Provenance signatures for the Miocene volcaniclastic succession of the Tufiti di Tusa Formation, southern Apennines, Italy

The Tufti di Tusa Formation, a siliciclastic turbidite system of lower Miocene age insouthern Italy, is mainly composed of volcaniclastic and quartzolithic sandstones interbedded withmudrocks. Sandstones are subdivided into four distinctive petrofacies, evolving from quartzolithicto volcaniclastic lithofeldspathic and feldspatholithic, reflecting detrital evolution from growingorogen (quartzolithic petrofacies) to active volcanism (volcaniclastic petrofacies). The mineralogicalcomposition of the associated mudrocks is predominantly characterized by phyllosilicates, mainlyillite/smectite mixed layers (I/S R1 associated with minor amounts of I/S R0 in the lower part of thesuccession, and I/S R3 in its upper part), together with illite, detrital micas and chlorite, and minoramounts of chlorite/smectite mixed layers and kaolinite, in addition to quartz, calcite and feldspars. Themost abundant phyllosilicates are I/S mixed layers, 10-Å minerals (illite and micas) and chlorite, whilekaolinite and chlorite–smectite mixed layers are present as a few per cent or in trace amounts. X-raydiffraction patterns show the occurrence of the ordered I/S R1 mixed layers in most samples but, at thetop of the succession, some samples are characterized by I/S R3 mixed layers, whilst in the lower partof the succession I/S R1 is associated with a lower amount of I/S R0. These features suggest that theTufiti di Tusa Formation experienced a medium diagenetic grade, and the occurrence of I/S R3 couldbe explained by K-availability in samples in the upper part of the succession. The lithic fragments insandstones are metasedimentary rocks of Palaeozoic age, and andesite to dacite volcanic rocks of earlyMiocene age. The associated mudrocks also contain trace element ratios (Cr/V, Y/Ni, La/Sc, Th/Sc,Th/Co, Th/Cr, Cr/Th and Eu/Eu∗) consistent with a provenance containing intermediate to silicicsources with scarce or absent basic rocks. The chemical index of alteration (63.2 to 71.6) suggests amoderate degree of weathering in the source. Furthermore, the K/Cs ratios of sediments confirm likelymoderate rather than intense weathering. The index of compositional variability (ICV) values (from 1.2to 2.5) are high enough to suggest the mudrocks are first-cycle sediments with little recycling. The Al–Ti–Zr diagram and the Th/Sc v. Zr/Sc plot indicate poor sorting and rapid deposition of the sediments.Detrital and sedimentary evolution of the Tufiti di Tusa Formation provides constraints, in terms ofrelations between a growing orogenic system and active volcanism in the Central Mediterranean, tocontribute to geodynamic and palaeogeographic reconstructions of the earliest collision in the southernApennines region.