scholarly journals A tectonic remnant of the mesoarchean oceanic lithosphere in the Belomorian Province, Fennoscandian Shield

2019 ◽  
pp. 46-71
Author(s):  
A. I. Slabunov ◽  
A. A. Shchipansky ◽  
V. S. Stepanov ◽  
I. I. Babarina
Keyword(s):  
Genetic Relationships ◽  
Mantle Peridotite ◽  
Oceanic Lithosphere ◽  
Fennoscandian Shield ◽  
Geological Mapping ◽  
Geochemical Data ◽  
Initial Stage ◽  
Geochemical Study ◽  
Ultramafic Complex ◽  
Belomorian Belt

The results of the detailed geological mapping, coupled with the isotope-geochemical study of a metamorphosed mafic-ultramafic complex known as the Central Belomorian Belt located in the Belomorian province of the Fennoscandian Shield, are reported. The protholith of the complex is ~ 2.9—3.1 Ga old. It has been subjected to two 2.87 and 1.87 Ga structural-metamorphic reworking. This complex is one of the oldest in the Belomorian Province. We present several lines of evidence showing that these lithologies constitute a tectonic remnant of the Mesoarchean oceanic lithosphere, rather than any other mafic-ulramafic complex from the other geodynamic settings. The Central-Belomorian high grade mafic-ultramafics reveal a clear geochemical coherency, which implies their genetic relationships. Their mafic protholiths stem from the partial melting of a mantle peridotite protholith. The petrologic modelling has shown that primary melts were formed in the garnet lherzolite field at a pressure of 3.5–3.8 GPa at ambient mantle potential temperatures of 1520–1550 °С which led to an emergence of ~ 25–30 thick oceanic crust. The available geochemical data suggest that the complex was formed at the initial stage of subduction. It marks the start of early continental crust-forming processes in the Belomorian Province.

Evolution of mantle peridotite rocks - structures generated in a transition from the ductile-brittle regime in the Equatorial Atlantic

2020 ◽  
Author(s):  
Leonardo Mairink Barão ◽  
Barbara Trzaskos ◽  
Rodolfo José Angulo ◽  
Maria Cristina de Souza
Keyword(s):  
Mantle Peridotite ◽  
Oceanic Lithosphere ◽  
Tectonic Stress ◽  
Fault Analysis ◽  
Geological Mapping ◽  
Deformation Mechanisms ◽  
Brittle Deformation ◽  
Equatorial Atlantic ◽  
Existing Structures ◽  
Fluid Interaction

<p>The exhumation of peridotite rocks in oceanic transform zones passes by the rheological transition between the ductile-brittle deformations until the complete emplacement in the oceanic lithosphere. São Pedro and São Paulo Archipelago, is located at 1° N latitude, 1000km from the Brazilian mainlad. Ten isles compose the archipelago with a total exposed area of 17 km². Those isles record the deformational products of ductile, brittle and the rocks/fluid interaction generating specific structures in each domain. The deformational stages are related to the transpressional and transtensional geodynamics of São Paulo Transform Fault (SPTF). The ductile-brittle fabrics were observed in a multiscale context, using drone images, geological mapping, fault analysis, and microstructural studies. Using all these tools to define the tectonic tensions and structures associated with a transition between ductile to the brittle deformational settings. Firstly during the transpressional context, the exhumation occurs associated with the ductile domain causing intense mylonitization in temperatures between 700° - 800°C. Leading to olivine and orthopyroxene recrystallization forming such as well-marked mylonitic foliation and rotated porphyroclast with left-lateral kinematic. The interaction with fluids initially originated from the mantle, generates fragmented crystals of amphibole and oxide-rich levels, marking the transition to semi-brittle deformation. The continuous and rapid uplift led to the superposition of deformation mechanisms, with reactivation of pre-existing structures and predominance of brittle deformation mechanisms. The tectonics associated with an NW-SE shortening in the transpressional tectonics context led to greater availability of hydrothermal fluids. Consequently, the formation of four serpentinization episodes, which are associated with semi-brittle to brittle transition, with temperatures between 300 - 400° C. The presence of serpentine marks the transition between semi-brittle to brittle regimes, whose dextral kinematics is marked by the domino faults, microfaults and gash veins. The kinematics at the brittle moment is compatible with the current movement of the SPTF. Finally, the complete exhumation and establishment of brittle mechanisms led to the carbonatation phase near the surface, with temperatures ranging from 150 - 300°C. The active NW-SE tectonic stress generated an E-W strike-slip faults that filled by carbonates, symbolizing the final exhumation stage.</p>

