2017 Vol. 42, No. 6
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2017, 42(6): 853-861.
doi: 10.3799/dqkx.2017.075
Abstract:
Previous studies show that the Early Cretaceous lithospheric mantle beneath Feixian (Shandong Province) in the eastern part of the North China Craton (NCC) was highly hydrous ( > 1 000×10-6, H2O wt.), in which the H2O content of olivine was > 180×10-6. Meanwhile the Early Cretaceous lithospheric mantle beneath Fushan (Shanxi Province) in the western part of the NCC was relatively dry, in which the H2O content of olivine was ~10×10-6. This contrast demonstrates that the hydration of the Early Cretaceous lithospheric mantle of eastern NCC was probably due to the westward subduction of the Pacific plate, and this high water content had significantly reduced the viscosity of the lithospheric mantle and provided a prerequisite for the destruction of the NCC. To explore the distribution of hydrous lithospheric mantle in the NCC, we measured the H2O content of the peridotite xenoliths hosted by the Early Cretaceous high-magnesium diorites of Tietonggou (Shandong Province) that is located between Feixian and Fushan.The H2O content of olivine in the Tietonggou peridotites is (6-24)×10-6 (average (15±7)×10-6) and comparable with that of the Fushan olivine, suggesting that the Early Cretaceous hydrous lithospheric mantle caused by the westward subduction of the Pacific plate was likely limited to the most eastern part of the NCC.
Previous studies show that the Early Cretaceous lithospheric mantle beneath Feixian (Shandong Province) in the eastern part of the North China Craton (NCC) was highly hydrous ( > 1 000×10-6, H2O wt.), in which the H2O content of olivine was > 180×10-6. Meanwhile the Early Cretaceous lithospheric mantle beneath Fushan (Shanxi Province) in the western part of the NCC was relatively dry, in which the H2O content of olivine was ~10×10-6. This contrast demonstrates that the hydration of the Early Cretaceous lithospheric mantle of eastern NCC was probably due to the westward subduction of the Pacific plate, and this high water content had significantly reduced the viscosity of the lithospheric mantle and provided a prerequisite for the destruction of the NCC. To explore the distribution of hydrous lithospheric mantle in the NCC, we measured the H2O content of the peridotite xenoliths hosted by the Early Cretaceous high-magnesium diorites of Tietonggou (Shandong Province) that is located between Feixian and Fushan.The H2O content of olivine in the Tietonggou peridotites is (6-24)×10-6 (average (15±7)×10-6) and comparable with that of the Fushan olivine, suggesting that the Early Cretaceous hydrous lithospheric mantle caused by the westward subduction of the Pacific plate was likely limited to the most eastern part of the NCC.
2017, 42(6): 862-880.
doi: 10.3799/dqkx.2017.523
Abstract:
The Gelale Cu-Au deposit in Tibet is an example to probe the regional tectonics, but its ore-forming age is poorly studied, which hinders further studies for the regional tectonics, magmatism and mineralization in the metallogenic belt. The ages and genesis of the intrusive rocks, and the ages of the deposit are determined for the first time in this paper by using the laser ablation-inductively coupled plasma-mass spectrometry(LA-ICP-MS) zircon U-Pb dating, Lu-Hf isotopic test and Re-Os isotopic dating methods. Early diorite yields age of 155.8±2.3 Ma and εHf(t) values of -14.68~-8.34 (-11.74 in average), which is the product of the southward subduction of the Bangong-Nujiang Tethys ocean. The age of the inter-mineral granodiorite is 88±1 Ma(MSWD=0.56, n=21), and yields zircon εHf(t) values between 5.84-9.20, with the average value of 7.72, while the ages of the late granite porphyry is 84.67±0.8 Ma(MSWD=1.9, n=18), and yields zircon εHf(t) values between 6.32-9.78, with the average value of 8.40. Both the granodiorite and granite porphyry emplaced in the Late Cretaceous, which is the product of the convergence of the Lhasa terrane and the Qiangtang terrane.The Re-Os isochron age of molybdenite in the district is 88.55±0.60 Ma (MSWD=0.60, n=8), which is close to the age of the mineralization rock (granodiorite). Comprehensive study shows that the magmatic activities of the deposit corresponed to the subduction and collision environment of the Bangong-Nujiang Tethys ocean, and the Galale copper-gold deposit is the product of the mineralization event of the collision stage.
