Journal
EARTH AND PLANETARY SCIENCE LETTERS
Volume 366, Issue -, Pages 71-82Publisher
ELSEVIER
DOI: 10.1016/j.epsl.2013.02.011
Keywords
Hf and O isotopes; clearly defined cores; zircon; S-type granitoids; magmatic evolution; jiangnan orogen
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Funding
- National Natural Science Foundation of China [41072144, 41222016]
- 973 project of China [2012CB416701]
- US National Science Foundation [EAR-0319230, 0744079, 1053466]
- Directorate For Geosciences
- Division Of Earth Sciences [1053466] Funding Source: National Science Foundation
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Zircons can retain a grain-scale record of granitoid compositional evolution that is accessible through microanalysis. In situ U-Pb, Hf and O isotope data yield new insights into the petrogenesis and evolution of the Neoproterozoic strongly peraluminous granitoids of the Jiangnan orogen (JO), southern China. A negative correlation of Th/U versus delta O-18 is found for most analyses. Some zircons from eastern JO granitoids show delta O-18 variations of 3-6% from core to rim, indicating a dramatic shift toward higher oxygen isotope values by voluminous partial melting of supracrustal rocks and signaling a transition from I-type-like to S-type-like magmas during the later stage of magmatic evolution. This mechanism provides a reasonable explanation why some granitoids have intermediate geochemical features between S-type and I-type granites. Hf isotope trends indicate that a larger proportion of mature continental crust was incorporated into the magma sources of the western JO granitoids, whereas more juvenile arc crust was incorporated into the eastern JO magmas. No significant depleted mantle-derived mafic magma was injected into the JO granitoid magmas. Instead, radiogenic Elf and Nd signatures in JO granitoids reflect incorporated juvenile arc crust and document crustal growth in southern China during the Early Neoproterozoic (ca. 900 Ma). Thus, our zircon data suggest that strongly peraluminous granitoids, which are widely regarded as the products of orogenesis that primarily recycle evolved crust, can also record important information about early crustal growth. (C) 2013 Elsevier B.V. All rights reserved.
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