We present zircon ages and geochemical data for the Hongshishan Carboniferous Alaskan-type mafic–ultramafic complex exposed in the Beishan area along the Sino–Mongolian boundary, southern margin of the Central Asian...We present zircon ages and geochemical data for the Hongshishan Carboniferous Alaskan-type mafic–ultramafic complex exposed in the Beishan area along the Sino–Mongolian boundary, southern margin of the Central Asian Orogenic Belt. This complex mainly consists of dunite,harzburgite, lherzolite, wehrlite, and gabbro, which intrudes Early Carboniferous volcanic rocks and reveals a zoned structure. Zircons of a gabbro sample yielded a 206Pb/238 U age of 357 ± 4 Ma, reflecting the time of Early Carboniferous magmatism. Zircon ages were also obtained for an andesite(322 ± 3 Ma) and a basaltic andesite(304 ± 2 Ma).High initial Nd isotope whole-rock values suggest that the Hongshishan gabbro [e_(Nd(t))= +9.6-+10.2] and basalt[eNd(t)= +10.0-+10.8] were derived from a depleted mantle source. Slightly lower eNd(t)values for the ultramafic rocks [eNd(t)= +8.5-+8.7] suggest some interaction of the parental magma with the continental crust. In contrast, the Late Carboniferous Quershan samples in this area represent subduction-related arc volcanic rocks with Adakite-like compositions. The early Carboniferous Hongshishan Alaskan-type complex was interpreted to represent the remnants of a magma chamber that crystallized at the base of a mature island arc, whereas the Quershan island arc volcanic rockssuggest the resurrection of the subduction process after arccontinent collision and uplift of the roots of the arc.展开更多
In the Dabudaer region of the Tianshuihai Massif （Xinjiang, Northwest China）, metavolcanic rocks within the mainly meta- sedimentary Bulunkuoler Group are basalt, basaltic andesite, and rhyolite. In situ zircon U-Pb...In the Dabudaer region of the Tianshuihai Massif （Xinjiang, Northwest China）, metavolcanic rocks within the mainly meta- sedimentary Bulunkuoler Group are basalt, basaltic andesite, and rhyolite. In situ zircon U-Pb LA-ICP-MS dating on rhyolite magmatic zircons yielded an age of 2481±14 Ma, interpreted as the eruption age of the Bulunkuoler Group volcanic rocks. The basalt and basaltic andesite are low-A1 tholeiite series and the rhyolite is low-Al calc-alkaline series. All of rocks are charac- terized by enrichment of LREE and LILE （Rb, Th and Ba）, depletion of P, Nb, Ta and Ti, and absence of Eu anomalies. The Cnd（t） of basalts ranges from 3.14 to 4.88 indicating a depleted mantle source. The trace element signatures show that these magmas experienced intense crustal contamination during their ascent. Direct evidence for crustal contamination is the xenocrystic zircons in the ryholite, with ages back to ca. 3300 Ma. The primitive-mantle normalized and Zr/Y-Zr diagrams for the basic volcanic rocks show that they formed in an intra-continental tectonic setting. Combined with the previous studies and compared with North China Craton Neoarchean basic volcanic rocks, it is supposed that the Bulunkuoler Group volcanic rocks reflect the Palaeoproterozoic mantle magma underplating and interaction with felsic crust.展开更多
基金financially supported by the National Natural Science Foundation of China (Grant Nos.40703012,41030314)Geological Survey of China (Grant Nos.1212011120332,DD20160123-05)Chinese Ministry of Science and Technology (Grant 2012FY120100)
文摘We present zircon ages and geochemical data for the Hongshishan Carboniferous Alaskan-type mafic–ultramafic complex exposed in the Beishan area along the Sino–Mongolian boundary, southern margin of the Central Asian Orogenic Belt. This complex mainly consists of dunite,harzburgite, lherzolite, wehrlite, and gabbro, which intrudes Early Carboniferous volcanic rocks and reveals a zoned structure. Zircons of a gabbro sample yielded a 206Pb/238 U age of 357 ± 4 Ma, reflecting the time of Early Carboniferous magmatism. Zircon ages were also obtained for an andesite(322 ± 3 Ma) and a basaltic andesite(304 ± 2 Ma).High initial Nd isotope whole-rock values suggest that the Hongshishan gabbro [e_(Nd(t))= +9.6-+10.2] and basalt[eNd(t)= +10.0-+10.8] were derived from a depleted mantle source. Slightly lower eNd(t)values for the ultramafic rocks [eNd(t)= +8.5-+8.7] suggest some interaction of the parental magma with the continental crust. In contrast, the Late Carboniferous Quershan samples in this area represent subduction-related arc volcanic rocks with Adakite-like compositions. The early Carboniferous Hongshishan Alaskan-type complex was interpreted to represent the remnants of a magma chamber that crystallized at the base of a mature island arc, whereas the Quershan island arc volcanic rockssuggest the resurrection of the subduction process after arccontinent collision and uplift of the roots of the arc.
基金supported by the China Geological Survey (Grant No. 1212010610102)National Natural Science Foundation of China (Grant No. 40872084)
文摘In the Dabudaer region of the Tianshuihai Massif （Xinjiang, Northwest China）, metavolcanic rocks within the mainly meta- sedimentary Bulunkuoler Group are basalt, basaltic andesite, and rhyolite. In situ zircon U-Pb LA-ICP-MS dating on rhyolite magmatic zircons yielded an age of 2481±14 Ma, interpreted as the eruption age of the Bulunkuoler Group volcanic rocks. The basalt and basaltic andesite are low-A1 tholeiite series and the rhyolite is low-Al calc-alkaline series. All of rocks are charac- terized by enrichment of LREE and LILE （Rb, Th and Ba）, depletion of P, Nb, Ta and Ti, and absence of Eu anomalies. The Cnd（t） of basalts ranges from 3.14 to 4.88 indicating a depleted mantle source. The trace element signatures show that these magmas experienced intense crustal contamination during their ascent. Direct evidence for crustal contamination is the xenocrystic zircons in the ryholite, with ages back to ca. 3300 Ma. The primitive-mantle normalized and Zr/Y-Zr diagrams for the basic volcanic rocks show that they formed in an intra-continental tectonic setting. Combined with the previous studies and compared with North China Craton Neoarchean basic volcanic rocks, it is supposed that the Bulunkuoler Group volcanic rocks reflect the Palaeoproterozoic mantle magma underplating and interaction with felsic crust.
