East Sakhalin island arc paleosystem of the Sea of Okhotsk region
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Abstract The Gangdese magmatic belt is located in the southern margin of the Lhasa terrane, south Tibet. Here zircon U–Pb ages and Hf isotopic data, as well as whole‐rock geochemistry and Sr–Nd isotopes on andesites from the Bima Formation with a view to evaluating the history of the Gangdese magmatism and the evolution of the Neotethys Ocean. Zircon U–Pb dating yields an age of ca 170 Ma from six samples, representing the eruptive time of these volcanic rocks. Zircon Hf isotopes show highly positive ε H f (t) values of +13 to +16 with a mean of +15.2. Whole‐rock geochemical and Sr–Nd isotopic results suggest that the magma source of these andesites was controlled by partial melting of a depleted mantle source with addition of continental‐derived sediments, similar to those in the southern arcs of the Lesser Antilles arc belt. In combination with published data, the volcanic rocks of the Bima Formation are proposed to have been generated in an intra‐oceanic arc system, closely associated with northward subduction of the Neotethyan oceanic lithosphere.
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The Journal of the Japanese Association of Mineralogists Petrologists and Economic Geologists (1986)
Two petrographic provinces are classified in the Miocene volcanic rocks widely exposed in areas to the east of the Quaternary volcanic front of Northeast Japan. The first is that of the island arc tholeiite in the Kitakami river area, where rocks are basalts, andesites and dacites, all being of the island arc tholeiite or calc-alkali rock series. On the other hand, the second is a mixed province of the oceanic tholeiite and the island arc tholeiite series, in which occur, in association with the island arc tholeiitic rocks, basalts and andesites occasionally rich in TiO2 and FeO*, icelandite-like andesites and dacites similar in composition to rocks of the oceanic regions. Its area extends from Sendai southwards to the Abukuma mountains district. The boundary between the two provinces corresponds to the Matsushima-Honjo line defined by Oide and Onuma (1960).
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The Teneme Formation is located in the Mayari-Cristal ophiolitic massif and represents one of the three Cretaceous volcanic Formations established in northeastern Cuba. Teneme volcanics are cut by small bodies of 89.70 ± 0.50 Ma quarz-diorite rocks (Rio Grande intrusive), and are overthrusted by serpentinized ultramafics. Teneme volcanic rocks are mainly basalts, basaltic andesites, andesites, and minor dacites, and their geochemical signature varies between low-Ti island arc tholeiites (IAT) with boninitic affinity (TiO2 < 0.4 %; high field strength elements << N-type MORB) and typical oceanic arc tholeiites (TiO2 = 0.5-0.8 %). Basaltic rocks exhibit low light REE/Yb ratios (La/Yb < 5), typical of intraoceanic arcs and are comparable to Maimon Formation in Dominican Republic (IAT, pre Albian) and Puerto Rican lavas of volcanic phase I (island arc tholeiites, Aptian to Early Albian). The mantle wedge signature of the Teneme Formation indicates a highly depleted MORB-type mantle source, without any contribution of E-MORB or OIB components. Our results suggest that Teneme volcanism represents a primitive oceanic island arc environment. If the Late Cretaceous age (Turonian or early Coniacian) proposed for Teneme Formation is correct, our results indicate that the Cretaceous volcanic rocks of eastern Cuba and the Dominican Republic are not segments of a single arc system, and that in Late Cretaceous (Albian-Campanian) Caribbean island arc development is not represented only by calc-alkaline (CA) volcanic rocks as has been suggested in previous works.
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The Teneme Formation is located in the Mayari-Cristal ophiolitic massif and represents one of the three Cretaceous volcanic Formations established in northeastern Cuba. Teneme volcanics are cut by small bodies of 89.70 ± 0.50 Ma quarz-diorite rocks (Rio Grande intrusive), and are overthrusted by serpentinized ultramafics. Teneme volcanic rocks are mainly basalts, basaltic andesites, andesites, and minor dacites, and their geochemical signature varies between low-Ti island arc tholeiites (IAT) with boninitic affinity (TiO2 < 0.4 %; high field strength elements << N-type MORB) and typical oceanic arc tholeiites (TiO2 = 0.5-0.8 %). Basaltic rocks exhibit low light REE/Yb ratios (La/Yb < 5), typical of intraoceanic arcs and are comparable to Maimon Formation in Dominican Republic (IAT, pre Albian) and Puerto Rican lavas of volcanic phase I (island arc tholeiites, Aptian to Early Albian). The mantle wedge signature of the Teneme Formation indicates a highly depleted MORB-type mantle source, without any contribution of E-MORB or OIB components. Our results suggest that Teneme volcanism represents a primitive oceanic island arc environment. If the Late Cretaceous age (Turonian or early Coniacian) proposed for Teneme Formation is correct, our results indicate that the Cretaceous volcanic rocks of eastern Cuba and the Dominican Republic are not segments of a single arc system, and that in Late Cretaceous (Albian-Campanian) Caribbean island arc development is not represented only by calc-alkaline (CA) volcanic rocks as has been suggested in previous works.
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Northern Hokkaido is situated in the back arc region behind the arc-arc junction of the Kurile and Northeast Japan arc. The district is unique because it is located between two back-arc basins, Kurile and Japan basins. Tertiary small-scale shield-like volcanoes (flat lavas) and volcaniclastic formations are widely distributed in this district. 9 K-Ar ages and 148 major element chemistries for these volcanic rocks were determined to clarify their petrological features and tectonic evolution of this district. The newly determined and previously reported K-Ar ages indicate that the vigorous volcanic activity took place during a short period from 14 to 9 Ma in the district. Total volume of the volcanic rocks is more than 650 km3. The volume of the volcanic rocks decreases from east (Sea of Okhotsk side) to west (Japan Sea side), suggesting that the volcanism took place mainly in eastern to central part. Most of the volcanic rocks are calc-alkaline and low-K to medium-K tholeiitic andesites, common in island arc setting. However, high TiO2 andesites and icelandite-like dacites also occur along the Sea of Okhotsk. In addition, the volcanic rocks in northern Hokkaido show no systematic across-arc lateral variation in K2O content. The spatial variation in the chemical composition suggests that the Tertiary volcanism in northern Hokkaido was not caused by subduction of the Pacific plate. We presume that the volcanism was due to the episodic uprising of heat source (asthenospheric mantle?) which should be related to the opening of the Kurile basin.
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