract:
The Mesozoic tectonic evolution in Yunkai massif has always been one of hot topics in South China. Zircons from five metamorphic rocks including migmatite and gneiss and one granite from the metamorphic basement in Yunkai massif were measured by the LA-ICP-MS U-Pb dating method, yielding 7 metamorphic (anatectic) or magmatic ages (440.3±3.3 Ma, 230.2±2.9 Ma, 230.7±1.3 Ma, 459.5±2.7 Ma, 431.5±4.3 Ma, 229.2±5.4 Ma, 229.7±2.7 Ma) and 2 groups of detrital ages. Both the detrital zircons showed Archaean-Neoproterozoic age range with~1.0 Ga age peaks, which were similar with those of the Tiantangshan Group and the Yunkai Group. Together with the regional data, it was concluded that the Tiantangshan Group and the Yunkai Group, which were analogous in provenance and formed in Early Palaeozoic-Neoproterozoic, were broadly overprinted by the Indosinian metamorphism (anatexis)-deformation-fluid activities after the Caledonian tectonic-thermal events, resulting in differences in metamorphic grade and appearance. In situ zircon Lu-Hf isotopic analysis from four samples show that both the isotopic compositions of Caledonian metamorphic and anatectic zircons were similar with each other, which was ascribed to inheriting the compositions of provenance rocks, whereas the different isotopic compositions of Indosinian metamorphic and anatectic zircons could have been caused by individual mechanism of metamorphic and anatectic processes. It was inferred that the dominant Paleo-Mesoproterozoic crustal material played important role in the metamorphism and anatexis processes in Caledonian and Indosinian, and a few mantle-derived material was added in the anatectic processes in Caledonian and Indosinian with relatively remarkable contribution of mantle-derived material in Indosinian.
The Mesozoic tectonic evolution in Yunkai massif has always been one of hot topics in South China. Zircons from five metamorphic rocks including migmatite and gneiss and one granite from the metamorphic basement in Yunkai massif were measured by the LA-ICP-MS U-Pb dating method, yielding 7 metamorphic (anatectic) or magmatic ages (440.3±3.3 Ma, 230.2±2.9 Ma, 230.7±1.3 Ma, 459.5±2.7 Ma, 431.5±4.3 Ma, 229.2±5.4 Ma, 229.7±2.7 Ma) and 2 groups of detrital ages. Both the detrital zircons showed Archaean-Neoproterozoic age range with~1.0 Ga age peaks, which were similar with those of the Tiantangshan Group and the Yunkai Group. Together with the regional data, it was concluded that the Tiantangshan Group and the Yunkai Group, which were analogous in provenance and formed in Early Palaeozoic-Neoproterozoic, were broadly overprinted by the Indosinian metamorphism (anatexis)-deformation-fluid activities after the Caledonian tectonic-thermal events, resulting in differences in metamorphic grade and appearance. In situ zircon Lu-Hf isotopic analysis from four samples show that both the isotopic compositions of Caledonian metamorphic and anatectic zircons were similar with each other, which was ascribed to inheriting the compositions of provenance rocks, whereas the different isotopic compositions of Indosinian metamorphic and anatectic zircons could have been caused by individual mechanism of metamorphic and anatectic processes. It was inferred that the dominant Paleo-Mesoproterozoic crustal material played important role in the metamorphism and anatexis processes in Caledonian and Indosinian, and a few mantle-derived material was added in the anatectic processes in Caledonian and Indosinian with relatively remarkable contribution of mantle-derived material in Indosinian.
2018, 43(7): 2276-2293.
doi: 10.3799/dqkx.2018.529
Abstract:
Numerous researches have focused on the Early Paleozoic magmatic rocks widely developed in South China, because of their ambiguous petrogenesis. We present here the zircon U-Pb dating and geochemical data for the Ningtan gneissic granitic pluton in the Yunkai terrane, which experienced intensive tectonic-magmatic activity during the Early Paleozoic. Cathodoluminescence imaging reveals that these zircon crystals generally have oscillatory zoning and the inherited zircons are exposed. LA-ICP-MS zircon U-Pb dating of the three samples yielded weighted mean ages of 430±2 Ma, 426±4 Ma and 433±2 Ma, respectively indicating that the pluton was emplaced in the Early Paleozoic. The major element geochemistry is characterized by high content of Si, Al, low content of Mg, Ca and the appearance of corundum in CIPW standard mineral. The Ningtan pluton is composed of high-K calc alkaline peraluminous granitoids. The REE distribution curves show the seagull-shape, with strong depletion in Eu anomaly. They exhibit strongly negative high field strength elements and enrichment of light rare earth elements, large ion lithophile elements. The isotope data are characterized by high initial (87Sr/86Sr)i ratio (0.711 30 to 0.718 42), negative εNd(t) values (-8.6 to -8.1) and negative εHf(t) values (-10.9 to -2.5). The two stage Nd-isotope model ages (TDM2) are 1 827-1 848 Ma. The two stage Hf-isotope model ages (TDM2) mainly distribute in 1 600-2 000 Ma, with the peak value of~1 800 Ma. These geochemical data indicate that the Ningtan pluton belongs to the crust-derived granite category, originated from the remelting of Cathaysia Proterozoic basement, mainly metamorphic argillaceous rocks and sandstone. The emplacement of the Ningtan pluton, was formed in an extensional background, as a result of the intracontinental orogenic collapse of South China in Early Paleozoic.
Numerous researches have focused on the Early Paleozoic magmatic rocks widely developed in South China, because of their ambiguous petrogenesis. We present here the zircon U-Pb dating and geochemical data for the Ningtan gneissic granitic pluton in the Yunkai terrane, which experienced intensive tectonic-magmatic activity during the Early Paleozoic. Cathodoluminescence imaging reveals that these zircon crystals generally have oscillatory zoning and the inherited zircons are exposed. LA-ICP-MS zircon U-Pb dating of the three samples yielded weighted mean ages of 430±2 Ma, 426±4 Ma and 433±2 Ma, respectively indicating that the pluton was emplaced in the Early Paleozoic. The major element geochemistry is characterized by high content of Si, Al, low content of Mg, Ca and the appearance of corundum in CIPW standard mineral. The Ningtan pluton is composed of high-K calc alkaline peraluminous granitoids. The REE distribution curves show the seagull-shape, with strong depletion in Eu anomaly. They exhibit strongly negative high field strength elements and enrichment of light rare earth elements, large ion lithophile elements. The isotope data are characterized by high initial (87Sr/86Sr)i ratio (0.711 30 to 0.718 42), negative εNd(t) values (-8.6 to -8.1) and negative εHf(t) values (-10.9 to -2.5). The two stage Nd-isotope model ages (TDM2) are 1 827-1 848 Ma. The two stage Hf-isotope model ages (TDM2) mainly distribute in 1 600-2 000 Ma, with the peak value of~1 800 Ma. These geochemical data indicate that the Ningtan pluton belongs to the crust-derived granite category, originated from the remelting of Cathaysia Proterozoic basement, mainly metamorphic argillaceous rocks and sandstone. The emplacement of the Ningtan pluton, was formed in an extensional background, as a result of the intracontinental orogenic collapse of South China in Early Paleozoic.
