The transition from subduction arc to slab tearing: Evidence from Capraia Island, northern Tyrrhenian Sea

Abstract

The magmatic island of Capraia in the northern Tyrrhenian Sea records late stages in the evolution of a retreating subduction zone following continental accretion. Subduction rollback in the northern Tyrrhenian Sea was accompanied by an eastward migrating magmatic arc that coincided with Capraia at not, vert, similar7.7 Ma. This was followed by segmentation of the subducting slab through eastward propagating tear faults. We present high-precision, step-heating 40Ar/39Ar data that provide robust constraints for the timing of magmatism in Capraia, indicating that the island was subjected to two distinct magmatic episodes. The bulk of the island, characterised by typical calcalkaline, subduction-related volcanic rocks, formed during a relatively short period between 7.7 and 7.2 Ma. This major magmatic event was followed by a period of quiescence between 7.1 and 4.8 Ma. Magmatic activity resumed at 4.8 Ma, with the eruption of shoshonites from a monogenic centre in the southern part of the island. We interpret the latter as a magmatic event triggered by the formation of a tear fault within the subduction slab. The example provides a unique insight into the destruction of a subduction system during the interlinked process of subduction rollback, slab segmentation, and the development of slab tear faults.