ABSTRACT
Whereas subduction recycling of oceanic lithosphere is one of the central themes of plate tectonics, the recycling of continental lithosphere appears to be far more complicated and less well understood. Delamination and convective downwelling are two widely recognized processes invoked to explain the removal of lithospheric mantle under or adjacent to orogenic belts. Here we relate oceanic plate subduction to removal of adjacent continental lithosphere in certain plate tectonic settings. We have developed teleseismic body wave images from dense broadband seismic experiments that show higher than expected volumes of anomalously fast mantle associated with the subducted Atlantic slab under northeastern South America and the Alboran slab beneath the Gibraltar arc region; the anomalies are under, and are aligned with, the continental margins at depths greater than 200 kilometres. Rayleigh wave analysis finds that the lithospheric mantle under the continental margins is significantly thinner than expected, and that thin lithosphere extends from the orogens adjacent to the subduction zones inland to the edges of nearby cratonic cores. Taking these data together, here we describe a process that can lead to the loss of continental lithosphere adjacent to a subduction zone. Subducting oceanic plates can viscously entrain and remove the bottom of the continental thermal boundary layer lithosphere from adjacent continental margins. This drives surface tectonics and pre-conditions the margins for further deformation by creating topography along the lithosphere-asthenosphere boundary. This can lead to development of secondary downwellings under the continental interior, probably under both South America and the Gibraltar arc, and to delamination of the entire lithospheric mantle, as around the Gibraltar arc. This process reconciles numerous, sometimes mutually exclusive, geodynamic models proposed to explain the complex oceanic-continental tectonics of these subduction zones.
ABSTRACT
El CADASIL es una enfermedad cerebrovascular hereditaria autosómica dominante, causada por una mutación del gen Notch3. Sus principales manifestaciones clínicas consisten en migraña, episodios isquémicos cerebrales recurrentes, demencia y trastornos neuropsiquiátricos. Se caracteriza por acumulación de material granuloso osmófilo (GOM), localizado en la capa media de las arterias cerebrales de pequeño y de mediano calibre. Se presenta el caso clínico de una mujer de 53 años, que consultó por presentar episodios autolimitados de parestesias, localizadas en hemicara izquierda. En sus antecedentes familiares presenta un hermano fallecido por ictus isquémico y otro hermano, con ictus de repetición. Se realizó el diagnóstico de sospecha de CADASIL, hallándose en el estudio genético una mutación R90C. CADASIL es un síndrome clínico infrecuente, pero cuyo diagnóstico preciso es necesario para poder ofrecer a las familias afectadas un adecuado consejo genético(AU)
CADASIL is a cerebrovascular autosomal dominant hereditary disease caused by a mutation of the Notch3 gene. Its principal clinical manifestations consist in migraine, recurrent cerebral ischemic episodes, dementia and neuropsychiatric disorders. It is characterized by accumulation of granular osmiophilic material (GOM) located in the middle layer of the small and median sized cerebral arteries. A clinical case is presented of a 53-year old woman who consulted due to self-limited episodes of paresthesias located in the left hemiface. In her family background, she had a brother who had died due to ischemic stroke and another brother who had recurrent stroke. The diagnosis was made of suspicion of CADASIL, finding a R90C mutation in the genetic study. CADASIL is an uncommon medical syndrome but one which requires an exact diagnosis in order to be able to offer adequate genetic counseling to the affected families(AU)
