莺歌海盆地东侧物源年龄标志的建立:来自琼西6条主要河流碎屑锆石LA-ICP-MS U-Pb年龄的研究

Construction of age frequencies of provenances on the eastern side of the Yinggehai Basin:Studies of LA-ICP-MS U-Pb ages of detrital zircons from six modern rivers,western Hainan,China

利用阴极发光和LA-ICP-MS微区定年分析方法,对海南岛西部6条主要河流入海口现代沉积物700粒碎屑锆石进行了U-Pb年龄分析,获得644个有效数据。研究表明：（1）6条河流具有两组明显不同频谱特征,北部4条河流（珠碧江、昌化江、北黎河和感恩河）主要显示海西—印支期年龄峰（236-257Ma）,而南部两条河流（望楼河和宁远河）主要显示燕山晚期年龄峰（约99Ma）,这些年龄频谱的特征差异与各河流所流经区域出露的岩浆岩一致,反映了源区对河流碎屑沉积的控制和影响。（2）6条河流年龄变化范围为86-1 600 Ma,主要集中在80-300 Ma,并具有254、238和99 Ma 3个主要年龄峰以及159、1 400-1 600 Ma两个次要峰。254 Ma是源区海南岛不同于华南内陆的一次重要的二叠纪岩浆事件,与古特提斯洋的闭合、俯冲以及碰撞有关;238 Ma也是海南岛一次重要的岩浆事件。海南岛自245 Ma左右进入造山后的伸展环境,从南到北形成一系列三叠纪Ⅰ型和A型花岗岩,三叠纪和二叠纪花岗岩可能是一个事件的连续演化过程。99 Ma碎屑锆石与海南岛同安岭—牛腊岭玄武质安山岩流纹岩、屯昌埃达克岩以及昌江石碌花岗闪长斑岩年龄相匹配,反映了海南岛在燕山期可能受到古太平洋板块西向俯冲的影响。（3）琼西主要河流年龄特征与越南红河存在很大区别,琼西具有燕山晚期（约99 Ma）碎屑锆石年龄,并缺失与红河剪切带构造岩浆变质事件相匹配的喜山期年龄值（22-55 Ma）以及古老锆石年龄。

U-Pb dating of detrital zircons from sands along main rivers in western Hainan was carried out by using cathodoluminescence（CL） imaging and LA-ICP-MS microdomain analysis of 700 grains, and 644 valid data were obtained. The studies reveal that （1） the zircon age characteristics of the six rivers are of two markedly different groups： the samples from Zhubi Jiang, Changhua Jiang, Beili He and Ganen He in the north mainly display Hercynian-Indosinian ages （236 - 257 Ma）, while the Wanglou and Ningyuan rivers in the south show Late Yanshanian ages （ca. 99 Ma）, which are consistent with the ages of igneous rocks distributed along those rivers, reflecting that the sediments are controlled and influenced by the source areas; that （2） the zircon ages from the six rivers are scattered ranging from 86 Ma to 1600 Ma, but mainly concentrated in a range of 80 - 300 Ma, with three main peaks of ca. 254 Ma, ca. 238 Ma and ca. 99 Ma and two secondary peaks at 159 Ma and 1400 - 1600 Ma. The ca. 254 Ma event in Hainan Island is different from the inland South China Block in that it is an important Permian magmatic event closely related with the closure, subduction and collision of the Paleo-Tethys Ocean. The peak of ca. 238 Ma also indicates an important magmatic event in Hainan Island. Hainan had turned into a post-orogenic extensional environment since 245 Ma and forming a series of Triassic I-type and A-type granites from south to north. The Permian and Triassic granites might result from the same continuous evolution event. The detrital zircon ages of ca. 99 Ma can be matched with those of the Tonganling-Niulaling basaltic andesite-rhyolite, Tunchang adakite as well as the Shilu granodiorite, indicating that it might be affected by the westward subduction of the Paleo-Pacific plate; that （3） the major age spectrum of the western Hainan is quite different from that of the Red River in northern Vietnam in that it is characterized by the Yanshanian ages （ca 99 Ma） but lack of the Himalayan ages （22 - 55 Ma） corresponding to the tectonic-magrnatic-metamorphic events in the Red River Fault Zone and the older zircon ages.