Physical and chemical conditions of the formation and evolution of late pleistocene-holocene magmas of the Gorely and Mutnovsky volcanoes, southern Kamchatka

A detailed mineralogical and geochemical study of basic volcanic rocks from the modern edifices of the Gorely (Q₃⁴-Q₄⁴) and Mutnovsky (Q₃²-Q₄) volcanoes, as well as the results of numerical modeling with the COMAGMAT program, made it possible to estimate the role of fractional crystallization, the fluid regime, and geodynamic conditions in the petrogenesis of the studied basaltoids. The specific features of the evolution of magmas of the two volcanoes give grounds to suggest that beginning from the Late Pleistocene (Q₃⁴), all of the considered territory experienced a change in geodynamic regime, with an increasing role of extending strains in its evolution.     

Evolution stages and petrology of the Kekuknai volcanic massif as reflecting the magmatism in Backarc zone of Kuril-Kamchatka island arc system. Part 1. Geological position and geochemistry of volcanic rocks

The evolution of the Quaternary Kekuknai volcanic massif (the western flank of the Sredinnyi Range in Kamchatka) has been subdivided into five stages: (1) the pre-caldera trachybasaltbasaltic andesite, (2) the extrusive trachyandesite-trachydacite, (3) the early trachybasalt, (4) the middle hawaiitemugearite (with occasional occurrences of basaltic andesites), and (5) the late trachybasalt-hawaiitemugearite (with occasional andesites) of areal volcanism. On the basis of petrologic data we identified the island arc and the intraplate geochemical types of rocks in the massif. The leading part in petrogenesis was played by dynamics of the fluid phase with a subordinated role of fractional crystallization and hybridism. Successive saturation of rocks with the fluid phase in the course of melt evolution stopped at the time of caldera generation when most fluid mobile elements and silica had been extracted. The geological and petrologic data attest to the formation of the massif in the environment of a backarc volcanic basin during the beginning of rifting with active participation of mantle plume components.     

Transverse geochemical zonality: The Karymskii Volcanic Center

Variation in the geochemical characteristics of basalts has been found within the Karymskii Volcanic Center (KVC). The concentrations of potassium, titanium, phosphorus, large-cation, high-charge, rare and rare-earth elements increase from the frontal zone (Pribrezhnyi Yuzhnyi, Stena, Paleo-Semyachik and Malyi Semyachik, and Ditmara volcanoes) toward the backarc zone (Odnobokii, Pra-Karymskii, and Akademii Nauk volcanoes). High ratios of fluid-mobile elements to non-mobile ones in the basalts of the frontal zone provide evidence of low-temperature aqueous fluids being involved in magma generation, with these fluids separating from the subducted oceanic plate at low pressures. The backarc zone typically shows higher Th/Nd and Th/Yb ratios, suggesting high-temperature fluids that take part in magma generation with increasing depth (and increasing temperature) as far down as the top of the subducted plate. The variation in the geochemical characteristics of the KVC basalts from the frontal to the backarc zone is less pronounced than that in the lavas of Mutnovskii and Gorelyi volcanoes in southern Kamchatka. These differences may be related to the geodynamic parameters of the subduction zone in the East Kamchatka and the South Kamchatka segments of the Kamchatka island arc, primarily to the dip angle of the Benioff zone, the distance to the trench axis, the subduction age, and possibly to heterogeneities in the mantle wedge beneath the KVC.     

The Karymskii Volcanic Center: Volcanic rock geochemistry

This paper is concerned with the petrology and geochemistry of rocks found in the Karymskii Volcanic Center (KVC), which is the largest volcanic center in the Eastern volcanic belt of Kamchatka. The KVC has been built in a rhythmic manner since the Late Pliocene, forming successive differentiated rock complexes. The pattern of variation for major and minor elements in the KVC volcanic rocks can be explained by the fractionation of mineral phases from the parent melt. The process involved enrichment of the residual melts with alkalis and lithophile elements (Rb, Ba, Sr, Pb, Th, U, REE), as well as depletion in coherent elements (Ni, Cr, Sc, Ti). A geochemical study of the KVC volcanic rocks shows that these are typical island arc formations. The relationships between incompatible elements suggest a two-component magma generation system: a depleted mantle source (N-MORB) and suprasubduction fluids (an island arc component). The melt may have been contaminated by a metasomatically altered substratum in the top of the intermediate chamber with added crystalline cumulus phases (and melts) of the earlier magma generation phases in the KVC.     

