Geochronology and Geochemistry of the Neo-Proterozoic Amphibolites in the Muqitan Formation: Implications for the Tectonic Evolution of North Qinling Orogen
详细信息
- 责任者：Zhang Zhiguo (School of Engineering and Technology ; China University of Geosciences ; Beijing 100083 ; China) ; Chen Junlu
- 刊名：Acta Petrologica Sinica
- 出版年：2011
- 卷期：27(3)
- 关键词：角闪岩 ; amphibolites ; 玄武岩 ; basalts ; 岩石地球化学 ; lithogeochemistry ; 秦岭 ; Qinling Mountains
- 页码：p.757-769
- 图表：12 illus., 4 tables, 51 refs.
- 分类号：0801
- issnNo：ISSN1000-0569
- isbnNo：CN11-1922/P
摘要
The Muqitan ophiolitic mélange found within the Muqitan Formation near Muqitan region, the North Qinling Orogen. They mainly consist of amphibolite with minor meta-gabbro and meta-chert. Zircon LA-ICP-MS U-Pb dating yields an age of (762.5±4.6) Ma for the amphibolites, interpreted as crystallization time. The amphibolites are characterized by low TiO2 (0.57% ～2.16%), relatively low K2O/Na2O ratios (0.06～0.55) and moderate-high Mg# (45.3～68.7). They are geochemically similar to low Ti tholeiites. The Muqitan amphibolites have low REE contents, with differentiated LREE/HREE patterns and no Eu anomalies on the chondrite-normalized REE diagram, analogies to E-MORB. The amphibolites display an enrich elements Rb, Ba, Th, and La pattern, low (87Sr/86Sr)i ratios of 0.703 8 to 0.704 0 and high εNd(t) values of +4.1 to +6.9, suggesting a mantle origin, similar in composition to FOZO-like source. Their (Th/Nb)N, Nb/La and Ba/La ratio features indicate that these amphibolite have been experienced varying degrees of crustal contamination. All these data, combined with the regional geological features demonstrate that the Muqitan amphibolites are interpreted as remnants of the Shangdan ancient oceanic crust that would have formed during the inception of the oceanic open at ca. (762.5±4.6) Ma.