Premium
Geochemistry and chronology of the granites in Alasituo, west Tianshan Orogen: Implications for a magma mixing origin
Author(s) -
Han Yixiao,
Liu Yunhua,
Zhou Saifang,
Teng Fei,
Wei Juzhen,
Tian Runqing
Publication year - 2018
Publication title -
geological journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.721
H-Index - 54
eISSN - 1099-1034
pISSN - 0072-1050
DOI - 10.1002/gj.3216
Subject(s) - mafic , silicic , geology , geochemistry , zircon , igneous differentiation , magma , volcanic rock , felsic , basalt , volcano
There are intense magmatic activities in the Alasituo integrated gold exploration area, west Tianshan Orogen. On the basis of field characteristics, geochemistry features, and chronology in Alasituo, the formation mechanism of complex granite rocks was explored. The intrusive rocks are divided into 3 parts: a silicic endmember, a mafic endmember, and intermediate rocks. Mafic microgranular enclaves, as well as spotted structure, silicic veins intruding mafic rocks and plagioclase xenocrysts, developed in rocks. Under the microscope, there are many unbalanced mineral combinations, needle‐like apatites, and poikilitic structures. Futhermore, there is an obvious linear trend between the mafic endmember samples, intermediate samples, and the silicic endmember samples in Harker diagrams. All samples were evolved from magma mixing in TFe 2 O 3 ‐MgO diagram. The trace element concentrations of intermediate rocks have the transitional features of both silicic and mafic endmember rocks. The above characteristics show that rocks have experienced low degree and uneven physical and chemical magma mixing. The silicic endmember rocks have a high content of K 2 O + Na 2 O, Zr, Nb, Y, and REE; high Ga/Al ratios, and; low content of Sr, Eu, Ti, and P, which have the characteristics of A‐type granites with a crustal source. The high content of MgO, TFe 2 O 3, and low K 2 O/Na 2 O in mafic endmember rocks indicate a mantle source. The LA‐ICP‐MS U–Pb zircon age of the granodiorites is 350.3 ± 3.0 Ma. Combined with regional geological background and geochemical characteristics, the intrusive rocks were formed when the thinning lithosphere triggered mafic magma underplating, heating upper crust granites, and causing them partial melt.