摘要
按照花岗岩浆形成的不同方式、条件和过程可将花岗岩分成同熔和改造两个不同的成岩系列。以此为前提,我们发现同时代两个系列花岗岩带常平行成对分布,并与相应时期的B型俯冲或陆内俯冲带构成有规律的平行排布序列;据此提出了孪生花岗岩带的概念,并确定有A型、B型和AB型三种分带型式。本文以东秦岭燕山期孪生花岗岩带为例,系统阐述了产于陆内挤压-俯冲背景下A型孪生花岗岩带的特征、成因及其形成的构造模式,提出A型孪生花岗岩带是陆内挤压-俯冲的必然产物。
In this paper, calc-alkline granites (excluding A-and M-type)are divided into two kinds of petrogenic series according to their different mechanisms of magma generation. Granites of transformation series are the products of partial melting and/or metasomatism of continental rocks at favourite T-P conditions caused by the participation of H_2O-fluids derived from the depth (lower crust and/or upper mantle), which is characterized by a petrologic assemblage of mainly monzogranitic to granitic compositions and often associated closely with migmatites. While those of syntexis series are products of interaction and intermingling between deep sourced magmas and continental materials (rocks and magmas) in the processes of remehing or partial melting of continental rocks at appropriate T-P environments caused by the penetration of magmas at high temperature from the depth (usually from the mantle), which is characterized in petrology by a spectrum from intermediate-basic to acidic species and frequently coexists with cotemporaneous volcanics.
Based on this classification, the regularities of two series of granite belts related to B-type subduction and intracontinental eompression-subduction have been comprehensively studied. It is found that granites of two series often alingned in double zones parallel to cotemporaneous B-type subduction or intracontinental compression-subduction zones within ascending slabs to form regular zonations together with subduction zones, which is called twin granite belts. According to spatial relations between granite belts and subduction zones, twin granite belts could be distinguished into A-type, AB-type and B-type.
The zonation of granites of two series in northern part of East Qinlin area, which is related to Yanshanian intracontinental compression-subduetion, is one of typical examples of A-type twin granite belts. Detailed studies have revealed that during Yenshanian aera, a northward intracontinental subduction had occurred along the intracontinental decollement-subduction zone which is formed by intensive compression in S-N direction and, in shallow crust, divided into three large-scale ductile fault systems:Shangdan, Zhuxia and Waxuczi.Accompanied with the tectonic movement, double-granite belts (both aged 170～90Ma.) parellel to the subduction zone were developed within obducted slab, Laojunshan-Manglin batholith belt is near the subduction zone and is proved to be transformation series rock belt, Jinduicheng-Nannihu porphyry cupola and subvolcanic pipe belt is a little farther away from the subduction zone, and is proved to be syntexis one.Therefore a zonation of decollement-subduction zone→transformation series batholith zone→syntexis series porphyry zone was recognised in the area, which is a typical zonation of A-type twin granite belts developed in intracentinental compression-subduction environments.
In the paper, the tectonic setting and petrogenic features of the Yanshanian twin granite belts in East Qinlin area have been systematically elucidated, and a tectonic model for granitic magma genesis in intracontinental compression-subduction environment has been proposed.In this model the formation of A-type twin granite belts and its tectonic movement are closely connected with one another from the principles, rules and dynamics of material differentiation in lithosphere.
出处
《岩石学报》
SCIE
EI
CAS
CSCD
北大核心
1990年第1期1-12,共12页
Acta Petrologica Sinica
关键词
花岗岩
陆内俯冲
成因
Granite
Genetic series
Distribution regularities
Plate teetonies
Intracontinental subduction
East Qinlin
