A Neoarchean arc-back-arc system in Eastern Hebei, North China Craton: Constraints from zircon U-Pb-Hf isotopes and geochemistry of dioritic-tonalitic-trondhjemitic-granodioritic (DTTG) gneisses and felsic paragneisses
A Neoarchean arc-back-arc system in Eastern Hebei, North China Craton: Constraints from zircon U-Pb-Hf isotopes and geochemistry of dioritic-tonalitic-trondhjemitic-granodioritic (DTTG) gneisses and felsic paragneisses
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华北克拉通河北东部新太古代弧-后-弧系统：锆石U-Pb-Hf同位素及闪长岩-英闪长岩-长角闪长岩(DTTG)片麻岩和长英质副片麻岩地球化学的制约
DOI：
10.1016/j.precamres.2015.12.003
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发表时间：
2016
影响因子：
3.8
通讯作者：
Wang Wei
中科院分区：
文献类型：
--
作者：
Bai Xiang;Liu Shuwen;Guo Rongrong;Wang Wei
冀东遵化-青龙微地块广泛出露闪长-英云闪长-奥长-花岗闪长质（DTTG）片麻岩。对青龙地区DTTG片麻岩进行LA-ICP-MS锆石U-Pb同位素定年，其岩浆前体侵位时间为2517 ± 10 ~ 2505 ± 23 Ma。这些DTTG片麻岩的锆石具有正的Hf（t）值（0.0 ~+6.5），具有类似埃达克岩的地球化学特征，表现为较高的MgO、Mg#和（La/Yb）N比值。岩石成因研究表明，闪长质岩浆来源于亏损地幔橄榄岩，橄榄岩受到板片熔体/流体的强烈改造，英云闪长质-奥长花岗闪长质（TTG）岩浆是闪长质岩浆中以角闪石为主要分离相的高度分离结晶形成的。铅同位素分析表明，北方遵化地区长英质副片麻岩的原岩形成于晚新太古代，最大沉积年龄为2517 ± 20 Ma。大部分碎屑锆石的207 Pb/206 Pb年龄介于3432 ± 20 ~ 2502 ± 21 Ma之间，负的δ Hf（t）值介于-15.4 ~-2.4之间，计算的TDMCage年龄介于3995 ~ 3368 Ma之间。这表明它们是由Eo循环形成的，与东部陆块内部东南部古陆壳关系密切的古太古代地壳物质。结合前人的研究成果，认为遵化-青龙微地块基底岩石形成于新太古代弧-弧后体系，俯冲方向为现今的北西向南东。
Dioritic–tonalitic–trondhjemitic–granodioritic (DTTG) gneisses are widely exposed in the Zunhua–Qinglong microblock of Eastern Hebei, North China Craton (NCC). LA-ICP-MS zircon U–Pb isotopic dating for the DTTG gneisses in the Qinglong area reveals that their magmatic precursors were emplaced between 2517 ± 10 and 2505 ± 23 Ma. Zircons of these DTTG gneisses exhibit positiveɛHf(t) values of 0.0 to +6.5, with adakite-like geochemical features represented by relatively high MgO, Mg# and (La/Yb)Nratios. Petrogenetic studies reveal that dioritic magmas were derived from depleted mantle peridotites that were strongly modified by slab-derived melts/fluids and that the tonalitic–trondhjemitic–granodioritic (TTG) magmas were formed by a high degree of fractional crystallization in the dioritic magmas with hornblende as the primary fractionated phase.LA-ICP-MS zircon U–Pb isotopic analyses reveal that the protoliths of the felsic paragneisses in the Northern Zunhua area were deposited in the Late Neoarchean with a maximum depositional age of 2517 ± 20 Ma. Most of the detrital zircon grains display apparent207Pb/206Pb ages from 3432 ± 20 to 2502 ± 21 Ma, with negativeɛHf(t) values of −15.4 to −2.4 and calculated TDMCages between 3995 and 3368 Ma, suggesting that they were formed from the recycling of Eo- to Paleoarchean crustal materials closely related to the southeastern ancient continental crust of the interior Eastern Block. These data together with previous investigations reveal that the basement rocks of Zunhua–Qinglong microblock formed in a Neoarchean arc–back-arc system with the subduction direction from present northwest to southeast.