Early Neoproterozoic magmatism and Caledonian metamorphism recorded by the Mårma Terrane, Seve Nappe Complex, northern Swedish Caledonides

Abstract

Petrology, geochronology, and bulk rock chemistry are combined to investigate the early Neoproterozoic magmatism and Cambrian-Ordovician metamorphism in the northern Swedish Caledonides. This includes several lithologies of the Mårma terrane in the Seve Nappe Complex exposed in the Kebnekaise region. U–Pb zircon geochronology yielded crystallization ages of 835 ± 8 Ma for a mylonitic orthogneiss, 864 ± 3 Ma for the Vistas Granite and 840 ± 7 Ma for a related granitic dyke. While a gabbro and granodiorite intrusions gave U–Pb zircon crystallization ages of 856 ± 3 Ma and 850 ± 1 Ma, respectively. U–Pb monazite dating of the mylonitic orthogneiss gave an upper intercept age of 841 ± 7 Ma and a lower intercept age of 443 ± 20 Ma. Pressure-temperature estimates derived for the mylonitic orthogneiss reveal metamorphic peak-pressure and peak-temperature of 10.5–11.75 kbar and 550–610 °C and 7.4–8.1 kbar at 615–675 ℃, respectively. Metamorphic pressure-temperature estimates for the Vistas Granite yield 6.5–7.5 kbar at 600–625 ℃. Whole rock chemistry coupled with U–Pb geochronology indicate that bimodal magmatism was related to attempted rifting of Rodinia between 870-840 Ma. Thematic collection: This article is part of the Caledonian Wilson cycle collection available at: https://www.lyellcollection.org/topic/collections/the-caledonian-wilson-cycle Supplementary material: https://doi.org/10.6084/m9.figshare.c.6675075