High-pressure, high-temperature deformation of dunite, eclogite, clinopyroxenite and garnetite using in situ X-ray diffraction
High-pressure, high-temperature deformation of dunite, eclogite, clinopyroxenite and garnetite using in situ X-ray diffraction
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DOI：
10.1016/j.epsl.2017.06.019
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发表时间：
2017-09
影响因子：
5.3
通讯作者：
R. Farla;A. Rosenthal;C. Bollinger;S. Petitgirard;J. Guignard;N. Miyajima;T. Kawazoe;W. Crichton;D. Frost
中科院分区：
文献类型：
--
作者：
R. Farla;A. Rosenthal;C. Bollinger;S. Petitgirard;J. Guignard;N. Miyajima;T. Kawazoe;W. Crichton;D. Frost
为了研究大洋岩石圈俯冲对地幔对流的影响，采用大体积压力机结合同步辐射X射线衍射技术，对橄榄岩型上地幔中榴辉岩、石榴子石和单斜辉石的流变学进行了实验研究。实验在恒定应变速率（2× 10− 6-3× 10− 5 s− 1）、压力（4.3 - 6.7 GPa）和温度（1050 - 1470 K）的范围内进行。结果表明，榴辉岩石榴石和单斜辉石和橄榄岩橄榄石之间的强度变化很大。在低温下（< 1200 K），榴辉岩的强度比纯橄榄岩高1GPa以上。另一方面，在高温下（> 1400 K）榴辉岩比纯橄榄岩弱0.2 GPa或更多。石榴子石和单斜辉石在1200 K左右的温度下比纯橄榄岩具有更高的强度。然而，在较高的温度（1370 K），单斜辉石是显着弱于石榴子石（和纯橄榄岩）的五个以上的因素。我们解释这些观察矿物相之间的变形机制的过渡。在单斜辉石中，高温位错蠕变导致强度降低，取代了低温孪晶。而石榴石在所有实验条件下保持非常刚性时，名义上无水（“干”）。显微结构观察表明，单斜辉石和石榴石的相分离，晶体学和形状的优先方向，而不是在前者的发展，这表明整体弱地震各向异性。在橄榄岩为主的地幔榴辉岩体的检测可能只有通过观察高VP/VS 1比值。榴辉岩的流变性与纯橄榄岩相当或较弱，表明榴辉岩在对流地幔中有有效的搅拌和混合作用。
The rheology of eclogite, garnetite and clinopyroxenite in the peridotitic upper mantle was experimentally investigated in a large volume press combined with in situ synchrotron X-ray diffraction techniques to study the impact on mantle convection resulting from the subduction of oceanic lithosphere. Experiments were carried out over a range of constant strain rates (2× 10− 6–3× 10− 5 s− 1), pressures (4.3 to 6.7 GPa) and temperatures (1050 to 1470 K). Results show substantial strength variations among eclogitic garnet and clinopyroxene and peridotitic olivine. At low temperatures (< 1200 K), eclogite is over 1 GPa stronger than dunite. On the other hand, at high temperatures (> 1400 K) eclogite is weaker than dunite by 0.2 GPa or more. Garnetite and clinopyroxenite exhibit higher strength than dunite at approximately 1200 K. However, at higher temperature (1370 K), clinopyroxenite is significantly weaker than garnetite (and dunite) by more than a factor of five. We explain these observations by transitions in deformation mechanisms among the mineral phases. In clinopyroxene, high temperature dislocation creep resulting in a strength reduction replaces low temperature twinning. Whereas garnet remains very rigid at all experimental conditions when nominally anhydrous (‘dry’). Microstructural observations show phase segregation of clinopyroxene and garnet, development of a crystallographic and shape preferred orientation in the former but not in the latter, suggesting an overall weak seismic anisotropy. Detection of eclogite bodies in the peridotite-dominated mantle may only be possible via observation of high V P/V S 1 ratios. A comparable or weaker rheology of eclogite to dunite suggests effective stirring and mixing of eclogite in the convecting mantle.