Field geology, petrology and geochronology of pluton-dyke systems, the Trapecio and Ushuaia Peninsula dyke swarms (Fuegian Andes): emplacement conditions and relation with tectonics

GONZÁLEZ GUILLOT, MAURICIO; TORRES CARBONELL, PABLO J.; CAO, SEBASTIÁN; LOBO, CONSTANZA; BORDESE, SOFÍA; HOLLANDA, MARÍA-HELENA B.M.

JOURNAL OF THE GEOLOGICAL SOCIETY

GEOLOGICAL SOC PUBL HOUSE

Año: 2024

0016-7649

Wereport the field geology, petrography, geochemistry and geochronology data fortwo dyke swarms in the Fuegian Andes, with the aim of correlating them withknown suites and of improving the knowledge on the magmatism of the LateCretaceous rear-arc and its relation with ductile deformation. We also providekeys for correlation based on amphibole K2O content. The Trapeciodyke swarm is mildly alkaline and ferriferous, with a zircon U-Pb age of 75 Ma;thus it belongs to the Fuegian Potassic Magmatism (78-68 Ma). The UshuaiaPeninsula dyke swarm, also known as Ushuaia Peninsula Andesites (UPA), wasshown to be high-K calc-alkaline and magnesian. New radiometric ages gave 87-86Ma. While the UPA dyke swarm exhibits foliation associated with ductiledeformation, the Trapecio dyke swarm is post-kinematic and reveals emplacementcontrolled by the slaty cleavage in the metapelite host. Field and geophysicalevidence suggest both swarms overlie small upper-crustal plutons, mostly buried.The variable composition of dykes suggests a protracted history of dykeinjection, mostly fed from deeper reservoirs. Contact metamorphism around bothpluton-dyke systems is very weak. By comparison with adjacent plutons we arguethat the main variables controlling aureole development are small magma volumesand low injection rates.