HR: 0800h
AN: V51C-0722    [Abstracts]
TI: Early Cretaceous Erlangmiao Metaluminous A-type Granite in the Eastern Qinlin Orogen, central China: Geochronological and Geochemical Constraints
AU: * Zhang, J
EM: geomantleflow@163.com
AF: Faculty of Earth Sciences, China University of Geosciences, No. 388 Lumo Road, Hongshan District, Wuhan, 430074, China
AU: Ma, C
EM: cqma@cug.edu.cn
AF: Faculty of Earth Sciences, China University of Geosciences, No. 388 Lumo Road, Hongshan District, Wuhan, 430074, China
AU: Ma, C
EM: cqma@cug.edu.cn
AF: State Key Laboratory of Geological Processes and Mineral Resources, No. 388 Lumo Road, Hongshan District, Wuhan, 430074, China
AU: Sher, Z
EM: zbsher@cug.edu.cn
AF: Faculty of Earth Sciences, China University of Geosciences, No. 388 Lumo Road, Hongshan District, Wuhan, 430074, China
AU: Sher, Z
EM: zbsher@cug.edu.cn
AF: State Key Laboratory of Geological Processes and Mineral Resources, No. 388 Lumo Road, Hongshan District, Wuhan, 430074, China
AU: Wang, S
EM: aaawsm11@163.com
AF: Faculty of Earth Sciences, China University of Geosciences, No. 388 Lumo Road, Hongshan District, Wuhan, 430074, China
AU: Wang, L
EM: wanglianxun16@163.com
AF: Faculty of Earth Sciences, China University of Geosciences, No. 388 Lumo Road, Hongshan District, Wuhan, 430074, China
AU: Cao, Y
EM: Yunchengcao@163.com
AF: Faculty of Earth Sciences, China University of Geosciences, No. 388 Lumo Road, Hongshan District, Wuhan, 430074, China
AB: It is possible to study the Mesozoic lithospheric thinning and crust-mantle interaction due to Early Cretaceous intensive magmatism widely developed in the North China Block. As an important part of the Early Cretaceous magmatism in the North China Block, the widespread Early Cretaceous granites in the Dabieshan-Qinlin Orogen, situated in the southern margin of the North China Block, contain hornblende and/or biotite and are I-type granites, but other type granites are less reported. Early Cretaceous Erlangmiao garnet granite (EGG) with garnet and biotite found recently near Erlangmiao in Fangcheng County, Henan Province, China, has provided new constraints for evolvement of the Dabie-Qinlin Orogen. This abstract reports results of zircon U-Pb dating, elemental geochemistry, and Sr-Nd isotopic compositions of the EGG and its wall rocks in an attempt to constrain its petrogenesis and the Early Cretaceous tectonic evolution of the Dabie-Qinlin Orogen. The EGG, located in the eastern Qinlin Orogen, was emplaced in gneissic monzogranites (GG). There are abundant GG xenoliths and surmicaceous enclaves in the eastern margin of the stock. LA-ICPMS zircon U-Pb dating of the EGG suggests its crystallization at 118 ±2 Ma, whole-rock Rb-Sr isochron age, represented the cooling age of the EGG, is 110±1 Ma. The EGGs are syenogranites with almandine-Spessartine garnet and biotite. The EGGs are characterized by high SiO₂ and alkali contents, high FeOt/MgO ratio, low Al₂O₃ and CaO contents, and display high-K calc-alkaline and metaluminous characteristics. They show low total Rare Earth Element content (ΣREE), strong negative Eu anomaly, are generally enriched in Rb, Th, Ta, Nb, Zr, Hf, Y, Yb and depleted in Sr, Ba, Ce, P, Ti, and have high Rb, Rb/Sr and Ga/Al ratios. Al₂O₃, Fe₂O₃, K₂O, Zr, Rb, Pb of the EGGs decrease with increasing SiO₂ content. Initial ⁸⁷Sr/⁸⁶Sr ratios of the whole rocks range in 0.706-0.708, while the εNd(110Ma) values vary from -6.6 to -9.0 and Nd depleted mantle model ages are 1.5-1.7 Ga. Geochemistry and modal calculations suggest the EGGs are metaluminous A-type granites, underwent fractional crystallization of plagioclase, allanite and apatite, and formed in extensive background. We suggest the formation of the EGG is related to Early Cretaceous asthenosphere upwelling and lithosphere extension in Eastern China. The GGs-wall rocks of the EGG, crystallized at 128±2 Ma according to LA-ICPMS zircon U-Pb method, display metaluminous and high- K calc-alkaline characteristics. The GGs have high ΣREE, Sr/Y and (La/Yb)_N ratios, show middle negative Eu anomaly, are enriched in Light REE, Rb, Sr, Ba and depleted in Ta, Nb, Zr, Hf, Ti, P, Y. The isotope is homogeneous, Initial ⁸⁷Sr/⁸⁶Sr ratios of the whole rocks are 0.707, the ε Nd(130Ma) values are -11.2 and Nd depleted mantle model ages are about 1.9 Ga. It suggested that partial melting of crustal rocks may form high-temperature A-type granites. Comparing the characteristics of the EGGs and the GGs, we suggest that partial melting of the GGs formed the EGGs influenced by asthenosphere upwelling.
DE: 8109 Continental tectonics: extensional (0905)
DE: 8178 Tectonics and magmatism
SC: Volcanology, Geochemistry, Petrology [V]
MN: 2007 Fall Meeting