Tectonometamorphic zones were defined within the lower Paleozoic basement of the NW Argentine Andes in a transitional zone between two Andean segments of different geotectonic evolution. In the Cambrian, the Pacific edge of Gondwana changed from a passive to an active continental margin. This event began with folding of a Vendian/Eocambrian sediment wedge (Puncoviscana Formation and equivalents). The effects can be traced progressively over all structural levels with exposed depth increasing from north to south. Phenomena of a second deformation are of different nature and age but mostly characterized by shear belts causing large-scale crustal imbrication. In the lower tectonic levels this phase coincides with subduction-related magmatism of Ordovician age. A flat subduction slab is supposed, somewhat steeper in the northern than in the southern segment. The following anatectic-granitic magmatism and weak deformation in the Devonian may have marked a new change to passive margin conditions.

Basement

Devonian

Passive margin

Imbrication

Continental Margin

10.1029/gm040p0229

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Interpretación de las poblaciones de Circones detríticos en Unidades estratigráficas equivalentes del Ediacarano-Cámbrico de Argentina

Serie Correlación geológica/Serie correlación geológica (2010)

Florencio Gilberto Aceñolaza Alejandro J. Toselli Hubert Miller Christopher Adams

Fil: Acenolaza, Florencio Gilberto. Consejo Nacional de Investigaciones Cientificas y Tecnicas. Centro Cientifico Tecnologico Conicet - Tucuman. Instituto Superior de Correlacion Geologica. Universidad Nacional de Tucuman. Facultad de Ciencias Naturales e Instituto Miguel Lillo. Departamento de Geologia. Catedra Geologia Estructural. Instituto Superior de Correlacion Geologica; Argentina

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Joint Tectonics in a Folded Clastic Succession of the Variscan Orogen in the Rheinisches Schiefergebirge

Detlef Grzegorczyk Hubert Miller

The joint pattern of folded mid-Devonian sandstones was studied in the Western Sauerland (Volme valley near Lüdenscheid). The variable dip of joints parallel to the trace of regional folds (h 01 joints) can be interpreted as Case (b) is the most frequent one, but case (c) also occurs. h 01 joints formed at two different times during the folding. Early formed joints were externally and internally rotated and translated; a second set of joints formed, when about 80% of the folding was completed; they were only externally rotated. Vertical shear joints (hk 0) formed as paired sets acute-angled on both sides of the axis of maximum principal horizontal stress, and acute-angled on both sides of the axis of intermediate principal horizontal stress.

Devonian

Principal stress

Folding (DSP implementation)

10.1007/978-3-663-01886-5_8

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The Puncoviscana Formation of northwest Argentina: U-Pb geochronology of detrital zircons and Rb-Sr metamorphic ages and their bearing on its stratigraphic age, sediment provenance and tectonic setting

Neues Jahrbuch für Geologie und Paläontologie - Abhandlungen (2008)

Christopher Adams Hubert Miller Alejandro J. Toselli William L. Griffin

U-Pb ages of detrital zircons from greywacke, and Rb-Sr metamorphic ages of slate from the Puncoviscana Formation of northwest Argentina are reported, and used to constrain the depositional age, metamorphic history, and sedimentary provenance of these rocks.The detrital zircon ages define mainly Late Mesoproterozoic-Early Neoproterozoic (1150-850 Ma) and Late Neoproterozoic-Early Cambrian (650-520 Ma) populations, the relative proportions of which vary inversely with the age of the youngest zircons in the samples.The 1150-850 Ma population is present in all samples and dominates in those with relatively old grains (> 600 Ma) in the Late Neoproterozoic-Early Cambrian population.However, the Late Mesoproterozoic-Early Neoproterozoic population is substantially smaller in those samples in which the Late Neoproterozoic-Early Cambrian population dominates and contains relatively young grains (> 520 Ma).The youngest zircons, c. 520 Ma, are in the Rancagua (Cachi, Salta province) sample.They form a narrow, unimodal peak and may have originated from volcanic sources active during deposition, in which case these youngest zircons would constrain the depositional age of the sample to the late Early Cambrian.This is consistent with Rb-Sr ages of 550-500 Ma for samples of slate from the Puncoviscana Formation.The detrital zircon age populations suggest a sedimentary provenance in a continental hinterland with a stabilized, extensive Late Mesoproterozoic orogen (with minor Paleoproterozoic and Archean precursors) and a more variable Late Neoproterozoic orogen containing an evolving sequence of less extensive subcomponents.A direct relationship with the Brazilian Shield is thus suggested with sedimentary detritus originating within the active-margin orogens of the interior, but with ultimate deposition in the passive-margin environment of western Gondwanaland.

Geochronology

10.1127/0077-7749/2008/0247-0341

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Citations (83)

Kritische Betrachtungen zum geologischen Zusammenhang zwischen den chilenischen Anden und der Westantarktis

Geologische Rundschau (1967)

Hubert Miller

10.1007/bf01848747

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Citations (3)