G. Wörner - Academia.edu (original) (raw)

Papers by G. Wörner

Polarforschung, 1987

Sections through Shield Nunatak vo1cano, an alkali basaltic subglacial table-mountain from the Mt... more Sections through Shield Nunatak vo1cano, an alkali basaltic subglacial table-mountain from the Mt. Melbourne Volcanic Field, are descrlbed. Resting on a base of older lava flows and a fossile tillite iayer, the volcano is formed mainly by massive ash and lapilli (mass flow) deposits while pillow lavas are absent. The recurrent stage of emergence from subglacial to subaerial conditions is characterized by development of tuff rings from explosive interaction between magma and melt water, complex ash-and lapilli deposits, including lava flows brecciated by water-interaction and a subaerial basaltie ash-flow deposit. The sequence is capped by subaerial tuff rings, lava flows, scoria cones and reworked tephra. Available data on subaquatlc explosive voJcanism indicate that early Shield Nunatak basaltic lavas erupted under less than 300 m of ice cover: later Iavas erupted under shallow-water and subaerial conditions. Shield Nunatak probably formed during a glacial period (possibly the last) when the ice thtckness in the Mt. Melbourne area must have been at least 200 m greater than at present. The volcano has suffered only minor glacial erosion and still almost has its original shape. Zusammenfassung: Es werden Profile beschrieben durch einen alkalibasaltischen subglazialen Vulkan (Shield Nunatak) im Mt. Melbourne Vulkanfeld. Die Unterlage des Vulkans wird von einer Serie subaerischer Lavaströme intermediärer Zusammensetzung (Mugearit) gebildet. Über einer Lage von Paleo-Till bilden massive Aschenablagerungen die Basis der subglazialen Sequenz. Kissenlaven fehlen. Der Wechsel von subglazialen (subaquatischen) zu subaerischen Eruptionsbedingungen , d. h. das Stadium in dem der Vulkan bau über den Wasserspiegel hinausreichte, wird gekennzeichnet durch Tuffring-Ablagerungen, brecciierte Lavaströme und einen Aschenstrom. Diese vulkanischen Lockerprodukte entstanden durch die explosive Wechselwirkung zwischen flachem Wasser und Lava. Die Eruptionsfolge wird abgeschlossen durch subaerische Oberflächeneruption von Basaltschlacken und Lavaströmen. Betrachtungen über die explosiven Fragmentierungsprozesse in Abhängigkeit verschiedener Parameter (Magmatyp, Wassertiefe. etc.) deuten an, daß die Paleo-Bisdicke zur Zeit der Eruptionen des Shleld Nunatak (möglicherweise während der letzten Vereisungsphase) mindestens etwa 300 Meter betragen haben muß, ca. 200 Meter höher als heute. Der Vulkanbau hat nur wenig glaziale Erosion erlitten und hat heute noch nahezu seine ursprüngliche Ausdehnung.

Anales del Instituto de la Patagonia, 2013

Terrace systems indicate that the Seno Otway and Skyring, and the Última Esperanza fjord formed t... more Terrace systems indicate that the Seno Otway and Skyring, and the Última Esperanza fjord formed the largest interconnected proglacial lake system of southern Patagonia (5700 km 2) during the early deglaciation (<18 to 14 kyr BP). It drained through the eastern Seno Otway towards the Atlantic. The retreat of glaciers from the Jerónimo Channel at around 14.0 cal kyr caused a mega outflow event (320 km 3) which lowered the Seno Otway lake level by 95 m and initiated a marine transgression as well as an intensive long term erosion of newly exposed shore lines around the Seno Otway. Between 11 to 10 kyr BP a more limited marine transgression occurred to the eastern sector of Seno Skyring, probably through the Gajardo Channel. This was caused by a further glacier retreat around the Gran Campo Nevado Ice Cap (GCN) during the early Holocene southern hemisphere thermal maximum (after 12 kyr BP). The salinities of the Seno Otway (28-30 psu) and Seno Skyring (17-21 psu) remained low throughout the Holocene. However, restricted salinity variations occurred due to further isostatic changes affecting the marine water inflow across sills as well as the interplay of precipitation/evaporation. The salinity changes affected clay mineral flocculation and sediment transport as well as aquatic ecosystems. In particular, Neoglacial glacier advances modified the degree of the marine transgression in this Andean sector due to closure of fjords and isostatic effects. Glaciers closed the Gajardo Channel and the outflow of Lago Muñoz Gamero at least several times in the periods from 3.0 to 2.2 and from 1.0 to 0.1 kyr BP, and left some glacial clay fingerprints in Seno Otway and Skyring sediments. Aquatic environment in fjord regions with stepper slopes in the western Seno Skyring and Otway area were also affected by regular mass flow events, partly triggered by earthquakes and events of extreme precipitation. Holocene tephra depositon caused additional impacts.

