Disentangling tectonic cycles along a multiply deformed terrane margin: Structural and metamorphic evidence for mid-crustal reworking of the Angul granulite complex, Eastern Ghats Belt, India

Modern orogenic belts may be rifted and reworked during later tectonic cycles. In ancient collision zones, such as the Eastern Ghats Belt (EGB), India, identification of such processes is complicated by the multiply folded nature of the exposed deep crustal section. Along the northern EGB margin, (M1) granulite facies metamorphism (∼7–8 kbar, >760 °C) at ∼960–930 Ma outlasted D1 fabric formation, and D2 isoclinal folding and shearing. N-S trending mafic dykes and N-S trending, west-dipping shear zones accompanied D3 extension. Syn-D3 cooling and decompression caused garnet breakdown in mafic granulites. Granite and pegmatite emplacement at c. 850 Ma accompanied uplift on E-W trending, subvertical D4 shear planes. Top-to-the-south thrusting on WNW-ESE trending, north-dipping D5 shears resulted in regional-scale fabric reorientation. During M2 amphibolite facies metamorphism (∼5.5 kbar, 630 °C) at c. 700 Ma following D5, garnet reformed in mafic granulites, and stabilized within syn-D3 mafic dykes and syn-D4 granites. Thus, the terrane margin experienced heating, loading and uplift during a first tectonic cycle, followed by renewed burial during a later orogeny. Since the mesoscopic-scale folds correspond to shears that interfere in low strain zones, the structural pattern represents heterogeneous, rather than homogeneous strain accommodation during mid-crustal deformation.