The Gelale Cu-Au deposit in Tibet is an example to probe the regional tectonics, but its ore-forming age is poorly studied, which hinders further studies for the regional tectonics, magmatism and mineralization in the metallogenic belt. The ages and genesis of the intrusive rocks, and the ages of the deposit are determined for the first time in this paper by using the laser ablation-inductively coupled plasma-mass spectrometry(LA-ICP-MS) zircon U-Pb dating, Lu-Hf isotopic test and Re-Os isotopic dating methods. Early diorite yields age of 155.8±2.3 Ma and εHf(t) values of -14.68~-8.34 (-11.74 in average), which is the product of the southward subduction of the Bangong-Nujiang Tethys ocean. The age of the inter-mineral granodiorite is 88±1 Ma(MSWD=0.56, n=21), and yields zircon εHf(t) values between 5.84-9.20, with the average value of 7.72, while the ages of the late granite porphyry is 84.67±0.8 Ma(MSWD=1.9, n=18), and yields zircon εHf(t) values between 6.32-9.78, with the average value of 8.40. Both the granodiorite and granite porphyry emplaced in the Late Cretaceous, which is the product of the convergence of the Lhasa terrane and the Qiangtang terrane.The Re-Os isochron age of molybdenite in the district is 88.55±0.60 Ma (MSWD=0.60, n=8), which is close to the age of the mineralization rock (granodiorite). Comprehensive study shows that the magmatic activities of the deposit corresponed to the subduction and collision environment of the Bangong-Nujiang Tethys ocean, and the Galale copper-gold deposit is the product of the mineralization event of the collision stage.
2017, 42(6): 881-890.
doi: 10.3799/dqkx.2017.076
Abstract:
The Zhongba terrane is an important tectonic unit sandwiched between the northern and the southern ophiolitic sub-belts in the western segment of the Yarlung Zangbo Suture Zone (YZSZ), Southwest Tibet. Currently it is still unclear as to whether there exists the Early Paleozoic tectono-thermal events in this terrane as well as its tectonic affinity. BasedBaesed on field and petrological investigations, a suite of gneissic monzogranite that intruded into a biotite plagioclase gneiss was recognized near the Gongzhu Co area in the middle part of the Zhongba terrane in this study. U-Pb dating of zircon from the monzogranite yieldsed ages of ~478 Ma, indicating the deformation age for such rock at the Early Ordovician. These monzogranites are characterized by high Si and Al, relatively high contents of total alkalis, A/CNK=1.13-1.20, enrichment of large lithophile elements of Rb and K and depletion of Ba, Sr, Nb and Ti, which should be calc-alkalic alkaline, strong peraluminous granite. To our knowledge, this represents the first report of the Early Ordovician tectono-thermal events taken place within the Zhongba terrane from the western YZSZ. These gneissic monzogranites were formed by the upper crustal melting after subduction of the Proto-Tethys Ocean to the northern margin of the Gondwana supercontinent, and suggesting that the Zhongba terrane should belong to the northern margin of the eastern Gondwana supercontinent at the Early Paleozoic.
The Zhongba terrane is an important tectonic unit sandwiched between the northern and the southern ophiolitic sub-belts in the western segment of the Yarlung Zangbo Suture Zone (YZSZ), Southwest Tibet. Currently it is still unclear as to whether there exists the Early Paleozoic tectono-thermal events in this terrane as well as its tectonic affinity. BasedBaesed on field and petrological investigations, a suite of gneissic monzogranite that intruded into a biotite plagioclase gneiss was recognized near the Gongzhu Co area in the middle part of the Zhongba terrane in this study. U-Pb dating of zircon from the monzogranite yieldsed ages of ~478 Ma, indicating the deformation age for such rock at the Early Ordovician. These monzogranites are characterized by high Si and Al, relatively high contents of total alkalis, A/CNK=1.13-1.20, enrichment of large lithophile elements of Rb and K and depletion of Ba, Sr, Nb and Ti, which should be calc-alkalic alkaline, strong peraluminous granite. To our knowledge, this represents the first report of the Early Ordovician tectono-thermal events taken place within the Zhongba terrane from the western YZSZ. These gneissic monzogranites were formed by the upper crustal melting after subduction of the Proto-Tethys Ocean to the northern margin of the Gondwana supercontinent, and suggesting that the Zhongba terrane should belong to the northern margin of the eastern Gondwana supercontinent at the Early Paleozoic.
2017, 42(6): 891-908.
doi: 10.3799/dqkx.2017.077
Abstract:
The Ningzhen region in Jiangsu Province, representing the easternmost magmatic region within the Middle-Lower Yangtze River Metallogenic belt, and is an important component of the Middle-Lower Yangtze River magmatic rock belt. The Jiangmiao pluton is the only mafic intrusive body in the Ningzhen region, and its zircon U-Pb dating, petrological, mineralogical and geochemical data were obtained in this paper to constrain its origin and mantle source characteristics. Olivine gabbros, hornblende gabbros and pyroxene diorites are the main rock types of the pluton. The zircons from the pyroxene diorite yield a U-Pb age of 121±1 Ma. The zircon εHf(t) values are from -2.9 to -6.4. The Jiangmiao mafic rocks in the Ningzhen region are sodic, and are characterized by an enriched light rare earth elements(LREEs) pattern. They are enriched in large ion lithophile elements (LIEEs) such as K, Ba, Sr, but depleted in high field strength elements such as Nb, Ta, Ti, Zr and Hf.Jiangmiao mafic intrusive rocks have the highest εNd(t) and the lowest value of (87Sr/86Sr)i values among Mesozoic magmatic rocks in the Middle-Lower reaches of Yangtze River belt. Sr-Nd isotopic data suggest that asthenosphere-lithosphere interaction plays an important role in the generation of the Jiangmiao pluton. The trace element and isotopic data are consistent with crystallization fractionation and there is no significant crustal contamination during magma ascending and crystallization. Enriched LREEs and LILEs, together with depleted Nb, Ta, Ti, Zr and Hf, suggest that the mantle sources were metasomatized by slab-derived fluid/melt. Combining with regional geological, geochronological, mineralogical and geochemical data, the Jiangmiao maflc rocks in the Ningzhen region were probably formed in an extensional regime associated with westward subduction of the paleo-Paciflc plate.