The geochemical characteristics of the Jurassic plume magmatism within Ahlmannryggen massif (Queen Maud Land, East Antarctica)

2019 ◽  
Vol 486 (1) ◽  
pp. 98-102
Author(s):  
N. M. Sushchevskaya ◽  
B. V. Belyatsky ◽  
G. L. Leitchenkov ◽  
V. G. Batanova ◽  
A. V. Sobolev
Keyword(s):  
Mantle Peridotite ◽  
Oceanic Lithosphere ◽  
East Antarctica ◽  
Geochemical Characteristics ◽  
Mantle Melting ◽  
Plume Magmatism

Mesozoic dikes associated with the Karoo plume were studied within the East Antarctica where at Queen Maud Land on the Almannryggen massif high-Ti magnesian Fe-basalts were found. It is assumed that such basalts originate by means of the pyroxenite-containing mantle melting. The isotopic characteristics of the studied dolerites reflect the composition of the pyroxenite source - the ancient oceanic lithosphere (ЕМI), submerged at the mantle depths of 150-170 km in the paleosubduction zone of the Gondwanian continent and transformed 180 m.y. ago into the pyroxenite melt when interacting with the plume mantle peridotite.

Magnetite Redistribution during Multi-stage Serpentinization: Evidence from the Taishir massif, the Khantaishir Ophiolite, Western Mongolia

2021 ◽  
Author(s):  
Otgonbayar Dandar ◽  
Atsushi Okamoto ◽  
Masaoki Uno ◽  
Noriyoshi Tsuchiya
Keyword(s):  
Hydrogen Generation ◽  
Mantle Peridotite ◽  
Oceanic Lithosphere ◽  
Ultramafic Rocks ◽  
Western Mongolia ◽  
Fluid Infiltration ◽  
Multi Stage ◽  
Fe Content ◽  
Coarse Grains ◽  
Modal Abundance

<p>Magnetite commonly forms during serpentinization of mantle peridotite, involving the hydrogen generation within the oceanic lithosphere. Although magnetite is concentrated in veins, the mobility of iron during serpentinization is still poorly understood. The completely serpentinized ultramafic rocks (originally dunite) within the Taishir massif in the Khantaishir ophiolite, western Mongolia, include abundant magnetite + antigorite veins, which manifest novel distribution of magnetite. The serpentinite records the multi-stage serpentinization, in order of (1) Al-rich antigorite + lizardite mixture with hourglass texture (Al<sub>2</sub>O<sub>3</sub> = 0.46-0.69 wt%; Atg+Lz), (2) Al-poor antigorite composed of thick veins and their branches (Atg), and (3) chrysotile that cut all previous textures. The Mg# (= Mg/ (Mg + Fe<sub>total</sub>)) of Atg+Lz (0.94-0.96) is lower than Atg (0.99) and chrysotile (0.98). In the region of Atg+Lz, magnetite occurs as the arrays of fine grains (<50 μm) around the hourglass texture. In the Atg veins replacing Atg+Lz, magnetite disappears and re-precipitated as coarse grains (100-250 μm) in the center of some veins. As the extent of replacement of Atg+Lz by Atg veins increases, both modal abundance of magnetite and the bulk Fe content decrease. These characteristics indicate that hydrogen generation mainly occurred at the stage of Atg+Lz formation, and magnetite distribution was largely modified via dissolution and precipitation in response to later fluid infiltration associated with the Atg veins. This also indicates the high iron mobility within the serpentinized peridotites even after the primary stage of magnetite formation.</p>

scholarly journals Geological Map of a Treasure Chest of Geodiversity: The Lavagnina Lakes Area (Alessandria, Italy)

Geosciences ◽  
2019 ◽  
Vol 9 (5) ◽  
pp. 229 ◽  
Author(s):  
Marco Scarsi ◽  
Laura Crispini ◽  
Cristina Malatesta ◽  
Chiara Spagnolo ◽  
Giovanni Capponi
Keyword(s):  
Gold Mineralization ◽  
Scientific Research ◽  
Oceanic Lithosphere ◽  
Western Alps ◽  
Geological Mapping ◽  
Natural Park ◽  
Research Activities ◽  
Geological Map ◽  
Nw Italy ◽  
Treasure Chest

