114 research outputs found
Aeromagnetic anomalies reveal the link between magmatism and tectonics during the early formation of the Canary Islands
The 3-D inverse modelling of a magnetic anomaly measured over the NW submarine edifice of the
volcanic island of Gran Canaria revealed a large, reversely-magnetized, elongated structure following
an ENE-WSW direction, which we interpreted as a sill-like magmatic intrusion emplaced during the
submarine growth of this volcanic island, with a volume that could represent up to about 20% of the
whole island. The elongated shape of this body suggests the existence of a major crustal fracture in the
central part of the Canary Archipelago which would have favoured the rapid ascent and emplacement of
magmas during a time span from 0.5 to 1.9 My during a reverse polarity chron of the Earth’s magnetic
field prior to 16 Ma. The agreement of our results with those of previous gravimetric, seismological and
geodynamical studies strongly supports the idea that the genesis of the Canary Islands was conditioned
by a strike-slip tectonic framework probably related to Atlas tectonic features in Africa. These results do
not contradict the hotspot theory for the origin of the Canary magmatism, but they do introduce the
essential role of regional crustal tectonics to explain where and how those magmas both reached the
surface and built the volcanic edifices.Project CGL2015-63799-P of the
Spanish Ministry of Economy and Competitivenes
Controls on dryland mountain landscape development along the NW Saharan desert margin: Insights from Quaternary river terrace sequences (Dadès River, south-central High Atlas, Morocco)
This study documents river terraces from upstream reaches of the Dad es River, a major fluvial system
draining the south-central High Atlas Mountains. Terraces occur as straths with bedrock bases positioned
at 10 m altitudinal intervals up to 40 m (T1-T5) above the valley floor, becoming less common between
50 and 140 m. The rock strength, stratigraphy and structure of the mountain belt influences terrace
distribution. Terraces are absent in river gorges of structurally thickened limestone; whilst welldeveloped,
laterally continuous terraces (T1-T4) form along wide valleys occupying syncline structures
dominated by weaker interbedded limestone-mudstone. Terrace staircases develop in confined canyons
associated with weaker lithologies and influence from structural dip and stratigraphic configuration.
Terraces comprise a bedrock erosion surface overlain by fluvial conglomerates, rare overbank sands
and colluvium. This sequence with some OSL/IRSL age control, suggests terrace formation over a 100 ka
climate cycle with valley floor aggradation during full glacials and incision during glacial-interglacial
transitions. This integrates with other archives (e.g. lakes, glaciers, dunes), appearing typical of landscape
development along the NW Saharan margin south of the High Atlas, and similar to patterns in the
western-southern Mediterranean. The 100 ka climate cycle relationship suggests that the terrace
sequence documents Late-Middle Pleistocene landscape development.
Consistent altitudinal spacing of terraces and their distribution throughout the orogen suggests sustained
base-level lowering linked to uplift-exhumation of the High Atlas. Low incision rates (<0.2 mm
a 1) and general absence of terrace deformation suggests dominance of isostatically driven base-level
lowering with relief generation being Early Pleistocene or older.National Geographic research grant (8609-09
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