The Ningzhen region in Jiangsu Province, representing the easternmost magmatic region within the Middle-Lower Yangtze River Metallogenic belt, and is an important component of the Middle-Lower Yangtze River magmatic rock belt. The Jiangmiao pluton is the only mafic intrusive body in the Ningzhen region, and its zircon U-Pb dating, petrological, mineralogical and geochemical data were obtained in this paper to constrain its origin and mantle source characteristics. Olivine gabbros, hornblende gabbros and pyroxene diorites are the main rock types of the pluton. The zircons from the pyroxene diorite yield a U-Pb age of 121±1 Ma. The zircon εHf(t) values are from -2.9 to -6.4. The Jiangmiao mafic rocks in the Ningzhen region are sodic, and are characterized by an enriched light rare earth elements(LREEs) pattern. They are enriched in large ion lithophile elements (LIEEs) such as K, Ba, Sr, but depleted in high field strength elements such as Nb, Ta, Ti, Zr and Hf.Jiangmiao mafic intrusive rocks have the highest εNd(t) and the lowest value of (87Sr/86Sr)i values among Mesozoic magmatic rocks in the Middle-Lower reaches of Yangtze River belt. Sr-Nd isotopic data suggest that asthenosphere-lithosphere interaction plays an important role in the generation of the Jiangmiao pluton. The trace element and isotopic data are consistent with crystallization fractionation and there is no significant crustal contamination during magma ascending and crystallization. Enriched LREEs and LILEs, together with depleted Nb, Ta, Ti, Zr and Hf, suggest that the mantle sources were metasomatized by slab-derived fluid/melt. Combining with regional geological, geochronological, mineralogical and geochemical data, the Jiangmiao maflc rocks in the Ningzhen region were probably formed in an extensional regime associated with westward subduction of the paleo-Paciflc plate.
2017, 42(6): 909-926.
doi: 10.3799/dqkx.2017.083
Abstract:
order to understand tectonic-magmatic evolution of eastern section of West Kunlun orogen, a systematic field geological surveying, microscopic petrographic examination, LA-ICP-MS U-Pb zircon dating, and geochemistry study were carried out for the Suyingdi dykes. These dykes occur in groups or belts along an NE trending. The rock types of dykes include (garnet-bearing) diorite-porphyrite, hornblende andesite-porphyrite, and proterobase spessartite. Using LA-ICP-MS method, zircons in the (garnet-bearing) diorite-porphyrite samples show a weighted average age between 214±1 and 219±1 Ma, indicating that they formed in Late Triassic epoch, and they are probably tectonic-magmatic products of late period of Indosinian. The rocks belong to the calc-alkaline series, showing intermediate Si (SiO2=53.92%-62.95%), high Al (Al2O3=15.99%-17.69%), rich in Na (Na2O=2.63%-6.09%, Na2O/K2O=1.09-8.30), Ti(Ti2O=0.50%-0.76%), P(P2O5=0.14%-0.23%). The rocks also show a large range of Mg (Mg#=37.73-59.32), and their A/CNK values vary from 0.92 to 1.36. They show enrichment in LREE, Rb, Th, U, K; depletion in HREE, Nb, Ta, Ti, P; (La/Yb)N=7.24-20.02 and weak Ce and Eu anomalies. Suyingdi intermediate dykes are the product of crustal-mantle magma mixing which caused by back-arc extention of eastern section of West Kunlun in Late Triassic.
order to understand tectonic-magmatic evolution of eastern section of West Kunlun orogen, a systematic field geological surveying, microscopic petrographic examination, LA-ICP-MS U-Pb zircon dating, and geochemistry study were carried out for the Suyingdi dykes. These dykes occur in groups or belts along an NE trending. The rock types of dykes include (garnet-bearing) diorite-porphyrite, hornblende andesite-porphyrite, and proterobase spessartite. Using LA-ICP-MS method, zircons in the (garnet-bearing) diorite-porphyrite samples show a weighted average age between 214±1 and 219±1 Ma, indicating that they formed in Late Triassic epoch, and they are probably tectonic-magmatic products of late period of Indosinian. The rocks belong to the calc-alkaline series, showing intermediate Si (SiO2=53.92%-62.95%), high Al (Al2O3=15.99%-17.69%), rich in Na (Na2O=2.63%-6.09%, Na2O/K2O=1.09-8.30), Ti(Ti2O=0.50%-0.76%), P(P2O5=0.14%-0.23%). The rocks also show a large range of Mg (Mg#=37.73-59.32), and their A/CNK values vary from 0.92 to 1.36. They show enrichment in LREE, Rb, Th, U, K; depletion in HREE, Nb, Ta, Ti, P; (La/Yb)N=7.24-20.02 and weak Ce and Eu anomalies. Suyingdi intermediate dykes are the product of crustal-mantle magma mixing which caused by back-arc extention of eastern section of West Kunlun in Late Triassic.