… 2010, held 2-7 May …, 2010

We studied the shape of the most regular-shaped stratovolcanoes of the world to mathematically de... more We studied the shape of the most regular-shaped stratovolcanoes of the world to mathematically define the form of the ideal stratovolcano. Based on the Shuttle Radar Topographic Mission (SRTM) DEM data, we selected the 20 most circular and symmetrical ...

Sedimentary Geology, 2011

A large sedimentary forearc basin developed in Cenozoic times between the present-day Coastal Cor... more A large sedimentary forearc basin developed in Cenozoic times between the present-day Coastal Cordillera and the Western Cordillera of the Central Andes, called Moquegua basin in southern Peru. The basin is filled by Moquegua Group deposits (~50 to 4 Ma) comprising mostly siliciclastic mudstones, sandstones and conglomerates as well as volcanic intercalations. Several facies changes both, along orogenic strike and through time, are described and have led to subdivision into four sedimentary units (Moquegua A, B, C and D). In this paper we present a refined stratigraphic scheme of the Moquegua Group combined with the first provenance analysis of the Moquegua basin based on (i) semi-quantitative analysis of heavy mineral abundance, (ii) electron microprobe (EMP) and laser ablation (LA) ICP-MS analyses of single detrital amphibole and Fe-Ti oxide grains, and (iii) comparative analysis of the different potential source rocks to clearly identify the most likely sources. Results allow us to reconstruct sediment provenance and to relate changes of the erosion-sedimentation system in the Moquegua basin to the evolution of the Andean orogen. At~50 to~40 Ma the Moquegua basin was close to sea level and fed by low energy rivers transporting mainly metamorphic basement and Jurassic-Cretaceous sedimentary detritus from local and distal sources. The latter might be as far as the present Eastern Cordillera. From~35 Ma on the distal sediment sources were cut off by the uplift of the Altiplano and Eastern Cordillera leading to higher energy fluvial systems and increasing importance of local sources, especially the relevant volcanic arcs. From 25 Ma on volcanic arc rocks became the predominant sources for Moquegua Group sediments. The 10 Ma time lag observed between the onset of uplift-induced facies and provenance changes (at~35 Ma) and the onset of intense magmatic activity (at~25 Ma) suggests that magmatic addition was not the main driver for crustal thickening and uplift in the Central Andes during latest Eocene to Oligocene time.

