Interstitial Water Chemistry of Gas-Hydrate-Bearing Sections on the Middle America Trench Slope, Deep Sea Drilling Project Leg 84
Interstitial Water Chemistry of Gas-Hydrate-Bearing Sections on the Middle America Trench Slope, Deep Sea Drilling Project Leg 84
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深海钻探项目第 84 段中美洲海沟斜坡含天然气水合物部分的间隙水化学
DOI：
10.2973/dsdp.proc.84.130.1985
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发表时间：
1985
期刊：
影响因子：
--
通讯作者：
J. Gieskes
中科院分区：
文献类型：
--
作者：
R. Hesse;J. Lebel;J. Gieskes
在DSDP第84航次，在哥斯达黎加外海（565号地点）和危地马拉外海（568号和570号地点）的中美洲海沟斜坡上的三个含天然气水合物地点进行了钻探。根据地震剖面图（GUA-13），在危地马拉外海的中坡569号站点，可能存在水合物，尽管孔隙水的成分没有提供明确的证据。位于危地马拉海沟下部斜坡的566和567号地点似乎没有水合物，但566号孔底部蛇纹岩的裂缝除外。水合物承载站点565、568和570显示了水合物分解对孔隙水化学的影响，这些影响是在危地马拉海沟斜坡上的站点496和497的先前钻探期间确定的。这些变化包括氯度下降和δ 18 θ升高。然而，新的结果揭示了氯度降低和δ' O增加之间比以前认识到的更复杂的关系。在565点，δ 18 θ值在孔的中间部分减小，而氯度从孔的顶部到底部附近继续减小。火山玻璃的早期成岩蚀变被认为是O-同位素曲线中意想不到的最小值的一种机制。孔隙水/水合物系统的多重分馏作用需要解释568孔底部δ 18 O值大于2.7‰的原因，因为分馏系数α = 1.0027，这是单级分馏作用所能产生的最大值。在大多数情况下，来自水合物带的原位水样品未能显示未参与水合物形成的残余孔隙沃茨预期的高盐度。这可能是因为原位取样装置仍允许系统压降足以在取样口附近触发水合物分解。
On DSDP Leg 84, drilling was conducted at three gas-hydrate-bearing sites on the Middle America Trench slope off Costa Rica (Site 565) and off Guatemala (Sites 568 and 570). At Site 569, on the mid-slope off Guatemala, hydrates may be present, according to the seismic profile (GUA-13), although the pore-water composition does not provide clear evidence. Sites 566 and 567, on the lower Guatemala Trench slope, appear to be free of hydrates, except in fractures of serpentinite at the bottom of Hole 566. Hydrate-bearing Sites 565, 568, and 570 show the effects of hydrate decomposition on pore-water chemistry that have been established during previous drilling at Sites 496 and 497 on the Guatemala Trench slope. These include a chlorinity decrease and δ 1 8 θ increase downsection. The new results, however, reveal more complex relationships between the chlorinity decrease and δ' O increase than previously recognized. At Site 565, δ 1 8 θ values decrease in the middle section of the hole, whereas chlorinity continues to decrease from the top to near the bottom of the hole. Early diagenetic alteration of volcanic glass is suggested as a mechanism for the unexpected minimum in the O-isotope curve. Multiple fractionation by the pore-water/hydrate system is required to explain δ 1 8 O-values greater than 2.7‰ at the bottom of Hole 568, because with a fractionation factor of α = 1.0027, this is the maximum figure a single-stage fractionation could produce. In situ water samples from hydrate zones in most cases failed to display the elevated salinities expected for the residual pore waters not involved in hydrate formation. This is probably because the in situ sampling device still allows a systematic pressure drop sufficient to trigger hydrate decomposition in the immediate vicinity of the sample port.