Cyclic Brittle‐Ductile Oscillations Recorded in Exhumed High‐Pressure Continental Units: A Record of Deep Episodic Tremor and Slow Slip Events in the Northern Apennines

open2noThe geological record of deep fossil seismogenesis in subduction zones is limited due to common rock overprinting during exhumation and only a few regions expose well-preserved deeply exhumed structures. We investigated a mesoscopic contractional duplex formed at blueschist facies conditions in continental metasediments in the Northern Apennines (Italy). Field observations reveal strain partitioning within the duplex between metapelite bands, corresponding to high-strain zones, and metaquartzarenite bands, which form low-strain, imbricated metric horses. Dilational shear veins occur in both lithotypes and are composed of quartz and carpholite fibers defining a stretching lineation parallel to the regional SW-NE transport direction. Geometrical, cross cutting and petrographic relationships suggest that veins formed broadly syn-mylonitization. Thermodynamic modeling constrains the formation of the mylonitic foliation to >0.7 GPa and ∼400°C and the dilational shear veins vein to ∼1.1 GPa and 350°C. Therefore, we document a top-to-the-E-NE thrust that formed at the deepest conditions recorded by this unit of the Northern Apennines. In the thrusted continental metasediments, aqueous fluid locally released by metamorphic dehydration reactions transiently increased pore pressure, in turn triggering brittleductile cyclicity. We propose that blueschist facies dilational shear veins and mylonitic foliation represent a geological record of deep episodic tremor and slow slip events. To the best of our knowledge, this is the first time that these events are genetically associated with brittle and ductile structures of a mesoscopic duplex. We suggest that these structures could be common features of the high-pressure metamorphic units of the Apennine orogenic belt.This project has received funding from the European Union's Horizon 2020 research and innovation programme under the Marie Skłodowska-Curie grant agreement No 839779. Open Access Funding provided by Universita di Bologna within the CRUI-CARE AgreementopenGiuntoli, Francesco; Viola, GiulioGiuntoli, Francesco; Viola, Giuli

A likely geological record of deep tremor and slow slip events from a subducted continental broken formation.

open2noFluids in subduction zones play a key role in controlling seismic activity, drastically affecting the rheology of rocks, triggering mineral reactions, and lowering the effective stress. Fluctuating pore pressure is one important parameter for the switch between brittle and ductile deformation, thus impacting seismogenesis. Episodic tremor and slow slip events (ETS) have been proposed as a common feature of the geophysical signature of subduction zones. Their geological record, however, remains scanty. Only the detailed and further characterization of exhumed fossil geological settings can help fill this knowledge gap. Here we propose that fluctuating pore pressure linked to metamorphic dehydration reactions steered cyclic and ETS-related brittle and ductile deformation of continental crustal rocks in the subduction channel of the Apennines. Dilational shear veins and ductile mylonitic shear zones formed broadly coevally at minimum 1 GPa and 350 °C, corresponding to ~ 30–40 km depth in the subduction zone. We identify carpholite in Ca-poor metasediments as an important carrier of H2O to depths > 40 km in cold subduction zones. Our results suggest that the described (micro)structures and mineralogical changes can be ascribed to deep ETS and provide a useful reference for the interpretation of similar tectonic settings worldwide.This project has received funding from the European Union’s Horizon 2020 research and innovation programme under the Marie Skłodowska-Curie grant agreement No. 839779.openGiuntoli, F., Viola, G.Giuntoli, F., Viola, G

Synthetic biology of hypoxia.

