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Two Types of Archaean Grey Gneiss in North China and Their Geological Significance 1 , 2
Author(s) -
Renmin Wang
Publication year - 1994
Publication title -
acta geologica sinica ‐ english edition
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.444
H-Index - 61
eISSN - 1755-6724
pISSN - 1000-9515
DOI - 10.1111/j.1755-6724.1994.mp7004002.x
Subject(s) - archean , gneiss , geology , geochemistry , granulite , metamorphic rock , greenstone belt , tectonics , geomorphology , seismology , facies , structural basin
Grey gneisses are tonalitic intrusive rocks that have Archaean characteristics and tectonic significance. Archaean grey gneisses in North China may be classified into two types: the Zunhua type and the Hengshan type. Grey gneisses of the Zunhua type alternate with basic granulites, forming a bimodal migmatitic suite. The rock is characterized by complex mineral composition, highly varied REE patterns and positive Eu anomaly and originated from autochthonous or partly autochthonous deep ‐ level migmatization with a high degree (30% ±) of fusion. As the sub ‐ stratum in the root of the early ‐ stage high ‐ grade greenstone belt, they prevented basic rocks from sinking. Grey gneisses of the Hengshan type are characterized by a relatively distinct intrusion form, large ‐ amplitude upward emplacement, rather simple mineral composition, only slight changes of REE patterns and absence of Eu anomaly. The rock is a product of subduction and underthrusting of the high ‐ grade greenstone belt and then fusion and emplacement with a low degree (15% ±) of fusion. In this paper an attempt is made to furnish important information about palaeoplate tectonics and early crustal evolution by means of a study of grey gneisses.