The geodynamics of collision of a microplate (Chilenia) in Devonian times deduced by the pressure–temperature–time evolution within part of a collisional belt (Guarguaraz Complex, W-Argentina)

Abstract

The Guarguaraz Complex in West Argentina formed during collision between the microplate Chilenia and South America. It is composed of neritic clastic metasediments with intercalations of metabasic and ultrabasic rocks of oceanic origin. Prograde garnet growth in metapelite and metabasite occurred between 1.2 GPa, 470°C and 1.4 GPa, 530°C, when the penetrative s 2 -foliation was formed. The average age of garnet crystallization of 390 ± 2 Ma (2r) was determined from three four-point Lu-Hf mineral isochrones from metapelite and metabasite samples and represents the time of collision. Peak pressure conditions are followed by a decompression path with slight heating at 0.5 GPa, 560°C. Fluid release during decompression caused equilibration of mineral compositions at the rims and also aided Ar diffusion. An 40 Ar/ 39 Ar plateau age of white mica at 353 ± 1 Ma (1r) indicates the time of cooling below 350-400°C. These temperatures were attained at pressures of 0.2-0.3 GPa, indicative of an average exhumation rate of C1 mm/a for the period 390-353 Ma. Late hydrous influx at 0.1-0.3 GPa caused pervasive growth of sericite and chlorite and reset the Ar/Ar ages of earlier coarse-grained white mica. At 284-295 Ma, the entire basement cooled below 280°C (fission track ages of zircon) after abundant post-collisional granitoid intrusion. The deeply buried epicontinental sedimentary rocks, the high peak pressure referring to a low metamorphic geotherm of 10-12°C/km, and the decompression/heating path are characteristics of material buried and exhumed within a (micro) continent-continent collisional setting.

Stratigraphy, structure and geodynamic evolution of the Paleozoic rocks in the Cordillera del Viento (37º S latitude, Andes of Neuquén, Argentina)

“…Radiometric datings indicate an early-middle Permian age for the Huingancó Granite: granodiorite pluton of 287 ± 9 Ma (K-Ar whole rock, Suárez and de la Cruz, 1997), biotite-perthite granodiorite of 283 ± 2 Ma (U\Pb SHRIMP; Hervé et al, 2013) and rhyolite domes (Fig. 9 E) between 260 ± 10 Ma (Llambías, 1986) and 259 ± 18 Ma (JICA, 2001); while an ignimbrite from the base of the La Premia Formation gave an early Permian age of 282 ± 2 Ma (U-Pb zircon SHRIMP, . Although all the available radiometric ages in the CV indicate a Permian age, based on regional correlations with the Choiyoi Group of nearby areas, the age of the complex can be extended to the Early Triassic (Llambías et al, 2007;Heredia et al, 2012).…”

“…Recent U-Pb SHRIMP dating of detrital zircons indicate zircons of magmatic origin are mainly Devonian and Ordovician and of a maximum depositional age of 374 Ma (Late Devonian; Zappettini et al, 2012). Considering that the Devonian-Carboniferous boundary is placed at 359 million years ago, and that deformation affecting similar rocks in the Frontal Cordillera has been dated in the Late Devonian-early Carboniferous and the metamorphism in Middle-Late Devonian (Wilner et al, 2011), the age of these rocks can be established as Upper Devonian (Fig. 6).…”

Exhumation history and landscape evolution of the Sierra de San Luis (Sierras Pampeanas, Argentina) - new insights from low - temperature thermochronological data

“…This crustal mobility may be related with the development of shear zones under brittle-ductile conditions in several parts of the range during the Achalian Cycle, whose effects according to Sims et al (1997Sims et al ( , 1998 can be documented up to 355 Ma. Such significant episode of exhumation and uplift may also be linked to the collision of the Chilenia exotic terrane at the proto-pacific margin of Gondwana (Chanic orogeny) during the late Devonian (Ramos, 1988;Mpodozis and Ramos, 1989;Davis et al, 1999;Willner et al, 2011). During the Carboniferous to the Early Permian (Fig.12a), a mountainous landscape developed as suggested by Jordan et al (1989), associated with the down-wearing of the Early Carboniferous topography.…”

Reactivation of Paleozoic structures during Cenozoic deformation in the Cordón del Plata and Southern Precordillera ranges (Mendoza, Argentina)

“…The Chanic orogen had a characteristic double vergence with west-directed structures in the Frontal Cordillera and east-directed structures in the Precordillera (Heredia et al, 2012). The internal zones of the Chanic orogen are well exposed in the Frontal Cordillera, where rocks deformed under high metamorphic conditions are found (Willner et al, 2011, Heredia et al, 2012. It is commonly accepted that the suture between Chilenia and the proto-margin of Gondwana is located between the Frontal Cordillera and Precordillera (Ramos et al, 1989;Davis et al, 2000;Heredia et al, 2012), even though the position and polarity of the related subduction zone has remained a controversial topic.…”

“…2). This unit, named Guarguaraz Complex, is composed by preCarboniferous metasedimentary and metabasic (mafic and ultramafic) rocks (López de Azarevich et al, 2009;Gargiulo et al, 2011) deformed under HP (high pressure) conditions in Middle Devonian times, and later under LP (low pressure) conditions in early Carboniferous (Willner et al, 2011).…”