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Fig. 48 | Progress in Earth and Planetary Science

Fig. 48

From: The Atlantis Bank Gabbro Massif, Southwest Indian Ridge

Fig. 48

Orthogonal cartoons of a tectonic model for Atlantis Bank emplacement: a N-S cross-section of the paleo-rift valley and opposing outside and inside-corner highs ~ 15 km east of the ridge-transform intersection. The gabbro above the melt lens migrates diapirically as a mush, by crystal-plastic flow at low melt %, and then by solid-state crystal-plastic deformation. Small higher level intrusions locally crosscut the fabric of the rising gabbro diapir as an ongoing process. Heavy red line shows the detachment fault cutting through the dike-gabbro transition into partially molten gabbro. It extends beneath the rift valley, resulting in fault capture and asymmetric spreading of the lower crust to the south parallel to the transform. Late, interstitial melt moved upward (and laterally) to create an oxide gabbro rich zone in the upper 500 m of the lower crust and migrated into the detachment fault zone to form an oxide gabbro rich mylonite that extends over the core complex. Gray arrows show lithospheric flow which extends up to the dike-gabbro transition. Fields for brittle, crystal-plastic, and crystal mush deformation and flow are separated by the thin dashed lines. Note that the crystal-plastic field overlaps the partially molten region at low melt percent. b Three-dimensional cartoon looking from north to south at right angles to the cross-section in “A”. Late E-W brittle faulting during lithospheric rollover and mass wasting of the transverse ridge are excluded for simplicity. Unmodified by mass wasting in the cartoon, the detachment fault footwall smoothly curves downward to the transform floor across the gabbro-mantle contact. It also extends downward from the inside-corner high to its termination on the rift valley floor. Thus, the detachment fault termination (heavy red, dashed line) extends along the foot of the rift valley wall, then curves, and progressively evolves from a normal fault, to oblique slip, to strike-slip at the base of the transform wall. The extension of the fault down below the transform valley (heavy red line) forms one branch of an active negative fault flower structure that forms the plate boundary between the African and Antarctic Plates

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