Marble is associated with ultrahigh pressure eclogite in the Dabie Mountains.East China.U-Pb isotope data for the marble define a 238U-206Pb isochron age of 435±45a with an initial 206Pb/204Pb value of 18.075...Marble is associated with ultrahigh pressure eclogite in the Dabie Mountains.East China.U-Pb isotope data for the marble define a 238U-206Pb isochron age of 435±45a with an initial 206Pb/204Pb value of 18.075±0.006,The age of -435 Ma is interpreted to represent the time of limestone diagensis rather than the time of metarmorphic resetting accompanied by the formation of the ultrahigh pressure eclogites at Triassic.The paleontologic and stratigraphic studies also favor a local excursion in the carbon isotopic composition of the latest ordovician water within a sedimentary basin between the Sino-Korean and Yangtze cratos.Becasuse the latest ordovician limestone was involved in the eclogite formation,the continental collision between the Yangtze and Sino-Korean Plates would postdate ordovican.展开更多
The Yushugou terrain of high\|pressure granulite facies in southern Tianshan Mountain is composed mainly of an ophiolite suite. Most selected zircons are round or elliptical in shape, and some are of tetragonal prism ...The Yushugou terrain of high\|pressure granulite facies in southern Tianshan Mountain is composed mainly of an ophiolite suite. Most selected zircons are round or elliptical in shape, and some are of tetragonal prism with round edges. The granulometric analyses show that they are well sorted in sedimentation. ZrO\-2/HfO\-2 ratios in zircons range from 45 to 57. These characters, together with the petrologic and geochemical characters of plagioclase\|garnet\|orthopyroxenite bearing zircons, indicate that the protolith of plagioclase\|garnet\|orthopyroxenite may be derived mainly from volcanic base surge sedimentary debris in oceanic islands and from clays formed by seafloor weathering. Zircons are simply of pyroclastic debris. The ophiolite formation age of (440±18) Ma and the first\|stage metamorphic age (amphibolite or granulite facies) of (364±5) Ma were obtained with a method of multiple grains in different groups and a method of concordia plot. These ages provide important information on the temporal and spatial occurrence of southern Paleozoic Tianshan Ocean, the subduction rate of the oceanic crust and the formation mechanism of ophiolite of granulite facies.展开更多
The crystal form,chemical composition and U-Pb isotopic composition of various zircon fractions is a Middle Proterozoic granite pluton from the Baoban area suggest that the zircons are typically magmatogenic in nature...The crystal form,chemical composition and U-Pb isotopic composition of various zircon fractions is a Middle Proterozoic granite pluton from the Baoban area suggest that the zircons are typically magmatogenic in nature,and different from those of sedimentary and epigenetic orgins.The various zircon fractions yielded and age of about 1440.87Ma,which may represent the ge of zircon crystallization.The so-called aoban-group migmatite is,as a matter of fact,a Middle Proterozoic granite pluton.展开更多
文摘Marble is associated with ultrahigh pressure eclogite in the Dabie Mountains.East China.U-Pb isotope data for the marble define a 238U-206Pb isochron age of 435±45a with an initial 206Pb/204Pb value of 18.075±0.006,The age of -435 Ma is interpreted to represent the time of limestone diagensis rather than the time of metarmorphic resetting accompanied by the formation of the ultrahigh pressure eclogites at Triassic.The paleontologic and stratigraphic studies also favor a local excursion in the carbon isotopic composition of the latest ordovician water within a sedimentary basin between the Sino-Korean and Yangtze cratos.Becasuse the latest ordovician limestone was involved in the eclogite formation,the continental collision between the Yangtze and Sino-Korean Plates would postdate ordovican.
文摘The Yushugou terrain of high\|pressure granulite facies in southern Tianshan Mountain is composed mainly of an ophiolite suite. Most selected zircons are round or elliptical in shape, and some are of tetragonal prism with round edges. The granulometric analyses show that they are well sorted in sedimentation. ZrO\-2/HfO\-2 ratios in zircons range from 45 to 57. These characters, together with the petrologic and geochemical characters of plagioclase\|garnet\|orthopyroxenite bearing zircons, indicate that the protolith of plagioclase\|garnet\|orthopyroxenite may be derived mainly from volcanic base surge sedimentary debris in oceanic islands and from clays formed by seafloor weathering. Zircons are simply of pyroclastic debris. The ophiolite formation age of (440±18) Ma and the first\|stage metamorphic age (amphibolite or granulite facies) of (364±5) Ma were obtained with a method of multiple grains in different groups and a method of concordia plot. These ages provide important information on the temporal and spatial occurrence of southern Paleozoic Tianshan Ocean, the subduction rate of the oceanic crust and the formation mechanism of ophiolite of granulite facies.
基金This project was financially supported by the National Natural Science Foundation of China
文摘The crystal form,chemical composition and U-Pb isotopic composition of various zircon fractions is a Middle Proterozoic granite pluton from the Baoban area suggest that the zircons are typically magmatogenic in nature,and different from those of sedimentary and epigenetic orgins.The various zircon fractions yielded and age of about 1440.87Ma,which may represent the ge of zircon crystallization.The so-called aoban-group migmatite is,as a matter of fact,a Middle Proterozoic granite pluton.
