We use coupled zoned geochronology and thermodynamic modeling of garnet to elucidate the nature and scale of metamorphic dehydration during Eocene subduction of a quartzofeldspathic lithology from ...Sifnos, Greece. Two large garnet porphyroblasts were microdrilled to sample concentric growth zones, and these were dated using Sm–Nd geochronology. To put results in a geodynamic context and reveal the causes and consequences of garnet growth, we constructed thermodynamic forward models for a series of prescribed pressure–temperature (P–T) paths. Our data reveal three distinct phases of garnet growth: initial growth at 53.4±2.6 Ma (∼0.8 GPa and ∼300 °C), followed by a period of very limited growth until a second phase, at 47.22±0.36 Ma, and then a major pulse of growth, responsible for the majority of the final garnet volume, at 44.96±0.53 Ma (2.06–2.19 GPa and 490–550 °C). This suggests a >2 order of magnitude acceleration in volumetric growth rate from crystal core to rim, with the final growth pulse occurring rapidly (<0.8 My), during a period of nearly isobaric heating at >75 °C/My. This final pulse was accompanied by net bulk rock dehydration of ∼0.5 wt.%. Rapid heating during early stages of exhumation in the subduction channel, or by sharp thermal gradients related to slab-mantle coupling could be causes for this pulsed metamorphism and dehydration. The garnet data thus record a concentrated pulse of dehydration and heating during the otherwise slow and continuous process of subduction.
•Garnet geochronology and thermodynamic modeling reveal nature of Aegean subduction.•Garnet growth is used as a proxy for metamorphic dehydration.•Pulsed metamorphism and rapid dehydration during subduction.
Fungi have the ability to transform organic materials into a rich and diverse set of useful products and provide distinct opportunities for tackling the urgent challenges before all humans. Fungal ...biotechnology can advance the transition from our petroleum-based economy into a bio-based circular economy and has the ability to sustainably produce resilient sources of food, feed, chemicals, fuels, textiles, and materials for construction, automotive and transportation industries, for furniture and beyond. Fungal biotechnology offers solutions for securing, stabilizing and enhancing the food supply for a growing human population, while simultaneously lowering greenhouse gas emissions. Fungal biotechnology has, thus, the potential to make a significant contribution to climate change mitigation and meeting the United Nation's sustainable development goals through the rational improvement of new and established fungal cell factories. The White Paper presented here is the result of the 2nd Think Tank meeting held by the EUROFUNG consortium in Berlin in October 2019. This paper highlights discussions on current opportunities and research challenges in fungal biotechnology and aims to inform scientists, educators, the general public, industrial stakeholders and policymakers about the current fungal biotech revolution.
Estimated magnitudes of stress and strain rate in crustal rocks suggest that shear heating should contribute significantly to the thermal budget of deforming metamorphic systems. A simple ...one-dimensional thermal model is used to calculate magnitudes of shear heating in ductile shear zones based primarily on quartz flow laws, with consideration of additional models for wet feldspar and biotite. We calculate shear heating for likely ranges of key parameters, so that constraints can be placed on particular natural systems based on inferred stresses, durations of deformation, shear zone widths and metamorphic temperatures. By exploring large parameter spaces, our results should be appropriate for estimating shear heating experienced by a wide range of shear zones. Heating due to ductile deformation is highly dependent on these parameters and ranges from negligible to tens of degrees for most plausible deformation scenarios, and up to 200 °C in extreme cases. Results also predict that wet feldspar rheologies should produce significantly less shear heating than quartz and biotite schist rheologies. The width of a shear heating thermal anomaly can greatly exceed the width of the shear zone itself. For example, in a 0.5 km wide shear zone that experiences a maximum temperature increase of 100 °C in its core after approximately 1 Myr of deformation, a region ~1.0 km wide heats by at least 90 °C. Thermal weakening in our quartz rheology models is very rapid, so differential stresses on the order of 100 MPa should be short lived. These results can be used to better constrain magnitudes of shear heating in natural systems and can be extrapolated to infer the contribution of shear heating to evolving orogenic systems. We apply our results to the strike-slip Davenport and Norumbega shear zones (Australia and USA, respectively), also making tentative predictions for the thrust-sense Himalayan Main Central Thrust.
•Deformation can produce more heat than radiogenic decay in ordinary conditions.•Our calculations can be used to estimate shear heating from field-based observations.•Shear heating can range from negligible to 200 °C depending on deformation conditions.•Thermal softening is rapid, so high stresses in the crust may be transient.