2018, 43(7): 2294-2309.
doi: 10.3799/dqkx.2018.184
Abstract:
The study of the late Mesozoic granites in South China and its tectonic setting is a hotspot issue. In this paper, new zircon U-Pb ages and geochemical data of the Haiyan A-type granites and mafic microgranule enclaves (MMEs) in southern Guangdong are reported, and the petrogenesis and implications of these rocks are discussed. We present new zircon LA-ICP-MS U-Pb ages of the Haiyan granites and its MMEs, and the results of the age analyzing show that the granites and MMEs were generated in Early Cretaceous (144.0±1.7 Ma and 141.1±2.5 Ma, respectively). The Haiyan granites have the typical features of A-type granites, they are characterized by enrichment in silicon, alkali and iron contents, and depletion in magnesium and calcium contents, with high 10 000×Ga/A1 values and Zr+Nb+Ce+Y components. Small amounts of MMEs occur in the Haiyan granites, and they are characterized by enrichment in alkali and more enrichment in potassium contents, high aluminum and low titanium, strong enrichment in the large ion lithophile elements and light rare earth elements, belonging to shoshonitic rocks. Granites have ISr values of 0.706 6-0.712 2, εNd(t) values of -7.01——2.03. While MMES have relatively lower ISr values (0.708 5-0.711 1) and higher εNd(t) values (-6.99——2.23). Combining with geochemical and Sr-Nd isotopic compositions, we suggest that the Haiyan granites were likely generated by partial melting of the Mesoproterozoic crustal rocks, and the primitive compositions of shoshonitic MMEs likely originated from enriched mantle source somatized by subducted oceanic sediments. The findings of the Haiyan A-type granites and shoshonitic mafic enclaves suggest that the regional tectonic setting during the Early Cretaceous was in extension, and different from southeast coastal areas with compressive tectonic regime.
The study of the late Mesozoic granites in South China and its tectonic setting is a hotspot issue. In this paper, new zircon U-Pb ages and geochemical data of the Haiyan A-type granites and mafic microgranule enclaves (MMEs) in southern Guangdong are reported, and the petrogenesis and implications of these rocks are discussed. We present new zircon LA-ICP-MS U-Pb ages of the Haiyan granites and its MMEs, and the results of the age analyzing show that the granites and MMEs were generated in Early Cretaceous (144.0±1.7 Ma and 141.1±2.5 Ma, respectively). The Haiyan granites have the typical features of A-type granites, they are characterized by enrichment in silicon, alkali and iron contents, and depletion in magnesium and calcium contents, with high 10 000×Ga/A1 values and Zr+Nb+Ce+Y components. Small amounts of MMEs occur in the Haiyan granites, and they are characterized by enrichment in alkali and more enrichment in potassium contents, high aluminum and low titanium, strong enrichment in the large ion lithophile elements and light rare earth elements, belonging to shoshonitic rocks. Granites have ISr values of 0.706 6-0.712 2, εNd(t) values of -7.01——2.03. While MMES have relatively lower ISr values (0.708 5-0.711 1) and higher εNd(t) values (-6.99——2.23). Combining with geochemical and Sr-Nd isotopic compositions, we suggest that the Haiyan granites were likely generated by partial melting of the Mesoproterozoic crustal rocks, and the primitive compositions of shoshonitic MMEs likely originated from enriched mantle source somatized by subducted oceanic sediments. The findings of the Haiyan A-type granites and shoshonitic mafic enclaves suggest that the regional tectonic setting during the Early Cretaceous was in extension, and different from southeast coastal areas with compressive tectonic regime.
2018, 43(7): 2313-2329.
doi: 10.3799/dqkx.2018.180
Abstract:
For studying the Late Yanshan magmatism in South China hinterland, and analyzing its petrogenesis and tectonic significance, this paper carries out systematical geochronological, geochemical and Sm-Nd isotopic investigations on the Kunlunguan granitic pluton in central Guangxi. LA-ICP-MS zircon U-Pb dating yields a weighted mean 206Pb/238U age of 97.7±1.3 Ma (MSWD=1.6), implying its Late Yanshan intrusion time. Geochemical compositions show that it is enriched in Si (SiO2=69.42%-72.52%), alkali (total alkali=7.43%-8.43%), K(K2O=4.00%-5.02%, K2O/Na2O=1.17-1.62), Al(Al2O3=13.65%-14.25%), but depleted in Ca(CaO=1.20%-2.78%). Rb, Th, U, K, Pb elements are enriched in the intrusion while Ba, Nb, Sr, P, Ti elements are depleted. REE is characterized by obvious negative Eu anomalies (δEu=0.45-0.61), and exhibits right-dipping patterns with LREE enrichment. Its aluminum saturation index value (A/CNK) ranges from 0.93 to 1.16, while redman index value (δ) ranges from 2.06 to 2.41, indicating the intrusion belongs to high-K calc-alkaline series and metaluminous to peraluminous rocks. Its εNd(t) value varies between -7.68 to -10.31, and the correspondent two-stage Nd isotopic modal ages range from 1.52 to 1.73 Ga (average value is 1.58 Ga). Mineralogy and geochemical characteristics indicate that Kunlunguan pluton is A-type granite. It has formed by partial melting of the Cathaysia paleoproterozoic felsic crustal material, being mixed with some mantle drived mafic malts, under a low-pressure, high-temperature condition at an extensional tectonic setting. Taking the igneous and metallogenic events in central Guangxi and adjacent areas into consideration, this study suggests that the lithosphere of South China hinterland thinned in 100-90 Ma.
For studying the Late Yanshan magmatism in South China hinterland, and analyzing its petrogenesis and tectonic significance, this paper carries out systematical geochronological, geochemical and Sm-Nd isotopic investigations on the Kunlunguan granitic pluton in central Guangxi. LA-ICP-MS zircon U-Pb dating yields a weighted mean 206Pb/238U age of 97.7±1.3 Ma (MSWD=1.6), implying its Late Yanshan intrusion time. Geochemical compositions show that it is enriched in Si (SiO2=69.42%-72.52%), alkali (total alkali=7.43%-8.43%), K(K2O=4.00%-5.02%, K2O/Na2O=1.17-1.62), Al(Al2O3=13.65%-14.25%), but depleted in Ca(CaO=1.20%-2.78%). Rb, Th, U, K, Pb elements are enriched in the intrusion while Ba, Nb, Sr, P, Ti elements are depleted. REE is characterized by obvious negative Eu anomalies (δEu=0.45-0.61), and exhibits right-dipping patterns with LREE enrichment. Its aluminum saturation index value (A/CNK) ranges from 0.93 to 1.16, while redman index value (δ) ranges from 2.06 to 2.41, indicating the intrusion belongs to high-K calc-alkaline series and metaluminous to peraluminous rocks. Its εNd(t) value varies between -7.68 to -10.31, and the correspondent two-stage Nd isotopic modal ages range from 1.52 to 1.73 Ga (average value is 1.58 Ga). Mineralogy and geochemical characteristics indicate that Kunlunguan pluton is A-type granite. It has formed by partial melting of the Cathaysia paleoproterozoic felsic crustal material, being mixed with some mantle drived mafic malts, under a low-pressure, high-temperature condition at an extensional tectonic setting. Taking the igneous and metallogenic events in central Guangxi and adjacent areas into consideration, this study suggests that the lithosphere of South China hinterland thinned in 100-90 Ma.
