scholarly journals On the article “Weathered potassic volcanic rocks as protoliths of the hematitic phyllites of the southern Serra do Espinhaço (MinasGerais)”: a discussion

2021 ◽  
Vol 35 (1) ◽  
pp. 1-6
Author(s):  
Alexandre Cabral ◽  
Francisco de Abreu
Keyword(s):  
Trace Element ◽  
Continental Crust ◽  
Metamorphic Rock ◽  
Volcanic Rocks ◽  
Alkaline Basalt ◽  
Chemical Analyses ◽  
Three Samples ◽  
Trace Element Contents ◽  
Selection Of ◽  
Hematitic Phyllite

Chaves and Knauer (2020) have presented three new whole-rock chemical analyses of phyllitic hematite, a unique metamorphic rock of the southern Serra do Espinhaço. Based on their three samples and a selection of other three samples from the literature, Chaves and Knauer have proposed that the geochemical uniqueness of the rock – i.e., high contents of K2O, Al2O3 and Fe2O3, and depletion in SiO2 – would represent a weathered, feldspathoid-rich alkaline basalt. This contribution is a discussion of their new data, the trace-element contents of which are at odds with those of a potassic, mantle-derived volcanic protolith for the hematitic phyllite. Its Nb/Th ratios of ~3 and chondrite-normalised La/Yb ratios of ~9–17, for instance, are typical of the continental crust. We also point out aspects that escaped the attention of Chaves and Knauer (2020), one of which is the ubiquitous occurrence of tourmaline in the hematitic phyllite.

Relative roles of source composition, fractional crystallization and crustal contamination in the petrogenesis of Andean volcanic rocks

1984 ◽  
Vol 310 (1514) ◽  
pp. 675-692 ◽  
Keyword(s):  
Subduction Zone ◽  
Continental Crust ◽  
Fractional Crystallization ◽  
Magma Mixing ◽  
Volcanic Rocks ◽  
Crustal Contamination ◽  
Oceanic Lithosphere ◽  
Alkaline Basalt ◽  
Complex Process ◽  
Heterogeneous Mantle

There are well established differences in the chemical and isotopic characteristics of the calc-alkaline basalt—andesite-dacite-rhyolite association of the northern (n.v.z.), central (c.v.z.) and southern volcanic zones (s.v.z.) of the South American Andes. Volcanic rocks of the alkaline basalt-trachyte association occur within and to the east of these active volcanic zones. The chemical and isotopic characteristics of the n.v.z. basaltic andesites and andesites and the s.v.z. basalts, basaltic andesites and andesites are consistent with derivation by fractional crystallization of basaltic parent magmas formed by partial melting of the asthenospheric mantle wedge containing components from subducted oceanic lithosphere. Conversely, the alkaline lavas are derived from basaltic parent magmas formed from mantle of ‘within-plate’ character. Recent basaltic andesites from the Cerro Galan volcanic centre to the SE of the c.v.z. are derived from mantle containing both subduction zone and within-plate components, and have experienced assimilation and fractional crystallization (a.f.c.) during uprise through the continental crust. The c.v.z. basaltic andesites are derived from mantle containing subduction-zone components, probably accompanied by a.f.c. within the continental crust. Some c.v.z. lavas and pyroclastic rocks show petrological and geochemical evidence for magma mixing. The petrogenesis of the c.v.z. lavas is therefore a complex process in which magmas derived from heterogeneous mantle experience assimilation, fractional crystallization, and magma mixing during uprise through the continental crust.

Tectonic setting and regional correlation of Ordovician metavolcanic rocks of the Casco Bay Group, Maine: evidence from trace element and isotope geochemistry

2004 ◽  
Vol 141 (2) ◽  
pp. 125-140 ◽  
Author(s):  
DAVID P. WEST ◽  
RAYMOND A. COISH ◽  
PAUL B. TOMASCAK
Keyword(s):  
Trace Element ◽  
Continental Crust ◽  
Isotope Geochemistry ◽  
Tectonic Setting ◽  
Volcanic Rocks ◽  
Mafic Magma ◽  
Ocean Basin ◽  
Middle Ordovician ◽  
South Central ◽  
Back Arc

