海南公爱NW向韧性剪切带构造特征及其^(40)Ar-^(39)Ar年代学约束

MICROSTRUCTURAL CHARACTERISTICS OF THE NW- TRENDING SHEAR ZONES OF GONG'AI REGION IN HAINAN ISLAND AND ITS ^(40)AR- ^(39)AR GEOCHRONOLOGICAL CONSTRAINTS

在海南岛西部公爱地区识别出NW向韧性剪切带,其野外构造解析和显微构造分析表明,公爱NW向韧性剪切带早期为右旋剪切,变形温度约300～450℃。对该韧性剪切带糜棱岩样品中白云母单矿物的40Ar39Ar定年结果表明:样品04HN17和04HN18分别给出了250.0±1.0Ma和248.0±1.0Ma的40Ar/39Ar坪年龄,为印支早期变形产物。海南公爱NW向韧性剪切带变形运动学和变形时序与印支北部NW向韧性剪切带(如SongMa地区)具有很好的一致性,这为理解公爱地区早中生代构造演化及华南陆块和印支半岛印支期构造演化提供了新的信息。

All the structural and microstructural observations suggest the tectonic movement of dextral shearing for the NW-trending shear zones in Gong＇ai region, Hainan Island. According to the quartz c-axis preferred orientations of three mylonitic rock samples in NW-trending shear zone and the feldspar-quartz micro-deformation structures of these samples, we presume that the deformational temperature is about 450℃ to 300℃. Muscovite, separated from sample 04HN17 and sample 04HN18, both mylonitic rocks samples from Gong＇ai farmyard in NW-trending shear zones, yields well-defined ^40Ar-^39Ar plateau age of 250.0 ± 1.0Ma for about 87 % released ^39 Ar and 248.0± 1.0 Ma for about 68% released ^39Ar, respectively. These ages are interpreted to date cooling in terms of ^40Ar-^39Ar closure temperatures following synkinematic growth of muscovite as a consequence of mylonitic overprinting and deformation of NW-trending shear zones. The NW-trending shear zones in Gong＇ai region are similar to the NW-trending shear zones in northern Indochina block （ such as Song Ma region） in kinematics and deformation epoch during early Indosinian. It can offer new information in regard to the early Mesozoic structural development of Gong＇ai region in Hainan Island and the Indosinian structural development of Southern China and Indochina blocks.