U-Pb geochronology and geochemistry of late Palaeozoic volcanism in Sardinia(southern Variscides)

The latest Carboniferous to lower Permian volcanism of the southern Variscides in Sardinia developed in a regional continental transpressive and subsequent transtensile tectonic regime.Volcanism produced a wide range of intermediate-silicic magmas including medium-to high-K calc-alkaline andesites,dacites,and rhyolites.A thick late Palaeozoic succession is well exposed in the four most representative Sardinian continental basins(Nurra,Perdasdefogu,Escalaplano,and Seui-Seulo),and contains substantial stratigraphic,geochemical,and geochronological evidence of the area's complex geological evolution from the latest Carboniferous to the beginning of the Triassic.Based on major and trace element data and LA-ICP-MS U-Pb zircon dating,it is possible to reconstruct the timing of postVariscan volcanism.This volcanism records active tectonism between the latest Carboniferous and Permian,and post-dates the unroofing and erosion of nappes in this segment of the southern Variscides.In particular,igneous zircon grains from calc-alkaline silicic volcanic rocks yielded ages between299±1 and 288±3 Ma,thereby constraining the development of continental strike-slip faulting from south(Escalaplano Basin)to north(Nurra Basin).Notably,andesites emplaced in medium-grade metamorphic basement(Mt.Cobingius,Ogliastra)show a cluster of older ages at 332±12 Ma.Despite the large uncertainty,this age constrains the onset of igneous activity in the mid-crust.These new radiometric ages constitute:(1)a consistent dataset for different volcanic events;(2)a precise chronostratigraphic constraint which fits well with the biostratigraphic data and(3)insights into the plate reorganization between Laurussia and Gondwana during the late Palaeozoic evolution of the Variscan chain.

Advances and Practices on the Research, Prevention and Control of Land Subsidence in Coastal Cities

Land subsidence severely threatens most of the coastal plains around the world where high productive industrial and agricultural activities and urban centers are concentrated. Coastal subsidence damages infrastructures and exacerbates the effect of the sea-level rise at regional scale. Although it is a well-known process, there is still much more to be improved on the monitoring, mapping and modeling of ground movements, as well as the understanding of controlling mechanisms. The International Geoscience Programme recently approved an international project(IGCP 663) aiming to bring together worldwide researchers to share expertise on subsidence processes typically occurring in coastal areas and cities, including basic research, monitoring and observation, modelling and management. In this paper, we provide the research communities and potential stakeholders with the basic information to join the participating teams in developing this project. Specifically, major advances on coastal subsidence studies and information on well-known and new case studies of land subsidence in China, Italy, The Netherlands, Indonesia, Vietnam and Thailand are highlighted and summarized. Meanwhile, the networking, dissemination, annual meeting and field trip are briefly introduced.

Impact,Mechanism,Monitoring of Land Subsidence in Coastal Cities(Annual Work of IGCP 663)

Land subsidence is a worldwide geohazard consisting in the lowering of the ground surface due to natural and human-induced processes occurring in the shallow and deep subsoil.Over the last two decades,land subsidence has caused damages and widespread impacts to a variety of infrastructures in coastal cities(Ma et al.,2011;Liu et al.,2016;Minderhoud et al.,2018).

Continental Flood Basalts and Rifting: Geochemistry of Cenozoic Yemen Volcanic Province

