An insight on the polyphase thermal history of the Ghomarides and Upper Sebtides in the Internal Rif (North Morocco) by means of Raman spectroscopy on organic matter

2021 ◽  
Author(s):  
Andrea Schito ◽  
Achraf Atouabat ◽  
Rocco Calcagni ◽  
Sveva Corrado ◽  
David Muirhead ◽  
...  
Keyword(s):  
Raman Spectroscopy ◽  
Thermal Structure ◽  
Carbonaceous Material ◽  
Stability Field ◽  
Lower Paleozoic ◽  
Suitable Alternative ◽  
History Of ◽  
Maximum Temperatures ◽  
Paleozoic Rocks ◽  
Metamorphic Core

<p>The correct assessment of maximum temperatures experienced by rocks is an essential tool to unravel the evolution of the thermal structure of the crust during the main phases of an orogenesis. Given to broad P-T stability field of classical metamorphic mineralogical indicators, maximum temperatures derived from the analyses of carbonaceous material dispersed in rocks by means of Raman spectroscopy has shown to be a suitable alternative to classical geothermometer. Initially developed for high metamorphic rocks the use of this tools has recently been extended also at lower metamorphic degree and diagenesis. This allowed us to extend the analyses of paleotemperatures experienced by rocks from Ghomarides and Sebtides from the Internal Rif in North Morocco with respect to previous works. Ghomaride and Sebtides in this portion of the Rif-Betic-Tell chain, represent respectively the upper and lower plates of a metamorphic core complex  and are composed, the first, by Paleozoic rocks with a partially preserved Mesozoic-Cenozoic cover and the second by lower Paleozoic to Triassic deep-crustal mica-schists, migmatites and granulites associated with peridotites (Beni Bousera complex).</p><p>Our data suggest that the uppermost Tiszgarine Unit of the Upper Sebtides experienced warmer condition than previously observed. Moreover, we calculate the maximum temperatures experienced by the Ghomarides  during both the Eo and Late Variscan cycles showing that differences in temperature exist among the vary units that compose the complex. Finally, in the southern area our data suggest a less severe alpine heating related to the emplacement of the Beni Bousera peridotite, than previously calculated.</p>

The Potential Applications of Raman Spectroscopy in Unravelling Complex Palaeowildfire Ecosystems

2021 ◽  
Author(s):  
Thomas Theurer ◽  
David Muirhead ◽  
David Jolley ◽  
Dmitri Mauquoy
Keyword(s):  
Raman Spectroscopy ◽  
Carbonaceous Material ◽  
Complex Interactions ◽  
Intensity Changes ◽  
Potential Applications ◽  
Ecosystem Studies ◽  
History Of ◽  
The Impact ◽  
Unique Relationship

<p>Raman spectroscopy represents a novel methodology of characterising plant-fire interactions through geological history, with enormous potential. Applications of Raman spectroscopy to charcoal have shown that this is an effective method of understanding intensity changes across palaeofire regimes. Such analyses have relied on the determination of appropriate Raman parameters, given their relationship with temperature of formation and microstructural changes in reference charcoals. Quantitative assessments of charcoal microstructure have also been successfully applied to the assessment of carbonaceous maturation under alternate thermal regimes, such as pyroclastic volcanism. Palaeowildfire systems in association with volcanism may present a complex history of thermal maturation, given interactions between detrital charcoals and volcanogenic deposition. However, whilst palaeofire and volcanic maturation of carbonaceous material are well understood individually, their interaction has yet to be characterised. Here we present the first analysis of palaeofire charcoals derived from volcanic ignition utilising Raman spectroscopy. Our results indicate that complex interactions between volcanism and palaeofire systems may be better understood by the characterisation of charcoal microstructure, alongside palaeobotanical and ecosystem studies. Understanding the unique relationship between wildfires and volcanism, and the impact that this has on the fossil record, may better assist our understanding of wildfire systems in deep history. Further still, this highlights the potential for better understanding the socioecological impacts of modern and future wildfire systems closely associated with volcanic centres. </p>

A Pyrenean-like model for the Variscan belt in NW Africa : insights from thermometry-based Raman spectroscopy study in the Khenifra Basin

2020 ◽  
Author(s):  
Rémi Leprêtre ◽  
Andrea Schito ◽  
Rachid Ouchaou ◽  
Mohamed El Houicha ◽  
Francis Chopin
Keyword(s):  
Raman Spectroscopy ◽  
Thermal Structure ◽  
Early Carboniferous ◽  
Variscan Orogeny ◽  
Time Interval ◽  
Short Time Interval ◽  
Variscan Belt ◽  
Single Event ◽  
Maximum Temperatures ◽  
Short Time

