The influence of volcanic supply on the composition of modern river sands: the case study of the Ofanto river, Southern Italy

The Ofanto river drains volcanic rocks from the Monte Vulture, lacustrine-fluviolacustrine deposits associated with the same volcano and sedimentary deposits of the Southern Apennines and the Bradanic foredeep sequences. Comparing the modal composition of river sands and the outcrop area of different lithologies in the different sub-basins, an over-concentration of the volcaniclastic fraction, mainly represented by loose crystals of clinopyroxene, garnet and amphibole, is shown. This has been related to the preferential erosion of pyroclastic deposits, characterized by high production of sand-sized loose minerals, together with the carbonate lability and the low sand-sized detritus production from claystones and marls. The occurrence of volcaniclastic components upstream of Monte Vulture can be explained with a contribution from the lacustrine-fluviolacustrine deposits outcropping in the upstream sector or from pyroclastic fall deposits of Monte Vulture and/or Campanian volcanoes. This research shows that the volcanic record in the fluvial sands of the Ofanto river comes from weathering and sorting processes of volcaniclastic deposits rather than of the lavas building the main edifice. Therefore, caution must be taken during paleoenvironmental and paleoclimatic reconstructions when relating the type and abundance of the volcanic component in sediments to the weathering stage and evolutionary history of the volcano.Supplementary material at https://doi.org/10.6084/m9.figshare.c.5643959

Investigation of Rawa Dano Volcanic Deposits and Its Paleotopography Using Ground-Penetrating Radar

The detailed mechanisms of volcanic eruptions happened around Rawa Dano, Banten, Indonesia, remain undiscovered. One of the key features to this geological event is the presence of a 13.7 km × 6.5 km caldera-like morphology in the middle of Banten tuff deposits. Surface geological investigation in the area indicates that the eruptions are massive and occurred in several periods. Low-frequency ground-penetrating radar (GPR) signals are used as an aid to identify the unexposed part of the deposits in this volcanological study. Common-offset GPR surveys were carried out along three measurement lines traversing over the deposit outcrops. An outcrop which is exposed after sand mining activities at one of the survey locations shows dipping interfaces between the upper pyroclastic flow deposits, pumice-rich deposits, paleosol, and the lower pyroclastic fall deposits. These stratigraphic contacts are detected as well under the surface which are clearly recognizable in radar images. The GPR cross-section also shows some other reflections due to different deposit types. The overall results of the GPR profiles give the idea about the thickness of each type of volcanic deposits and the paleotopography in the surrounding area.

High Preservation Potential Volcaniclastic Sedimentation in the Serravallian Sequence of the Amantea Basin (Coastal Chain, North-Western Calabria)

Evidence of volcaniclastic sedimentation occurs in the first depositional sequence of the sedimentary succession of the Amantea Basin. Volcaniclastic deposits are intercalated in the upper part of a sandstone formation and these show a maximum thickness of about 8 m. The Amantea Basin is a Neogene depozone located along the Tyrrhenian margin of Calabria whose onset started during the Upper Serravallian. The source volcano to these materials had to have been located within or near to the marine basin in order to supply it with significant amounts of pyroclastic fragments emplaced by either pyroclastic fall/or flows during one or more explosive eruptions. The marine environment of volcaniclastic flows made up of pyroclastic fragments mixed with minor siliciclastic and carbonate material. The textural and structural features of the deposits and the composition of the volcanic glass fragments indicate an origin from a sub-aerial coeval explosive eruption, with initial sedimentation in a shallow marine environment, mixing with non-volcanic materials, reworking and final re-sedimentation into the basin. The age of the volcaniclastic/sedimentary sequence makes these deposits a marker for the geodynamic evolution of the area, and the lack of such horizons in the other coeval peri-Tyrrhenian basins allows us to consider the Amantea Basin as a confined elongated coastal basin area, whose tectonostratigraphic architecture denotes a structural partitioning of the eastern nascent Tyrrhenian Basin.

MONDACA VOLCANO LAHAR OF DECEMBER 3, 1762, MAULE REGION (35°28’S): ONE OF THE LARGEST VOLCANIC DISASTERS IN CHILEAN HISTORY