The aim of this work is to present a new georeferenced geological map of an area in the Ligurian Western Alps (Lavagnina Lakes area) that includes both a unique geodiversity and great biodiversity, a peculiar geological heritage, and cultural features. The study area is located in the northern part of the Capanne di Marcarolo Regional Natural Park, occurring in the southern Piedmont Region (Alessandria, NW Italy) and close to the suburbs of Genoa. This area has been studied by multi-disciplinary scientific researchers who, so far, have focused their attention on the occurrence of alkaline springs and investigation of different endemic floral species. Moreover, in the past, the Lavagnina Lakes area has been exploited due to the presence of gold mineralization, and several mining records are still visible. We performed detailed geological mapping at a 1:10,000 scale, and collected data that were later integrated into a digital GIS map. The database associated with the map contains information that may be interesting from different points of view: (i) scientific research; (ii) outreach and dissemination activities; and (iii) geotourism (i.e., trail networks and panoramic viewpoints). The area represents a section of the Jurassic Piedmont Ligurian oceanic lithosphere, showing several geologic processes on different scales, such as the serpentinization process and intense and widespread carbonation of ultramafic rocks; the area is, moreover, characterized by fault systems showing paleoseismic structures. Beyond scientific research activities (i.e., geology, geoarchaeology, and mining archaeology), the area can also be promoted for geotourism, outreach and dissemination activities, field trips for schools, and gold panning activities. Hence, our new digital map and our 3D model could be a useful tool to illustrate the main characteristics of the area, leading a non-expert public to explore different geological features in a relatively “small” area. In this way, our map could help to improve geotourism, be used as a tool for educational activities, and, finally, could also help the Capanne di Marcarolo Regional Natural Park to be recognized as a geopark.

Geochemistry, zircon geochronology, and isotopic systematics of the Zhanbuzhale granites in the East Kunlun, Qinghai Province, northwestern China: implications for the tectonic setting

2020 ◽  
Vol 57 (2) ◽  
pp. 275-291
Author(s):  
Hao-Ran Li ◽  
Ye Qian ◽  
Feng-Yue Sun ◽  
Liang Li
Keyword(s):  
Tectonic Setting ◽  
Alkali Feldspar ◽  
Northwestern China ◽  
Geochemical Data ◽  
Calc Alkaline ◽  
Qinghai Province ◽  
East Kunlun ◽  
Initial Stage ◽  
High K ◽  
Tethys Ocean

The Zhanbuzhale region, in the Eastern Kunlun Orogen of northwestern China, is characterized by large volumes of Phanerozoic granitoid rocks and is an ideal region for investigating the tectonic evolution of the Paleo-Tethys system. However, the exact timing of the final closure of the Paleo-Tethys Ocean and initial continental collision remains controversial because of a lack of precise geochronological and detailed geochemical data. In this paper, we report new zircon U–Pb ages and mineralogical, petrographic, and geochemical data for samples of Middle Triassic granodiorite and alkali feldspar granite from the Zhanbuzhale region. The zircon U–Pb ages indicate that the granodiorite and alkali feldspar granite formed at 239 and 236 Ma, respectively. The granodiorites are high-K calc-alkaline, metaluminous, high Sr content, high Sr/Y ratios, low Y content, and show adakite-like affinities. The alkali feldspar granites display high SiO2, extremely low MgO, and low Zr+Nb+Ce+Y contents as well as low Fe2O3t/MgO ratios, showing metaluminous to peraluminous and high-K calc-alkaline features. Geochemical and petrological characteristics of the alkali feldspar granites suggest that they are highly fractionated I-type granites. The granodiorites and alkali feldspar granites have zircon εHf(t) values ranging from –2.26 to –0.18, and from –2.17 to +2.18, respectively. Together with regional geological data, we propose that the Triassic (approximately 239–236 Ma) granitoids were generated during the later stages of northward subduction of the Paleo-Tethys oceanic plate, and that the initial stage of collision between the East Kunlun and the Bayan Har–Songpan Ganzi terrane occurred at approximately 236–227 Ma.

A Tectonic Remnant of the Mesoarchean Oceanic Lithosphere in the Belomorian Province, Fennoscandian Shield

Geotectonics ◽  
2019 ◽  
Vol 53 (2) ◽  
pp. 205-230 ◽  
Author(s):  
A. I. Slabunov ◽  
A. A. Shchipansky ◽  
V. S. Stepanov ◽  
I. I. Babarina
Keyword(s):  
Oceanic Lithosphere ◽  
Fennoscandian Shield

Geochemistry and petrology of 2.40–2.45Ga magmatic rocks in the north-western Belomorian Belt, Fennoscandian Shield, Russia

