CALCATAPUL

According to Proserpio (1978b) and Nullo (1978b), the Calcatapul Formation mostly consists of acid to intermediate metapyroclastic and volcanic rocks. In the area of the Quebrada Yancamil (NW of Gastre), these dominant rock types contain layers with accumulated lapilli (lens-shaped, feldspar-rich aggregates on a mm to cm scale), some rhyolite layers, and conglomerates. The latter contain pebbles of mudstones, pyroclastic rocks, and rhyolites of mm to dm sizes. The pyroclastic rocks occupy the entire northeastern part of the Calcatapul Formation near Estancia Yancamil. Fine-grained varieties contain angular rock fragments of mm to cm sizes (see also Proserpio, 1978b). In the southwestern part of the Formation, thick layers of metavolcanic rocks represent lava flows separated from one another by several m thick layers of dark phyllitic mud-/siltstone. In addition, dm-thick lenses of sandstones with quartz-conglomerates occur. According to the subvertical orientation of the main foliation, mostly parallel to the compositional layering (relic of bedding), the Calcatapul Formation is at least 1 km thick in the Yancamil exposure, without taking into account possible repetitions by folding. An along-strike continuation to the southeast is possible but not substantiated. There are no fossils reported from the unit, and such relics could not be found during our fieldwork. A (?) Middle Paleozoic (?Silurian, ?Devonian) age of the Formation was assumed by Proserpio (1978a,b). In the area of Yancamil, the deformed Calcatapul Formation also has been interpreted as mylonites. Together with additional occurrences, these were used as an essential argument for the existence of the dextral Gastre fault system (e.g. Rapela et al., 1991, 1992). Along its southwestern margin, the Formation is intruded by a coarse-grained granite , which shall be named Yancamil granite. Slices of pyroclastic rocks were enclosed by the granite just south of the irregular, wNW–SE-striking intrusive contact and farther southeast (Figs. 2, 5 and 6a). A later leucogranite facies intruded a dyke of the granite and the country rocks. Both types of intrusion are foliated together with the Calcatapul Formation rocks. In the area of Gastre, a suite of various granodiorites and granites has been named the “Gastre Suite” (or “superunit”) and dated as 220G3 Ma (Rb–Sr, whole-rock) by Rapela et al. (1992). In several outcrops from Gastre to the northwest of Sierra de Calcatapul (west of Puesto Uribe), m- to 10 mwide blocks of weakly foliated granites are enclosed by younger intrusive rocks of the Lipetren Formation.
The latter is widely distributed from Gastre to the northwestern parts of Sierra de Calcatapul and farther northwest. It has been interpreted as Permian or Permo-Triassic in age (e.g. Proserpio, 1978b; Nullo, 1978b, 1979; Volkheimer and Lage, 1981; Cucchi, 1993). The Formation consists of various unfoliated granites, rhyolites, porphyries, and aplites. The rocks have been collectively assigned to the“Lipetre´n Suite” (or “superunit”) and dated as 208G1 Ma (Rb–Sr, whole-rock) by Rapela et al. (1992). They intrude the Calcatapul Formation and lead to contact metamorphism of the northern occurrence (Nullo, 1978b). Injected dykes of its porphyries, mentioned by Proserpio (1978b), cut across the steeply inclined succession and Yancamil granite intrusion.

FORMACION CALCATAPUL
According to Proserpio (1978b) and Nullo (1978b), the Calcatapul Formation mostly consists of acid to intermediate metapyroclastic and volcanic rocks. In the area of the Quebrada Yancamil (NW of Gastre), these dominant rock types contain layers with accumulated lapilli (lens-shaped, feldspar-rich aggregates on a mm to cm scale), some rhyolite layers, and conglomerates. The latter contain pebbles of mudstones, pyroclastic rocks, and rhyolites of mm to dm sizes. The pyroclastic rocks occupy the entire northeastern part of the Calcatapul Formation near Estancia Yancamil. Fine-grained varieties contain angular rock fragments of mm to cm sizes (see also Proserpio, 1978b). In the southwestern part of the Formation, thick layers of metavolcanic rocks represent lava flows separated from one another by several m thick layers of dark phyllitic mud-/siltstone. In addition, dm-thick lenses of sandstones with quartz-conglomerates occur. According to the subvertical orientation of the main foliation, mostly parallel to the compositional layering (relic of bedding), the Calcatapul Formation is at least 1 km thick in the Yancamil exposure, without taking into account possible repetitions by folding. An along-strike continuation to the southeast is possible but not substantiated. There are no fossils reported from the unit, and such relics could not be found during our fieldwork. A (?) Middle Paleozoic (?Silurian, ?Devonian) age of the Formation was assumed by Proserpio (1978a,b). In the area of Yancamil, the deformed Calcatapul Formation also has been interpreted as mylonites. Together with additional occurrences, these were used as an essential argument for the existence of the dextral Gastre fault system (e.g. Rapela et al., 1991, 1992). Along its southwestern margin, the Formation is intruded by a coarse-grained granite , which shall be named Yancamil granite. Slices of pyroclastic rocks were enclosed by the granite just south of the irregular, wNW–SE-striking intrusive contact and farther southeast (Figs. 2, 5 and 6a). A later leucogranite facies intruded a dyke of the granite and the country rocks. Both types of intrusion are foliated together with the Calcatapul Formation rocks. In the area of Gastre, a suite of various granodiorites and granites has been named the “Gastre Suite” (or “superunit”) and dated as 220G3 Ma (Rb–Sr, whole-rock) by Rapela et al. (1992). In several outcrops from Gastre to the northwest of Sierra de Calcatapul (west of Puesto Uribe), m- to 10 mwide blocks of weakly foliated granites are enclosed by younger intrusive rocks of the Lipetren Formation. The latter is widely distributed from Gastre to the northwestern parts of Sierra de Calcatapul and farther northwest. It has been interpreted as Permian or Permo-Triassic in age (e.g. Proserpio, 1978b; Nullo, 1978b, 1979; Volkheimer and Lage, 1981; Cucchi, 1993). The Formation consists of various unfoliated granites, rhyolites, porphyries, and aplites. The rocks have been collectively assigned to the“Lipetre´n Suite” (or “superunit”) and dated as 208G1 Ma (Rb–Sr, whole-rock) by Rapela et al. (1992). They intrude the Calcatapul Formation and lead to contact metamorphism of the northern occurrence (Nullo, 1978b). Injected dykes of its porphyries, mentioned by Proserpio (1978b), cut across the steeply inclined succession and Yancamil granite intrusion.