Calcite Marbles as Records of Episodic Deformation During Exhumation of High‐Pressure Rocks (Syros Island, Aegean Region)

Abstract We present new calcite microstructural, petrofabric, and grain size data from high‐pressure marbles, integrated with microstructural observations from associated greenschist‐facies rocks, to investigate spatio‐temporal variations in deformation intensity during the exhumation of the Cycladic Blueschist Unit in southern Syros Island (Cycladic Massif, Greece). Our results reveal a pronounced spatial and temporal heterogeneity in deformation intensity across different structural levels and metamorphic conditions. Intense deformation occurred under eclogite‐ to early blueschist‐facies conditions was followed by a period of deformation cessation, marked by the widespread development of columnar aragonite microstructure, indicative of static conditions. Deformation resumed during continued exhumation at lower‐pressure blueschist‐facies conditions, becoming increasingly localized in the lower structural levels, where the columnar fabric underwent dynamic recrystallization, while the upper levels remained undeformed. At greenschist‐facies conditions, deformation ceased and was restricted to narrow, foliation‐parallel bands, with no direct link to major tectonic structures. Our results suggest an early exhumation characterized by intense top‐to‐SE deformation, possibly related to internal imbrication of the rock pile. Subsequently, rocks were exhumed as a coherent body via a top‐to‐NE extrusion mechanism that operated from blueschist‐ to greenschist‐facies conditions with the deformation becoming progressively localized along the bounding faults of the wedge. High‐pressure marbles provide robust markers of deformation heterogeneity and play a critical role in distinguishing discrete deformation phases from eclogite‐ to greenschist‐facies conditions. Our findings underscore the value of integrating calcite microstructures with mineral and structural data to resolve the complex deformation histories associated with the exhumation of high‐pressure rocks.