A paleointensity study on middle Miocene to Pliocene volcanic rocks from south-eastern Spain

Abstract

Abstract Thirteen middle-Miocene to Pliocene volcanic sites, belonging to four different types of volcanism (calc-alkaline volcanism, potassic calc-alkaline and shoshonitic volcanism, lamproitic volcanism and basaltic alkaline volcanism), have been sampled in south-eastern Spain for paleointensity determinations. Rock-magnetic studies yield low-Ti titanomagnetite as the main carrier of remanence, showing also the presence of titanohematites in several cases. Analysis of hysteresis parameters indicates a PSD domain structure. Paleointensity determinations were performed with the Coe (1967) method. Of the 90 paleointensity determinations carried out, 29 provide successful determinations which fulfil selection criteria; most of these were in samples of lamproitic volcanism. Only four lamproitic sites out of the 13 studied ones yield reliable results. All have a similar age of approximately 7 M.y. Virtual dipole moments (VDM) of three of these display values between approximately 4·1022 A m2 and 8·1022 A m2, thus providing new paleointensity data for a time interval (between 4 and 8 M.a.), with a lack of Thellier-type paleointensity determinations. The fourth site shows a much lower paleointensity of 1.6·1022 A m2, and may correspond to a polarity transition, in accordance with its paleo-directional results.