Tertiary pegmatite dikes of the Central Alps

The largest field of Alpine Oligocene pegmatite dikes is in the Central Alps within the Southern Steep Belt (SSB) of the Alpine nappes; it extends for about 100 km in an E–W direction and 15 km in a N–S direction north of the Periadriatic Fault, from the Bergell pluton (to the east) to the Ossola valley (to the west). The pegmatite field geographically overlaps (1) the highest temperature domain of the Lepontine Barrovian metamorphic dome and (2) the zone of Alpine migmatization. We have studied pegmatites in two areas: (1) the Codera area on the western border of the Bergell pluton and (2) the Bodengo area between the Mera and the Mesolcina valleys. Most pegmatites show a simple mineral assemblage consisting of K-feldspar, quartz, and muscovite ± biotite, and only a minor percentage of the dikes (< 5%) contains Sn-Nb-Ta-Y-REE-U oxide, Y-REE phosphate, Mn-Fe-phosphate, Ti-Zr-silicate, Be-Y-REE-U-silicate and oxide minerals (beryl, chrysoberyl, bertrandite, bavenite, and milarite), garnet (almandine-spessartine), tourmaline (schorl to rare elbaite), bismuthinite, magnetite, and rarely dumortierite and helvite. The mineral assemblages, geological context, and chemical compositions allow the distinction between LCT (lithium, cesium, tantalum) and mixed LCT-NYF (niobium, yttrium, fluorine) pegmatites (with only one exception of an NYF dike in the Bodengo area). The LCT pegmatites of the Central Alps did not reach a high degree of geochemical evolution. The most fractionated pegmatites are found in the Codera area and contain Mn-rich elbaite, triplite, pink-beryl, and Cs-Rb-rich feldspar. In the Bodengo area pegmatites locally contain miarolitic cavities and the most evolved pegmatites correspond to the beryl-columbite-phosphate type. From a structural point of view two main types of pegmatites can be distinguished: (1) pegmatites that were involved in ductile deformation and (2) pegmatites that postdated the main ductile deformation of the SSB. Many pegmatites of the Codera valley belong to the first structural type: they were emplaced at relatively high ambient temperature (ca. 500 °C) and locally show a pervasive recrystallization of quartz and a mylonitic structure. The Codera dikes trend about 70° and are steeply dipping. In the Bodengo area the main set of pegmatites (trending approximately N–S to NNE–SSW) crosscuts the ductile deformation structures of the SSB, but the area also includes an earlier generation of boudinaged and folded pegmatite dikes. The undeformed pegmatites from this area may contain miarolitic pockets. There is no systematic difference in the mineral assemblage between the two structural types of pegmatites. However, the chemistry of pegmatite minerals, especially of garnet, in addition to field data suggests that the dikes of the Codera and Bodengo areas represent two distinct generations of pegmatites. Structural data and the few existing radiometric ages suggest that pegmatites were emplaced over a time span between 29 and 25 Ma (and possibly as young as 20 Ma), with the youngest dikes postdating the ductile deformations of the Alpine nappes. The present work presents a first comprehensive field description and geochemical – mineralogical characterization of the Alpine pegmatite field of the Central Alps

Seismic energy partitioning inferred from pseudotachylyte-bearing faults (Gole Larghe Fault, Adamello batholith, Italy)

Fracture energy EG (the energy used for expanding a rupture surface area) is the fraction of work during seismic faulting that is required for creation of (i) new surfaces in the slip zone, and (ii) damage zone in the wall rocks. Partitioning of the earthquake energy between EG and frictional heat EH, determines the features of the rupture propagation and the mechanical behavior of the fault. The cataclastic microstructures associated with pseudotachylyte (solidified clast-laden friction-induced melt produced during coseismic slip) veins might contain information about the partitioning. In this preliminary study we used microstructural observations on pseudotachylytes from the Gole Larghe Fault zone (Southern Alps, Italy) to determine both EH and EG. The EH for unit fault surface area is estimated from pseudotachylyte vein thickness 2w. The energy required to produce friction melt is EH = [(1- f) H+ cP(Tm-Thr)]r 2w where f is the volume ratio of lithic clasts within the pseudotachylyte, H is the latent heat of fusion, cP is the specific heat at constant pressure, (Tm-Thr) is the difference between initial melt temperature and host rock temperature and r is the density. The EG is estimated by multiplying the newly created grain surface per unit of fault area by the specific surface energy (J m-2). In fact the studied pseudotachylyte vein contains plagioclase clasts displaying a characteristic internal fragmentation not observed in the host rock. This indicates a direct association between newly created grain surfaces and the seismic rupture process via pseudotachylyte production. It follows that pseudotachylytes might yield information on the energy partitioning between EG and EH

