Journal
LITHOS
Volume 300, Issue -, Pages 314-329Publisher
ELSEVIER
DOI: 10.1016/j.lithos.2017.12.010
Keywords
Granites; Two-sided ridge subduction; Geochemistry and zircon geochronology; Sr-Nd-Hf isotopes; Central Asian Orogenic Belt
Categories
Funding
- National Natural Science Foundation of China [41502209]
- Chinese State 973 Project [2015CB250901]
- Science Foundation of China University of Petroleum, Beijing [2462014YJRC031]
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The Central Asian Orogenic Belt (CAOB) evolved through a long-lived orogeny involving multiple episodes of subduction and accretion marking a major phase of continental growth during the Paleozoic. The northern part of the Western Junggar region (NW Junggar) offers a window into these processes, particularly to constrain the timing of closure of the Paleo-Asian Ocean. Here we report geochemical, geochronological, and isotopic data from K feldspar granites and adakitic rocks from the NW Junggar region. Zircon U-Pb ages suggest that the granites were emplaced during Early Silurian to the Early Carboniferous (434-328 Ma). The granites show geochemical characteristics similar to those of A-type granites, with high SiO2 (71.13-76.72 wt%), Na2O + K2O (8.00-9.59 wt%), and Al2O3 (12.28-14.08 wt%), but depleted Sr, Nb, Ta and Eu. They display moderate to high positive epsilon Nd(t) and epsilon Hf(t) values (4.26-8.21 and 7.69-14.60, respectively) and young Nd and Hf model ages (T2Dm-Nd = 489-740 Ma and T2DM-Hf = 471-845 Ma), suggesting magma derivation through partial melting of lower crust in the Boshchekul-Chingiz and Zharma-Saur arcs. The adakites are characterized by high Sr content (406.5-751.6 ppm), and low Y (13.8-16.4 ppm) and Yb (1.5-1.8 ppm) content, yielding relatively high Sr/Y ratios (25.38-49.41) similar to those of modern adakites. They have high positive epsilon Nd(t) and epsilon Hf(t) values (7.85-8.25 and 13.23-15.97, respectively) and young Nd and Hf model ages (T2Dm-Nd = 429-535 Ma and T2DM-Hf = 355-550 Ma), indicating that their source magmas were likely derived from partial melting of the oceanic crust beneath the Boshchekul-Chingiz arc. The petrogenesis and distribution of the A-type granites and adakites, as well as the tectonic architecture of the region, suggest that a ridge subduction event might have occurred during the Early Silurian to Early Carboniferous. In combination with previous studies in the Chinese Altai, we suggest a two-sided ridge subduction model for the Junggar-Altai region. (C) 2017 Elsevier B.V. All rights reserved.
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