班公湖-怒江缝合带东段八宿地区花岗岩体差异性隆升:来自锆石和磷灰石裂变径迹证据

Differential uplift of granitic pluton in the Basu region of the eastern Bangonghu-Nujiang suture zone:Evidences from zircon and apatite fission tracks

班公湖-怒江缝合带为青藏高原内部分隔羌塘和拉萨两地块的构造边界,是研究青藏高原构造演化的重要窗口之一。该缝合带自西向东分为西段(班公湖至改则)、中段(安多至东巧)和东段(丁青至怒江),其中东段的研究程度较低。本次以东段八宿县郭庆乡一条花岗岩高程剖面为研究对象,采用激光剥蚀电感耦合等离子体质谱仪(LA-ICPMS)法对锆石和磷灰石开展裂变径迹测试。花岗岩锆石U-Pb年龄为~180 Ma,指示其结晶时代为早侏罗世。锆石和磷灰石裂变径迹年龄分别为180~130 Ma、86~61 Ma,对应的年龄-海拔曲线分别为负斜率和正斜率。QTQt模拟显示花岗岩高程剖面顶部在130~60 Ma时剥蚀冷却速率快,中部在130~40 Ma时剥蚀冷却速率居中,而底部在~130 Ma之后一直保持最低的剥蚀冷却速率。这种差异性隆升源自班公湖-怒江缝合带东段的南向俯冲板片断离早于北向俯冲板片断离。

The Bangonghu-Nujiang suture zone is an important tectonic boundary,separating the Qiangtang and Lhasa blocks within the Tibetan Plateau(TP).This suture zone is one of the important geological windows for deciphering the growth history of TP.It can be divided into three parts:the western(from Banggong Lake to Gaze),middle(from Anduo to Dongqiao)and eastern(from Dingqing to Nujiang)sections.Few studies were undertaken in the eastern section.In this study,a vertical profile of granite near Guoqing Village of Basu County is considered for the fission track dating research,including zircon fission track(ZFT)and apatite fission track(AFT)with laser ablation inductively coupled plasma mass spectrometry(LA-ICPMS).The zircon U-Pb ages are centered at~180 Ma,indicating that its crystallization age is the Early Jurassic.The ages of ZFT and AFT range at 180~130 Ma and 86~61 Ma,respectively.The Age-Elevation Relations(AER)of ZFT and AFT have a negative and positive slope,respectively.The QTQt simulation shows that the upper sample had experienced a fast-rate erosion during about 130~60 Ma,the middle had undergone a middle-rate erosion during 130~40 Ma,and the lower had maintained the slowest erosion since~130 Ma.This differential uplift was caused by the earlier time of slab break-off in southward subduction than that in the northward subduction.