Static stress drop associated with brittle slip events on exhumed faults

We estimate the static stress drop on small exhumed strike-slip faults in the Lake Edison granodiorite of the central Sierra Nevada (California). The sub-vertical strike-slip faults were exhumed from 4-15 km depth, and were chosen because they are exposed in outcrop along their entire tip-to-tip lengths of 8-12 m. Slip nucleated on joints and accumulated by ductile shearing (forming quartz mylonites from early quartz vein filling in joints) and successive brittle faulting (forming epidote-bearing cataclasites). The occurrence of thin, < 1 mm wide, pseudotachylytes along some small faults throughout the study area suggests that some portion of the brittle slip was seismic. We suggest that the contribution of seismic slip to the total slip along the studied cataclasite-bearing small faults may be estimated by the length of epidote-filled, rhombohedral dilatational jogs (rhombochasms) distributed semi-periodically along the length of the faults. The interpretation that slip recorded by rhombochasms occurred in single events is based on evidence that: 1) epidote crystals are randomly oriented and undeformed within the rhombochasm; and 2) cataclasite structure in principal slip zones does not include clasts of previous cataclasite. We thereby constrain both the rupture length and slip. Based on these measurements, we calculate stress drops ranging over 90-250 MPa, i.e., one to two orders of magnitude larger than typical seismological estimates for earthquakes, but similar in magnitude to recent observations of small (< M2) earthquakes from the San Andreas Fault Observatory at Depth (SAFOD). These inferred seismic ruptures occurred along small, deep-seated faults, and, given the calculated stress drops and observations that brittle faults exploited joints sealed by quartz-bearing mylonite, we conclude that these were “strong” faults

Crystallographic control and texture inheritance during mylonitization of coarse grained quartz veins

Quartz veins within Rieserferner pluton underwent deformation during post-magmatic cooling at temperature around 450 \ub0C. Different crystallographic orientations of cm-sized quartz vein crystals conditioned the evolution of microstructures and crystallographic preferred orientations (CPO) during vein-parallel simple shear up to high shear strains (\u3b3 48 10). For \u3b3 b 2, crystals stretched to ribbons of variable aspect ratios. The highest aspect ratios resulted from {m}baN glide in ribbons with c-axis sub-parallel to the shear zone vorticity Y-axis. Ribbons with c-axis orthogonal to Y (XZ-type ribbons) were stronger and hardened more quickly: they show lower aspect ratios and \ufb01ne (grain size ~10\u201320 \u3bcm) recrystallization along sets of microshear zones (\u3bcSZs) exploiting crystallographic planes. Distortion of XZ-type ribbons and recrystallization preferentially exploited the slip systems with misorientation axis close to Y. New grains of \u3bcSZs initiated by subgrain rotation recrystallization (SGR) and thereupon achieved high angle misorientations by a concurrent process of heterogeneous rigid grain rotation around Y associated with the con\ufb01ned shear within the \u3bcSZ. Dauphin\ue9 twinning occurred pervasively, but did not play a dominant role on \u3bcSZ nucleation. Recrystallization became widespread at \u3b3 N 2 and pervasive at \u3b3 48 10. Ultramylonitic quartz veins are \ufb01ne grained (~10 \u3bcm, similar to new grains of \u3bcSZ) and show a CPO banding resulting in a bulk c-axis CPO with a Y-maximum, as part of a single girdle about orthogonal to the foliation, and orientations at the pole \ufb01gure periphery at moderate to high angle to the foliation. This bulk CPO derives from steady-state SGR associated with preferential activity, in the different CPO bands, of slip systems generating subgrain boundaries with misorientation axes close to Y. The CPO of individual recrystallized bands is largely inherited from the original crystallographic orientation of the ribbons (and therefore vein crystals) from which they derived. High strain and pervasive recrystallization were not enough to reset the initial crystallographic heterogeneity and this CPO memory is explained by the dominance of SGR. This contrast with experimental observation of a rapid erasure of a pristine CPO by cannibalism from grains with the most favourably oriented slip system under dominant grain boundary migration recrystallization