2018, 43(7): 2330-2349.
doi: 10.3799/dqkx.2018.178
Abstract:
The temporal and spatial distribution of Indonesian granitoid in northern Yuechengling batholith is still uncertained. In this paper, a compilation of petrology, zircon U-Pb chronology, geochemistry and Nd-Hf isotopes was used on the granitoid to solve this uncertainty. The result shows Indonesian granitoid spreads in north area of the border with the age of 236-222 Ma, and mainly consists of medium to fine grained tourmaline-bearing monzogranites, with accessory minerals assemblage of zircon, zoisite (and/or clinozoisite), apatite and garnet. The granitic samples have characteristics of high SiO2, alkaline, low CaO, MgO, P2O5 contents, and weak to strong peraluminous (A/CNK=1.07-1.17), with enrichment of Rb, Th, U and strong depletion of Ba, Sr, Eu, Nb, Ti elements. Source of early stage of Indonesian granitic rocks mainly consisting of metagreywackes, with small amount of new crustal component. Those of late stage are inhomogeneous mixing of metagreywackes and metapelites. Granitic rocks of both stage have stable high negative εNd(t)(-9.3——10.6) and εHf(t) (-5.4——11.9) ratios with source's average crustal residence age of ca 1.8 Ga. Integrated with Indonesian tectonic involvement of South China, formation of granitic magma is perhaps due to dehydration melting of mica-riched metasediments during post-orogenic thickened crust environment, migration and emplacement of the magma is controlled by relaxation of deep fault adjacent to the batholith.
The temporal and spatial distribution of Indonesian granitoid in northern Yuechengling batholith is still uncertained. In this paper, a compilation of petrology, zircon U-Pb chronology, geochemistry and Nd-Hf isotopes was used on the granitoid to solve this uncertainty. The result shows Indonesian granitoid spreads in north area of the border with the age of 236-222 Ma, and mainly consists of medium to fine grained tourmaline-bearing monzogranites, with accessory minerals assemblage of zircon, zoisite (and/or clinozoisite), apatite and garnet. The granitic samples have characteristics of high SiO2, alkaline, low CaO, MgO, P2O5 contents, and weak to strong peraluminous (A/CNK=1.07-1.17), with enrichment of Rb, Th, U and strong depletion of Ba, Sr, Eu, Nb, Ti elements. Source of early stage of Indonesian granitic rocks mainly consisting of metagreywackes, with small amount of new crustal component. Those of late stage are inhomogeneous mixing of metagreywackes and metapelites. Granitic rocks of both stage have stable high negative εNd(t)(-9.3——10.6) and εHf(t) (-5.4——11.9) ratios with source's average crustal residence age of ca 1.8 Ga. Integrated with Indonesian tectonic involvement of South China, formation of granitic magma is perhaps due to dehydration melting of mica-riched metasediments during post-orogenic thickened crust environment, migration and emplacement of the magma is controlled by relaxation of deep fault adjacent to the batholith.
2018, 43(7): 2350-2369.
doi: 10.3799/dqkx.2018.569
Abstract:
The Echeng pluton is one of the six large plutons in southeastern Hubei Province, which is located in the northernmost of the region. The Chengchao iron deposit, the largest skarn iron deposit in the Middle-Lower reaches of Yangtze River belt, has occurred in the southern contact zone of the Echeng pluton. Many researches have showed that the Chengchao iron mineralization was closely connected with the magma evolution of the Echeng complex, whereas whether the mineralization is related to granitic rocks or dioritic rocks is still controversial. In this paper, we present U-Pb age, geochemical, and Sr-Nd-Hf isotopic data to provide constraints on the petrogenesis of the Echeng intrusion and discuss the relationship of magma evolution and iron mineralization. The Echeng complex mainly consists of granite, quartz monzonite, granite porphyry and small-scale diorite. LA-ICP-MS zircon U-Pb data indicates that the Echeng complex began to emplace at 140±1 Ma by medium-grained diorite phase, subsequently fine-grained diorite (132±2 Ma), granite porphyry (130±2 Ma), granite including medium-fine grained (129±2 Ma) and medium-grained (129±1 Ma) phases and quartz monzonite (129±1 Ma) were emplaced in order. According to geochemical characteristics, all the rocks can broadly be divided into two groups:(1) granitoids including granite, granite porphyry, hornblende quartz monzonite are potassic and are characterized by high SiO2, low TiO2, FeOt, MnO, MgO concentrations; (2) diorite including fine and medium grained diorites, are sodic and are characterized by low SiO2, high TiO2, FeOt, MnO, MgO concentrations. These rocks are enriched in light rare earth elements (LREEs) and large ion lithophile elements (LILE) such as Rb, Th, and depleted in high field strength elements(HFSE) such as Nb, P and Ti. Moreover, the Echeng granitoids show obviously negative Eu anomalies but the diorites have no such a signature. The Echeng granitoids have more negative εNd(t) values ranging from -11.7 to -10.1 and zircon εHf(t) values ranging from -22.91 to -9.83, and the diorites have relatively high εNd(t) value (-7.6) and zircon εHf(t) values ranging from -12.04 to -4.69. The geochemical and isotopic data suggests that the Echeng granitoids belong to highly fractionated I-type granites and were mainly derived from partial melting of the Paleoproterozoic basement, possibly with the addition of a small amount of mantle-derived materials, whereas the diorites were mainly originated from the enriched lithospheric mantle, followed by a certain degree of crystallization fractionation. The new geochronological data suggests that the Echeng granitoids and fine-grained diorite broadly coeval with the main mineralization of the Chengchao iron deposit. Combining with field contact relationship and previous research results, the Chengchao iron mineralization was probably related to the Echeng granitoids and fine-grained diorite. Based on the mineralizations in southeastern Hubei Province, magmatism is more closely related to iron mineralization with the increases of differentiation degrees and crustal contributions in the magma source.
