The variations in source rocks and melting conditions of granites can provide essential clues for the crustal magmatic response in orogenic process.Based on geochronology,whole-rock and mineral chemistry,this paper re...The variations in source rocks and melting conditions of granites can provide essential clues for the crustal magmatic response in orogenic process.Based on geochronology,whole-rock and mineral chemistry,this paper reveals two different granites in the Northern Qinling migmatite complex,which reveal obvious differences in source region and melting condition.The older granodiorite(402±0.8 Ma)displays typical Na-rich adakite affinity,i.e.,high Na_(2)O/K_(2)O(2.04 to 2.64)and Sr/Y(96 to 117)ratios,they have relative evolved isotopic compositions(ε_(Nd)(t)=-0.52 to-0.04;zirconε_(Hf)(t)=-0.06 to+7.78).The younger leucogranite(371±2 Ma)displays higher SiO_(2)(72.32 to 73.45 wt%),lower(TFeO+MgO+CaO+TiO_(2))contents(<2 wt%)and depleted Sr-Nd-Hf isotopic compositions(i.e.,ε_(Nd)(t)=+2.6 to+3.0;zirconε_(Hf)(t)=+5.94 to+14.12),as well as high 10000×Ga/Al and TFe O/Mg O ratios,indicating that they represent highly fractionated I-type granites that derived from melting of juvenile crust.The variations in source rocks and melting condition of the two granites indicating a tectonic switch from compression to extension in 400 to 370 Ma,this switch is later than that in the eastern section of the North Qinling,indicating a scissor collision process between the South Qinling and North China Craton(NCC)in Devonian era.展开更多
Zircons were separated from granitoids, gneisses, and sedimentary rocks of the Chinese Altai. Those with igneous characteristics yielded U-Pb ages of 280-2800 Ma, recording a long history of magmatic activity in the r...Zircons were separated from granitoids, gneisses, and sedimentary rocks of the Chinese Altai. Those with igneous characteristics yielded U-Pb ages of 280-2800 Ma, recording a long history of magmatic activity in the region. Zircon Hf isotopic compositions show an abrupt change at ~420 Ma, indicating that prior to that time the magmas came from both ancient and juvenile sources, whereas younger magmas were derived mainly from juvenile material. This may imply that the lithosphere was signifi- cantly modified in composition by a rapid addition of melt from the mantle. We suggest that this dramatic change was due to the onset of ridge subduction, which can account not only for the formation of voluminous granitoids, mafic rocks with complex compositions, and the association of adakite + high-Mg andesite + boninite + Nb-enriched basalt, but also for the coeval high-T, low-P metamorphism.展开更多
The basement rocks in the Kuluketage area are composed predominately of tonalite-trondhjemite-granodiorite rocks, and occured mainly in Xinger and Korla. U-Pb dating of TTG gneiss near Korla yielded a late Neoarchean ...The basement rocks in the Kuluketage area are composed predominately of tonalite-trondhjemite-granodiorite rocks, and occured mainly in Xinger and Korla. U-Pb dating of TTG gneiss near Korla yielded a late Neoarchean weighted mean 207Pb/206Pb age of 2.65 Ga, which is the oldest published age for the TTG rocks in the Kuluketage area and thus suggests that Archean terrane in the area was formed in the late Neoarchean. The Korla gneiss is much younger than the TTG rocks in the northern Altyn Tagh, eastern Tarim Craton, indicating that the oldest terrane of the Tarim Craton was exposed probably in the northern Altyn Tagh. Until late Neoarchean, the Tarim continent extends to the Kuluketage area and finally had generated a relatively large uniform Archean basement within the craton. Zircon Hf isotopic analyses of the TTG gneiss give low εHf(t) values (-5 to 1) with Paleoarchean to Mesoarchean two-stage model ages (TDM2) between 3.0 and 3.3 Ga, suggesting that the basement rocks in the northern Tarim Craton were derived dominately from partial melting of Paleoarchean to Mesoarchean juvenile crustal material. The Hf model ages, therefore, indicate that no continent crust older than 3.3 Ga existed in the Kuluketage area.展开更多
