Intracontinental reworking in capricorn Orogen, Western Australia: the 1680-1620 Ma Mangaroon Orogeny

Structures and metamorphic mineral assemblages throughout much of the Proterozoic Capricorn Orogen have been attributed to the 1830-1780 Ma Capricorn Orogeny, However, in the northern part of the Gascoyne Complex at the exposed western end of the orogen, precursor sediments to pelitic gneiss and metamorphosed feldspathic sandstone were deposited after 1680 +/- 13 Ma. The sediments were first deformed and intruded by voluminous granites during intracontinental reworking (the Mangaroon Orogeny) between 1680 Ma and 1620 Ma. The Mangaroon Orogeny comprises a subhorizontal gneissic layering and peak metamorphic conditions of upper amphibolite facies (D-1m/ M-1m) followed by upright, macroscopic southeast-trending folds and an associated subvertical foliation formed at greenschist faces (D-2m/M-2m). Schlieric biotite-muscovite granodiorte dated at 1677 +/- 5 Mo represents an anatectic melt that intruded during D-2m. Cross-cutting biotite and biotite-muscovite monzogranites mainly crystallised at ca 1680-1660 Mo, but granite plutons were emplaced across the Gascoyne Complex until 1620 Mo. Our findings invalidate correlation of these metasedimentary rocks with lower grade rocks of the upper Wyloo Group along the northern margin of the orogen, and necessitate a reassessment of tectonic activity in the orogen attributed to the Capricorn Orogeny.