文档共享_Beijing SHRIMP Center

你好,请

SHRIMP U-Pb zircon geochronology and its implications on the Xilin Gol Complex，Inner Mongolia,China [查看] SHIGuanghai、LIUDunyi、ZHANGFuqin、JIANPing、MIAOLaicheng、SHIYuruo、

Abstract The Xilin Gol Complex, consisting of deformed and metamorphosed rocks, was exposed as a large geological unit within the Central Asian Orogenic Belt, but its forming and subsequent deformed and metamorphic time has been an issue of little consensus. Petrographic analyses and SHRIMP dating on biotite-plagioclase gneiss, one of the major rocks within the Xilin Gol Complex, in southeast Xilinhot City, Inner Mongolia, China, where the Xilin Gol Complex was identified and named, yield its lower limit age of 437 ± 3 Ma (2s ) by its magmatic zircon SHRIMP U-Pb dating, and an upper limit age of 316 ± 3Ma (2s ), which was constrained by SHRIMP dating of magmatic zircons from adjacent undeformed garnet-bearing granite which intruded the Complex.The Complex was thus determined to be formed and subsequently deformed/metamorphosed from the late Ordovician-early Silurian to the mid-Carboniferous. Consequently, it is not the Precambrian terrane as previously considered by most geologists. More or less, the major rock —— biotiteplagioclase gneiss within the Complex is more likely to be Paleozoic fore-arc turbidite formation before metamorphism and intensive deformation, in which the detrital zircons gave sporadic Precambrian ages as old as up to 3.1 Ga. The source of the turbidite formation is multiple, which may be derived either from the North China Craton, or from the South-Mongolia Micro-continent, or probably came from a potential and undiscovered in situ terranes aged 600—800 Ma or even up to ca 3.1 Ga near the Complex.

Emplacement age and tectonic implications of the Xilinhot A-type granite in Inner Mongolia,China [查看] SHIGuanghai、MIAOLaicheng、ZHANGFuqing、JIANPing、FANWeiming、LIUDunyi

Abstract A new rock type of granite, approximate 45km2 in area and located about 10 km south of Xilinhot, Inner Mongolia, was found in the Sunitezuoqi (or called Suzuoqi)-Xilinhot tectonic belt and identified as an A-type miarolitic intrusion. The pluton has miarolitic structure and is composed chiefly of perthite, quartz, euhedral albite and potassium feldspar. Various types of textures occur in the pluton, such as perthitie, graphic and myrmekite textures.Only quartz is found in miarolitic cavity. This A-type granite with seagull-shaped REE patterns and obvious negative Eu anomaly (d Eu = 0.24—0.28) is high in SiO2 (76%—77%), K and Na (Na2O + K2O = 7.75%—8.15%) and low in Ca (CaO= 0.20%—0.22%), Fe and Mg. Both petrographical observations and chemical compositions indicate that it is an A-type granite. Zircon SHRIMP U-Pb analyses indicate that this A-type granite was emplaced at 276 ± 2 Ma and coeval with the same type of granites in the adjacent areas. Therefore, it suggests that this pluton was likely formed in a post-orogenic extensional setting and probably related to break-off of subducted slabs in Central Asian Orogenic Belt (CAOB), which indicate that the Sunitezuoqi-Xilinhot belt was tectonically evolved into post-orogenic stage since early Permian.

Zircon SHRIMP U-Pb dating for gabbro at Chaotiehe in the Haicheng area- eastern Liaoning [查看] MIAOLaiCheng、ZHANGFuQin、LIUDunYi、SHIYuRuo、XIEHangQiang

Chaotiehe gabbroic intrusion in the eastern part of Liaoning Province was dated by the zircon SHRIMP U-Pb technique. The results gave an emplacement age of 126±4 Ma, indicating that the intrusion thus formed during the lithospheric thinning of the North China Craton (NCC) in the Early Cretaceous rather than in a rifting setting during the Paleoproterozoic as previously thought. The gabbroic intrusion contains abundant old zircons with Paleoproterozoic (2.10–2.46 Ga and ca. 1.87 Ga) and Neoproterozoic(747–969 Ma) ages. The Paleoproterozoic zircons were probably derived from NCC itself, whereas the Neoproterozoic ones were likely from materials of the Yangtze Craton that had previously been subducted beneath NCC. These geochronological dates are of important implications for understanding the Mesozoic crustal evolution of NCC.

SHRIMP U-Pb zircon age of the Jinbaoshan ultramafic intrusion, Yunnan Province, SW China [查看] TAOYan、MAYanSheng、MIAOLaiCheng、ZHUFeiLin

SHRIMP U-Pb zircon dating gives ages of 260.6 ± 3.5 Ma and 260.7 ± 5.6 Ma for serpentinised wehrlite and plag-hornblendite in the Jinbaoshan ultramafic intrusion, respectively. The results indicate that the Jinbaoshan intrusion was emplaced at ca.260 Ma and contemporaneous with the Emeishan continental flood basalts (ECFB), similar to other mafic-ultramafic intrusions of the Emeishan large igneous province(LIP). The new ages provide a geochronological constraint on the origin of the Jinbaoshan ultramafic intrusion. It confirms that the Jinbaoshan ultramafic intrusion belongs to the Emeishan LIP that formed at ca. 260 Ma.

SHRIMP Zircon U-Pb Dating of Gabbro and Granite from the Huashan Ophiolite,Qinling Orogenic Belt,China Neoproterozoic Suture on the Northern Margin of the Yangtze Craton [查看] SHIYuruo、LIUDunyi、ZHANGZongqing、MIAOLaicheng、ZHANGFuqin、XUEHongmei

Abstract: The recently identified Huashan ophiolitic melange was considered as the eastern part of the Mianliie suture in the Qinling orogenic belt. SHRIMP zircon U-Pb geochronology on gabbro from the Huashan ophiolite and granite intruding basic volcanic rocks indicates crystallization ages of 947±14 Ma and 876±17 Ma respectively. These ages do not support a recently proposed Hercynian Huashan Ocean, but rather favor that a Neoproterozoic suture assemblage (ophiolite) is incorporated into the younger (Phanerozoic) Qinling orogenic belt.