Geochronology and petrogenesis of Neoarchean potassic meta-granites from Huai'an Complex: Implications for the evolution of the North China Craton
Geochronology and petrogenesis of Neoarchean potassic meta-granites from Huai'an Complex: Implications for the evolution of the North China Craton
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DOI：
10.1016/j.gr.2011.01.009
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发表时间：
2011-07
影响因子：
6.1
通讯作者：
Huafeng Zhang;M. Zhai;M. Santosh;Chunrong Diwu;Sheng‐Rong Li
中科院分区：
文献类型：
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作者：
Huafeng Zhang;M. Zhai;M. Santosh;Chunrong Diwu;Sheng‐Rong Li
华北陆块中北部淮安杂岩中新太古代钾质变花岗岩包括浅色正长花岗岩、黑云二长花岗岩和含石榴子石正长花岗岩。高压石榴麻粒岩与花岗岩类呈透镜状、席状或碎裂脉状产出。本文报道了淡色正长花岗岩的SHRIMP锆石U-Pb数据，其形成年龄为2493± 6 Ma（MSWD=1）;黑云母二长花岗岩和石榴子石正长花岗岩的LA-ICP-MS U-Pb数据，其形成年龄分别为2437± 10 Ma（MSWD=2.0）和1977- 2003 Ma。本文还报道了这些岩石的变质年龄。石榴正长花岗岩中锆石的年龄为1800 Ma。地球化学研究表明，MgO含量低（0.5-0.06wt.%），Cr（6.19-0.53ppm）和Ni（27.66-2.01ppm），SiO2（62.3 - 76.8wt.%）变化内容，表明它们来自地壳来源。浅色正长花岗岩表现出升高的正Eu异常，减少Sr，Th，U，和散装稀土元素的浓度，Th/U比，而Rb和Ba值增加，Th/U比降低，表明流体-熔体相互作用。浅色正长花岗岩具有较高的Sr、Ba含量和Sr/Y、（La/Yb）N比值，较低的Y和HREE含量，锆石εHf（t）值为+1.7 ~+5.8，Hf模式年龄为2.60-2.73Ga，反映其成因为超厚的榴辉岩组成的幼年下地壳部分熔融或残留物中的榴辉岩矿物组合。黑云母-二长花岗岩的εNd（t）值为+2.3 ~+2.5，模式年龄<2.60Ga，表明它们是由石榴角闪岩组成的增厚的幼年地壳部分熔融，或残留石榴子石和角闪岩，随后经历以斜长石沉淀为主的分馏作用而形成的。石榴子石-正长花岗岩显示出不同的SiO2含量（62.3-72.3wt.%），Zr（491- 1096 ppm）、Ga（23.5-31.2ppm）、Zn（38- 124 ppm）、Y（34.1-85.6ppm）和Nb（9.4-90.0ppm）丰度较高，104×Ga/Al比值为3.1-4.2。它们也具有低Sr（50- 161 ppm）和强烈的Eu负异常。结合Nd模式年龄（2.46-2.50Ga）和相对恒定的负εNd（t）值（−2.5-−2.9）（随SiO2含量增加），这些特征表明A型花岗岩与板内伸展或裂谷环境有关，岩浆演化来自新太古代英云闪长质岩石的部分熔融。花岗岩类独特的地球化学特征和锆石饱和温度表明在相对较低的压力（6- 10 kbar）下具有较高的熔融温度（900-1000°C）。在前人工作的基础上，结合我们的新数据，我们将这一现象联系起来。2500- 2450 Ma和2000 Ma岩浆事件为新太古代微地块和古元古代移动的活动带的拼合。1800- 1820 Ma的变质年龄可能反映了角闪岩相的退变质事件。
Neoarchean potassic meta-granites occurring in the Huai'an Complex within the north central part of the North China Craton (NCC) comprise leucocratic syenogranites, biotite monzogranites, and garnet-bearing syenogranites. High-pressure garnet–granulites occur as lenses, sheets or dismembered dikes with the granitoids. Here we present SHRIMP zircon U–Pb data from the leucocratic syenogranites which show an age of 2493±6Ma (MSWD=1), and LA-ICP-MS U–Pb data from the biotite-monzogranites and garnet–syenogranites, revealing their formation ages of 2437±10Ma (MSWD=2.0) and 1977–2003Ma, respectively. We also report metamorphic ages of ca. 1800Ma from zircons in the garnet–syenogranites. Geochemical studies show low MgO (0.5–0.06wt.%), Cr (6.19–0.53ppm) and Ni (27.66–2.01ppm) with varying SiO2(62.3 to 76.8wt.%) contents, indicating their derivation from a crustal source. The leucosyenogranites exhibit elevated positive Eu anomalies with decreasing Sr, Th, U, and bulk REE concentrations, and Th/U ratio, whereas Rb and Ba values increase with decreasing Th/U ratio, indicating fluid–melt interaction. The leucosyenogranites have high Sr and Ba contents and Sr/Y and (La/Yb)Nratios and low Y and HREEs, with zircon εHf(t) values ranging from +1.7 to +5.8 and Hf model ages of 2.60–2.73Ga, reflecting their derivation by partial melting of overthickened juvenile lower crust of eclogitic composition, or an eclogitic mineral assemblage in the residue. Geochemical compositions of the biotite–monzogranites, with positive εNd(t) values (+2.3 to +2.5) and model ages <2.60Ga, indicate that they are evolved partial melts from a thickened juvenile crust of garnet amphibolite composition, or with garnet and amphiboles in the residue, followed by fractionation dominated by plagioclase precipitation. The garnet–syenogranites display variable contents of SiO2(62.3–72.3wt.%), and relatively high Zr (491–1096ppm), Ga (23.5–31.2ppm), Zn (38–124ppm), Y (34.1–85.6ppm) and Nb (9.4–90.0ppm) abundances with 104×Ga/Al ratios of 3.1–4.2. They also possess low Sr (50–161ppm) concentrations and strong negative Eu anomalies. These features, integrated with Nd model ages of 2.46–2.50Ga and relatively constant negative εNd(t) values (−2.5 to −2.9) with increasing SiO2contents, suggest A-type granitic affinities of intraplate extensional or rift setting with evolution of the magma from partial melts derived from Neoarchean tonalitic rocks. The distinct geochemical features and zircon saturation temperatures of the granitoids are indicative of high melting temperatures (900–1000°C) at relatively low pressures (6–10kbar). Based on previous works and our new data, we link the ca. 2500–2450Ma and 2000Ma magmatic events to a Neoarchean amalgamation of microblocks and Paleoproterozoic mobile belts. The metamorphic ages of 1800–1820Ma might reflect an amphibolite facies retrograde event.