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Deeply subducted continental fragments - Part 2: Insight from petrochronology in the central Sesia Zone (western Italian Alps)

Subducted continental terranes commonly comprise an assembly of subunits that reflect the different tectono-metamorphic histories they experienced in the subduction zone. Our challenge is to unravel how, when, and in which part of the subduction zone these subunits were juxtaposed. Petrochronology offers powerful tools to decipher pressure–temperature–time (P–T–t) histories of metamorphic rocks that preserve a record of several stages of transformation. A major issue is that the driving forces for re-equilibration at high pressure are not well understood. For example, continental granulite terrains subducted to mantle depths frequently show only partial and localized eclogitization. The Sesia Zone (NW Italy) is exceptional because it comprises several continental subunits in which eclogitic rocks predominate and high-pressure (HP) assemblages almost completely replaced the Permian granulite protoliths. This field-based study comprises both main complexes of the Sesia terrane, covering some of the recently recognized tectonic subunits involved in its assembly; hence our data constrain the HP tectonics that formed the Sesia Zone. We used a petrochronological approach consisting of petrographic and microstructural analysis linked with thermodynamic modelling and U–Th–Pb age dating to reconstruct the P–T–t trajectories of these tectonic subunits. Our study documents when and under what conditions re-equilibration took place. Results constrain the main stages of mineral growth and deformation, associated with fluid influx that occurred in the subduction channel. In the Internal Complex (IC), pulses of fluid percolated at eclogite facies conditions between 77 and 55 Ma with the HP conditions reaching  ∼  2 GPa and 600–670 °C. By contrast, the External Complex (EC) records a lower pressure peak of  ∼  0.8 GPa for 500 °C at  ∼  63 Ma. The juxtaposition of the two complexes occurred during exhumation, probably at  ∼  0.8 GPa and 350 °C; the timing is constrained between 46 and 38 Ma. Mean vertical exhumation velocities are constrained between 0.9 and 5.1 mm year−1 for the IC, up to its juxtaposition with the EC. Exhumation to the surface occurred before 32 Ma, as constrained by the overlying Biella Volcanic Suite, at a mean vertical velocity between 1.6 and 4 mm year−1. These findings constrain the processes responsible for the assembly and exhumation of HP continental subunits, thus adding to our understanding of how continental terranes behave during subduction

Deformation Mechanisms of Blueschist Facies Continental Metasediments May Offer Insights Into Deep Episodic Tremor and Slow Slip Events

Abstract Exhumed fossil subduction zones are archives of the deformation conditions and mechanisms from depths not directly accessible. Microstructural analysis of samples exhumed therefrom offers insights into the micromechanics and deformation processes associated with subduction such as earthquakes, slow earthquakes, and aseismic creep. Subducted and exhumed continental metasediments of the Tuscan Metamorphic Units of the Italian Northern Apennines contain a mylonitic foliation and quartz and carpholite dilational hydroshear veins with crack-and-seal textures, both developed at blueschist facies conditions (350?400°C, ?1 GPa). As shown by overprinting relationships and mineral assemblages, these two structure types formed broadly coeval within the stability field of carpholite. Metaconglomerates and metaquartzarenites deformed mainly by dissolution-precipitation creep and secondary by dislocation creep. Microstructural and electron backscatter diffraction analyses of the veins suggest only limited recrystallization of quartz fibers by subgrain rotation recrystallization, with adjacent metapelite bands acting as decollement horizons, likely by slip on the basal plane of phyllosilicates. We estimated differential stresses of 43?55 MPa and strain rates between 10?13 and 10?14 s?1 from the vein recrystallized quartz fibers. We propose these microstructures and deformation mechanisms to represent a geological evidence of deep episodic tremor and slow slip events in subducted continental metasediments. Pore pressure cyclically reached supralithostatic values triggering tremors causing fracturing of all involved lithotypes. Likely, slow slip was accommodated preferentially by slip on phyllosilicate bands. Aseismic creep occurred mainly by dislocation creep with subgrain rotation recrystallization in vein quartz, slip on the basal plane of phyllosilicates, and dissolution and precipitation creep in the host rock

Functional Balancing of the Hypoxia Regulators RAP2.12 and HRA1 Takes Place in vivo in Arabidopsis thaliana Plants

