Sierra Pintada
East of Las Salinas a gabbro occurs which contains abundant, interstitial nepheline.
Alkaline rocks in Argentina occur essentially in the west of the country in a zone parallel to the Andean chain, and associated with voluminous but predominantly calc-alkaline and tholeiitic volcanics. Few detailed petrological accounts of the alkaline rocks are available, but a general review has been given by Quartino and Llambias (1964).
East of Las Salinas a gabbro occurs which contains abundant, interstitial nepheline.
Among the voluminous volcanics of the Cordillera Principal alkaline rocks are scarce. However, tephrites and basanites, essexites with nepheline, analcime and biotite, trachytes and trachydolerites and rocks described as bostonites, but containing sodalite and nepheline, all occur.
This volcanic province extending for 70 km north-south and 20 km east-west comprises flows and plugs of basanite and olivine basalt, with some pyroclastics, and plugs and necks of nephelinite, tephrite and phonolite.
Among the basaltic rocks of the Rio Chubut Medio are rocks identified as pantellerites.
In the Sarmiento area occur numerous sills, ring dykes and radial dykes of alkaline basic rocks, principally teschenites, with differentiates of nepheline, analcime and zeolite syenites. They intrude tuffs of the Bajo Barreal Formation. Analcime basanite lavas are widespread in the area.
Remnants of the Patagonian basalt plateau between 45°and 47°S extend from the border with Chile eastwards to about 68° 30'W (Baker et al., 1981). The basalts form conspicuous mesetas and in the northeast of the area intrusive alkaline complexes occur around Sarmiento (008-00-014).
Two intrusions of teschenite with syenitic differentiates occur to the south of Lago Buenos Aires, one 11 km southeast of Los Antiguos, the other in the Rio Jeinemeni on the border with Chile, 30 km south-southwest of Los Antiguos (Busteros & Lapido, 1983, Fig. 1).
Essexites and essexitic gabbros are described from the Rio Carbon area, northeast of Lago San Martin. They contain orthoclase and a little analcime, and are only marginally alkaline.