Vol 33, No 1 (2025)
- Year: 2025
- Articles: 5
- URL: https://journals.eco-vector.com/0869-5903/issue/view/13043
- DOI: https://doi.org/10.31857/S0869-5903331
Full Issue
Articles
Late Pleistocene basitic magmatism and Its Relation to large caldera-forming eruptions on Iturup Island on example of Klumba volcano, Kuril Islands
Abstract
The basaltic andesite volcano Klumba is the only post-caldera volcano in the center of one of the most powerful explosive eruptions that occurred at the end of the Neopleistocene in Great Kuril Ridge (GKR) and formed a thick sequence of dacitic pumice tuffs on the Vetrovoy Isthmus on the Iturup Island. A detailed study of mineralogy and olivine-hosted fluid and melt inclusions in the rocks of the Klumba volcano, showed that the feeding magma evolved within the arc crust at depths between 15.5 and 7 km and was related to Mg-rich (up to 9.8 wt. % MgO), low-potassium and low-alumina basaltic andesite melts, which initially contained about 5–6 wt. % H2O. Olivine and Cr-Al spinel are the earliest minerals, which are later joined by plagioclase and pyroxenes. The crystallization of the basaltic andesites occurred at temperatures of about 1000–1200°C. The melt was saturated with carbon dioxide fluid, containing minor amounts of SO2. The Pleistocene basaltic andesitic magmatism in the central part of the Iturup Island was predominantly intrusive and resulted in the formation of a large trans-crustal magmatic system (TCMS), which could include the dacitic reservoir that fed the explosive eruption of the Vetrovoy Isthmus. The plumbing system of the Klumba volcano is considered to be a part of this TCMS with impulsive injections of variously differentiated basaltic andesite magmas. It is assumed that such systems may have been developed on the scale of the whole island. The processes duration and the amount of intruded magma may have been sufficient to cause partial melting in the upper parts of the island-arc crust and to form magma reservoirs of powerful explosive caldera-forming eruptions.
3–26
Carbonatization of Serpentinites of the Mid-Atlantic Ridge: 2. Evolution of chemical and isotopic (δ¹⁸O, δ¹³С, Rb, Sr, Sm, Nd) compositions during exhumation of abyssal peridotites
Abstract
The alteration of oceanic lithosphere by fluids is the primary driver of water-rock reactions with ultramafic and mafic rocks that transform CO2 into carbonates. Carbonation of peridotites involve the generation of carbonate veins and large-scale carbonatization of serpentinized peridotites exposed on the ocean floor at slow-spreading and ultraslow-spreading ridges and in ophiolites on continents. We report geochemical and isotope data (δ¹⁸O, δ¹³C, Rb, Sr, Sm, Nd) on ultramafic rocks that provide insights into the isotopic trends and fluid evolution of peridotite carbonation and help to understand heterogeneities in alteration and carbonization within peridotite-dominated serpentinization system. The main goal of this work is to reconstruct the hydration history and to understand conditions, isotope and chemical changes during carbonatization and serpentinization of mantle peridotites. Our studies show a comparative analysis of petrological, geochemical, isotope data (strontium, neodymium, oxygen and carbon) and degree of fluid–rock interaction during uplift and emplacement of carbonated serpentinites and present a reconstruction of the long-term fluid interaction of abyssal peridotites from the Mid-Atlantic Ocean Ridge.
27–44
Petrogenesis and sources for rocks of the alkaline rare-metal Burpala intrusion (Northern Baikal Region)
Abstract
The results of petrologic and geochemical study of rocks of the Burpala alkaline intrusion composed of quartz syenites, alkaline nepheline-free and nepheline syenites, including ore-bearing ones, which is part of the Late Paleozoic North Baikal alkaline province, are presented. The studied rocks by chemical composition belong to foid monzosyenites, foid syenites and syenites, ranging from agpaitic to miascitic varieties. Close Sr-Nd isotopic characteristics, configuration of geochemical spectra confirm the syngenetic nature of magmas from which nepheline, alkaline and quartz syenites crystallized. Negative Eu anomaly in REE spectra and rather low Mg# of rocks testify in favor of a long process of fractional crystallization of rocks from the melt of alkaline-basic composition. The isotopic and geochemical characteristics of rocks of the Burpala intrusion reflect the predominance of metasomatized lithospheric mantle in the source. The formation of the rocks of the intrusion, according to the features of the trace element and isotopic data, was complicated by assimilation of upper crustal material, which was the most possible factor that determined the genetic relationship between nepheline and quartz syenites within the intrusion.
45–67
Origin of the Earth’s first felsic material: a hydrogen perspective?
Abstract
We present experimental results on melting model basalt komatiite (ВК) and enstatite chondrite (ЕСН) compositions at temperature T = 1300оС and hydrogen pressure РH₂ = 100 МПа. The experiments model interaction of Magma Ocean with the early Earth hydrogen atmosphere. The experiment products consist of silicate glasses (quenched melts) that are considerably depleted in FeO but enriched in lithophile oxides and H2O, and the iron phase with minor amounts of Si and O. Estimated equilibrium oxygen fugacity in the runs is approximately 2 log units below that of the Fe-FeO buffer. Calculations of fractional crystallization of the experimental melt demonstrate that the final products correspond to granodiorite consisted of two feldspars, clinopyroxene and quartz with minor biotite for the initial BK composition, and quatz-two feldspars-two mica granite for the initial ECH. It is shown that differentiation of the ЕСН may result in crystallization of zircon in a range T = 730–750оС. A model assuming interaction of magma ocean with a thick nebular hydrogen atmosphere with subsequent differentiation explains the formation of silica-rich water bearing melts by internal processes of planetary evolution, and does not invoke pre-conditioning of forming hydrated proto-crust.
“The only thing we know for certain is that (Hadean Earth) produced and somehow preserved the mineral zircon (ZrSiO4).” (Harrison, 2009).
68–78
On the possibility of discrimination of post-collisional and within-plate A-type granitoids based on geochemical data
Abstract
Based on the results of discriminant analysis of samples of Phanerozoic intraplate and post-collisional A-type granitoids with similar geochemical characteristics, a diagram is proposed that allows typing at least part of the A-granitoid samples. The applicability of the proposed diagram for the typification of not only Phanerozoic, but also Precambrian A-type granitoids is shown.
79–88