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Montero-López, Carolina
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Montero-López, Carolina
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- PublicationRestrictedRemarkable variability in dyke features at the Vicuña Pampa Volcanic Complex, Southern Central Andes(2017-09)
; ; ; ; ; ; ; ; ; ; ; ; ; Dykes at the Vicuña Pampa Volcanic Complex, which are mostly basaltic (trachy)-andesite and (trachy)-andesite, are exposed at the base and along the walls of a large depression resulting from intense degradation. Dykes intruding stiff layers (lavas, plugs and necks) are thin, mostly dip >60° and have coherent textures, whereas dykes intruding more compliant materials (breccias and conglomerates) tend to be thicker, have lower dips and have coherent, brecciated or mixed textures (coherent and brecciated textural domains in a single or compound dyke). Single dykes with brecciated and mixed textures are only found intruding near-surface units. Dykes with mixed textures always have sharp contacts between domains. Dykes with sinuous domain contacts and enclaves of one domain inside the other are interpreted as resulting from dyke arrest, partial cooling and reinjection of new magma. Dykes with straight domain contacts are considered to be compound dykes, with a new dyke intruding along the margins of an older, solidified one.648 3 - PublicationRestrictedConstruction and degradation of a broad volcanic massif: The Vicuña pampa volcanic complex, southern central Andes, NW Argentina(2017-05)
; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ;; ; ; ;The Vicuña Pampa volcanic complex, at the SE edge of the arid Puna Plateau of the Central Andes, records the interplay between volcanic construction and degradational processes. The low-sloping Vicuña Pampa volcanic complex, with a 1200-mdeep, southeastward- opening depression, was previously interpreted as a collapse caldera based on morphological considerations. However, characteristic features associated with collapse calderas do not exist, and close inspection instead suggests that the Vicuña Pampa volcanic complex is a strongly eroded, broad, massif-type composite volcano of mainly basaltic to trachyandesitic composition. Construction of the Vicuña Pampa volcanic complex occurred during two distinct cycles separated by the development of the depression. The first and main cycle took place at ca. 12 Ma and was dominated by lava flows and subordinate scoria cones and domes. The second cycle, possibly late Mio-cene in age, affected the SW portion of the depression with the emplacement of domes. We interpret the central depression as the result of a possible sector collapse and subsequent intense fluvial erosion during middle to late Miocene time, facilitated by faulting, steepened topography, and wetter climate conditions compared to today. We estimate that ~65% of the initial edifice of ~240 km3 was degraded. The efficiency of degradation processes for removing mass from the Vicuña Pampa volcanic complex is surprising, considering that today the region is arid, and the stream channels within the complex are predominantly transport limited, forming a series of coalesced, aggraded alluvial fans and eolian infill. Hence, the Vicuña Pampa volcanic complex records the effects of past degradation efficiency that differs substantially from that of today.617 3