Ordovician metamorphic rocks of the Casco Bay Group are exposed in an approximately 170 km long NE-trending belt (Liberty-Orrington belt) in southern and south-central Maine. Geochemical analysis of rocks within the Spring Point Formation (469±3 Ma) of the Casco Bay Group indicate that it is an assemblage of metamorphosed bimodal volcanic rocks. The mafic rocks (originally basalts) have trace element and Nd isotopic characteristics consistent with derivation from a mantle source enriched by a crustal and/or subduction component. The felsic rocks (originally rhyolites and dacites) were likely generated through partial melting of continental crust in response to intrusion of the mafic magma. Relatively low initial εNd values for both the mafic (−1.3 to +0.6) and felsic (−4.1 to −3.8) rocks suggest interactions with Gander zone continental crust and support a correlation between the Casco Bay Group and the Bathurst Supergroup in the Miramichi belt of New Brunswick. This correlation suggests that elements of the Early to Middle Ordovician Tetagouche-Exploits back-arc basin can be traced well into southern Maine. A possible tectonic model for the evolution of the Casco Bay Group involves the initiation of arc volcanism in Early Ordovician time along the Gander continental margin on the eastern side of the Iapetus Ocean basin. Slab rollback and trenchward migration of arc magmatism initiated crustal thinning and rifting of the volcanic arc around 470 Ma and resulted in the eruption of the Spring Point volcanic rocks in a back-arc tectonic setting.

scholarly journals Evolution of Subduction Dynamics beneath West Avalonia in Middle to Late Ordovician Times

Lithosphere ◽  
2020 ◽  
Vol 2020 (1) ◽  
pp. 1-22
Author(s):  
Pierre Jutras ◽  
J. Brendan Murphy ◽  
Dennis Quick ◽  
Jaroslav Dostal
Keyword(s):  
Trace Element ◽  
Partial Melting ◽  
Volcanic Rocks ◽  
Upper Ordovician ◽  
The North ◽  
Trace Element Contents ◽  
Element Contents ◽  
Arc Setting ◽  
Back Arc ◽  
High Degree

Abstract Middle to Upper Ordovician volcanic rocks in the Arisaig area of Nova Scotia, Canada, constitute the only known record of volcanism in West Avalonia during that interval. Hence, they have been extensively studied to test paleocontinental reconstructions that consistently show Avalonia as a drifting microcontinent during that period. Identification of volcanic rocks with an intermediate composition (the new Seaspray Cove Formation) between upper Darriwilian bimodal volcanic rocks of the Dunn Point Formation and Sandbian felsic pyroclastic rocks of the McGillivray Brook Formation has led to a reevaluation of magmatic relationships in the Ordovician volcanic suite at Arisaig. Although part of the same volcanic construction, the three formations are separated by significant time-gaps and are shown to belong to three distinct magmatic subsystems. The tectonostratigraphic context and trace element contents of the Dunn Point Formation basalts suggest that they were produced by the high-degree partial melting of an E-MORB type source in a back-arc extensional setting, whereas trace element contents in intermediate rocks of the Seaspray Cove Formation suggest that they were produced by the low-degree partial melting of a subduction-enriched source in an arc setting. The two formations are separated by a long interval of volcanic quiescence and deep weathering, during which time the back-arc region evolved from extension to shortening and was eventually onlapped by arc volcanic rocks. Based on limited field constraints, paleomagnetic and paleontological data, this progradation of arc onto back-arc volcanic rocks occurred from the north, where an increasingly young Iapetan oceanic plate was being subducted at an increasingly shallow angle. Partial subduction of the Iapetan oceanic ridge is thought to have subsequently generated slab window magmatism, thus marking the last pulse of subduction-related volcanism in both East and West Avalonia.

Tokoro Belt (NE Hokkaido): an exhumed, Jurassic – Early Cretaceous seamount in the Late Cretaceous accretionary prism of northern Japan

2019 ◽  
Vol 158 (1) ◽  
pp. 72-83 ◽  
Author(s):  
Shunta Sakai ◽  
Naoto Hirano ◽  
Yildirim Dilek ◽  
Shiki Machida ◽  
Kazutaka Yasukawa ◽  
...  
Keyword(s):  
Trace Element ◽  
Late Cretaceous ◽  
Far East ◽  
Volcanic Rocks ◽  
Low Grade ◽  
Alkaline Basalt ◽  
Shield Volcano ◽  
Widespread Occurrence ◽  
Ocean Island ◽  
Basalt Type