2017, 42(6): 927-940.
doi: 10.3799/dqkx.2017.073
Abstract:
In order to determine the formation time, magma source, and tectonic setting of the gneissic granodiorite in Manite area, East Kunlun, zircon U-Pb dating, Hf isotope data and geochemistry of the gneissic granodiorite are studied in this paper. The chronology indicates that the magmatic zircon LA-ICP-MS (laser ablation inductively coupled plasma mass spectrometry) U-Pb weighted mean age of the Manite gneissic granodiorite in the East Kunlun is 495.6±1.1 Ma (MSWD=0.13), belonging to the Late Cambrian. The gneissic granodiorites have SiO2 of 61.47%-63.99%, Na2O of 2.91%~3.64%, K2O of 0.93%-2.31%, CaO of 4.29%-6.52%, ALK of 3.92%-5.69% and A/CNK=0.83~0.97. Chemically, they are metaluminous and belong to calc-alkaline rock series. The gneissic granodiorite is characterized by the enrichment of LILEs (Rb and K) and incompatible elements(Th and U), and depletion of HFSEs(Nb, Ta, Zr and Ti). The ratios of Nb/Ta, La/Nb, Th/Nb and Th/La show crustal characteristics. The εHf(t) values of zircons from the gneissic granodiorite range from 12.2-15.0, their Hf two-stage model ages vary from 506 to 662 Ma. The initial materials are mainly derived from the juvenile crust. The gneissic granodiorite falls into the volcano arc granite area with the determination of trace elements in Rb-(Y+Nb) tectonic discrimination diagram and falls into the zone of pre-plate collision with the characteristics of active continental margin before the collision. Combined with the geochronological data, geochemical characteristics and the regional tectonic evolution, it is concluded that the gneissic granodiorite in the Manite area was formed in the environment of Proto-Tethys Ocean crust subduction, presumably it belongs to the southward subduction of oceanic crust. The crust between the Qaidam massif and Wanbaogou oceanic plateau occurred bidirectional subduction to the south and the north.
In order to determine the formation time, magma source, and tectonic setting of the gneissic granodiorite in Manite area, East Kunlun, zircon U-Pb dating, Hf isotope data and geochemistry of the gneissic granodiorite are studied in this paper. The chronology indicates that the magmatic zircon LA-ICP-MS (laser ablation inductively coupled plasma mass spectrometry) U-Pb weighted mean age of the Manite gneissic granodiorite in the East Kunlun is 495.6±1.1 Ma (MSWD=0.13), belonging to the Late Cambrian. The gneissic granodiorites have SiO2 of 61.47%-63.99%, Na2O of 2.91%~3.64%, K2O of 0.93%-2.31%, CaO of 4.29%-6.52%, ALK of 3.92%-5.69% and A/CNK=0.83~0.97. Chemically, they are metaluminous and belong to calc-alkaline rock series. The gneissic granodiorite is characterized by the enrichment of LILEs (Rb and K) and incompatible elements(Th and U), and depletion of HFSEs(Nb, Ta, Zr and Ti). The ratios of Nb/Ta, La/Nb, Th/Nb and Th/La show crustal characteristics. The εHf(t) values of zircons from the gneissic granodiorite range from 12.2-15.0, their Hf two-stage model ages vary from 506 to 662 Ma. The initial materials are mainly derived from the juvenile crust. The gneissic granodiorite falls into the volcano arc granite area with the determination of trace elements in Rb-(Y+Nb) tectonic discrimination diagram and falls into the zone of pre-plate collision with the characteristics of active continental margin before the collision. Combined with the geochronological data, geochemical characteristics and the regional tectonic evolution, it is concluded that the gneissic granodiorite in the Manite area was formed in the environment of Proto-Tethys Ocean crust subduction, presumably it belongs to the southward subduction of oceanic crust. The crust between the Qaidam massif and Wanbaogou oceanic plateau occurred bidirectional subduction to the south and the north.
2017, 42(6): 941-956.