1998 ◽  
Vol 92 (3) ◽  
pp. 223-250 ◽  
Author(s):  
S.B Lobach-Zhuchenko ◽  
N.A Arestova ◽  
V.P Chekulaev ◽  
L.K Levsky ◽  
E.S Bogomolov ◽  
...  
Keyword(s):  
Fennoscandian Shield ◽  
The North ◽  
Magmatic Rocks ◽  
North Western ◽  
Belomorian Belt

scholarly journals Reconnaissance geochemical and geophysical exploration for gold at Iri gold field, north central Nigeria

2020 ◽  
Vol 18 (2) ◽  
pp. 19-31
Author(s):  
Ahmed Sidi Aliyu ◽  
Nuhu Musa Waziri ◽  
Hadiza Liman Mohammad ◽  
Mohammed Abubakar Mohammed ◽  
Apeh Aromeh Gideon
Keyword(s):  
Gold Mineralization ◽  
Structural Features ◽  
Parent Material ◽  
Geological Mapping ◽  
Magnetic Data ◽  
Geochemical Data ◽  
Aeromagnetic Data ◽  
Geophysical Exploration ◽  
Rock Types ◽  
Soils And Sediments

Reconnaissance geochemical and geophysical exploration for gold was carried out at IRI Gold field. Geological mapping was conducted and rocks, soils and sediments samples were collected. The outcome revealed rocks of the basement complex of Nigeria made up of mainly, Migmatite Gneiss, Older Granite and the Schist. The major lithology in the area is silicified sheared rocks and large quartz vein. Isolated occurrence of undifferentiated schist was found as parent material on which quartzite intruded possibly during a major geological activity. Shattering of the rocks left boulders and rubbles of quartzite all around two major ridges within the study area. The rocks have shown weak geochemical anomaly except in two locations were positive anomalies were observed and identified as target for further exploration. Gold veins are prominent in the area suggesting potential gold mineralization. Interpretation of the aeromagnetic data give the orientations of the structural features, the major structural trend in the area is NE-SW. The lineaments extracted from the magnetic data range in length from 46.43m to about 1251.66m. Most of the lineaments extracted from the area are subsurface within the quartz-mica and migmatites while some of them have surface expressions even though not clearly defined. These magnetic lineaments could be the contacts between two rock types of contrasting magnetic   susceptibility   or   edges   of   structures   that   could   be faults or intrusive bodies. Interpreted satellite data show several subsurface structures which could be hosts to gold mineralization in the area. Results of the geochemical analysis of rocks, soils and sediments were super imposed on the interpreted aeromagnetic data and similar geochemical and geophysical signatures were established.   Index Terms: Gold mineralization, aeromagnetic data, geochemical data, schist belt, Nigeria

scholarly journals Archean Rocks of the Diorite Window Block in the Southern Framing of the Monchegorsk (2.5 Ga) Layered Mafic-Ultramafic Complex (Kola Peninsula, Russia)

Minerals ◽  
2020 ◽  
Vol 10 (10) ◽  
pp. 848
Author(s):  
Pavel Pripachkin ◽  
Tatiana Rundkvist ◽  
Nikolay Groshev ◽  
Aiya Bazai ◽  
Pavel Serov
Keyword(s):  
Kola Peninsula ◽  
Geochemical Data ◽  
Pb Isotope ◽  
Garnet Porphyroblasts ◽  
Isotope Data ◽  
Ultramafic Complex ◽  
Archean Basement ◽  
Monchegorsk Complex

The intermediate rocks classified as diorite-gneisses occur within the southern part of the Monchegorsk (2.5 Ga) layered mafic-ultramafic complex (Kola Peninsula, Russia). These diorite-gneisses belong to a block historically known as the diorite window (DW) block. The same rocks occur in a framing of the Monchegorsk complex. The DW block is predominantly composed of diorite-gneisses and, to a lesser degree, of amphibolites. Multi-ordinal banding, complex folding, boudinage and metamorphic transformations, garnet porphyroblasts, and tourmaline veinlets are typical of the diorite-gneisses. In accordance with the U-Pb isotope data, the age of the diorite-gneisses in the DW block is 2736.0 ± 4.6 Ma. The Sm-Nd mineral (garnet, biotite, and tourmaline) isochron for the DW rocks has yielded an age of 1806 ± 23 Ma (related to the processes of the Svecofennian orogeny). The DW diorite-gneisses are compared with the metadiorites of the Gabbro-10 massif. The latter is a part of the Monchegorsk complex, with U-Pb crystallization age of 2498 ± 6 Ma. On the basis of geological and isotope-geochemical data, it is shown that the DW rocks belong to the Archean basement while the Gabbro-10 metadiorites probably represent one of the late-magmatic phases of the Monchegorsk complex.

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