AbstractThe Tokoro Belt exposed in NE Hokkaido (Japan) represents part of a Late Cretaceous accretionary complex, which includes variously metamorphosed volcanic rocks that are interbedded with chert, lenticular limestone and some fore-arc sedimentary rocks. The Tokoro Belt is notably different from other Late Cretaceous accretionary complexes around the Pacific Rim because of widespread occurrence of basalts and volcaniclastic rocks in it. The Nikoro Group, characterized by widespread occurrence of volcanic rocks, is divided into western, eastern and southern sections based on the internal structure, geochemical affinities and metamorphic grades of their volcanic lithologies. OIB (ocean island basalt)-type volcanic rocks with low-grade metamorphic overprint predominate in the western and southern sections, whereas MORB (mid-ocean ridge basalt)- and OIA (ocean island alkaline basalt)-type rocks in the eastern section with partly high-pressure metamorphism make up the northern part of the eastern section. Trace element patterns display transitional trends from MORB to OIA geochemical affinities. OIB-type rocks display trace element characteristics similar to those of shield volcano lavas on Hawaii, rather than small and mainly alkaline, Polynesian hotspot lavas; furthermore, they show significant HREE (heavy rare earth element) enrichment probably caused by plume–ridge interaction. Widespread OIBs in the Tokoro Belt represents tectonic slices of a large (>80 km wide) Hawaiian-style, seamount shield volcano on the Izanagi oceanic plate that was accreted into the continental margin of Far East Asia in the Late Cretaceous.

Crustal assimilation in the Burnt Lake metavolcanics, Grenville Province, southeastern Ontario, and its tectonic significance

1997 ◽  
Vol 34 (9) ◽  
pp. 1272-1285 ◽  
Author(s):  
T. E. Smith ◽  
P. E. Holm ◽  
N. M. Dennison ◽  
M. J. Harris
Keyword(s):  
Rare Earth ◽  
Trace Element ◽  
Partial Melting ◽  
Continental Crust ◽  
Fractional Crystallization ◽  
Volcanic Rocks ◽  
Lake Area ◽  
Depleted Mantle ◽  
Mafic Magmas ◽  
Back Arc

Three intimately interbedded suites of volcanic rocks are identified geochemically in the Burnt Lake area of the Belmont Domain in the Central Metasedimentary Belt, and their petrogenesis is evaluated. The Burnt Lake back-arc tholeiitic suite comprises basalts similar in trace element signature to tholeiitic basalts emplaced in back-arc basins formed in continental crust. The Burnt Lake continental tholeiitic suite comprises basalts and andésites similar in trace element composition to continental tholeiitic sequences. The Burnt Lake felsic pyroclastic suite comprises rhyolitic pyroclastics having major and trace element compositions that suggest that they were derived from crustal melts. Rare earth element models suggest that the Burnt Lake back-arc tholeiitic rocks were formed by fractional crystallization of mafic magmas derived by approximately 5% partial melting of an amphibole-bearing depleted mantle, enriched in light rare earth elements by a subduction component. The modelling also suggests that the Burnt Lake continental tholeiitic rocks were formed by contamination – fractional crystallization of mixtures of mafic magmas, derived by ~3% partial melting of the subduction-modified source, and rhyolitic crustal melts. These models are consistent with the suggestion that the Belmont Domain of the Central Metasedimentary Belt formed as a back-arc basin by attenuation of preexisting continental crust above a westerly dipping subduction zone.

Isolated alkaline basalt occurrences in the northern Spessart, Germany: Outposts of the Early Miocene Vogelsberg shield volcano?

2020 ◽  
Vol 196 (3) ◽  
pp. 199-219
Author(s):  
Martin Okrusch ◽  
Ulrich Schüssler ◽  
Paul Van Den Bogaard ◽  
Nikola Koglin ◽  
Helene Brätz ◽  
...  
Keyword(s):  
Trace Element ◽  
Volcanic Rocks ◽  
Stage I ◽  
Alkaline Basalt ◽  
Spinel Lherzolite ◽  
Shield Volcano ◽  
Mineral Contents ◽  
Special Position ◽  
Spatial Part ◽  
Volcanic Suite

Four isolated occurrences of Tertiary volcanic rocks in the northern Spessart at Beilstein, Hoher Berg, Madstein and Kasselgrund are relics of volcanic vents or dikes. They display alkaline basalts (s. l.) with mainly trachybasaltic composition, which, from normative mineral contents, may be designated as nepheline-bearing alkali-olivine basalts and basanites. In part, centimetre-sized xenoliths of spinel lherzolite occur. According to Ar-Ar dating, the alkaline basalts (s. l.) from Kasselgrund have erupted at 18.1 ± 0.3 or 19.3 ± 0.4 Ma, those of Hoher Berg between c. 18 and c. 21 Ma. These ages correspond to the Vogelsberg eruption stage I. A slightly younger Ar-Ar age of 16.8 ± 0.3 Ma was recorded for the Beilstein basalt, which is in chronological accordance to the turn of Vogelsberg eruption stages II and III. Samples of all four occurrences reveal major and trace element compositions, which are different from those of the Vogelsberg basalts. Compositions of basalts of the stage III from Vogelsberg coincide most with the Spessart basalts. This signals a special position of the northern Spessart volcanic rocks either as a discrete spatial part of the Vogelsberg volcanic suite or as smaller, independent eruption centres.

