The genesis of intermediate-silicic intrusive rocks and their enclaves in Tongling are closely related to Fe, Cu mineralization, which may provide petrologic informa- tion on lithospheric dynamics in this region. Tong...The genesis of intermediate-silicic intrusive rocks and their enclaves in Tongling are closely related to Fe, Cu mineralization, which may provide petrologic informa- tion on lithospheric dynamics in this region. Tongguanshan quartz diorite and its enclaves, representatives of the Meso- zoic intermediate-silicic intrusive rocks in the Tongling area, were studied using approaches of petrography, electron microprobe mineral chemistry and the LA-ICPMS zircon U-Pb dating. The chemical compositions of pyroxene and amphibole in pyroxene-amphibole cumulate, quartz-diorite host rock from Tongguanshan show correlative variations. The Al contents of the minerals in pyroxene-amphibole cu- mulate are higher than those in the host rocks, indicating that the cumulate crystals were crystallized before the em- placement of host magma. The consistent mineral chemical compositions between the Tongguanshan quartz diorite and the microgranular diorite enclave indicate that the enclave and host rock were crystallized under similar conditions and therefore are closely genetically related. The LA-ICPMS zircon U-Pb dating suggests that the crystallization age of Tongguanshan quartz diorite is 137.5±1.1 Ma, consistent with the previous dates by different methods. However, the present U-Pb dating also revealed the presence of late- Archean relict cores, demonstrating that older lower crustal materials were involved in the generation of Mesozoic mag- matic rocks in this area. Furthermore, the dating results show that the crystallization age of the microgranular diorite enclave is 137.5 ±2.4 Ma, the same as the crystallization age of the host magma. By integrating the previous Sr-Nd-Pb isotope data, it is also discussed the petrogenesis of quartz diorite and its enclaves in Tongguanshan.展开更多
Single zircon LAM-ICPMS U-Pb dating indi-cates that the Guidong granitic complex is a multistage ba-tholith formed during Indosinian-Yanshanian time. The Luxi body (239 ± 5 Ma) and the Xiazhuang body (235.8 ±...Single zircon LAM-ICPMS U-Pb dating indi-cates that the Guidong granitic complex is a multistage ba-tholith formed during Indosinian-Yanshanian time. The Luxi body (239 ± 5 Ma) and the Xiazhuang body (235.8 ± 7.6 Ma) intruded during Indosinian time, whereas the Aizi body (160.1 ± 6.1 Ma) and the Siqian body (151 ± 11 Ma) formed during Yanshanian time. Inherited zircons (1275—2137 Ma) in the Xiazhuang body imply that at least part of the source rocks of the Guidong complex are from the Proterozoic basement of southeast China. Detailed single zirconLAM-ICPMS U-Pb dating results provide important evi-dence for understanding the evolution, tectonic setting andmineralisation of the complex.展开更多
Detailed studies indicate that the main rock type of the Neogene high-potassium calc-alkaline volcanic rock association from north Qiangtang is andesite, dacite and rhyolite. They belong to typical crust-generation ma...Detailed studies indicate that the main rock type of the Neogene high-potassium calc-alkaline volcanic rock association from north Qiangtang is andesite, dacite and rhyolite. They belong to typical crust-generation magmatic system and originate from the special thickened crust of the Tibetan Plateau by dehydration melting. This group of rocks exhibits LREE enrichment but no remarkable Eu anomaly that shows their source region should be a thickened deep crust consisting of eclogitic mass group, implying that the crust had been thickened and an eclogitic deep crust had been formed during the Neogene period in Qiangtang area. This understanding is important and significant to making further discussion on the uplift mechanism and continental dynamics of the Tibetan Plateau.展开更多
