Two Stages of Late Mesozoic Magmatism in Southern Dalat Zone Associated with Paleo-Pacific Subduction Constrained by Whole-Rock Chemistry and Geochronology Combined with New Findings on Zircon Chemical Composition

IF 0.7 4区地球科学 Q4 GEOSCIENCES, MULTIDISCIPLINARY Doklady Earth Sciences Pub Date : 2024-05-13 DOI:10.1134/s1028334x24601251

Nong Thi Quynh Anh, Tran Van Xuan, Pham Trung Hieu, Pham Minh, Nguyen Tuan, Nguyen Xuan Kha, Truong Quoc Thanh

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Abstract

Late Mesozoic granitoids in the Dalat Zone are widely accepted to be formed in two main stages of magmatism corresponding to Paleo-Pacific subduction and post-orogenic regimes. This study focuses on the transitional phase (ca. 20 Ma interval) between these two stages with representatives of the Deoca granitoids and Ankroet granite in the southern Dalat Zone, mainly along the coastal line from Vung Tau to Binh Thuan. The Deoca rock suite comprises coarse- to medium-grained granites, fine-grained granophyric granite, and dyke phases while the Ankroet suite mainly comprises medium- to fine-grained granite. Although the whole-rock chemical characteristics of these two rock suites to some extent overlap each other with the peraluminous and calc-alkaline signatures and the similarities in element abundance yet exhibit distinction. Rocks of the Deoca suite are characterized by typical arc-like affinities with strong positive anomalies of Rb, Th, U, Pb, and Nd, and negative anomalies of Ba, Nb, Sr, P, Eu, and Ti. The Ankroet granite is especially more depleted in Sr, P, Eu, and Ti and enriched in Rb, Th, U, Ta, and Pb in comparison with the Deoca rock suite and can be categorized as “within-plate” granite formed in the following extensional stage. Zircon U–Pb geochronology of the two rock suites distinguishes two magmatic stages, 93.6 ± 1.3 Ma for the Deoca rocks and 73.3 ± 1.8 Ma for the Ankroet rocks. Zircon Hf isotopic compositions indicate the similarities in source materials of these two rock suites, but they might have been influenced by different geodynamics and magma differentiation processes. Zircon Hf isotopic compositions of the studied rocks are compared to those from the adjacent area (Cambodia, Datlat-Kratie Belt) and suggest that Carboniferous-Permian magmas generating inherited zircons in Cambodia are most likely the source materials of Late Mesozoic plutonic rocks in the Dalat Zone/Cambodia (Dalat-Kratie Belt). This study highlights the distinction of these two rock suites by new observations on zircon morphology and composition. Although they are both enriched in heavy REE relative to light REE, enriched in Ce and depleted in Eu and typical for magmatic zircons, samples of the Ankroet suite tend to be more enriched in REEs compared to those of the Deoca suite, except Eu with strong Eu anomaly. This may indicate the higher involvement of hydrothermal processes on Ankroet granite that is supported by common CL-dark rims of zircon.

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与古太平洋俯冲有关的南大叻区中生代晚期岩浆活动的两个阶段：全岩化学和地质年代学的约束以及锆石化学成分的新发现

摘要：人们普遍认为达叻区的中生代晚期花岗岩是在两个主要岩浆形成阶段形成的，这两个阶段分别对应古太平洋俯冲机制和后成因机制。本研究的重点是这两个阶段之间的过渡阶段（约 20 Ma 间隔），其代表岩体为达叻区南部的 Deoca 花岗岩和 Ankroet 花岗岩，主要分布在从 Vung Tau 到 Binh Thuan 的沿海地带。Deoca 岩组包括粗粒至中粒花岗岩、细粒花岗岩和堤相，而 Ankroet 岩组主要包括中粒至细粒花岗岩。虽然这两个岩组的全岩化学特征在一定程度上相互重叠，具有过铝和钙碱性特征，元素丰度也很相似，但还是有区别的。德奥卡岩相的岩石具有典型的弧状亲和性，Rb、Th、U、Pb 和 Nd 呈强正异常，Ba、Nb、Sr、P、Eu 和 Ti 呈负异常。与 Deoca 岩组相比，Ankroet 花岗岩的 Sr、P、Eu 和 Ti 尤其贫化，而 Rb、Th、U、Ta 和 Pb 则富集，可归类为在随后的扩展阶段形成的 "板内 "花岗岩。两套岩石的锆石U-Pb地质年代可分为两个岩浆阶段，Deoca岩石为93.6 ± 1.3 Ma，Ankroet岩石为73.3 ± 1.8 Ma。锆石Hf同位素组成表明这两个岩套的岩源材料相似，但可能受到不同地球动力学和岩浆分异过程的影响。将所研究岩石的锆石 Hf 同位素组成与邻近地区（柬埔寨，达拉特-桔井带）的锆石 Hf 同位素组成进行了比较，结果表明，在柬埔寨产生继承锆石的石炭纪-二叠纪岩浆很可能是达拉特区/柬埔寨（达拉特-桔井带）中生代晚期深成岩的来源材料。本研究通过对锆石形态和成分的新观察，强调了这两种岩石套件的区别。虽然相对于轻型 REE，它们都富含重型 REE，富含 Ce，贫化 Eu，是岩浆锆石的典型特征，但与 Deoca 岩石组相比，Ankroet 岩石组的样品往往富含更多的 REEs，只有 Eu 岩石组具有强烈的 Eu 异常。这可能表明 Ankroet 花岗岩中热液过程的参与程度较高，锆石中常见的 CL-暗色边缘也证明了这一点。

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来源期刊

Doklady Earth Sciences 地学-地球科学综合

CiteScore

1.40

自引率

22.20%

发文量

138

审稿时长

3-6 weeks

期刊介绍： Doklady Earth Sciences is a journal that publishes new research in Earth science of great significance. Initially the journal was a forum of the Russian Academy of Science and published only best contributions from Russia. Now the journal welcomes submissions from any country in the English or Russian language. Every manuscript must be recommended by Russian or foreign members of the Russian Academy of Sciences.