doi: 10.3799/dqkx.2017.074
Abstract:
In order to determine the metallogenic physicochemical condition, ore-forming materials, ore-forming fluid and metallogenic mechanism of Galonggema VMS (volcanogenic massive sulfide) deposit in the northern Sanjiang metallogenic belt, China, orebody features, fluid inclusion microthermometry, laser Raman spectroscopy, and S, Pb, H, O isotopes are studied in this paper. It is found that deposit is hosted in the Late Triassic Batang Group dacite-volcanic tuff and consists of two parts, namely, lower ore belt of vein-stockwork mineralization system belonging to hydrothermal fluid supply channel, and upper ore belt of exhalative-chemical deposit system of submarine basin brine pond. Fluid inclusions (FIs) in vein-stockwork mineralization are both aqueous and gas-rich, homogenization temperature from 175.6 to 263.3 ℃, and salinities of 1.05%-6.29% NaCl equivalent (eqv.) and densities of 0.820-0.935 g/cm3. Laser Raman spectroscopic analyses of the gas phase components of FIs show they are dominated by H2O, CO2 and minor amounts of N2. Fluid inclusions in barite in exhalative-chemical deposit system are only aqueous FIs, homogenization temperature from 105.2 to 157.1 ℃, and salinities of 0.18%-5.55% NaCl eqv. and densities of 0.735-1.173 g/cm3 suggesting from lower ore belt to upper ore belt metallogenic temperature drops, salinities does not change, and the density of fluid increases. Hydrogen and oxygen isotopic study (δ18OH2O: 0.25‰-1.75‰, δD: -103.2‰ to -65.3‰) shows that metallogenic fluid is a mixture of seawater and magmatic water. The predecessors research results of sulfur isotope previous research indicates that the sulfur were provided by magma and bacteria reduction seawater sulfate or basement rock. Lead isotopic compositions of galena show 206Pb/204Pb ratios ranging from 18.449 to 18.519, 207Pb/204Pb ratios from 15.677 to 15.777, and 208Pb/204Pb ratios from 38.875 to 39.145, respectively. Lead isotopes has high radioactive lead isotope compositions with μ values of 9.65~9.80. It suggests that the lead mainly was sourced from crustal components and little from magma. The mixing of ore-forming fluid and seawater is the main metallogenic mechanism of Galonggema deposit.
In order to determine the metallogenic physicochemical condition, ore-forming materials, ore-forming fluid and metallogenic mechanism of Galonggema VMS (volcanogenic massive sulfide) deposit in the northern Sanjiang metallogenic belt, China, orebody features, fluid inclusion microthermometry, laser Raman spectroscopy, and S, Pb, H, O isotopes are studied in this paper. It is found that deposit is hosted in the Late Triassic Batang Group dacite-volcanic tuff and consists of two parts, namely, lower ore belt of vein-stockwork mineralization system belonging to hydrothermal fluid supply channel, and upper ore belt of exhalative-chemical deposit system of submarine basin brine pond. Fluid inclusions (FIs) in vein-stockwork mineralization are both aqueous and gas-rich, homogenization temperature from 175.6 to 263.3 ℃, and salinities of 1.05%-6.29% NaCl equivalent (eqv.) and densities of 0.820-0.935 g/cm3. Laser Raman spectroscopic analyses of the gas phase components of FIs show they are dominated by H2O, CO2 and minor amounts of N2. Fluid inclusions in barite in exhalative-chemical deposit system are only aqueous FIs, homogenization temperature from 105.2 to 157.1 ℃, and salinities of 0.18%-5.55% NaCl eqv. and densities of 0.735-1.173 g/cm3 suggesting from lower ore belt to upper ore belt metallogenic temperature drops, salinities does not change, and the density of fluid increases. Hydrogen and oxygen isotopic study (δ18OH2O: 0.25‰-1.75‰, δD: -103.2‰ to -65.3‰) shows that metallogenic fluid is a mixture of seawater and magmatic water. The predecessors research results of sulfur isotope previous research indicates that the sulfur were provided by magma and bacteria reduction seawater sulfate or basement rock. Lead isotopic compositions of galena show 206Pb/204Pb ratios ranging from 18.449 to 18.519, 207Pb/204Pb ratios from 15.677 to 15.777, and 208Pb/204Pb ratios from 38.875 to 39.145, respectively. Lead isotopes has high radioactive lead isotope compositions with μ values of 9.65~9.80. It suggests that the lead mainly was sourced from crustal components and little from magma. The mixing of ore-forming fluid and seawater is the main metallogenic mechanism of Galonggema deposit.
2017, 42(6): 957-943.
doi: 10.3799/dqkx.2017.80
Abstract:
Researches on the Daleishan gneissic granites can constrain Neoproterozoic Rodinia supercontinent breakup in the northern margin of Yangtze craton. In this paper, zircon U-Pb dating, in-situ Lu-Hf isotope and whole-rock geochemical compositions analyses are presented for the Daleishan gneissic granites in the northern margin of the Yangtze craton. The results show that the Daleishan gneissic granites have high contents of SiO2 (73.18%-77.40%) and alkali (8.07%-8.70%), but low contents of Al2O3 (12.11%-13.92%) and MgO (0.10%-0.34%), and display enrichment in Ga, Rb, Th, Zr, Hf but depletion in Nb, Sr, P, Ti, which indicates the post-orogenic A-type affinity. Zircons selected from two Daleishan gneissic granitic samples show typical oscillatory zone structure with high ratios of Th/U (greater than 0.5), exhibiting the magmatic zircon genesis. LA-ICP-MS (laser ablation inductively coupled plasma mass spectrometry) zircon U-Pb data from the two samples yield Neoproterozoic crystallization ages of 801.3±3.0 Ma (MSWD=0.62) and 796.1±6.3 Ma (MSWD=1.70), respectively, which are interpreted to represent the intrusion time. In-situ Hf isotopic compositions show that the two gneissic granitic samples have wide range of εHf(t) values that are indicative of a heterogeneity property. εHf(t) values of these zircon ranges from -7.5 to +8.0, with the positive εHf(t) values, coinciding with the single phase model age (tDM1) of the depleted mantle of (1 242-1 059 Ma), and the negative εHf(t) values coinciding with two-phase model age (tDM2) of the crustal of (1 636-1 981 Ma), suggesting that the oldest existing material in the region belongs to Paleoproterozoic (as old as 1 981 Ma). These data show that the source materials of the Daleishan A-type granites were usually derived from Palaeoproterozoic ancient crust. The magmatic source of the granites was originated from the crust-mantle migmatization, and the mantle composition could have been generated from the upwelling of the mantle magma in the extensional background. Combining with the pre-existing regional publications, it is proposed that the Daleishan A-type granite was formed at the crustal extensional background in the continental back-arc setting associated with the assembly-break up process of the Rodinia supercontinent.