<p>The Variscan belt in NW Africa is an intracontinental belt, resulting from far-field compressional stress during the closure of the Rheic Ocean between the Late Carboniferous and the Early Permian. In the classical view, this orogen building was preceded by a pre-orogenic stage, namely the Eo-variscan stage, suggested to have occurred at the Late Devonian-Early Carboniferous transition.</p><p>This view is now questioned, for multiple reasons. A first structural reason aims at re-interpreting the so-called Eovariscan features as extensional ones. Indeed, although many structures have been described, their integration into a compressional setting is not straightforward. A second reason is geodynamical, since this peculiar stage is bracketed between two general extensional phases recorded at the scale of NW Africa, and this leaves a very short time interval to proceed to a compressional phase that is geodynamically not integrated until today. At last, a third reason stems from early findings from metamorphic works in the Western Meseta that demonstrated the occurrences of previously unnoticed high geothermal gradients inside numerous Early Carboniferous basins (Chopin et al., 2014 ; Wernert et al., 2016 ; Delchini et al., 2018 ; Lahfid et al., 2019).</p><p>In this work, we sampled the Khenifra Basin within the easternmost part of the Western Meseta, where the Eovariscan deformation was defined (Allary et al., 1972). We carried on structural observations into the basement and sampled both the Ordovician basement and the Middle(?)-Late Visean series of the basin, which is thought the be extensional. Maximum temperatures reached by the 77 sampled rocks were obtained from the analysis of organic matter with the use of the Raman spectroscopy. The examination of this new dataset demonstrates that the Ordovician series acquired temperatures through a single event, consistently with their common record of the Eovariscan deformation. Instead, the unconformable Visean series on top of the basement show a pronounced basinal asymmetry, from low temperatures (< 160°C) to temperatures equivalent to the Ordovician ones (> 250°C). The Visean series do not record the Eovariscan deformation, and their thermal structure was acquired before the Variscan event, regarding their repartition within the basin. The examination of the different hypotheses for the timing of the maximal temperature acquisition (Variscan, compressional Eovariscan and extensional Eovariscan) leads to a single option only compatible with an extensional Eovariscan context.</p><p>The renewal on the knowledge about the early stages of the Variscan orogeny in NW Africa allows us to consider a Pyrenean-like model for the formation of this intraplate belt, resulting from the inversion of hot Early Carboniferous rifted basins.</p>

Low-temperature thermal history of the Gilmore Dome area, Fairbanks Mining District, Alaska

1993 ◽  
Vol 30 (4) ◽  
pp. 764-768 ◽  
Author(s):  
John M. Murphy ◽  
Arne Bakke
Keyword(s):  
Gold Deposit ◽  
Fission Track ◽  
Hydrothermal Fluids ◽  
Mining District ◽  
Cooling Path ◽  
Alteration Assemblage ◽  
Zircon Fission Track ◽  
History Of ◽  
Maximum Temperatures ◽  
Fission Track Ages

Eight apatite and two zircon fission-track ages provide evidence of complex Tertiary thermal overprinting by hydrothermal fluids in the Gilmore Dome area. Five ages on apatite from the Fort Knox gold deposit average 41 Ma, one from the Stepovich prospect is 80 Ma, and two from Pedro Dome average 67 Ma. Elevations of these samples overlap but their ages do not, indicating that each area experienced a different thermal history.Ages of apatite from the Fort Knox gold deposit decrease with elevation from 42 to 36 Ma but have data trends indicative of complex cooling. Two ~51 Ma ages on zircon indicate that maximum temperatures approached or exceeded ~180 °C. An alteration assemblage of chalcedony + zeolite + calcite + clay in the deposit resulted from deposition by a paleo-hydrothermal system. The data suggest that the system followed a complex cooling path from > 180 to < 110 °C between 51 and 36 Ma, and that final cooling to below 60 °C occurred after ~25 Ma.The 80 Ma age from Stepovich prospect either resulted from cooling after intrusion of the underlying pluton (~90 Ma) or records postintrusion thermal overprinting sometime after ~50 Ma. The 67 Ma samples from Pedro Dome may also have experienced partial age reduction during later heating. The differences in the data from the different areas and the presence of a late alteration assemblage at Fort Knox suggest that the fluids responsible for heating were largely confined to the highly fractured and porous Fort Knox pluton.

scholarly journals Pyrite and pyrrhotite in a prograde metamorphic sequence, Hyland River region, SE Yukon: implications for orogenic gold