Based on the LAM-ICPMS analytic results on the trace elements of clinopyroxenes in peridotitic xenoliths occurring in early-Cretaceous basalts from western Xinjiang, the properties and the deep processes, including pa...Based on the LAM-ICPMS analytic results on the trace elements of clinopyroxenes in peridotitic xenoliths occurring in early-Cretaceous basalts from western Xinjiang, the properties and the deep processes, including partial melting and mantle metasomatism, of the subcontinental lithospheric mantle beneath the Tuoyun Basin are analyzed. In the northern edge of the Tarim Basin (southwest Tian-shan), the Mesozoic subcontinental lithosphere which has experienced the effect of partial melting (【10%) and intricate mantle metasomatism is characterized by Phanerozoic ’ocean-type’ mantle. The superposed influence of SiO2-un-saturated silicate melt and carbonate melt probably results in the metasomatic medium which resembles the hydrous silicated carbonate melt in some aspects. By comparing Tuoyun mantle with Cenozoic main mantle beneath eastern China, the properties are similar, while the former shows finer grain and higher diopside content of the peridotites and more conspicuous modal metasomatism.展开更多
A growing body of evidence shows that volcanism near the Permian-Triassic boundary（PTB） may be crucial in triggering the Permian–Triassic（P–Tr） mass extinction. Thus, the ash beds near the PTB in South China may...A growing body of evidence shows that volcanism near the Permian-Triassic boundary（PTB） may be crucial in triggering the Permian–Triassic（P–Tr） mass extinction. Thus, the ash beds near the PTB in South China may carry information on this event. Three volcanic ash layers, altered to clay, outcropped in the PTB beds in Zunyi Section, Guizhou Province, Southwest China. The U-Pb ages, trace elements, and Hf-isotope compositions of zircon grains from these three ash beds were analyzed using LA-ICPMS and LA-MC-ICPMS. The zircons are mainly magmatic in origin（241-279 Ma） except for two inherited/xenocrystic zircons（939 and 2 325 Ma）. The ages of these magmatic zircons indicate three episodes of magmatism which occurred around the MiddleLate Permian boundary（-261.5 Ma, MLPB）, the Wuchiapingian-Changhsingian boundary（-254.5 Ma, WCB）, and the PTB（-250.5 Ma）, respectively. The first two episodes of magmatism near the MLPB and WCB may be attributed to magmatic inheritance or re-deposition. All magmatic zircons share similar trace-element and Hf-isotope compositions. They have Y, Hf, Th and U contents and Nb/Ta ratios are typical of zircons from silicic calc-alkaline magmas. These zircons also exhibit enriched Hf-isotope compositions with _（εHf）（t） values of-11.4 to ＋0.2, which suggests that the three magmatic episodes involved melting of the continental crust. The more enriched Hf-isotope composition （_（εHf）（t）=-11.4--4.8） of Bed ZY13（-250.5 Ma） implies more input of ancient crustal material in the magma. Integration of the Hf-isotope and trace-element compositions of magmatic zircons suggest that these three episodes of magmatism may take place along the convergent continent margin in or near southwestern South China as a result of the closure of the Palaeo-Tethys Ocean.展开更多
The occurrence of moissanite(SiC), as xenocrysts in mantle-derived basaltic and kimberlitic rocks sheds light on the interplay between carbon, hydrogen and oxygen in the lithospheric and sublithospheric mantle. SiC is...The occurrence of moissanite(SiC), as xenocrysts in mantle-derived basaltic and kimberlitic rocks sheds light on the interplay between carbon, hydrogen and oxygen in the lithospheric and sublithospheric mantle. SiC is stable only at fO2< △IW-6, while the lithospheric mantle and related melts commonly are considered to be much more oxidized. SiC grains from both basaltic volcanoclastic rocks and kimberlites contain metallic inclusions whose shapes suggest they were entrapped as melts. The inclusions consist of Si^0+ Fe3Si7± FeSi2 Ti ± CaSi2Al2± FeSi2Al3± CaSi2, and some of the phases show euhedral shapes toward Si^0. Crystallographically-oriented cavities are common in SiC, suggesting the former presence of volatile phase(s), and the volatiles extracted from crushed SiC grains contain H2+ CH4± CO2± CO.Our observations suggest that SiC crystalized from metallic melts(Si-Fe-Ti-C ± Al ± Ca), with dissolved H2+ CH4± CO2± CO derived from the sublithospheric mantle and concentrated around interfaces such as the lithosphere-asthenosphere and crust-mantle boundaries. When mafic/ultramafic magmas are continuously fluxed with H2+ CH4 they can be progressively reduced, to a point where silicide melts become immiscible, and crystallize phases such as SiC. The occurrence of SiC in explosive volcanic rocks from different tectonic settings indicates that the delivery of H2+ CH4 from depth may commonly accompany explosive volcanism and modify the redox condition of some lithospheric mantle volumes. The heterogeneity of redox states further influences geochemical reactions such as melting and geophysical properties such as seismic velocity and the viscosity of mantle rocks.展开更多
