Late Neoarchean crust-mantle geodynamics : evidence from Pingquan Complex of the Northern Hebei Province, North China Craton
Late Neoarchean crust-mantle geodynamics : evidence from Pingquan Complex of the Northern Hebei Province, North China Craton
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DOI：
10.1016/j.precamres.2017.06.007
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发表时间：
2017-12
影响因子：
3.8
通讯作者：
Wei Wang;Shuwen Liu;Peter A. Cawood;R. Guo;Xiaojing Bai;Boran Guo
中科院分区：
文献类型：
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作者：
Wei Wang;Shuwen Liu;Peter A. Cawood;R. Guo;Xiaojing Bai;Boran Guo
中国克拉通北缘晚太古代洋内弧为研究太古宙地幔物质来源和壳幔地球动力学提供了重要信息。平泉杂岩和整个冀北杂岩位于弧体的中部，与横贯北向的中国造山带的北部部分重叠。锆石U-Pb年龄数据显示，平泉杂岩由∼2537~2515 Ma闪长岩片麻岩、∼250 6~250 3 Ma角闪岩和∼2491 Ma石英二长闪长-二长花岗片麻岩组成，以正锆石εHf(T)(−0.6~+5.4)为主，低于同时代亏损地幔。平泉杂岩除二长花岗片麻岩来自幼年变质岩芯的部分熔融外，其余岩石均来自交代岩石圈地幔，并经历了单斜辉石、角闪石和斜长石的不同分馏，没有明显的地壳混染。中等亏损的锆石εHf(T)和较高的Sm/Hf和Nb/Ta(大多分别为1.3 4~3.96和15.5 0~32.5 8)表明，岩石圈地幔在熔融前由俯冲的远洋沉积物变质为含金红石榴辉岩而富集。大洋内俯冲开始于∼2.55亿Ga或更早的EB西北边缘近海。板片玄武岩的部分熔融发生在∼2542-2499 Ma，熔体受地幔楔形物质的污染形成TTGS。同时，弧下岩石圈地幔受到板片玄武岩和远洋沉积物释放的流体和熔体的富集化，该中等亏损地幔的部分熔融产生了∼2537-2503 Ma闪长岩和玄武岩。随着弧最后一次吸积到EB的大陆边缘，板片回滚/折断和软流圈地幔上涌触发了交代岩石圈地幔和地壳深熔的部分熔融，产生了∼2491 Ma的石英二长闪长岩和二长花岗岩。因此，NHB记录了与大洋俯冲和弧陆增生有关的新太古代地壳生长，强调了解决地幔来源和壳幔相互作用的性质对认识太古代地壳生长和演化的重要性。
A late Neoarchean intra-oceanic arc along the northwestern margin of Eastern Block (EB), North China Craton, provides important insights into the nature of Archean mantle sources and crust-mantle geodynamics. The Pingquan Complex and the entire Northern Hebei Province (NHB) are located in the middle part of the arc, and overlap the northern extent of the trans-North China Orogen. Zircon U-Pb isotopic age data reveal that the Pingquan Complex consists of ∼2537–2515 Ma dioritic gneisses, ∼2506–2503 Ma amphibolites, and ∼2491 Ma quartz monzodioritic to monzogranitic gneisses, and they show dominantly positive zircon εHf(t) (−0.6 to +5.4) that are lower than coeval model depleted mantle values.Geochemical data for the Pingquan rocks and synchronous metabasalts and granitoid gneisses of Huai’an-Xuanhua and Dantazi complexes in the NHB are integrated. Except for the monzogranitic gneisses that were derived from partial melting of juvenile metagreywackes, the other rocks of the Pingquan Complex were derived from a metasomatized lithospheric mantle, and subjected to variable fractionation of clinopyroxene, hornblende and plagioclase, without significant crustal contamination. Moderately depleted zircon εHf(t), and high Sm/Hf and Nb/Ta (mostly of 1.34–3.96 and 15.50–32.58, respectively) suggest that the lithospheric mantle was enriched by subducted pelagic sediments metamorphosed to rutile-bearing eclogites before melting.Late Neoarchean crust-mantle geodynamic processes in the NHB are reconstructed. Intra-oceanic subduction initiated offshore the northwestern margin of the EB at ∼2.55 Ga or earlier. Partial melting of slab basalts occurred at ∼2542–2499 Ma, with the melts contaminated by mantle wedge materials forming TTGs. Meanwhile, the sub-arc lithospheric mantle was enriched by fluids and melts released from slab basalts and pelagic sediments, and partial melting of this moderately depleted mantle generated ∼2537–2503 Ma diorites and basalts. Following final accretion of the arc onto the continental margin of the EB, the slab rollback/breakoff and asthenospheric mantle upwelling triggered partial melting of the metasomatized lithospheric mantle and crustal anatexis, generating ∼2491 Ma quartz monzodioritic and monzogranitic rocks.Accordingly, the NHB records Neoarchean crustal growth linked to oceanic subduction and arc-continent accretion, and highlights the importance of resolving the nature of mantle sources and crust-mantle interactions in understanding Archean crustal growth and evolution.