Neoarchaean metamorphic evolution of the Yilgarn Craton: A record of subduction, accretion, extension and lithospheric delamination

Abstract

Abstract The greater part of the metamorphic record of the Yilgarn Craton formed during a protracted middle Neoarchaean orogenic cycle, spanning from about 2750 to 2620\u202fMa. At least six distinct metamorphic events are defined by parageneses in different tectono-stratigraphic settings. This review characterizes the middle Neoarchaean metamorphic response of the entire craton using large databases. Rock descriptions from ~60,000 sites in government databases and ~1040 PT determinations from all sources, are used to construct metamorphic map patterns for each of these metamorphic events. P-T paths and timing of each metamorphic event are characterized using petrology and the well-constrained PT determinations from this study (n\u202f=\u202f287), combined with metamorphic age determinations from all sources (n\u202f=\u202f114). The spatial patterns and metamorphic conditions of each event, provides critical constraints on tectonic settings and changes in tectonics over 130 million years. The record of metamorphism in conjunction with stratigraphic, kinematic and magmatic constraints shows that the Neoarchaean craton evolved from an accretionary crustal growth phase (Ma and M1), to thermal reworking of the crust during massive influx of granitic intrusions (M2), and lithospheric extension after the termination of subduction (M3). These events were followed by lithospheric delamination, resulting in a craton-wide, diffusion-delayed thermal pulse that coincided with renewed contraction (M4). M1 metamorphism at 2748\u202f±\u202f19, 2727\u202f±\u202f8 and 2706\u202f±\u202f10\u202fMa experienced high-P/moderate-T hairpin, clockwise P-T paths during burial of magmatic arc margins during terrane accretion events. M2 regional-contact type metamorphism at 2671\u202f±\u202f6\u202fMa tracked low-P/moderate-T clockwise P-T paths in back-arc settings during voluminous felsic magmatism related to shallow subduction. M3 metamorphism at 2656\u202f±\u202f5\u202fMa experienced low-P/moderate-T anticlockwise P-T paths in post-volcanic rift basins formed during lithospheric extension. M4 metamorphic peaks at 2644\u202f±\u202f4 and 2629\u202f±\u202f7\u202fMa experienced low-P/high-T clockwise P-T paths during regional-scale thermal pulses resulting from lower-crust and mantle lithosphere delamination at 2665–2668\u202fMa.