海南岛北部晚中-新生代剥露过程的低温年代学约束

【目的】研究海南岛大地构造在中-新生代的隆升剥露过程与热演化史,为华南地块的构造演化提供有力证据。【方法】利用磷灰石裂变径迹(AFT)、磷灰石及锆石(U-Th)/He等构造热年代学研究方法,重建海南岛北部岩体的构造-热演化历史,分析侵入岩体在不同构造热演化阶段的冷却剥蚀速率,并进一步探讨岩体隆升过程的动力学过程。【结果】AFT年龄介于(33.3±2.5)~(45.0±3.5)Ma之间,磷灰石平均长度为(12.68±0.28)~(13.04±0.9)μm;磷灰石(U-Th)/He(AHe)单颗粒年龄(36.3±2.2)~(60.2±3.7)Ma,锆石(U-Th)/He(ZHe)单颗粒年龄为(79.5±4.9)~(98.4±6.1)Ma及(37.1±2.3)~(59.6±3.7)Ma。联合反演热史揭示,研究区岩体自晚白垩世(约100 Ma)以来的冷却过程有明显的差异性,可分为4个阶段:1)约100~45 Ma相对缓慢冷却阶段;2)约45~35 Ma快速冷却剥蚀阶段;3)约30~35 Ma至10 Ma缓慢冷却过程;4)约10 Ma以来再次快速冷却剥露。【结论】海南岛北部花岗岩体阶段性抬升冷却与(古)太平洋板块的俯冲后撤、西南部印度-欧亚大陆碰撞和中新世晚期菲律宾海板块向西俯冲挤压有关。海南岛北部在Ⅰ、Ⅱ期(始新世晚期)剥蚀阶段基本造成总剥蚀量的2/3。

Denudation History of Northern Hainan Island Since Late Mesozoic-Cenozoic: Evidence from Low-Temperature Thermochronology

【Objective】This study aims to explore the uplift-exhumation and tectonothermal evolution of Hainan Island and provide evidence for tectonic evolution of the South China.【Method】Structural thermochronology methods such as apatite fission track(AFT),apatite and zircon(U-Th)/He were employed to reconstruct the tectonothermal history of the northern Hainan Island,calculate the cooling rate at different stages of thermal history,and analyze the dynamic process of the northern Hainan Island plutons uplift.【Result】AFT age is between 33.3±2.5 and 45.0±3.5 Ma;the average length of apatite(U-Th)/He(AHe)is between 12.68±0.28 and 13.04±0.9μm;the single grains age of apatite(U-Th)/He(AHe)is between 36.3±2.2 and 60.2±3.7 Ma;the single grains age of zircon(U-Th)/He(ZHe)from 79.5±4.9 to 98.4±6.1 Ma and 37.1±2.3 to 59.6±3.7 Ma,respectively.The results of thermal history inversion shows that there are obvious differences in the cooling process during the upper cretaceous(about 100Ma),which can divided into four phases:(1)the first slow cooling stage from about 100 to 45 Ma;(2)the first fast-cooling and denudation stage between ca.45 and 35 Ma;(3)the second slow cooling stage during ca.35-10 Ma;and(4)a second fast cooling and denudation stage since about 10 Ma.【Conclusion】The different uplift-cooling may be associated with the subduction of the Pacific Plate of South China block,India-Eurasia collision in the southwestern China and the tectonic uplift of the Qinghai-Tibet plateau,and the westward subduction and compression of the Philippine Sea Plate in the late Miocene.The 2/3 of the total denudation was eroded during the Ⅰ and Ⅱ denudation stage before late Eocene.