Abstract
Abstract Three generations of mylonites discovered in the northern Prince Charles Mountains (nPCM) are associated with episodes of crustal thickening and thinning. Firstâgeneration mylonites (MY1) are shallow thrusts which preâdate both folding and peak metamorphic conditions, and formed during early crustal thickening. Secondâgeneration mylonites (MY2) are significant subvertical normal faults that formed at conditions of c. 5 kbar and 700° C, and throughout the nPCM consistently display NWâblock uplift. It is argued that MY2 uplift was rapid in the northâwest, produced exhumation of approximately 6â7 km, and caused reâequilibration of most nPCM assemblages at lower pressures. It is suggested that features of this terrane may be reconciled with a tectonic model involving simultaneous crustal thickening and lithospheric thinning; MY2 uplift may reflect isostatically induced uplift. In contrast, the adjacent east Lambert Glacier Region (eLGR) was unaffected by MY2 uplift and remained at lower crustal levels. PâT trajectories across this oblique terrane thus reflect a gradual transition in uplift rates: nPCM paths preserve mostly cooling after partial MY2 exhumation, while those in the eLGR are dominated by slower uplift which facilitated the retrograde growth of coronas and symplectites at amphibolite facies conditions. Amphibolite facies thirdâgeneration mylonites, MY3, postâdate the preserved PâT segments and are lowâangle normal faults which indicate consistent easterly transport across the entire terrane. It is proposed that they are related to tectonic collapse.
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