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Phanerozoic Androgenic Magmatism
Published in O.A. Bogatikov, R.F. Fursenko, G.V. Lazareva, E.A. Miloradovskaya, A. Ya, R.E. Sorkina, Magmatism and Geodynamics Terrestrial Magmatism Throughout the Earth’s History, 2020
The Karoo Trap Province of South Africa covers an area of 140,000 km2, with a trap thickness of up to 1 km. The main peak of activity is dated at about 190 Ma ago (Ellam and Cox, 1989). It is believed that the origin of the trap province is closely related to the opening of the Indian Ocean, at the time when Gondwana broke up into Africa and Antarctica. In the Nuanetsi area, at the base of the trap section, nephelinites occur in small quantities, overlapped by Letaba high-magnesian basalts (9% MgO). Tholeiite basalts of the Sabie River Formation are found up section, interbedded with rhyolites in the upper part of the series.
Health risk assessment and prevalence of fluoride in groundwater around the geological diversity of Ambadongar South Gujarat, India
Published in Human and Ecological Risk Assessment: An International Journal, 2020
K. D. Shirke, Ajaykumar Kadam, N. J. Pawar
The majority of higher values of F− are seen in deeper aquifers as compared to shallower one. Enriched F− values are seen in the wells belonging to Nephelinite lithology followed by sandstone and limestone. Nephelinite contains minerals like nepheline, plagioclase, hornblende and K feldspar which are Na rich. The alkaline water depleted in Ca and enriched in Na is capable of releasing F from F− bearing minerals. High F− concentrations present in groundwater from calcium (Ca) poor aquifers and may also increase in groundwater where cation exchange of sodium (Na) for calcium takes place (Sadia Bibi et al 2017). Lower F− values are recorded in carbonatites, as carbonatites contain more than 10% fluorapatite and primary apatites and secondary phosphates which do not release much F− into water possibly due to their low solubility (Young et al. 2011; Singh and Mukherjee. 2015) Water rich in Na has higher capacity to release F− from fluorite bearing minerals. High F− concentration is seen in water with sodium bicarbonate facies (Singh and Mukherjee 2015; Rashid et al. 2018). The dissolution of fluorite takes place as:
Influence of host magma alkalinity on trachytic melts formed during incongruent orthopyroxene dissolution in mantle xenoliths
Published in New Zealand Journal of Geology and Geophysics, 2020
Andreas Auer, Marco Brenna, James M. Scott
The Auckland Volcanic Field (AVF – 36°56′58.4″S 174°46′59.3″E) was formed by at least 53 individual and dispersed eruptions over the past 180 kyr, with the last only 500 years ago (Leonard et al. 2017). Eruption products range in composition from subalkalic basalt to basanite and nephelinites (McGee et al. 2013). Peridotite xenoliths occur in at least four locations within the Auckland Volcanic Field (Brothers and Rodgers 1969; Reay and Sipiera 1987; Brenna et al. 2018). The xenoliths are dominantly lherzolitic, but there has been a little comprehensive study of the mineralogy and geochemistry other than an investigation of material from Pupuke Maar by Brenna et al. (2018). Samples were selected from both the Three Kings volcano in the central portion of the field and Pupuke Maar.