Pleistocene-Holocene Monogenetic Volcanism at Malko-Petropavlovsk Zone of Transverse Dislocations on Kamchatka: Geological Setting, Spatial, Geochemical Paticular Features and Potential Volcanic Hazards


 Based on government statistical data ~80% of the local Kamchatkan population (~250 ka people) live in the major cities on the coastal line of Avacha Gulf . It is the main transport seaway to Kamchatka , and and important Asia - North America air transport corridor. The Avacha Gulf is located in the Malko-Petropavlovsk zone of transverse dislocations (MPZ) on the extension of deep transform fault on the boundary between various ly aged slabs. Most of monogenetic cinder cones chaotic distributed in relation to the trench and belong to the long-living rupture zones of MPZ. Some of the monogenetic volcanoes are parasitic cones on the slopes of Koryaksky and Avachinsky stratovolcanoes and related with their magma plumbing systems. We here present new results of the geochemical and isotopic stud ies of monogenetic volcanism in MPZ. Based on whole rock and trace element geochemistry, Sr-Nd-Pb isotopic ratios of monogenetic volcanism, ­­ magmas were shown to sample the enriched mantle source with dominance decompression melting without significant inputs of the slab`s components. Calculations of the P, T conditions suggest magma residence of monogenetic cinder cones on the Moho boundary. That correlates with the geophysical observation of crustal discontinuity under the MPZ. Monogenetic cinder cones have an active magma plumbing system because during the Holocene time were several periods of activations. Presented results show necessary install continuous monitoring of environment changing around the Avacha Gulf and more serious attention from government and science. A more detailed investigation of MPZ will help degrease potential risks of eruptions from monogenetic volcanoes for human and infrastructures.


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The volcanism in island arcs settings is a dominant mechanism for formation crust in continental margins. Since    (Nurmukhamedov, Sidorov, 2019). The high heat flow (~80 mVt/m 2 ) measurements in MPZ, while in the surrounding area is 40-93 60 mVt/m 2 (Sugrobov, Yanovsky, 1991). The finding of alkalic and sub alkalic rock in the frontal zone in MPZ enabled some of 94 the researchers to suggest about unusual subduction origin of the Miocene magmas (Mitichkin et al., 1998;Baluev et al., 1984; 95 Sheimovich et al., 2005).

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Volcanism in MPZ occurs in two types: along the polygenic stratovolcanoes with parasitic cones on the slopes and 97 numerous independent monogenetic cinder cones, e.g. extrusive domes (Fig. 2b, 3d)  Koryaksky and Avachinsky volcanoes with known historic eruptions and volcanoes Kozelsky, Vilyuchinsky volcanoes without 99 known historic eruptions. Most of the cinder cones concentrate in Paratunka and Bolshoy Vilyui rivers valleys (Fig. 1b, 2a, 3).  2009). In the south part of Avacha Gulf is an isolated island near Vilyuchinsk city (Fig. 1, 2c). This is a cinder cone with basaltic 05 magmas. Volume of the cone is less than 3-4 km 3 (Dubik, Ogorodov, 1970). Cinder cones on the north of Avacha Gulf are 06 parasitic cones of Koryaksky and Avachinsky volcanoes (Fig. 1). Only one isolated cinder cone located on the beach near 07 Petropavlovsk-Kamchatsky city. According to personal communication with Melekestsev I.V., in the mid-1970 years, it was some 08 activity fixed there. People felt gas emission and heard some crackles. Not surprising, this cinder cone located mainly on the 09 regional fault (Fig. 1b). This regional fault is a margin of the Avachinsky graben (Fig. 1c, 13) and well detected by geophysical 10 data (Nurmukhamedov, Sidorov, 2019), basement heterogenity (Sheimovich, Sidorov, 2000), geological observations (Aprelkov

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Extrusive domes mainly localized on the north of MPZ. One of the best examples is Mishennaya (Target) Mountain ( Fig.   13 2b, 3d). It is the extrusive dome with a diameter in the basement ~ 1 x 2 km (Sheimovich et al., 2007). It is a landmark hill with 14 385 m in altitude in downtown Petropavlovsk-Kamchatsky city with a viewpoint and TV station, while its slopes are covered with 15 residential and government buildings (Fig. 2 d). Areal extent of the Mishennaya dome is estimated as 0,3 km 2 (Grib, 1985). The  intrusion (Grib, 1985). Age of the Mishennaya Mountain according to fission-track analyses is 700±200 ka (Geological map., 19 2000) and 600±200 ka was obtained by K-Ar dating of hornblendes (Sheimovich et al., 2007 identified under the water on the north part of the Avacha Gulf (Dmitriev, Ezhov, 1977). We therefore indicate that a simple 27 compilation of existing data for domes similar to Mt. Mishennaya identify their wide-spread abundance requiring dedicated effort 28 to determine their age, mode of emplacement and composition, as well as relation (or lack of it) to the other stratovolcanoes in the 29 area, an attempt that we initiate in this study.

