A new model, partially based on the three most widely cited previous hypotheses, is proposed to explain the genesis of the Canary Islands. From the hotspot hypothesis it retains the notion that the islands originated from a thermal anomaly in the mantle. From the propagating fracture hypothesis it takes the critical role of regional fractures in the onset of magmatism. The uplifted block hypothesis contributes with the notion that the islands are in their present freeboard attitude due to the action of tectonic forces.The main drawbacks of the three preceding hypotheses are solved within this unifying approach: the thermal anomaly is an upper mantle residue from an old plume, and therefore it does not carry (or does it in a highly diluted form) the typical geophysical and geochernical plume signatures; the fractures are well developed on the continental and oceanic crust, but not in the extremely thick sedimentary pile between the Canary Islands and Africa; and the Canary Islands uplift took place through transpressive shears, and not by means of purely reverse faults. This unifying model, which integrates the thermal and tectonic histories of the lithosphere and the sublithospheric mantle, is considered to be a valid approach to a number of volcanic areas where, as has been highlighted in recent years, pure hotspot or pure fracture models are found wanting to explain oceanic or (less frequently) continental volcanic lines.
apparent head of Chasma Boreale was interpreted as an impact crater. Then, the Viking images showed the crater A detailed geomorphological study of Chasma Boreale, a did not exist, and other questions were raised over the widely known feature of Mars' north polar cap, has been carried out for the first time, along with a quantitative paleohydro-feasibility of the subglacial river.logical model. It is concluded that the chasma was eroded Clifford (1980Clifford ( , 1987 has studied in detail the mechaby a flow whose discharge was on the order of magnitude of nisms for a catastrophic water release from the permafrost,
109 m sec ؊1 . This catastrophic flow is thought to have been looking for analogs on both Earth and Mars. His comparipreceded by a powerful sapping process, caused by a tectoni-son with Ravi Vallis, a box-headed channel on Mars equacally focused thermal event. Several lines of evidence indicate tor (1ЊS, 43Њ) is particularly compelling, because of the tectonic control in the distribution and present aspect of most angular, straight head and huge flow marks. His hypothesis of the polar troughs. This tectonic forcing probably played a of glaciovolcanic outburst water flows (jö kulhlaups of Icemajor role in the inception of not only Chasma Boreale but landic authors) also seems appropriate, since this mechaalso other polar reentrants as well.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.