INVESTIGADORES
VIRAMONTE Jose German
artículos
Título:
ProterozoicPaleozoic development of the basement of the Central Andes (1826°S) a mobile belt of the South American craton
Autor/es:
LUCASSEN F.; BECCHIO R.A.; H. WILKE; FRANZ G.; THIRLWALL M.; VIRAMONTE JOSÉ G.; WEMMER K.
Revista:
JOURNAL OF SOUTH AMERICAN EARTH SCIENCES
Editorial:
PERGAMON-ELSEVIER SCIENCE LTD
Referencias:
Lugar: Amsterdam; Año: 2000 p. 697 - 715
ISSN:
0895-9811
Resumen:
he Late PrecambrianEarly Paleozoic metamorphic basement forms a
volumetrically important part of the Andean crust. We investigated its
evolution in order to subdivide the area between 18 and 26°S into
crustal domains by means of petrological and age data (SmNd isochrons,
KAr). The metamorphic crystallization ages and tDM
ages are not consistent with growth of the Pacific margin north of the
Argentine Precordillera by accretion of exotic terranes, but favor a
model of a mobile belt of the Pampean Cycle. Peak metamorphic conditions
in all scattered outcrop areas between 18 and 26°S are similar and
reached the upper amphibolite facies conditions indicated by mineral
paragensis and the occurrence of migmatite. SmNd mineral isochrons
yielded 525±10, 505±6 and 509±1 Ma for the Chilean Coast Range, the
Chilean Precordillera and the Argentine Puna, and 442±9 and 412±18 Ma
for the Sierras Pampeanas. Conventional KAr cooling age data of
amphibole and mica cluster around 400 Ma, but are frequently reset by
Late Paleozoic and Jurassic magmatism. Final exhumation of the Early
Paleozoic orogen is confirmed by Devonian erosional unconformities.
SmNd depleted mantle model ages of felsic rocks from the metamorphic
basement range from 1.4 to 2.2 Ga, in northern Chile the average is
1.65±0.16 Ga (1σ; n=12), average tDM of both gneiss and metabasite in NW Argentina is 1.76±0.4 Ga (1σ; n=22),
and the isotopic composition excludes major addition of juvenile mantle
derived material during the Early Paleozoic metamorphic and magmatic
cycle. These new data indicate a largely similar development of the
metamorphic basement south of the Arequipa Massif at 18°S and north of
the Argentine Precordillera at 28°S. Variations of metamorphic grade and
of ages of peak metamorphism are of local importance. The protolith was
derived from Early to Middle Proterozoic cratonic areas, similar to the
Proterozoic rocks from the Arequipa Massif, which had undergone
Grenvillian metamorphism at ca. 1.0 Ga.