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

1. 对从 EPR 的 Hess Deep 和加勒比海的中开曼海槽获得的超镁铁质岩石进行了岩石学检查，以了解它们的差异（如果有的话），具体取决于扩散率。地幔橄榄岩为方辉橄榄岩（Hess Deep）或二辉橄榄岩（MCT），但两者之间的纯橄榄岩仅略有不同。这种差异与原始 MORB 成分变化一致，该变化仅略微依赖于铺展率。因此，纯橄榄石-方棉岩可能与原生MORB处于平衡状态。纯橄榄岩-方棉岩和MORB都是高压MORB与最上地幔橄榄岩反应的产物。2．将阿曼蛇绿岩中的地幔橄榄岩（可能形成于快速扩张的山脊）和蜥蜴橄榄岩（可能形成于缓慢扩张的山脊）与海底橄榄岩进行了比较。阿曼蛇绿岩的地幔部分以方辉橄榄岩为主，与赫斯深渊相似。在地幔剖面的较深处发现了含 Cpx 的方辉橄榄岩和二辉橄榄岩，并且可以详细讨论快速扩张的山脊下方的熔融过程。蜥蜴橄榄岩主要为二辉橄榄岩至方辉橄榄岩，其中含有铬#为0.3.3的尖晶石。对来自亚特兰蒂斯浅滩的地幔橄榄岩（SWIR）进行了检查，以了解超慢扩张脊下方的熔化过程。在亚特兰蒂斯二号自由区的斜坡上，证实了从二辉橄榄岩到方辉橄榄岩的向上岩性变化，这可以给我们对洋脊下方地幔熔化的空间和温度规律带来限制。

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.