silicic magmatism
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Minerals ◽  
2022 ◽  
Vol 12 (1) ◽  
pp. 105
Author(s):  
Vasily Shcherbakov ◽  
Ilya Bindeman ◽  
Viktor Gazeev

Significant volumes of rhyolites and granites of the Pliocene-Pleistocene age are exposed in the collision zone of the Greater Caucasus, Russia. The volcanic history of the region includes ignimbrites and lavas associated with the Chegem caldera (2.9 Ma) and Elbrus volcano (1.98 and 0.7 Ma) and rhyolitic necks and granites in Tyrnyauz (1.98 Ma). They are characterized by a similar bulk and mineral composition and close ratios of incompatible elements, which indicates their related origin. The 1.98 Ma Elbrus ignimbrites, compared to the 2.9 Ma Chegem ignimbrites, have elevated concentrations of both compatible (Cr, Sr, Ca, Ni) and incompatible elements (Cs, Rb, U). We argue that the Elbrus ignimbrites were produced from magma geochemically similar to Chegem rhyolites through fractionation crystallization coupled with the assimilation of crustal material. The 1.98 Ma Eldjuta granites of Tyrnyauz and early ignimbrites of the Elbrus region (1.98 Ma) are temporally coeval, similar mineralogically, and have comparable major and trace element composition, which indicates that the Elbrus ignimbrites probably erupted from the area of modern Tyrnyauz; the Eldjurta granite could represent a plutonic reservoir that fed this eruption. Late ignimbrites of Elbrus (0.7 Ma) and subsequent lavas demonstrate progressively more mafic mineral assemblage and bulk rock composition in comparison with rhyolites. This indicates their origin in response to the mixing of rhyolites with magmas of a more basic composition at the late stage of magma system development. The composition of these basic magmas may be close to the basaltic trachyandesite, the flows exposed along the periphery of the Elbrus volcano. All studied young volcanic rocks of the Greater Caucasus are characterized by depletion in HSFE and enrichment in LILE, Li, and Pb, which emphasizes the close relationship of young silicic magmatism with magmas of suprasubduction geochemical affinity. An important geochemical feature is the enrichment of U up to 8 ppm and Th up to 35 ppm. The trace element composition of the rocks indicates that the original rhyolitic magma of Chegem ignimbrites caldera was formed at >80%–90% fractionation of calc-alkaline arc basalts with increased alkalinity. This observation, in addition to published data for isotopic composition (O-Hf-Sr) of the same units, shows that the crustal isotopic signatures of silicic volcanics may arise due to the subduction-induced fertilization of peridotites producing parental basaltic magmas before a delamination episode reactivated the melting of the former mantle and the lower crust.


2022 ◽  
Author(s):  
Clinton I. Barineau ◽  
et al.

Sample Preparation and Geochemical Analysis Methodology; Table S1: Major oxide percentages for metaigneous rocks of the Wedowee-Emuckfaw-Dahlonega basin; Table S2: Measured isotope ratios and normalized U-Pb ages calculated without 204Pb Correction; Table S3: Lu-Hf isotope analyses; Table S4: Latitude-longitude (WGS84), geologic unit, and age information for samples analyzed as part of this project.


2021 ◽  
Author(s):  
Clinton I. Barineau ◽  
et al.

Sample Preparation and Geochemical Analysis Methodology; Table S1: Major oxide percentages for metaigneous rocks of the Wedowee-Emuckfaw-Dahlonega basin; Table S2: Measured isotope ratios and normalized U-Pb ages calculated without 204Pb Correction; Table S3: Lu-Hf isotope analyses; Table S4: Latitude-longitude (WGS84), geologic unit, and age information for samples analyzed as part of this project.


2021 ◽  
Author(s):  
Clinton I. Barineau ◽  
et al.

Sample Preparation and Geochemical Analysis Methodology; Table S1: Major oxide percentages for metaigneous rocks of the Wedowee-Emuckfaw-Dahlonega basin; Table S2: Measured isotope ratios and normalized U-Pb ages calculated without 204Pb Correction; Table S3: Lu-Hf isotope analyses; Table S4: Latitude-longitude (WGS84), geologic unit, and age information for samples analyzed as part of this project.


2021 ◽  
Author(s):  
Clinton I. Barineau ◽  
et al.

Sample Preparation and Geochemical Analysis Methodology; Table S1: Major oxide percentages for metaigneous rocks of the Wedowee-Emuckfaw-Dahlonega basin; Table S2: Measured isotope ratios and normalized U-Pb ages calculated without 204Pb Correction; Table S3: Lu-Hf isotope analyses; Table S4: Latitude-longitude (WGS84), geologic unit, and age information for samples analyzed as part of this project.


2021 ◽  
Vol 363 ◽  
pp. 106336
Author(s):  
Qian-ru Cai ◽  
Man-lan Niu ◽  
Xiao-yu Yuan ◽  
Qi Wu ◽  
Guang Zhu ◽  
...  

2021 ◽  
Author(s):  
Steffi Burchardt ◽  
Birgir Oskarsson ◽  
Ludvik Gustafsson ◽  
Silvia Berg ◽  
Morten Riishuus

The Borgarfjörður-Loðmundarfjörður area in Northeast Iceland hosts an unusual volume of silicic rocks, as well as volcanic and sub-volcanic structures emplaced in the Miocene between 13.5 and 12.2 Ma. Here, we summarise the geology of the area and present a new geological map to summarise the current state of knowledge. We describe the prominent features of the volcanic centres, as well as regional marker horizons. Notably, the volume of silicic rocks, the distribution of eruptive centres, calderas, and intrusion swarms, as well as the interplay between regional flood basalts and silicic magmatism indicate a rift zone architecture different to that of the present day.


2021 ◽  
Vol 97 (3) ◽  
pp. 227-237
Author(s):  
Kasturi Chakraborty ◽  
Prabir Kumar Mukhopadhyay ◽  
Sandip Nandy
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