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- Title
长江中下游—大别造山带中生代火山岩特征及成因.
- Authors
闫峻
- Abstract
Mesozoic magmatism occurred extensively in the middle and lower reaches of the Yangtze River and the Dabie orogenic belt in central-eastern China, and the volcanic rocks were all concentrated in the middle stage, with ages of 135-127 Ma and 133-125 Ma, respectively. Many Mesozoic volcanic basins in the middle and lower reaches of the Yangtze River develop high-potassium calc-alkaline bimodal volcanic rocks and intermediate-basic olivine-andranite volcanic rocks. These rocks are enriched in large-ion lithophile elements, depleted in high-field-strength elements, weakly enriched in Sr-Nd-Hf isotopes, and have high radiogenic Pb isotopic compositions, indicating the addition of crustal components in the mantle source region. Among them, the intermediate-basic volcanic rocks originated from the enriched lithospheric mantle and were metasomatized by the hydrous melt precipitated by the subducting oceanic slab, and the ultra-alkaline volcanic rocks in the late stage originated from the asthenospheric mantle metasomatized by similar metasomatous media, indicating the magma source area deepening. The Mesozoic volcanic rocks in the Dabie orogenic belt include high-potassium calc-alkaline series and ultra-potassium series, all of which are enriched in large-ion lithophile elements, depleted of high-field-strength elements, highly enriched in Sr-Nd-Hf isotopes, and have low radiogenic Pb isotopes The composition is significantly different from that in the middle and lower reaches of the Yangtze River. Among them, the high-potassium calc-alkaline volcanic rocks originated from the metasomatically enriched lithospheric mantle, and the metasomatous medium was the precipitated melt of the South China continental crust that was deeply subducted in the Indosinian period, while the ultrapotassium volcanic rocks in the late stage originated deeper and were deeply subducted. Under high pressure, the South China continental crust decomposed polysilicon muscovite to produce the mantle source region of melt metasomatism. The mantle-derived volcanic rocks in the middle and lower reaches of the Yangtze River record the direct material contribution of the subducted Paleo-Pacific plate, while the mantle source region in the Dabie orogenic belt records the information of the Indosinian subducted continental crust. The volcanic rocks of the two tectonic units both showed the deepening of the magma source area in the early and late stages. The middle and lower reaches of the Yangtze River corresponded to the low-angle subduction of the Paleo-Pacific plate and the rewinding of the subducted slab (about 130 Ma), while the Dabie orogen was in the Under the dynamic mechanism of the subduction and rollback of the ancient Pacific plate, the collapse of the orogenic belt and the delamination of the lithosphere occurred.
- Publication
East China Geology / Huadong dizhi, 2022, Vol 43, Issue 4, p375
- ISSN
2096-1871
- Publication type
Article
- DOI
10.16788/j.hddz.32-1865/P.2022.04.001