Evolution of Pliocene and Quaternary volcanism in the segment of the southern Andes between 38[degree] and 39[degree]S

Thesis/Dissertation · Fri Jan 01 04:00:00 EST 1988

OSTI ID:6822069

Munoz-Bravo, J O

The Quaternary orogenic volcanic belt is divided into the volcanic front, located in the Main Cordillera, and other arc centers to the east along precordilleran uplifts. Intra-arc alkaline basalts have been erupted along the valleys flanking the precordilleran uplifts. South of 39[degree]S intra-arc extension is absent and distinctive orogenic arc and back-arc tectonic and petro-chemical environment are restricted to the Main Cordillera and to the east, in the Patagonian extra-Andean plateau region. Magmatism in the present-day volcanic belt between 38[degree] and 39[degree]S began in the Pliocene, when the centers forming the volcanic front developed east of the Main Cordillera, along the Copahue-Pino Hachado precordilleran uplift. These Pliocene centers erupted along the volcanic front. During the Early Pleistocene, the centers at the southeast end of this uplift erupted magmas of progressively more alkaline affinity. By the Late Pleistocene, magmatic activity in the centers had diminished, the volcanic front had migrated westward to its current locality, and alkaline intra-arc and back-arc basaltic volcanism had been initiated in the valleys flanking the Copahue-Pino Hachado uplift. The Early Pleistocene alkaline arc lavas as well as the Quaternary alkaline basalts have higher La/Yb, La/Sm and Ce/Yb ratios than, but Ba/La and 87Sr/86Sr ratios similar to, the subalkaline magmas erupted along both the Pliocene and late Quaternary volcanic fronts. Their TiO[sub 2] contents, La/Nb ratios and Ta and Nb negative anomaly are intermediate between subalkaline arc magmas and alkaline lavas of the Patagonian plateau basalts south of 39[degree]S.

• Research Organization: Colorado Univ., Boulder, CO (United States)
• OSTI ID: 6822069
• Country of Publication: United States
• Language: English

Related Subjects

58 GEOSCIENCES
580000* -- Geosciences
ALKALINE EARTH ISOTOPES
ALKALINE EARTH METALS
ANDES
BARIUM
BASALT
BETA DECAY RADIOISOTOPES
CENOZOIC ERA
CHALCOGENIDES
CHEMISTRY
ELECTRON CAPTURE RADIOISOTOPES
ELEMENTS
EVEN-EVEN NUCLEI
EVEN-ODD NUCLEI
GEOCHEMISTRY
GEOLOGIC AGES
GEOLOGIC HISTORY
HOURS LIVING RADIOISOTOPES
IGNEOUS ROCKS
INTERMEDIATE MASS NUCLEI
ISOMERIC TRANSITION ISOTOPES
ISOTOPE RATIO
ISOTOPES
LANTHANUM
MAGMA
MAGMATISM
METALS
MOUNTAINS
NIOBIUM
NUCLEI
OXIDES
OXYGEN COMPOUNDS
PLEISTOCENE EPOCH
PLIOCENE EPOCH
QUATERNARY PERIOD
RADIOISOTOPES
RARE EARTHS
ROCKS
SAMARIUM
STABLE ISOTOPES
STRONTIUM 86
STRONTIUM 87
STRONTIUM ISOTOPES
TANTALUM
TECTONICS
TERTIARY PERIOD
TITANIUM COMPOUNDS
TITANIUM OXIDES
TRANSITION ELEMENT COMPOUNDS
TRANSITION ELEMENTS
VOLCANIC REGIONS
VOLCANIC ROCKS
VOLCANISM
YTTERBIUM