Journal of Volcanology and Geothermal Research, 1990

Five diverse, well documented, chemically zoned magmas have been chosen from the literature to de... more Five diverse, well documented, chemically zoned magmas have been chosen from the literature to demonstrate the extent and patterns of density and viscosity gradients in zoned magma chambers. The patterns are used to assess implications for development of zonation, and withdrawal dynamics and preservation of systematic chemical variations in the final pyroclastic deposit. These examples are: Bishop Tuff, California (high-silica rhyolite); Los Humeros, Mexico (calc-alkaline rhyolite to andesite); Fogo A, Azores (trachyte); Laacher See, Eifel (phonolite) and Tenerife, Canary Islands (phonolite). It was necessary to make several simplifying assumptions in order to calculate viscosity and density profiles through each system; results are particularly sensitive to magmatic water and crystal contents. Nevertheless, the following conclusions can be drawn: (1) Small, strongly zoned, alkaline magma systems which evolved through fractional crystallisation of a basaltic parent (Fogo A, Laacher See) have suffered a partial time-integrated volatile depletion prior to eruption. The most likely mechanism of volatile loss is degassing of the uppermost, highly differentiated, "cupola" magma layer. (2) Eruption withdrawal dynamics are critically dependent on density gradients (and therefore on volatile content and phenocryst abundance), while viscosity variations play a subordinate r61e in the chosen examples. (3) Formation of a chemically zoned tephra sequence by eruption of chemically zoned felsic magma requires a pre-eruptive volatile gradient in the magma chamber. (4) Withdrawal-layer thicknesses during eruptions from naturally zoned magma chambers are of the order of 100 m. (5) The quantitative treatment of gravitational liquid segregation processes by Nilson et ah (1985) successfully predicts times required for zonation of magma bodies: typically 103-104 years for small alkaline systems, and > 105 years for large silicic systems.

Journal of Volcanology and Geothermal Research, 2007

Magmas may experience closed-or open-system evolution during their ascent and evolution in the up... more Magmas may experience closed-or open-system evolution during their ascent and evolution in the upper crust. Chemically closedsystem processes can involve heat transfer from underplating mafic magmas or decompression due to magma ascent. On the other hand, newly injected magmas can mix with the residing magma and hybridize. Plagioclase zonation patterns and electron microprobe major and trace element analysis constrain these contrasting scenarios for andesites from the 80 km 3 El Misti stratovolcano (5822 m) and a field of relatively small monogenetic Andahua scoria cones, both in southern Peru. In particular, Fe concentration in plagioclase reveals valuable information within a magmatic system to explore the dominance of closed-vs. open-system processes. Large and correlated Anorthite-Fe contrasts at resorption zones identify compositional mixing related to recharge. Subhorizontal An-Fe variations record thermal or water-induced effects. El Misti volcano, a large but still relatively youthful stratovolcano, is dominated during most of its approx. 120 ka history by closed-system effects during its evolution. Recharge and mixing mostly occurred cryptically as it is not recorded in drastic compositional changes in magmas or their phenocrysts. A small volume erupted at El Misti, however, is affected by strong open-system behaviour as reflected in strongly correlated variations in An and Fe contents of plagioclase compositions. Its crystal population is texturally and chemically very similar to lavas of the monogenetic cinder cones of the Andahua Volcanic Field. For the El Misti magma reservoir, resorption events caused by thermal effects or magma ascent are more frequent in comparison to the actual eruption frequencies. Many cycles of closed-system evolution (heat transfer and decompression) therefore occurred without resulting in an eruption. Plagioclase zonations from lavas of the monogenetic Andahua field indicate that any mafic batch that intruded the much smaller reservoirs immediately triggered an eruption. By contrast, a large magma system that feeds El Misti volcano can easily accommodate a new batch without causing eruption.

Journal of South American Earth Sciences, 2013

Timing, amount, and mechanisms of uplift in the Central Andes have been a matter of debate in the... more Timing, amount, and mechanisms of uplift in the Central Andes have been a matter of debate in the last decade. Our study is based on the Cenozoic Moquegua Group deposited in the forearc basin between the Western Cordillera and the Coastal Cordillera in southern Peru from w50 to w4 Ma. The Moquegua Group consists mainly of mud-flat to fluvial siliciclastic sediments with upsection increasing grain size and volcanic intercalations. Detrital zircon UePb dating and fission track thermochronology allow us to refine previous sediment provenance models and to constrain the timing of Late Eocene to Early Miocene Andean uplift. Uplift-related provenance and facies changes started around 35 Ma and thus predate major voluminous ignimbrite eruptions that started at w25 by up to 10 Ma. Therefore magmatic addition to the crust cannot be an important driving factor for crustal thickening and uplift at Late Eocene to Early Oligocene time. Changes in subduction regime and the subducting plate geometry are suggested to control the formation of significant relief in the area of the future Western Cordillera which acts as an efficient large-scale drainage divide between Altiplano and forearc from at least 15.5 to 19 S already at w35 Ma. The model integrates the coincidence of (i) onset of provenance change no later than 35 Ma, (ii) drastic decrease in convergence rates at w40, (iii) a flat-subduction period at around w40 to w30 Ma leading to strong interplate coupling, and (iv) strong decrease in volcanic activity between 45 and 30 Ma.