The Echeng pluton is one of the six large plutons in southeastern Hubei Province, which is located in the northernmost of the region. The Chengchao iron deposit, the largest skarn iron deposit in the Middle-Lower reaches of Yangtze River belt, has occurred in the southern contact zone of the Echeng pluton. Many researches have showed that the Chengchao iron mineralization was closely connected with the magma evolution of the Echeng complex, whereas whether the mineralization is related to granitic rocks or dioritic rocks is still controversial. In this paper, we present U-Pb age, geochemical, and Sr-Nd-Hf isotopic data to provide constraints on the petrogenesis of the Echeng intrusion and discuss the relationship of magma evolution and iron mineralization. The Echeng complex mainly consists of granite, quartz monzonite, granite porphyry and small-scale diorite. LA-ICP-MS zircon U-Pb data indicates that the Echeng complex began to emplace at 140±1 Ma by medium-grained diorite phase, subsequently fine-grained diorite (132±2 Ma), granite porphyry (130±2 Ma), granite including medium-fine grained (129±2 Ma) and medium-grained (129±1 Ma) phases and quartz monzonite (129±1 Ma) were emplaced in order. According to geochemical characteristics, all the rocks can broadly be divided into two groups:(1) granitoids including granite, granite porphyry, hornblende quartz monzonite are potassic and are characterized by high SiO2, low TiO2, FeOt, MnO, MgO concentrations; (2) diorite including fine and medium grained diorites, are sodic and are characterized by low SiO2, high TiO2, FeOt, MnO, MgO concentrations. These rocks are enriched in light rare earth elements (LREEs) and large ion lithophile elements (LILE) such as Rb, Th, and depleted in high field strength elements(HFSE) such as Nb, P and Ti. Moreover, the Echeng granitoids show obviously negative Eu anomalies but the diorites have no such a signature. The Echeng granitoids have more negative εNd(t) values ranging from -11.7 to -10.1 and zircon εHf(t) values ranging from -22.91 to -9.83, and the diorites have relatively high εNd(t) value (-7.6) and zircon εHf(t) values ranging from -12.04 to -4.69. The geochemical and isotopic data suggests that the Echeng granitoids belong to highly fractionated I-type granites and were mainly derived from partial melting of the Paleoproterozoic basement, possibly with the addition of a small amount of mantle-derived materials, whereas the diorites were mainly originated from the enriched lithospheric mantle, followed by a certain degree of crystallization fractionation. The new geochronological data suggests that the Echeng granitoids and fine-grained diorite broadly coeval with the main mineralization of the Chengchao iron deposit. Combining with field contact relationship and previous research results, the Chengchao iron mineralization was probably related to the Echeng granitoids and fine-grained diorite. Based on the mineralizations in southeastern Hubei Province, magmatism is more closely related to iron mineralization with the increases of differentiation degrees and crustal contributions in the magma source.
2018, 43(7): 2370-2388.
doi: 10.3799/dqkx.2018.577
Abstract:
NE-SW mafic dykes are widespread in the Dahongshan region, northern Yangtze block. They mainly emplaced the pre-Nanhua basement rock, e.g. dolomite, sandstone and slate, and scarcely found in Nanhuan system and its overlying strata. It has been controversial for their formation age and background of the mafic dykes for a long time. In this paper, LA-ICP-MS zircon dating for 4 mafic dykes from Qilichong, Yaojiaju, Yaojiachong and Liuguan yield U-Pb ages of 433.7 Ma, 435.6 Ma, 433.4 Ma and 436.4 Ma respectively. All the ages belong to the Early Silurian and are consistent within measuring errors, and offer precise isotope chronology to the mafic dykes in the Dahongshan region. The mafic dykes in the Dahongshan region are characterized by subalkalic series, high ∑REE content, medium differentiation between LREE and HREE, enriched LILEs and depleted HFSEs, Zr > 100×10-6, TiO2 > 2%, and Zr/Y > 3.5. Accordingly, it is suggested that they may have formed in a continental extension environment. We have discerned Early Paleozoic mafic dykes swarm indicative of continental extension in the northern Yangtze block for the first time. It provides powerful evidence that the Dahongshan region in the northern Yangtze block shows NE regional extension. Additionally, we tentatively thought that the south Qinling-Dabie mountain and the north Yangtze block belong to same extensional epicontinental rift environment although different sedimentary strata appeared between them in Early Paleozoic.
NE-SW mafic dykes are widespread in the Dahongshan region, northern Yangtze block. They mainly emplaced the pre-Nanhua basement rock, e.g. dolomite, sandstone and slate, and scarcely found in Nanhuan system and its overlying strata. It has been controversial for their formation age and background of the mafic dykes for a long time. In this paper, LA-ICP-MS zircon dating for 4 mafic dykes from Qilichong, Yaojiaju, Yaojiachong and Liuguan yield U-Pb ages of 433.7 Ma, 435.6 Ma, 433.4 Ma and 436.4 Ma respectively. All the ages belong to the Early Silurian and are consistent within measuring errors, and offer precise isotope chronology to the mafic dykes in the Dahongshan region. The mafic dykes in the Dahongshan region are characterized by subalkalic series, high ∑REE content, medium differentiation between LREE and HREE, enriched LILEs and depleted HFSEs, Zr > 100×10-6, TiO2 > 2%, and Zr/Y > 3.5. Accordingly, it is suggested that they may have formed in a continental extension environment. We have discerned Early Paleozoic mafic dykes swarm indicative of continental extension in the northern Yangtze block for the first time. It provides powerful evidence that the Dahongshan region in the northern Yangtze block shows NE regional extension. Additionally, we tentatively thought that the south Qinling-Dabie mountain and the north Yangtze block belong to same extensional epicontinental rift environment although different sedimentary strata appeared between them in Early Paleozoic.
2018, 43(7): 2389-2403.
doi: 10.3799/dqkx.2018.179
Abstract:
As a typical case of the Neoproterozoic magmatism in South Qinling, the Pailou porphyritic monzogranite exposed in the western margin of Wudang uplift. Zircon U-Pb dating on the granite yields an age of 667.2±3.5 Ma. The granite shows sub-alkaline and metaluminous affinities, with Na2O+K2O and A/CNK values ranging 8.31%-8.47% and 0.89-0.94, respectively. The monzogranite enriched in LILEs (i.e. Rb, K, U and Pb) and HFSEs (i.e. Nb and Ti), and depleted in Sr, P, Ti and HREE. Due to the high content of Zr+Nb+Y+Ce and ratios of 10 000 Ga/Al and FeOT/(FeOT+MgO), as well as characteristic minerals of hastingsite and ferropargasite, the Pailou monzogranite displaying A1-type geochemical features. The zircon εHf(t) values of the study rocks mainly vary from -1.8 to +1.5, indicating that the magma likely to have been sourced from mantle metasomatized by asthenosphere, OIB-like melts, with minor crustal assimilation. Based on modal calculations of trace elements, the fractional crystallization of plagioclase and pyroxene has been proposed during magmatic evolution. Integrating the data obtained from studies on geology, geochronology, geochemistry and isotopic compositions, we propose that the Pailou magmatism was the product of norogenic magmatism and formed in tectonic setting of a back-arc rift setting that probably developed in relation to slab tearing during continued slab rollback.
As a typical case of the Neoproterozoic magmatism in South Qinling, the Pailou porphyritic monzogranite exposed in the western margin of Wudang uplift. Zircon U-Pb dating on the granite yields an age of 667.2±3.5 Ma. The granite shows sub-alkaline and metaluminous affinities, with Na2O+K2O and A/CNK values ranging 8.31%-8.47% and 0.89-0.94, respectively. The monzogranite enriched in LILEs (i.e. Rb, K, U and Pb) and HFSEs (i.e. Nb and Ti), and depleted in Sr, P, Ti and HREE. Due to the high content of Zr+Nb+Y+Ce and ratios of 10 000 Ga/Al and FeOT/(FeOT+MgO), as well as characteristic minerals of hastingsite and ferropargasite, the Pailou monzogranite displaying A1-type geochemical features. The zircon εHf(t) values of the study rocks mainly vary from -1.8 to +1.5, indicating that the magma likely to have been sourced from mantle metasomatized by asthenosphere, OIB-like melts, with minor crustal assimilation. Based on modal calculations of trace elements, the fractional crystallization of plagioclase and pyroxene has been proposed during magmatic evolution. Integrating the data obtained from studies on geology, geochronology, geochemistry and isotopic compositions, we propose that the Pailou magmatism was the product of norogenic magmatism and formed in tectonic setting of a back-arc rift setting that probably developed in relation to slab tearing during continued slab rollback.
