Mathematics – Logic
Scientific paper
Nov 1982
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1982esrv...18..411r&link_type=abstract
Earth Science Reviews, Volume 18, Issue 3-4, p. 411-411.
Mathematics
Logic
5
Scientific paper
New geological evidence and geochronological data obtained within the Patagonian Cordillera between Lat. 47° and 49°S, allow the redefinition of an Andean region with different and characteristic geological evolution compared to the adjacent segments. An acidic Middle Jurassic volcanism covered a “metamorphic basement” formed by low-grade metasediments and metabasites of Upper Paleozoic age. Dike swarms of basic alkaline rocks were emplaced since the Cretaceous in a marginal basin developed on the Jurassic sialic crust. The outcrop density of such bodies seems to indicate an attenuation of the sialic crust, towards the south, where oceanic crust of Upper Jurassic-Lower Cretaceous age floored the marginal basin. The Cretaceous volcanic activity is well developed in the adjacent sectors, but almost absent in the studied segment. Several magmatic pulses lead to the final emplacement of the Patagonian batholith which yields its peak activity around 98 m.y. and presents typical geochemical variations. The Upper Cretaceous and Cenozoic magmatism are mainly exposed to the east of the cordillera and are represented by a series of alkali plateau basalts. Different pulses of activity have been recorded during Eocene, Upper Miocene, Pliocene and even during Quaternary times, associated with deep crustal fractures and probable upper-mantle origin, as evidenced by the low 87Sr/86Sr ratios and the ultramafic and mafic xenoliths of the lavas. Granitic stocks in the Andean domain are post-orogenic in relation to a compressive tectonic phase during Miocene times. The Upper Cenozoic calc-alkaline volcanism presents a gap in this segment of the Andean belt, probably related with the post-Miocene migration of the Chile rise.
Mun˜Oz J.
Niemeyer Hendrik
Ramos Victor A.
Skarmeta J.
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