Abstract. Tephra layers produced by volcanic eruptions are widely
used for correlation and dating of various deposits and landforms, for
synchronization of disparate paleoenvironmental archives, and for
reconstruction of magma origin. Here we present our original database
TephraKam, which includes chemical compositions of volcanic glass in tephra
and welded tuffs from the Kamchatka volcanic arc. The database contains 7049
single-shard major element analyses obtained by electron microprobe and 738
trace element analyses obtained by laser ablation inductively coupled plasma
mass spectrometry on 487 samples collected in close proximity to their volcanic
sources in all volcanic zones in Kamchatka. The samples characterize about
300 explosive eruptions, which occurred in Kamchatka from the Miocene up to
recent times. Precise or estimated ages for all samples are based on
published 39Ar∕40Ar dates of rocks and 14C dates of host
sediments, statistical age modeling and geologic relationships with dated
units. All data in TephraKam are supported by information about source
volcanoes and analytical details. Using the data, we present an overview of
geochemical variations in Kamchatka volcanic glasses and discuss applications
of these data for precise identification of tephra layers, their source
volcanoes, and temporal and spatial geochemical variations in pyroclastic rocks
in Kamchatka. The data files described in this paper are available on
ResearchGate at https://doi.org/10.13140/RG.2.2.23627.13606 (Portnyagin et
al., 2019).
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.
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