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Magmatism in the Context of the Present-Day Tectonic Settings
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
O.A. Bogatikov, V.I. Kovalenko, E.V. Sharkov, V.V. Yarmolyuk
Continental rifts are characterized by a distinct longitudinal and transverse zoning. The distribution pattern of igneous rocks, as reflected in the Ethiopian–Kenyan rift system, provides the best example of longitudinal igneous zoning probably associated with a change of rift type. From north to south there is a sequence of igneous assemblages, from tholeiitic basalt with poorly developed alkaline comendite in the Afar rift valley, through moderately alkaline olivine basalts containing pantellerites in the main Ethiopian valley and alkaline basalts with trachytes in the Kenyan Rift, to high-alkaline basanite–nephelinite lavas in the southern Kenyan Rift (Almond, 1986). The transverse zoning in this rift zone is represented by a transition from high-alkaline assemblages of the plateau occurring on the rift flanks, to less alkaline in the rift valleys themselves. A certain type of transverse zoning may occur within the entire rift system. For example, in East Africa, the eastern branch (Kenyan Rift) and western branch (Tanganyika Rift) are characterized respectively by K–Na and K alkaline magmatism; in the Baikal Rift Zone potassic magmatism is typical of the Khubsugul Rift, while its remaining part is dominated by K–Na igneous assemblages.
The effect of stress level on the compressive strength of the rock samples subjected to cyclic loading
Published in Vladimir Litvinenko, EUROCK2018: Geomechanics and Geodynamics of Rock Masses, 2018
Melek Hanım Beşer, Kerim Aydiner
Thin sections were prepared to analyze the mineralogical and petrographic properties of the rock. According to the results of analyses, this rock generally shows porphyritic, microlitic porphyritic and hyalo-microlitic porphyritic texture. It is observed that main components of most of these rocks are leucite, calcitic plagioclase, pyroxene (%20), amphibole (3–5%), biotite (3–5%) and opaque (2%) minerals. The secondary minerals are chlorite, calcite, zeolite and clay minerals. As a result of microscopic examination, this rock is located tephrite/basanite groups. Also, this rock is named as tephrite due to the olivine absence.
Petrogenetic links between the Dunedin Volcano and peripheral volcanics of the Karitane Suite
Published in New Zealand Journal of Geology and Geophysics, 2018
Oliver E. McLeod, James D. L. White
The Karitane Suite samples analysed in this study include basanites, trachybasalts, trachyandesites and phonolites that span from 42 to 57 wt% SiO2 (Figure 4). The basanites are the most silica-poor (42–46 wt%) and MgO-rich (c.8 wt%) rocks (Figure 10; Table 4), and contain high amounts of CaO (9.4–10.9 wt%) and Ni (169 ppm). The Seaward Hill hawaiites (46–48 wt% SiO2) contain similar amounts of total Fe (12.8 wt%), TiO2 (2.5 wt%) and K2O (1.3 wt%) to the basanites, higher amounts of Al2O3 (15.3 vs. 13–14 wt%), and lower MgO (6.6 wt%) and CaO (8.5 wt%). Of the more evolved rocks, the trachyandesites are defined by SiO2 contents of 55.7–56.1 wt%, with high contents of Al2O3 (18.4–19 wt%) and K2O (4.4–5 wt%), and low contents of MgO (∼1 wt%) and CaO (3–4 wt%). Karitane Suite phonolites and trachyandesites contain similar amounts of SiO2 (55.7 wt%), total FeO (6.3 wt%) and K2O (4.9 wt%) but phonolites are more depleted in MgO (0.5 wt%), CaO (∼1 wt%) and TiO2 (0.2 wt%) and they have higher Al2O3 (19 wt%). Phonolite exhibits extreme enrichment in Na2O (10.6 wt%) relative to trachyandesite.