Plants are known to respond to variations in cellular oxygen availability and distribution by quickly adapting the transcription rate of a number of genes, generally associated to improved energy usage pathways, oxygen homeostasis and protection from harmful products of anaerobic metabolism. In terrestrial plants, such coordinated gene expression program is promoted by a conserved subfamily of ethylene responsive transcription factors called ERF-VII, which act as master activators of hypoxic gene transcription. Their abundance is directly regulated by oxygen through a mechanism of targeted proteolysis present under aerobic conditions, which is triggered by ERF-VII protein oxidation. Beside this, in Arabidopsis thaliana, the activity of the ERF-VII factor RAP2.12 has been shown to be restrained and made transient by the hypoxia-inducible transcription factor HRA1. This feedback mechanism has been proposed to modulate ERF-VII activity in the plant under fluctuating hypoxia, thereby enhancing the flexibility of the response. So far, functional balancing between RAP2.12 and HRA1 has been assessed in isolated leaf protoplasts, resulting in an inverse relationship between HRA1 amount and activation of RAP2.12 target promoters. In the present work, we showed that HRA1 is effective in balancing RAP2.12 activity in whole arabidopsis plants. Examination of a segregating population, generated from RAP2.12 and HRA1 over-expressing plants, led to the first quantitative proof that, over a range of either transgene expression levels, HRA1 counteracts the phenotypic and transcriptional effects of RAP2.12. This report supports the occurrence of fine-tuned regulation of the hypoxic response under physiological growth conditions

Validation of the Italian Versions of the Flourishing Scale and of the Scale of Positive and Negative Experience

Researchers are divided between those who consider well-being as a single global construct and those who maintain the need to keep the hedonic and eudaimonic components of well-being separate. Diener et al. proposed two separate scales for measuring well-being: the Flourishing Scale (FS) for eudaimonic well-being and the Scale of Positive and Negative Experience (SPANE) for hedonic well-being. The aim of this article is to validate the Italian versions of the FS and SPANE, and to provide support for the usefulness of distinct measures of well-being components. In Study 1, we examined an Italian undergraduate student sample ( n = 684), whereas in Study 2 we considered two samples of unemployed ( n = 282) and healthy control individuals ( n = 426). Through multigroup confirmatory factor analysis, we demonstrated that the Italian FS and SPANE obtained strict measurement invariance across administration methods (paper-and-pencil and Internet) and strong measurement invariance across different groups (unemployed individuals seeking work and a healthy control group). In our data, we found a superior fit for a two-factor model over a one-factor model of well-being, which suggests the utility of separate measures of well-being components. Concurrent validity was verified with other well-being, depression, and anxiety measures. Furthermore, we showed that flourishing is more strongly related to the cognitive component of subjective well-being than hedonic affect. In summary, the Italian FS and SPANE are reliable and valid instruments, and may be beneficial in their applications in future Italian studies on well-being

Validation of the Italian Versions of the Flourishing Scale and of the Scale of Positive and Negative Experience

Researchers are divided between those who consider well-being as a single global construct and those who maintain the need to keep the hedonic and eudaimonic components of well-being separate. Diener et al. proposed two separate scales for measuring well-being: the Flourishing Scale (FS) for eudaimonic well-being and the Scale of Positive and Negative Experience (SPANE) for hedonic well-being. The aim of this article is to validate the Italian versions of the FS and SPANE, and to provide support for the usefulness of distinct measures of well-being components. In Study 1, we examined an Italian undergraduate student sample ( n = 684), whereas in Study 2 we considered two samples of unemployed ( n = 282) and healthy control individuals ( n = 426). Through multigroup confirmatory factor analysis, we demonstrated that the Italian FS and SPANE obtained strict measurement invariance across administration methods (paper-and-pencil and Internet) and strong measurement invariance across different groups (unemployed individuals seeking work and a healthy control group). In our data, we found a superior fit for a two-factor model over a one-factor model of well-being, which suggests the utility of separate measures of well-being components. Concurrent validity was verified with other well-being, depression, and anxiety measures. Furthermore, we showed that flourishing is more strongly related to the cognitive component of subjective well-being than hedonic affect. In summary, the Italian FS and SPANE are reliable and valid instruments, and may be beneficial in their applications in future Italian studies on well-being