The origin of zircon grains, and other exotic minerals of typical crustal origin, in mantle-hosted ophiolitic chromitites are hotly debated. We report a population of zircon grains with ages ranging from Cretaceous(99...The origin of zircon grains, and other exotic minerals of typical crustal origin, in mantle-hosted ophiolitic chromitites are hotly debated. We report a population of zircon grains with ages ranging from Cretaceous(99 Ma) to Neoarchean(2750 Ma), separated from massive chromitite bodies hosted in the mantle section of the supra-subduction(SSZ)-type Mayari-Baracoa Ophiolitic Belt in eastern Cuba. Most analyzed zircon grains(n = 20, 287 ± 3 Ma to 2750 ± 60 Ma) are older than the early Cretaceous age of the ophiolite body, show negativeε_(Hf)(t)(-26 to-0.6) and occasional inclusions of quartz, K-feldspar,biotite, and apatite that indicate derivation from a granitic continental crust. In contrast, 5 mainly rounded zircon grains(297±5 Ma to 2126±27 Ma) show positive εHf(t)(+0.7 to +13.5) and occasional apatite inclusions, suggesting their possible crystallization from melts derived from juvenile(mantle)sources. Interestingly, younger zircon grains are mainly euhedral to subhedral crystals, whereas older zircon grains are predominantly rounded grains. A comparison of the ages and Hf isotopic compositions of the zircon grains with those of nearby exposed crustal terranes suggest that chromitite zircon grains are similar to those reported from terranes of Mexico and northern South America. Hence, chromitite zircon grains are interpreted as sedimentary-derived xenocrystic grains that were delivered into the mantle wedge beneath the Greater Antilles intra-oceanic volcanic arc by metasomatic fluids/melts during subduction processes. Thus, continental crust recycling by subduction could explain all populations of old xenocrystic zircon in Cretaceous mantle-hosted chromitites from eastern Cuba ophiolite.We integrate the results of this study with petrological-thermomechanical modeling and existing geodynamic models to propose that ancient zircon xenocrysts, with a wide spectrum of ages and Hf isotopic compositions, can be transferred to the mantle wedge above subducting slabs by cold plumes.展开更多
文摘The genesis of intermediate-silicic intrusive rocks and their enclaves in Tongling are closely related to Fe, Cu mineralization, which may provide petrologic informa- tion on lithospheric dynamics in this region. Tongguanshan quartz diorite and its enclaves, representatives of the Meso- zoic intermediate-silicic intrusive rocks in the Tongling area, were studied using approaches of petrography, electron microprobe mineral chemistry and the LA-ICPMS zircon U-Pb dating. The chemical compositions of pyroxene and amphibole in pyroxene-amphibole cumulate, quartz-diorite host rock from Tongguanshan show correlative variations. The Al contents of the minerals in pyroxene-amphibole cu- mulate are higher than those in the host rocks, indicating that the cumulate crystals were crystallized before the em- placement of host magma. The consistent mineral chemical compositions between the Tongguanshan quartz diorite and the microgranular diorite enclave indicate that the enclave and host rock were crystallized under similar conditions and therefore are closely genetically related. The LA-ICPMS zircon U-Pb dating suggests that the crystallization age of Tongguanshan quartz diorite is 137.5±1.1 Ma, consistent with the previous dates by different methods. However, the present U-Pb dating also revealed the presence of late- Archean relict cores, demonstrating that older lower crustal materials were involved in the generation of Mesozoic mag- matic rocks in this area. Furthermore, the dating results show that the crystallization age of the microgranular diorite enclave is 137.5 ±2.4 Ma, the same as the crystallization age of the host magma. By integrating the previous Sr-Nd-Pb isotope data, it is also discussed the petrogenesis of quartz diorite and its enclaves in Tongguanshan.
基金supported by the National Natural Science Foundation of China(Grant Nos.40125007,40132010 and 40221301).
