Thermal aureole provoked by the intrusion of the Totoró pluton over micaschists of the Seridó Group, Ediacaran of the Borborema Province, NE Brazil

The Borborema Province, NE Brazil, is marked by significant Ediacaran plutonism. In this geological context, the Totoró pluton, Rio Grande do Norte, produces an extensive metamorphic aureole along the contact with micaschist of the Seridó Group. This contribution reports data from field work, petrography, mineral chemistry and rock petrophysics aiming to characterize this aureole. The Totoró pluton is an NNE-SSW elongate mafic to felsic body including diorite, gabbro-norite, granodiorite/tonalite (the main facies), biotite-bearing equigranular to porphyritic granite, and fine- to medium-grained granite. Geothermometric calculations based on mineral chemistry permitted estimating pressures of 1.6 – 2.7 kbar and temperature of 800 – 900ºC for the emplacement of the pluton. The thermal aureole can reach up to 2 km away from the contact and consists of: (i) migmatized schist immediately adjacent to the contact, often with leucosomes subconcordant with the S2 tectonic fabric of the host rocks; (ii) an intermediate zone with sillimanite (± cordierite + garnet + biotite); (iii) a zone with cordierite (± staurolite ± andalusite + garnet + biotite); (iv) an external zone of fine-grained micaschist. Petrophysical modelings reveal that the temperature next to the pluton reached 688 – 756ºC. Minerals of the metamorphic aureole define a low angle S2 schistosity (D2/M2 event in amphibolite to pyroxene hornfels facies), which are overprinted by open to tight folds, that evolve via strong transposition to generate mylonites in NE-SW to N-S directed shear zones, which represent the last ductile event (D3/M3). The results indicate that some regional batoliths (e.g., Acari, Totoró, Umarizal) were emplaced in a relatively shallow crust that provided locally very high geothermal gradient.A Província Borborema, NE do Brasil, é marcada por volumoso plutonismo ediacarano. Neste contexto geológico, o plutão Totoró, um corpo alongado NNE-SSW, compõe-se de uma sequência de tipos básicos a intermediários, incluindo dioritos e gabro-noríticos (mais precoces), granodioritos / tonalitos (predominante), biotita granitos equigranulares, biotita granitos porfiríticos e hololeucogranitos finos a médios. Dados químicos permitem estimar pressões de 1,6-2,7 kbar e temperaturas de 800-900oC para sua colocação. O calor aportado provocou uma auréola termal que se estende até 2 km do contato, constituída por: (i) xisto migmatizado imediatamente adjacente ao contato, com frequentes soleiras de leucossoma subconcordantes com a trama tectônica S2 da encaixante; (ii) uma zona intermediária com sillimanita (± cordierita + granada + biotita); (iii) uma zona com aparecimento de cordierita (± estaurolita ± andaluzita + granada + biotita); e (iv) uma zona externa com micaxisto de fina granulação. Modelamento baseado em petrofísica de rocha mostra que a temperatura na borda do plutão atingiu 688-756°C, diminuindo para 500oC a 1800 m do contato, com tempo de resfriamento estimado de 365.000 anos. Os minerais produzidos no efeito termal delineiam a xistosidade S2, de baixo ângulo (evento D2/M2 na fácies anfibolito ou piroxênio hornfels), os quais são afetados por dobras abertas a fechadas, normais, progredindo para forte transposição e milonitos em zona de cisalhamento NE-SW a N-S, representando o último evento dúctil, retrometamórfico (fácies xisto verde), na região (D3/M3). Os resultados obtidos revelam que pelo menos parte dos batólitos na região em tela se posicionou em níveis crustais relativamente rasos sob condições de alto gradiente geotérmico, porém ainda registrando a fase de arrefecimento da tectônica dúctil regional

