Zircon U-Pb-Hf isotopes and bulk-rock geochemistry of gneissic granites in the northern Jiamusi Massif, Central Asian Orogenic Belt: implications for Middle Permian collisional orogeny and Mesoproterozoic crustal evolution

• Published in: International geology review Vol. 55; no. 9; pp. 1109 - 1125
• Main Authors: Cui, Pei-Long, Sun, Jing-Gui, Han, Shi-Jiong, Zhang, Peng, Zhang, Yong, Bai, Ling-An, Gu, A-Lei
• Format: Journal Article
• Language: English
• Published: Philadelphia Taylor & Francis 10.07.2013; Taylor & Francis Ltd
• Subjects: Jiamusi Massif; Mesoproterozoic crustal evolution; Middle Permian collisional orogeny; U-Pb geochronology; zircon Hf isotopes
• ISSN: 0020-6814; 1938-2839
• DOI: 10.1080/00206814.2013.767489

We conducted bulk-rock geochemical and zircon U-Pb-Hf isotope analyses of gneissic granites from the northern Jiamusi Massif, in order to investigate their sources, petrogenesis, and geodynamic significance. Zircons contain fine-scale oscillatory zoning with high Th/U ratios (0.12-0.80), indicative of a magmatic origin. U-Pb dating indicates that they formed during the middle Permian (264 ± 4.2 Ma to 268.6 ± 0.81 Ma), and contain a 531 Ma inherited zircon core. The gneissic granites have high contents of K 2 O + Na 2 O and Al 2 O 3 , and low MgO and CaO. With A/CNK ratios of 1.01-1.11, they are classified as peraluminous calc-alkaline to alkaline S-type syn-collisional granites. Enriched in large ion lithophile elements such as K, Rb, Ba, and Th, they are depleted in high field strength elements such as Nb, Ta, and Ti. Bulk-rock geochemical analyses display moderately negative Eu anomalies (Eu/Eu*) of 0.36-0.52, and (La/Yb) N ratios of 13.24-29.51. In situ Hf analyses of zircon gave ϵ Hf (t) values of -0.1 to -3.2 and crustal average model ages ( ) of 1.35-1.4 Ga. These data suggest that the gneissic granites formed by partial melting of Mesoproterozoic continental crust during a middle Permian collisional event. Hf isotopes indicate the substantial presence of Mesoproterozoic juvenile crust in the northern Jiamusi Massif, derived from depleted mantle that underwent crustal contamination at 1.4-1.35 Ga. The Jiamusi Massif provides a local record of the assimilation and subsequent rifting of the Rodinia-Gondwana supercontinent.