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Igneous Petrology and the Nature of Magmas
Published in Dexter Perkins, Kevin R. Henke, Adam C. Simon, Lance D. Yarbrough, Earth Materials, 2019
Dexter Perkins, Kevin R. Henke, Adam C. Simon, Lance D. Yarbrough
The occurrence of rhyolite and basalt, without rocks of intermediate composition, is termed bimodal volcanism. Bimodal volcanism is often associated with rifts in Earth’s continental crust which, given enough time, may become the sites of new oceans. Bimodal volcanism is also commonly associated with hot spots where upwelling heat rises from the mantle as a thermal plume that can cause melting and so produce volcanism. The Yellowstone region is characterized by both rifts and a major hot spot.
Geochemical patterns of late Cenozoic intraplate basaltic volcanism in northern New Zealand and their relationship to the behaviour of the mantle
Published in New Zealand Journal of Geology and Geophysics, 2021
Ian E. M. Smith, Shane J. Cronin
Fifty kilometres to the south of the Whangarei Field are the Ti Point basalts a part of the Miocene bimodal volcanism linked to the migrating arc; these have clear arc-type affinities (Smith et al. 1993; Huang et al. 2000). The various chemical signatures and their spatial relationships can be reconciled if the mantle source beneath Northland is made up of a primary mantle component (KBIVF signature) together with a minor subduction modified component (Ti Point signature). We suggest that as subduction and its associated volcanic arcs migrated southward in response to late Tertiary plate readjustments, mantle flowed in from the north to replace that beneath the northern part of the peninsula. This flow would be enhanced by continued subduction and slab roll back associated with the development of subduction-related volcanism initially as the Coromandel Arc and then as the Taupo Volcanic Zone of the central North Island. The Whangarei field marks the southern limit to influx of new mantle material. Beneath Whangarei subduction-modified mantle mixed with incoming unmodified mantle and volcanism began later than in the KBIVF to produce the observed differences between the two Northland fields. The development of a Nb anomaly in the WVF volcanoes is an indication of a subduction zone component in its source. To the south, subduction-modified mantle supplied basaltic magma to the bimodal complexes that developed as the arc migrated southward.
Two belts of HTLP sub-regional metamorphism in the New England Orogen, eastern Australia: occurrence and characteristics exemplified by the Wongwibinda Metamorphic Complex
Published in Australian Journal of Earth Sciences, 2020
K. Jessop, N. R. Daczko, S. Piazolo
The similarities between the Early-Permian Inland Belt HTLP occurrences and those of the Mid-Permian Coastal Belt, together with bimodal volcanism indicative of extension, imply that a zone of rifting was active along the Coastal Belt. All HTLP occurrences are located within the Shoalwater Formation, the youngest units of the Carboniferous accretionary complex and likely the last part to be affected by eastwards-migrating rifting. Metamorphism related to extension (ca 280–270 Ma) occurred during the last stages of the relax phase of the NEO. Subsequent typical extensional bimodal volcanism (ca 269–262 Ma) overlaps with the estimated beginning of Hunter-Bowen phase compression in this area (Hoy & Rosenbaum, 2017; Hoy, Rosenbaum, Mortimer, & Shaanan, 2018; Rosenbaum, Slade, & Hoy, 2020). Extension may have remained active after the initiation of subduction zone advance perhaps due to the presence of oroclines in the SNEO creating torsional stresses in the NNEO.
Sedimentary basin formation associated with a silicic large igneous province: stratigraphy and provenance of the Mesoproterozoic Roopena Basin, Gawler Range Volcanics
Published in Australian Journal of Earth Sciences, 2018
The best is parallel to the Roopena Basin occurs beneath cover at Prominent Hill, where a high energy fluvio-lacustrine succession was deposited synchronous with bimodal volcanism (Belperio et al., 2007; Bull et al., 2015). At Prominent Hill the sedimentary succession comprises a fining upwards sequence of sandstone, greywacke, siltstone and dolomitic limestone, interlayered with andesitic lavas, and intruded by andesitic dykes and sills (Bull et al., 2015). This sedimentary succession is interpreted to have been deposited in an east–west-trending fault-bound graben, in which fault movement occurred synchronous with sedimentation, volcanism and mineralisation (Belperio et al., 2007). Similar sedimentary facies occur at Olympic Dam, including mudstone, sandstone and polymictic volcaniclastic conglomerate (McPhie et al., 2011, 2016). These sedimentary facies occur within the Olympic Dam Breccia Complex and are interpreted to represent the relicts of a syn-Gawler Range Volcanics sedimentary basin, possibly bound by regional northeast- and northwest-striking faults (McPhie et al., 2016).