排序方式: 共有71条查询结果,搜索用时 140 毫秒
1.
Discovery of eclogite at northern margin of Qaidam Basin, NW China 总被引:19,自引:0,他引:19
Jingsui Yang Zhiqin Xu Haibing Li Cailai Wu Junwen Cui Jianxin Zhang Wen Chen 《科学通报(英文版)》1998,43(20):1755-1755
Eclogite was first discovered at the northern margin of the Qaidam Basin in this study. It occurs as pods in the gneiss sequence of Middle to Upper Proterozoic age and is mainly composed of garnet, omphacite, phengite and rutile. The garnets contain 44%-62% of almandine, 15%-33% of grossular and 12%-30% of pyrope molecules, and the omphacites contain 40%-46% of jadeite. Applying garnet_clinopyroxene thermometry and jadeite geobarometry, the peak conditions of eclogite facies metamorphism occurred at about (722±123)℃ and at the pressure of up to c. 22 ×10 8 Pa. 相似文献
2.
Carbon isotope anomaly in marbles associated with eclogites from the Dabie Mountains 总被引:1,自引:0,他引:1
This is a report of carbon isotope anomaly in marbles associated with the UHP eclogites from the Dabie Mountains. The results
place constraints on the degree of crust-mantle interaction during the UHP metamorphism. 相似文献
3.
《科学通报(英文版)》1998,43(16):1362-1362
Isotopic geochemical characteristics of helium in garnet and omphacite of eclogite in the Dabie Mountains are discussed. Concentrations of 3He and 4He in garnet and omphacite are 3.9×10 -14- 24.0×10 -14 and 0.48×10 -7-9.42×10 -7cm+3·g -1, respectively. Values of 3He/ 4He have a range of (1.19-4.63)×10 -7. Helium in the eclogite is derived from both mantle and crust. Isotopic geochemical data of helium indicate that eclogite in the Dabie Mountains might be formed in depleted mantle and the age of the cologite would be Indo-China epoch. 相似文献
4.
5.
Retrograded eclogites in the Archaean North China Craton and their geological implication 总被引:1,自引:0,他引:1
《科学通报(英文版)》1996,41(4):315-315
6.
An ultrahigh pressure ductile shear mélange crops out on the beach of Yangkou Bay near Qingdao City. The mélange is composed of weakly deformed blocks in a highly ductilly flow mylonites. Ultrahigh pressure metamorphic (UHPM) tectonite includes strongly deformed eclogite and mylonitized eclogite. Coesite occurs in the tectonite as both interstitial mineral and inclusions in garnet and omphacite, indicating that the deformation took place in the stability field of coesite (800—850℃, >30 GPa) in the upper mantle. Coesite is rounded or short prismatic grains with undulatory extinction, and often fractured, suggesting brittle deformation. Garnet is also characterized by brittle fractures and sometimes necked and slightly elongated. Omphacite is elongated, with long axis preferred orientation. Undulatory extinction, subgrains and dynamically recrystallized grains suggest plastic flow of omphacite. Ultrahigh pressure metamorphic tectonite was probably formed in the ductile shear zone during the early stage of exhumation of the ultrahigh pressure metamorphic rocks. Its kinematic indicators point to the transport direction of the UHPM slab during the early stage of exhumation. 相似文献
7.
The U-Pb isotope compositions of rutile, omphacite and garnet in the eclogite from the Jinheqiao area in the Southern Dabie ultrahigh-pressure metamorphic zone were analyzed. The consistent high precision U-Pb age (218 ±(1.2) Ma of rutile in eclogite from the Dabie Mountains was obtained by two ways of isochron and common Pb correction based on the composition of omphacite. This proves that the omphacite in eclogite has a U/Pb ratio (μ = 2.8) low enough to be used for common Pb correction in the analyses of rutile. Under the rapid cooling condition (40℃/Ma) the closure temperature for U-Pb diffusion in rutile is about 470℃. Thus, this U-Pb age of rutile proves that 218 Ma should be the cooling age of eclogite at 470℃ instead of the peak metamorphic age. 相似文献
8.
Qiuli?Li Shuguang?LiEmail author Hongying?Zhou Huimin?Li Ji’an?Hong Qingchen?Wang H.?J.?Massonne 《科学通报(英文版)》2002,47(1):62-65
The U-Pb isotope compositions of rutile, omphacite and garnet in the eclogite from the Jinheqiao area in the Southern Dabie ultrahigh-pressure metamorphic zone were analyzed. The consistent high precision U-Pb age (218 ± 1.2) Ma of rutile in eclogite from the Dabie Mountains was obtained by two ways of isochron and common Pb correction based on the composition of omphacite. This proves that the omphacite in eclogite has a U/Pb ratio (m = 2.8) low enough to be used for common Pb correction in the analyses of rutile. Under the rapid cooling condition (40℃/Ma) the closure temperature for U-Pb diffusion in rutile is about 470℃. Thus, this U-Pb age of rutile proves that 218 Ma should be the cooling age of eclogite at 470℃ instead of the peak metamorphic age. 相似文献
9.
This note reports the SHRIMP U-Pb data of zircons from the Caledonian Xiongdian eclogite, western Dabie Mountains. Zircons from the rock occur mainly in garnet and other metamorphic minerals with sharp boundaries and exhibit textures growing under metamorphic conditions. Analyses of 7 grains give 206Pb/238U ages ranging from 335 to 424 Ma, showing a certain degree of radiogenic lead loss. This suggests a minimum age of (424±5) Ma for the metamorphic zircons, as well as the high-pressure metamorphic event. The outer peripheral zone of a zircon gives 206Pb/238U age of about 300 Ma. Combined with Sm-Nd, 40Ar-39Ar, U-Pb and 207Pb/206Pb ages, the peak metamorphism of the Xiongdian eclogite is documented between 424—480 Ma. 相似文献
10.
Breakdown of lawsonite subsequent to peak UHP metamorphism in the Dabie terrane and its implication for fluid activity 总被引:4,自引:0,他引:4
LIXuping LIYiliang SHUGuiming 《科学通报(英文版)》2005,50(13):1366-1372
Abundant occurrences of quartz vein within eclogites in the Dabie-Sulu orogen provide us an opportunity to study metamorphic fluid flow during subduction and exhumation of continental crust. It is, however, usually short of petrological constraints on pressure and temperature of vein formation. This study focuses on kyanite-quartz veins within Iow-T/high-P eclogite in the Dabie terrane that contain unique polycrystalline aggregates, interpreted as pseudomorphs after porphyroblasts of lawsonite. Coesite pseudomorphs were found for the first time in garnet from eclogite, resulting in a revised estimate of peak P-T conditions at 670℃ and 3.3 GPa for the eclogite. This indicates a stability field at graphite/diamond transition, thus upgrading the HP unit to a UHP unit. Neither foliation texture, undulose extinction of quartz nor coesite were observed in quartz veins,although the peak P-T conditions were estimated the same as that in host eclogite in light of thermodynamic calculation based on mineral assemblage in kyanite-quartz veins.Therefore, the formation of the kyanite-quartz veins as wellas the breakdown of lawsonlte into the kyanite-quartz-zoisite assemblage took place during exhumation subsequent to the peak UHP conditions. In this regard, the continental subduction not only brought the water of water-bearing mineral such as lawsonite into the deep mantle, but also released the water from the mineral during exhumation. 相似文献