<p>The Neoproterozoic (834 &#8211; 778 Ma) Ambaji granulite witnessed four deformation phases (D<sub>1</sub>- D<sub>4</sub>), of which the D<sub>2</sub> deformation phase was most significant for the exhumation of granulites in the ductile regime. We performed a field study to investigate the tectonic evolution of the D<sub>2</sub> deformation phase and investigated the deformation evolution of the ductile extrusion of the Ambaji granulite by estimating the vorticity of flow (Wm) with the Rigid Grain Net and strain ratio/orientation techniques.</p><p>During the D<sub>2</sub> deformation phase, the S<sub>1</sub> fabric was folded by F<sub>2</sub> folds that are coaxial with the F<sub>1</sub> folds. The F<sub>2</sub> folds were produced in response to NW-SE compression. Because the large shear zones are oriented parallel to the axial plane of the F<sub>2</sub> folds, they likely formed simultaneously during the D<sub>2</sub> deformation phase. Compression during the D<sub>2</sub> deformation phase accommodated most of the exhumation of the granulite along the shear zones. D<sub>2</sub> shearing was constrained between 834&#8239;&#177;&#8239;7 to 778&#8239;&#177;&#8239;8&#8239;Ma (Monazite ages).</p><p>The shear zones evolved from a high temperature (>700&#8239;&#176;C) thrust-slip shearing event in the lower-middle crust to a low temperature (450&#8239;&#176;C) retrograde sinistral shearing event at the brittle-ductile-transition (BDT). The&#160;Wm&#160;estimates of 0.32&#8211;0.40 and 0.60 coincide with the high temperature event and suggests pure shear dominated deformation. The low temperature phase coincides with&#160;Wm&#160;estimates of 0.64&#8211;0.87 and ~1.0, implying two flow regimes. The shear zone was first affected by general non-coaxial deformation and gradually became dominated by simple shearing.</p><p>We interpreted that the high temperature event happened in a compressive tectonic regime, which led to horizontal shortening and vertical displacement of the granulite to the BDT. The low temperature event occurred in a transpressive tectonic setting that caused the lateral displacement of the granulite body at BDT depth. The Wm values indicate a non-steady strain during the exhumation of granulite. From the BDT to surface, the Ambaji granulite exhumed through the NW-SE directed extension for normal faults via brittle exhumation through crustal extension and thinning.</p>
In Situ and Step‐Heating
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Ar/
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Ar Dating of White Mica in Low‐Temperature Shear Zones (Tenda Massif, Alpine Corsica, France)
