The Coorg Block in southern India is one of the oldest crustal fragments on the globe and is composed of Mesoarchean magmatic suites, dominantly charnockites, gabbros and their variants that were metamorphosed under granulite facies conditions. Here we investigate a suite of charnockites, metagabbros and amphibolite from this block by undertaking detailed field studies, petrological and geochemical analysis, and zircon and monazite isotope geochronology. Phase equilibria modeling using pseudosection computations shows ultrahigh-temperature metamorphic conditions yielding a P-T range of 10–11 kbar at 1000 °C for the charnockite assemblage and 8–9 kbar at 950 °C for the metagabbro. Geochemistry indicates that the felsic and mafic rocks are sub-alkaline and represent a tholeiitic magma series. The rocks were derived possibly through fractionation of a reduced primary magma in a Mesoarchean subduction-related setting. Zircon grains from the charnockites and gabbros show magmatic textures, with LREE depletion and HREE enrichment, negative La, Pr, Nd, Eu and positive Ce, Sm, Gd anomalies, and Th/U ratios consistent with magmatic crystallization. We present zircon and monazite U–Pb data from a comprehensive suite of samples that indicate timing of peak of magmatic emplacement for both the charnockite and gabbroic suites occurred at ∼ 3.15 Ga, closely followed by metamorphism at ∼ 3.0 Ga. The presence of magmatic xenocrysts of up to ∼ 3.5 Ga in some of these rocks suggest older crustal components in the basement. Zircon Lu–Hf analyses suggest that the amphibolite and gabbro were mostly derived from depleted mantle sources whereas the charnockite suite involved both juvenile and reworked Paleoarchean components. The tectonic setting of these felsic and mafic magmatic rock suites correlates with a Mesoarchean subduction system, complementing recent models on the emergence of modern-style plate tectonics in the early Earth. We correlate the Mesoarchean arc magmatic suites in the Coorg Block to the building blocks of the core of the Earth’s oldest supercontinent Ur, with the surrounding Neoarchean granulite blocks and their equivalents in other cratonic fragments to the ‘expanded Ur’.

印度南部的 Coorg 地块是地球上最古老的地壳碎片之一，由中太古代岩浆岩组成，主要是在麻粒岩相条件下变质的褐云母、辉长岩及其变体。在这里，我们通过进行详细的实地研究、岩石学和地球化学分析以及锆石和独居石同位素地质年代学，调查了该区块中的一套霞诺石、变辉石和角闪岩。使用拟断面计算的相平衡建模表明，超高温变质条件在 1000 °C 时产生 10-11 kbar 的钙锰矿组合，在 950 °C 时产生 8-9 kbar 的变辉长岩。地球化学表明，长英质和镁铁质岩石呈亚碱性，代表拉斑岩浆系列。这些岩石可能是通过中太古代俯冲相关环境中减少的原生岩浆的分馏而产生的。来自钙锰矿和辉长岩的锆石颗粒显示岩浆结构，具有 LREE 耗竭和 HREE 富集，负 La、Pr、Nd、Eu 和正 Ce、Sm、Gd 异常，以及与岩浆结晶一致的 Th/U 比值。我们提供了来自一套综合样品的锆石和独居石 U-Pb 数据，这些样品表明钙锰矿和辉长岩岩浆侵位的峰值时间发生在 ~ 3.15 Ga，紧随其后的是 ~ 3.0 Ga 的变质作用。岩浆捕虏晶的存在其中一些岩石中高达 ~ 3.5 Ga 表明基底中有更古老的地壳成分。锆石 Lu-Hf 分析表明，角闪岩和辉长岩主要来自贫化的地幔源，而闪锌矿岩组包括新生的和改造后的古太古代成分。这些长英质和镁铁质岩浆岩套件的构造背景与中太古代俯冲系统相关，补充了早期地球现代板块构造出现的最新模型。我们将 Coorg 地块中的中太古代弧形岩浆岩套与地球上最古老的超大陆 Ur 核心的构造块联系起来，将周围的新太古代麻粒岩块及其在其他克拉通碎片中的等价物与“膨胀的 Ur”联系起来。这些长英质和镁铁质岩浆岩套件的构造背景与中太古代俯冲系统相关，补充了早期地球现代板块构造出现的最新模型。我们将 Coorg 地块中的中太古代弧形岩浆岩套与地球上最古老的超大陆 Ur 核心的构造块联系起来，将周围的新太古代麻粒岩块及其在其他克拉通碎片中的等价物与“膨胀的 Ur”联系起来。这些长英质和镁铁质岩浆岩套件的构造背景与中太古代俯冲系统相关，补充了早期地球现代板块构造出现的最新模型。我们将 Coorg 地块中的中太古代弧形岩浆岩套与地球上最古老的超大陆 Ur 核心的构造块联系起来，将周围的新太古代麻粒岩块及其在其他克拉通碎片中的等价物与“膨胀的 Ur”联系起来。