High temperature alteration of Abyssal ultramafics from the Islas Orcadas Fracture Zone, South Atlantic
High temperature alteration of Abyssal ultramafics from the Islas Orcadas Fracture Zone, South Atlantic
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南大西洋奥卡达斯群岛断裂带深渊超镁铁质的高温蚀变
DOI：
10.1007/bf00374687
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发表时间：
1985
影响因子：
3.5
通讯作者：
H. Dick
中科院分区：
文献类型：
--
作者：
K. Kimball;F. Spear;H. Dick
沿着西南印度洋海脊(6°E和54°S)从Islas Orcadas断裂带挖出的超镁铁质岩石显示出从高于600℃(可能高达900℃)到低于50℃的渐进水化作用的证据。超镁铁质岩石中存在两种主要的蚀变类型，这两种类型都是水化反应的结果。第一类蚀变包括原始单斜辉石、斜方辉石和橄榄石的水化作用，形成角闪石、滑石、次生橄榄石和蛇纹石。二是脉型蚀变，形成角闪石、绿泥石、滑石、蛇纹石等矿脉。-这种改变似乎是间歇性的。岩相学提出的事件序列为：1)单斜辉石变为角闪石；2)斜辉石变为滑石或滑石+橄榄石；3)超溶角闪脉；4)阳起岩+角闪岩脉共存；5)绿泥石、绿泥石+阳起石或绿泥石+次生单斜辉石脉状；6)滑石脉；7)蛇纹岩脉；8)普遍的蛇纹岩化。-蚀变流体最有可能是海水。认为高温变化可能反映了海水进入上地幔的环流。
Ultramafic rocks dredged from the Islas Orcadas Fracture Zone, along the SW Indian Ocean Ridge (6° E and 54° S), show evidence of progressive hydration beginning at temperatures greater than 600° C (and perhaps as high as 900° C) and continuing to less than 50° C. There are two principal types of alteration present in the ultramafic rocks, both of which are the result of hydration reactions. The first type of alteration involves hydration of original clinopyroxene, orthopyroxene and olivine to amphibole, talc, secondary olivine, and serpentine. The second is a vein type of alteration and results in the formation of veins of amphibole, chlorite, talc and serpentine. — The alteration appears to be episodic. The sequence of events suggested by the petrography is: 1) clinopyroxene altering to amphibole; 2) orthopyroxene altering to talc, or talc + olivine; 3) supersolvus hornblende veining; 4) coexisting actinolite + hornblende veining; 5) chlorite, chlorite + actinolite, or chlorite + secondary clinopyroxene veining; 6) talc veining; 7) serpentine veining; and 8) pervasive serpentinization. — The alteration fluid is most likely seawater. It is suggested that the high temperature alterations may reflect seawater circulation into the upper mantle.