Sources of Eocene Magmatism in Western Kamchatka by the Geochemical and Sr–Nd–Pb Isotope Characteristics of Basites

Doklady Earth Sciences - The isotope and geochemical characteristics of Eocene–Oligocene igneous rocks of Western Kamchatka were studied. It was shown that igneous rocks of the Eocene Kinkil...     

Neogene basanites in western Kamchatka: Mineralogy,geochemistry, and geodynamic setting

Neogene (N ₁ ² -N ₂ ¹ ?) K-Na alkaline rocks were found in western Kamchatka as a subvolcanic basanite body at Mount Khukhch. The basanites have a microphyric texture with olivine phenocrysts in a fine-grained doleritic groundmass. The olivine contains inclusions of Al-Cr spinel. The microlites consist of clinopyroxene, plagioclase, magnetite, and apatite, and the interstitial phases are leucite, nepheline, and analcime. The Mount Khukhch basanites are characterized by elevated concentrations of MgO, TiO₂, Na₂O, and K₂O, high concentrations of Co, Ni, Cr, Nb, Ta, Th, U, LREE (La_N/Yb_N = 10.8?12.6, Dy_N/Yb_N = 1.4?1.6) at moderate concentrations of Zr, Hf, Rb, Ba, Sr, Pb, and Cu. The values of indicator trace-element ratios suggest that basanites in western Kamchatka affiliate with the group of basaltoids of the within-plate geochemical type: Ba/Nb = 10?12, Sr/Nb = 17?18, Ta/Yb = 1.3?1.6. The basanites of western Kamchatka show many compositional similarities with the Miocene basanites of eastern Kamchatka, basanites of some continental rifts, and basalts of oceanic islands (OIB). The geochemistry of these rocks suggests that the basanite magma was derived via the ～6% partial melting of garnet-bearing peridotite source material. The crystallization temperatures of the first liquidus phases (olivine and spinel) in the parental basanite melt (1372–1369°C) and pressures determined for the conditions of the “mantle” equilibrium of the melt (25–26 kbar) are consistent with the model for the derivation of basanite magma at the garnet depth facies in the mantle. The geodynamic environment in which Neogene alkaline basaltic magmas occur in western Kamchatka was controlled by the termination of the Oligocene—Early Miocene subduction of the Kula oceanic plate beneath the continental margin of Kamchatka and the development of rifting processes in its rear zone. The deep faulting of the lithosphere and decompression-induced magma generation simultaneous with mantle heating at that time could be favorable for the derivation of mantle basite magmas.     

Large-volume silicic volcanism in Kamchatka: Ar–Ar and U–Pb ages,isotopic, and geochemical characteristics of major pre-Holocene caldera-forming eruptions

The Kamchatka Peninsula in far eastern Russia represents the most volcanically active arc in the world in terms of magma production and the number of explosive eruptions. We investigate large-scale silicic volcanism in the past several million years and present new geochronologic results from major ignimbrite sheets exposed in Kamchatka. These ignimbrites are found in the vicinity of morphologically-preserved rims of partially eroded source calderas with diameters from ～ 2 to ～ 30 km and with estimated volumes of eruptions ranging from 10 to several hundred cubic kilometers of magma. We also identify and date two of the largest ignimbrites: Golygin Ignimbrite in southern Kamchatka (0.45 Ma), and Karymshina River Ignimbrites (1.78 Ma) in south-central Kamchatka. We present whole-rock geochemical analyses that can be used to correlate ignimbrites laterally. These large-volume ignimbrites sample a significant proportion of remelted Kamchatkan crust as constrained by the oxygen isotopes. Oxygen isotope analyses of minerals and matrix span a 3‰ range with a significant proportion of moderately low-δ¹⁸O values. This suggests that the source for these ignimbrites involved a hydrothermally-altered shallow crust, while participation of the Cretaceous siliceous basement is also evidenced by moderately elevated δ¹⁸O and Sr isotopes and xenocryst contamination in two volcanoes. The majority of dates obtained for caldera-forming eruptions coincide with glacial stages in accordance with the sediment record in the NW Pacific, suggesting an increase in explosive volcanic activity since the onset of the last glaciation 2.6 Ma. Rapid changes in ice volume during glacial times and the resulting fluctuation of glacial loading/unloading could have caused volatile saturation in shallow magma chambers and, in combination with availability of low-δ¹⁸O glacial meltwaters, increased the proportion of explosive vs effusive eruptions. The presented results provide new constraints on Pliocene–Pleistocene volcanic activity in Kamchatka, and thus constrain an important component of the Pacific Ring of Fire.