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A new genetic model for the copper mineralisation of the Polish Kupferschiefer
Published in Adam Piestrzyński, Mineral Deposits at the Beginning of the 21st Century, 2001
D.J. Blundell, D.H.M. Alderton, P. H. Karnkowski, S. Oszczepalski, V. Stroetmann-Heinen, H. Kucha
Karnkowski (1999) has described how the Polish Basin developed in the Late Permian as a group of linked sub-basins with similar subsidence and lithostratigraphic histories. The lowest units, of Autunian age, contain sandstones and si listones and are overlain by lavas and pyroclastics of a volcanic sequence. The volcanic rocks are mainly rhyolites and rhyo-dacites, but trachytes and trachy-basalts occur locally. Although the volcanics can attain a thickness of 1000 m in places (up to 2,500 m in northern Germany), in the Lower Silesian Basin they do not exceed 200 m. The volcanic sequence is overlain by conglomerates, which contain volcanic clasts indicative of localised erosion. The Autunian volcanic rocks formed in a syn-rift environment and were subjected to domino-style faulting with erosion of uplifted footwall blocks,
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
Volcanic activity at Jeju Island (33°21′40.7″N 126°31′55.5″E), to the south of the Korean Peninsula, began in the Pleistocene (c. 1.7 Ma) with submarine to subaerial eruptions intercalated with periods of quiescence and sedimentation forming the basal Seoguipo Formation (Sohn and Park 2004). This was subsequently covered by lava flows and domes erupted from dispersed vents that built a composite shield-like edifice mostly after 0.5 Ma (Brenna et al. 2015). Some of these lavas host peridotite xenoliths, such as at Sinsanri (Choi et al. 2002), where some of our samples were collected. Activity at Jeju Island continued into the Holocene, with additional peridotite xenoliths in our study coming from the youngest dated volcano, the Songaksan tuff ring, which erupted c. 3700 years BP (Sohn et al. 2015). Songaksan comprises a tuff ring with a nested scoria and spatter complex with ponded lavas. The composition within the eruption sequence ranges from trachybasalt to basaltic trachyandesite (Brenna et al. 2011, 2012).
Geology of New Zealand’s Sub-Antarctic Islands
Published in New Zealand Journal of Geology and Geophysics, 2019
James M. Scott, Ian M. Turnbull
The southern part of the Auckland Islands/Motu Maha group comprises over 700 m of stacked lava flows forming the Carnley shield volcano (Figures 11, 13A, 13B). Early descriptions by Hector (1870) and Speight and Finlayson (1909) have been amplified by Adams (1983), Adams et al. (1983), Gamble and Adams (1985), Ritchie and Turnbull (1985), Gamble et al. (1986), Gamble and Thomson (1990), and Gamble et al. (2018). The flows generally dip gently away from an inferred eruptive centre around Musgrave Peninsula (Gamble and Adams 1985), with minor eruptive centres elsewhere, such as at Fairchild's Garden. The oldest rocks are tuffs and pillow lavas intermingled with the Musgrave Formation and resting on Musgrave Granite. Well-rounded clast-supported and locally derived volcanic conglomerate beds, rarely with granitic pebbles (Adams et al. 1983), are preserved between flows (Figure 13C). There are also rare examples of inter-flow coals and carbonaceous sediments (e.g. Speight and Finlayson 1909; Ritchie and Turnbull 1985). Trachyandesite, basalt and trachybasalt compositions dominate the volcanic pile, with small volumes of trachyte and rhyolite present low in the sequence (Gamble and Adams 1985; Gamble et al. 2018). The entire volcanic succession is cut by a NE-SW trending dike swarm, which diminishes in intensity upward (Gamble and Adams 1985; Gamble et al. 2018). These dikes have compositions similar to the lava flows (Gamble et al. 2018). On McClure Head and Circular Head in the interior of Carnley Harbour, an intrusive complex of coarse grained, biotite-bearing, olivine gabbro and intimately associated minor felsic rocks including plagiogranite (Denison and Coombs 1977; Adams et al. 1983; Gamble and Adams 1985; Gamble et al. 2018; Figure 13D) was emplaced into the base of the volcanic series. K-Ar ages from two gabbroic samples of Circular Head Gabbro yield ages of 12.5–19.9 Ma but with large uncertainties (Denison and Coombs 1977).