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Archean crustal evolution of the Jiaodong Peninsula, China, as revealed by zircon SHRIMP geochronology, elemental and Nd-isotope geochemistry

Bor-ming Jahn^*, Dunyi Liu^**,,, Yusheng Wan^**,, Biao Song^**, and Jiashan Wu

^* Institute of Earth Sciences, Academia Sinica, Taipei 115, Taiwan
^** Beijing SHRIMP Center, Beijing 100037, China
Institute of Geology, Chinese Academy of Geological Sciences, Beijing, 100037, China

jahn{at}earth.sinica.edu.tw

Corresponding author: liudunyi{at}bjshrimp.cn

The Jiaodong Terrane in eastern Shandong Province is an important part of the Eastern Block of the North China Craton (NCC). In order to better understand the Precambrian crustal evolution of the NCC, we conducted a study of zircon geochronology, bulk-rock elemental and Nd-isotope geochemistry on gneisses and granodiorites from the Jiaodong Terrane. Zircon U-Pb SHRIMP analyses on biotite leptites and TTG gneisses yielded two groups of ages, one at ca. 2.90 Ga, and the other at 2.71 to 2.73 Ga. The new age results establish the existence of Mesoarchean and Neoarchean continental crust in the Jiaodong Terrane. The association of leptites, interpreted as metadacitic rocks, and TTG gneisses at 2.9 Ga was likely generated in an island-arc system, hence implying that plate tectonics, similar to the modern regime, was operative during the Mesoarchean. On the other hand, the results also indicate that the period of 2.71 to 2.73 Ga represents the most significant crust-forming episode in the Jiaodong Terrane. This is in contrast to the general understanding that the most important period of crustal growth and related metamorphism/deformation in the NCC took place in the terminal Archean (2.5 Ga). The geochemical and age constraints of the Neoarchean TTG rocks suggest that their formation was not related to subduction of oceanic crust, but to underplating and subsequent partial melting of lower crustal mafic rocks. Nd isotope data indicate that the Mesoarchean and Neoarchean rocks were mainly derived from juvenile sources with a limited amount of old crustal component. Like in other parts of the NCC, these rocks represent a juvenile addition to the late Archean continental crust. Finally, the formation of supracrustal rocks and most TTG gneisses in the period of 2.9 to 2.7 Ga distinguishes the Jiaodong Terrane from other tectonic units of the North China Craton.

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