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.

Geochemical Characteristics of Jurassic Plume Magmatism in Ahlmannryggen Massif (Queen Maud Land, East Antarctica)

2019 ◽  
Vol 486 (1) ◽  
pp. 529-532 ◽  
Author(s):  
N. M. Sushchevskaya ◽  
B. V. Belyatsky ◽  
G. L. Leitchenkov ◽  
V. G. Batanova ◽  
A. V. Sobolev
Keyword(s):  
East Antarctica ◽  
Geochemical Characteristics ◽  
Plume Magmatism

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>

Tectono-magmatic evolution of the Karoo and Kerguelen plumes and their impact onto magmatism of the East Antarctica

2021 ◽  
Author(s):  
Nadezda Sushchevskaya ◽  
German Leitchenkov ◽  
Boris Belyatsky
Keyword(s):  
Melting Process ◽  
Oceanic Lithosphere ◽  
East Antarctica ◽  
Igneous Provinces ◽  
Igneous Province ◽  
Dronning Maud Land ◽  
Tectonic Development ◽  
Characteristic Features ◽  
Intrusive Activity ◽  
Lambert Glacier

<p>The Mesozoic Karoo-Maud and Kerguelen plumes had a significant influence on Gondwana and the oceanic lithosphere. Jurassic magmatism, formed under the influence of a huge Karoo plume at 184–178 Ma ago, covered large areas of the Dronning Maud Land in East Antarctica. Later, 130 – 0 m.y. ago, under the influence of the Kerguelen plume, magmatism formed in the area of the Lambert glacier, and the Gaussberg volcano (Quaternary time) appeared, located on the coast opposite the Kerguelen archipelago. We assume that the Karoo mantle plume initiated the formation of a “mega-apophyses” from the main plume manifestation area within the Karoo province in the southeastern African continet (ca. 2000 km in diameter). These mega-apophyses are represented by the Ferrar Igneous Province (ca. 3000 km long area of intrusive activity along the Transantarctic Mountains) and a supposed igneous province (ca. 1500 km long) covering the East Antarctic coast between the Lazarev and Cosmonauts Seas. Based on petrological and geochemical studies, the characteristic features of magmas of the Karoo, Dronning Maud Land, and Ferrar igneous provinces have been determined, which indicate that for all magmas associated with Karoo and Kerguelen plumes, the main source of melt enrichment is a mantle source with characteristics of the EM-II component (most typically for magmas of the Ferrar Province). It reflects the properties of an enriched, fluid-rich, ancient continental mantle, metasomatized at the early stages of the tectonic development of the region and involved in the melting process. A rarer admixture of the ancient lithospheric component (EM-I, with <sup>206</sup>Pb/<sup>204</sup>Pb = 16.5 and <sup>143</sup>Nd/<sup>144</sup>Nd = 0.5122) was revealed in both plumes. The existence of mantle plumes in the Southern Hemisphere and their long-term development had a significant impact on the structure and evolution of the East Antarctica.</p>

scholarly journals Petrology and Geochemistry of Serpentinites Associated with the Ultra-High Pressure Lago di Cignana Unit (Italian Western Alps)

2019 ◽  
Vol 60 (6) ◽  
pp. 1229-1262 ◽  
Author(s):  
Mattia Gilio ◽  
Marco Scambelluri ◽  
Samuele Agostini ◽  
Marguerite Godard ◽  
Daniel Peters ◽  
...  
Keyword(s):  
High Pressure ◽  
Subduction Zone ◽  
Closed System ◽  
Host Rock ◽  
Mantle Peridotite ◽  
Oceanic Lithosphere ◽  
Western Alps ◽  
Plate Interface ◽  
Ultra High Pressure ◽  
Depleted Mantle

AbstractIn the Western Alps, the ophiolitic Zermatt–Saas Zone (ZSZ) and the Lago di Cignana Unit (LCU) record oceanic lithosphere subduction to high (540°C, 2·3GPa) and ultra-high pressure (600°C, 3·2GPa), respectively. The top of the Zermatt–Saas Zone in contact with the Lago di Cignana Unit consists of olivine + Ti-clinohumite-bearing serpentinites (the Cignana serpentinite) hosting olivine + Ti-clinohumite veins and dykelets of olivine + Ti-chondrodite + Ti-clinohumite. The composition of this serpentinite reveals a refertilized oceanic mantle peridotite protolith that became subsequently enriched in fluid-mobile elements (FME) during oceanic serpentinization. The olivine + Ti-clinohumite veins in the Cignana serpentinite display Rare Earth Element (REE) and FME compositions quite similar to the host-rock, which suggests closed-system dehydration of this serpentinite during subduction. The Ti-chondrodite-bearing dykelets are richer in REE and FME than the host-rock and the dehydration olivine + Ti-clinohumite veins: their Nd composition points to a mafic protolith, successively overprinted by oceanic metasomatism and by subduction zone recrystallization. These dykelets are comparable in composition to eclogites within the ultra-high pressure LCU that derive from subducted oceanic mafic crust. Different from the LCU, serpentinites from the core domains of the ZSZ display REE compositions indicating a depleted mantle protolith. The oceanic serpentinization of these rocks led to an increase in FME and to seawater-like Sr isotope compositions. The serpentinites sampled at increasing distance from the ultra-high pressure LCU reveal different mantle protoliths, still preserve an oceanic geochemical imprint and contain mafic dykelets affected by oceanic metasomatism. The subduction zone history of these rocks thus occurred under relatively closed system conditions, the only possible change during subduction being an enrichment in As and Sb recorded by the serpentinites closer to the crustal LCU. The ZSZ and Cignana serpentinites thus likely evolved in a slab setting and were weakly exposed to interaction with slab-derived fluids characteristic of plate interface settings. Our data suggest two possible scenarios for the evolution of the studied ZSZ and Cignana serpentinites. They are either part of a coherent ophiolite unit whose initial lithospheric mantle was variably affected by depletion and re-fertilization processes, or they belong to separate tectonic slices derived from two different oceanic mantle sections. In the Cignana serpentinite atop the ZSZ, the presence of Ti-chondrodite dykelets similar in composition to the LCU eclogites suggests these two domains were closely associated in the oceanic lithosphere and shared the same evolution to ultra-high pressure conditions during Alpine subduction.

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>

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