A fission-track and (U-Th)/He thermochronometric study of the northern margin of the South China Sea: an example of a complex passive margin
A fission-track and (U-Th)/He thermochronometric study of the northern margin of the South China Sea: an example of a complex passive margin
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DOI：
10.1016/j.tecto.2009.04.030
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发表时间：
2009-09
期刊：
影响因子：
2.9
通讯作者：
Y. Yi;A. Carter;B. Xia;Lin Ge;S. Brichau;Hu Xiaoqiong
中科院分区：
文献类型：
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作者：
Y. Yi;A. Carter;B. Xia;Lin Ge;S. Brichau;Hu Xiaoqiong
利用锆石裂变径迹（ZFT）、磷灰石裂变径迹（AFT）和（U-Th）/He热年代学数据，重建了华南大陆边缘新生代的折返历史。从海岸到大陆内部的一条由南向北的样品样带获得的ZFT年龄介于116.6±4.7 Ma和87.3±4.0 Ma之间，表明晚白垩世样品位于上地壳5-6 km深处。磷灰石FT年龄范围为60.9±3.6 - 37.3±2.3 Ma，平均径迹长度为13.26±0.16 µm-13.95±0.19 µm，而AHe年龄略年轻，为47.5±1.9-15.3±0.5 Ma。这些结果表明，在新生代的大部分时间里，取样的岩石位于地壳顶部1-1.5公里处。结合FT和（U-Th）/He数据集的热历史模拟揭示了一个共同的三个阶段的冷却历史，不同的系统在内陆远离裂谷边缘的时间。1)快速冷却的初始阶段向北延伸，2）相对（但不完美）的热停滞期在~70-60 °C，从南到北持续时间增加; 3）最终阶段冷却到表面温度，在15和10 Ma之间开始。岩石隆起和侵蚀的时间和模式不适合传统的被动边缘景观模型，需要最年轻的折返年龄集中在或接近裂谷边缘。华南边缘的历史更为复杂，在活动边缘期的地壳弱化的帮助下，紧接着中国南海的裂谷和开放。这种流变学的继承性形成了一个地壳急剧变薄的过渡带，它充当了一个弯曲的过滤器，将华南地块的北方边缘与南部的活动裂谷区断开。因此，尽管华南边缘显示出裂陷大陆边缘的许多特征，但其折返历史并不符合被动边缘的传统形象。
Zircon fission track (ZFT), apatite fission track (AFT) and (U–Th)/He thermochronometric data are used to reconstruct the Cenozoic exhumation history of the South China continental margin. A south to north sample transect from coast to continental interior yielded ZFT ages between 116.6±4.7 Ma and 87.3±4.0, indicating that by the Late Cretaceous samples were at depths of 5–6 km in the upper crust. Apatite FT ages range between 60.9±3.6 and 37.3±2.3 Ma with mean track lengths between 13.26±0.16 µm and 13.95±0.19 µm whilst AHe ages are marginally younger 47.5±1.9–15.3±0.5 Ma. These results show the sampled rocks resided in the top 1–1.5 km of the crust for most of the Cenozoic. Thermal history modeling of the combined FT and (U–Th)/He datasets reveal a common three stage cooling history which differed systematically in timing inland away from the rifted margin. 1) Initial phase of rapid cooling that youngs to the north, 2) a period of relative (but not perfect) thermal stasis at ~70–60 °C which increases in duration from the south to the north; 3) final-stage cooling to surface temperatures that initiated in all samples between 15 and 10 Ma. The timing and pattern of rock uplift and erosion does not fit with conventional passive margin landscape models that require youngest exhumation ages to be concentrated at or close to the rifted margin. The history of South China margin is more complex aided by weakened crust from the active margin period that immediately preceded rifting and opening of the South China Sea. This rheological inheritance created a transition zone of steeply thinned crust that served as a flexural filter disconnecting the northern margin of the South China block and site of active rifting to the south. Consequently whilst the South China margin displays many features of a rifted continental margin its exhumation history does not conform to conventional images of a passive margin.