北武夷资溪-光泽岩体锆石U-Pb年代学——对确定华南内陆印支期岩浆活动时空分布与形成环境的意义

Zircon U-Pb Geochronology of Zixi-Guangze Complexes in North Wuyishan Region: Implications for Temporal and Spatial Distribution and Tectonic Setting of the Indosinian Magmatism in South China Interior

通过对北武夷地区资溪-光泽杂岩体LA-ICP-MS锆石U-Pb定年分析,获得资溪岩体的年龄为236~238 Ma。结合收集的华南内陆地区已有的印支期岩浆岩的年龄资料,观察其年龄在SE-NW向和SW-NE向的时空变化情况,发现华南内陆印支期岩浆岩年龄分布具有从东南沿海到北西内陆地区呈逐渐年轻的趋势,而在大致沿武夷山走向的南西到北东方向上呈宽阔的近水平的线性分布趋势。印支期沿海岩浆弧在~260 Ma消失20 Ma之后,~240 Ma在距离海沟大约400~500 km的武夷山地区大规模出现,是水平俯冲造成的华南内陆新生岩浆弧形成,类似于新生代北美拉拉米造山和墨西哥中部的水平俯冲情况。由于加厚的中、下地壳温度较高,少量水平俯冲前端脱水形成的地幔岩浆侵入中、下地壳,带来的热很容易造成中、下地壳物质发生部分熔融,形成北武夷地区大量印支期花岗质岩浆岩。

Precise U-Pb zircon geochronological results show that the Zixi-Guangze granitic complexes were formedduring236-238Ma.Combined with our new ages and compilation of age data of the Indosinian granites from the SouthChina interior,the Indosinian magmatism in the South China shows a trend of NW-ward younger toward the cratonicinterior,and a broad horizontal linear distribution from Southwest to Northeast along the Wuyishan region.A number ofca.240Ma granitic rocks occur in the Wuyishan region at a distance of approximately400-500km away from thetrench,suggesting that a continental magmatic arc probably resumed since ca.240Ma along the Wuyishan region after amagmatic gap due to flat-slab subduction.Our analysis indicates that the renewed arc magmatism in the Wuyishanregion is related to dehydration of serpentinization mantle wedge at front of the flat-slab.