Percutaneous pericardiocentesis for pericardial effusion: predictors of mortality and outcomes

Pericardial effusion can dangerously precipitate patient’s hemodynamic stability and requires prompt intervention in case of tamponade. We investigated potential predictors of in-hospital mortality, a composite outcome of in-hospital mortality, pericardiocentesis-related complications, and the need for emergency cardiac surgery and all-cause mortality in patients undergoing percutaneous pericardiocentesis. This is an observational, retrospective, single-center study on patients undergoing percutaneous pericardiocentesis (2010–2019). We enrolled 81 consecutive patients. Median age was 71.4&nbsp;years (interquartile range [IQR] 58.1–78.1&nbsp;years) and 51 (63%) were male. Most of the pericardiocentesis were performed in an urgency setting (76.5%) for cardiac tamponade (77.8%). The most common etiology was idiopathic (33.3%) followed by neoplastic (22.2%). In-hospital mortality was 14.8% while mortality during follow-up (mean 17.1&nbsp;months) was 44.4%. Only hemodynamic instability (i.e., cardiogenic shock, hypotension refractory to fluid challenge therapy and inotropes) was associated with in-hospital mortality at the univariate analysis (odds ratio [OR] 7.2; 95% confidence interval [CI] 1.76–29.4). Non-neoplastic/non-idiopathic etiology and hemodynamic instability were associated with the composite outcome of in-hospital mortality, need for emergency cardiac surgery, or pericardiocentesis-related complications (OR 5.75, 95% CI 1.65–20.01, and OR 5.81, 95% CI 2.11–15.97, respectively). Multivariate Cox regression analysis adjusted for possible confounding variables (age, coronary artery disease, and hemodynamic instability) showed that neoplastic etiology was independently associated with medium-term mortality (hazard ratio [HR] 4.05, 95% CI 1.45–11.36). In a real-world population treated with pericardiocentesis for pericardial effusion, in-hospital adverse outcomes and medium-term mortality are consistent, in particular for patients presenting with hemodynamic instability or neoplastic pericardial effusion

Myrmekite and strain weakening in granitoid mylonites

At mid-crustal conditions, deformation of feldspar is mainly accommodated by a combination of fracturing, dissolution\u2013precipitation, and reaction-weakening mechanisms. In particular, K-feldspar is reaction-weakened by the formation of strain-induced myrmekite \u2013 a \ufb01ne-grained symplectite of plagioclase and quartz. Here we use electron backscattered diffraction to (i) investigate the microstructure of a granodiorite mylonite, developed at 3c 450 \ub0C during cooling of the Rieserferner pluton (Eastern Alps); and (ii) assess the microstructural processes and the weakening associated with myrmekite development. Our analysis shows that the crystallographic orientation of plagioclase in pristine myrmekite was controlled by that of the replaced K- feldspar. Myrmekite nucleation resulted in both grain-size reduction and anti-clustered phase mixing by heterogeneous nucleation of quartz and plagioclase. The \ufb01ne grain size of sheared myrmekite promoted grain-size-sensitive creep mechanisms including \ufb02uid-assisted grain boundary sliding in plagioclase, coupled with heterogeneous nucleation of quartz within creep cavitation pores. Flow laws, calculated for monomineralic quartz, feldspar, and quartz + plagioclase aggregates (sheared myrmekite) during deformation at 450 \ub0C, show that grain-size-sensitive creep in sheared myrmekite accommodated strain rates several orders of magnitude higher than monomineralic quartz layers deforming by dislocation creep. Therefore, diffusion creep and grain size-sensitive processes contributed signi\ufb01cantly to bulk rock weakening during mylonitization. Our results have implications for modelling the rheology of the felsic middle crust

