Insights into the North Patagonian Massif lower crust: petrology and microstructure of meta-igneous granulite xenoliths.

MUCKENSTURM, N; KACZMAREK, M. A.,; GREGOIRE, M.; NTAFLOS, TH.; BJERG, E. A.; MOUTHEREAU, F.

JOURNAL OF PETROLOGY

OXFORD UNIV PRESS

Lugar: Oxford; Año: 2024

0022-3530

The continental lower crust constitutes a key zone for understanding the mantle-crust magmatic and mechanical transfers, but the scarcity of lower crust samples make its study complicated. Here, we characterise the petrological, geochemical and petrophysical processes structuring the lower crust of the North Patagonian Massif (NPM; Rio Negro Province, Argentina) with a suite of mafic granulite xenoliths and four websterite xenoliths. Those xenoliths were brought up by alkaline lavas from 5 volcanic centres erupted between the Oligocene and Pleistocene. Electron microprobe and LA-ICPMS have been used to obtain in-situ geochemical data on minerals, while microstructural data have been acquired through Electron Backscatter Diffraction (EBSD). Both granulites and websterites display a granoblastic texture and sometimes a weak inherited magmatic layering. Mafic granulite xenoliths show an assemblage of plagioclase + clinopyroxene ± orthopyroxene commonly associated with spinel or titanomagnetite. Websterites xenoliths show an association of clinopyroxene + orthopyroxene + spinel, along with accessory plagioclase. Mafic granulites and websterites have a SiO2 content ranging from 44 to 53 wt % while their Mg# varies from 39 to 67. Clinopyroxenes are characterised by weak upward convex chondrite-normalised REE patterns (LREE