2018, 43(7): 2404-2419.
doi: 10.3799/dqkx.2018.187
Abstract:
The Huangchengshan deposit is the largest high-sulfidation epithermal silver deposit in the Western Dabie orogen. Silver mineralization characterized by argentiferous quartz veins is controlled by fractures of volcanic apparatus, and is spatially associated with volcanic rocks of Chenpeng Formation. In situ zircon U-Pb dating yielded 133.4±1.5 Ma (1σ, MSWD=1.3) and 133.1±0.8 Ma (1σ, MSWD=0.59) for the tuff and rhyolite from Chenpeng Formation, respectively, indicating an Early Cretaceous volcanism. The data also suggest a syngenetic volcanogenic epithermal mineralization age of ca.133 Ma for the Huangchengshan silver deposit. Rhyolites of the Chenpeng Formation display high contents of SiO2 (73.83% to 77.38%) and K2O (4.65% to 9.31%), belonging to high-K calc-alkaline series. Their A/CNK ratios range from 1.09 to 1.31, exhibiting peraluminous characteristics. Rare earth elements show light rare earth elements (LREEs) enrichment and flat heavy rare earth elements (HREEs) patterns, with moderate negative Eu anomalies (δEu=0.33-0.88). They are enriched in large ion lithophile elements (LILEs), but depleted in Ba, Nb, Ta, P and Ti. These geochemical characteristics show affinity to highly fractionated granites. The rhyolites have high ISr values (0.708 220 to 0.708 741) and negative εNd(t) values (-17.2 to -18.5), with two-stage Nd model ages of 2.32 to 2.43 Ga. Zircon εHf(t) values are negative (-22.3 to -26.1) with an calculated two-stage Hf model ages of 2.29 to 2.49 Ga. The geochemical and Sr-Nd-Hf isotopic signatures suggest that the rhyolite is likely to be derived by partial melting of the ancient lower crust of the Yangtze Block. We propose that this volcanism and related Huangchengshan silver deposit formed in a transitional stage from crustal compression to extension driven by delamination of thickened lower crust during the Early Cretaceous.
The Huangchengshan deposit is the largest high-sulfidation epithermal silver deposit in the Western Dabie orogen. Silver mineralization characterized by argentiferous quartz veins is controlled by fractures of volcanic apparatus, and is spatially associated with volcanic rocks of Chenpeng Formation. In situ zircon U-Pb dating yielded 133.4±1.5 Ma (1σ, MSWD=1.3) and 133.1±0.8 Ma (1σ, MSWD=0.59) for the tuff and rhyolite from Chenpeng Formation, respectively, indicating an Early Cretaceous volcanism. The data also suggest a syngenetic volcanogenic epithermal mineralization age of ca.133 Ma for the Huangchengshan silver deposit. Rhyolites of the Chenpeng Formation display high contents of SiO2 (73.83% to 77.38%) and K2O (4.65% to 9.31%), belonging to high-K calc-alkaline series. Their A/CNK ratios range from 1.09 to 1.31, exhibiting peraluminous characteristics. Rare earth elements show light rare earth elements (LREEs) enrichment and flat heavy rare earth elements (HREEs) patterns, with moderate negative Eu anomalies (δEu=0.33-0.88). They are enriched in large ion lithophile elements (LILEs), but depleted in Ba, Nb, Ta, P and Ti. These geochemical characteristics show affinity to highly fractionated granites. The rhyolites have high ISr values (0.708 220 to 0.708 741) and negative εNd(t) values (-17.2 to -18.5), with two-stage Nd model ages of 2.32 to 2.43 Ga. Zircon εHf(t) values are negative (-22.3 to -26.1) with an calculated two-stage Hf model ages of 2.29 to 2.49 Ga. The geochemical and Sr-Nd-Hf isotopic signatures suggest that the rhyolite is likely to be derived by partial melting of the ancient lower crust of the Yangtze Block. We propose that this volcanism and related Huangchengshan silver deposit formed in a transitional stage from crustal compression to extension driven by delamination of thickened lower crust during the Early Cretaceous.
2018, 43(7): 2420-2437.
doi: 10.3799/dqkx.2018.549
Abstract:
The East Kunlun orogenic belt is characterized by widespread Early-Middle Triassic Epoch granitic rocks with a large proportion of mafic enclaves therein, however, there is still lack of petrography and mineralogy studies on the Mafic enclaves with different textures. In this paper, a systematic petrography and mineral chemistry study has been carried out for the representative Xiangjia granite pluton as well as the enclosed Mafic enclaves, which have clarified the processes of crust-mantle interaction in East Kunlun area. Studies on petrography have shown that the mafic enclaves have some disequilibrium textures and some phenomenon point to rapid crystallization, such as needle-like apatite, needle-like amphibole and augen-shaped quartz, all of which suggest the possible of magma mixing process, and the enclave with ophitic-gabbro texture likely to be the basic end-member. In addition, multi-stage growing of feldspar indicates there might be multi-mixing process. Whole rock geochemistry shows that the mafic enclaves have lower Mg# and higher Fe# values relative to their host rocks (Mg#:0.39-0.56, Fe#:0.44-0.62). Electron microprobe investigation shows that enclaves have two kinds of amphiboles, one kind in mafic enclaves (TiO2:2.1%-2.9%, SiO2:41.75%-44.49%) crystallized from mantle-derived basic magma in the early stage, while the other kind (TiO2:1.0%-1.8%, SiO2:42.49%-48.10%) probably crystallized from the mixed magma in the shallow crust level. Some biotites (MgO:9.78%-11.53%, Mg#:0.462-0.541) are similar to biotites crystallizing in the mantle-derived magma. The rhythmic zoning and geochemistry contents of Plagioclases show that they may have suffered the process of magma mixing. Calculated results by geobarameter indicate that the mantle-derived basic magma crystallized under 5×108 bar, i.e. about 18 km depth, producing the high-Ti amphiboles, and then mixed with the acid magma. The mixed magma emplaced to upper crust, maybe at 2.5×108 bar, i.e. about 8km depth, producing the Low-Ti amphiboles. All these features above show that the East Kunlun orogenic belt might have experienced crust-mantle interaction repeatly during the Triassic Epoch, and the injection of mantle magma played an important role in the crustal growth and crust anatexis. The wide crust-mantle interaction may be the response to the slab break-off of Animaqing Ocean during the Triassic Period.
