琼东南晚二叠世I型花岗岩成因及其构造指示
Petrogenesis of Late Permian I-Type Granites in SE Hainan Island and Its Tectonic Implication for Paleotethyan Evolution

海南岛地处东古特提斯构造域东缘，是研究古特提斯东缘演化的重要地区.对海南岛东南部长征和陵水花岗闪长岩的LA-ICP-MS锆石U-Pb定年结果显示两者的结晶年龄分别为251±2 Ma和256±1 Ma，指示其形成于晚二叠世.样品的K2O/Na2O比值较低(0.2～0.9)，铝饱和指数(A/CNK)为0.74～0.96，FeOT/MgO约为0.90，CIPW计算结果中标准矿物刚玉分子含量0.00～0.18%，小于1%，岩石薄片镜下可见大量角闪石，而未见白云母、堇青石和石榴子石，并具有相对负的ε Nd( t )值(-6.0～-3.2)和锆石原位ε Hf( t )值(-4.4～+0.2)，属于准铝质钙碱性I型花岗岩.长征和陵水花岗闪长岩源岩为亚碱性变基性岩，其形成与金沙江-哀牢山-松马-邦溪-晨星古特提斯弧后盆地的闭合有关.
Hainan Island is located in the convergence zone of the Pacific and Tethys tectonic domains and is a key area for investigating the Pacific and Tethyan evolution of the Indochina and South China blocks. In this paper, a set of new zircon U-Pb and Lu-Hf isotopic data, along with whole-rock elemental and Sr-Nd isotopic analytical results for the Changzheng and Lingshui granitoid plutons in Southeast Hainan Island are presented. The Changzheng and Lingshui granodiorites yield Late Permian LA-ICP-MS zircon U-Pb ages of 251± 2 Ma and 256±1 Ma, respectively. They show K2O/Na2O=0.2-0.9, FeOT/MgO ratios of 0.90, A/CNK=0.74-0.96 with 0.00-0.18 vol.% corundum. Their ε Nd( t ) values range from -6.0 to -3.2 and in-situ zircon ε Hf( t ) values from -4.4 to +0.2. Such signatures, in combination with the absence of muscovite, cordierite and garnet, suggest that these Late Permian granodiorites are I-type granites. The Changzheng and Lingshui granites were derived from the subalkaline metabasites in response to the closure of the Jinshajiang-Ailaoshan-Songma-Bangxi-Chenxing branch/back-arc basin during Paleotethyan evolution