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Characteristics and tectonic environment of Zhigoumen pluton in Longshoushan area(PDF)

《地球科学与环境学报》[ISSN:1672-6561/CN:61-1423/P]

Issue:
2005年第02期
Page:
5-11
Research Field:
Publishing date:

Info

Title:
Characteristics and tectonic environment of Zhigoumen pluton in Longshoushan area
Author(s):
HU Neng-gao; XU An-dong; YANG Jia-xi
Shcool of Earth Sciences and Resources Management,Chang’an University , Xi’an 710054,China
Keywords:
Qilian Fold Belt ; post-collision granite ; tectonic enviromment ; anatexis ; Gansu Province
PACS:
P588.1
DOI:
-
Abstract:
The Zhig oumen pluto n(age of 374 ±38 Ma), intr uded into the Long shoushan Gro up a t the wester n ma rgin of the No r th China Plate , is composed dominantly of g ranite , mo nzog ranite et al. . On the basis of the field relations and pet rog raphic data , the pluto n can be divided into three units fr om ear ly to late :Zhig oumen unit , Wa nw anjua n unit a nd Maluw an unit. The ro cks of the pluton have w(SiO2)=65. 94 %～ 75. 18 %, w(K2O)=2. 36 %～ 4. 35 % and w(Na2O)=3. 53 %～ 5. 47 %, w (CaO), w(TFeO) and w(MgO) decrease with increasing w(SiO2). All r ocks are moderately per aluminous with ANKC of 1. 01～ 1. 09, and magmatic type belo ng s to calc-alkalic series with σ=1. 99～ 2. 64 and Peaco ck index =55. 6. As compa red with ty pical g ranites , the trace elements of Li, Cs and Rb are low er , a nd S r and Ba higher . There is, from ea rly to la te units , a weakly tendency of decrease in Rb /Sr and increa se in Sr , Ba , Co and Ba /K. The Wanw anjua n unit is simila r to the Maluw an unit in Σ REE(152. 11～ 171. 94×10-6),δEu(0. 91 ～ 1. 10)and REE patter n, but the Zhig oumen unit differ s from them , it ha s low er ΣREE(46. 62×10-6)), low er ΣLREE / ΣH REE(3. 53)and hig he r δEu(1. 60). Gener ally , La is po sitive ly cor related to La /Sm , and δEu and Σ REE v ary consistently w ith DI. The Zhig oumen pluto n, formed after the co llision stage of the Qinling Fold Belt , be long s to po st-collisio n g ra nite ty pe , because the rocks a re simila r to the gr anites of the Lachlan Fold Belt in the plots such as w (Cao)/ w (Na2O) vs. w(Al2O3)/ w (TiO2). I t is po ssible that the Zhigo umen pluto n is derived fr om the me lting of the subducted v olca nic rocks of the Qilian Fold Belt.

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