Hiperestentsioa: kontinenteen apurketa ulertzeko eredu berri bat

Abstract

Kontinenteen apurketa luzaroan ikertu den prozesu geologikoa da. Rifting deritzon prozesu horrek milioika urte irauten ditu, eta kontinente-ertzetan, mendikateetan eta bestelako ingurune geologikoetan topatzen dira fenomeno tektoniko horren aztarnak. Plaka tektonikoen banaketaren interpretazioa, ordea, eboluzionatuz doa ikertzaileen ulermenaren eta aurrerapen teknologikoen arabera. Hiperestentsioaren ideia da interpretazio horren azken berrikuntza. Ideia hori litosfera kontinentalaren deformazio polifasikoan barneratzen da, litosferaren muturreko luzapenean oinarrituz, hain zuzen. Ertz egonkorretan eta gerriko orogenikoetan identifikaturiko egitura geologiko eta eremu estruktural bereizgarriek ahalbidetzen dute fenomeno horren bilakaeraren nolakotasuna definitzea. Magman txiroak bezala ezagutzen diren ertz egonkorretako eremu horiek dira hurbileko domeinua, necking domeinua, urruneko domeinua edo hiperluzatua eta kanpoko domeinua. Domeinu horietako bakoitza riftingaren deformazio faseekin lotzen da; fase horiek litosfera kontinentalaren luzapena, mehetzea, mantuaren azaleratzea eta lurrazal ozeanikoaren zabaltzea dira. Esan bezala, iraganean hiperluzatutako arroetan ari da garatzen ikerketa, eta hipotesi horren bitartez ulertzen hasia da, honezkero, Euskokantauriar arroa (EKA) barneratzen duen Iberia eta Eurasia arteko Mesozoikoko rift-sistemaren garapena. Urteetan arroan bildutako datuek, behintzat, horretara bultzatzen dute. Pirinioen mendebaldean deskribaturiko mantuaren azaleratzeak eta arroan deskribaturiko hamaika prozesuk indartu dute Kretazeoko riftingean hiperestentsioak izan zezakeen garrantzia; azken horrek, gainera, garai hartako EKAren eboluzio geologikoaren paradigma argitu dezake.; Continental breakup is a geological process which has been deeply learnt. The keys of that tectonic phenomena, the so-called rifting process that lasts millions of years, can be found worldwide within rifted margins, mountain chains and other geological settings. However, the interpretation of tectonic plate rupture evolves while researcher´s comprehension and technology advance. Hyperextension is the last update within that interpretation. This revolutionary idea involves the extreme polyphasic extensional deformation of the continental lithosphere. Characteristic geological structures and structural domains identified within passive margins and orogenic belts, allow to define the evolution of this phenomena. Domains such as the proximal domain, necking domain, distal or hyperextended domain and outer domain are distinguishing features within magma poor rifted margins. These domains are linked to specific deformation phases during rifting, being stretching and thinning of continental lithosphere, mantle exhumation and oceanic crust spreading part of these process. As said, research is being carried out in hyperextended basins, and the evolution of the Iberia-Eurasia Mesozoic rift system, which involves the Basque-Cantabrian Basin (BCB), is already being understood within that hypothesis. Data collected over years in the BCB, at least, suggest that. Mantle exhumation described in the western Pyrenees and several processes linked to that within the BCB, reinforces the significance that hyperextension could have occurred during the Cretaceous rifting, shedding light to the paradigm concerning the evolution of the BCB.