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
In the peralumineous granite of Yajiangqiao zircon population can be divided into two groups (i.e. Zircon Ⅰ and Zircon Ⅱ), which were formed in magmatic chamber and in emplacement place, respectively. The Hf isotope...In the peralumineous granite of Yajiangqiao zircon population can be divided into two groups (i.e. Zircon Ⅰ and Zircon Ⅱ), which were formed in magmatic chamber and in emplacement place, respectively. The Hf isotope compositions of two stages of zircon show that the host magma was essentially derived from crustal material by melting. However, some higher 176Hf/177Hf ratios indicate that the granitic zircons should contain fine crystal of zircon formed in mantle-derived magma. In fact, the backscattered electron imaging and the electron microprobe analysis reveal that there is another type of zircon included within Zircon Ⅰ, which is quite different from Zircon Ⅰ and Zircon Ⅱ in morphology and chemistry. They are considered to be the product of the mantle-derived magma intruded into the granitic magma chamber at the beginning of anatexis. Thus, it is suggested that the formation of Yajiangqiao granite is related to the underplating of mantle magma.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
Ca is a minor component of olivine (oliv). Its concentration measured by electron microprobe (EMP) is about 0.1—0.5%, which is close to the minimum detection limit. As Ca distribution between oliv and clinopyroxene (...Ca is a minor component of olivine (oliv). Its concentration measured by electron microprobe (EMP) is about 0.1—0.5%, which is close to the minimum detection limit. As Ca distribution between oliv and clinopyroxene (cpx)has the possibility of being used as geothermobarometers, it is very important to measure accurately the Ca content in oliv. Proton-induced X-ray emission (PIXE) technique as a new high energy analysis method shows advantage in high sensitivity and accuracy of microanalyses and begins to be展开更多
Knowledge of the trace element distributions and concentrations in main mineral phases of mantle-derived rocks is particularly useful for understanding the partial melting, depletion and enrichment processes, and meta...Knowledge of the trace element distributions and concentrations in main mineral phases of mantle-derived rocks is particularly useful for understanding the partial melting, depletion and enrichment processes, and metasomatism in the earth’s mantle. Trace element data on mantle peridotites were usually obtained with large uncertainty by neutron activation analysis in China previously. We have determined trace element concentration of 173 grains of clinopyroxene (cpx) in 50 peridotite xenoliths from different areas in China using the pro-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supposed by the National Natural Science Foundation of China(Grant Nos.40172023 and 40132010).
文摘In the peralumineous granite of Yajiangqiao zircon population can be divided into two groups (i.e. Zircon Ⅰ and Zircon Ⅱ), which were formed in magmatic chamber and in emplacement place, respectively. The Hf isotope compositions of two stages of zircon show that the host magma was essentially derived from crustal material by melting. However, some higher 176Hf/177Hf ratios indicate that the granitic zircons should contain fine crystal of zircon formed in mantle-derived magma. In fact, the backscattered electron imaging and the electron microprobe analysis reveal that there is another type of zircon included within Zircon Ⅰ, which is quite different from Zircon Ⅰ and Zircon Ⅱ in morphology and chemistry. They are considered to be the product of the mantle-derived magma intruded into the granitic magma chamber at the beginning of anatexis. Thus, it is suggested that the formation of Yajiangqiao granite is related to the underplating of mantle magma.
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.
文摘Ca is a minor component of olivine (oliv). Its concentration measured by electron microprobe (EMP) is about 0.1—0.5%, which is close to the minimum detection limit. As Ca distribution between oliv and clinopyroxene (cpx)has the possibility of being used as geothermobarometers, it is very important to measure accurately the Ca content in oliv. Proton-induced X-ray emission (PIXE) technique as a new high energy analysis method shows advantage in high sensitivity and accuracy of microanalyses and begins to be
文摘Knowledge of the trace element distributions and concentrations in main mineral phases of mantle-derived rocks is particularly useful for understanding the partial melting, depletion and enrichment processes, and metasomatism in the earth’s mantle. Trace element data on mantle peridotites were usually obtained with large uncertainty by neutron activation analysis in China previously. We have determined trace element concentration of 173 grains of clinopyroxene (cpx) in 50 peridotite xenoliths from different areas in China using the pro-
