辽西医巫闾山地区晚侏罗世花岗岩脉中热液锆石的成因与定年

辽西医巫闾山变质核杂岩经历过两阶段演化,晚侏罗世发育了围绕核部医巫闾山岩体周缘展布的长环形韧性剪切带(称为医巫闾山剪切带),早白垩世西侧叠加了北北东走向瓦子峪伸展韧性剪切带.在医巫间山剪切带及其变形下盘中侵入了大量的晚侏罗世花岗岩脉,其所含的锆石包括古老继承锆石、新生岩浆锆石、热液锆石等多种类型.根据锆石阴极发光图像、...

Genesis and geochronology of hydrothermal zircons from Late Jurassic granitic dikes in Yiwulvshan area, western Liaoning

The Yiwulvshan metamorphic core complex in western Liaoning has experienced two stages of extensional evolution from late Jurassic an annular ductile shear zone(called Yiwulvshan shear zone) developed around the central Yiwulvshan pluton to early Cretaceous overprinted by thewell known NNE striking Waziyu ductile shear zone in the west.A large amount of late Jurassic granitic dikes，containing several types of zircons including old inherited zircons，new magmatic zircons and hydrothermal zircons，intruded in the Yiwulvshan shear zone and its deformed footwall.According to the characteristics of cathodoluminescence image，REE pattern and U，Th，Pb content，these hydrothermal zircons could be divided into three genetic types：dissolution reprecipitation，direct crystallization by a zircon saturated aqueous fluid and metasomatic alteration in hydrothermal fluid.They are all highly enriched in U，Pb，P，Y，Nb，Hf，Ta and other elements except for Th element，which leads to the Th/U ratios about 01.The former two types of hydrothermal zircons are also strongly rich in rare earth elements(REE)with flatchondrite normalized REE pattens.But the third type has lower LREE and higher abundances of HREE with a steeper chondrite normalized REE patten，significantly different from magmatic zircon and the former hydrothermal zircons，also disagreed with others points.The analyses show that reasonable ages are unable to obtain from hydrothermal zircons with high common Pb content，but most of lower common Pb of hydrothermal zircons give a reliable age about 147 Ma，tightly following the emplacement of dikes(155～147 Ma)and effectively recording the late stage of late Jurassic tectonic magmatic events.