文摘Single zircon LAM-ICPMS U-Pb dating indi-cates that the Guidong granitic complex is a multistage ba-tholith formed during Indosinian-Yanshanian time. The Luxi body (239 ± 5 Ma) and the Xiazhuang body (235.8 ± 7.6 Ma) intruded during Indosinian time, whereas the Aizi body (160.1 ± 6.1 Ma) and the Siqian body (151 ± 11 Ma) formed during Yanshanian time. Inherited zircons (1275—2137 Ma) in the Xiazhuang body imply that at least part of the source rocks of the Guidong complex are from the Proterozoic basement of southeast China. Detailed single zirconLAM-ICPMS U-Pb dating results provide important evi-dence for understanding the evolution, tectonic setting andmineralisation of the complex.
基金the National Natural Science Foundation of China (Grant No. 40072029) and the National Key Project for Basic Research on the Tibetan Plateau (G1998040801).
文摘Detailed studies indicate that the main rock type of the Neogene high-potassium calc-alkaline volcanic rock association from north Qiangtang is andesite, dacite and rhyolite. They belong to typical crust-generation magmatic system and originate from the special thickened crust of the Tibetan Plateau by dehydration melting. This group of rocks exhibits LREE enrichment but no remarkable Eu anomaly that shows their source region should be a thickened deep crust consisting of eclogitic mass group, implying that the crust had been thickened and an eclogitic deep crust had been formed during the Neogene period in Qiangtang area. This understanding is important and significant to making further discussion on the uplift mechanism and continental dynamics of the Tibetan Plateau.
基金This work was supported by the National Natural Science Foundation of China (Grant Nos. 40072021 and 49733110) and the State Key Basic Research Development Program (Grant No. G1999043303).
文摘Based on the LAM-ICPMS analytic results on the trace elements of clinopyroxenes in peridotitic xenoliths occurring in early-Cretaceous basalts from western Xinjiang, the properties and the deep processes, including partial melting and mantle metasomatism, of the subcontinental lithospheric mantle beneath the Tuoyun Basin are analyzed. In the northern edge of the Tarim Basin (southwest Tian-shan), the Mesozoic subcontinental lithosphere which has experienced the effect of partial melting (【10%) and intricate mantle metasomatism is characterized by Phanerozoic ’ocean-type’ mantle. The superposed influence of SiO2-un-saturated silicate melt and carbonate melt probably results in the metasomatic medium which resembles the hydrous silicated carbonate melt in some aspects. By comparing Tuoyun mantle with Cenozoic main mantle beneath eastern China, the properties are similar, while the former shows finer grain and higher diopside content of the peridotites and more conspicuous modal metasomatism.
基金supported by an aid grant from Chengdu Center, China Geological Survey (No. 12120113049100-1)the National Natural Science Foundations (Nos. 40572068, 40839903 and 41272044)+1 种基金the "111" Program (No. B08030)an aid grant (No. GBL11206) from the State Key Laboratory of Biogeology and Environmental Geology, China University of Geosciences (Wuhan), China
文摘A growing body of evidence shows that volcanism near the Permian-Triassic boundary（PTB） may be crucial in triggering the Permian–Triassic（P–Tr） mass extinction. Thus, the ash beds near the PTB in South China may carry information on this event. Three volcanic ash layers, altered to clay, outcropped in the PTB beds in Zunyi Section, Guizhou Province, Southwest China. The U-Pb ages, trace elements, and Hf-isotope compositions of zircon grains from these three ash beds were analyzed using LA-ICPMS and LA-MC-ICPMS. The zircons are mainly magmatic in origin（241-279 Ma） except for two inherited/xenocrystic zircons（939 and 2 325 Ma）. The ages of these magmatic zircons indicate three episodes of magmatism which occurred around the MiddleLate Permian boundary（-261.5 Ma, MLPB）, the Wuchiapingian-Changhsingian boundary（-254.5 Ma, WCB）, and the PTB（-250.5 Ma）, respectively. The first two episodes of magmatism near the MLPB and WCB may be attributed to magmatic inheritance or re-deposition. All magmatic zircons share similar trace-element and Hf-isotope compositions. They have Y, Hf, Th and U contents and Nb/Ta ratios are typical of zircons from silicic calc-alkaline magmas. These zircons also exhibit enriched Hf-isotope compositions with _（εHf）（t） values of-11.4 to ＋0.2, which suggests that the three magmatic episodes involved melting of the continental crust. The more enriched Hf-isotope composition （_（εHf）（t）=-11.4--4.8） of Bed ZY13（-250.5 Ma） implies more input of ancient crustal material in the magma. Integration of the Hf-isotope and trace-element compositions of magmatic zircons suggest that these three episodes of magmatism may take place along the convergent continent margin in or near southwestern South China as a result of the closure of the Palaeo-Tethys Ocean.
