The Tam Ky-Phuoc Son Shear Zone (TKPSSZ) is one of the most pronounced crustal structures in central Vietnam and juxtaposes high-grade rocks of the Kontum Massif against lower grade rocks of the Truong Son Fold Belt. An internal zone comprises highly strained rocks, including ultramafic-mafic tectonites, bounded by mylonitic zones that straddle tens to hundreds of kilometers. An external zone comprises mainly high-grade metamorphic complexes (southern flank), and weakly metamorphosed siliciclastic and carbonate rocks with subordinate greenstone (northern flank). Detailed structural analysis reveals that the shear zone is a multi-deformed terrane: D1 produced a regional high grade schistosity and mylonitization; D2 generated regional northwest-southeast trending fold arrays and brittle-ductile shear zones; D3 locally produced northeast-trending folds; brittle faulting occurred during D4-D5. U-Pb dating of zircon and monazite suggests that D1 involved metamorphism and felsic magmatism at ca. 430Ma, recording part of a regional collisional orogeny. Monazite and titanite growth at ca. 250-240Ma in basement rocks is synchronous with widespread syn- to post-D2 magmatism between ca. 260 and 245Ma suggesting a second major collisional event during the Indosinian Orogeny. D3 may have occurred as part of (or soon after) this Permo-Triassic event. Deformation during post-collisional stages, perhaps in response to extrusion/wedging and oroclinal rotation of terranes, led to post-D3 structures (D4-D5). The E-W trending TKPSSZ is here shown to be a continuation of the N-S trending Po Ko Shear Zone (PKSZ). Most of the significant lode gold occurrences in central Vietnam occur along this TKPSSZ-PKSZ structure and are associated with, and controlled by, D1 ductile to ductile-brittle high-strain zones. Mineralized later-stage structures support remobilization and reconcentration of ore during subsequent events at ca. 240Ma (Re-Os molybdenite age). The TKPSSZ-PKSZ D1 structure likely represents part of a paleosuture zone, marking the closure of an ancient ocean basin through terrane assembly in the Early Paleozoic.
- Suture zone
- Tectonic mélange
- Dac Sa and Bong Mieu gold deposits