Neoproterozoic Eclogite-to Granulite-Facies Transition in the Ubendian Belt, Tanzania, and the Timescale of Continental Collision

Abstract In collision-type orogens, where high-pressure and ultrahigh-pressure (HP–UHP) metamorphism usually occurs, deeply subducted continental slabs with eclogitized mafic rocks often undergo recrystallization/overprinting various geothermal gradients after the peak conditions at lower-to-middle-crustal levels. During crustal stabilization, transition from eclogite-to granulite-facies is common. We conducted metamorphic petrology zircon geochronology on (1) bimineralic (2) partially granulitized eclogites Neoproterozoic Ufipa Terrane (Southwestern Tanzania). Microtextural relationships mineral chemistry define three stages: eclogite (M1), HP overprinting (M2), amphibolite-facies retrogression (M3). The has a basaltic composition lacks M2 minerals. contrast, kyanite characterized by gabbro-dioritic whole-rock contains inherited magmatic zircon. Although matrix highly granulitized, garnet contain eclogite-facies inclusions. Phase equilibria modeling revealed P–T of 2.1–2.6 GPa 650–860°C for M1 stage 1.4–1.6 750–940°C stage. Zircon inclusions Eu anomaly in REE patterns yielded age 588 ± 3 Ma. overgrowths surrounding Paleoproterozoic cores 562 A weak negative absence eclogitic suggest growths These new data indicate an time 26 4 million years (Myr), suggesting rate rock exhumation toward lower level 0.7–1.5 mm/year. Furthermore, density evolution model indicates that buoyant host orthogneiss low-density plays important role carrying high-density eclogite. Our 2D thermomechanical also suggests slab break-off angle subduction <20° triggers sliver 20–30 Myr granulite large HP–UHP terranes major collision zones.