Fluid evolution in an Oceanic Core Complex: A fluid inclusion study from IODP hole U1309 D-Atlantis Massif, 30°N, Mid-Atlantic Ridge
Fluid evolution in an Oceanic Core Complex: A fluid inclusion study from IODP hole U1309 D-Atlantis Massif, 30°N, Mid-Atlantic Ridge
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DOI：
10.1002/2013gc004975
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发表时间：
2014-04-01
影响因子：
3.5
通讯作者：
Cliff, Robert A.
中科院分区：
文献类型：
--
作者：
Castelain, Teddy;McCaig, Andrew M.;Cliff, Robert A.
在海底缓慢扩张的滑脱模式中，向上凸的滑脱断层在板块分离速度中所占比例较高，海底显露出辉长岩和蛇纹橄榄岩。大型、寿命长的热液系统（例如 TAG）位于离轴位置，可能受到沿滑脱断层向上流动的流体控制，岩浆热源深达 7 公里平方英尺。此前尚未研究过这种深层循环对流体温度和盐度演变的影响。对在亚特兰蒂斯地块海洋核心复合体（北纬 30 度，大西洋中脊）回收的辉绿岩、辉长岩和长辉石中捕获的流体包裹体进行的显微测温揭示了岩浆出溶、相分离以及热液流体与先前相分离流体之间混合的证据。鉴定出四种类型的流体包裹体，盐度范围为 1.4 至 35 wt% NaCl，但最常见的包裹体的盐度接近海水（3.4 wt% NaCl）。均一温度范围为 160 至 >400 摄氏度，最高温度是捕获在长白铁矿中的高盐度包裹体，最低温度是捕获在石英脉中的低盐度包裹体。亚特兰蒂斯地块的流体历史是在已发表的地块热测时数据的背景下解释的，并与 TAG 热液场下推断的循环模式进行比较，以更好地限制捕获的压力温度条件以及在 IODP 孔 U1309D 流体采样的岩石折返历史中何时被捕获。
In the detachment mode of slow seafloor spreading, convex-upward detachment faults take up a high proportion of the plate separation velocity exposing gabbro and serpentinized peridotite on the seafloor. Large, long-lived hydrothermal systems such as TAG are situated off axis and may be controlled by fluid flow up a detachment fault, with the source of magmatic heat being as deep as 7 kmbsf. The consequences of such deep circulation for the evolution of fluid temperature and salinity have not previously been investigated. Microthermometry on fluid inclusions trapped in diabase, gabbro, and trondjhemite, recovered at the Atlantis Massif Oceanic Core Complex (30 degrees N, Mid-Atlantic Ridge), reveals evidence for magmatic exsolution, phase separation, and mixing between hydrothermal fluids and previously phase-separated fluids. Four types of fluid inclusions were identified, ranging in salinity from 1.4 to 35 wt % NaCl, although the most common inclusions have salinities close to seawater (3.4 wt % NaCl). Homogenization temperatures range from 160 to >400 degrees C, with the highest temperatures in hypersaline inclusions trapped in trondjhemite and the lowest temperatures in low-salinity inclusions trapped in quartz veins. The fluid history of the Atlantis Massif is interpreted in the context of published thermochronometric data from the Massif, and a comparison with the inferred circulation pattern beneath the TAG hydrothermal field, to better constrain the pressure temperature conditions of trapping and when in the history of exhumation of the rocks sampled by IODP Hole U1309D fluids have been trapped.