The East Kunlun orogenic belt is characterized by widespread Early-Middle Triassic Epoch granitic rocks with a large proportion of mafic enclaves therein, however, there is still lack of petrography and mineralogy studies on the Mafic enclaves with different textures. In this paper, a systematic petrography and mineral chemistry study has been carried out for the representative Xiangjia granite pluton as well as the enclosed Mafic enclaves, which have clarified the processes of crust-mantle interaction in East Kunlun area. Studies on petrography have shown that the mafic enclaves have some disequilibrium textures and some phenomenon point to rapid crystallization, such as needle-like apatite, needle-like amphibole and augen-shaped quartz, all of which suggest the possible of magma mixing process, and the enclave with ophitic-gabbro texture likely to be the basic end-member. In addition, multi-stage growing of feldspar indicates there might be multi-mixing process. Whole rock geochemistry shows that the mafic enclaves have lower Mg# and higher Fe# values relative to their host rocks (Mg#:0.39-0.56, Fe#:0.44-0.62). Electron microprobe investigation shows that enclaves have two kinds of amphiboles, one kind in mafic enclaves (TiO2:2.1%-2.9%, SiO2:41.75%-44.49%) crystallized from mantle-derived basic magma in the early stage, while the other kind (TiO2:1.0%-1.8%, SiO2:42.49%-48.10%) probably crystallized from the mixed magma in the shallow crust level. Some biotites (MgO:9.78%-11.53%, Mg#:0.462-0.541) are similar to biotites crystallizing in the mantle-derived magma. The rhythmic zoning and geochemistry contents of Plagioclases show that they may have suffered the process of magma mixing. Calculated results by geobarameter indicate that the mantle-derived basic magma crystallized under 5×108 bar, i.e. about 18 km depth, producing the high-Ti amphiboles, and then mixed with the acid magma. The mixed magma emplaced to upper crust, maybe at 2.5×108 bar, i.e. about 8km depth, producing the Low-Ti amphiboles. All these features above show that the East Kunlun orogenic belt might have experienced crust-mantle interaction repeatly during the Triassic Epoch, and the injection of mantle magma played an important role in the crustal growth and crust anatexis. The wide crust-mantle interaction may be the response to the slab break-off of Animaqing Ocean during the Triassic Period.
2018, 43(7): 2438-2448.
doi: 10.3799/dqkx.2018.132
Abstract:
In Western Hunan-Eastern Guizhou metallogenetic belt, the Huayuan ore concentration area with ten-million-tons expected reserves of Pb and Zn, is one of the world-class super-large Pb-Zn ore deposits. Rouxianshan Pb-Zn deposit located in the center of Huayuan area, is a typical deposit in the Yutang ore field. This study carries out Rb-Sr geochronology study of sphalerites from Rouxianshan, and utilizes phase-seperation method to achieve an ideal Rb-Sr isochron line, yielding an Early Devonian age of 412±6 Ma (MSWD=1.5, initial 86Sr/87Sr=0.709 32), which is meaningful for constraining the ore-forming age in Huayuan area. The fluid inclusions, Sr-S-Pb isotopic composition of ore samples from Rouxianshan have also been analyzed. The results indicate that the ore-forming fluid may have originated from a mixture of strata-sealed water and transporting fluid, and the ore is characterized by Pb-Sr isotopic composition from upper crust. Further, the Pb in ores mainly comes from the wall rocks, and the S attributed to the thermo-chemical sulfate reduction (TSR) of overlying gypsum-bearing rock formation.
In Western Hunan-Eastern Guizhou metallogenetic belt, the Huayuan ore concentration area with ten-million-tons expected reserves of Pb and Zn, is one of the world-class super-large Pb-Zn ore deposits. Rouxianshan Pb-Zn deposit located in the center of Huayuan area, is a typical deposit in the Yutang ore field. This study carries out Rb-Sr geochronology study of sphalerites from Rouxianshan, and utilizes phase-seperation method to achieve an ideal Rb-Sr isochron line, yielding an Early Devonian age of 412±6 Ma (MSWD=1.5, initial 86Sr/87Sr=0.709 32), which is meaningful for constraining the ore-forming age in Huayuan area. The fluid inclusions, Sr-S-Pb isotopic composition of ore samples from Rouxianshan have also been analyzed. The results indicate that the ore-forming fluid may have originated from a mixture of strata-sealed water and transporting fluid, and the ore is characterized by Pb-Sr isotopic composition from upper crust. Further, the Pb in ores mainly comes from the wall rocks, and the S attributed to the thermo-chemical sulfate reduction (TSR) of overlying gypsum-bearing rock formation.
2018, 43(7): 2449-2464.
doi: 10.3799/dqkx.2018.554
Abstract:
The Pb-Zn deposits of Huayuan ore-concentrated district in northwest Hunan Province are located on the southeastern margin of the Yangtze Craton. It has been one of the most important giant Pb-Zn deposits in Xiangxi-Exi metallogenic belt. Through the microthermometric and component analysis of the fluid inclusion, and the C, H, O isotope study of the Pb-Zn deposits in Huayuan ore-concentrated district, the results show that fluid inclusions hosted in sphalerite and calcite have total homogenization temperatures concentrated of 120 to 200℃ and calculated salinities concentrated of 8% to 20% NaCleqv. Compositionally, the fluid inclusions are dominated by Ca2+, Na+, Mg2+, SO42- and Cl-, whereas the gaseous species consist of H2O, N2, CO2 with a small amount of CO, CH4, H2. Based on hydrogen isotopes of fluid inclusion waters and oxygen isotopic compositions of calcite, the ore fluids have δDSMOW and δ18O fluid of -60.4‰ to -33.0‰ and 3.8‰ to 9.2‰, respectively. Thus, the isotope data suggest that the ore-forming fluids were mostly derived from formation water, with variable amounts of meteoric water. The δ13CPDB and δ18OSMOW of calcite range from -4.89‰ to 0.57‰ and from 13.37‰ to 21.73‰, respectively, indicating that carbon in the ore-forming fluids was mainly sourced from carbonate wall rocks through water-rock reactions. Precipitation of the sulfide ores was attributed to mixing of two end-member fluids, i.e., metalliferous fluid and organic-and sulfate-rich fluids. Integration of geological and geochemical data suggest that the Pb-Zn deposits of Huayuan ore-concentrated district can be best classified as the MVT Pb-Zn deposit.
The Pb-Zn deposits of Huayuan ore-concentrated district in northwest Hunan Province are located on the southeastern margin of the Yangtze Craton. It has been one of the most important giant Pb-Zn deposits in Xiangxi-Exi metallogenic belt. Through the microthermometric and component analysis of the fluid inclusion, and the C, H, O isotope study of the Pb-Zn deposits in Huayuan ore-concentrated district, the results show that fluid inclusions hosted in sphalerite and calcite have total homogenization temperatures concentrated of 120 to 200℃ and calculated salinities concentrated of 8% to 20% NaCleqv. Compositionally, the fluid inclusions are dominated by Ca2+, Na+, Mg2+, SO42- and Cl-, whereas the gaseous species consist of H2O, N2, CO2 with a small amount of CO, CH4, H2. Based on hydrogen isotopes of fluid inclusion waters and oxygen isotopic compositions of calcite, the ore fluids have δDSMOW and δ18O fluid of -60.4‰ to -33.0‰ and 3.8‰ to 9.2‰, respectively. Thus, the isotope data suggest that the ore-forming fluids were mostly derived from formation water, with variable amounts of meteoric water. The δ13CPDB and δ18OSMOW of calcite range from -4.89‰ to 0.57‰ and from 13.37‰ to 21.73‰, respectively, indicating that carbon in the ore-forming fluids was mainly sourced from carbonate wall rocks through water-rock reactions. Precipitation of the sulfide ores was attributed to mixing of two end-member fluids, i.e., metalliferous fluid and organic-and sulfate-rich fluids. Integration of geological and geochemical data suggest that the Pb-Zn deposits of Huayuan ore-concentrated district can be best classified as the MVT Pb-Zn deposit.
