K-Ar ages of a basanitoid lava flow of Nanzaki volcano and underlying Miocene andesites from the Irozaki area, Izu Peninsula, Central Japan.
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The Journal of the Japanese Association of Mineralogists Petrologists and Economic Geologists (1976)
The Akima, Aima-gawa and Kennomine formations of the Neogene system are distributed between the Quaternary Asama and Haruna volcanoes, which occupy the south-western part of Gunma Prefecture. The Pliocene Kennomine formation overlies unconformably the Akima and Aima-gawa formations of the Upper Miocene time (Akima Collaborative Research Group, 1975). These formations mainly consist of pyroclastic rocks and volcanic rocks which occur in the form of lava flows and intrusive masses. The main part of these volcanic rocks is made of two pyroxene andesites of hypersthenic rock series, while a little amount of siliceous basaltic rocks of the same rock series are also observed in the early stage of volcanism in this district. Twenty representative andesites and basalts are chemically analysed and 87Sr/86Sr ratios are determined for five andesites. They are characterized by low alkali contents, especially low potassium contents. The AFM diagram, (FeO+0.9×Fe2O3)/MgO-SiO2 diagram and (Na2O+ K2O)-SiO2 diagram show that andesites and basalts correspond to those of calc-alkalic type with low alkali contents and those of low alkali tholeiitic type respectively. These volcanic rocks have low K2O/Na2O ratios resembling to those of volcanics of pigeonitic rock series from Izu-Hakone region. Five andesites have 87Sr/86Sr ratios ranging from 0.7041 to 0.7043 and the average is 0.7042. These ratios are similar to those of volcanic rocks of the L zone recently proposed by Shuto (1974a, 1974b) and Shuto and Kagami (1975). Considering from the results of the present work, it may be concluded that the genesis of volcanic rocks in the above formations can not be ascribed to the contamination with granitic material in magma and that andesites are derived by fractional crystallization of certain basic andesitic (basaltic andesitic) magma probably originated from the upper mantle material presumably of peridotitic composition.
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THERMAL CONTACT WITH THE VOLCANIC ROCK AT KAMIONNA NEAR BOCHNIA (Carpathians) South of Bochnia V. Uhlig (1838) discovered a few occurrences of andesites and dacites. Their geological position and age have been established only recently by K. Skoczylas-Ciszewska (1956) who stated that the rocks in question occur as veins or tuffaceaus intercaIations in sediments of Upper Cretaceous and Paleocene age. Thus these rocks may correspond with the volcanic rocks of the Wadowice area described by A. Gawel, M. Ksiązkiewicz (1936) and T. Wieser (1954). While Upper Cretaceous-Paleocene age of the tuffs in both areas area has been proved beyond doubts (aIso Lower Eocene tuffs have been found, Ksiązkiewicz 1956) the age of volcanic rocks was not cIearly stated; neither in the Wadowice area (Lanckorona) nor in the Żegocina region. In either areas volcanic rocks occur as large or small blocks in zones of very complex structure and, so far in no case a termally altered contact has been found.
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The present paper focuses on the geology, petrography, and geochemistry of the well-known Dokhan volcanics encountered in the northern part of the Eastern Desert of Egypt. The basalts, andesites, rhyolites, and agglomerates exposed at the Makhar Seal (flood plain) as well as Wadi Abu Zoghot, Wadi El-Ghafiryia, Wadi Al-Radah Luman, Wadi Al-Ushsh, Wadi Umm Sidrah, and Gabal Ghuwayrib are herein examined as sources of coarse aggregate in concrete mixes. A representative total of 28 samples—collected from different Dokhan volcanics—was studied in terms of field geology, petrography, and geochemistry wherein a variety of experiments related to construction material validation apply. The petrographic examination revealed that the studied Dokhan volcanics consist of basic, intermediate, and acidic volcanic igneous rocks. These rocks are represented through basalts, andesites, imperial porphyry, dacites, rhyodacites, rhyolites, and their pyroclastics. Furthermore, the applied geochemical analysis indicated that the studied Dokhan volcanics are alkaline to sub-alkaline, calc-alkaline and classified as basalts, basaltic andesites, andesites, trachyandesites, trachydacites, trachytes, and rhyolites, indicating an initial potential as aggregate for concrete mixes. Finally, the results obtained from incorporating Dokhan volcanics as aggregates in concrete mixes demonstrated a significant improvement in regard to the properties of the comprising concrete mixes. Herein, a higher compressive strength was witnessed after 28 days for Dokhan volcanic concrete, when compared to concrete comprising dolomite aggregate, amounting to an average increase that exceeded 36%.
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K-Ar dating and petrologic description were carried out on the Inase valcanic rocks from eastern part of the Kitakami district of Iwate Prefecture, Northeast Japan. We obtained K-Ar whole rock ages of 15.1±0.4 Ma and 15.5±0.4 Ma for two andesites. The results of the present and previous K-Ar age detamination indicate that the volcanic activities in the Inase district took place in the range of 15.5-13.2 Ma. The chemical compositions of representative 32 andesitic samples were determined by XRF technique. The upper Inase volcanics composed of tholeiitic andesites with SiO2 of 53.61-60.61% have chemical characters similar broadly to those of the Quaternary andesites from the NE Japan arc, whereas the lower Inase ones composed also of tholeiitic andesites with SiO2 of 53.86-55.28% are characterized by high contents of HFS elements such as P, Ti, Nb, Y and Zr, suggesting that the latter are different in chemical compositions from the typical island arc andesites. We estimated the trace element composition of the primary magmas of the lower and upper Inase volcanics using the method of Sakuyama and Nesbitt (1986) and Yoshida and Aoki (1988). The process identification diagram for the primary magma compositions of the Inase volcanics and the Quaternary volcanics in the NE Japan arc and the surrounding areas suggests that the upper Inase primary magma may be derived from the magma source chemically similar to the present sub-continental mantle beneath the NE Japan arc, while the lower Inase primary magma may be derived from the magma source which is more enriched in HFS element contents than the sub-continental mantle.
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