Constraining the timing of crustal thickening using garnet geochronology – An argument against subduction-driven orogenesis in the Dom Feliciano Belt, Brazil

<p>Metamorphic minerals in the Brusque Complex of the northern Dom Feliciano Belt, Brazil, provide new insights into the timing and mode of regional convergence, challenging a long-lived subduction-collision model for orogenesis. The key evidence for subduction is an extensive linear belt of granitic rocks (the Granite Belt) that intruded the length of the hinterland of the Dom Feliciano Belt between ~630─580 Ma, and that is inferred to represent arc magmatism above the subducting Adamastor Ocean prior to continental collision. The study area comprises supracrustal units of a foreland fold-and-thrust belt outcropping along the western edge of the symmetric Kaoko─Dom Feliciano orogenic system. The integrated study of primary metamorphic mineral assemblages and associated deformation fabrics support the interpretation of a fold-and-thrust belt environment, with early tectonic movement top-to-NW away from the hinterland. P─T estimates constrained by garnet compositions indicate peak metamorphic conditions of 540─570°C and 5.5─6.5kbar, in line with typical geothermal gradients associated with orogenic metamorphism. The timing of early garnet growth, and by inference the early stages of crustal thickening in the foreland, is constrained by Lu─Hf garnet geochronology at ~660─650 Ma. The data indicate that the onset of metamorphism and deformation in the orogenic foreland occurred ~20–30 m.y. prior to intrusion of extensive granitic magmatism into the orogenic hinterland. The timing of early orogenic thickening in the foreland precludes the interpretation of the Granite Belt as an arc above a large-scale subduction zone in the lead up to orogenesis. Instead, it is interpreted to represent syn-orogenic magmatism typical for hinterland domains in other ancient and recent orogenic systems.</p><p>We appreciate financial support from Diku Norway and CAPES Brazil (project UTF-2018-10004), and from the Czech Science Foundation (project no. 18-24281S). This work was partly supported by the Research Council of Norway through the funding to The Norwegian Research School on Dynamics and Evolution of Earth and Planets, project number 249040/F60.</p>

Central European Variscan Basement in the Outer Carpathians: A Case Study from the Magura Nappe, Outer Western Carpathians, Poland

Exotic crystalline blocks within the Outer Carpathian flysch have the potential to establish the nature of their eroded basement source(s) and thus to reconstruct the paleogeography of the Outer Carpathians. Petrological investigations (including mineral analyses) coupled with zircon and apatite U-Pb dating were performed on an exotic crystalline block within Eocene siliciclastic rocks in the Rača Zone of the Magura Nappe in the Outer Western Carpathians, Poland. This exotic block is a large (c. 1 m diameter) pink porphyritic granitoid block found in the Osielczyk Stream, southeast of Osielec village in the Makowski Beskid mountains. The timing of magmatic crystallization is constrained by a U-Pb zircon age of 315.9 ± 2.6 Ma (MSWD = 0.69), while inherited zircon cores yield Archean (c. 2780 Ma), Cadomian (541.8 ± 6.7 Ma; MSWD = 0.53), Devonian (417 ± 11 Ma; MSWD = 0.57) and Early Variscan (c. 374 Ma) ages. Apatites from the same sample yield a Tera Wasserburg lower intercept U-Pb age of 311.3 ± 7.5 (MSWD = 0.87). The granitoid exhibits geochemical characteristics typical of I-type granites and eNd(316 Ma) = 2.15 (with a TDM model age of 1.18 Ga) and 87Sr/86Sr(316 Ma) = 0.704710. These data suggest a likely source region in the Saxo-Danubian Granite Belt, which possibly formed the basement of the Fore-Magura Ridge.

Distinguishing tectonic versus climatic forcing on landscape evolution: An example from SE Tibetan Plateau

Distinguishing climate from tectonic forcing in shaping the Earth’s surface has been a long-standing issue in the Earth sciences. Great debate exists regarding when and how the SE Tibetan Plateau achieved its current low-relief topography, and both lateral extrusion and lower crust flow have been proposed as the dominant mechanism. Reconstruction of the exhumation history of the SE Tibetan Plateau is key to understanding these formation processes and resolving the significance of different forcing mechanisms. Here we report zircon and apatite (U-Th)/He ages from steep transects across the Lincang granite belt of the SE Tibetan Plateau. Our results reveal a two-stage exhumation history during the Cenozoic with rapid cooling phases in the late Eocene and the middle Miocene. In the late Eocene, the climate was generally dry and there is plenty of evidence for increased extrusion and upper crustal shortening. We suggest tectonic processes are responsible for the first inferred cooling. In contrast, the Asian summer monsoon precipitation increased during the middle Miocene, and we posit the middle Miocene cooling phase records a phase of rapid river incision triggered by the intensified precipitation and associated fault movements. The results are consistent with recent paleo-altimetry work in this region suggesting that the present-day topography of the SE Tibetan Plateau had been largely constructed by the late Eocene. Together, these data suggest that extrusion and/or upper crustal shortening setup the first order topography of the SE Tibetan Plateau, which was then modified by climate-triggered fluvial incision and feedbacks initiated in the middle Miocene.