Trace Element Contents in Thyroid Cancer Investigated by Instrumental Neutron Activation Analysis

2018 ◽  
Vol 1 (1) ◽  
pp. 1-13
Keyword(s):  
Thyroid Cancer ◽  
Neutron Activation Analysis ◽  
Instrumental Neutron Activation Analysis ◽  
Activation Analysis ◽  
Neutron Activation ◽  
Trace Element ◽  
Thyroid Tissue ◽  
Tissue Levels ◽  
Trace Element Contents ◽  
Element Contents

Background: Thyroid cancer is an internationally important health problem. The aim of this exploratory study was to evaluate whether significant changes in the thyroid tissue levels of Ag, Co, Cr, Fe, Hg, Rb, Sb, Sc, Se, and Zn exist in the malignantly transformed thyroid. Methods: Thyroid tissue levels of ten trace elements were prospectively evaluated in 41 patients with thyroid malignant tumors and 105 healthy inhabitants. Measurements were performed using non-destructive instrumental neutron activation analysis with high resolution spectrometry of long-lived radionuclides. Tissue samples were divided into two portions. One was used for morphological study while the other was intended for trace element analysis. Results: It was found that contents of Ag, Co, Cr, Hg, and Rb were significantly higher (approximately 12.8, 1.4, 1.6, 19.6, and 1.7 times, respectively) in cancerous tissues than in normal tissues. Conclusions: There are considerable changes in trace element contents in the malignantly transformed tissue of thyroid.

scholarly journals The role of sulphur on the melting of Ca-poor sediment and on trace element transfer in subduction zones: an experimental investigation

2021 ◽  
Author(s):  
Anne-Aziliz Pelleter ◽  
Gaëlle Prouteau ◽  
Bruno Scaillet
Keyword(s):  
Trace Element ◽  
Partial Melting ◽  
Subduction Zones ◽  
Sediment Flux ◽  
Arc Magmas ◽  
Trace Element Contents ◽  
The Stability ◽  
Element Transfer ◽  
High Sediment

Abstract We performed phase equilibrium experiments on a natural Ca-poor pelite at 3 GPa, 750-1000 °C, under moderately oxidizing conditions, simulating the partial melting of such lithologies in subduction zones. Experiments investigated the effect of sulphur addition on phase equilibria and compositions, with S contents of up to ∼ 2.2 wt. %. Run products were characterized for their major and trace element contents, in order to shed light on the role of sulphur on the trace element patterns of melts produced by partial melting of oceanic Ca-poor sediments. Results show that sulphur addition leads to the replacement of phengite by biotite along with the progressive consumption of garnet, which is replaced by an orthopyroxene-kyanite assemblage at the highest sulphur content investigated. All Fe-Mg silicate phases produced with sulphur, including melt, have higher MgO/(MgO+FeO) ratios (relative to S-free/poor conditions), owing to Fe being primarily locked up by sulphide in the investigated redox range. Secular infiltration of the mantle wedge by such MgO and K2O-rich melts may have contributed to the Mg and K-rich character of the modern continental crust. Addition of sulphur does not affect significantly the stability of the main accessory phases controlling the behaviour of trace elements (monazite, rutile and zircon), although our results suggest that monazite solubility is sensitive to S content at the conditions investigated. The low temperature (∼ 800 °C) S-bearing and Ca-poor sediment sourced slab melts show Th and La abundances, Th/La systematics and HFSE signatures in agreement with the characteristics of sediment-rich arc magmas. Because high S contents diminish phengite and garnet stabilities, S-rich and Ca-poor sediment sourced slab melts have higher contents of Rb, B, Li (to a lesser extent), and HREE. The highest ratios of La/Yb are observed in sulphur-poor runs (with a high proportion of garnet, which retains HREE) and beyond the monazite out curve (which retains LREE). Sulphides appear to be relatively Pb-poor and impart high Pb/Ce ratio to coexisting melts, even at high S content. Overall, our results show that Phanerozoic arc magmas from high sediment flux margins owe their geochemical signature to the subduction of terrigenous, sometimes S-rich, sediments. In contrast, subduction of such lithologies during Archean appears unlikely or unrecorded.

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