青藏高原东南螺髻山晚新生代以来的隆升历史与构造响应

The Sichuan-Yunnan faulted block is located within southeastern region of the Tibetan Plateau. Revealing response between uplift history of mountains and deformation behavior of faults along margins of this block is needed to understand plateau growth and mountain-building mechanism. However, low-thermochronologic studies along the eastern margin of this block have been selectively conducted in different regions, specifically focused in areas of the Gongga Shan while little in the Luoji Shan. This fund is mainly to collect metamorphic sandstone and granite in the northern and southern region of the Luoji Shan from two complete sampling transects with great relief, and to reveal late-Cenozoic uplift history of the Luoji Shan through low thermochronology like AFT, ZFT and (U-Th)/He dating methods. This study provides new data for completing and understanding spatial-temporal staged uplift process of the southern region of Tibetan Plateau and fault behavior along margins of the Sichuan-Yunnan faulted block, and may favor for constraining timing of active evolution of the Anninghe-Zemuhe fault along this block.

川滇地块是青藏高原东南重要的活动地块，研究该地块边界带附近山体的隆升历史与周围断裂活动之间的关系，对于认识青藏高原生长过程和隆升机制有着重要的科学意义，然而川滇地块东边界地区的低温热年代学研究程度却还存在较大差异，目前研究主要集中于贡嘎山一带，而其东边界中南部的螺髻山一带却还鲜有这方面研究的报道。本项目拟在螺髻山北部变质砂岩地区和南部花岗岩地区各采集一套大跨度、完整的年龄样品剖面，通过磷灰石和锆石裂变径迹法及（U-Th）/He法等低温热年代学方法揭示螺髻山晚新生代以来的隆升历史，这一方面为完善和理解青藏高原东南地区的时-空阶段性隆升过程和地块边界断层的变形响应模式积累新的资料，另一方面也可能有助于认识川滇地块东边界安宁河-则木河断层活动性演化的时间节点。

本项目基本按照原基金计划执行，在螺髻山南北两侧花岗岩和变质砂岩中共采集31个样品，构成2个年龄高程剖面（海拔高差分别为3000 m-1400 m和3800 m-1400 m）。测年结果显示锆石裂变径迹没有退火，年龄反映的是更老的造山事件，南侧磷灰石U-Th/He测年存在He丢失年龄偏老，南侧磷灰石AFT和北侧的锆石U-Th/He测年具有较好的测年结果。这些测年结果表明：螺髻山快速剥蚀的起始时间要早于13 Ma，中中新世以来的剥蚀速率大约为0.12-0.30 km/m.y.，也可能存在10 Ma以来剥蚀速率突然减小的可能性(早期在10-13 Ma剥蚀速率为0.20-0.55 km/m.y，然后降低为~0.03 km/m.y.)。综合该区域的其他低温热年代学研究资料，我们认为青藏高原东南缘地区剥蚀过程存在不均一性，不支持下地壳流模式，与高原隆升过程中的块体挤出变形模式更吻合，这也可能暗示川滇地块东边界鲜水河-安宁河-则木河-小江断裂系的最新起始活动时间早于13 Ma。