The Mondaca volcano is a rhyolitic thick lava-field, located in the vicinity of the nascent Lontué River Valley in the northern part of the Southern Andes. It reached a total volume of ~ 0.85 km3, and formed 4 subunits, named Mondaca 1, 2, 3 and 4, which correspond to successive emissions of rhyolitic blocky lavas, sourced at a rounded dome structure. They present well-preserved flow structures and, in the vicinity, restricted to the south and east of the dome, pyroclastic fall, as well as block’n ash deposits are also exhibited. Downstream, along the Lontué River, a laharic deposit is recognized. The lahar was generated after the collapse of an ephemeral ~0.44 km3 lake generated after the river obstruction during the first eruptive phase. Proximal lahar facies are well exposed between 5 and 30 km from their source. The profuse agricultural activity has completely obliterated the lahar's medial facies deposits along the central valley, but are well identified at the mouth of the Mataquito River, 180 km downstream, as a beige-coloured layer, interbedded within dark coastal beach-sands. The identification of superelevation deposits formed during the debris flow emplacement along the Lontué river valley, allows to determine high flow mobility, with estimated velocities that locally reached between 20 and 114 km/h. Petrographic characteristics in addition to whole-rock chemical analyses of lavas, pyroclasts and juvenile blocks of the laharic deposit, indicate that all they correspond to High K calcoalkaline rhyolites with subalkaline affinity. These antecedents, together with the geographical continuity between the lavas and debris deposits along Lontué and Mataquito rivers, corroborate facies correlation and common origin as the result of the complex evolution of the Mondaca volcano. Being a fundamentally effusive eruption that could not be observed from Curicó, the collateral consequences would have been catastrophic over a vast area to the south of that city, and evidences one of the largest volcanic catastrophes in Chilean history.

MAGMATIC EVOLUTION of the ALADAĞ VOLCANIC SYSTEM and SOUTHERN EDGE OF THE ERZURUM-KARS VOLCANIC PLATEAU (SARIKAMIŞ, CITY of KARS, NE TURKEY)

<p>The Erzurum-Kars Volcanic Plateau (EKVP) was formed by volcanic eruptions during the Messinian-Zanclean (~5.5 Ma) period, related to a continental collision event between Eurasia and Arabia, initiated ~15 Ma ago. The EKVP unconformably overlies a series of older sedimentary formations spanning in age from Cretaceous to Miocene. It starts with a ~400 m thick pyroclastic-rich layer at its bottom, named the Akkoz basal tuff, consisting of rhyolitic and dacitic ignimbrites, pyroclastic fall and surge deposits, which are intercalated with andesitic and dacitic lavas. Upper layers of the plateau are dominated by andesitic and basaltic andesitic lavas (~100 m).</p><p>In the northwest of the study area, an eroded stratovolcano, named Hamamlı volcano, which is possibly coeval with the plateau volcanism is present. It covers ~280 km<sup>2</sup> area and consists of a thick sequence of rhyolitic lavas, tuffs, ignimbrites, perlites and obsidians. The best preserved volcanic edifice in the study area is the Greater Aladağ Stratovolcano with a footprint of ~230 km<sup>2</sup>. It is composed of intermediate lavas with andesitic, dacitic, trachy-andesitic compositions, erupted ~3.55 Ma in Piacenzian. A small volcanic cone, named in this study as the Lesser Aladağ volcano, sits on the northern flank of the Greater Aladağ. Lesser Aladağ has an elliptical shape and is composed of basaltic-andesitic and basaltic trachy-andesitic lavas. Three semi-circular shaped rhyolitic domes called the Odalar rhyolite sit on the southern and eastern slopes of the Greater Aladağ. In the N and NE, the Aladağ volcanic sequence is unconformably overlain by a younger (~2.7 Ma) sequence of olivine basalts and basaltic andesites, which is known as the Kars volcanic plateau.</p><p>All volcanic products in the study area are calc-alkaline in character with a clear subduction signature. Results from our petrological modelling studies indicate that the magmas that fed the Aladağ volcanic system were evolved in a chamber, which was periodically replenished by fresh and primitive basaltic magma. Our assimilation model results based on the equations of DePaolo (1981) and Aitcheson and Forrest (1994) show that fractional crystallization was more important than crustal assimilation process in evolved lavas of the Aladağ system. Interestingly, EC-AFC model results indicate that some of the youngest basalts from the Kars volcanic plateau contain higher degrees of crustal assimilation relative to more evolved lavas.</p><p>Crystal chemistry of amphiboles by EMP from the amphibole-bearing lavas of the Akkoz basal tuff layer indicates that they had experienced crystallization pressures between 5.63 and 6.45 kbar and temperatures between 949 and 1026 °C during their magma chamber evolution. On the other hand, pyroxene thermo-barometry of the Aladağ units has given crystallization pressures between 0.8 and 4.8 kbar, and temperatures from 1025 to 1078 °C, implying polybaric fractionation. Calculated crystallization pressures and temperatures from the younger lavas of the Kars volcanic plateau are ~8.8 kbar and ~1179 °C respectively. Our partial melting models indicate that the primitive basaltic magmas might have been derived from a metasomatised spinel peridotite source with varying melting degrees from 0.7% to 2%.</p>