Jurassic to Miocene K–Ar dates from eastern central Patagonian Cordillera plutons, Chile (45°–48° S)

Abstract

Thirty-nine K-Ar and one Ar-Ar radiometric dates from the eastern central MesoCenozoic Patagonian Batholith and eastern satellite plutons of the Aysén Region, of southern Chile between latitudes 45°and 48°S, combined with previous dating of seven plutons, have yielded six age groups: (1) Middle to Late Jurassic, (2) Early Cretaceous, (3) mid-Cretaceous, (4) Late Cretaceous, (5) Oligocene and (6) Miocene. In general, the Cretaceous and younger ages correspond to previous reported ages for other parts of the main batholith, but for the satellite plutons to the east show a wider age spectrum than the previously accepted Late Miocene dates. These results indicate a relatively continuous Late Jurassic to mid-Cretaceous plutonism, known to have been coeval with volcanic activity, followed by intermittent magmatism. Biotite K-Ar dates of c. 143-151 and 106-109 Ma, from cataclastic granitoids, may be marking the time of deformation. A review of all radiometric data on magmatic rocks from the region between 45°and 48°S in Chile shows a gap in Palaeocene ages that may correlate with a period of low-angle (flat slab) subduction between 65-50 Ma.

Distinguishing crustal recycling and juvenile additions at active continental margins: the Paleozoic to recent compositional evolution of the Chilean Pacific margin (36–41°S)

“…Very similar compositions were reported from the Cretaceous and Tertiary intrusions of the North Patagonian batholiths between 44 -478S (e.g. Pankhurst et al, 1999;Suárez and De La Cruz, 2001) and from the mid-Tertiary magmatism east of the Main Cordillera ( Fig. 5a; Muñoz et al, 2000).…”

Cooling histories and deformation of plutonic rocks along the Liquiñe-Ofqui Fault Zone, Southern Chile (41°-42°15'S)

“…K-Ar, U-Pb and particularly Rb-Sr wholerock isochron data from plutonic rocks between ~41°S and 47°S reveal a systematic pattern with Jurassic to early Cretaceous intrusions at the eastern and western margins of the NPB, and Miocene ages towards the center (Hervé et al, 1979;Munizaga et al, 1988;Parada et al, 1987;Pankhurst et al, 1992Pankhurst et al, , 1999Suárez and De la Cruz, 2001). The episodic development of the NPB appears to be correlated with periods of increased convergence rates along the South American margin (Pankhurst et al, 1999).…”

Cuenca de retroarco toarciana en Patagonia central (Chubut), Argentina: cierre, migracion del arco y ambiente tectonico durante el Jurasico Medio.

“…It represents an important contractional tectonic episode that, according to the exposed evidences would have taken place during the Middle Jurassic. Intense deformation has been observed in the Toarcian beds of the Osta Arena Formation, deposited in the Chubut Basin and Recently, Rapela et al(2003) have indicated a southwestward migration of the magmatic arc from the Upper Triassic-early Lower Jurassic Central Patagonian Batholith to the Late Jurassic plutons located along the eastern side of the Patagonian Batholith (Suárez and De la Cruz, 2001).…”

“…tectonic phase sometime during the intervening period. Also during the Middle Jurassic the Toarcian magmatic arc, that had a NNW orientation, ceased and the subsequent magmatic arc was emplaced further to the southwest (Rapela et al, 2003) and is identified in the Patagonian Cordillera, forming part of the Patagonian Batholith, with a north-south orientation, during the Late Jurassic (Suárez and De la Cruz, 2001). Hence, a major tectonism occurred during the Middle Jurassic with the closure of the Chubut Basin and the abrupt migration of the magmatic arc from a northeastern position to a southwestern location.…”