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Debris Fan Produced by Failure of Canyon-Blocking pyroclastic flows

Journal of Water Resource and Protection 2024年第5期16卷 328-360页

作者： Michael L. Cummings Department of Geology Portland State University Portland Oregon USA

Ash-rich pyroclastic flows from the cataclysmic eruption of Mount Mazama (~7700 yr. B. P.), Cascade volcanic arc, Oregon, entered and blocked the narrow, bedrock-lined canyon of the Williamson River approximately 35 to 44 km from the source volcano. The blockage impounded a body of water which then released producing four stratigraphic units in the downstream debris fan. The four stratigraphic units are a boulder core comprised of locally sourced bedrock boulders and three sand-rich units including a fine-grained sand unit, a sandy pumice gravel (±basalt/hydrovolcanic tuff) unit, and a pumice pebble-bearing, crystal-rich sand unit. Hand-drilled auger holes up to ~1.6 m deep were used to obtain samples of the sand-rich units. Units were delimited using surface and down-hole observations, composition and texture, estimated density, statistical parameters of grain size, and vertical and lateral distribution of properties. Overtopping followed by rapid incision into the ash-rich pyroclastic flows progressively cleared the canyon, but a bedrock knickpoint near the head of the canyon limited the volume of debris available for transport to about 0.04 km3 to 0.08 km3. Co-deposition of bedrock boulders and lithic-rich sand was followed by rapid deposition with minimal reworking of remobilized pyroclastics. Continued draining of the impounded lake sent hyperconcentrated flows onto the debris fan depositing pumice-rich gravels that graded upward to crystal-rich sands.

关键词： Outburst Flood Mount Mazama Debris Fan Canyon Blockage pyroclastic flows

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Constraints on unconsolidated pyroclastic flow sediments related REE enrichments originated from potassic-alkaline Gölcük stratovolcano: Darıdere-Direkli-Yakaören (DDY) table 4deposits, southwestern Anatolia of Turkey

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Acta Geochimica 2021年第6期40卷 926-944页

作者： Murat Budakoglu Ali Tugcan Unluer Zeynep Doner Huseyin Kocaturk Mustafa Kaya Mustafa Kumral M.Sezai Kirikoglu Department of Geological Engineering Faculty of MinesIstanbul Technical UniversityIstanbulTurkey

In the last five decades,Rare Earth Elements(REE)are mostly produced from carbonatite complexes and alkaline magmatic *** this respect,pyroclastic flows produced by the potassic-alkaline Gölcük volcanism in the Isparta(SW,Turkey)angle stand out as an important target area where REE enrichments can be *** study focuses on the REE potential,geochemical and mineralogical characteristics of REE-bearing minerals as well as formation modeling of unconsolidated pyroclastic flows in Darıdere-Direkli-Yakaören(DDY)deposits in ***-bearing minerals of DDY deposits which contain abundant trachytic-trachyandesitic rock fragments were determined as fluorapatite,britholite,and chevkinite by using XRD and SEM–EDX *** to the geochemical analysis,the vast majority of RREE(up to 996 ppm)content is LREE such as La,Ce and ***ıdere is the most REE enriched region followed by Yakaören and Direkli regions in terms of LREE(574.9 ppm),relative to MREE(38.5 ppm)and HREE(5.28 ppm)*** results are also on par with subduction-related Italian extrusive carbonatites such as Polino,Cupaello and San *** DDY deposits can also be comparable with intraplate extrusive REE deposits in terms of LREE enrichments,however,HREE,Nb,Th and Zr values are generally *** RREE concentrations tend to rise with the increasing contents of alkaline elements(Na and K),HFSE(such as Nb and U),as well as LILE(Ba,Sr and Rb)and are negatively affected by sedimentary carbonate *** economic value of the DDY deposits can gain importance due to the increasing global demand for LREE’s.

关键词： pyroclastic flows Rare Earth Elements(REE) Apatite Britholite Chevkinite Alkaline-Ultrapotasic magmatism

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