Journal of South American Earth Sciences, 2000

Exposures of metamorphic basement in the Central Andes are scarce and reconstructions of the hist... more Exposures of metamorphic basement in the Central Andes are scarce and reconstructions of the history of the Paci®c margin of Gondwanaland must rely on a few isolated outcrops. We studied two areas of exposed basement in northernmost Chile (Belen) and westernmost Bolivia (Cerro Uyarani). The Belen metamorphic complex has been known for some time and consists of fault-bounded amphibolites, gneisses, schists, and minor quartzites overlain by folded Mesozoic to Cenozoic strata. The Cerro Uyarani is the only basement outcrop on the Bolivian Altiplano and has only recently been found and studied by geological reconnaissance. It consists of foliated ma®c and felsic granulites, charnockites, and amphibolites. How do these basement occurrences compare and how do they relate to the other Precambrian crustal domains in the Central Andes? To answer these questions, we used geothermobarometers to reconstruct the P±T conditions of metamorphism, as well as geochemical analyses and petrological methods to study these rocks. The two basement blocks were found to have distinct geological histories and are probably separated by a major crustal domain boundary. Isotopic ®ngerprinting by Pb-isotopes clearly exclude Laurentian crustal components either in the protoliths or as reworked material. This signature is quite distinct from basement rocks farther south in Chile and northwestern Argentina.

Journal of Petrology, 2010

Uranium-series dating of carbonatitic ejecta clasts constrains the crystallization and differenti... more Uranium-series dating of carbonatitic ejecta clasts constrains the crystallization and differentiation timescales of the Laacher See volcano, which erupted 6•3 km 3 of magma (dense rock equivalent) during one of the largest Late Quaternary eruptions in Central Europe. Carbonatites form a distinct population among plutonic ejecta that are present in the middle and late erupted Laacher See tephra. Characteristic trace element patterns of the carbonatites, including negative Eu anomalies, and mantle-like oxygen isotopic compositions preserved in zircon indicate that the Laacher See carbonatites are cogenetic with their phonolite host. Carbonatite U^Th zircon isochron ages range from 32•6 AE 4•1 ka (2; MSWD ¼1•7; n ¼ 24) to near-eruption age (12•9 ka). Uranium-series carbonatite ages qualitatively agree with alkali feldspar compositions that lack prominent magmatic zonation, but show evidence for perthitic unmixing during subsolidus residence at elevated temperatures (57008C) in an intrusive carapace surrounding the liquiddominated interior of the magma system (47208C). Model differentiation ages and crystallization ages for the carbonatites overlap within a few thousand years as resolved by U^Th dating and indicate rapid crystallization following carbonatite segregation from its parental phonolite. Model differentiation and zircon isochron ages peak at 17ka,suggestingamajorphaseofdifferentiationoftheLaacherSeemagmasystematthistime,althoughtheonsetofphonolitedifferentiationdatesbacktoatleast17 ka, suggesting a major phase of differentiation of the Laacher See magma system at this time, although the onset of phonolite differentiation dates back to at least 17ka,suggestingamajorphaseofdifferentiationoftheLaacherSeemagmasystematthistime,althoughtheonsetofphonolitedifferentiationdatesbacktoatleast10^20 kyr prior to eruption. Phenocrysts in the middle and late erupted phonolite magma crystallized shortly before eruption, and the lack of older crystals implies crystal removal through settling or resorption. Crystal ages from both crystal-rich and liquid-dominated parts of a magma system are thus complementary, and reveal different aspects of magma differentiation and residence timescales.