Researches on the Daleishan gneissic granites can constrain Neoproterozoic Rodinia supercontinent breakup in the northern margin of Yangtze craton. In this paper, zircon U-Pb dating, in-situ Lu-Hf isotope and whole-rock geochemical compositions analyses are presented for the Daleishan gneissic granites in the northern margin of the Yangtze craton. The results show that the Daleishan gneissic granites have high contents of SiO2 (73.18%-77.40%) and alkali (8.07%-8.70%), but low contents of Al2O3 (12.11%-13.92%) and MgO (0.10%-0.34%), and display enrichment in Ga, Rb, Th, Zr, Hf but depletion in Nb, Sr, P, Ti, which indicates the post-orogenic A-type affinity. Zircons selected from two Daleishan gneissic granitic samples show typical oscillatory zone structure with high ratios of Th/U (greater than 0.5), exhibiting the magmatic zircon genesis. LA-ICP-MS (laser ablation inductively coupled plasma mass spectrometry) zircon U-Pb data from the two samples yield Neoproterozoic crystallization ages of 801.3±3.0 Ma (MSWD=0.62) and 796.1±6.3 Ma (MSWD=1.70), respectively, which are interpreted to represent the intrusion time. In-situ Hf isotopic compositions show that the two gneissic granitic samples have wide range of εHf(t) values that are indicative of a heterogeneity property. εHf(t) values of these zircon ranges from -7.5 to +8.0, with the positive εHf(t) values, coinciding with the single phase model age (tDM1) of the depleted mantle of (1 242-1 059 Ma), and the negative εHf(t) values coinciding with two-phase model age (tDM2) of the crustal of (1 636-1 981 Ma), suggesting that the oldest existing material in the region belongs to Paleoproterozoic (as old as 1 981 Ma). These data show that the source materials of the Daleishan A-type granites were usually derived from Palaeoproterozoic ancient crust. The magmatic source of the granites was originated from the crust-mantle migmatization, and the mantle composition could have been generated from the upwelling of the mantle magma in the extensional background. Combining with the pre-existing regional publications, it is proposed that the Daleishan A-type granite was formed at the crustal extensional background in the continental back-arc setting associated with the assembly-break up process of the Rodinia supercontinent.
2017, 42(6): 974-989.
doi: 10.3799/dqkx.2017.078
Abstract:
Deformation experiment at high temperature and high pressure is one of the important approaches to understand the rheological properties of minerals in the earth's deep interior. The deformation-DIA (D-DIA) is a newly developed apparatus for deformation experiments at high temperature and high pressure, which is typically capable of generating pressures up to 15 GPa and temperatures up to 2 000 K. The D-DIA coupled with synchrotron X-ray diffraction is mainly used for quantitative studies of rheological properties of materials under high temperature and high pressure. The configuration and operating principle of D-DIA apparatus installed at Brookhaven national lab in USA are summarized in this paper. The in-situ observation of deformation processes using synchrotron X-ray diffraction and mechanical data (e.g., stress, strain and strain rate) analysis are also discussed. This technical development provides an important opportunity to investigate rheological properties of high-pressure phases under the conditions in the earth's deep interior.
Deformation experiment at high temperature and high pressure is one of the important approaches to understand the rheological properties of minerals in the earth's deep interior. The deformation-DIA (D-DIA) is a newly developed apparatus for deformation experiments at high temperature and high pressure, which is typically capable of generating pressures up to 15 GPa and temperatures up to 2 000 K. The D-DIA coupled with synchrotron X-ray diffraction is mainly used for quantitative studies of rheological properties of materials under high temperature and high pressure. The configuration and operating principle of D-DIA apparatus installed at Brookhaven national lab in USA are summarized in this paper. The in-situ observation of deformation processes using synchrotron X-ray diffraction and mechanical data (e.g., stress, strain and strain rate) analysis are also discussed. This technical development provides an important opportunity to investigate rheological properties of high-pressure phases under the conditions in the earth's deep interior.