Petrogenesis of the Cenozoic magmatism in north-western Iran

A petrological study has been conducted on three volcanic districts (Tafresh, Nowbaran and Bijar-Qorveh) of NW Iran with the purpose to give a contribution to the scientific community about the tectono-magmatic framework of the Arabia-Eurasia collision zone. These volcanoes belong to the so-called Urumieh-Dokthar Magmatic Arc (UDMA) running from NW to SE along the western margin of Iran, whose volcanism is related to the NE-ward Neotethys Ocean subduction beneath the Iranian plate since Early Cretaceous time, evolved into Arabia-Iran continental collision during early Cenozoic. Tafresh investigated rocks mainly range from basaltic andesites to rhyolites and are probably linked to closed-system magma evolutionary processes. Such processes involved fractionation of i) mainly ferromagnesian minerals and plagioclase, followed by ii) removal of plagioclase and lesser amphibole (with minor clinopyroxene) and finally iii) lesser alkali feldspar and minor amphibole in the most evolved terms. LILE-enriched and HFSE-depleted geochemical signature (likely originated from a hydrous primitive melt equilibrated with a spinel-bearing peridotite source) inferred the typical subduction-related trend emplaced in a subduction-related setting. Strongly evolved rocks are supposed to be derived from crustal anatexis of a mixed meta-sedimentary source. One sample shows distinctive adakitic signature (high La/Yb and Sr/Y ratios, low Yb and HFSE contents) which are interpreted as the product of the melting of a meta-mafic source rock (i.e., subducted oceanic slabs) with residual garnet and amphibole. Differently, Nowbaran Quaternary melanephelinites result by far the most peculiar igneous rocks of the entire Bitlis-Zagros Orogen. The absence of feldspars and melilite is coupled with extremely low SiO2 content and very high CaO and Al2O3 abundances, leading to ultracalcic compositions. Moreover, these rocks show high Mg# and very high Ni and Cr values, which likely suggest a primitive character of these melts. Isotopic ratios and primitive-mantle normalized pattern indicate hybrid sources, as their trend exhibits subduction-related imprinting mixed with HiMU-OIB features. Such uncommon compositions are thought to be unlikely derived from a classic four-phase (i.e. C-H-free) peridotitic mantle or from digestion of carbonatic compositions. More likely, they are generated from carbonated apatite-hornblendite-rich metasomes which are considered as the products of interaction between peridotitic matrix and partial melts derived from arc cumulates (formed by crystallization of hydrous and CO2-bearing magmas generated during previous subduction-related arc). On the other hand, two main volcanic cycles have been recognized in Bijar-Qorveh area. Upper Miocene (~9.2-8.3 Ma) compositions mostly range from trachy-andesites to trachytes (with minor rhyolitic terms) whereas Pleistocene (~1.3-0.5 Ma) samples are mostly represented by trachybasalts and tephrites, with lesser alkali basalts. Major and trace elements of Miocene rocks (i.e., Dehgolan and Qorveh) likely suggest fractional crystallization of ferromagnesian minerals then followed by removal of plagioclase and amphibole. These rocks exhibit high-K calcalkaline affinity, as also shown by primitive mantle-normalized patterns characterized by strong LILE and LREE enrichments, typical of subduction-related magmas. Only three Dehgolan samples show by far higher K2O-TiO2-P2O5 and Rb contents, which are thought to be related to a Ti-phlogopite-rich source rock. Quaternary samples (i.e., Qezelke Kand, Bijar and Takab) consist of alkaline series showing mainly sodic to strictly potassic (i.e. Takab) affinity. They show high Mg#, Ni and Cr content which probably is indicative that primary magma was not affected by extensive fractionation. Moreover, isotopic ratios and incompatible multielemental patterns show mixed features of both intraplate-like and subduction-related end members. Takab rocks always cluster distinctly, showing higher K2O and Rb abundances which could be linked to a phlogopite-rich mantle source. Noteworthy, Qezelke Kand outcrops are characterized by the association of basic products with four high silica rocks which have been referred to as adakites, likely deriving from the melting of subducted basalts in eclogite facies. Bijar-Qorveh Miocene high-K volcanic products represent the final magmatic phase of the calcalkaline volcanism occurring in Central Iran during Tertiary period, whereas Quaternary basic magmatism is to be considered as the expression of regional tensional tectonics or related to variations in the source mineralogy during melting processes

Geomorphometry 2020. Conference Proceedings

Geomorphometry is the science of quantitative land surface analysis. It gathers various mathematical, statistical and image processing techniques to quantify morphological, hydrological, ecological and other aspects of a land surface. Common synonyms for geomorphometry are geomorphological analysis, terrain morphometry or terrain analysis and land surface analysis. The typical input to geomorphometric analysis is a square-grid representation of the land surface: a digital elevation (or land surface) model. The first Geomorphometry conference dates back to 2009 and it took place in Zürich, Switzerland. Subsequent events were in Redlands (California), Nánjīng (China), Poznan (Poland) and Boulder (Colorado), at about two years intervals. The International Society for Geomorphometry (ISG) and the Organizing Committee scheduled the sixth Geomorphometry conference in Perugia, Italy, June 2020. Worldwide safety measures dictated the event could not be held in presence, and we excluded the possibility to hold the conference remotely. Thus, we postponed the event by one year - it will be organized in June 2021, in Perugia, hosted by the Research Institute for Geo-Hydrological Protection of the Italian National Research Council (CNR IRPI) and the Department of Physics and Geology of the University of Perugia. One of the reasons why we postponed the conference, instead of canceling, was the encouraging number of submitted abstracts. Abstracts are actually short papers consisting of four pages, including figures and references, and they were peer-reviewed by the Scientific Committee of the conference. This book is a collection of the contributions revised by the authors after peer review. We grouped them in seven classes, as follows: • Data and methods (13 abstracts) • Geoheritage (6 abstracts) • Glacial processes (4 abstracts) • LIDAR and high resolution data (8 abstracts) • Morphotectonics (8 abstracts) • Natural hazards (12 abstracts) • Soil erosion and fluvial processes (16 abstracts) The 67 abstracts represent 80% of the initial contributions. The remaining ones were either not accepted after peer review or withdrawn by their Authors. Most of the contributions contain original material, and an extended version of a subset of them will be included in a special issue of a regular journal publication