Isotopic and Petrologic Investigation, and a Thermomechanical Model of Genesis of Large-Volume Rhyolites in Arc Environments: Karymshina Volcanic Complex, Kamchatka, Russia

Abstract

The Kamchatka Peninsula of eastern Russia is currently one of the most volcanically active areas on Earth where a combination of >8 cm/yr subduction convergence rate and thick continental crust generates large silicic magma chambers, reflected by abundant large calderas and caldera complexes. This study examines the largest center of silicic 4-0.5 Ma Karymshina Volcanic Complex, which includes the 25 × 15 km Karymshina caldera, the largest in Kamchatka. A series of rhyolitic tuff eruptions at 4 Ma were followed by the main eruption at 1.78 Ma and produced an estimated 800 km 3 of rhyolitic ignimbrites followed by high-silica rhyolitic post-caldera extrusions. The postcaldera domes trace the 1.78 Ma right fracture and form a continuous compositional series with ignimbrites. We here present results of a geologic, petrologic, and isotopic study of the Karymshina eruptive complex, and present new Ar-Ar ages, and isotopic values of rocks for the oldest pre-1.78 Ma caldera ignimbrites and intrusions, which include a diversity of compositions from basalts to rhyolites. Temporal trends in δ 18 O, 87 Sr/ 86 Sr, and 144 Nd/ 143 Nd indicate values comparable to neighboring volcanoes, increase in homogeneity, and temporal increase in mantle-derived Sr and Nd with increasing differentiation over the last 4 million years. Data are consistent with a batholithic scale magma chamber formed by primarily fractional crystallization of mantle derived composition and assimilation of Cretaceous and younger crust, driven by basaltic volcanism and mantle delaminations. All rocks have 35-45% quartz, plagioclase, biotite, and amphibole phenocrysts. Rhyolite-MELTS crystallization models favor shallow (2 kbar) differentiation conditions and varying quantities of assimilated amphibolite partial melt and hydrothermally-altered silicic rock. Thermomechanical modeling with a typical 0.001 km 3 /yr eruption rate of hydrous basalt into a 38 km Kamchatkan arc crust produces two magma bodies, one near the Moho and the other engulfing the entire section of upper crust. Rising basalts are trapped in the lower portion of an upper crustal magma body, which exists in a partially molten to solid state. Differentiation products of basalt periodically mix with the resident magma diluting its crustal isotopic signatures. Bindeman et al. Isotopic and Thermomechanical Model of Karymshina Caldera At the end of the magmatism crust is thickened by 8 km. Thermomechanical modeling show that the most likely way to generate large spikes of rhyolitic magmatism is through delamination of cumulates and mantle lithosphere after many millions of years of crustal thickening. The paper also presents a chemical dataset for Pacific ashes from ODDP 882 and 883 and compares them to Karymshina ignimbrites and two other Pleistocene calderas studied by us in earlier works.

TephraKam: geochemical database of glass compositions in tephra and welded tuffs from the Kamchatka volcanic arc (northwestern Pacific)

“…Holocene tephra layers mantle the topography and, being interlayered with paleosol or peat horizons, form a sequence that provides a nearly continuous record of the Holocene explosive activity (e.g., Bazanova and Pevzner, 2001;Braitseva et al, 1998Braitseva et al, , 1996Braitseva et al, , 1995Braitseva et al, , 1997Kyle et al, 2011;Pevzner, 2010;Pevzner et al, 1998;Ponomareva et al, 2015aPonomareva et al, , b, 2017. Earlier pre-Holocene pyroclastic products are mostly ignimbrite (pumiceous or welded tuffs), which survived through glacial stages better than loose pyroclastics and in many cases experienced alteration (Bindeman et al, 2019(Bindeman et al, , 2010Ponomareva et al, 2018;Seligman et al, 2014). These deposits are partly eroded by glacial processes, buried by younger deposits, and/or covered with dense vegetation, which hampers their identification.…”

“…Knowledge of tephra ages (or at least approximate age ranges) is crucial for their use as marker horizons. For many tephras in our database, the age estimates are available from published data (Auer et al, 2009;Bazanova and Pevzner, 2001;Bazanova et al, 2019;Bindeman et al, 2019Bindeman et al, , 2010Braitseva et al, 1998Braitseva et al, , 1991Braitseva et al, , 1995Churikova et al, 2015;Cook et al, 2018;Dirksen, 2009;Dirksen and Bazanova, 2009;Dirksen and Melekestsev, 1999;Florensky, 1984;Kozhurin et al, 2006;Masurenkov, 1980;Melekestsev et al, 1992Pevzner, 2015;Plechova et al, 2011;Ponomareva et al, 2018Ponomareva et al, , 2013bPonomareva et al, , 2017Ponomareva et al, , 2015bPonomareva et al, , 2006Ponomareva, 1990;Seligman et al, 2014;Volynets et al, 1998;Zaretskaia et al, 2001;Zaretskaya et al, 2007;Zelenin et al, 2020). In this case, we report bibliographical references and details on the age estimates and dating techniques.…”

“…One Holocene tephra (KHG from Khangar vol-cano) was found in the Greenland ice and dated with the help of the Greenland Ice Core Chronology 2005 (GICC05, Cook et al, 2018;Rasmussen et al, 2006;Vinther et al, 2006). A total of 21 welded tuff units were dated by 39 Ar/ 40 Ar (Bindeman et al, 2019(Bindeman et al, , 2010Seligman et al, 2014). For undated samples, the age estimates were derived from their stratigraphic relationships with the dated ones.…”

Stratigraphy, structure and geology of Late Miocene Verkhneavachinskaya caldera with basaltic-andesitic ignimbrites at Eastern Kamchatka

“…The 40 Ar/ 39 Ar dating of groundmass in the ignimbrite samples was performed at the University of Wisconsin-Madison Rare Gas Geochronology Lab (B. Jicha, analyst) under the framework of a joint project for the study of large-volume caldera-forming eruptions in Kamchatka (Bindeman et al 2010(Bindeman et al , 2019. In order to estimate the age of early stage of caldera-forming eruptions we analyzed the lowermost ignimbrite layers (01L-2009, 25L-2009) in outcrops (Fig.…”

TephraKam: Geochemical database of glass compositions in tephra and welded tuffs from the Kamchatka volcanic arc (NW Pacific)

“…Bazanova and Pevzner, 2001; Braitseva et al, 1998;Braitseva et al, 1996;Braitseva et al, 1995;Braitseva et al, 1997;Kyle et al, 2011;Pevzner, 2010;Pevzner et al, 1998;Ponomareva et al, 2015a;Ponomareva et al, 2017;Ponomareva et al, 2015b). Earlier, pre-Holocene pyroclastic products are mostly ignimbrite (pumiceous or welded tuffs), which survived through glacial stages better than loose pyroclastics and in many cases experienced alteration (Bindeman et al, 2019;Bindeman et al, 2010;Ponomareva et al, 2018;Seligman et al, 2014). These deposits are partly eroded by glacial processes, buried by younger deposits, and/or covered with dense vegetation, which hampers their identification.…”