Early Paleozoic subduction in the Indochina interior: Revealed by Ordo-Silurian mafic-intermediate igneous rocks in South Laos
Early Paleozoic subduction in the Indochina interior: Revealed by Ordo-Silurian mafic-intermediate igneous rocks in South Laos
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DOI：
10.1016/j.lithos.2020.105488
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发表时间：
2020-06
期刊：
影响因子：
3.5
通讯作者：
Yuejun Wang;Yukun Wang;Xin Qian;Yuzhi Zhang;Chengshi Gan;Vongpaseuth Senebouttalath;Yang Wang
中科院分区：
文献类型：
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作者：
Yuejun Wang;Yukun Wang;Xin Qian;Yuzhi Zhang;Chengshi Gan;Vongpaseuth Senebouttalath;Yang Wang
印度支那内陆早古生代的构造性质和随后的造山过程仍然知之甚少。本研究介绍了老挝南部的一般地质情况，并提出了一套新的锆石使用单键 Pb 和 Hf 单键 O 同位素分析，以及老挝南部镁铁质-中质火成岩的全岩元素和 Sr-Nd-Pb 同位素数据。先前绘制的长山地区南部鄂尔多-志留系地层的代表性样本给出的形成年龄为 434–438 Ma。来自 Tam Ky-Phuoc Son 构造带的五个样本产生了锆石，其使用键 Pb 年龄为 447–485 Ma。相应的锆石εHf(t)、δ18O和TDM值分别在+1.6~ -6.5、6.1–8.6‰和1.02–1.79 Ga范围内。老挝南部 45 块毫克数=42-69 的镁铁质中型火成岩，SiO2=53.04-61.66wt%，Al2O3=12.13-20.92wt%，MgO=2.73-9.55wt%，其特征是 LILE 富集，HFSE 贫化， Nb单键Ta负异常。它们的 (87Sr/86Sr) 比率范围为 0.7044 至 0.7109，εNd(t) 值范围为 -6.2 至 -2.6，其中 (206Pb/204Pb)i= 18.08–18.68，(207Pb/204Pb)i= 15.50–15.77，并且(208Pb/204Pb)i= 38.04–38.97。十个辉长岩样品，毫克数= 77-79，显示出与其他镁铁质-中质火成岩相似的不相容元素比率和Sr-Nd-Pb-Hf-O同位素组成，但具有较低的SiO2和较高的MgO、Cr、Ni和V含量，反映了原生镁铁质岩浆。这些特征表明，楔形源是由沉积物衍生成分重新改造而成的。结合越南中部的其他地质观测，我们提出了一个北向年轻的早古生代火成岩事件，以应对印度支那内陆不断增长的增生造山作用。印度支那内陆早古生代 Tam Ky-Phuoc Son 洋向南的消耗持续到至少约 430 Ma，印度支那北部与昆嵩地体的组合可能在泥盆纪早期终止。
The early Paleozoic tectonic nature and subsequent orogenic process remain poorly known in the Indochina interior. This study introduces the general geology of South Laos and presents a set of new zircon Usingle bondPb and Hfsingle bondO isotopic analyses, and whole-rock elemental and Sr-Nd-Pb isotopic data for the mafic-intermediate igneous rocks in South Laos. The representative samples from the previously-mapped Ordo-Silurian strata in the southern Truong Son zone give the formation ages of 434–438 Ma. Five samples from the Tam Ky-Phuoc Son tectonic zone yield zircon Usingle bondPb ages of 447–485 Ma. The corresponding zirconεHf(t), δ18O andTDMvalues are in range of +1.6~ −6.5, 6.1–8.6‰, and 1.02–1.79 Ga, respectively. Forty-five mafic-intermediate igneous rocks in South Laos with mg-number = 42–69 have SiO2= 53.04–61.66 wt%, Al2O3= 12.13–20.92 wt% and MgO = 2.73–9.55 wt%, and are characterized by enrichment in LILEs and depletion in HFSEs with Nbsingle bondTa negative anomalies. Their (87Sr/86Sr)iratios range from 0.7044 to 0.7109 andεNd(t) values from −6.2 to −2.6, with (206Pb/204Pb)i= 18.08–18.68, (207Pb/204Pb)i= 15.50–15.77, and (208Pb/204Pb)i= 38.04–38.97. Ten gabbroic samples, with mg-number = 77–79, show similar incompatible elemental ratios and Sr-Nd-Pb-Hf-O isotopic compositions with the other mafic-intermediate igneous rocks, but have lower SiO2and higher MgO, Cr, Ni and V contents, reflective of a primary mafic magma. Such characteristics suggest a newly-modified wedge source by recycled sediment-derived components. In combination with other geological observations in Central Vietnam, we propose a northerly-younging early Paleozoic igneous event in response to the on-growing accretionary orogenesis in the Indochina interior. The southward consumption of the early Paleozoic Tam Ky-Phuoc Son Ocean in the Indochina interior continued until at least ~430 Ma and the assemblage of the Northern Indochina with the Kontum terrane likely terminated at the early Devonian.