The Sivorg Terrane is the largest crustal block of the Heimefrontfjella.
It consists of a thick supracrustal sequence of metavolcanic and metasedimentary
rocks that are intruded by a wide range of predominantly granitic
plutonic rocks. The protolith ages of the metavolcanic rocks have been dated
at ~1170-1140 Ma and the granitoid intrusions at ~1110-1050 Ma. The best
estimate for Grenville-age metamorphism in the Sivorg Terrane is 1090-1060
Ma. Unlike the other two terranes in the Heimefrontfjella, the Sivorg Terrane
records intense reworking of Mesoproterozoic rocks during the Late Neoproterozoic-
Cambrian East African – Antarctic Orogeny. U-Pb detrital zircon
provenance analyses from two samples indicate that at least two age-groups of
different supracrustal sequences crop out in the Sivorg Terrane. The older,
preorogenic sequence gave youngest detrital ages of ~1140 Ma, which are
interpreted as dating the maximum deposition age of the original sediment.
These rocks also provide evidence of a Palaeoproterozoic to Archaean foreland.
The second sample is dominated by Mesoproterozoic to late Neoproterozoic
detrital zircons, with a significant proportion of ages ranging from 1100
to 980 Ma. The youngest ages significantly postdate the Grenville-age metamorphism,
so the sediments must have been deposited after or during the Late
Mesoproterozoic orogenesis and, as such, might represent remnants of a
molasse deposit of the orogen.
The Betsiaka Group, located on the northern edge of the Bemarivo Domain in northern Madagascar, consists of metamorphic felsic rocks, amphibolite, and marbles. These rocks are overlain by the Permo-Triassic sedimentary cover to the northwest and are separated by a fault from the Neoproterozoic volcanic rocks of the Bemarivo Domain. This study aims to determine the provenance and geodynamic evolution of the Betsiaka Group. Orthoamphibolites are associated with siliciclastic sedimentary rocks and exhibit geochemical characteristics of back-arc basin basalts. A quartzite from the Betsiaka Group contains detrital zircon with a youngest single grain U–Pb age of 1771 ± 28 Ma, with peaks at 2500and 1850 Ma. An orthogneiss intruding this group has concordant zircon grains interpreted to date the protolith’s crystallization at 841 ± 3.2Ma. The detrital zircon age pattern corresponds to that of the Aravalli Craton in India, suggesting that the northern Madagascar crustal fragment may have been formed off the coast of NW India between 1770 and 1000 Ma. This fragment could have been connected with other crustal fragments, now part of the SE Arabian plate, showing similar detrital zircon patterns in Neoproterozoic sedimentary rocks and sharing a calc-alkaline magmatism around 840 Ma.