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《Geochimica》 1998-06
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ZIRCON U-Pb AGE AND ITS GEOLOGICAL SIGNIFICANCE OF HIGH-PRESSURE TERRANE OF GRANULITE FACIES IN YUSHUGOU AREA, SOUTHERN TIANSHAN MOUNTAIN

Wang Runsan; Wang Yan; Li Huimin;Zhou Dingwu; Wang Juli (Department of Geology, Northwest University, Xi'an, 710069)(Tianjin Institute of Geology and Mineral Resources, CAGS, Tianjin 300170)  
The Yushugou high-pressure terrain of granulite facies in southern Tianshan Mountain is basically composed of ophiolite rock. Zircon grains are selected from the rock in the upper part of the terrain, and most of them are round or elliptical, some are tetragonal prism with round edges. The granulometric analyses show that they are well-sorted in sedimentation. The ZrO2/ HfO2 ratios range from 45 to 57. These characteristics mentioned above, together with the petrological and geochemical ones of plagioclase-garnet-orthopyroxenite, indicate that the protolith of the rock bearing the zircons may be mainly derived from volcanic surf sedimentary debris in oceanic island and from clay formed by weathered seafloor, and the zircons are simply volcanic debris. The ophiolite age is about 440Ma and the metamorphic age of the first stage (amphibolite facies or granulite facies) is about 364Ma obtained with the method of concordia diagram. The ages provide an important evidence for determining the space-time extension of Paleozoic southern Tianshan ocean, calculating the subduction rate of oceanic crust and studying the formation mechanism of ophiolite of granulite facies.
【Fund】: 国家自然科学基金!49472135
【CateGory Index】: P597
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