Rift formation is a crucial topic in global tectonics. The Yemen rift-related area is one of the most important provinces, being connected to the rifting processes of the Gulf of Aden, the Red Sea and Afar Triangle. In this paper, a review of the Yemen volcanic province and its relations with the Red Sea rifting are presented. Tertiary continental extension in Yemen resulted in the extrusion of large volumes of effusive rocks. This magmatism is divided in the Oligo-Miocene Yemen Trap Series (YTS) separated by an unconformity from the Miocene-Recent Yemen Volcanic Series (YVS). Magmas of the YTS were erupted during the synrift phase and correlate with the first stage of sea-floor spreading of the Red Sea and the Gulf of Aden (30 - 15 Ma), whereas the magmas of the YVS were emplaced during the post rift phase (10 - 0 Ma). A continental within plate character is recognized for both the YTS and YVS basalts. The YTS volcanic rocks are contemporaneous with, and geochemically similar to, the Ethiopian rift volcanism, just as the volcanic fields of the YVS are geochemically alike to most of the Saudi Arabian volcanics. YTS and YVS have analogous SiO2 ranges, but YVS tend to have, on average, higher alkalis and MgO contents than YTS. Fractional crystallization processes dominate geochemical variations of both series. Primitive magmas (MgO > 7.0%) are enriched in incompatible elements and LREEs with respect to primitive mantle, but YVS are more enriched than YTS. To first order, the different geochemical patterns agree with different degrees of partial melting of an astenospheric mantle source: 25% - 30% of partial melting for YTS and 10% - 3% for YVS. Secondly, the higher degree of enrichment in incompatible elements of YVS reflects also greater contribution of a lithospheric mantle component in their source region.

New application of open source data and Rock Engineering System for debris flow susceptibility analysis

This research describes a quantitative,rapid,and low-cost methodology for debris flow susceptibility evaluation at the basin scale using open-access data and geodatabases.The proposed approach can aid decision makers in land management and territorial planning,by first screening for areas with a higher debris flow susceptibility.Five environmental predisposing factors,namely,bedrock lithology,fracture network,quaternary deposits,slope inclination,and hydrographic network,were selected as independent parameters and their mutual interactions were described and quantified using the Rock Engineering System(RES)methodology.For each parameter,specific indexes were proposed,aiming to provide a final synthetic and representative index of debris flow susceptibility at the basin scale.The methodology was tested in four basins located in the Upper Susa Valley(NW Italian Alps)where debris flow events are the predominant natural hazard.The proposed matrix can represent a useful standardized tool,universally applicable,since it is independent of type and characteristic of the basin.

Cambro-Silurian magmatisms at the northern Gondwana margin(Penninic basement of the Ligurian Alps)

The Early Paleozoic evolution of the northern margin of Gondwana is characterized by several episodes of bimodal magmatism intruded or outpoured within thick sedimentary basins. These processes are well recorded in the Variscan blocks incorporated in the Ligurian Alps because they experienced low temperature Alpine metamorphism. During the Paleozoic, these blocks, together with the other Alpine basements, were placed between the Corsica-Sardinia and the Bohemian Massif along the northern margin of Gondwana. In this framework, they host several a variegated lithostratigraphy forming two main complexes(Complexs I and II) that can be distinguished by both the protoliths and their crosscutting relationships, which indicate that the acidic and mafic intrusives of Complex II cut an already folded sequence made of sediments, basalts and granitoids of Complex I. Both complexes were involved in the Variscan orogenic phases as highlighted by the pervasive eclogite-amphibolite facies schistosity(foliation II). However, rare relicts of a metamorphic foliation at amphibolite facies conditions(foliation I)is locally preserved only in the rocks of Complex I. It is debatable if this schistosity was produced during the early folding event e occurred between the emplacement of Complex I and II e rather than during an early stage of the Variscan metamorphic cycle.New SHRIMP and LA ICP-MS Ue Pb zircon dating integrated with literature data, provide emplacement ages of the several volcanic or intrusive bodies of both complexes. The igneous activity of Complex I is dated between 507 ± 15 Ma and 494 ± 5 Ma, while Complex II between 467 ± 12 Ma and 445.5 ± 12 Ma.The folding event recorded only by the Complex I should therefore have occurred between 494 ± 5 Ma and 467 ± 12 Ma. The Variscan eclogite-amphibolite facies metamorphism is instead constrained between ~420 Ma and ~300 Ma. These ages and the geochemical signature of these rocks allow constraining the Early Paleozoic tectono-magmatic evolution of the Ligurian blocks, from a middleeupper Cambrian rifting stage, through the formation of an Early Ordovician volcanic arc during the Rheic Ocean subduction, until a Late Ordovician extension related to the arc collapse and subsequent rifting of the PaleoThetys. Furthermore, the ~420-350 Ma ages from zircon rims testify to thermal perturbations that may be associated with the Silurian rifting-related magmatism, followed by the subduction-collisional phases of the Variscan orogeny.

