Origin of MORB deduced from the deep-seated rocks from the ocean floor

1.超镁铁质岩石从赫斯深，EPR，并从开曼海槽，加勒比海，岩石学检查，他们的差异，如果有的话，取决于扩展速度。地幔橄榄岩为黑橄榄岩（赫斯深部）或二辉橄榄岩（MCT），但纯橄榄岩-橄榄岩在两者之间仅略有不同。这种差异是一致的原始MORB组成的变化，只有轻微依赖于扩展速率。因此，纯橄榄岩-橄榄岩可能与原生MORB处于平衡状态。纯橄榄岩-橄榄岩和MORB都是高压MORB与地幔最上部橄榄岩反应的产物。阿曼蛇绿岩中的地幔橄榄岩，可能形成于快速扩张的山脊，和Luppers橄榄岩，可能形成于一个缓慢扩张的山脊与洋底橄榄岩进行了比较。阿曼蛇绿岩的地幔部分以辉绿帘石为主，与赫斯深海的辉绿帘石相似。在地幔剖面的深部发现了含Cpx的方辉橄榄岩和二辉橄榄岩，可以详细讨论快速扩张的脊下的熔融过程。绿辉橄榄岩主要为二辉橄榄岩至辉橄榄岩，含整合纯橄榄岩，含尖晶石，Cr#为0.3.3。通过对亚特兰蒂斯岸地幔橄榄岩SWIR的研究，了解了超慢速扩张脊下的熔融过程。在Atlantis II FZ的一个斜坡上，证实了从二辉橄榄岩到辉橄榄岩的向上岩性变化，这可以给我们提供洋脊下地幔熔融的空间和温度原因的约束。

1. Ultramafic rocks obtained from Hess Deep, EPR, and from Mid-Cayman Trough, the Caribbean, were petrologically examined to their difference, if any, depending on the spreading rate. The mantle peridotite is harzburgite (Hess Deep) or lherzolite (MCT), but the dunite-troctolite are only slightly different between the two. This difference is concordant with the primitive MORB compositional variation that is only slightly dependent on spreading rate. The dunite-troctolite are, thus, possibly in equilibrium with the primary MORB.Both the dunite-troctolite and MORB are the product of reaction between high-pressure MORB and peridotite at the uppermost mantle.2. The mantle peridoitites in the Oman ophiolite, possibly formed at a fast-spreading ridge, and the Lizard peridotite, possibly formed at a slow-spreading ridge were compared with the ocean-floor peridotites. The mantle section of the Oman ophiolite is dominated by harzburgite similar to that from Hess Deep. Cpx-bearing harzburgite and lherzolite were found in deeper parts of the mantle section, and the melting process beneath a fast-spreading ridge can be discussed in detail. The Lizard peridotite is dominantly lherzolite to harzburgite with concordant dunite which has spinel with Cr# of 0.3.3. The mantle peridotite from the Atlantis Bank, SWIR, was examined to know the melting process beneath a ultra-slow spreading ridge. An upward lithological variation from lherzolite to harzburgite on a slope of the Atlantis II FZ was confirmed, which can give us constraints on the space and temperature legime of mantle melting beneath the ridge.