The Pampean flat slab in central Chile and Argentina is characterized by the inland migration and subsequent cessation of arc volcanism since the mid‐Miocene. Slab flattening also affects the ...distribution and number of intermediate‐depth earthquakes and the evolution of the overlying continental thermal structure. In this study, we combine thermal‐mechanical models with petrological models to examine temporal changes in pressure, temperature, and composition during flat‐slab subduction and estimate water carrying capacity, predicted melt distributions and predicted changes in melt composition. Model results indicate that the present‐day flattened Nazca plate carries water to ∼700 km inland from the trench and could cause flux melting if the material above the slab remains fertile. Observed slab seismicity matches areas where hydrated materials have ∼>3 wt% H2O in the oceanic crust and mantle lithosphere. Seismicity increases as slab water carrying capacity decreases (slab dehydration). As P‐T conditions and compositions of the rock trapped above the slab change during slab flattening, flux melting switches from a peridotite‐dominated early phase to a combined mid‐ocean ridge basalt/eclogite and peridotite melting at ∼8 Ma. The results provide broad consistency with known earthquake distributions, seismic velocities, and observed temporal and spatial changes in volcanic patterns above the Pampean flat slab and point toward the role of melt depletion in the decrease and ultimate cessation of arc volcanism in this region.
Key Points
We estimate the water carrying capacities, melt distributions, and composition during the Pampean flat‐slab subduction
The predicted hydrated areas match the observed slab seismicity in the Pampean region
Flux melting above the flat slab is predicted to migrate inland, providing constraints on the causes of the spatiotemporal changes in magmatism
The Central Atlantic Magmatic Province (CAMP) is the large igneous province (LIP) that coincides with the breakup of the supercontinent Pangea. Major and trace element data, Sr‐Nd‐Pb radiogenic ...isotopes, and high‐precision olivine chemistry were collected on primitive CAMP dikes from Virginia (VA). These new samples were used in conjunction with a global CAMP data set to elucidate different mechanisms for supercontinent breakup and LIP formation. On the Eastern North American Margin, CAMP flows are found primarily in rift basins that can be divided into northern or southern groups based on differences in tectonic evolution, rifting history, and supercontinental inheritance. Geochemical signatures of CAMP suggest an upper mantle source modified by subduction processes. We propose that the greater number of accretionary events, or metasomatism by sediment melts as opposed to fluids on the northern versus the southern Laurentian margin during the formation of Pangea led to different subduction‐related signatures in the mantle source of the northern versus southern CAMP lavas. CAMP samples have elevated Ni and low Ca in olivine phenocrysts indicating a significant pyroxenite component in the source, interpreted here as a result of subduction metasomatism. Different collisional styles during the Alleghanian orogeny in the North and South may have led to the diachroneity of the rifting of Pangea. Furthermore, due to a low angle of subduction, the Rheic Plate may have underplated the lithosphere then delaminated, triggering both the breakup of Pangea and the formation of CAMP.
Key Points:
Arc‐like chemistry may be inherited from Paleozoic subduction events
Olivine chemistry suggests a significant pyroxenite component in CAMP's source
Delamination may explain CAMP's timing and progression from North to South
Constraining conditions and mechanisms of the early stages of exhumation from within subduction zones is challenging. Although pressure, temperature, and age can be inferred from the exhumed rock ...record, it is generally difficult to derive each of these parameters from any single rock, thus demanding assumptions that diverse data from multiple samples can be safely combined into a single pressure‐temperature‐time (P‐T‐t) path that might then be used to infer tectonic context and mechanisms of exhumation. Here, we present new thermobarometric and geochronologic information preserved in a single sample from Syros, Greece, to deduce the conditions and rates of the earliest phase of exhumation as a part of the well‐preserved high‐pressure metamorphic rocks of the Cycladic Blueschist Unit (CBU). The sample studied here is a garnet‐bearing, quartz‐mica schist that records two distinct metamorphic events. Results from thermodynamic models and quartz‐in‐garnet elastic geobarometry show that metamorphic garnet cores formed as P‐T conditions evolved from ∼485°C and 2.2 GPa to 530°C and 2.0 GPa, and that garnet rims formed as conditions evolved from ∼560°C and 2.1 GPa to ∼550°C and 1.6 GPa. Sm‐Nd geochronology on garnet cores and rims yields ages of 45.3 ± 1.0 and 40.5 ± 1.9 Ma, respectively, thus indicating a 4.8 ± 2.1 Myr growth span. Given the decompression path calculated based on garnet core and rim P‐T estimates, we conclude that the distinct phases of garnet growth preserve evidence of the initial exhumation of portions of the CBU.
Plain Language Summary
Constraining the evolution of rocks formed at great depths (>60 km) and their subsequent returned to Earth's surface is a challenging endeavor, because information regarding the pressure, temperature, and timing of formation is typically elucidated through the study of multiple samples and thus through the comparison of different datasets. Here, we present pressure, temperature, and age data that were derived by analyzing garnet crystals within a single sample from a well‐known paleo‐subduction zone locate in Syros, Greece. Our results show that the sample records two metamorphic events that occurred as a result of initial ascent to the surface from depths of ∼66 to 48 km.
