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Dipartimento di Scienze della Terra, Universita’ di Pisa
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- PublicationRestrictedA late Cretaceous contamination episode of the European–Mediterranean mantle(2008-01-10)
; ; ; ; ;Piromallo, C.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma1, Roma, Italia ;Gasperini, D.; Dipartimento di Scienze della Terra, Universita' di Pisa, Pisa, Italy ;Macera, P.; Dipartimento di Scienze della Terra, Universita' di Pisa, Pisa, Italy ;Faccenna, C.; Dipartimento di Scienze Geologiche, Università di Roma 3, Rome, Italy; ; ; One of the most challenging issues about the Tertiary–Quaternary alkaline magmatism spreading across the Euro-Mediterranean region is the assessment of both the nature of its mantle source and the mechanism responsible for the common HIMU-like (High μ=high 238U/204Pb) character of erupted lavas, enduring over about 100 million years in diverse tectonic environments. In this paper we try to reconcile geochemical and geophysical data through a multidisciplinary investigation on geochemistry, timing and locations of the main Na-rich alkaline volcanic centers, seismic tomographic images and plate kinematics. We propose that the common component of the Euro-Mediterranean mantle derives from a contamination episode triggered by the rise of the Central Atlantic Plume (CAP) head. Plate reconstruction shows that at late Cretaceous- Paleocene time the oldest magmatic centers of the Euro-Mediterranean region were located more than 2000 km SW of their present day position, in proximity of the CAP hot spot location, where seismic tomography detects a broad low seismic velocity region in the lower mantle. The northeastward migration of the Eurasian and African plates could have involved also part of the CAP contaminated mantle, which moved in the same direction being coupled to the lithospheric plates, thus explaining the presence of geochemically-uniform material spread in the sub-lithospheric Euro-Mediterranean mantle. During the Tertiary, regional-scale convection and related processes such as rifting, back-arc spreading, slab detachment/windows, may have favored upwelling and partial melting of the frayed plume head material via adiabatic decompression, shaping the spatial and temporal distribution of HIMU-like volcanics. The growing supply of subducted lithosphere may explain as well the increase of crustal isotopic signatures of alkaline magmas with time. In our opinion, the Euro-Mediterranean upper mantle contamination can be eventually related to a global event occurred during the Cretaceous as a consequence of a mantle avalanche caused by the Tethys closure.261 527 - PublicationRestrictedGeodynamic implications of deep mantle upwelling in the source of Tertiary volcanics from the Veneto region (South-Eastern Alps)(2003)
; ; ; ; ; ; ; ;Macera, P.; Dipartimento di Scienze della Terra, Universita’ di Pisa ;Gasperini, D.; Dipartimento di Scienze della Terra, Universita’ di Pisa ;Piromallo, C.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma1, Roma, Italia ;Blichert-Toft, J.; Ecole Normale Superieure, Lyon ;Bosch, D.; Universite ‘‘Montpellier 2", Montpellier ;Del Moro, A.; Istituto di Geoscienze e Georisorse, C.N.R., Pisa ;Martin, S.; Dipartimento di Chimica Fisica Matematica, Universita` Insubria, Como; ; ; ; ; ; Major and trace element and Sr–Nd–Hf–Pb isotopic data for the most primitive Tertiary lavas from the Veneto region (South-Eastern Alps, Italy) show the typical features of HIMU hotspot volcanism, variably diluted by a depleted asthenospheric mantle component (87Sr/86Sri=0.70306–0.70378; "Ndi=+3.9 to +6.8; "Hfi=+6.4 to +8.1, 206Pb/204Pbi=18.786–19.574). P-wave seismic tomography of the mantle below the Veneto region shows the presence of low-velocity anomalies at depth, which is consistent with possible upwellings of plume material. Between the depths of 100–250 km the velocity anomalies are approximately 2–2.5% slower than average, implying a temperature excess of about 220–280 K, in agreement with estimates for other mantle plumes in the world. In this context, the Veneto volcanics may represent the shallow expression of a mantle upflow. The presence of a HIMU-DM component in a collision environment has significant geodynamic implications. Slab detachment and ensuing rise of deep mantle material into the lithospheric gap is proposed to be a viable mechanism of hotspot magmatism in a subduction zone setting.242 23