2008 Joint Meeting of The Geological Society of America, Soil Science Society of America, American Society of Agronomy, Crop Science Society of America, Gulf Coast Association of Geological Societies with the Gulf Coast Section of SEPM

Paper No. 6
Presentation Time: 9:15 AM

Petrological Relationships between Mantle Xenolths and their Host Magmas in the Alkaline Province Mexico

TREVIÑO CAZARES, Adalberto1, RAMIREZ FERNANDEZ, Juan Alonso1 and VELASCO TAPIA, Fernando2, (1)Facultad de Ciencias de la Tierra, Universidad Autonoma de Nuevo Leon, Carretera Linares Cerro Prieto km. 8, Hacienda de Guadalupe, A.P. 104, Linares, 67700, Mexico, (2)Facultad de Ciencias de la Tierra, Universidad Autonoma de Nuevo Leon, AP 104, Carretera Linares Cerro Prieto Km. 8, Linares, 67700, Mexico, adtrevin@mail.uanl.mx

Along the periphery of Sierra de San Carlos-Cruillas and Sierra de Tamaulipas outcrops Tertiary-Quaternary volcanic rocks containing ultramafic xenoliths from the Mantle. The host rocks are alkaline and basaltic, and have characteristics of primary magmas from subcontinental zones (SiO2 = 40.6–49.7%, MgO = 5.62–11.6%, Mg-v = 59.2–69.7).

Primitive Mantle normalized patterns are similar to extension-related mafic magmas. These patterns indicate that host magmas were generated in a highly-incompatible elements enriched Mantle zone. This is supported by an enrichment in light REE ([La/Yb]N = 10.8–27.1) and the behavior of immobile trace elements. The tectonomagmatic discrimination diagrams indicate that host magmas were generated in an intraplate environment.

Using a REE partial melting model, it was pointed out that Mantle represented by the xenoliths cannot reproduce the REE-patterns of the host magmas. After the application of an inverse melting model, the host magmas were generated in the spinel lherzolite stability field, in a more enriched zone (highly incompatible elements).

The xenoliths are spinel-lherzolites, harzburgites and rare dunites. They have are protogranular, nevertheless, a few xenoliths displayed protogranular- porphyroclastic transitional textures, indicating that the xenoliths come from stable zones with little or no deformation. The mineralogy (olivine + orthopyroxene + clinopyroxene ± spinel) is typical of unaltered Mantle nodules. The core and rim compositions in olivine range from Fo86 to Fo92, whereas orthopyroxenes are characterized by En87–91 and clinopyroxenes by En43–45-Fs2.74–9.31-Wo49–51. Chromiferous spinels have Mg/(Mg + Fe+2) = 0.70–0.81 and Cr/(Cr + Al) = 0.10–0.35.

Primitive Mantle-normalized multielements diagrams and Chondrite-normalized REE patterns for xenoliths, pointed out that they represent an enriched Mantle for the SSCC area, and a lesser enriched Mantle for the ST.

The xenoliths equilibrated at 820-1190°C and from 10-25 kbar.