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In this study, we have collected ~35 samples of Pleistocene-Holocene magmatic rocks. The sampling localities are shown

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The whole-rock chemistry was studied on an Axios mAX vacuum wavelength dispersive XRF spectrometer 38 (PANalytical Company (Netherlands)) at the Analytical center IGEM. The measurement accuracy was controlled by international uncertainties were estimated from the systematic analysis of the BHVO-2, AGV-2 rocks and calculated less than 10%.

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The high-precision MC-ICP-MS method (Rekhämper, Halliday, 1998) was used in this study for analysis of Pb isotope 44 compositions in volcanic rocks, using the approach described in detail (Chernyshev et al., 2007). Analyses of Pb isotope ratios 45 were carried out on a NEPTUNE mass-spectrometer (Thermo Scientific, Germany) at the Laboratory of Isotope Geochemistry 46 and Geochronology IGEM. For analysis, 0.04-0.06 g of the whole rock powder was taken. Samples were dissolved in an HNO 3 + HF (1: 3) mixture for two days at 140° C. Subsequently, the solution was evaporated to dry salts. Separation of Pb from major and

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The Nd-Sr isotopic studies were carried out using a Sector 54 mass-spectrometer (Micromass), using a multi-dynamic mode       To check the role of the km slab depth) and Avachinsky (~94 km slab depth) and Koryaksky (~107 km slab depth) are tracing arc perpendicular structure 80 (Fig. 4). Extrusive domes mainly are on the northern part of MPZ. Cinder cones focus on distance on 190 km and more to the 81 trench. Locations are chaotic and not dependent on the slab. But most of the cinder cones are concentrated on the southern part of 82 MPZ. One cinder cone is located on the Khalaktyrsky beach, on the marked boundary of Avachinsky graben (Fig. 1 b).

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Geochronology for monogenetic cones is in urgent need for radiogenic dating. Current knowledge is based on relationship 84 with geological suites and tephrachronology. All stratovolcanoes in MPZ start formed at least since the Late Pleistocene and were      normalised patterns of rare earth elements, the Eu anomalies are not observed (Fig. 9). The heavy REE elements with smaller 24 ionic radius (e.g. Lu, Yb, Tm, Er) are near the same for all the rocks. In opposite are a slight enrichment of La, Ce, Pr, Ns, Sm for 25 monogenetic cinder cones (Fig. 9a), Koryaksky (Fig. 9d) and Vilyuchinsky (Fig. 9 c) stratovolcanoes.

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The Sr-Nd isotopic ratios vary within narrow ranges (Fig. 10 a). Monogenetic extrusive dome shows similar variations as ratios, as variated 87 Sr/ 86 Sr isotopic ratios. The lower 143 Nd/ 144 Nd isotopic ratios could be interpreted as a contents slightly enrichment 31 mantle component, like E-MORB (Fig. 10 a). The lead isotopic composition is the same as for rocks from the East volcanic belt 32 and Southern Kamchatka (Fig. 10 b). The coefficient of variations for Pb isotopic ratios estimated as a ν (%) are: ν6/ 4 = 0.29, ν7/ 4 = 33 0.14 и ν8/ 4 = 0.20%. The variations are relatively small, but are almost an order higher than the analytical error. Various aged rocks    (Fig. 2). The elevated points offer recreational opportunities and vistas for the city, bay and 69 the ocean. Cinder cones on the coastline are quaried as road and construction material to build roads and structures, for example 70 the fish processing plants. One monogenetic cinder cones near the Vilyuchinsk city is a large factory specialising in the 71 development of gravels and sands.

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The elevated grounds of local cinder cones provide shelter and escape routes for potential tsunami. This is especially 73 important, because last ~4200 years were observed 33 tsunamis records on Khalaktyrsky beach (Pinegina et al., 2018).

