Numerical models of mantle lithosphere weakening, erosion and delamination induced by melt extraction and emplacement
Numerical models of mantle lithosphere weakening, erosion and delamination induced by melt extraction and emplacement
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DOI：
10.1007/s00531-016-1343-y
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发表时间：
2016-06
影响因子：
2.3
通讯作者：
H. Wallner;H. Schmeling
中科院分区：
文献类型：
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作者：
H. Wallner;H. Schmeling
由下面的伸展和加热引起的大陆裂谷以各种方式影响着岩石圈或克拉通。火山作用和熔融侵入作用往往伴随着岩石圈的变薄、减弱甚至破裂而发生。虽然岩石圈的机械缩颈模型经常被应用，但熔融的方面以及熔体在较浅深度的迁移和侵位所造成的影响还没有被很好地理解。发展了一种两相流方法，该方法采用熔体提取和浅侵位与热弱化相关联，并与观测结果进行了比较。这一对比结果表明，部分熔体和软流圈岩浆源对于提高伸展过程中岩石圈-软流圈边界的上升速率具有重要意义。采用欧拉格式的有限差分方法对粘塑性流动的热力物理过程进行了二维近似。求解了多组分(壳-地幔)两相(熔体-基质)体系的质量守恒方程、动量守恒方程和能量守恒方程。流变学依赖于温度和应力。考虑到贫化和富集化，熔化和凝固过程由简化的线性二元固溶体模型控制。熔体被提取并侵位在岩石圈地幔和地壳中预定的深度区域(侵位带)。应用了压实Boussinesq近似；它的有效性与完全压实公式进行了比较，发现对于亚层熔融模型的情况是完全令人满意的。根据鲁文佐里地区的地球动力学情况，一个简单的模型通常会导致软流圈上隆，并伴随着岩石圈底部的熔融侵蚀。即使对温度异常采取保守的方法，与没有熔化的模型相比，单独融化也会使岩石圈的侵蚀速度增加一倍。随着熔体的提取和侵入，岩石圈-软流圈边界的侵蚀和上涌速度加快了3-4倍。在极端情况下，如果减弱使悬挂的地幔块完全解耦，就可能发生拆沉。侵位带长达约70公里的模型与观测结果吻合得很好，特别是对于基于地震学和岩石学数据的概念。
Continental rifting caused by extension and heating from below affects the lithosphere or cratons in various ways. Volcanism and melt intrusions often occur along with thinning, weakening and even breaking lithosphere. Although mechanical necking models of the lithosphere are often applied, the aspects of melting and the implications due to melt transport and emplacement at shallower depths are not well understood. A two-phase flow approach employing melt extraction and shallow emplacement associated with thermal weakening is developed and compared with observations. The results of this comparison indicate the importance of partial melts and an asthenospheric magma source for increasing the rising rate of the lithosphere–asthenosphere boundary during extension. Thermo-mechanical physics of visco-plastic flow is approximated using the Finite Difference method with Eulerian formulation in 2D. The conservation of mass, momentum and energy equations are solved for a multi-component (crust–mantle) and two-phase (melt–matrix) system. Rheology is temperature- and stress-dependent. In consideration of depletion and enrichment melting and solidification are controlled by a simplified linear binary solid solution model. Melt is extracted and emplaced in predefined depth regions (emplacement zones) in the lithospheric mantle and crust. The Compaction Boussinesq Approximation was applied; its validity was tested against the Full Compaction formulation and found fully satisfactory for the case of sublithospheric melting models. A simple model guided by the geodynamic situation of the Rwenzori region typically results in updoming asthenosphere with melt-assisted erosion of the lithosphere’s base. Even with a conservative approach for a temperature anomaly melting alone doubles the lithospheric erosion rate in comparison with a model without melting. With melt extraction and intrusion lithospheric erosion and upwelling of the lithosphere–asthenosphere boundary speeds up by a factor 3–4. In an extreme case, delamination may occur if weakening fully decouples a hanging mantle block. Models with an emplacement zone of up to approximately 70 km agree well with observations, especially for a concept based on seismological and petrological data.