Variable crustal thickness in the Oman ophiolite: Implication for oceanic crust
Variable crustal thickness in the Oman ophiolite: Implication for oceanic crust
复制标题
阿曼蛇绿岩的地壳厚度变化：对洋壳的影响
DOI：
10.1029/96jb00195
复制
发表时间：
1996
影响因子：
--
通讯作者：
B. Ildefonse
中科院分区：
文献类型：
--
作者：
A. Nicolas;F. Boudier;B. Ildefonse
通过对阿曼蛇绿岩辉长岩单元32个详细剖面的研究，得出该单元平均厚度为3.6km的结论。下部层状辉长岩占辉长岩单元的三分之二，上部均质片理化辉长岩占辉长岩单元的三分之一。假设上覆的玄武质盖层（席状岩墙和喷出岩）厚1.5-2公里，阿曼蛇绿岩中的地壳平均剖面比通常认为在快速扩张脊产生的标准6公里厚的洋壳薄0.5-1公里，这一点进行了讨论。辉长岩厚度在5.4公里和1.5公里之间的变化记录。在整个蛇绿岩带中，特别是在东南方辉橄榄岩中，存在一种普遍的相关性，即最薄的辉长岩单元（2.2-2.5 km厚）覆盖在最厚的（300-700 m）过渡带上，该过渡带将辉长岩单元与地幔方辉橄榄岩分隔开，而最厚的辉长岩单元（3.6-3.9 km厚）覆盖在最薄的（5-100 m）过渡带上。较薄的辉长岩单元和较厚的过渡区的组合被观察到以上地幔底辟或域，按照我们的结构模型，被增生以上底辟，并在扩展方向漂移。如果假设喷出玄武岩和席状岩墙复合体单元具有恒定的厚度，那么如此大的变化表明，在起源脊以下的莫霍面也有类似的变化;特别是，地幔底辟上方的莫霍面应该比远离底辟的莫霍面浅1-1.5 km。由于阿曼蛇绿岩被认为来自快速扩张的古山脊，因此，正如Barth和Mutter [本期]以及Wang等人[本期]所建议的那样，这种隆起应该在实际的快速扩张山脊中检测到。
From 32 detailed cross sections through the gabbro unit of the Oman ophiolite, it is concluded that the thickness of this unit is on average 3.6 km. The lower layered gabbros represent two thirds, and the upper homogeneous foliated gabbros represent one third the gabbro unit. Assuming that the overlying basaltic lid (sheeted dikes and extrusives) is 1.5–2 km thick, the average crustal section in the Oman ophiolite is 0.5–1 km thinner than the standard 6-km-thick oceanic crust usually considered to be produced at fast spreading ridges, a point which is discussed. Variations in gabbro thickness between 5.4 km and 1.5 km are recorded. There is a general correlation throughout the ophiolite belt, particularly in the southeastern massifs, such that the thinnest gabbro units (2.2–2.5 km thick) overlay the thickest (300–700 m) transition zones which separate them from the mantle harzburgites and the thickest gabbro units (3.6–3.9 km thick) overlay the thinnest (5–100 m) transition zones. The combination of thinner gabbro units and thicker transition zones is observed above mantle diapirs or in domains which, following our structural models, were accreted above diapirs and have drifted in the spreading direction. If it is assumed that the extrusive basalt and the sheeted dike complex units have a constant thickness, such large variations indicate similar variations in the Moho level below the ridge of origin; in particular, the Moho above mantle diapirs should be some 1–1.5 km shallower than away from diapirs. As the Oman ophiolite is considered to derive from a fast spreading paleoridge, this doming should be detected in actual fast spreading ridges, as suggested by Barth and Mutter [this issue] and Wang et al. [this issue].