Abstract: The evolution of continental crust in convergent margins can be explored in southernmost South America (54-56°S). Plutonic rocks of the Fuegian Batholith and the rear-arc satellite Ushuaia Pluton were emplaced within the magmatic arc and the Fuegian fold-and-thrust belt, respectively. They record subduction zone processes in two distinct tectonic settings during the evolution of the Rocas Verdes Basin. We report new U-Pb zircon geochronology, bulk rock chemistry, Sr-Nd isotope data, and EPMA and in-situ LA-ICP-MS analyses of amphibole from ‘hornblendites’ and gabbroic-granitoid suites in order to evaluate the origin and evolution of the magmatic plumbing systems in the upper plate of the subduction zone. Textural relationships and amphibole compositions in hornblendite indicate crystallization at lower crustal depths with pressures of 7-8 kbar in the Fuegian Batholith and of 5-6 kbar in the Ushuaia Pluton. Lower Cretaceous suites of hornblendite and calc-alkaline hornblende-gabbro, diorite and tonalite in the Fuegian Batholith have eNdt values ranging between +2 and +4. They were emplaced within an island arc coeval with mid-oceanic type spreading in the Rocas Verdes back-arc basin. Isotope ratios and amphibole compositions in hornblendite indicate crystallization from primitive and hydrous sub-alkaline basaltic melts with relatively low LREE/HREE and low alkali contents. The Late Cretaceous plutons in the fold-and-thrust belt were emplaced after the tectonic juxtaposition of Rocas Verdes ophiolitic complexes. The Ushuaia Pluton, consisting of clinopyroxene-hornblende cumulates, hornblende-gabbro, diorite and monzodiorite, was emplaced during the waning stage of Late Cretaceous magmatism. In this case hornblendite amphiboles show high contents of alkalis, LREE and incompatible elements with a strong crustal affinity (Th, Ba, Rb). The enriched incompatible trace element patterns indicate their derivation from K-rich transitional magmas formed in supra-subduction settings. Chemical variations in amphibole from hornblendites and spatially related plutonic rocks are evaluated in terms of fluid flux from the subducted slab and partial melting of the sub-arc mantle, ultimately controlled by the thermal state of the subducted slab and convergence rates.

中文翻译：

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南美洲最南端 Fuegian Andes 白垩纪岩浆弧角闪石和深成岩套角闪石微量元素组成及岩石成因

摘要：南美洲最南端（54-56°S）可以探索会聚边缘的大陆地壳演化。Fuegian Batholith和弧后卫星Ushuaia Pluton的深成岩分别位于岩浆弧和Fuegian褶皱冲断带内。他们记录了 Rocas Verdes 盆地演化过程中两种不同构造环境中的俯冲带过程。我们报告了新的 U-Pb 锆石年代学、大块岩石化学、Sr-Nd 同位素数据以及来自“角闪石”和辉长花岗岩套件的角闪石的 EPMA 和原位 LA-ICP-MS 分析，以评估其起源和演化俯冲带上板块的岩浆管道系统。角闪石中的结构关系和角闪石成分表明在下地壳深度结晶，Fuegian 基岩中的压力为 7-8 kbar，乌斯怀亚岩体中的压力为 5-6 kbar。Fuegian Batholith中的角闪石和钙碱性角闪石-辉长岩、闪长岩和闪长岩的下白垩统套件的eNdt值介于+2和+4之间。它们被安置在 Rocas Verdes 弧后盆地中与中大洋类型同时期的岛弧内。角闪石中的同位素比和角闪石组成表明，从原始和含水的亚碱性玄武岩熔体中结晶，LREE/HREE 和碱含量相对较低。褶皱冲断带中的晚白垩世岩体是在 Rocas Verdes 蛇绿岩杂岩构造并置后就位的。乌斯怀亚冥王星，由单斜辉石-角闪石堆积体、角闪石-辉长岩、闪长岩和二闪长岩组成，位于晚白垩世岩浆作用减弱阶段。在这种情况下，角闪石角闪石显示出高含量的碱、轻稀土和具有强地壳亲和力的不相容元素（Th、Ba、Rb）。富集的不相容微量元素模式表明它们源自在超俯冲环境中形成的富钾过渡岩浆。角闪石和空间相关的深成岩角闪石的化学变化是根据俯冲板片的流体通量和亚弧地幔的部分熔化来评估的，最终由俯冲板片的热状态和收敛速度控制。在晚白垩世岩浆活动减弱阶段被侵位。在这种情况下，角闪石角闪石显示出高含量的碱、轻稀土和具有强地壳亲和力的不相容元素（Th、Ba、Rb）。富集的不相容微量元素模式表明它们源自在超俯冲环境中形成的富钾过渡岩浆。角闪石和空间相关的深成岩角闪石的化学变化是根据俯冲板片的流体通量和亚弧地幔的部分熔化来评估的，最终由俯冲板片的热状态和收敛速度控制。在晚白垩世岩浆活动减弱阶段被侵位。在这种情况下，角闪石角闪石显示出高含量的碱、轻稀土和具有强地壳亲和力的不相容元素（Th、Ba、Rb）。富集的不相容微量元素模式表明它们源自在超俯冲环境中形成的富钾过渡岩浆。角闪石和空间相关的深成岩角闪石的化学变化是根据俯冲板片的流体通量和亚弧地幔的部分熔化来评估的，最终由俯冲板片的热状态和收敛速度控制。富集的不相容微量元素模式表明它们源自在超俯冲环境中形成的富钾过渡岩浆。角闪石和空间相关的深成岩角闪石的化学变化是根据俯冲板片的流体通量和亚弧地幔的部分熔化来评估的，最终由俯冲板片的热状态和收敛速度控制。富集的不相容微量元素模式表明它们源自在超俯冲环境中形成的富钾过渡岩浆。角闪石和空间相关的深成岩角闪石的化学变化是根据俯冲板片的流体通量和亚弧地幔的部分熔化来评估的，最终由俯冲板片的热状态和收敛速度控制。