Sheeted intrusion of granitic magmas in the upper crust – Emplacement and thermal evolution of the Guandacolinos pluton, NW Argentina

ROCHER, SEBASTIÁN; ALASINO, PABLO H.; LARROVERE, MARIANO A.; MACCHIOLI GRANDE, MARCOS; MORENO, JUAN A.; DAHLQUIST, JUAN A.; MORALES CÁMERA, MATÍAS M.

TECTONOPHYSICS

ELSEVIER SCIENCE BV

Año: 2021 vol. 816

0040-1951

The Lower Carboniferous Guandacolinos pluton of northwestern Argentina (Western Sierras Pampeanas) preservesfield, structural, and petrological evidence of sheet-like transport and assembly of granitic magmas in theupper crust. The pluton is a relatively small (~24 km2) subduction-related granitic body, elongated in map view,and hosted in Neoproterozoic metamorphic rocks. Exceptional exposure records a subparallel array of steep NNESSWtrending structures, including steep contacts partly concordant with host rock structure, numerous sheets ofgranite separated by host rock rafts, abundant xenoliths, and magmatic and solid-state foliations. Along theeastern half of the pluton, the granite is massive and host rock inclusions are less abundant. Regional markers ofthe host rock are deflected along a concordant bulged contact in the northeastern region of the pluton. Fieldrelations indicate emplacement by multiple material transfer processes including fracture propagation, magmawedging, stoping, and lateral shortening. Contrasting mechanisms imply a changing mechanical response of hostrock and multiple stages of intrusion. Emplacement began with dominant brittle fracturing and intrusion ofsheets influenced by host rock anisotropies, followed by a viscoelastic phase were larger batches of magmacaused downward transfer of stoped blocks, lateral expansion, and minor ductile deformation of the host rock.Thermal modelling indicates that the construction of the pluton required lateral accretion rates in the order ofdm/years and less than a few tens of thousands of years to form. This case study documents the ability ofincrementally assembled sheeted intrusions to efficiently heat rocks of the upper crust and trigger conditionsfavourable for transfer and storage of magma.