The reaction mechanism of fluid-induced partial melting of gabbro in the oceanic crust
The reaction mechanism of fluid-induced partial melting of gabbro in the oceanic crust
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洋壳中流体诱发辉长岩部分熔融的反应机制
DOI：
10.1127/0935-1221/2013/0025-2314
复制
发表时间：
2013
影响因子：
2.1
通讯作者：
S. Feig
中科院分区：
文献类型：
--
作者：
J. Koepke;S. Feig
由于在非常高的温度下流体/岩石相互作用而引起的海洋辉长岩的含水部分熔融被认为是洋壳内长英质岩性形成的重要过程。为了详细研究含水部分熔融的主要反应机理，以毫米级未改性橄榄石辉长岩（“微岩”）块体为粗粒起始材料，在温度范围为 860-1020 °C、压力为 200 MPa 的内热压力容器中进行了水饱和部分熔融实验。尽管远离全局平衡，但观察到的相关系和成分趋势与为实现全局平衡而设计的类似实验调查所预期的一样，使用的是相同起始辉长岩的细粒粉末。实验结果使我们能够制定橄榄石辉长岩水合部分熔融的一般流体诱导反应作为温度的函数： at T≤980℃, 橄榄石+单斜辉石+斜长石(I)+H2O⇒角闪石+斜方辉石+斜长石(II)+ 含水 斜长花岗岩 熔体;at T≥980℃ , 橄榄石(I)+单斜辉石(I)+斜长石(I)+H2O⇒橄榄石 (II)+单斜辉石(II)+斜长石(II)+ 含水 斜花岗岩 熔体。在这些微岩部分熔融实验中获得的特征和成分特征与来自缓慢扩张的山脊的一些天然海洋辉长岩的晚期组合的相应特征非常一致，这意味着一些天然晚期共生岩可以更好地解释为含水部分熔融事件后留下的残余相，而不是晚期演化渗滤熔体的结晶。在 940 °C 进行的一项实验产生了含有液滴的硅酸盐熔体池。第二熔体富含典型的微量元素（P、Zr、Cl 作为代表），这被解释为液体不混溶性的影响。在第一次熔体中观察到的一些微量元素的浓度异常高，这与使用平衡分配系数建模得出的微量元素浓度相矛盾。一个模型表明，在含水部分熔融的第一阶段，亚微米尺寸的相（如磷灰石、锆石和从主体辉长岩中的后期熔体在晶界上结晶的氧化物）可能被迫进入包含其微量元素库存的第一熔体。一个可能的结果是，流体引起的大洋辉长岩部分熔融的第一次熔融可能被视为天然 MORB 或洋中脊产生的相应长英质岩性污染的一个可能来源。
Hydrous partial melting of oceanic gabbro as a consequence of fluid/rock interaction at very high temperatures is regarded as an important process for the formation of felsic lithologies within the oceanic crust. In order to investigate the principal reaction mechanism of hydrous partial melting in detail, water-saturated partial melting experiments were conducted in an internally heated pressure vessel in the temperature range 860–1020 °C and 200 MPa pressure,fO2~NNO, with mm-sized blocks of unmodified olivine gabbro (“microrocks”) used as a coarse-grained starting material. Although far from global equilibrium, the observed phase relations and compositional trends are as expected from a similar experimental survey designed for achieving global equilibrium, using a fine-grained powder of the same starting gabbro. The experimental results allow us to formulate a general fluid-induced reaction for hydrous partial melting of olivine gabbro as a function of temperature: at T≤980°C, olivine+clinopyroxene+plagioclase(I)+H2O⇒amphibole+orthopyroxene+plagioclase(II)+ hydrous plagiogranitic melt;at T≥980°C, olivine(I)+clinopyroxene(I)+plagioclase(I)+H2O⇒olivine (II)+clinopyroxene(II)+plagioclase(II)+ hydrous plagiogranitic melt.Textural features and compositional characteristics obtained in these partial-melting experiments on microrock are in good agreement with corresponding features of late-stage assemblages in some natural oceanic gabbros from slow-spreading ridges, implying that some of the natural late-stage parageneses can be better explained as residual phases left back after a hydrous partial-melting event rather than by crystallization of a late evolved percolating melt.One experiment performed at 940 °C produced pools of silicate melt containing droplets of a second melt strongly enriched in typical trace elements (P, Zr, Cl as proxies), which is interpreted as an effect of liquid immiscibility. The observation of unusually high concentrations of some trace elements within the first melts is in contradiction with trace-element concentrations derived from modelling using equilibrium partition coefficients. A model is implied that during the very first stage of hydrous partial melting, sub-micrometre sized phases like apatite, zircon and oxides crystallized on grain boundaries from a late-stage melt in the host gabbro may be forced into the very first melt which incorporated their trace-element inventory. A possible consequence is that the very first melts of fluid-induced partial melting of oceanic gabbro may be regarded as one possible source for the contamination of natural MORB or of corresponding felsic lithologies generated at mid-ocean ridges.
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DOI：
10.6028/jres.107.054
发表时间：
2002-11
影响因子：
1.5
作者：
Jarosewich E
通讯作者：
Jarosewich E
影响因子：
2.4
作者：
J. Koepke;S. Feig;J. Snow
通讯作者：
J. Koepke;S. Feig;J. Snow
影响因子：
--
作者：
A. Nicolas;D. Mainprice;F. Boudier
通讯作者：
A. Nicolas;D. Mainprice;F. Boudier
苏格兰喀里多尼德群岛设得兰群岛海洋碎片的 U/Pb 年龄：来自“第 3 层”剪切带深熔斜长花岗岩的证据
影响因子：
2.3
作者：
J. Spray;Gregory R. DUNNINGf
通讯作者：
Gregory R. DUNNINGf
影响因子：
4.4
作者：
ALBAREDE, F;PROVOST, A
通讯作者：
PROVOST, A