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Carboniferous Post‐collisional Rift Volcanism of the Tianshan Mountains, Northwestern China
Author(s) -
Linqi XIA,
Xueyi XU,
Zuchun XIA,
Xiangmin LI,
Zhongping MA,
Lishe WANG
Publication year - 2003
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.1755-6724.2003.tb00751.x
Subject(s) - geology , rift , carboniferous , geochemistry , mantle plume , volcanic rock , partial melting , mantle (geology) , igneous rock , fractional crystallization (geology) , large igneous province , silicic , lithosphere , volcano , petrology , paleontology , tectonics , magmatism , structural basin
Abstract The Tianshan Carboniferous post‐collisional rift volcanic rocks occur in northwestern China as a large igneous province. Based on petrogeochemical data, the Tianshan Carboniferous post‐collisional rift basic lavas can be classified into two major magma types: (1) the low‐Ti/Y type situated in the eastern‐central Tianshan area, which exhibits low Ti/Y (<500), Ce/Yb (<15) and SiO 2 (43–55%), and relatively high Fe 2 O 3 T (6.4–11.5%); (2) the high‐Ti/Y type situated in the western Tianshan area, which has high Ti/Y (>500), Ce/Yb (>11) and SiO 2 (49–55%), and relatively low Fe 2 O 3 T (5.8–7.8%). Elemental data suggest that chemical variations of the low‐Ti/Y and high‐Ti/Y lavas cannot be explained by fractional crystallization from a common parental magma. The Tianshan Carboniferous basic lavas originated most likely from an OIB‐like asthenospheric mantle source ( 87 Sr/ 86 Sr( t ) ∼ 0.703–0.705, ε Nd ( t ) ∼ +4 to +7). The crustal contamination and continental lithospheric mantle have also contributed significantly to the formation of the basic lavas of the Tianshan Carboniferous post‐collisional rift. The silicic lavas were probably generated by partial melting of the crust. The data of this study show that spatial petrogeochemical variations exist in the Carboniferous post‐collisional rift volcanics province in the Tianshan region. Occurrence of the thickest volcanics dominated by tholeiitic lavas may imply that the center of the mantle‐melting anomaly (mantle plume) was in the eastern Tianshan area at that time. The basic volcanic magmas in the eastern Tianshan area were generated by a relatively high degree of partial melting of the mantle source around the spinel‐garnet transition zone, whereas the alkaline basaltic lavas are of the dominant magma type in the western Tianshan area, which were generated by a low degree of partial melting of the mantle source within the stable garnet region, thus the basic lavas of the western Tianshan area might have resulted from relatively thick lithosphere and low geothermal gradient.