Early Mesozoic granitoids from SW Vietnam and SE Cambodia – an example of the southeastern extension of the Southeast Asian granite belt

<p>Early Mesozoic magmatism in Indochina and its vicinities in Sundaland (SE Asia) has been usually ascribed to be in connection with one of three approximately coeval tectonic regimes: 1) the Indochina-Sibumasu amalgamation leading to the closure of the Paleotethys during the Late Paleozoic – Early Mesozoic forming the Thai-Malaysia tin-bearing granite belt, 2) the Indochina-South China amalgamation along the northern boundary of Indochina closing another branch of the Paleotethys during Late Paleozoic – Triassic times, and 3) the early stage of an active margin with subduction of the Paleo-Pacific plate during Triassic-Jurassic times.</p><p>Scattered granitic plutons (185–210 Ma) located in southern Cambodia and some islands in southernmost Vietnam are distributed along the N-S Rach Gia-Nam Can fault which is a large-scale fault active during the Early Mesozoic. The studied rocks can be distinguished based on petrological features: weakly foliated biotite-rich granite (Hon Khoai Island, SW Vietnam), biotite-tourmaline-bearing granite (Hon Da Bac Island, SW Vietnam), and coarse-grained biotite granite (Tamao, SE Cambodia). The Honkhoai granites are a range of dark to light coloured granites due to a variation in biotite content and display a foliation. They usually contain amphibole, ilmenite, and monazite. The Hondabac granites comprise dark-colored granodiorites and granites with biotite, tourmaline, ilmenite, apatite, fluorite, epidote, and subordinate titanite. The Tamao granites are mainly composed of biotite aggregates with sporadic muscovite and accessory phases such as ilmenite, apatite, and fluorite.</p><p>Zircon U-Pb ages yield 189 ± 1 to 206 ± 2 Ma for the Honkhoai rocks, 192 ± 1 to 202 ± 1 Ma for the Hondabac rocks, and 189 ± 2 Ma for the Tamao rocks. Apparently, these Late Triassic - Early Jurassic granitoids are chronologically consistent with all three tectonic events. However, geographical and geochemical arguments favor a connection to the Thai-Malaysia tin-bearing granites. Similarities include high silica content and predominantly high-K to calc-alkaline affinities. Trace element composition is characterized by enrichments in Cs, Rb, Th, U, and Pb, and depletion in Ba, Sr, Nb, P, and Ti. All analyzed rock samples show (La/Yb)n values of 4.05–17.27 and negative Eu anomalies (Eu/Eu*=0.15–0.65). The whole-rock and biotite chemistry point to an arc-related tectonic setting for the Hondabac rock, while the Honkhoai and Tamao rocks are ambiguous in the tectonic regime but likely close to syn-collision and within-plate field, respectively. Geobarometry of the Honkhoai rocks using the Al-in-amphibole geobarometer yields crystallization pressure up to 3 kbar.</p><p>We conclude that the studied rocks formed during the closure of the Palaeotethys along the western boundary of the Indochina block, particularly similar to the Thai-Malaysia granite belt. Hence, the Sukhothai-Chantaburi Terrane may be extended southeastward as far as to the Hon Khoai Island (Southernmost Vietnam).</p>

Geology and mineralogy of the Novo-Akhmirovskoe deposit of lithium topaz-zinnwaldite granites (East Kazakhstan)

Research subject. The Novo-Akhmirovskoe lithium-bearing deposit in the East Kazakhstan region, which is represented by an intrusive layer of topaz-zinnwaldite granites, is located within of the Kalba-Narym-Koktogai lithium-tantalum raremetal-granite belt. Being part of the Altai collision system, this belt is considered unique in terms of its length (more than 1000 km). Ores in the Novo-Akhmirovskoe deposit are represented by massive to low porphyry leucocratic granites composed of quartz (30–40%), albite (25–40%), microcline (15–35%), lithium mica varying in composition from zinnwal dite to lepidolite (up to 10%) and topaz (up to 5%). According preliminary estimates, the Novo-Akhmirov deposit is factually a poor lithium deposit with the Li2O content of 0.2–0.4 wt % and the estimated Li2O reserves of 110 thousand tones. Despite the favourable infrastructure and close proximity of this stock to Ust-Kamenogorsk mining and chemical-metallurgical enterprises, its ore-generating potential has not been sufficiently studied.Materials and Methods. In this research, we obtained new data on the geological structure, age, mineral composition and formation conditions of topaz-zinnwaldite granites in the Novo-Akhmirovskoe deposit. In addition, a comparative analysis of these ores with the topaz-biotite granites of the Black Sopka massif (0.6–0.7 wt % Li2O in protolitionite) and spodumene granite porphyries of the Alakha stock (Li2O = 0.9–1.1 wt %) was conducted. Results and Discussion. It is concluded that the development of this unique nonpegmatite lithium-bearing deposit requires deep exploratory drilling, mineralogical and technological research of core samples and reconsideration of economic efficiency parameters.

