Laser Raman spectroscopy and cathodoluminescence （CL） images show that most zircon crystals separated from paragneiss in the main drill hole of the Chinese Continental Scientific Drilling Project （CCSD-MH） at Maob...Laser Raman spectroscopy and cathodoluminescence （CL） images show that most zircon crystals separated from paragneiss in the main drill hole of the Chinese Continental Scientific Drilling Project （CCSD-MH） at Maobei, southwestern Sulu terrane, contain low-pressure mineral-bearing detrital cores, coesite-bearing mantles and quartz-bearing or mineral inclusion-free rims. SHRIMP U-Pb dating on these zoned zircons yield three discrete and meaningful age groups. The detrital cores yield a large age span from 659 to 313 Ma, indicating the protolith age for the analyzed paragnelss is Paleozoic rather than Proterozoic. The coesite-bearing mantles yield a weighted mean age of 228 ± 5 Ma for the UHP event. The quartz-bearing outmost rims yield a weighted mean age of 213 ± 6 Ma for the retrogressive event related to the regional amphibolite facies metamorphism in the Sulu UHP terrane. Combined with previous SHRIMP U-Pb dating results from orthogneiss in CCSD-MH, it is suggested that both Neoproterozoic granitic protolith and Paleozoic sedimentary rocks were subducted to mantle depths in the Late Triassic. About 15 million years later, the Sulu UHP metamorphic rocks were exhumed to mid-crustal levels and overprinted by an amphibolite-facies retrogressive metamorphism. The exhumation rate deduced from the SHRIMP data and metamorphic P-T conditions is about 6.7 km/Ma. Such a fast exhumation suggests that the Sulu UHP paragnelss and orthogneiss returned towards the surface as a dominant part of a buoyant sliver, caused as a consequence of slab breakoff.展开更多
Eclogite, one of the important lithologies in the main hole of the Chinese Continental Scientific Drilling （CCSD） Project, exists above the depth of 3 245 m and has distinctive responses of gamma-ray, compensating d...Eclogite, one of the important lithologies in the main hole of the Chinese Continental Scientific Drilling （CCSD） Project, exists above the depth of 3 245 m and has distinctive responses of gamma-ray, compensating density and neutron well-logging, and so on. In this study, according to the diversities of minerals and chemical components and well-logging responses, edogites are classified from three aspects of origin, content of oxygen, and sub-mineral. We studied the logging identification method for eclogite sub-classes based on multi-element statistics and reconstructed 11 kinds of eclogite. As a result, eclogites can be divided into 6 types using well logs. In the light of this recognition, the eclogite in the main hole is divided into 20 sections, and the distribution characters of all sub-classes of eclogite are analyzed, which will provide important data for geological research of CCSD.展开更多
基金funded by the National Natural Science Foundation of China(grant No.40399143)the National 973 Project of the Chinese Ministry of Science and Technology(grant No.2003CB716502)the Programme of Excellent Youth Scientists of the Ministry of Land and Resources of China.
文摘Laser Raman spectroscopy and cathodoluminescence （CL） images show that most zircon crystals separated from paragneiss in the main drill hole of the Chinese Continental Scientific Drilling Project （CCSD-MH） at Maobei, southwestern Sulu terrane, contain low-pressure mineral-bearing detrital cores, coesite-bearing mantles and quartz-bearing or mineral inclusion-free rims. SHRIMP U-Pb dating on these zoned zircons yield three discrete and meaningful age groups. The detrital cores yield a large age span from 659 to 313 Ma, indicating the protolith age for the analyzed paragnelss is Paleozoic rather than Proterozoic. The coesite-bearing mantles yield a weighted mean age of 228 ± 5 Ma for the UHP event. The quartz-bearing outmost rims yield a weighted mean age of 213 ± 6 Ma for the retrogressive event related to the regional amphibolite facies metamorphism in the Sulu UHP terrane. Combined with previous SHRIMP U-Pb dating results from orthogneiss in CCSD-MH, it is suggested that both Neoproterozoic granitic protolith and Paleozoic sedimentary rocks were subducted to mantle depths in the Late Triassic. About 15 million years later, the Sulu UHP metamorphic rocks were exhumed to mid-crustal levels and overprinted by an amphibolite-facies retrogressive metamorphism. The exhumation rate deduced from the SHRIMP data and metamorphic P-T conditions is about 6.7 km/Ma. Such a fast exhumation suggests that the Sulu UHP paragnelss and orthogneiss returned towards the surface as a dominant part of a buoyant sliver, caused as a consequence of slab breakoff.
基金This paper is supported by the Engineering Center of Chinese Continental Scientific Drilling (No. CCSD2004-04-01)the Focused Subject Program of Beijing (No. XK104910598).
文摘Eclogite, one of the important lithologies in the main hole of the Chinese Continental Scientific Drilling （CCSD） Project, exists above the depth of 3 245 m and has distinctive responses of gamma-ray, compensating density and neutron well-logging, and so on. In this study, according to the diversities of minerals and chemical components and well-logging responses, edogites are classified from three aspects of origin, content of oxygen, and sub-mineral. We studied the logging identification method for eclogite sub-classes based on multi-element statistics and reconstructed 11 kinds of eclogite. As a result, eclogites can be divided into 6 types using well logs. In the light of this recognition, the eclogite in the main hole is divided into 20 sections, and the distribution characters of all sub-classes of eclogite are analyzed, which will provide important data for geological research of CCSD.
