Geological feature of Barrovian-type metamorphism and its tectonic implications:Insights from the Scottish Highlands and Himalayan orogen
Barrovian-type metamorphic zone is a product of metamorphism of Al-rich pelitic rocks under intermediate geothermal gradient at convergent plate margins,widely exposed in various orogens worldwide.While the mineral assemblages and metamorphic pressure-temperature conditions of Barrovian-type metamorphic zones in different regions are similar,the spatial distribution features of distinct metamorphic zones characterized by index minerals exhibit notable differences.The Scottish Highlands showcases a typical Barrovian-type metamorphic zone,whereas the Himalayan orogen exposes an inverted Barrovian-type metamorphic zone.The two types document diverse metamorphic and tectonic evolution processes,acting as natural laboratories for comparing and investigating the spatiotemporal evolution of thermal structure and dynamic regime of collision orogens as well as the geodynamic mechanism.This study utilizes the Scottish Highlands and Himalayan orogen as case studies,comparing the petrological and petrochronological features of the typical and inverted Barrovian-type metamorphic zones,and discussing the formation mechanisms of the two types.Studies in the two regions have unique characteristics.Investigations in the Scottish Highlands primarily concentrate on the heating mechanism,highlighting the significant influence of external heat source from asthenospheric mantle and its derived magmas on the development of Barrovian-type metamorphic zone.In contrast,investigations in the Himalayan orogen predominantly focus on the structural processes,emphasizing the role of in-sequence thrusting in the formation of inverted metamorphic zone.On this basis,this study extends the perspective from Barrivoan-type metamorphic zone to Barrovian-type metamorphism,comprehensively examining its heating mechanism and tectonic setting,and subsequently exploring its implication for collisional orogen and crustal reworking processes.
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