Zircon U-Pb Ages,Hf Isotopic Composition of Zhizhong Granitic Intrusion in Ledong Area of Hainan Island and Their Tectonic Implications
WEN Shunv;LIANG Xinquan;FAN Weiming;WANG Yuejun;CHI Guoxiang;LIANG Xirong;ZHOU Yun;JIANG Ying;State Key Laboratory of Isotope Geochemistry,Guangzhou Institute of Geochemistry,Chinese Academy of Sciences;University of Chinese Academy of Sciences;Department of Geology,University of Regina,Regina,Saskatchewan;
Late Paleozoic to Early Mesozoic( Hercynian to Indosinian) granitic intrusions widely distribute in Hainan Island,South China. However,no consensus has been achieved in terms of the related tectonic regime of these magmatism activities,the Late Paleozoic granites,in particular. Aiming to provide insights into the time of intrusion,petrogenesis and tectonic setting of the Late Paleozoic granites,zircons from the Zhizhong granite,which is located in the Ledong area in southwestern Hainan Island,were analyzed. In-situ zircon U-Pb geochronology and Hf isotope analysis of zircons were analyzed in Northwestern University using LA-ICPMS methods. Zircons from two samples( HN0832 and HN0909) yield similar weighted mean206Pb /238U ages of 272. 4 ± 1. 5 Ma( n = 21) and271. 7 ± 3. 0 Ma( n = 16),respectively. The ages are interpreted as the intrusive age,i. e.,the Zhizhong granite intruded in late Early Permian. The εHf( t) values of the zircons range from-3. 7 to +2. 8,while the Hf two-stage modal ages vary from 1. 12 Ga to 1. 53 Ga with a peak at 1. 33 ～ 1. 41 Ga,demonstrating a mantle input for the Zhizhong granite. Thus,a mixed crust-mantle source is envisaged. Furthermore,the parent melts of the Zhizhong granite possibly derived from the melting of the Mesoproterozoic igneous rocks beneath Hainan Island with significant contribution of asthenosphere melts. Moreover,the age peaks of the two-stage Hf modal ages( 1. 3 ～ 1. 4 Ga)of the Zhizhong Granite are similar to the whole rock two-stage Nd modal ages( 1. 4 ～ 1. 6 Ga) of the coeval granites in the adjacent region,which implies that Mesoproterozoic is an important episode of crustal growth in Hainan Island. Combining the regional deformation,sedimentary records and palaeomagnetic data,it can be deduced that the late Early Permian magmatism in Hainan Island was probably geodynamically linked to the collision between the Indochina and South China Block,following the closure of the Paleo-Tethys Ocean rather than the westward subduction of the Paleo-Pacific Plate beneath the Eurasian continent.