Rheology of Mantle Minerals at High Pressure

Weidner地球是一个动态的身体，不断进化，改变海洋的形状，建造山脉。 我们对这些现象的理解包括对矿物在高温下的塑性行为的认识。 板块构造论认为，稳定的地表板块与地球深部是机械隔离的。 热演化模型通过矿物的垂直流动来传递热量。 冰川的反弹证明了下面的粘性流动。这是一项研究压力对地球地幔主要矿物塑性特性的影响的建议。 虽然我们在过去几年中大大提高了对矿物流动特性的理解，但压力的影响仍然受到很大的限制。 在幂律蠕变制度的橄榄石流的活化体积的估计引起的不确定性的粘度在岩石圈的基础上的1000倍。 这种不确定性比含水量或部分熔化的总影响更大。 此外，高压形式的橄榄石（控制地球深处流动的相态）的流动特性几乎是未知的，研究人员一直在开发能够解决这一问题的新工具。 使用同步加速器X射线源，可以在多砧压机中测量样品的衍射光谱和直接图像，同时样品处于高压和高温下。 他们现在可以根据X射线衍射信号确定应力场，并根据阴影图像确定应变。 一个完整的数据收集周期大约需要三分钟。 因此，200秒的时间分辨率是可能的，并且可以获得这些参数的时间导数。 应力精度为几十MPa，应变速率为10-7 s-1。 研究人员已经证明，他们可以在几个加热/压缩循环的每一个过程中在样品中产生应力场。 因此，纹理和缺陷结构可以在实验过程中平衡。有了这个奖项，研究人员将研究橄榄石，wadsleyite，ringwoodite，石榴石和钙钛矿在高压下的流动特性。 他们将在斯托尼布鲁克的高压实验室合成样品，并将使用布鲁克海文国家实验室和阿贡国家实验室的同步加速器进行流变学研究。 结果将解释其含义的深源地震和地幔粘度结构。 --

EAR-0229260WeidnerThe Earth is a dynamic body, constantly evolving, changing the shapes of oceans, building mountains. Our understanding of these phenomena includes a recognition of the plastic behavior of minerals at high temperature. Plate tectonics asserts that stable surface plates are mechanically isolated from the deep Earth. Thermal evolutionary models transport heat by vertical flow of minerals. The rebound from glaciers is testimony to the viscous flow beneath. This is a proposal to study the effects of pressure on the plastic character of the major minerals of the Earth's mantle. While we have vastly improved our understanding of the flow properties of minerals over the past several years, the effects of pressure are still poorly constrained. Estimates of activation volume for olivine flow in the power law creep regime give rise to an uncertainty in viscosity at the base of the lithosphere of 1000 fold. This uncertainty is greater that the total effect of water content or partial melting. Furthermore, the flow characteristics of the high-pressure forms of olivine, the phases that control flow in the deep Earth, are virtually unknown.The investigators have been developing new tools capable of attacking this problem. Using synchrotron x-ray sources, it is possible to measure both diffraction spectra and direct images of samples in a multi-anvil press while the sample is at high pressure and temperature. They can now determine the stress field from the x-ray diffraction signal and strain from shadow-graph images. One complete data collection cycle takes about three minutes. Thus, time resolution of 200 seconds is possible and time derivatives of these parameters can be obtained. Stress accuracy is a few tens of MPa, and strain rates of 10-7 s-1 can be resolved. The investigators have demonstrated that they can create a stress field in the sample during each of several heating/compression cycles. Thus, texture and defect structures can equilibrate during the experiment.With this award, the researchers will investigate the flow properties of olivine, wadsleyite, ringwoodite, garnet, and perovskite at high pressure. They will synthesize the samples in the high-pressure laboratory at Stony Brook, and will use the synchrotrons at Brookhaven National Labs and at Argonne National Labs for the rheology study. Results will be interpreted in terms of their implications on deep focus earthquakes and mantle viscosity structure. --