Paired metamorphism in the Neoarchean: A record of accretionary-to-collisional orogenesis in the North China Craton
Paired metamorphism in the Neoarchean: A record of accretionary-to-collisional orogenesis in the North China Craton
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DOI：
10.1016/j.epsl.2020.116355
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发表时间：
2020-08-01
影响因子：
5.3
通讯作者：
Fu, Dong
中科院分区：
文献类型：
--
作者：
Huang, Bo;Kusky, Timothy M.;Fu, Dong
成对变质作用是太古代会聚板块边缘不对称俯冲的标志，但在太古代岩石记录中很少有时空上相互联系的成对变质带的记载。登封杂岩是华北陆块南部新太古代一个典型的花岗岩-绿岩带。利用岩石学、地质年代学和对不同岩石构造单元岩石的相平衡约束，我们提出了一种新的岩石构造模式。2.54-2.50 Ga登封杂岩是一条时空上相互联系的新太古代成对变质带的残余。在杂岩的西部，来自一个主要变基性单元（MBU）的石榴石斜长角闪岩记录了6.3-10 kbar的峰值P-T条件，类似于675-750 ℃，对应于类似于720-1200 ℃/GPa的高温压比（TIP）。英云闪长岩-奥长花岗岩-花岗闪长岩（TTG）片麻岩保留了部分熔融的证据，也与相对较高的TIP（类似于875-1400 ℃/GPa）一致。在登封杂岩的东部，两个石榴石斜长角闪岩和三个石榴石石英云母片岩从一个占主导地位的变质沉积单元（MSU）记录峰值P-T条件>9.8千巴和类似于525-655摄氏度，对应于中间温压比类似于425-600摄氏度/GPa。锆石和钛铁矿U-Pb定年，加上现有的年龄后运动侵入体，限制变质年龄约。2.52-2.50 Ga。变质作用的P-T资料表明，早元古代MSU被埋藏至>30 km，然后被折返至近地表。结合现代构造和地球化学资料，认为登封杂岩记录了新太古代的成对变质作用，其中较高的热梯度反映了弧-弧前区，较低的热梯度对应于增生杂岩。我们的数据表明，南NCC经历了增生碰撞造山作用与洋内俯冲，弧前增生（约。2.54-2.50 Ga），以及随后的弧-大陆碰撞（约。2.50-2.47 Ga）。NCC中成对变质作用的识别与太古代晚期广泛的俯冲和板块构造体制的运作是一致的。(C)2020 Elsevier B. V.保留所有权利。
Paired metamorphism is the hallmark of asymmetric subduction at Phanerozoic convergent plate margins, yet spatially and temporally linked paired metamorphic belts have rarely been documented in the Archean rock record. Here, we investigate the Neoarchean Dengfeng Complex, a typical granite-greenstone belt in the southern part of the North China Craton (NCC). Using petrography, geochronology, and phase equilibrium constraints on rocks from different lithostructural units, we suggest the ca. 2.54-2.50-Ga Dengfeng Complex represents a remnant of a spatially and temporally linked Neoarchean paired metamorphic belt. In the western part of the complex, a garnet amphibolite from a dominantly metabasic unit (MBU) records near peak P-T conditions of 6.3-10 kbar and similar to 675-750 degrees C, corresponding to a high thermobaric ratio (TIP) of similar to 720-1200 degrees C/GPa. Tonalite-trondhjemite-granodiorite (TTG) gneisses preserve evidence for partial melting, also consistent with relatively high TIP (similar to 875-1400 degrees C/GPa). In the eastern part of the Dengfeng Complex, two garnet amphibolites and three garnet quartz-mica schists from a dominantly metasedimentary unit (MSU) record peak P-T conditions of >9.8 kbar and similar to 525-655 degrees C, corresponding to intermediate thermobaric ratios of similar to 425-600 degrees C/GPa. Zircon and titanite U-Pb dating, coupled with existing ages of post-kinematic intrusions, constrain the metamorphic age to ca. 2.52-2.50 Ga. The metamorphic P-T data indicate that the MSU was buried to >30 km then exhumed to the near-surface by the early Paleoproterozoic. Our metamorphic results, when combined with recent structural and geochemical data, suggest the Dengfeng Complex records Neoarchean paired metamorphism, in which the higher thermal gradients reflect the arc-forearc region and the lower thermal gradients correspond to the accretionary complex. Our data indicate that the southern NCC experienced accretionary-to-collisional orogenesis with intra-oceanic subduction, forearc accretion (ca. 2.54-2.50 Ga), and subsequent arc-continent collision (ca. 2.50-2.47 Ga). The recognition of paired metamorphism in the NCC is consistent with widespread subduction and the operation of a plate tectonic regime in the late Archean. (C) 2020 Elsevier B.V. All rights reserved.