Multistage tectono-stratigraphic evolution of the Canavese Intracontinental Suture Zone:New constraints on the tectonics of the Inner Western Alps

The Canavese Intracontinental Suture Zone(CISZ) within the Inner Western Alps represents the remnant of a long-lived minor subduction zone involving a narrow, thinned continental crust/oceanic lithosphere seaway between two continental domains of the Adria microplate(i.e., the Sesia Zone and the IvreaVerbano Zone). As opposed to many suture zones, the CISZ mostly escaped pervasive tectonic deformation and metamorphism, thus preserving the original stratigraphy and allowing the relationships between tectonics and sedimentation to be defined. Through detailed geological mapping(1:5000 scale),structural analysis, stratigraphic and petrographic observations, we document evidences for the late Paleozoic to late Cenozoic tectonic evolution of the CISZ, showing that it played a significant role in the context of the tectonic evolution of the Inner Western Alps region from the early to late Permian Pangea segmentation, to the Jurassic Tethyan rifting, and up to the subduction and collisional stages,forming the Western Alps. The site of localization/formation of the CISZ was not accidental but associated with the re-use of structures inherited from regional-scale wrench tectonics related to the segmentation of Pangea, and from the subsequent extensional tectonics related to the Mesozoic rifting, as documented by crosscutting relationships between stratigraphic unconformities and tectonic features. Our findings document that evidences derived from stratigraphy, facies indicators, and relationships between tectonics and sedimentation in the shallow crustal portions of suture zones, such in the CISZ, are important to better constrain the tectonic history of those metamorphic orogenic belts around the world in which evolutionary details are commonly complicated by high-strain deformation and metamorphic transformations.

Revision of the Conodont Mockina slovakensis and Its Paleogeographic Implications for the Upper Triassic Intraplatform Basins of the Alps

Mockina slovakensis,thought to have evolved from Epigondolella praeslovakensis,is an important species of the Norian(Upper Triassic),generally considered as the representative of the uppermost Alaunian to upper Sevatian in the Tethys.The previous description of M.slovakensis was incomplete,thus has led to some misidentifications.We thus update the description of M.slovakensis and discuss its comparisons and occurrence based on the new conodont investigations in Dolomia di Forni and the data from previous literatures.The conodont assemblage in the succession of Dolomia di Forni is dominated by M.slovakensis,along with rare M.postera and E.praeslovakensis.We described two morphotypes of M.slovakensis(morphotypes A and B),on the basis of shape of the lateral profile.These two morphotypes can also be observed in the E.praeslovakensis.Moreover,M.slovakensis is usually documented as almost monospecific conodont association in intraplatform basins,thus its paleogeographic implications are also discussed.

Evolutionary Process from Mockina bidentata to Parvigondolella andrusovi:Evidence from the Pizzo Mondello Section,Sicily,Italy

During their last phase of evolution,the pectiniform conodont elements manifested an evident trend of simplification and miniaturization.This phase started from the late Norian(Sevatian)in the Late Triassic and the evolutionary process of genus Mockina to Parvigondolella,in particular between Mockina bidentata and Parvigondolella andrusovi,is one of the most significant examples.Parvigondolella has been reported worldwide since it was first described in the early 1970s.However,it has recently been suggested that genus Parvigondolella is an ecostratigraphic morphotype of genus Mockina,and thus a phenotype controlled by the environmental conditions,and not an independent taxon.In the Pizzo Mondello Section(Sicily,Italy),transitional forms between M.bidentata and P.andrusovi have been found at different evolutionary stages.We have investigated the oceanic conditions at the time by using redox-sensitive elements(Mn,Fe,V,Cr,and Ni)and seawater temperatures from biogenetic δ^(18)Ophos to understand the possible environmental influences on the phylogenetic evolution between Mockina and Parvigondolella.The geochemical and isotope analyses indicate that the redox condition and temperature were stable during the evolution of genus Parvigondolella in Pizzo Mondello,confirming that genus Parvigondolella is a real taxon and not a phenotype.A new conodont species named Parvigondolella ciarapicae n.sp.is described here for the first time.