Subduction to accretion in the southern Irumide Belt: Perspective from geochronology and petrology of granulites and charnockites in NW Mozambique

In the Mesoproterozoic Southern Irumide Belt, Tete Province, NW Mozambique, granulite-facies metavolcaniclastic rocks and orthogneisses from the Chidzolomondo Complex provide new constraints on the subduction and accretionary phases of the belt evolution. The complex comprises a metavolcano-sedimentary succession intruded by syn- to post-orogenic granitoids, charnockites and gabbros. The paragneisses exhibit a calc-alkaline chemical composition akin to intermediate magmatic rocks found in volcanic arcs. They are interpreted as products of a three-component mixture, consisting of pelite-aluminous, quartz, and reworked mafic volcanic rocks. A paragneiss sample contains detrital zircon with ages mainly between 1344 and 1098 Ma and epsilon Hf(t) values between -10 to +7, defining a maximum depositional age of 1121 +/- 2 Ma. A charnockitic gneiss, dated at 1097 +/- 3 Ma, and a metagabbro, dated at 1061 +/- 3 Ma, respectively, represent the syn- and late-orogenic magmatic events. Both rocks exhibit juvenile epsilon Hf(t) signatures ranging from +1.5 to +4.5. The mineral assemblage of cordierite + garnet + orthopyroxene in metavolcaniclastic rocks, and plagioclase + hypersthene + diopside in the metagabbro, provide evidence of the HT-LP metamorphic conditions. Phase equilibria modeling of a paragneiss indicates that the peak metamorphic conditions reached approximately 785-795 degrees C and 3.7-4.2 kbar. By dating of zircon overgrowths in granulite-facies gneisses, we characterized the orogenic (M1) and thermal (M2) metamorphisms that affected the complex. The M1 event records the subduction-type and accretion metamorphism dated between 1092 and 1060 Ma. The M2 event, identified in the metagabbro sample close to the contact with a charnockite intrusion, yielded an age of 1023 +/- 12 Ma for the thermal metamorphism. Intrusive charnockite and a gabbro record the post-orogenic magmatism with ages of 1026 +/- 4 Ma and 1026 +/- 12 Ma, respectively. The results provide a timeline for the last orogenic events of the Southern Irumide Belt, including the maximum depositional age of the Chidzolomondo Complex at ca. 1120 Ma, syn-orogenic magmatism and metamorphism until ca. 1060 Ma, and late- to post-orogenic magmatism and metamorphism between 1050 and 1020 Ma.

Automated summary

The rocks from the Chidzolomondo Complex in the Southern Irumide Belt in NW Mozambique provide new insights into the subduction and accretionary phases of the belt's evolution. These rocks exhibit different chemical compositions and ages, which also provide evidence for the metamorphic processes and formation.