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Late Jurassic-Early Cretaceous Plutonism in the Northern Part of the Precambrian North China Craton： SHRIMP Zircon U-Pb Dating of Diorites and Granites from the Yunmengshan Geopark, Beijing [查看] SHIYuruo、ZHAOXitao、MAYinsheng、HUDaogong、LIUQisheng、WUZhenhan、ZHAOYuanyi、LIUDunyi

Abstract：The Yunmengshan Geopark in northern Beijing is located within the Yanshan range．It contains the Yunm engshan batholith．which is dominated by two plutons：the Yunmengshan gneissic granite and the Shicheng gneissic diorite．Four samples of the Yunmengshan gneissic granite give SHRIMP zircon U—Pb ages from 145 to 141 Ma。whereas four samples of the Shicheng gneissic diorite have ages from 159 Ma to 151 M a．Dikes that cut the Yunmengshan diorite record SHRIMP zircon U-Pb are of 162±2 and 156+4 Ma．The cumulative plots of zircons from the diorites show a peak age of 155 Ma．without inherited zircon cores．and the peak age of 142 Ma for granite is interpreted as the emplacement age of the Yunm engshan granitic pluton，whose igneous zircons contain inherited zircon cores．The data presented here show that there were two pulses of m agm atism ：early diorites。followed c13 Ma later by true granites．which incorporated material from an older continental crust．

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.

Finding of Neoproterozoic (~775 Ma) magmatism recorded in metamorphic complexes from the North Qilian orogen Evidence from SHRIMP zircon U-Pb dating [查看] Chien-YuanTseng、Houng-YiYang、WANYusheng、LIUDunyi、Da-JenWen、Tzung-ChiLin、Kuo-AnTung

SHRIMP U-Pb dating was carried out on zircons from the Niuxinshan gneissic granite and the Leigongshan gneissic tonalite in the North Qilian orogen, NW China. The results yield weighted aver-aged 206Pb/238U ages of 776±10 Ma and 774±23 Ma respectively. Igneous morphology, oscillatory zonings, and relatively high Th/U ratios for these zircons suggest magmatic origin. These ages are interpreted as timing of magma emplacement and thus repre-senting a Neoproterozoic (~775 Ma) magmatic event in the North Qilian area. It is suggested that this magmatism is probably related to breakup of the supercontinent Rodinia. This finding, together with the similar ages of 750 to 800 Ma reported for neighboring terranes of South-central Qilian and North Qaidam, is of significance to understanding of the Rodinia evolution in West China.