Mass transfer from the Alps to the Apennines: volumetric constraints in the provenance study of the Macigno-Modino source-basin system Chattian-Aquitanian, northwestern Italy

A quantitative provenance approach is applied to the Late Oligocene-Early M iocene Macigno-Modino turbidite complex which accumulated in the foreland b asin developed in front of the growing Northern Apennines, but was supplied from the rapidly rising Western Alps, at the northwestern end of the basin . As well as the traditional recognition of source rock Lithologies and the ir gross paleogeographic location, the provenance approach adopted here eva luates the relative contributions to the elastic complex from different typ es of source rock, and estimates the volume of material transferred from th e Alps to the Apennines within the Macigno-Modino source-basin system, and the overall volume of rock assumed to have undergone erosion in order to su pply it. These elements are used to constrain the possible source of the cl astics and to infer the main paleogeological features of the source area. I t is concluded that an estimated volume of ca. 17-20 x 10(3) km(3) of basem ent (mainly metamorphic) rocks, together with ca. 103 km3 of intermediate c omposition volcanic rocks was transferred as detritus from the Western Alps area to the Northern Apennines foreland basin, creating the 250-300 km lon g, 50 km wide and up to 2.7 km thick Macigno-Modino elastic complex. Lithol ogy and paleogeography, combined with volume estimates and current knowledg e of the regional geology of the Western Alps, consistently suggest that th e bulk of the sediments funnelled into the Macigno-Modino complex were deri ved from the uplifted Ivrea crustal block, which formed a crystalline massi f some 5000 km(2) in extent, that rose ca. 3 km during the Oligocene, formi ng one of the main elements of Western Alpine geology during that time. (C) 1999 Elsevier Science B.V. All rights reserved.