Geophysical and magneto-structural study of the Maâdna structure (Talemzane, Algeria): Insights on its age and origin

Autor: E. H. Meziane, M. Ayache, Ludovic Ferrière, Nacer-Eddine Merabet, Said Maouche, Mohamed Hamoudi, Pierre Rochette, Abdeslam Abtout, A. Lamali, Jérôme Gattacceca
Přispěvatelé: Centre de Recherche en Astronomie Astrophysique et Géophysique (CRAAG), Centre européen de recherche et d'enseignement des géosciences de l'environnement (CEREGE), Institut de Recherche pour le Développement (IRD)-Institut National de la Recherche Agronomique (INRA)-Aix Marseille Université (AMU)-Collège de France (CdF (institution))-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS), National History Museum, Vienna, German Research Centre for Geosciences - Helmholtz-Centre Potsdam (GFZ), Aix Marseille Université (AMU)-Institut national des sciences de l'Univers (INSU - CNRS)-Collège de France (CdF (institution))-Institut de Recherche pour le Développement (IRD)-Centre National de la Recherche Scientifique (CNRS)-Institut National de la Recherche Agronomique (INRA), Centre National de la Recherche Scientifique (CNRS)-Institut de Recherche pour le Développement (IRD)-Collège de France (CdF)-Institut national des sciences de l'Univers (INSU - CNRS)-Aix Marseille Université (AMU)-Institut National de la Recherche Agronomique (INRA)
Jazyk: angličtina
Rok vydání: 2016
Předmět:
Zdroj: Meteoritics and Planetary Science
Meteoritics and Planetary Science, 2016, 51 (12), pp.2249-2273. ⟨10.1111/maps.12715⟩
Meteoritics and Planetary Science, Wiley, 2016, 51 (12), pp.2249-2273. ⟨10.1111/maps.12715⟩
ISSN: 1086-9379
1945-5100
DOI: 10.1111/maps.12715⟩
Popis: International audience; The Maâdna structure is located approximately 400 km south of Algiers (33°19' N, 4°19' E) and emplaced in Upper-Cretaceous to Eocene limestones. Although accepted as an impact crater on the basis of alleged observations of shock-diagnostic features such as planar deformation features (PDFs) in quartz grains, previous works were limited and further studies are desirable to ascertain the structure formation process and its age. For this purpose, the crater was investigated using a multidisciplinary approach including field observations, detailed cartography of the different geological and structural units, geophysical surveys, anisotropy of magnetic susceptibility, paleomagnetism, and petrography of the collected samples. We found that the magnetic and gravimetric profiles highlight a succession of positive and negative anomalies, ones that might indicate the occurrence of a causative material which is at least in part identical. Geophysical analysis and modeling suggest the presence of this material within the crater at a depth of about 100 m below the surface. Using soil magnetic susceptibility measurements, the shallowest magnetized zone in the central part of the crater is identified as a recently deposited material. Paleomagnetic and rock magnetic experiments combined with petrographic observations show that detrital hematite is the main magnetic carrier although often associated with magnetite. A primary magnetization is inferred from a stable remanence with both normal and reverse directions, carried by these two minerals. Although this is supposed to be a chemical remagnetization, its normal polarity nature is considered to be a Pliocene component, subsequent to the crater formation. The pole falls onto the Miocene-Pliocene part of the African Apparent Polar Wander Path (APWP). Consequently, we estimate then formation of the Ma^adna crater to have occurred during the time period extending from the Late Miocene to the Early Pliocene. Unfortunately, our field and laboratory investigations do not allow us to confirm an impact origin for the crater as neither shatter cones, nor shocked minerals, were found. A dissolved diapir with inverted relief is suggested as an alternative to the impact hypothesis, which can still be considered as plausible. Only a drilling may provide a definite answer.
Databáze: OpenAIRE
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