The earthquake cycle in the dry lower continental crust: insights from two deeply exhumed terranes (Musgrave Ranges, Australia and Lofoten, Norway)

This paper discusses the results of field-based geological investigations of exhumed rocks exposed in the Musgrave Ranges (Central Australia) and in Nusfjord (Lofoten, Norway) that preserve evidence for lower continental crustal earthquakes with focal depths of approximately 25–40 km. These studies have established that deformation of the dry lower continental crust is characterized by a cyclic interplay between viscous creep (mylonitization) and brittle, seismic slip associated with the formation of pseudotachylytes (a solidified melt produced during seismic slip along a fault in silicate rocks). Seismic slip triggers rheological weakening and a transition to viscous creep, which may be already active during the immediate post-seismic deformation along faults initially characterized by frictional melting and wall-rock damage. The cyclical interplay between seismic slip and viscous creep implies transient oscillations in stress and strain rate, which are preserved in the shear zone microstructure. In both localities, the spatial distribution of pseudotachylytes is consistent with a local (deep) source for the transient high stresses required to generate earthquakes in the lower crust. This deep source is the result of localized stress amplification in dry and strong materials generated at the contacts with ductile shear zones, producing multiple generations of pseudotachylyte over geological time. This implies that both the short- and the long-term rheological evolution of the dry lower crust typical of continental interiors is controlled by earthquake cycle deformation. This article is part of a discussion meeting issue ‘Understanding earthquakes using the geological record’.</jats:p

Earthquake nucleation in the lower crust by local stress amplification

Deep intracontinental earthquakes are poorly understood, despite their potential to cause significant destruction. Although lower crustal strength is currently a topic of debate, dry lower continental crust may be strong under high-grade conditions. Such strength could enable earthquake slip at high differential stress within a predominantly viscous regime, but requires further documentation in nature. Here, we analyse geological observations of seismic structures in exhumed lower crustal rocks. A granulite facies shear zone network dissects an anorthosite intrusion in Lofoten, northern Norway, and separates relatively undeformed, microcracked blocks of anorthosite. In these blocks, pristine pseudotachylytes decorate fault sets that link adjacent or intersecting shear zones. These fossil seismogenic faults are rarely >15 m in length, yet record single-event displacements of tens of centimetres, a slip/length ratio that implies >1 GPa stress drops. These pseudotachylytes represent direct identification of earthquake nucleation as a transient consequence of ongoing, localised aseismic creep

The management of acute venous thromboembolism in clinical practice. Results from the European PREFER in VTE Registry

Venous thromboembolism (VTE) is a significant cause of morbidity and mortality in Europe. Data from real-world registries are necessary, as clinical trials do not represent the full spectrum of VTE patients seen in clinical practice. We aimed to document the epidemiology, management and outcomes of VTE using data from a large, observational database. PREFER in VTE was an international, non-interventional disease registry conducted between January 2013 and July 2015 in primary and secondary care across seven European countries. Consecutive patients with acute VTE were documented and followed up over 12 months. PREFER in VTE included 3,455 patients with a mean age of 60.8 ± 17.0 years. Overall, 53.0 % were male. The majority of patients were assessed in the hospital setting as inpatients or outpatients (78.5 %). The diagnosis was deep-vein thrombosis (DVT) in 59.5 % and pulmonary embolism (PE) in 40.5 %. The most common comorbidities were the various types of cardiovascular disease (excluding hypertension; 45.5 %), hypertension (42.3 %) and dyslipidaemia (21.1 %). Following the index VTE, a large proportion of patients received initial therapy with heparin (73.2 %), almost half received a vitamin K antagonist (48.7 %) and nearly a quarter received a DOAC (24.5 %). Almost a quarter of all presentations were for recurrent VTE, with &gt;80 % of previous episodes having occurred more than 12 months prior to baseline. In conclusion, PREFER in VTE has provided contemporary insights into VTE patients and their real-world management, including their baseline characteristics, risk factors, disease history, symptoms and signs, initial therapy and outcomes