2018, 43(7): 2465-2483.
doi: 10.3799/dqkx.2018.520
Abstract:
To understand the evolution of ore-forming fluids and the mechanism of lead-zinc mineral deposition in the Huayuan lead-zinc deposit, summarize the genesis of the deposit and establish a metallogenic model to guide the prospecting and exploration of lead-zinc deposits in the region, petrophysical observation, micro-temperature measurement, Raman spectroscopy and synchrotron radiation X-ray fluorescence microprobe analysis were carried out on the fluid inclusions in sphalerite, calcite and fluorite in the main mineralization stage. In this paper The results show that the ore-forming fluid temperature of lead-zinc deposit in the Huayuan area is mainly 150-220℃, and the total salinity is generally 13%-23% NaCleqv (mostly > 15% NaCleqv) Density > 1 g/cm3. The ore fluid is NaCl-CaCl2-MgCl2-H2O brine system. The homogenization temperature of the ore-forming fluid has a tendency to decrease from north to south. The main components of the fluid are Ca2+, Mg2+, Na+, Cl-, and have the characteristics of hot brine system in the basin. CO2 and CH4 are commonly observed as gas phase of fluid inclusions. Pb and Zn contents above determination limits were examined in the fluid inclusions of both calcite and fluorite. The ore-forming fluids in the Huayuan ore field belong to the low-temperature, medium-high salinity, medium-high density hydrothermal solution, the composition is sodium and calcium chloride-based basin brine. The direction of fluid flow is from north to south. the fluid is derived from formation water, atmospheric precipitation and a small amount of metamorphic water. The precipitation of lead-zinc minerals is related to the thermochemical reduction of sulfate. Sphalerite, galena, calcite and fluorite may have precipitated from the same ore-forming fluid rich in Pb, Zn, Mn, Fe, As, Cr, in the same ore-forming period and under the same conditions.
To understand the evolution of ore-forming fluids and the mechanism of lead-zinc mineral deposition in the Huayuan lead-zinc deposit, summarize the genesis of the deposit and establish a metallogenic model to guide the prospecting and exploration of lead-zinc deposits in the region, petrophysical observation, micro-temperature measurement, Raman spectroscopy and synchrotron radiation X-ray fluorescence microprobe analysis were carried out on the fluid inclusions in sphalerite, calcite and fluorite in the main mineralization stage. In this paper The results show that the ore-forming fluid temperature of lead-zinc deposit in the Huayuan area is mainly 150-220℃, and the total salinity is generally 13%-23% NaCleqv (mostly > 15% NaCleqv) Density > 1 g/cm3. The ore fluid is NaCl-CaCl2-MgCl2-H2O brine system. The homogenization temperature of the ore-forming fluid has a tendency to decrease from north to south. The main components of the fluid are Ca2+, Mg2+, Na+, Cl-, and have the characteristics of hot brine system in the basin. CO2 and CH4 are commonly observed as gas phase of fluid inclusions. Pb and Zn contents above determination limits were examined in the fluid inclusions of both calcite and fluorite. The ore-forming fluids in the Huayuan ore field belong to the low-temperature, medium-high salinity, medium-high density hydrothermal solution, the composition is sodium and calcium chloride-based basin brine. The direction of fluid flow is from north to south. the fluid is derived from formation water, atmospheric precipitation and a small amount of metamorphic water. The precipitation of lead-zinc minerals is related to the thermochemical reduction of sulfate. Sphalerite, galena, calcite and fluorite may have precipitated from the same ore-forming fluid rich in Pb, Zn, Mn, Fe, As, Cr, in the same ore-forming period and under the same conditions.
2018, 43(7): 2484-2495.
doi: 10.3799/dqkx.2018.566
Abstract:
The Wulun lead-zinc deposit lies to the northwest of Jiangnan (Xuefeng) orogenic belt on the southeastern margin of Yangtze block, as a newly discovered hydrothermal vein type of lead-zinc deposit in the lead-zinc ore belt along the Wanmingang anticline in northwestern Hunan. The ore bodies outcrop in the Lower Ordovician Tongzi and Honghuayuan formations as steep-dipping veins controlled by NW trending faults which derived by NE trending Bitiexi-Chenjiahe fault. Rb-Sr dating of sphalerite yielded an isochron age of 238.9±4.5 Ma (MSWD=1.8) with initial 87Sr/86Sr value of 0.710 86±0.000 16 for the deposit, which shows that the end of Middle Triassic is the main mineralization period for the Wulun lead-zinc deposit. Integrated with the existing metallogenic geochronology data, and the discussing of the geodynamical setting, it is indicated that there are at least twice lead-zinc mineralization in northwestern Hunan, which was respectively related to the post-orogenic extension of late Caledonian tectonism and the local stretching derived from collision of South China block in the early Indosinian. The metallogenic materials of Wulun lead-zinc deposit shall be mainly derived from the clastic rocks with high ore-forming elements in the Nanhua-Early Cambrian stratas underlying the ore-bearing layers. The relatively high initial Sr isotope ratio indicates that the influence of continental crust was obvious in the metallogenic process.
The Wulun lead-zinc deposit lies to the northwest of Jiangnan (Xuefeng) orogenic belt on the southeastern margin of Yangtze block, as a newly discovered hydrothermal vein type of lead-zinc deposit in the lead-zinc ore belt along the Wanmingang anticline in northwestern Hunan. The ore bodies outcrop in the Lower Ordovician Tongzi and Honghuayuan formations as steep-dipping veins controlled by NW trending faults which derived by NE trending Bitiexi-Chenjiahe fault. Rb-Sr dating of sphalerite yielded an isochron age of 238.9±4.5 Ma (MSWD=1.8) with initial 87Sr/86Sr value of 0.710 86±0.000 16 for the deposit, which shows that the end of Middle Triassic is the main mineralization period for the Wulun lead-zinc deposit. Integrated with the existing metallogenic geochronology data, and the discussing of the geodynamical setting, it is indicated that there are at least twice lead-zinc mineralization in northwestern Hunan, which was respectively related to the post-orogenic extension of late Caledonian tectonism and the local stretching derived from collision of South China block in the early Indosinian. The metallogenic materials of Wulun lead-zinc deposit shall be mainly derived from the clastic rocks with high ore-forming elements in the Nanhua-Early Cambrian stratas underlying the ore-bearing layers. The relatively high initial Sr isotope ratio indicates that the influence of continental crust was obvious in the metallogenic process.