Friend or foe: Challenges to collaboration success at different lifecycle stages for regional small tourism firms in Australia

Small tourism businesses are essential to Australia’s economy and development, particularly in regional and rural areas, where a majority of these firms are located. It is important to understand the operation of regional small tourism business, to create strategies for their sustained success into the future. This research paper explores collaboration as an operation of small tourism businesses, by understanding the extent to which small tourism firms face challenges in collaborating at different stages of their business life cycle, and how these challenges to collaboration can be overcome. Collaboration is the selected concept examined within this study as it exposes businesses to shared knowledge, resources, marketing, and capabilities, which these businesses alone would not typically possess. To understand this further, reponses about collaborative behavior were gathered from 24 small tourism operators/managers from The Granite Belt region in South-East Queensland, Australia. Tourism operators recognized several hindrances to successful collaboration: (1) a limited understanding of what collaboration is and how it can be enacted, (2) the informal nature of current collaborations, (3) unbalanced efforts from stakeholders within the collaborations, (4) competition between stakeholders, (5) differing opinions of collaborating businesses, and (6) perceived failure or misdirected leadership from local governing bodies. Using these challenges, a framework was developed that makes recommendations to tourism scholars, organizations, operators, and local councils on how to overcome these hindrances by improving communication, formalizing selected collaborative efforts, and reporting on collaborations.

THE GEOCHEMICAL CHARACTERISTIC OF MAJOR ELEMENT OF GRANITOID OF NATUNA, SINGKEP, BANGKA AND SIBOLGA

A study of geochemical characteristic of major elelemnt of granitoid in Western Indonesia Region was carried out at Natuna, Bangka, Singkep and Sibolga. The SiO2 contents of the granites are 71.16 to 73.02 wt%, 71.77 to 75.56wt% and 71.16 to 73.02wt% at Natuna, Bangka, and Singkep respectively, which are classified as acid magma. While in Sibolga the SiO2 content from 60.27 to 71.44wt%, which is classified as intermediate to acid magma. Based on Harker Diagram, the granites from Natuna, Bangka and Singkep as a co-genetic. In other hand the Sibolga Granite show as a scatter pattern. Granites of Natuna, Bangka and Singkep have the alkaline-total (Na2O + K2O) between 6.03 to 8.51 wt% which are classified as granite and alkali granite regime. K2O content ranges from 3.49 to 5.34 wt% and can be classified as calc-alkaline type. The content of alkaline-total of Sibolga granite between 8.12 to 11.81 wt% and classified as a regime of syenite and granite. The range of K2O is about 5.36 to 6.94wt%, and assumed derived from high-K magma to ultra-potassic types. Granites of Natuna, Bangka and Singkep derived from the plutonic rock types and calc-alkaline magma, while Sibolga granite magma derived from K-high to ultra-potassic as a granite of islands arc. Based on the chemical composition of granite in Western Indonesian Region can be divided into two groups, namely Sibolga granite group is representing the Sumatera Island influenced by tectonic arc system of Sumatera Island. Granites of Bangka and Singkep are representing a granite belt in Western Indonesian Region waters which is influenced by tectonic of back arc.Keywords: magma, geochemical characteristic, major element and Western Indonesian Region Kajian karakteristik geokimia dari unsur utama granitoid di Kawasan Barat Indonesia telah dilakukan di daerah Natuna, Bangka, Singkep dan Sibolga. Kandungan SiO2 granit Natuna antara 71,16 - 73,02%, Bangka antara 71,77 - 75,56%, Singkep antara 72,68 - 76,81% termasuk dalam magma asam. Granit Sibolga memiliki kandungan SiO2 antara 60,27 - 71,44% termasuk dalam magma menengah - asam. Berdasarkan Diagram Harker, granit Natuna, Bangka dan Singkep mempunyai asal kejadian yang sama (ko-genetik), sedangkan granit Sibolga membentuk pola pencar. Granit Natuna, Bangka dan Singkep mengandung total alkalin (K2O+Na2O) antara 6,03 - 8,51% termasuk dalam jenis rejim granit dan alkali granit. Berdasarkan kandungan K2O antara 3,49 - 5,34 %berat, bersifat kalk-alkali. Granit Sibolga mengandung total alkali antara 8,12 - 11,81% termasuk dalam rejim syenit dan granit, dan berdasarkan kandungan K2O antara 5,36 - 6,94% berasal dari jenis magma K-tinggi sampai ultra-potassik. Granit Natuna, Bangka dan Singkep berasal dari jenis batuan beku dalam dan magma kalk-alkalin yang berhubungan dengan penunjaman, sedangkan granit Sibolga berasal dari jenis magma K-tinggi - ultra-potassik sebagai granit busur kepulauan. Berdasarkan komposisi unsur kimia utama, granit di Kawasan Barat Indonesia dapat dibagi dalam dua, yaitu granit Sibolga yang mewakili P. Sumatera, dipengaruhi oleh sistem tektonik busur P. Sumatera. Granit Bangka dan Singkep dapat mewakili suatu jalur granit di perairan Kawasan Barat Indonesia yang dipengaruhi oleh tektonik busur belakang. Kata kunci: jenis magma, karakteristik geokimia, unsur utama, dan Kawasan Barat Indonesia