Expedition 360 summary-猫眼课题宝

DOI：

10.14379/iodp.proc.360.101.2017

发表时间：

2017-01

期刊：

影响因子：

通讯作者：

中科院分区：

其他

文献类型：

作者：

H. Dick;C. MacLeod;P. Blum;N. Abe;D. Blackman;J. Bowles;M. Cheadle;K. Cho;J. Ciążela;J. Deans;V. Edgcomb;C. Ferrando;B. Ghosh;B. Ildefonse;Kendrick;J. Koepke;J. Leong;Chuan-Zhou Liu;Q. Ma;T. Morishita;A. Morris;J. Natland;T. Nozaka;O. Pluemper;A. Sanfilippo;J. Sylvan;Tivey;R. Tribuzio;L. Viegas

国际海洋发现计划（IODP）第360次考察是SloMo（“低速扩张海脊下地壳和莫霍面的性质”的缩写）项目第一阶段的第一站，这是一个多阶段钻探计划，计划钻穿全球地震速度不连续面的最外层，即莫霍洛维奇地震不连续面（莫霍面）。莫霍面对应于压缩波速度的增加，通常在海洋下方约7公里处，通常被认为是地壳和地幔之间的边界。另一种模式，即莫霍面是地幔中的水化前沿，最近在海底和断裂带壁上发现了丰富的部分蛇纹化橄榄岩，例如在亚特兰蒂斯银行，一个11-13 My的古老的升高的海洋核杂岩，毗邻西南印度洋脊的亚特兰蒂斯II转换。U1473 A孔是在360号考察期间在亚特兰蒂斯岸的山顶上钻凿的，距离以前的两个大洋钻探计划（ODP）孔1-2公里：735 B孔（1987年ODP 118航次和1997年ODP 176航次钻凿）和1105 A孔（1998年ODP 179航次钻凿）。通过沿转换墙沿着40 km的挖掘和潜水，追踪到地幔橄榄岩/辉长岩接触带。该接触面位于钻井现场下方转换壁上约4200 m深度处，但向南20 km处明显变浅，在2563 m深度处的露头中观察到该接触面。然而，在Atlantis Bank下方约5-6 km处和转换墙下方<4 km处发现了莫霍面反射，这表明地震不连续性可能不代表地壳/地幔边界，而是一种蚀变（蛇纹石化）前缘。这反过来又提出了一个有趣的可能性，即与蛇纹岩化相关的甲烷生成可能支持海洋基底深处的一个全新的行星生物圈。SloMo项目试图在亚特兰蒂斯银行测试这些假设，并评估下地壳和上地幔的自然碳封存过程。SloMo第1航段的主要目的是探索735 B孔中确定的地层的横向变化。通过对U1473 A孔、735 B孔和1105 A孔的比较，我们可以证明在~128 ky的时间段内，岩浆增生和稳态拆离断层作用过程的连续性和复杂的相互作用。初步评估表明，下地壳的这些部分是由重复的侵入循环构成的，在孔U1473 A中，大约有三个向上分化的数百米规模的橄榄石辉长岩体，与孔735 B较深部分的情况大致相似。第360次考察的具体目标侧重于了解岩浆作用和构造作用如何在适应海底扩张方面相互作用，磁反转边界如何在下地壳中表现出来，评估下地壳和浅地幔在全球碳循环中的作用，以及限制海洋岩石圈深层生命的范围和性质。

International Ocean Discovery Program (IODP) Expedition 360 was the first leg of Phase I of the SloMo (shorthand for “The nature of the lower crust and Moho at slower spreading ridges”) Project, a multiphase drilling program that proposes to drill through the outermost of the global seismic velocity discontinuities, the Mohorovičić seismic discontinuity (Moho). The Moho corresponds to a compressional wave velocity increase, typically at ~7 km beneath the oceans, and has generally been regarded as the boundary between crust and mantle. An alternative model, that the Moho is a hydration front in the mantle, has recently gained credence upon the discovery of abundant partially serpentinized peridotite on the seafloor and on the walls of fracture zones, such as at Atlantis Bank, an 11–13 My old elevated oceanic core complex massif adjacent to the Atlantis II Transform on the Southwest Indian Ridge. Hole U1473A was drilled on the summit of Atlantis Bank during Expedition 360, 1–2 km away from two previous Ocean Drilling Program (ODP) holes: Hole 735B (drilled during ODP Leg 118 in 1987 and ODP Leg 176 in 1997) and Hole 1105A (drilled during ODP Leg 179 in 1998). A mantle peridotite/gabbro contact has been traced by dredging and diving along the transform wall for 40 km. The contact is located at ~4200 m depth on the transform wall below the drill sites but shoals considerably 20 km to the south, where it was observed in outcrop at 2563 m depth. Moho reflections, however, have been found at ~5–6 km beneath Atlantis Bank and <4 km beneath the transform wall, leading to the suggestion that the seismic discontinuity may not represent the crust/mantle boundary but rather an alteration (serpentinization) front. This in turn raises the interesting possibility that methanogenesis associated with serpentinization could support a whole new planetary biosphere deep in the oceanic basement. The SloMo Project seeks to test these hypotheses at Atlantis Bank and evaluate the processes of natural carbon sequestration in the lower crust and uppermost mantle. A primary objective of SloMo Leg 1 was to explore the lateral variability of the stratigraphy established in Hole 735B. Comparison of Hole U1473A with Holes 735B and 1105A allows us to demonstrate a continuity of process and complex interplay of magmatic accretion and steady-state detachment faulting over a time period of ~128 ky. Preliminary assessment indicates that these sections of lower crust are constructed by repeated cycles of intrusion, represented in Hole U1473A by approximately three upwardly differentiated hundreds of meter–scale bodies of olivine gabbro broadly similar to those encountered in the deeper parts of Hole 735B. Specific aims of Expedition 360 focused on gaining an understanding of how magmatism and tectonism interact in accommodating seafloor spreading, how magnetic reversal boundaries are expressed in the lower crust, assessing the role of the lower crust and shallow mantle in the global carbon cycle, and constraining the extent and nature of life at deep levels within the ocean lithosphere.

Expedition 360 summary

文献摘要

相似文献