Journal of Asian Earth Sciences, 2014

This study explores the potential of detrital rutile geochemistry and thermometry as a provenance... more This study explores the potential of detrital rutile geochemistry and thermometry as a provenance tracer in rocks from the Central Dabie ultrahigh-pressure metamorphic (UHPM) zone in east-central China that formed during Triassic continental collision. Trace element data of 176 detrital rutile grains selected from local river sediments and 91 rutile grains from distinct bedrocks in the Shuanghe and Bixiling areas, obtained by both electron microprobe (EMP) and in situ LA-ICP-MS analyses, suggest that geochemical compositions and thermometry of detrital rutiles are comparable to those from their potential source rocks. After certification of the Cr-Nb discrimination method for the Central Dabie UHPM zone, we show that 29% of the detrital rutiles in the Shuanghe area were derived from metamafic sources whereas in the Bixiling area that it is up to 76%. Furthermore, the proportion of distinct types of detrital rutiles combined with modal abundances of rutile in metapelites and metamafic bedrocks can be used to estimate the proportion of different source lithologies. Based on this method the proportion of mafic source rocks was estimated to $10% at Shuanghe and >60% at Bixiling, respectively, which is consistent with the proportions of eclogite (the major rutile-bearing metamafic rock) distribution in the field. Therefore, the investigation of detrital rutiles is a potential way to evaluate the proportion of metamafic rocks and even to prospect for metamafic bodies in UHPM terranes. Zr-in-rutile temperatures were calculated at different pressures and compared with temperatures derived from rock-in rutiles and garnet-clinopyroxene Fe-Mg thermometers. Temperatures calculated for detrital rutiles range from 606°C to 707°C and 566°C to 752°C in Shuanghe and Bixiling, respectively, at P = 3 GPa with an average temperatures of ca. 630°C for both areas. These temperature averages and ranges are similar to those calculated for rutiles from surrounding source rocks. Combined with comparable Zr distribution characteristics between detrital and source rock rutiles, demonstrating a close source-sediment link for rutiles from clastic and rock in UHPM terranes. Thus rutiles can be accurate tracers of source rock lithologies in sedimentary provenance studies even at a small regional scale. In Bixiling, Nb/Ta ratios of metamafic and metapelitic detrital rutiles fall between 11.0 to 27.3 and 7.7 to 20.5, respectively. In contrast, in Shuanghe, these ratios are highly variable, ranging from 10.9 to 71.0 and 7.6 to 87.1, respectively. When ignoring four outlier compositions with extremely high Nb/Ta in Shuanghe, a distinct clustering of Nb/Ta ratios in rutiles is shown: metapelitic detrital rutiles have Nb/Ta of 7-40 vs. metamafic detrital rutiles with Nb/Ta = 11-25. The Nb/ Ta characteristics in detrital rutiles from both areas may reflect the degree of fluid-rock interaction during metamorphism and/or different source lithologies. Therefore, the trace element compositions in detrital rutiles can accurately trace the lithology, proportion and fluid-rock interaction of different source rocks.

