苏南晚二叠世末期双峰次火山岩的发现和单颗粒锆石U－Pb年代学意义

苏南晚二叠世末期双峰次火山岩的发现和单颗粒锆石Ｕ－Ｐｂ年代学意义方中，李惠民，夏邦栋，楚雪君，刘寿和，王学锋（南京大学地球科学系，江苏南京，２１０００８；天津地质矿产研究所，天津，３００１７０）关键词晚二叠世，双峰火山岩，同生锆石，捕虏晶锆石，Ｕ－Ｐ...

Newly discovered bimodal subvolcanic rocks in the Late Permian of Southern Jiangsu and single zircon U-Pb geochronology

Some basalts and rhyodacites have been discovered from the Later Permian Longtan Formation in Southern Jiangsu. The basalts and rhyodacites intruded into the coal-seam in the upper part of the formation. A hacked dale of SiO2(wt.%)between the two kinds of rocks are over 10% in the study area, and over 18% in the Xialishan Coal Mine near Zhenjiang City, where a set of the bimodal subvolcanic rocks are closely assgciated with each other in the coal-seam.Single zircon U-Pb ages are 231.2 ± 2.5Ma and 236.5± 11.4Ma measured from contemporaneous zircons of the basalt and the rhyodacite respectively. Besides,there are some xenocrystal zircons found from both of the rocks. From the basalt the single xenocrystal zircon U-Pb ages are 2281Ma and 746Ma, and other single xenocrystal zircon U-Pb ages are 1949 Ma, 1792Ma, 661Ma and 542Ma from the rhyodacite. The xenocrystal zircons show that the basalts were contaminated by the Precambrian crustal rocks. The old zircons in the rhyodacite are about one-third the total zircon grains, this stands to reason that Precambrian rocks used to be important sources of the acid lava.