基金supported by the National Natural Science Foundation of China(Grant Nos.41102037,41421002)the Foundation for the Author of National Excellent Doctoral Dissertation of China(Grant No.201324)research grant of State Key Laboratory of Continental Dynamics(Grant No.SKLCD-04)。
文摘The variations in source rocks and melting conditions of granites can provide essential clues for the crustal magmatic response in orogenic process.Based on geochronology,whole-rock and mineral chemistry,this paper reveals two different granites in the Northern Qinling migmatite complex,which reveal obvious differences in source region and melting condition.The older granodiorite(402±0.8 Ma)displays typical Na-rich adakite affinity,i.e.,high Na_(2)O/K_(2)O(2.04 to 2.64)and Sr/Y(96 to 117)ratios,they have relative evolved isotopic compositions(ε_(Nd)(t)=-0.52 to-0.04;zirconε_(Hf)(t)=-0.06 to+7.78).The younger leucogranite(371±2 Ma)displays higher SiO_(2)(72.32 to 73.45 wt%),lower(TFeO+MgO+CaO+TiO_(2))contents(<2 wt%)and depleted Sr-Nd-Hf isotopic compositions(i.e.,ε_(Nd)(t)=+2.6 to+3.0;zirconε_(Hf)(t)=+5.94 to+14.12),as well as high 10000×Ga/Al and TFe O/Mg O ratios,indicating that they represent highly fractionated I-type granites that derived from melting of juvenile crust.The variations in source rocks and melting condition of the two granites indicating a tectonic switch from compression to extension in 400 to 370 Ma,this switch is later than that in the eastern section of the North Qinling,indicating a scissor collision process between the South Qinling and North China Craton(NCC)in Devonian era.
基金Supported by National Basic Research Program of China (Grant No. 2007CB411308)Hong Kong RGC Grants (Grant Nos. HKU704307P and 704004P)+1 种基金National Natural Science Foundation of China (Grant Nos. 40772130, 40803009)CAS/SAFEA International Partnership Program for Creative Research Teams
文摘Zircons were separated from granitoids, gneisses, and sedimentary rocks of the Chinese Altai. Those with igneous characteristics yielded U-Pb ages of 280-2800 Ma, recording a long history of magmatic activity in the region. Zircon Hf isotopic compositions show an abrupt change at ~420 Ma, indicating that prior to that time the magmas came from both ancient and juvenile sources, whereas younger magmas were derived mainly from juvenile material. This may imply that the lithosphere was signifi- cantly modified in composition by a rapid addition of melt from the mantle. We suggest that this dramatic change was due to the onset of ridge subduction, which can account not only for the formation of voluminous granitoids, mafic rocks with complex compositions, and the association of adakite + high-Mg andesite + boninite + Nb-enriched basalt, but also for the coeval high-T, low-P metamorphism.
基金supported by National Basic Research Program of China (Grant No. 2007CB411308)National Natural Science Foundation of China (Grant Nos. 40803009 and 40772130)CAS/SAFEA International Partnership Program for Creative Research Teams
文摘The basement rocks in the Kuluketage area are composed predominately of tonalite-trondhjemite-granodiorite rocks, and occured mainly in Xinger and Korla. U-Pb dating of TTG gneiss near Korla yielded a late Neoarchean weighted mean 207Pb/206Pb age of 2.65 Ga, which is the oldest published age for the TTG rocks in the Kuluketage area and thus suggests that Archean terrane in the area was formed in the late Neoarchean. The Korla gneiss is much younger than the TTG rocks in the northern Altyn Tagh, eastern Tarim Craton, indicating that the oldest terrane of the Tarim Craton was exposed probably in the northern Altyn Tagh. Until late Neoarchean, the Tarim continent extends to the Kuluketage area and finally had generated a relatively large uniform Archean basement within the craton. Zircon Hf isotopic analyses of the TTG gneiss give low εHf(t) values (-5 to 1) with Paleoarchean to Mesoarchean two-stage model ages (TDM2) between 3.0 and 3.3 Ga, suggesting that the basement rocks in the northern Tarim Craton were derived dominately from partial melting of Paleoarchean to Mesoarchean juvenile crustal material. The Hf model ages, therefore, indicate that no continent crust older than 3.3 Ga existed in the Kuluketage area.
