A wealth of P–T–t information from metasediments in the HP–UHP terrane of the Pohorje Mountains, Slovenia, elucidates the evolution of the Eastern Alps

IF 3.5 2区 地球科学 Q1 GEOLOGY Journal of Metamorphic Geology Pub Date : 2023-07-26 DOI:10.1111/jmg.12740
Botao Li, Hans-Joachim Massonne, Xiaoping Yuan
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引用次数: 1

Abstract

Contrasting views exist in regard of the evolution of metamorphic rocks in the southeastern Pohorje Mountains (Mts), located in the southeastern Eastern Alps. Major debated points are whether micaschists have experienced ultrahigh-pressure metamorphism in the Late Cretaceous (Eo-Alpine) and whether they were continuously exhumed or experienced a multiple subduction–exhumation process from that time on. Therefore, we studied micaschist sample 18Slo39 with two generations of garnet and phengitic muscovite from this area. Our detailed study of this rock included petrographic observations, chemical analyses of minerals with the electron microprobe, pseudosection modelling, conventional geothermometry, and monazite in-situ U-Th-Pb dating using laser-ablation inductively coupled plasma (ICP) mass spectrometry. The following results were obtained: The studied micaschist was subject to a peak pressure of 1.31 ± 0.14 GPa at 603 ± 26°C in Eo-Alpine times: 90.62 ± 2.78 (2σ) Ma (Stage I). Contact metamorphism at pressure–temperature conditions of 0.66 ± 0.10 GPa and 577 ± 23°C was induced by the intrusion of the Pohorje pluton (Stage III). We determined an early Miocene age of 18.33 ± 0.43 (2σ) Ma for this intrusion. Based on this study and the previously reported data for a micaschist (16Slo12) taken in the vicinity of sample 18Slo39, a geodynamic model is proposed for the region of the Pohorje Mts considering Eo-Alpine subduction of oceanic crust and European continental crust, of which the micaschist was part of. Another high-pressure event in the Eocene (Stage II) was the result of intracontinental subduction because of transpression by the Periadriatic fault system that separates the Eastern Alps from the Southern Alps. This type of subduction gave rise to magma generation and ascent to form the Pohorje pluton, which caused contact metamorphism in its vicinity.

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斯洛文尼亚波霍杰山脉HP‐UHP地体变质沉积物中丰富的P‐T‐T信息阐明了东阿尔卑斯山脉的演化
关于位于东阿尔卑斯东南部的波荷杰山脉东南部变质岩的演化,存在着截然不同的观点。目前争论的主要问题是,晚白垩世(古阿尔卑斯)云母岩屑是否经历了超高压变质作用,以及从那时起,云母岩屑是连续被挖掘出来的,还是经历了多次俯冲-挖掘过程。因此,我们对该地区的云母岩18Slo39样品进行了两代石榴石和白云母的研究。我们对该岩石进行了详细的研究,包括岩石学观察、电子探针矿物化学分析、伪剖面建模、常规地热测量,以及利用激光烧蚀电感耦合等离子体(ICP)质谱法对独居石进行原位U-Th-Pb测年。结果表明:研究的云母岩在603±26℃(90.62±2.78 (2σ) Ma)的始高寒期(90.62±2.78 (2σ) Ma)经历了1.31±0.14 GPa的峰值压力,在0.66±0.10 GPa和577±23℃的压力-温度条件下发生了接触变质作用(第三阶段),确定了该侵入岩的早中新世年龄为18.33±0.43 (2σ) Ma。在此基础上,结合已有报道的18Slo39样品附近的云母岩(16Slo12)资料,提出了一个考虑洋壳和欧洲大陆地壳的ew - alpine俯冲作用的Pohorje Mts地区地球动力学模型,其中云母岩是其中的一部分。始新世(第二阶段)的另一个高压事件是由于分隔东阿尔卑斯和南阿尔卑斯的外亚得里亚海断裂系统的挤压作用造成的陆内俯冲。这种俯冲作用引起岩浆生成和上升,形成了波荷杰岩体,并在其附近引起了接触变质作用。
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来源期刊
CiteScore
6.60
自引率
11.80%
发文量
57
审稿时长
6-12 weeks
期刊介绍: The journal, which is published nine times a year, encompasses the entire range of metamorphic studies, from the scale of the individual crystal to that of lithospheric plates, including regional studies of metamorphic terranes, modelling of metamorphic processes, microstructural and deformation studies in relation to metamorphism, geochronology and geochemistry in metamorphic systems, the experimental study of metamorphic reactions, properties of metamorphic minerals and rocks and the economic aspects of metamorphic terranes.
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