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首页> 外文期刊>Geosciences >Pressure–Temperature History of the 3 Ga Tartoq Greenstone Belt in Southwest Greenland and Its Implications for Archaean Tectonics
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Pressure–Temperature History of the 3 Ga Tartoq Greenstone Belt in Southwest Greenland and Its Implications for Archaean Tectonics

机译：格陵兰西南部> 3 Ga Tartoq绿岩带的压力-温度史及其对古构造的启示

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The Tartoq greenstone belt of southwest Greenland represents a well-preserved section through 3 Ga old oceanic crust and has the potential to provide important constraints on the composition and geodynamics of the Archaean crust. Based on a detailed structural examination, it has been proposed that the belt records an early style of horizontal convergent plate tectonics where elevated temperatures, compared to the modern-day, led to repeated aborted subduction and tonalite–trondhjemite–granodiorite (TTG) type melt formation. This interpretation hinges on pressure–temperature (P–T) constraints for the belt, for which only preliminary estimates are currently available. Here, we present a detailed study of the pressure–temperature conditions and metamorphic histories for rocks from all fragments of the Tartoq belt using pseudosection modelling and geothermobarometry. We show that peak conditions are predominantly amphibolite facies, but range from 450 to 800 °C at up to 7.5 kbar; reaching anatexis with formation of TTG-type partial melts in the Bikuben segment. Emplacement of the Tartoq segments into the host TTG gneisses took place at approximately 3 Ga at 450–500 °C and 4 kbar as constrained from actinolite–chlorite–epidote–titanite–quartz parageneses, and was followed by extensive hydrothermal retrogression related to formation of shear zone-hosted gold mineralisation. Tourmaline thermometry and retrograde assemblages in mafic and ultramafic lithologies constrain this event to 380 ± 50 °C at a pressure below 1 kbar. Our results show that the convergent tectonics recorded by the Tartoq belt took place at a P–T gradient markedly shallower than that of modern-day subduction, resulting in a hot, weak and buoyant slab unable to generate and transfer ‘slab pull’, nor sustain a single continuous downgoing slab. The Tartoq belt suggests that convergence was instead accomplished by under-stacking of slabs from repeated aborted subduction. The shallow P–T path combined with thermal relaxation following subduction stalling subsequently resulted in partial melting and formation of TTG melts.
机译：格陵兰西南部的Tartoq绿岩带代表了一个> 3 Ga老洋壳的保存完好的断面，并有可能对古生硬壳的组成和地球动力学提供重要的限制。根据详细的结构检查，已提出该带记录了早期的水平会聚板块构造形式，与现代相比，温度升高导致反复俯冲俯冲和斜方晶石-长白云母-碎屑闪长岩（TTG）型熔体编队。这种解释取决于传送带的压力-温度（PT）约束，目前只有初步估算可用。在这里，我们使用伪截面模型和地热气压计，详细研究了塔尔托克带所有片段的岩石的压力-温度条件和变质历史。我们显示峰值条件主要是闪石相，但范围在450至800°C，最高7.5 kbar。在Bikuben段中形成了TTG型部分熔体，达到了厌食症。在阳起石-绿泥石-锂辉石-钛铁矿-石英共生物的约束下，Tartoq片段在450-500°C约3 Ga和4 kbar受制于TTG片麻岩中，随后伴随着大量的热液倒退剪切带主持的金矿化。镁铁质和超镁铁质岩性中的电气石测温和逆行组合将这一事件在低于1 kbar的压力下限制在380±50°C。我们的结果表明，由塔尔托克带记录的收敛构造发生在一个P-T梯度上，明显比现代俯冲要浅，从而导致一个炎热，薄弱和浮力的板块无法生成和传递“板块拉力”，也没有维持单个连续下降平板。塔尔托克（Tartoq）带表明，收敛是通过反复中止俯冲将板块堆放不足而实现的。俯冲失速后的浅层P路径与热弛豫相结合，随后导致部分熔融并形成了TTG熔体。

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