日喀则蛇绿岩研究中的几个问题

日喀则蛇绿岩是中国最著名的蛇绿岩,但是,许多问题存在争论,许多现象没有搞清楚。文中讨论了日喀则蛇绿岩中一些重要的现象以及对目前发现的许多矛盾如何考虑的问题。例如,(1)日喀则蛇绿岩中是否存在席状岩墙群?是否存在席状岩床群?本文认为,席状岩墙群应当是存在的,因为有不对称冷凝边出现。而席状岩床群可能是有问题的,岩床作为侵入体可以出现在许多地方,但是,蛇绿岩中不可能出现席状岩床群,尤其还把它作为蛇绿岩岩石组合的一个单元。笔者认为,所谓的席状岩床群可能是席状岩流群,它不是一个独立的单元,是玄武岩单元下部的成员。(2)日喀则蛇绿岩是否统统是蛇绿岩是一个需要考虑的问题,雅鲁藏布江东西两段出现的岩石组合及其产出背景与日喀则地区的蛇绿岩明显不同,其中有些可能未必是蛇绿岩。(3)自1972年彭罗斯会议以来,蛇绿岩研究发展到现在,可能已经进入了一个关键时期。文中回顾了蛇绿岩的定义及其构造意义,指出1972年彭罗斯会议关于蛇绿岩的定义仍然是适用的。蛇绿岩可以概括为洋壳+地幔,这个洋壳来自板块扩张脊,是年轻的;这个地幔是大洋岩石圈地幔,也可能保留有古老岩石圈地幔的印记。蛇绿岩产于板块扩张脊,这是蛇绿岩构造含义的唯一解,蛇绿岩不存在多解性。(4)日喀则蛇绿岩的许多基本观点主要是法国学者提出来的,如关于岩床群的见解,慢速扩张的见解等。但是,上述见解是否都是对的是需要思考的。日喀则蛇绿岩具有得天独厚的条件,我们应当很好利用这个条件,努力把我们的研究做好,为全球蛇绿岩研究贡献我们的一份力量。

Some problems on the Xigaze ophiolite

The Xigaze ophiolite is the most famous ophiolite in China and there are some debates in the academia about a number of phenomena. In this paper, the author discussed some phenomena in Xigaze ophiolite and how to think about these contradictions. For example, (1) Are there sheeted dike swarms in Xigaze ophiolite? Are there sheeted sill swarms? The author thinks there are sheeted dike swarms in Xigaze ophiolite. The sill swarms should be sheeted flow swarms because of the sill swarms never exist in plate spreading ridge. Sheeted flow swarms located in the lower part of the basalt unit rather than another independent unit. (2) It is a question to be considered whether the Xigaze ophiolite is all ophiolite. The rock assemblage and its background of the east and west part of the Yalung Zangbo is obvious different from the Xigaze ophiolite, some of them may not ophiolite. (3) The ophiolite research may enter a critical period since Penrose meeting in 1972. This paper reviews the definition and its significance in construction of ophiolite, points out that the definition of ophiolite is still applicable in the 1972 Penrose meeting. The ophiolite can be summarized as oceanic crust + the mantle, the oceanic crust is young, which comes from spreading ridge. The mantle is oceanic lithosphere mantle, may retained some mark of the ancient lithospheric mantle. The ophiolite originated in plates spreading ridge, this is the only tectonic meaning of the ophiolite. (4) Many basic views of Xigaze ophiolite are mainly from French scholars, such as sill swarms, slow-spreading ridge theory. But, it is to be considered whether these views are right. Xigaze ophiolite has advantageous conditions, we should make proper use of this condition, make our contributions to global ophiolite research.