Source of highly potassic basalts in northeast China: Evidence from Re-Os, Sr-Nd-Hf isotopes and PGE geochemistry
Source of highly potassic basalts in northeast China: Evidence from Re-Os, Sr-Nd-Hf isotopes and PGE geochemistry
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中国东北地区高钾玄武岩来源：来自Re-Os、Sr-Nd-Hf同位素和PGE地球化学的证据
DOI：
10.1016/j.chemgeo.2013.08.007
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发表时间：
2013-10-24
期刊：
影响因子：
3.9
通讯作者：
Yang, Yue-Heng
中科院分区：
文献类型：
--
作者：
Chu, Zhu-Yin;Harvey, Jason;Yang, Yue-Heng
中国东北五连池—二克山（WDLC和EKS）极年轻（0.5 ma ~ 1721 AD）高钾玄武岩的起源一直是争论的焦点。在这项研究中，我们提出了新的主要、痕量和铂族元素（PGE）数据以及这些钾质玄武岩的Re-Os、Lu-Hf和Sr-Nd同位素分析，以进一步限制它们的来源。结果表明，WDLC和EKS玄武岩的锇同位素比值介于0.1187和0.17之间，相对于IPGE (Os、Ir和Ru), PPGE （Pt和Pd）相对于IPGE （Os、Ir和Ru）只有轻微的富集。Os-187/Os-188与1/Os的正相关表明，这些玄武岩在岩浆上升过程中可能经历了约2-8%的下大陆地壳添加。另一方面，在岩浆上升过程中，次大陆岩石圈地幔（SCLM）衍生的原生硫化物和/或PGE微合金似乎可能在某些玄武岩中结合，这些玄武岩保留了特别非放射性成因的Os成分。来自地壳和SCLM污染的复杂信号相互作用意味着玄武岩的Os同位素系统不能明确地识别WDLC和EKS玄武岩的来源。轻稀土元素（LREE）和大离子亲石元素（LILE）的强富集，高k、类em1的Sr-Nd-Hf同位素特征，特别是重稀土元素（Sm/Yb）(N) = 9.7 +/- 0.6)的强分馏，表明WDLC和EKS玄武岩主要来源于SCLM中含辉云母的石榴石橄榄岩。结合较低的Ce/Pb比值（接近9.4-13.5），认为WDLC和EKS玄武岩最可能的来源是被剥离的古老下大陆地壳交代的SCLM。这与先前的假设不同，先前的假设认为软流圈的来源主要来自于剥离的古软流层或俯冲的海洋地壳与沉积物，或者软流层的来源是由元古代深层软流层的熔体交代的。(C) 2013 Elsevier b.v.版权所有
The origin of the very young (0.5 Mato 1721 AD) Wudalianchi-Erkeshan(WDLC and EKS) highly potassic basalts in northeast (NE) China has been the subject of considerable debate. In this study, we present new major-, trace- and platinum group element (PGE) data together with Re-Os, Lu-Hf, and Sr-Nd isotopic analyses for these potassic basalts in order to further constrain their source. It has been shown that the WDLC and EKS basalts have unradiogenic to only moderately radiogenic osmium isotope ratios with Os-187/Os-188 ranging from 0.1187 to similar to 0.17, and only slight PPGE (Pt and Pd) enrichments relative to IPGE (Os, Ir and Ru). The positive correlations between Os-187/Os-188 and 1/Os suggests that these basalts have probably experienced about 2-8% of lower continental crust addition during magma ascent. On the other hand, the incorporation of sub-continental lithospheric mantle (SCLM)-derived, primary sulphides and/or PGE micro-alloys during magma ascent seems likely in some basalts, which preserve particularly unradiogenic Os compositions. The complex interplay of signatures derived from crustal and SCLM contamination means that the Os isotope systematics of the basalts do not unequivocally fingerprint the source of the WDLC and EKS basalts.The strong enrichments of light rare earth elements (LREE) and large ion lithophile elements (LILE), high-K, EM1-like Sr-Nd-Hf isotopic characteristics, and particularly strong fractionation of the heavy REE ((Sm/Yb)(N) = 9.7 +/- 0.6), suggest that the WDLC and EKS basalts mainly originated from phlogopite-bearing garnet-peridotite in the SCLM. Combined with low Ce/Pb ratios ( similar to 9.4-13.5), the most likely source of WDLC and EKS basalts is SCLM that has been metasomatized by delaminated old, lower continental crust. This is different from previous hypotheses that implicate a dominantly asthenospheric source with a contribution from delaminated ancient SCLM or subducted oceanic crust with sediments, or a SCLM source that has been metasomatized by melts derived from deep asthenosphere during the Proterozoic. (C) 2013 Elsevier B. V. All rights reserved.