Key Points
Metamorphic garnets record two stages of growth during HP/LT metamorphism and exhumation of the Cycladic Blueschist Unit (CBU) on Syros, Greece
Garnet growth spanned 4.8 ± 2.1 Myr including decompression from 2.1 to 1.6 GPa
Garnets in this sample record a part of the CBU that was exhumed as a series of tectonic slices on Syros
Biofoundries provide an integrated infrastructure to enable the rapid design, construction, and testing of genetically reprogrammed organisms for biotechnology applications and research. Many ...biofoundries are being built and a Global Biofoundry Alliance has recently been established to coordinate activities worldwide.
The filamentous fungus Aspergillus nidulans has been a tractable model organism for cell biology and genetics for over 60 years. It is among a large number of Aspergilli whose genomes have been ...sequenced since 2005, including medically and industrially important species. In order to advance our knowledge of its biology and increase its utility as a genetic model by improving gene annotation we sequenced the transcriptome of A. nidulans with a focus on 5' end analysis.
Strand-specific whole transcriptome sequencing showed that 80-95% of annotated genes appear to be expressed across the conditions tested. We estimate that the total gene number should be increased by approximately 1000, to 11,800. With respect to splicing 8.3% of genes had multiple alternative transcripts, but alternative splicing by exon-skipping was very rare. 75% of annotated genes showed some level of antisense transcription and for one gene, meaB, we demonstrated the antisense transcript has a regulatory role. Specific sequencing of the 5' ends of transcripts was used for genome wide mapping of transcription start sites, allowing us to interrogate over 7000 promoters and 5' untranslated regions.
Our data has revealed the complexity of the A. nidulans transcriptome and contributed to improved genome annotation. The data can be viewed on the AspGD genome browser.
We present data on the pressure and temperature (P–T) conditions experienced by metamorphic rocks of the Meguma Terrane, Nova Scotia, Canada, also utilizing three‐dimensional microstructural data on ...one sample to better constrain the mechanisms that controlled garnet crystallization. Inverse and forward thermodynamic modelling place peak P–T conditions in the southwestern Meguma Terrane at ~650°C and 4.5 kbar. Interpretation of these results with petrographic observations and previous P–T constraints across the terrane suggests that amphibolite facies metamorphism occurred during the Devonian Neoacadian orogeny (406–388 Ma). Integration of quantitative 3D textural data with an estimated metamorphic heating rate of <5°C/Myr is consistent with amphibolite facies metamorphism resulting from tectonic loading during the Neoacadian orogeny, though the exact nature of the orogeny is still not well understood. Further, the intrusion of granitic plutons into the Meguma metasediments at 373 Ma likely locally drove metamorphic recrystallization (polymetamorphism). The 3D size, shape, and location of garnet crystals in one sample reveal that the rate‐limiting step for garnet crystallization was likely the diffusion of aluminium through the intergranular matrix at length scales less than the mean nearest neighbour distance between garnet crystals. Nucleation was aided by epitaxial overgrowth onto a muscovite substrate, though it appears there may have been a decoupling between minerals providing a substrate and those providing nutrients during garnet growth.
Serpentinization is an important geochemical process that affects the chemistry and petrophysical properties of the oceanic lithosphere and supports life through abiogenic formation of hydrogen. ...Here, we document through detailed mineralogical evidence and equilibrium thermodynamic models the importance of water (H
2
O) and silica (SiO
2
) activities on mineral assemblages produced during progressive serpentinization of a harzburgite. We describe a harzburgite from the Santa Elena Ophiolite in Costa Rica that is ~30 % serpentinized. Serpentine + brucite ± magnetite veins occur in olivine, Al-rich serpentine + talc veins occur in orthopyroxene, and Al-rich serpentine ± talc ± brucite veins occur at the boundary of orthopyroxene and olivine. Bulk vein chemistry and element distribution maps demonstrate distinct chemical zonations within veins and chemical gradients between orthopyroxene- and olivine-dominated areas. Specifically, the sample records (1) varying brucite composition depending on whether or not it is associated with magnetite, (2) formation of magnetite from Fe-rich brucite (±Fe-rich serpentine) during olivine hydration, where magnetite coexists with brucite Mg#96 and serpentine Mg#99, (3) chemical gradients in Si, Al, Cr, and Ca within and between orthopyroxene- and olivine-hosted veins, and 4) local (different) equilibrium assemblages within different zones of veins. The studied sample preserves rarely observed textures documenting continuous replacement of olivine, rather than individual vein generations and overprinting that is typically observed in more intensely serpentinized peridotites. Furthermore, the presence of a discrete sequence of vein textures and mineralogy allows direct comparison between mineral textures and equilibrium thermodynamic models and permits new insights into mineral reactions during serpentinization.
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