Unzipping the Patagonian Andes—Long-lived influence of rifting history on foreland basin evolution

Abstract

The Andean Cordillera is widely considered to be one of the type examples of a convergent margin setting. In the southernmost Andes, however, rifting and volcanism predated mid-Cretaceous breakup of Gondwana and formation of the South Atlantic Ocean by up to 40 m.y. and culminated in the opening of the Rocas Verdes backarc basin east of the Mesozoic Patagonian Batholith. We present new U-Pb geochronology from the Austral sector (49°S-50°S) that indicates rift volcanism occurred between 154 and 147 Ma near the northern terminus of the basin. Available data and observations from the southern Rocas Verdes Basin indicate larger-magnitude and longer-duration extension compared to the northern basin region. The Rocas Verdes Basin underwent progressive northward propagation and opening and was later backfilled concomitantly with the opening of the southern Atlantic Ocean by north-to-south deposition within a retroarc foreland setting. The influence of the inherited tectonic fabric of the Rocas Verdes backarc basin on the subsequent foreland basin explains many unique characteristics of the Patagonian Andes, such as a protracted deep basin that formed atop the previously rifted and weakened crust. Moreover, the early rift history helps account for intraplate deformation of southernmost South America during the opening of the South Atlantic Ocean.

Down‐slope facies variability within deep‐water channel systems: Insights from the Upper Cretaceous Cerro Toro Formation, southern Patagonia

“…The present study only briefly summarizes the primary sources for detrital zircon grains: (i) pre‐Jurassic ages (>200 Ma) derived from the East Andean Metamorphic complexes (e.g. Faúndez et al ., ; Herve et al ., ; Hervé et al ., ), Upper Jurassic and earliest Cretaceous ( ca 160 to 140 Ma) rift volcanics associated with the El Quemado Complex and the Tobifera Formation (Calderón et al ., ; Malkowski et al ., ) and the South Patagonia arc and batholith system between ca 157 Ma and 75 Ma (Hervé et al ., ). Given that rifting occurred in a backarc setting, there is an overlap in rift volcanism and timing of magmatism in the South Patagonian batholith (Calderón et al ., ).…”

“…The Jurassic to Early Cretaceous Rocas Verdes Basin formed in a backarc extensional setting associated with the break‐up of Gondwana (Katz, ; Dalziel et al ., ; De Wit & Stern, ; Biddle et al ., ; Wilson, ). Within the study area, extensional volcanism occurred between 154 Ma and 147 Ma (Stern & Mukasa, ) but more regional crustal extension spans ca 190 to 137 Ma (Stern et al ., ; Pankhurst et al ., ). Lithospheric extension is recorded through bimodal volcanism including widespread silicic volcanism of the El Quemado, Ibañez and Tobífera formations of western Patagonia, and mafic to intermediate volcanism associated with the Sarmiento, Capitán Aracena, Carlos III and Tortuga ophiolite complexes (Fig.…”

Refining stratigraphy and tectonic history using detrital zircon maximum depositional age: an example from the Cerro Fortaleza Formation, Austral Basin, southern Patagonia

“…The extensional history of the Austral sector was described by Malkowski et al . () and Ramos et al . ().…”

Cretaceous Intraplate Contraction in Southern Patagonia: A Far‐Field Response to Changing Subduction Dynamics?

“…In the Southern Andes Cretaceous contraction is marked by the younging southward closure of the oceanic‐floored Rocas Verdes Basin. This process started with coarse‐clastic deposition first in the north of this area around 112 Ma (Malkowski et al, ) and propagated southward up to ~89–85 Myr (McAtamney et al, ).…”

“…To do so, we compiled a data set of available radiometric ages (U/Pb, Ar/Ar, K/Ar, and Rb/Sr) between 46° and 49°30°S from Cretaceous plutonic and volcanic rocks with arc geochemical signatures (Hervé et al, ; Pankhurst et al, ; Parada et al, ; Poblete et al, ; V. A. Ramos, ; Suárez & De La Cruz, ; Tippet et al, ; Townley, ; Weaver et al, ). The fact that this area did not experienced Late Jurassic back‐arc oceanic spreading as the region to the south of 50°S (Malkowski et al, ) makes it suitable for this analysis. We elaborated a time‐space plot diagram which is helpful to determine spatial changes in arc position through time (Coney & Reynolds, ; Figure c).…”