Collaborative Research: Constraining Mantle Rheology, Mantle Flow, and Crust/Mantle Coupling Beneath New Zealand

0409564黑格大陆动力学的一个关键问题是：“什么是系统的流变学？“岩石在韧性状态下是通过扩散蠕变（应变率与应力成正比）还是通过位错蠕变（应力加倍会使应变率增加约10倍）变形？” 下地壳是相对较强，地壳和地幔之间的应变有效耦合，还是较弱，如经典的“果冻三明治”模型？ 上地幔是如预期的那样是强的，还是弱的，由于高挥发分含量？ 上地幔的变形是局部的，沿着地壳断层下的剪切带，还是像薄粘片模型那样分布的？这是一个将利用地震各向异性测量地幔应变的项目，当与矿物物理学相结合时，将限制变形机制，从而限制流变学。 PI坚持认为，新西兰的走滑系统是研究这些关系的最佳场所，因为信号大而简单，受到地质学、GPS和过去4500万年来已知的相对板块运动的限制。 具体而言，该项目涉及：1）部署30台海底地震仪; 2）使用各种技术测量地震各向异性（横波分裂、表面波色散、Pn和Sn走时以及接收器函数）; 3）计算地幔有限应变场，这可能是各向异性的原因，受新西兰相对板块运动和观测应变的约束，并考虑温度和变形机制的各种垂直和横向分布;（4）结合实验室、理论和地震学对各向异性的约束来限定位错蠕变发生的条件。

0409564HagerOne of the critical questions in Continental Dynamics is: "What is the rheology of the system?" Do rocks deform in the ductile regime by diffusion creep (with strain rate proportional to stress), or by dislocation creep (where doubling the stress increases strain rates ~10 times)?. Is the lower crust relatively strong, with efficient coupling of strain between the crust and mantle, or weak, as in the classic "jelly sandwich" model? Is the upper mantle strong, as expected for dry peridotite, or weak, due to high volatile content? Is deformation in the upper mantle localized along shear zones beneath crustal faults, or distributed, as in thin viscous sheet models?This is a project that will use seismic anisotropy to measure strain in the mantle and that when combined with mineral physics, to constrain deformation mechanisms and therefore to constrain rheology. The PIs maintain that the strike-slip system in New Zealand is the best place to study these relationships because the signal is large and simple with constraints at the surface provided by geology, GPS, and known relative plate motions for the last 45 million years. Specifically the project involves: 1) Deployment of 30 Ocean Bottom Seismographs; 2) Measurement of seismic anisotropy using a variety of techniques (shear-wave splitting, surface wave dispersion, Pn and Sn travel times, and receiver functions); 3) Calculations of mantle finite strain fields that might be responsible for anisotropy, constrained by relative plate motions and observed strain in New Zealand and considering a variety of vertical and lateral distributions of temperature and deformation mechanisms; and 4) Combination of laboratory, theoretical and seismological constraints on anisotropy to bound the conditions under which dislocation creep occurs.