Metasomatized mantle under the Eastern Mexican Alkaline Province: evidence from the Oligocene Rincon Murillo Gabbro, Sierra de San Carlos-Cruillas, NE Mexico

The Cenozoic Sierra de San Carlos-Cruillas (SSCC) magmatic complex belongs to the Eastern Mexican Alkaline Province (EMAP). The SSCC mainly consists of plutonic and subvolcanic bodies displaying diverse lithological compositions. These rocks exhibit both OIB- and arc-like geochemical characteristics. In this contribution, we present new petrographic, geochemical, isotopic, and geochronological data of the Rincon Murillo Gabbro (RMG), situated in the southern part of the SSCC. The RMG is nepheline normative and displays an OIB-like intraplate character. Laser ablation ICP-MS U-Pb analyses on titanites yielded Oligocene (Rupelian) crystallization ages of 31.8 +/- 1.8 and 31.0 +/- 1.7 Ma. The Sr-87/Sr-86((i)) (0.703400-0.704159) and Nd-143/Nd-144((i)) (0.512732-0.512815) ratios indicate a mantle origin. Trace element data indicate the participation of different enriched mantle components in the source. One component is related to previous subduction processes, generating the HFSE-depleted arc-like magmas of San Jose Gabbro in the northern part of SSCC. The second component is related to deep mantle melts with a slightly carbonatitic signal and HFSE-enriched fluids derived from the subducted Hess conjugate plateau generating different enriched sources in the upper mantle under the SSCC. The passage, eclogitization, detachment and foundering of the Hess plateau gave rise to an asthenospheric upwelling that triggered the low to moderate partial melting degrees (3-15%) of an amphibole-bearing garnet peridotite, generating the OIB-like parental magmas of RMG, located in the southern part of SSCC. Two-component mixing, and AFC models indicate that variable degrees of crystal fractionation and minor crustal assimilation are involved in the evolution of Rincon Murillo Gabbro.