High‐temperature seawater circulation throughout crust of oceanic ridges: A model derived from the Oman ophiolites
High‐temperature seawater circulation throughout crust of oceanic ridges: A model derived from the Oman ophiolites
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DOI：
10.1029/2002jb002094
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发表时间：
2003-08
影响因子：
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通讯作者：
A. Nicolas;D. Mainprice;F. Boudier
中科院分区：
文献类型：
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作者：
A. Nicolas;D. Mainprice;F. Boudier
[1]我们在这里描述的高温（HT-700°C）和非常高的温度（VHT-1000 °C）的补给和排放系统，负责在阿曼蛇绿岩壳的起源洋中脊的HT-VHT热液蚀变。补给系统是一个规则的平行微裂缝网络，宽度不到一毫米，它将海水带到岩浆房的墙壁上，在那里触发了含水熔融。排放系统是由含水熔融产生的单斜辉石、闪长岩辉长岩脉组成的网络;向上，这些HT-VHT辉长岩脉逐渐变成有充分记录的低温（LT）（400-500°C）热液脉。微裂纹，辉长岩脉，静脉优先平行于辉长岩席脉和岩浆线理包围辉长岩。因此，补给系统和排泄系统的裂缝都平行于古脊面。在脆性场中，断裂是由与海底扩张有关的张应力引起的。在韧性场中，温度高达10900 °C时，微裂纹的张开归因于辉长岩冷却过程中热收缩的各向异性。辉长岩组构和各向异性是这样的诱导微裂纹也平行于脊面。在1200°C（岩浆房温度）和12700 °C（脆-韧性极限）之间的热收缩产生0.1%的差异应变，与从辉长岩中微裂纹的宽度和间距推断的差异应变相当。活动时间，流体速度和微裂缝中的流体通量的简单估计占所有可用的数据，并表明，在微裂缝中，活动是短暂的和偶发的。
[1] We describe here the high-temperature (HT ∼ 700°C) and very high temperature (VHT ∼ 1000 °C) recharge and discharge systems which are responsible for HT-VHT hydrothermal alterations at the oceanic ridge of origin in the crust of Oman ophiolites. The recharge system is a regular network of parallel microcracks, a fraction of a millimeter wide, which carries seawater to the walls of the magma chamber where hydrous melting is triggered. The discharge system is a network of clinopyroxene, pargasite gabbroic dikes issued from the hydrous melting; upsection, these HT-VHT gabbroic dikes grade into the well-documented low-temperature (LT) (400–500°C) hydrothermal veins. Microcracks, gabbroic dikes, and veins are preferentially parallel to the diabase-sheeted dikes and normal to magmatic lineations in enclosing gabbros. Thus the fractures of both the recharge and discharge systems are parallel to the paleoridge plane. In the brittle field, fracturing is induced by tensional stress related to seafloor spreading. In the ductile field and up to temperatures of ∼900°C, opening of microcracks is ascribed to the anisotropy of thermal contraction during gabbros cooling. Gabbro fabrics and anisotropy are such that the induced microcracks are also parallel to the ridge plane. Thermal contraction between 1200°C (temperature of magma chamber) and ∼700°C (brittle-ductile limit) produces a differential strain of 0.1% comparable to that deduced from width and spacing of microcracks in the gabbros. Simple estimates on activity time, fluid velocity, and fluid flux in microcracks account for all available data and suggest that in microcracks, activity was short lived and episodic.