2017, 42(6): 990-1007.
doi: 10.3799/dqkx.2017.079
Abstract:
Melt inclusion has been widely used in the research of volcanic and some magmatic systems, and now gradually applied to economic geology because of its absolute advantage over whole-rock analysis in preserving the primary metal and volatile composition of ore-forming magmas. In this paper, we firstly present melt inclusion formation and post-entrapment modification on its composition, then summarize the commonly used analytical techniques for melt inclusion studies, and finally take porphyry Cu-(Mo-Au) and porphyry Mo systems as examples to introduce its applications in economic geology, including determination of ore-forming metals, volatile composition, and fluid-melt partition coefficients. Considering the facts that most melt inclusions have been modified to a certain degrees after their entrapment, and that the modification mechanism for most rock-forming minerals has not been well understood, attention has to be paid to the melt inclusion data and associated interpretation.With the improvement of analytical methods, such ambiguous post-entrapment modification mechanism may be resolved in the near future, and in turn it can promote the applications of melt inclusion. The successful applications of melt inclusion in porphyry Cu-(Mo-Au) and porphyry Mo systems confirm that melt inclusion has been an important and powerful tool in studying ore-forming metals and volatile evolution in ore-forming magma systems in comparison with whole-rock study.
Melt inclusion has been widely used in the research of volcanic and some magmatic systems, and now gradually applied to economic geology because of its absolute advantage over whole-rock analysis in preserving the primary metal and volatile composition of ore-forming magmas. In this paper, we firstly present melt inclusion formation and post-entrapment modification on its composition, then summarize the commonly used analytical techniques for melt inclusion studies, and finally take porphyry Cu-(Mo-Au) and porphyry Mo systems as examples to introduce its applications in economic geology, including determination of ore-forming metals, volatile composition, and fluid-melt partition coefficients. Considering the facts that most melt inclusions have been modified to a certain degrees after their entrapment, and that the modification mechanism for most rock-forming minerals has not been well understood, attention has to be paid to the melt inclusion data and associated interpretation.With the improvement of analytical methods, such ambiguous post-entrapment modification mechanism may be resolved in the near future, and in turn it can promote the applications of melt inclusion. The successful applications of melt inclusion in porphyry Cu-(Mo-Au) and porphyry Mo systems confirm that melt inclusion has been an important and powerful tool in studying ore-forming metals and volatile evolution in ore-forming magma systems in comparison with whole-rock study.
2017, 42(6): 1008-1025.
doi: 10.3799/dqkx.2017.534
Abstract:
The black siliceous mudstones of the Upper Permian Dalong Formation in Sichuan basin are important target zones for shale gas exploration. To facilitate the unconventional hydrocarbon resources exploration in this area, scanning electron microscope (SEM) and elemental geochemistry were used to investigate organic matter types, distribution characteristics and enrichment factors in Dalong Formation. According to SEM pictures, organic matter in the Dalong Formation can be divided into morphological organic matter, amorphous organic matter and bitumen. Morphological organic matter is the result of selected preservation, discretely distributed in all lithology samples; disperse organic matter, which can be seen in siliceous mudstones but rarely in siliceous limestone samples, is the principle part of TOC (total organic carbon) of the Dalong Formation, reflecting the adsorption of clay minerals; bitumen formed from dissolved organic matter migration and subsequent high thermal evolution, is distributed in siliceous limestone and limestone samples, rarely in siliceous mudstone samples. Geochemical data indicate that anoxic environment is beneficial to the preservation of organic matter, but the productivity is the main factor to control the change of content of total organic carbon (TOC). Comprehensive correlation research shows that the sea-level rise of the Late Permian led to the increased productivity and anoxic water column in the adjacent oceanic basin. The high content of TOC in organic-matter-rich black siliceous mudstone is the result of sedimentary environment and mineral absorption, and also reflects preservation state of primary organic matter. Migration bitumen should be excluded for hydrocarbon source rock evaluation.
The black siliceous mudstones of the Upper Permian Dalong Formation in Sichuan basin are important target zones for shale gas exploration. To facilitate the unconventional hydrocarbon resources exploration in this area, scanning electron microscope (SEM) and elemental geochemistry were used to investigate organic matter types, distribution characteristics and enrichment factors in Dalong Formation. According to SEM pictures, organic matter in the Dalong Formation can be divided into morphological organic matter, amorphous organic matter and bitumen. Morphological organic matter is the result of selected preservation, discretely distributed in all lithology samples; disperse organic matter, which can be seen in siliceous mudstones but rarely in siliceous limestone samples, is the principle part of TOC (total organic carbon) of the Dalong Formation, reflecting the adsorption of clay minerals; bitumen formed from dissolved organic matter migration and subsequent high thermal evolution, is distributed in siliceous limestone and limestone samples, rarely in siliceous mudstone samples. Geochemical data indicate that anoxic environment is beneficial to the preservation of organic matter, but the productivity is the main factor to control the change of content of total organic carbon (TOC). Comprehensive correlation research shows that the sea-level rise of the Late Permian led to the increased productivity and anoxic water column in the adjacent oceanic basin. The high content of TOC in organic-matter-rich black siliceous mudstone is the result of sedimentary environment and mineral absorption, and also reflects preservation state of primary organic matter. Migration bitumen should be excluded for hydrocarbon source rock evaluation.
