The genesis of felsic magmatism during the closure of the Northeastern Paleo-Tethys Ocean: Evidence from the Heri batholith in West Qinling, China
The genesis of felsic magmatism during the closure of the Northeastern Paleo-Tethys Ocean: Evidence from the Heri batholith in West Qinling, China
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东北古特提斯洋闭合过程中长英质岩浆作用的成因——来自西秦岭赫日岩基的证据
DOI：
10.1016/j.gr.2020.02.014
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发表时间：
2020
影响因子：
6.1
通讯作者：
Guo-Chen Dong
中科院分区：
文献类型：
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作者：
Hui-Qiang Xing;Xiao-Wei Li;Ji-Feng Xu;Xuan-Xue Mo;Wei Shan;Hong-Xia Yu;Jun-Qiang Hu;Xiong-Fei Huang;Guo-Chen Dong
为了更好地了解汇聚大陆边缘大量硅质岩的成因，我们对青藏高原东北部西秦岭赫日岩基进行了综合研究，获得了年代学、矿物学和同位素（包括全岩Sr-Nd-Pb、原位锆石Hf）数据。岩基由准铝质至弱过铝质花岗闪长岩 (235–233 Ma) 和具有 I 型亲和力的斑状花岗闪长岩 (230–223 Ma) 组成。两种岩性具有相似的主量元素、微量元素和单键 Nd 同位素组成。详细的元素数据表明，这些花岗闪长岩经历了角闪石和磷灰石的分级结晶，并有一定程度的斜长石（即筛状斜长石核）堆积。除斑状花岗闪长岩外，其他分析样品的 Pb 同位素均具有高放射成因性和均匀性（（206Pb/204Pb）t：17.263–18.472，（206Pb/204Pb）t：15.571–15.591，（206Pb/204Pb）t： 38.032–38.304)，加上初始 Sr ((87Sr/86Sr)t：0.707251–0.708103) 和 Nd (εNd(t) = -7.1 至 -6.3) 同位素的有限变化，两阶段模型年龄 (TDM2) 为 1.58–1.52 Ga。这些因素共同表明推导自 地壳下层的中元古代基底岩石，或不同年龄成分的综合混合，产生了地壳平均居住年龄。斑状花岗闪长岩的单键 Nd 同位素组成与花岗闪长岩惊人地相似。与角闪岩的实验熔体成分相比，由于角闪石和黑云母的不一致分解，赫里花岗岩可能源自无流体条件下的角闪岩源。根据西秦岭花岗岩侵入体的时空分布和区域构造演化，我们认为赫日岩基是在华北克拉通（NCC）与华南克拉通（SCC）最初碰撞过程中形成的，并伴随着古特提斯洋的闭合。考虑到之前公布的数据和我们的新数据，我们认为赫里花岗岩主要是由下地壳角闪岩的部分熔融产生的，还有少量来自地幔的熔融物。
To better understand the origin of voluminous silicic rocks in a convergent continental margin, we conducted an integrated study in which we have obtained geochronological, mineralogical, and isotopic (including whole-rock Sr–Nd–Pb, in-situ zircon Hf) data of the Heri batholith in West Qinling on the NE Tibetan Plateau. The batholith is composed of metaluminous to weakly peraluminous granodiorites (235–233 Ma) and porphyritic granodiorites (230–223 Ma) with an I-type affinity. Both lithologies share similar major, trace elemental and Srsingle bondNd isotopic compositions. Detailed elemental data demonstrate that these granodioritic rocks underwent fractional crystallization of hornblende and apatite, with plagioclase (i.e. sieve-textured plagioclase cores) accumulation to some extent. Except for porphyritic granodiorites, the Pb isotopes for other analyzed samples are characterized by high radiogenicity and uniformity ((206Pb/204Pb)t: 17.263–18.472, (206Pb/204Pb)t: 15.571–15.591, and (206Pb/204Pb)t: 38.032–38.304), together with limited variations in initial Sr ((87Sr/86Sr)t: 0.707251–0.708103) and Nd (εNd(t) = −7.1 to −6.3) isotopes with two-stage model ages (TDM2) of 1.58–1.52 Ga. These factors collectively point to a derivation from the Mesoproterozoic basement rocks at the lower crustal level, or a comprehensive mixing of different-age components that generated an average crustal residence age. The Srsingle bondNd isotopic compositions of the porphyritic granodiorites are strikingly similar to those of granodiorites. Compared with the experimental melt compositions of amphibolites, the Heri granitoids are probably derived from an amphibolitic source under fluid-absent conditions due to the incongruent breakdown of amphibole and biotite. Based on the temporal–spatial distribution of granitic intrusions in West Qinling and the regional tectonic evolution, our interpretation is that the Heri batholith was formed during the initial collision between the North China Craton (NCC) and the South China Craton (SCC), which was accompanied by the closure of the Paleotethyan Ocean. Considering both previously published data and our new data, we propose that the Heri granitoids were mainly generated by the partial melting of lower crustal amphibolites, with minor mantle-derived melts.