Neoarchean suprasubduction zone ophiolite discovered from the Miyun Complex: Implications for Archean–Paleoproterozoic Wilson cycle in the North China Craton
Neoarchean suprasubduction zone ophiolite discovered from the Miyun Complex: Implications for Archean–Paleoproterozoic Wilson cycle in the North China Craton
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DOI：
10.1016/j.precamres.2020.105710
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发表时间：
2020-06
影响因子：
3.8
通讯作者：
M. Santosh;P. Gao;Bing Yu;Cheng‐Xue Yang;Sanghoon Kwon
中科院分区：
文献类型：
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作者：
M. Santosh;P. Gao;Bing Yu;Cheng‐Xue Yang;Sanghoon Kwon
北中国克拉通是研究太古代-古元古代地壳演化的窗口。伴随着新太古代微块的拼合，NCC在古元古代经历了又一次漫长的威尔逊旋回，经历了俯冲-吸积-碰撞过程。本文报道了中国大陆密云杂岩中新发现的一套超俯冲带蛇绿岩套，该套蛇绿岩系保存了一套罕见的、接近完整的蛇绿岩序列，包括蛇纹岩、二辉橄榄岩、橄榄斜辉岩、方辉橄榄岩、辉长岩、辉长岩、闪长岩、二长岩、变质玄武岩和奥长花岗岩，并与带状铁建造(BIF)有关。该套岩石的地球化学特征与超俯冲蛇绿岩杂岩的特征一致，镁铁质和中间成分具有岛弧玄武岩(IAT)和大洋中脊玄武岩(MORB)的亲和性。二辉橄榄岩中的锆石颗粒确定了三组207Pb/206Pb加权平均年龄：2500 Ma±10.12 Ma，2237 Ma±10.47 Ma，1843℃±10.30 Ma，代表随后的热事件。橄榄石单斜辉石岩、辉长岩和石英二长岩中的大多数锆石颗粒的207Pb206Pb加权平均年龄分别为2510 Ma±919 Ma、2495 Ma±910 Ma和2486 Ma±921 Ma。奥长花岗岩的加权平均年龄为2476±99.4 Ma。密云套所有岩石类型的年龄数据显示，在2486 Ma和1832 Ma左右有两个明显的年龄峰，对应于岩浆分异和随后变质的时间。锆石Lu-Hf同位素数据显示出明显的正ɛHf(T)值，范围为0.35-7.05，表明岩浆来源于新太古代至古元古代亏损地幔(幼年)源区。锆石TDM年龄在2670 Ma出现峰值，证实了新太古代成分。密云蛇绿岩的岩浆形成时间与北海台所描述的其他罕见的新太古代-早古元古代蛇绿岩套的岩浆形成时间基本一致，包括宜水和遵化的蛇绿岩套。此外，最近报道的阿拉斯加型侵入岩和密云杂岩周围弧根镁铁质-超镁铁质杂岩的证据表明，与俯冲有关的岩浆作用仍在继续，最终碰撞发生在古元古代晚期，年龄约为1.84Ga。我们认为，在太古-古元古代过渡期间，伴随着以2.6-2.5Aa绿岩带为标志的多条封海带上的古微块体的拼接，以及微块体边缘的高级变质作用，从古元古代早期到晚古元古代，NCC经历了另一次重大的威尔逊旋回，经历了较大的地壳块体和弧间杂岩的长期俯冲、吸积和碰撞，导致了最终的克拉通化。
The North China Craton (NCC) offers a window to Archean–Paleoproterozoic crustal evolution. Following the amalgamation of microblocks during Neoarchean, the NCC witnessed another protracted Wilson cycle in the Paleoproterozoic with subduction-accretion-collision process. Here we report a newly identified suprasubduction zone ophiolite suite from the Miyun complex in the NCC where a rare and near-complete ophiolite succession is preserved including serpentinite, lherzolite, olivine clinopyroxenite, websterite, gabbro, dolerite, diorite, monzonite, metabasalts and trondhjemite, in association with Banded Iron Formation (BIF). The geochemical features of the suite are consistent with those of suprasubduction ophiolite complexes, with the mafic and intermediate members displaying Island Arc Tholeiite (IAT) and Mid-Ocean Ridge Basalt (MORB) affinity. Zircon grains from lherzolite define three groups of207Pb/206Pb weighted mean ages at 2500 ± 12 Ma marking the formation age, and 2237 ± 47 Ma, and 1843 ± 30 Ma representing subsequent thermal events. The majority of zircon grains in olivine clinopyroxenite, gabbro, and quartz monzonite yield207Pb/206Pb weighted mean ages of 2510 ± 19 Ma, 2495 ± 10 Ma, and 2486 ± 21 Ma respectively. Those from the trondhjemite show weighted mean age of 2476 ± 9.4 Ma. The compiled age data from all the rock types in the Miyun suite show two distinct age peaks at ca. 2486 Ma and 1832 Ma, corresponding to the timing of magma differentiation and subsequent metamorphism. The zircon Lu-Hf isotope data display distinct positive ɛHf(t) values in the range 0.35–7.05, suggesting magma derived from Neoarchean to Paleoproterozoic depleted mantle (juvenile) source. The zircon TDMages show a peak at 2670 Ma, confirming Neoarchean components. The timing of magma formation in the Miyun ophiolite is broadly identical to those of the other rare Neoarchean – early Paleoproterozoic ophiolite suites described from the NCC including those from Yishui and Zunhua. Furthermore, evidence from the recently reported Alaskan-type intrusions and arc root mafic-ultramafic complexes around Miyun complex with ages in the range of 2.4–2.0 Ga suggest continued subduction-related magmatic processes, with final collision in latest Paleoproterozoic at around 1.84 Ga. We propose that following the assembly of ancient microblocks along multiple zones of ocean closure marked by major greenstone belts of 2.6–2.5 Ga, and high-grade metamorphism along the margins of the microblocks during Archean–Paleoproterozoic transition, the NCC went through another major Wilson cycle from early to late Paleoproterozoic involving prolonged subduction, accretion and collision of larger crustal blocks and intervening arc complexes, leading to final cratonization.