Evidence of oblique collision between the Aravalli Delhi Mobile Belt and Marwar Craton along the Phulad – Ranakpur paleo-suture zone: Implication for the partition transpression style deformation during the Grenville-age orogeny

The Neoproterozoic tectonics at the northeast–southwest trending western margin of the Aravalli-Delhi Mobile Belt (ADMB) along the South Delhi Fold belt (SDFB) is highly debated due to the spread of geochronological data from different parts of the belt. The dataset of the magmatic and metamorphic ages of the granitic rocks ranges from Stenian to Tonian Period. However, there is a lack of clarity on whether the orogenesis of the belt (SDFB) along Phulad-Ranakpur Lineament (PRL) is associated with the Grenvillian orogeny or it is a much younger Pan-African orogeny. Therefore, the tectono-stratigraphy of the region to elucidate the overall formation of the Greater Indian Landmass (GIL) is difficult to understand. To solve this problem, a comprehensive study through systematic geological mapping, structural analysis, metamorphic and geochronological study has been conducted in and around Kumbhalgarh-Sayra-Ranakpur area, Rajasthan, India. The study demarcates three phases of deformation (D₁, D₂ and D₃) and their subsequent prograde/retrograde metamorphic events in the calcareous rocks. The first generation isoclinal, reclined (F₁) folds are the result of D₁ event which are synchronous with prograde amphibolite facies metamorphism (~5 kbar, 650 ^oC). This is followed by (D₂) formation of outcrop to map-scale upright (F₂) folds. D₃ is marked by ‘partitioned transpression’ along subvertical shear zones (Steep zones) within the folded sequences of SDFB. Oblique slip dextral-reverse movement (D_3a) along the Kumbhalgarh Steep Zone (KSZ) formed an outcrop-scale positive flower like structure. At the western limit of the SDFB, along the PRL, the Ranakpur Shear Zone (RSZ) shows rotated and steepened hinges of the F₂ folds (D_3b). U-Pb zircon dating is done for the zircon grains derived from the intrusive granites associated with different phases of deformation. The oldest granitic intrusion (strongly deformed pink granite from RSZ: pre-D₂) occurred at ca. 990 Ma which indicates a Grenville-age orogeny for the SDFB rocks. The leucocratic granites from the KSZ (post-D₂, but pre-D₃) suggests ca. 850 Ma age. However, the third deformation (D₃ = D_3a and D_3b), a progressive interlinked transpression, is identified as a ca. 822-819 Ma event from the granite ages. Undeformed leucocratic granite from RSZ shows the youngest age of ca. 819 Ma as a late-tectonic event and that marks the final suturing event between the ADMB and MC along the Phulad-Ranakpur paleo-suture zone to form the GIL. The geochemical signatures of the different varieties of granites from different parts of the SDFB also supports a collisional setting for the granite magmatism. The spacial distribution of early (ca. 1000-900 Ma) and late (ca. 800-700 Ma) Tonian magmatic and metamorphic ages over the SDFB demarcate that there is a younging trend from Beawar and Sendra area in the north to Mt. Abu and Ambaji area in the south. Hence, it can be concluded that the collision of the two blocks (ADMB and MC) started in the northern part and eventually the growth of the GIL took place through different stages of oblique collision in a pulsating manner through the Early Neoproterozoic.