碱性岩及碱性与亚碱性岩系列的界线——基于全球火山岩数据的探讨

Alkaline rock and the distinction between alkaline and sub-alkaline: A discussion on data of global volcanic rocks

国际地球科学联合会规定,碱性岩必须要有实际碱性矿物和/或似长石出现作为标志,但同时又同意TAS图中B区的玄武岩可以细分为碱性玄武岩和亚碱性玄武岩,取决于它们是否有标准矿物霞石出现。有标准矿物霞石出现的玄武岩归入碱性玄武岩,夏威夷岩有霞石标准矿物出现,是碱性玄武岩。碱性玄武岩和夏威夷岩分别出现在TAS图上的两个区(碱性玄武岩在B区,夏威夷岩在S1区),这是否存在概念上的混乱?早先学术界关于碱性和碱性岩的定义并不完美,由许多学者厘定的碱性-亚碱性的界线区分的不是拉斑与碱性系列,而是正常系列与粗玄岩系列。采用全球火山岩数据考察TAS图及碱性-亚碱性界线,发现碱性与碱性岩在术语的解释上存在瑕疵并提出解决的方案。

What is the true meaning of commonly used alkaline and sub-alkaline curves?It is reasonable for the International Union of Geological Sciences to make the requirement that alkaline rocks must have actual alkaline minerals and/or feldspar appearance as markers.However,the International Union of Geological Sciences also agrees that the basalt in area B of the TAS diagram could be subdivided into alkaline basalt and sub-alkaline basalt,depending on whether they have standard mineral nepheline.The basalt of the standard mineral nepheline is classified as alkaline basalt,while the Hawaiian rock is the alkaline basalt,due to the existence of standard minerals of nepheline.Why do they appear in the two districts on the TAS diagram(alkaline basalt in area B,Hawaiian Rock in the S1 area),and is this a conceptual confusion?It seems that the previous academic definition of alkaline and alkaline rock is somewhat confusing,the alkaline-sub-alkaline boundary determined by many experts is not the tholeiite and alkaline series,but is between normal series and dolerite series.In this paper,the global volcanic rock data are used to investigate TAS diagram and alkaline-sub-alkaline boundary,and it is found that alkaline and alkaline rocks are defective in the interpretation of terms and thus this paper proposes solutions.This matter involves the basic theory of petrology,to which the academia should pay more attention.