Crustal rheology of southern Tibet constrained from lake-induced viscoelastic deformation
Crustal rheology of southern Tibet constrained from lake-induced viscoelastic deformation
复制标题
DOI：
10.1016/j.epsl.2018.11.014
复制
发表时间：
2019-01-15
影响因子：
5.3
通讯作者：
Bills, Bruce G.
中科院分区：
文献类型：
--
作者：
Henriquet, Maxime;Avouac, Jean-Philippe;Bills, Bruce G.
我们利用气候驱动的湖平面变化所伴随的回弹来探索西藏岩石圈的流变性。在现代十年时间尺度上，我们使用了InSAR测量的思陵措周围的形变。在千年时间尺度上，我们使用思陵措和扎日南措周围的全新世古海岸线。我们使用文献和数字高程模型中的时间约束来约束它们的年龄和几何形状。我们观察到古湖负荷质心附近地区在高水位后的一个小的下沉和一个低幅度的短波长外凸起。在一个由带有刚性底座的粘性通道上的弹性盖组成的模型中，这些观测排除了厚的低粘度通道的存在，并且需要一个薄的弹性盖。基于蒙特卡罗反演，我们约束了盖层可能的等效弹性厚度的范围(20公里厚的通道，地壳粘度较低(<；5×10(18)Pa.s))。在这些不同的时间尺度上推断出的不同流变学可以用Burgers体的中下地壳流变学来解释，其短期粘度为10(18)Pa.s，长期粘度为1020Pa.s，或者更好的解释为粘度的垂直变化。为了说明后一种说法，我们表明，在十年和全新世时间尺度上的观测结果可以通过假设在地壳中部深度(10到30公里深)嵌入较高粘度地壳(>；10(20)Pa.s)的低粘性区(1018Pa.s)来协调。在这两种情况下，由湖泊几何形状引起的形变信号在空间上的干扰，以及在时间上通过对湖平面变化的粘弹性响应导致的古岸线的有限变形。而在任何情况下，上地壳的弹性盖层都需要薄(20公里)，这是以前一些全新世古海岸线研究中推断的。从长远来看，岩石圈的有效弹性厚度必须逐渐下降到上地壳弹性盖层的值(
We probe the rheology of the Tibetan lithosphere using the rebound that accompanied climate-driven lake level variations. At the modern decadal time scale, we used deformation around Siling Tso measured from InSAR. At the millennial time scale, we use Holocene paleoshorelines around Siling Tso and Zhari Nam Tso. We use chronological constraints from the literature and Digital Elevation Models to constrain their ages and geometry. We observe a small post-highstand subsidence of the area near the center of mass of the paleolake-load and a low-amplitude short-wavelength outer bulge. In the context of a model consisting of an elastic lid over a viscous channel with a rigid base, these observations preclude the existence of a thick low viscosity channel and require a thin elastic lid. Based on Monte Carlo inversion, we constrain the range of possible equivalent elastic thickness of the lid (20 km thick channel with lower crustal viscosity (< 5 x 10(18) Pa.s). The different rheologies inferred at these different time-scales could be explained by a Burgers body rheology of the middle and lower crust, with a short-term viscosity of 10(18) Pa.s and long-term viscosity of 1020 Pa.s, or even better by vertical variations of viscosity. To illustrate the latter claim, we show that the observations at the decadal and Holocene time scales can be reconciled by assuming a low viscosity zone (1018 Pa.s) at mid-crustal depth (between 10 and 30 km depth) embedded in a higher viscosity crust (>10(20) Pa.s). In both cases, the interferences in space of the deformation signals induced by the lakes geometry, and in time through the viscoelastic response to the lake level variations results in limited distortion of the paleo-shorelines. While the elastic lid in the upper crust needs in any case to be thin (20 km) inferred in some previous studies of Holocene paleoshorelines. In the longer term, the effective elastic thickness of the lithosphere must drop asymptotically to the value of the elastic lid in the upper crust (