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The energy cone simulation results suggest that if the current monogenetic volcanoes would be active again, it would be 90 produce block and lava flows. This is especially important for area with red color (H/L>0.21) (Fig. 11 b). However, risks of 91 potential volcanic hazard would be distributed on the distance more than 10 km (pale pink color). The highest risks of potential 92 volcanic dangerous are valley of Paratunka river, because there are the highest concentrations of monogenetic cinder cones ( Fig.   93 11 b). The closest villages are Paratunka and Termalny with total population ~ 3700 men (Fig. 11 a). But in the valley of 94 Paratunka river located development resorts with tourists and visitors. Additionally, along the Paratunka river is road, which is  ocean. These places have risks from magma-water interaction and it would be important because there are setlements and fish-03 cathers companies (Fig. 11 b).

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This work presented rich new analytical dataset for monogenetic volcanoes in an attempt to determine their origin. We 07 interpret these data because it has direct implications on potential characher of magmatic eruptions.

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Fluid-immobile elements are good indicators of the extent of melting process in the mantle wedge, as well as the degree of its 09 prior melting/enrichment. The biggest Nb-Ta minimums of the monogenetic cinder cones on spider diagrams indicate a different from an N-MORB type of mantle. It is a good correlate with Sr-Nd isotopic ratios (Fig. 10 a, b), where monogenetic cinder cones localized in the rear arc and characterized by higher contents of rare earth elements (Fig. 9 d). Simultaneously, the frontal 20 volcanoes are Avachinsky and Kozelsky have rocks with significant variations of La, Ce, Sm and etc (Fig. 9 e, f). This data cannot 21 be explained by classical across-arc magma variations formed by different degrees of partial melting of an uniform mantle. In order to check melting regime we used ratios of La/Yb, Ba/La, Nb/Yb (Fig. 13). Maximum La/Yb correlate with minimum Ba/La 23 content for monogenetic volcanoes (Fig. 13a), which made difference from polygenetic volcanoes. Together changes of Nb/Ta 24 and Ta and the highest contents indicate for decompression melting for monogenetic volcanoes (Fig. 13 b). Variations of fluid-25 immobile (Fig. 14 a, b) and mobile elements (Fig. 14 c, d) versus to distance to trench not show classical across arc variations.

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From the front to rear zone degrease contents of Nb and Ta (Fig. 14 a, b), but contents of Ba, Th (Fig. 14 c, d)     Th/Nd (Fig. 12 c, d) and 206 Pb/ 204 Pb ratios (Fig. 10 c, d) suggest sedimentary melts under the Koryaksky stratovolcano. This is a 37 common feature for rear arc volcanoes. In opposite, frontal volcanoes, e.g. Avachinsky, Kozelsky, and Mishennaya extrusive 38 dome, have the higher Ba/Nb, Sb/Nb ratios (Fig. 12 c, d). These testify for significant input of the shallow slab component, e.g.     16). The absence of peripheral, shallow magma chambers suggests feeding of these deep reservoirs by regional faults (Fig. 1) that 52 control the distribution of volcanism. Such faults were observed near the Vilyuchinsky volcano (Florensky, Bazanova, 1989; observations on one of the active fault near the Petropavlovsk-Kamchatsky city ork were registered energy, i.e. seismicity and 57 "superintensive fault movements" along the fault (Churikov, Kuzmin, 1998

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The authors declare that they have no conflict of interest.

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All authors contributed to the study conception and design. OB-K wrote the original draft. IB reviewed and edited the draft.

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CA prepared lead isotopes and improved interpretation of isotopic data. LY estimated Sr-Nd isotopic ratios. PA obtained trace 89 elements geochemistry. KO worked with geophysical data and organized field works.             Modelling of hazards from monogenetic volcanoes.: a infrastructures, main cities with human density are shown; b An energy-cone simulation result of monogenetic volcanism based on volcanic hazards assessment support system (Takarada, 2017). H/L is a ratio of relative height (H) and lateral travel distance of the volcanic gravity ow (L). More details for modelling parameters are in the text and Takarada (2017). Note: The designations employed and the presentation of the material on this map do not imply the expression of any opinion whatsoever on the part of Research Square concerning the legal status of any country, territory, city or area or of its authorities, or concerning the delimitation of its frontiers or boundaries. This map has been provided by the authors.     The designations employed and the presentation of the material on this map do not imply the expression of any opinion whatsoever on the part of Research Square concerning the legal status of any country, territory, city or area or of its authorities, or concerning the delimitation of its frontiers or boundaries. This map has been provided by the authors.