2021 ◽  
Author(s):  
C D W Padget ◽  
D R M Pattison ◽  
D P Moynihan ◽  
O Beyssac
Keyword(s):  
Raman Spectroscopy ◽  
Phase Equilibrium ◽  
Source Region ◽  
Carbonaceous Material ◽  
Orogenic Gold ◽  
Metamorphic Rocks ◽  
Small Interval ◽  
River Region ◽  
Gradual Release ◽  
Fluid Release

The distribution of pyrite and pyrrhotite is documented within an andalusite-sillimanite type (high-temperature, low-pressure) metasedimentary succession exposed in the Hyland River region of southeastern Yukon, Canada. The following metamorphic zones are recognized: chlorite, biotite, cordierite/staurolite (porphyroblast-in), andalusite, sillimanite, and K-feldspar + sillimanite. Pyrite occurs in the chlorite zone through the biotite zone, while pyrrhotite occurs from the chlorite zone to K-feldspar + sillimanite zone. The pyrite-pyrrhotite transition, therefore, occupies an interval in the chlorite and lower biotite zones that is terminated upgrade by a pyrite-out isograd in the upper part of the biotite zone or lowest grade part of the cordierite/staurolite zone. Pressure and temperature conditions of the rocks were estimated from phase equilibrium modelling and from Raman spectroscopy of carbonaceous material (RSCM) thermometry. Modelling indicates pressures of 3.7-4.1 kbar with temperatures of ~425 °C at the biotite isograd, 560-570 °C for chlorite-out/porphyroblast-in, ~575 °C for andalusite-in, 575-600 °C for the sillimanite isograd, and 645-660 °C at the K-feldspar + sillimanite isograd. RSCM temperatures are greater than or equal to 420 °C in the Chl zone, 500 °C at the Bt isograd, 525-550 °C for porphyroblast-in isograd, ~550 °C at the And isograd, and 580 °C at the Sil isograd. These results suggest the pyrite-pyrrhotite transition occurs from less than or equal to 420°C to ~560 °C. Thermodynamic modelling shows 0.6 wt. % H2O is released during metamorphism over the ~140 °C interval of the pyrite-pyrrhotite transition. The gradual release of fluid in the biotite zone is interpreted to have broadened the pyrite-pyrrhotite transition compared to other studies that predict a small interval of vigorous fluid release associated with volumetric chlorite consumption. Samples from the pyrite-pyrrhotite transition zone contain lower whole rock and pyrite Au values than samples from unmetamorphosed/lower rocks, suggesting that Au was removed from the rock at conditions below the pyrite-pyrrhotite transition (&amp;lt;420 °C). The chlorite zone and higher-grade metamorphic rocks of the Hyland River area do not appear to be a plausible source region for orogenic gold.

scholarly journals Mesoscale heat waves induced by orography

2008 ◽  
Vol 2 (1) ◽  
pp. 139-143 ◽  
Author(s):  
I. Gladich ◽  
I. Gallai ◽  
D. B. Giaiotti ◽  
Gp. Mordacchini ◽  
A. Palazzo ◽  
...  
Keyword(s):  
Internal Wave ◽  
Heat Waves ◽  
Thermal Structure ◽  
Thermal Fluctuation ◽  
Atmospheric Model ◽  
Wave Pattern ◽  
Night Time ◽  
Thermal Anomalies ◽  
Maximum Temperatures ◽  
Friuli Venezia Giulia

Abstract. This work is devoted to the analysis of an unusual and sudden thermal fluctuation that interested portions of Friuli Venezia Giulia (Italy) during the night of 27 July 1983. The whole 1983 summer was extremely warm in Europe and in particular on the Italian peninsula, from the Alps down to Sicily. Nevertheless, the day of 27 July 1983 in Friuli Venezia Giulia deserves special attention because the observed maximum temperatures did not occur during day-time but during night-time (from 23:00 up to 24:00 LT, 21:00–22:00 UTC). Peaks of 34.8°C and values of relative humidity of the order of 28% were registered by the official network of weather stations. This event interested mainly the central-eastern part of the plain of Friuli Venezia Giulia, a few kilometers far from the Slovenian border and relieves. The thermal anomalies lasted up to an hour, then temperatures decreased toward values more usual for the climate of the month. The study of this event is carried out with the aid of the AR-WRF numerical atmospheric model, initialized through the ECMWF analysis. The numerical simulations highlight the important role played by orography, jointly with the peculiar thermal structure of the atmosphere, for the enhancing of the internal wave pattern over that area. According to the sensitivity studies realized, the amplification of the internal wave pattern might represent a possible explanation for that meteorological enigma.

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