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Indosinian Tectonic Setting of the Southern Yidun Arc: Constraints from SHRIMP Zircon Chronology and Geochemistry of Dioritic Porphyries and Granites
Author(s) -
Shuwen LIU,
Zongqi WANG,
Quanren YAN,
Qiugen LI,
Dehui ZHANG,
Jianguo WANG,
Bin YANG,
Libing GU,
Fengshan ZHAO
Publication year - 2006
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.1755-6724.2006.tb00256.x
Subject(s) - zircon , geology , geochemistry , craton , petrogenesis , oceanic crust , subduction , crust , continental crust , partial melting , mantle wedge , continental margin , mantle (geology) , petrology , tectonics , paleontology
A mass of granitoid and dioritic intrusions are distributed in the southern Yidun Arc, among which the representative Indosinian intrusions include the Dongco and Maxionggou granitoid intrusions in Daocheng County and hypabyssal intrusions intruding into arc volcanic rocks near the Xiangcheng town. The Dongco and Maxionggou granitoid intrusions consist mainly of porphyraceous monzogranites, megacryst monzogranites and aplite granites. The Xiangcheng hypabyssal intrusions are composed dominantly of dioritic porphyries. SHRIMP zircon ages of 224±3 Ma and 222±3 Ma have been obtained for the Dongco granitoid intrusion and the Xiangcheng dioritic porphyries, respectively. The Xiongcheng dioritic porphyries show a calc‐alkaline geochemical feature, and are characterized by higher Sr/Y ratios, depletive Nb, Ta, P and Ti, enriched LILEs, and lower ɛ Nd ( t ) (= −3.27), suggesting that they might be derived from mantle source magmas that were obviously contaminated by continent crustal materials. However, the Dongco and Maxionggou granitoids belong to high‐potassium calcalkaline series with a per‐metaluminous feature, and are characterized by higher CaO/(σFeO+MgO) and Al 2 O 3 /(σFeO+ MgO) ratios, lower (La/Yb) n and Sr/Y ratios, depletive Nb, Ta, Sr, P and Ti, enriched LILEs, and very low ɛ Nd ( t ) (= −8.10), indicating that the granitoids might be derived from partial melting of continental crust materials mainly of graywacke. Petrogenesis of Dongco and Maxionggou granitoids implies that there was an oceanic crust between the Zongza continental block (ZCB) and western margin of the Yangtze Craton (WMYZC). And the oceanic crust slab subducted westward during the Indosinian Epoch, producing an Andes‐type continent marginal arc and a back‐arc basin at the WMSCC. Then the oceanic basin closed and a sinistrally lateral collision occurred at ca. 224 Ma‐222 Ma between the ZCB and the WMYZC, causing partial melting of sediments in the back‐arc basin to generate granitoid magmas of the Dongco and Maxionggou intrusions