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Neoproterozoic boninite-series rocks in South China: A depleted mantle source modified by sediment-derived melt

Zhao, Jun-Hong and Asimow, Paul D. (2014) Neoproterozoic boninite-series rocks in South China: A depleted mantle source modified by sediment-derived melt. Chemical Geology, 388 . pp. 98-111. ISSN 0009-2541.

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A series of Neoproterozoic boninitic pillow lavas are hosted in Early Neoproterozoic strata along the southeastern margin of the Yangtze Block. These lavas record a period of subduction initiation during the secular evolution of South China. In this work we present analytical results from three units of pillow lavas (the Zhangyuan, Shexian and Lushan units) that form a common liquid line of descent with the previously reported 830-Ma boninites in the region, suggesting that they were produced by differentiation from similar parental melts. MELTS calculations show that major element compositions require fractionation of olivine + clinopyroxene + plagioclase + spinel from primary boninitic melts to have been accompanied by variable amounts of crustal contamination. The pillow lavas from the three localities show similar rare earth element patterns and arc-like primitive mantle normalized trace element patterns. They have high ^(206)Pb/^(204)Pb (18.41–19.33), ^(207)Pb/^(204)Pb (15.63–15.79) and ^(208)Pb/^(204)Pb ratios (38.78–40.26). Their ε_(Nd) values decrease from the Lushan lavas (+ 0.7 to + 1.9) to the Shexian lavas (− 0.5 to − 1.1) to the Zhangyuan lavas (− 4.0 to − 1.0), reaching values lower than the upper-level crustal contaminants and therefore indicating progressive enrichment of their sources by sediment melts. Compared with nearby but older (850 Ma) MORB-like tholeiitic basalts, which yield mantle potential temperature below 1400 °C and H_2O contents nearly 0.13 wt.%, the primary magmas of the boninite series rocks in this study were formed under higher pressures (3.5–1.0 GPa) and mantle potential temperatures (1440–1500 °C) with high H_2O contents (3420 to 4830 ppm), clear slab-derived sedimentary melt input, and harzburgite residues. The introduction of slab-derived water and sedimentary melt components into the mantle wedge at such high pressures, together with high temperatures and high degrees of melting, indicate that within a time span of only 20 million years after subduction initiation (850 to 830 Ma), the slab subducting under the southeastern margin of the Yangtze Block achieved substantial penetration to depth and interacted with hot overlying mantle, before subduction was abruptly ended by the amalgamation of the Yangtze and Cathaysia blocks.

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Asimow, Paul D.0000-0001-6025-8925
Additional Information:© 2014 Elsevier B.V. Received 9 March 2014, Revised 10 July 2014, Accepted 1 September 2014, Available online 11 September 2014. Editor: D.B. Dingwell. This work was substantially supported by the National Nature Science Foundation of China (41073026, 41373016), FOK YING TONG Education Foundation, the Program for New Century Excellent Talents in University (NCET), and the Special Fund for Basic Scientific Research of Central Colleges, China University of Geosciences (Wuhan). PDA was supported in part by the US National Science Foundation through award GI-1226270. Reviews by Donald Dingwell, Paul T. Robinson and an anonymous referee are gratefully acknowledged.
Funding AgencyGrant Number
National Nature Science Foundation of China41073026
National Nature Science Foundation of China41373016
Program for New Century Excellent Talents in University (NCET)UNSPECIFIED
China University of GeosciencesUNSPECIFIED
Subject Keywords:Boninite series basalts; Forearc; Neoproterozoic; South China
Record Number:CaltechAUTHORS:20150105-112511328
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Official Citation:Jun-Hong Zhao, Paul D. Asimow, Neoproterozoic boninite-series rocks in South China: A depleted mantle source modified by sediment-derived melt, Chemical Geology, Volume 388, 21 November 2014, Pages 98-111, ISSN 0009-2541, (
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:53179
Deposited By: Ruth Sustaita
Deposited On:05 Jan 2015 20:36
Last Modified:03 Oct 2019 07:48

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