The granulitic xenoliths discovered in the late Cretaceous basaltic rocks from Tuoyun basin, western Xinjiang Province contain the assemblage of Opx + Cpx + Pl ± Grt ± Qtz ± Kfs. Mineral chemistry, petr...The granulitic xenoliths discovered in the late Cretaceous basaltic rocks from Tuoyun basin, western Xinjiang Province contain the assemblage of Opx + Cpx + Pl ± Grt ± Qtz ± Kfs. Mineral chemistry, petrochemistry and zircon U-Pb ages from the xenoliths have been reported in the paper. Petrogenesis, the lower crustal nature and the mantle-crust interaction reflected by the granulites are discussed as well. Tuoyun granulites are mainly mafic with few intermediate components, and represent the magmatic products underwent granulite-facies metamorphism in lower crustal condition. Equilibrium temperature and the maximum pressure estimates of the granulites are 910 ± 35℃ and 13.5 × 108 Pa respectively, indicating that the crust beneath southwestern Tianshan had the thickness of less than 44 km and high geotherm (e.g. > 80 mW/m2) when the host magma erupted. During their formation, the fractional crystallization of olivine, pyroxene, plagioclase and ilmenite, plagioclase accumulation and the contamination of felsic components or fluid metasomatism processes had happened. Metamorphic zircon U-Pb age of 253 Ma may record the crust-mantle interaction caused by the orogenic root delamination beneath the southwestern Tianshan.展开更多
Mafic granulite xenoliths collected from Cenozoic basalts in SE China can be classified as magmatic granulite and cumulate granulite. Magmatic granulites are characterized by highly concentrated AI2O3, K2O, P2O5, Ba, ...Mafic granulite xenoliths collected from Cenozoic basalts in SE China can be classified as magmatic granulite and cumulate granulite. Magmatic granulites are characterized by highly concentrated AI2O3, K2O, P2O5, Ba, Sr, Pb and REE, and low contents of Nb, Zr, Hf and Th, and have an incompatible element abundance pattern similar to that of continental arc basalts. Cumulate granulites are depleted in K2O, P2O5, Rb, Cs and Ba. These granulite xenoliths were the prod-ucts of crystallization and recrystallization of the basaltic magma underplating into crust-mantle boundary in Late Mesozoic. Sr and Nd isotopic compositions and variation trend of these mafic rocks are the result of crust-mantle mixing and controlled by assimilation and fractional crystallization process (AFC). However, trace element and major element variations were mainly controlled by fractional crystallization. The granulites are similar in geochemistry to surface Late Mesozoic gabbro and basalt in the study area, suggesting a close petrogenetic link between them. Late Mesozoic basaltic magma activities are the most important cause for the formation of extensive contemporaneous granite and rhyolite in the study area. This study and previous data indicate that the lower crust beneath South China is composed of a variety of Paleo- to Meso-proterozoic metamorphic rocks and Late Mesozoic mafic granulites.展开更多
Zircon SHRIMP U-Pb dating was carried out for an intermediate granulite xenolith in Cenozoic alkali basalt from Nushan. The results suggest that the lower crust beneath Nushan may have formed at about 2400—2200 Ma, a...Zircon SHRIMP U-Pb dating was carried out for an intermediate granulite xenolith in Cenozoic alkali basalt from Nushan. The results suggest that the lower crust beneath Nushan may have formed at about 2400—2200 Ma, and have been subjected to granulite-facies metamorphism at 1915±27 Ma. The old age of the Nushan lower crust is consistent with the geochemical similarities between Nushan granulite xenoliths and Archean-Paleoproterozoic granulite terrains in the North China craton, but it is not distinguishable from high-grade metamorphic rocks in the Yangtze craton where such old ages were also reported. Significant Pb-loss occurs in the Nushan zircons, implying important influence of widespread Mesozoic to Cenozoic underplating in East China on the lower crust beneath Nushan.展开更多
The lower crustal xenolith of mafic two_pyroxene granulite (the majority) and hypersthene granulite in the Cenozoic basalt at Hannuoba have the characteristics of igneous blastic structure and granulite facies metamor...The lower crustal xenolith of mafic two_pyroxene granulite (the majority) and hypersthene granulite in the Cenozoic basalt at Hannuoba have the characteristics of igneous blastic structure and granulite facies metamorphic recrystallization. Study on the zircon chronology and REE geochemistry of granulite xenolith shows that the underplating of basic magma into the lower crust during late Mesozoic led to the formation of mafic accumulate, which further through metamorphism of granulite facies formed the high_density and high_velocity crustal bottom layer at the lower crust. This suggests that the underplating of mantle magma is the important way for the vertical overgrowth of continental crust since the Phanerozoic and provides new evidence for crust_mantle interaction.展开更多
Backscattered electron images, in situ Hf isotopes, U-Pb ages and trace elements of zircons in a banded granulite xenolith from Hannuoba basalt have been studied.The results show that the banded granulite is a sample ...Backscattered electron images, in situ Hf isotopes, U-Pb ages and trace elements of zircons in a banded granulite xenolith from Hannuoba basalt have been studied.The results show that the banded granulite is a sample derived from the early lower crust of the North China craton.It is difficult to explain the petrogenesis of the xenolith with a single process. Abundant information on several processes,however, is contained in the granulite. These processes include the addition of mantle material, crustal remelting,metamorphic differentiation and the delamination of early lower crust. About 80% of zircons studied yield ages of 1842±40Ma, except few ages of 3097-2824 Ma and 2489-2447Ma. The zircons with ages older than 2447Ma have high εHr(up to+18.3) and high Hf model age (2.5-2.6Ga), indicating that the primitive materials of the granulite were derived mainly from a depleted mantle source in late Archean. Most εHr of the zircons with early Proterozoic U-Pb age vary around zero, but two have high εHr up to+9.2-+10.2, indicating mantle contribution during the collision and assembly between the Eastern and Western blocks in the early Proterozoic that resulted in the amalgamation of the North China craton.展开更多
基金supported by the National Natural Science Foundation of China(Grant Nos.40273001,40425002)the EYTP(Grant No.2003-119).
