HR: 1340h
AN: V13A-0511    [Abstracts]
TI: Spot U-Pb and Hf Isotope Analyses of Detrital Zircons from the Khondalites in the Western Block of the North China Craton
AU: Xia, X
EM: xpxia@hotmail.com
AF: Department of Earth Sciences, the University of Hong Kong, Pokflam road, Hong Kong, 086-02 China
AU: * Sun, M
EM: minsun@hkucc.hku.hk
AF: Department of Earth Sciences, the University of Hong Kong, Pokflam road, Hong Kong, 086-02 China
AU: Zhao, G
EM: gzhao@hkucc.hku.hk
AF: Department of Earth Sciences, the University of Hong Kong, Pokflam road, Hong Kong, 086-02 China
AU: Luo, Y
EM: luoyan@hkusua.hku.hk
AF: Department of Earth Sciences, the University of Hong Kong, Pokflam road, Hong Kong, 086-02 China
AB: High-grade metapelitic rocks, named khondalites, occur along the north margin of the Ordos Terrane, the Western Block of the North China Craton. Their provenance is considered to be the basement of this terrane, which is covered by Mesozoic-Cenozoic basin sediments. Detrital zircons from khondalites of Jining and Wulashan Complexes were analyzed by LA-ICPMS in this study. Most of the detrital zircons yield U-Pb ages of 1.9-2.1 Ga, showing that Paleoproterozoic rocks were predominant in their provenance. Their maximum depositional age and metamorphic ages are constrained to be 1.84 and 1.81 Ga, respectively. Hf isotope analysis was conducted on detrital zircons from the Wulashan khondalite. ݏHf values vary between -8 and +9, suggesting crystallization of zircons from magmas derived from underlying old crust and juvenile materials from the mantle. The lowest ݏHf values with different ages define an evolutionary line that intersects the depleted mantle line at about 2.6 Ga in a ݏHf vs. time diagram. This implies that rocks extracted from the depleted mantle at about 2.6 Ga may be predominant in the lower crust. All detrital zircons from one sample have U-Pb ages exclusively at about 2.0 Ga and possess positive ݏHf from +1 to +9, clearly recording a significant juvenile crustal growth event at about 2.0 Ga. The above results suggest that the Ordos Terrane of the Western Block may have a major crustal extraction at about 2.6 Ga and a significant juvenile crustal growth at about 2.0 Ga. This is in striking contrast with the Eastern Block, where Archean rocks are important in the basement. Therefore, our data clearly demonstrate that the Ordos Terrane developed separately from the Eastern Blocks, until they collided to form the coherent North China Craton.
DE: 3600 MINERALOGY AND PETROLOGY
DE: 3620 Mineral and crystal chemistry (1042)
DE: 3630 Experimental mineralogy and petrology
DE: 3660 Metamorphic petrology
DE: 3694 Instruments and techniques
SC: Volcanology, Geochemistry, Petrology [V]
MN: Fall Meeting 2005