期刊
INTERNATIONAL GEOLOGY REVIEW
卷 64, 期 10, 页码 1431-1449出版社
TAYLOR & FRANCIS INC
DOI: 10.1080/00206814.2020.1818142
关键词
Tonalite-trondhjemite; fractional crystallization; Cambrian magmatism; enclave; interlayer; north Qilian suture zone
类别
资金
- National Natural Science Foundation of China [41903022,91955202]
The late Cambrian tonalite-trondhjemite association in the eastern segment of North Qilian suture zone provides important insights into the sub-arc magmatic process and tectonic evolution, with evidence suggesting that these rocks were likely formed in a continental-arc rifting environment. The geochemical characteristics of these rocks indicate minimal contribution from the continental crust, with a common basaltic parental magma undergoing crystal fractionation in the early stage of subduction due to slab rollback.
The late Cambrian tonalite-trondhjemite association in the eastern segment of North Qilian suture zone (E. NQSZ) is important for understanding of the sub-arc magmatic process and tectonic evolution. Here we report data for feldspar-quartz porphyry and fine-grained trondhjemite with abundant tonalite enclave/interlayer from the Leigongshan (LGS) pluton, and medium-grained tonalite from the Beilinggou (BLG) pluton. Zircon U-Pb ages suggest emplacement of the plutons at ca. 506-481 Ma, associated with early subduction of the North Qilian Ocean. The LGS tonalite enclave/interlayers and trondhjemite hosts share many characteristics in common, including the same mineralogy and texture, similar mineral chemistry, whole-rock trace element ratio and Sr-Nd isotopic compositions. The tonalite enclave/interlayers probably represent quenched blobs/layers of an evolved, tonalitic magma branch resulting from periodic injection of magma into the magma chamber. All the LGS-BLG tonalite-trondhjemites display low abundances of incompatible trace elements (e.g., K, Rb, Th, Zr and REE) and depleted Sr-Nd-Hf isotopes (Sr-87/Sr-86 = 0.707490-0.707840; epsilon(Nd)(t) = +4.0-4.3; zircon epsilon(Hf)(t) = +4.0-13.1), indicating little/no contribution of the continental crust. Geochronological and geochemical consistency between the coeval arc sodium-rich volcanic rocks and studied tonalite-trondhjemites further suggests crystal fractionation of a common basaltic parental magma. The parental magma was generated in continental-arc rifting environments due to slab rollback in the early stage of subduction.
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