Nature and distribution of dykes and related melt migration structures in the mantle section of the Oman ophiolite

摘要: [1] We conducted a comprehensive field, petrographic, and microprobe study of the dykes porous flow channels cropping out in Oman harzburgites. The 36 rock types we recognized among about 1000 samples can be grouped two main magma suites contrasted terms structural textural characteristics, modal composition, order crystallization, phase chemistry. One suite (troctolites, olivine gabbros, opx-poor gabbronorites, rare oxyde gabbros) derives from MORB-like melts. other (pyroxenites, opx-rich diorites, tonalite-trondhjemites) melts richer silica water than MORBs ultradepleted incompatible elements. Dykes MORB are restricted to few areas, covering only 25% mantle section. This is an unexpected result as deep crust made essentially cumulates Their texture, relations with host harzburgites point high temperatures at time crystallization (likely above 1100°C, up 1200°C for part them), i.e., conditions close “asthenosphere/lithosphere” boundary. largest outcrop enclosing like 80 km long 10 wide corridor, parallel strike sheeted dyke complex centered on area where former upwelling has been unambiguously defined (the Maqsad “diapir”). A occurrences smaller have lesser abundance troctolites (i.e., high-temperature cumulates). We interpret troctolite zones witnesses diapirs frozen various stages their development. belonging depleted most common characteristics show that they crystallized colder melt range 600°C 1100°C). possible origin parent this situ partial melting shallow partly hydrated lithosphere residual after extraction. Our data support view feeding chambers focused (and likely episodic) process involving rise hot base through lithospheric lid accreted during previous diapiric event. They suggest also beneath spreading centers place important petrologic processes, some them predicted basis composition (e.g., fractionation inside conduits) ones remelting lithosphere).