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Petrogenesis and Crust-Mantle Interaction of Mid-Triassic Yangba Pluton from Kangxian in Gansu Province(PDF)

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

Issue:
2006年第02期
Page:
11-18
Research Field:
Publishing date:

Info

Title:
Petrogenesis and Crust-Mantle Interaction of Mid-Triassic Yangba Pluton from Kangxian in Gansu Province
Author(s):
QIN Jiang-feng; LAI Shao-cong; BA I Li
Department of Geology, Northwest University, Xi’an 710069, Shaanxi, China
Keywords:
Yangba Pluton;  Mid-Triassic;  magmatic mixing;  crust-mantle interaction;  crust growth;  Gansu Province
PACS:
P588.1
DOI:
-
Abstract:
The Yangba granodiorite pluton, located in Yangba Town, southern Kangxian, Gansu Province, NW China, presents the typical geological and petrographical features of mixing of two different magmas in composi- tion. Melanocratic magmatic enclaves are well developed in the pluton. They are mainly fine-grained or micro- granular diorites and quartz diorites, and have clear contact border with host rocks. Some features suggest that the magmatic enclaves have quenched rim texture: long-pillared hornblende; long-sheeted biotite; acicular apa- tite; corrosion borders of plagioclase xenocrysts and quartz aggregates in the enclaves. The detailed studies of pe- trology and geochemistry conclude that the micrograular enclaves are characterized by higher(La/Yb)N(32.82～ 51. 78), higher Rb/Sr(0.11～ 0.27)and lowerδ(Eu)(0.75～ 0.84)than host rock((La/Yb)N= 22.18～ 29.51, Rb/Sr= 0.085～ 0.107,δ(Eu)= 0.84～ 0.89). Hence, it is impossible to regard the microgranular enclaves as refractory residue. The high Mg# of both enclave and host rock(enclave Mg#= 55.6～ 60.1, host rock Mg#= 50. 8～ 54.5)suggest that the microgranular enclaves are mantle-derived and host rocks are lower crust melts which are contaminated by mantle-source materials. Combining with petrographical evidence, it can be infered that the microgranular enclaves are the products of quenching and crystallization of hot, mantle-derivered mafic magma intruding granodiorite magma chamber. Therefore the hybrid petrogenesis of Yangba pluton suggests an important crust-mantle interaction and crust vertical growth of northwestern Yangtze Plate during Mid-Triassic.

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Last Update: 2006-06-20