文摘The granulitic xenoliths discovered in the late Cretaceous basaltic rocks from Tuoyun basin, western Xinjiang Province contain the assemblage of Opx + Cpx + Pl ± Grt ± Qtz ± Kfs. Mineral chemistry, petrochemistry and zircon U-Pb ages from the xenoliths have been reported in the paper. Petrogenesis, the lower crustal nature and the mantle-crust interaction reflected by the granulites are discussed as well. Tuoyun granulites are mainly mafic with few intermediate components, and represent the magmatic products underwent granulite-facies metamorphism in lower crustal condition. Equilibrium temperature and the maximum pressure estimates of the granulites are 910 ± 35℃ and 13.5 × 108 Pa respectively, indicating that the crust beneath southwestern Tianshan had the thickness of less than 44 km and high geotherm (e.g. > 80 mW/m2) when the host magma erupted. During their formation, the fractional crystallization of olivine, pyroxene, plagioclase and ilmenite, plagioclase accumulation and the contamination of felsic components or fluid metasomatism processes had happened. Metamorphic zircon U-Pb age of 253 Ma may record the crust-mantle interaction caused by the orogenic root delamination beneath the southwestern Tianshan.
基金supported by the National Natural Science Foundation of China (Grant Nos. 49773191, 40132010, 40125007 and 49632080) Major State Basic Research Program (Grant No. G1999043202) an Australia-China Institutional Links Program and the International Coo
文摘Mafic granulite xenoliths collected from Cenozoic basalts in SE China can be classified as magmatic granulite and cumulate granulite. Magmatic granulites are characterized by highly concentrated AI2O3, K2O, P2O5, Ba, Sr, Pb and REE, and low contents of Nb, Zr, Hf and Th, and have an incompatible element abundance pattern similar to that of continental arc basalts. Cumulate granulites are depleted in K2O, P2O5, Rb, Cs and Ba. These granulite xenoliths were the prod-ucts of crystallization and recrystallization of the basaltic magma underplating into crust-mantle boundary in Late Mesozoic. Sr and Nd isotopic compositions and variation trend of these mafic rocks are the result of crust-mantle mixing and controlled by assimilation and fractional crystallization process (AFC). However, trace element and major element variations were mainly controlled by fractional crystallization. The granulites are similar in geochemistry to surface Late Mesozoic gabbro and basalt in the study area, suggesting a close petrogenetic link between them. Late Mesozoic basaltic magma activities are the most important cause for the formation of extensive contemporaneous granite and rhyolite in the study area. This study and previous data indicate that the lower crust beneath South China is composed of a variety of Paleo- to Meso-proterozoic metamorphic rocks and Late Mesozoic mafic granulites.
基金supported by the National Natural Science Foundation of China(Grant No.49925308).
文摘Zircon SHRIMP U-Pb dating was carried out for an intermediate granulite xenolith in Cenozoic alkali basalt from Nushan. The results suggest that the lower crust beneath Nushan may have formed at about 2400—2200 Ma, and have been subjected to granulite-facies metamorphism at 1915±27 Ma. The old age of the Nushan lower crust is consistent with the geochemical similarities between Nushan granulite xenoliths and Archean-Paleoproterozoic granulite terrains in the North China craton, but it is not distinguishable from high-grade metamorphic rocks in the Yangtze craton where such old ages were also reported. Significant Pb-loss occurs in the Nushan zircons, implying important influence of widespread Mesozoic to Cenozoic underplating in East China on the lower crust beneath Nushan.
文摘The lower crustal xenolith of mafic two_pyroxene granulite (the majority) and hypersthene granulite in the Cenozoic basalt at Hannuoba have the characteristics of igneous blastic structure and granulite facies metamorphic recrystallization. Study on the zircon chronology and REE geochemistry of granulite xenolith shows that the underplating of basic magma into the lower crust during late Mesozoic led to the formation of mafic accumulate, which further through metamorphism of granulite facies formed the high_density and high_velocity crustal bottom layer at the lower crust. This suggests that the underplating of mantle magma is the important way for the vertical overgrowth of continental crust since the Phanerozoic and provides new evidence for crust_mantle interaction.
文摘Backscattered electron images, in situ Hf isotopes, U-Pb ages and trace elements of zircons in a banded granulite xenolith from Hannuoba basalt have been studied.The results show that the banded granulite is a sample derived from the early lower crust of the North China craton.It is difficult to explain the petrogenesis of the xenolith with a single process. Abundant information on several processes,however, is contained in the granulite. These processes include the addition of mantle material, crustal remelting,metamorphic differentiation and the delamination of early lower crust. About 80% of zircons studied yield ages of 1842±40Ma, except few ages of 3097-2824 Ma and 2489-2447Ma. The zircons with ages older than 2447Ma have high εHr(up to+18.3) and high Hf model age (2.5-2.6Ga), indicating that the primitive materials of the granulite were derived mainly from a depleted mantle source in late Archean. Most εHr of the zircons with early Proterozoic U-Pb age vary around zero, but two have high εHr up to+9.2-+10.2, indicating mantle contribution during the collision and assembly between the Eastern and Western blocks in the early Proterozoic that resulted in the amalgamation of the North China craton.