2018, 43(7): 2496-2517.
doi: 10.3799/dqkx.2018.571
Abstract:
Changde-Anren fault is a NW-trending deep fault in eastern Hunan, and its geological features, activity history and tectonic attributes have not been studied systematically. Based on regional geological survey and research data, the authors summarized the general features of the fault, analyzed the nature, genesis and forming ages of the secondary structures origined from the fault, and then reconstructed the activity history, probed in the tectonic attributes and deformation mechanisms of the fault. Main conclusions are as follows:Changde-Anren fault is a NW-trending (330°) basement hidden fault with outcropped fault only in part of north segment and appears as a NW-striking magma-uplift belt. It is a deep major fault breaking through the middle and lower crust and cutting into lithospheric mantle, and dipping northeast with dip angle of 54°. The fault experienced long-term activity as follows. It was a transform fault with strike-slip motion during Neoproterozoic Lengjiaxi Period, strike-slipped dextrally under regional S-N compression in Wuling Movement causing the clockwise rotation of the structural lineaments to the north of Taojiang, extended and controlled the sedimentary facies in Early Banxi Period and Early Nanhua, strike-slipped dextrally under regional S-N compression and fromed secondary NWW-trending thrust faults in Caledonian Movement, strike-slipped sinistrally with thrust and formed secondary NW-trending sinistral strike-slip fault and Anren "y"-type structure under regional NW to NWW compression in late Middle Triassic Indosinian Movement, strike-slipped dextrally under regional S-N compression and formed secondary NWW-trending thrust faults and uplifts during Late Trias-Early Jurassic, strike-slipped sinistrally under regional NWW compression and formed secondary NEE-trending dextral strike-slip fault in Middle Jurassic Early Yanshanian Movement, extended and formed small-scale NW-trending regulative faults controlling the boundary of the southwest end of NNE-trending faulted basins during Cretaceous-Paleogene. Changde-Anren fault was probably a transform fault crosscutting back-arc basin and island arc on the southeastern margin of Yangtze block and Huanan ocean. The uplift along Changde-Anren fault was formed in Indosinain Movement controlled by deep thrust, and rose further for large-scale granitic magmatism in Late Triassic. The hidden properties of the fault were provided by several facts such as follows:The fault developed in Lengjiaxi Group and Nanhua as synsedimentary fault but not in Sinian-Upper Paleozoic; there existed weak detachment layer of Jinjiadong Formation at the bottom of Sinian; NE to NNE-trending major faults cut Changde-Anren fault into several segments with relative independent motion; there occurred a large number of granitic bodies and Cretaceous-Paleogene basins.
Changde-Anren fault is a NW-trending deep fault in eastern Hunan, and its geological features, activity history and tectonic attributes have not been studied systematically. Based on regional geological survey and research data, the authors summarized the general features of the fault, analyzed the nature, genesis and forming ages of the secondary structures origined from the fault, and then reconstructed the activity history, probed in the tectonic attributes and deformation mechanisms of the fault. Main conclusions are as follows:Changde-Anren fault is a NW-trending (330°) basement hidden fault with outcropped fault only in part of north segment and appears as a NW-striking magma-uplift belt. It is a deep major fault breaking through the middle and lower crust and cutting into lithospheric mantle, and dipping northeast with dip angle of 54°. The fault experienced long-term activity as follows. It was a transform fault with strike-slip motion during Neoproterozoic Lengjiaxi Period, strike-slipped dextrally under regional S-N compression in Wuling Movement causing the clockwise rotation of the structural lineaments to the north of Taojiang, extended and controlled the sedimentary facies in Early Banxi Period and Early Nanhua, strike-slipped dextrally under regional S-N compression and fromed secondary NWW-trending thrust faults in Caledonian Movement, strike-slipped sinistrally with thrust and formed secondary NW-trending sinistral strike-slip fault and Anren "y"-type structure under regional NW to NWW compression in late Middle Triassic Indosinian Movement, strike-slipped dextrally under regional S-N compression and formed secondary NWW-trending thrust faults and uplifts during Late Trias-Early Jurassic, strike-slipped sinistrally under regional NWW compression and formed secondary NEE-trending dextral strike-slip fault in Middle Jurassic Early Yanshanian Movement, extended and formed small-scale NW-trending regulative faults controlling the boundary of the southwest end of NNE-trending faulted basins during Cretaceous-Paleogene. Changde-Anren fault was probably a transform fault crosscutting back-arc basin and island arc on the southeastern margin of Yangtze block and Huanan ocean. The uplift along Changde-Anren fault was formed in Indosinain Movement controlled by deep thrust, and rose further for large-scale granitic magmatism in Late Triassic. The hidden properties of the fault were provided by several facts such as follows:The fault developed in Lengjiaxi Group and Nanhua as synsedimentary fault but not in Sinian-Upper Paleozoic; there existed weak detachment layer of Jinjiadong Formation at the bottom of Sinian; NE to NNE-trending major faults cut Changde-Anren fault into several segments with relative independent motion; there occurred a large number of granitic bodies and Cretaceous-Paleogene basins.
2018, 43(7): 2518-2526.
doi: 10.3799/dqkx.2018.517
Abstract:
The central anticline of the western Hubei is located in the tectonic zone of the Yangtze block and the central Sichuan (western Hubei) foreland basin, which possesses important advantages for the study of regional tectonic evolution. In this paper, according to the detailed field geological survey and evidences form apatite fission track simulation, five stages of tectonic activities have been identified:(1) tectonic uplift at 187.4 Ma-180.1 Ma that resulted in the parallel unconformity between the Jiuligang Formation and the Tongzhuyuan Formation. (2) tectonic subsidence and deposition of terrestrial sediments at 180.1 Ma-115.6 Ma. (3) slowl tectonic uplift once again associated with land erosion during 115.6 Ma-78.8 Ma. (4) subsidence again and the deposition of Cretaceous Paomagang Formation during the period of 78.8 Ma-63.6 Ma. (5) followed by great uplift until a small subsidence at 2.6 Ma of the Quaternary. Based on the tectonic evolution and the application of balanced profile technology, the regional tectonic pattern of extrusion-stretching process was established.
The central anticline of the western Hubei is located in the tectonic zone of the Yangtze block and the central Sichuan (western Hubei) foreland basin, which possesses important advantages for the study of regional tectonic evolution. In this paper, according to the detailed field geological survey and evidences form apatite fission track simulation, five stages of tectonic activities have been identified:(1) tectonic uplift at 187.4 Ma-180.1 Ma that resulted in the parallel unconformity between the Jiuligang Formation and the Tongzhuyuan Formation. (2) tectonic subsidence and deposition of terrestrial sediments at 180.1 Ma-115.6 Ma. (3) slowl tectonic uplift once again associated with land erosion during 115.6 Ma-78.8 Ma. (4) subsidence again and the deposition of Cretaceous Paomagang Formation during the period of 78.8 Ma-63.6 Ma. (5) followed by great uplift until a small subsidence at 2.6 Ma of the Quaternary. Based on the tectonic evolution and the application of balanced profile technology, the regional tectonic pattern of extrusion-stretching process was established.