基金supported by grants from the ARC Centre of Excellence for Core to Crust Fluid Systems。
文摘The occurrence of moissanite(SiC), as xenocrysts in mantle-derived basaltic and kimberlitic rocks sheds light on the interplay between carbon, hydrogen and oxygen in the lithospheric and sublithospheric mantle. SiC is stable only at fO2< △IW-6, while the lithospheric mantle and related melts commonly are considered to be much more oxidized. SiC grains from both basaltic volcanoclastic rocks and kimberlites contain metallic inclusions whose shapes suggest they were entrapped as melts. The inclusions consist of Si^0+ Fe3Si7± FeSi2 Ti ± CaSi2Al2± FeSi2Al3± CaSi2, and some of the phases show euhedral shapes toward Si^0. Crystallographically-oriented cavities are common in SiC, suggesting the former presence of volatile phase(s), and the volatiles extracted from crushed SiC grains contain H2+ CH4± CO2± CO.Our observations suggest that SiC crystalized from metallic melts(Si-Fe-Ti-C ± Al ± Ca), with dissolved H2+ CH4± CO2± CO derived from the sublithospheric mantle and concentrated around interfaces such as the lithosphere-asthenosphere and crust-mantle boundaries. When mafic/ultramafic magmas are continuously fluxed with H2+ CH4 they can be progressively reduced, to a point where silicide melts become immiscible, and crystallize phases such as SiC. The occurrence of SiC in explosive volcanic rocks from different tectonic settings indicates that the delivery of H2+ CH4 from depth may commonly accompany explosive volcanism and modify the redox condition of some lithospheric mantle volumes. The heterogeneity of redox states further influences geochemical reactions such as melting and geophysical properties such as seismic velocity and the viscosity of mantle rocks.
基金financially supported by FEDER Funds,the Spanish Project CGL2015-65824 granted by the Spanish“Ministerio de Economía y Competitividad”to JAPthe Ramón y Cajal Fellowship RYC-2015-17596 to JMGJ
文摘The origin of zircon grains, and other exotic minerals of typical crustal origin, in mantle-hosted ophiolitic chromitites are hotly debated. We report a population of zircon grains with ages ranging from Cretaceous(99 Ma) to Neoarchean(2750 Ma), separated from massive chromitite bodies hosted in the mantle section of the supra-subduction(SSZ)-type Mayari-Baracoa Ophiolitic Belt in eastern Cuba. Most analyzed zircon grains(n = 20, 287 ± 3 Ma to 2750 ± 60 Ma) are older than the early Cretaceous age of the ophiolite body, show negativeε_(Hf)(t)(-26 to-0.6) and occasional inclusions of quartz, K-feldspar,biotite, and apatite that indicate derivation from a granitic continental crust. In contrast, 5 mainly rounded zircon grains(297±5 Ma to 2126±27 Ma) show positive εHf(t)(+0.7 to +13.5) and occasional apatite inclusions, suggesting their possible crystallization from melts derived from juvenile(mantle)sources. Interestingly, younger zircon grains are mainly euhedral to subhedral crystals, whereas older zircon grains are predominantly rounded grains. A comparison of the ages and Hf isotopic compositions of the zircon grains with those of nearby exposed crustal terranes suggest that chromitite zircon grains are similar to those reported from terranes of Mexico and northern South America. Hence, chromitite zircon grains are interpreted as sedimentary-derived xenocrystic grains that were delivered into the mantle wedge beneath the Greater Antilles intra-oceanic volcanic arc by metasomatic fluids/melts during subduction processes. Thus, continental crust recycling by subduction could explain all populations of old xenocrystic zircon in Cretaceous mantle-hosted chromitites from eastern Cuba ophiolite.We integrate the results of this study with petrological-thermomechanical modeling and existing geodynamic models to propose that ancient zircon xenocrysts, with a wide spectrum of ages and Hf isotopic compositions, can be transferred to the mantle wedge above subducting slabs by cold plumes.