2017, 42(6): 1026-1038.
doi: 10.3799/dqkx.2017.081
Abstract:
Critical zone science is a novel discipline in earth sciences. International researchers investigate on this discipline mainly through critical zone observatory (CZO), with the aim to develop the framework of this discipline and to serve for economic development and ecological protection. In China, CZO studies have just been initiated. Shenongjia Dajiuhu is a typical subalpine peatland, dominated by Sphagnum, in the middle latitude. This peatland is a head source of Duhe River, which finally drains into the Danjiangkou Reservoir. In 2013, Dajiuhu peatland was listed as a Ramsar Wetlands site. With these merits, Dajiuhu is a perfect place to monitor the peatland dynamics. Based on the over ten years' studies on paleoclimate and modern processes in Dajiuhu, we initialed a CZO monitoring program in Dajiuhu in the early 2014. This program considers all elements in the critical zone, with special attention to organisms, water and greenhouse gases. Monitoring points are established in the peatland and the surrounding lakes and rivers, to explore the relationship among wetlands. Within the peatland, both the surficial and deep processes are monitored. To date, most measurements were completed in the field, to eliminate the influence of sample storage. This paper presents both the progresses of our work and the outlooks for the CZO in Dajiuhu. In the near future, we should pay more attention to improvement of the monitoring techniques and facilities, and focus on responses of the carbon cycle to climate changes especially droughts, and evaluation of the influence of climate change and human activities on the ecosystem function of the subalpine wetland. In addition, collaborations with domestic and international researchers will be strengthened. The final objective is to fulfil the theory for subalpine peatland critical zone, and to build the model of peatland critical zone, and to serve for wetland protection and sustainable development.
Critical zone science is a novel discipline in earth sciences. International researchers investigate on this discipline mainly through critical zone observatory (CZO), with the aim to develop the framework of this discipline and to serve for economic development and ecological protection. In China, CZO studies have just been initiated. Shenongjia Dajiuhu is a typical subalpine peatland, dominated by Sphagnum, in the middle latitude. This peatland is a head source of Duhe River, which finally drains into the Danjiangkou Reservoir. In 2013, Dajiuhu peatland was listed as a Ramsar Wetlands site. With these merits, Dajiuhu is a perfect place to monitor the peatland dynamics. Based on the over ten years' studies on paleoclimate and modern processes in Dajiuhu, we initialed a CZO monitoring program in Dajiuhu in the early 2014. This program considers all elements in the critical zone, with special attention to organisms, water and greenhouse gases. Monitoring points are established in the peatland and the surrounding lakes and rivers, to explore the relationship among wetlands. Within the peatland, both the surficial and deep processes are monitored. To date, most measurements were completed in the field, to eliminate the influence of sample storage. This paper presents both the progresses of our work and the outlooks for the CZO in Dajiuhu. In the near future, we should pay more attention to improvement of the monitoring techniques and facilities, and focus on responses of the carbon cycle to climate changes especially droughts, and evaluation of the influence of climate change and human activities on the ecosystem function of the subalpine wetland. In addition, collaborations with domestic and international researchers will be strengthened. The final objective is to fulfil the theory for subalpine peatland critical zone, and to build the model of peatland critical zone, and to serve for wetland protection and sustainable development.
2017, 42(6): 1039-1044.
doi: 10.3799/dqkx.2017.082
Abstract:
Hydroxyl radical (·OH) is the most reactive oxidant in nature, which significantly impacts the transformation of substance and contaminants. Previous studies have substantiated that exposure of groundwater to O2 can produce ·OH through Fe2+ oxygenation. However, the effect of groundwater compositions on Fe2+ oxygenation and ·OH production remainsis unclear. Therefore, this study evaluates the influence of groundwater components (Ca2+, Mg2+, humic acid (HA) and phosphate) on Fe2+ oxygenation and resultant ·OH production. Results show that at pH 6.5, 0.357 mM Fe2+ was completely oxidized within 5 h with production of 1.8 μM ·OH. Ca2+ (1-6 mM) and Mg2+ (1-4 mM) had no obvious influence on Fe2+ oxidation and ·OH production. HA (10-30 mg/L) promoted Fe2+ oxidation and ·OH production, and the promotion increased with the decrease in pH. Phosphate (0.01-0.03 mM) inhibited Fe2+ oxidation and ·OH production in initial stage while promoted Fe2+ oxidation and ·OH production later on.
Hydroxyl radical (·OH) is the most reactive oxidant in nature, which significantly impacts the transformation of substance and contaminants. Previous studies have substantiated that exposure of groundwater to O2 can produce ·OH through Fe2+ oxygenation. However, the effect of groundwater compositions on Fe2+ oxygenation and ·OH production remainsis unclear. Therefore, this study evaluates the influence of groundwater components (Ca2+, Mg2+, humic acid (HA) and phosphate) on Fe2+ oxygenation and resultant ·OH production. Results show that at pH 6.5, 0.357 mM Fe2+ was completely oxidized within 5 h with production of 1.8 μM ·OH. Ca2+ (1-6 mM) and Mg2+ (1-4 mM) had no obvious influence on Fe2+ oxidation and ·OH production. HA (10-30 mg/L) promoted Fe2+ oxidation and ·OH production, and the promotion increased with the decrease in pH. Phosphate (0.01-0.03 mM) inhibited Fe2+ oxidation and ·OH production in initial stage while promoted Fe2+ oxidation and ·OH production later on.