Contributions to Mineralogy and Petrology, 2007

Volatile element, major and trace element compositions were measured in glass inclusions in olivi... more Volatile element, major and trace element compositions were measured in glass inclusions in olivine from samples across the Kamchatka arc. Glasses were analyzed in reheated melt inclusions by electron microprobe for major elements, S and Cl, trace elements and F were determined by SIMS. Volatile element-trace element ratios correlated with fluid-mobile elements (B, Li) suggesting successive changes and three distinct fluid compositions with increasing slab depth. The Eastern Volcanic arc Front (EVF) was dominated by fluid highly enriched in B, Cl and chalcophile elements and also LILE (U, Th, Ba, Pb), F, S and LREE (La, Ce). This arc-front fluid contributed less to magmas from the central volcanic zone and was not involved in back arc magmatism. The Central Kamchatka Depression (CKD) was dominated by a second fluid enriched in S and U, showing the highest S/K 2 O and U/Th ratios. Additionally this fluid was unusually enriched in 87 Sr and 18 O. In the back arc Sredinny Ridge (SR) a third fluid was observed, highly enriched in F, Li, and Be as well as LILE and LREE. We argue from the decoupling of B and Li that dehydration of different water-rich minerals at different depths explains the presence of different fluids across the Kamchatka arc. In the arc front, fluids were derived from amphibole and serpentine dehydration and probably were water-rich, low in silica and high in B, LILE, sulfur and chlorine. Large amounts of water produced high degrees of melting below the EVF and CKD. Fluids below the CKD were released at a depth between 100 and 200 km due to dehydration of lawsonite and phengite and probably were poorer in water and richer in silica. Fluids released at high pressure conditions below the back arc (SR) probably were much denser and dissolved significant amounts of silicate minerals, and potentially carried high amounts of LILE and HFSE.

Contributions to Mineralogy and Petrology, 1999

Whole rock and mineral stable isotope and microprobe analyses are presented from granitoids of th... more Whole rock and mineral stable isotope and microprobe analyses are presented from granitoids of the North Chilean Precordillera. The Cretaceous to Tertiary plutonic rocks contain important ore deposits and frequently display compositional and textural evidence of hydrothermal alteration even in barren rocks. Deuteric alteration includes replacement of biotite and amphibole by chlorite and epidote, sericitization and saussuritization of feldspars, and uralitization of clinopyroxene and/or amphibole. While whole rock compositions are not signi®cantly aected, compositional variations in amphiboles suggest two types of hydrothermal alteration. Hornblende with actinolitic patches and rims and tight compositional trends from hornblende to Mg-rich actinolite indicate increasing oxygen fugacity from magmatic to hydrothermal conditions. Uralitic amphiboles exhibiting irregular Mg-Fe distribution and variable Al content are interpreted as re¯ecting subsolidus hydration reactions at low temperatures. The dD values of hydrous silicates vary from A63 to A105&. Most d 18 O values of whole rocks are in the range of 5.7 to 7.7& and are considered normal for igneous rocks in the Andes. These d 18 O values also coincide well with the oxygen isotope composition of geochemically similar recent volcanics from the Central Andean Volcanic Zone (d 18 O=7.0±7.4&). Only one sample in this study (d 18 O=3.0&) appears to be depleted by isotope exchange with light meteoric water at high temperatures. The formation of secondary minerals in all other intrusions is mainly the product of deuteric alteration. This also holds true for the sample from El Abra, the only pluton associated with mineralization. This indicates the dominant role of a magmatic rather than a meteoric¯uid in the alteration of the Cretaceous and Tertiary granitoids in northern Chile.

Bulletin of Volcanology, 2005

Ubinas volcano has had 23 degassing and ashfall episodes since A.D. 1550, making it the histori c... more Ubinas volcano has had 23 degassing and ashfall episodes since A.D. 1550, making it the histori cally most active volcano in southern Peru. Based on fieldwork, on interpretation of aerial photographs and satellite images, and on radiometric ages, the eruptive history of Ubinas is divided into two major periods. Ubinas I (Middle Pleistocene >376 ka) is characterized by lava flow activity that formed the lower part of the edi fice. This edifice collapsed and resulted in a debris-ava

Bulletin of Volcanology, 2010

The giant ignimbrites that erupted from the Cerro Galán caldera complex in the southern Puna of t... more The giant ignimbrites that erupted from the Cerro Galán caldera complex in the southern Puna of the high Andean plateau are considered to be linked to crustal and mantle melting as a consequence of delamination of gravitationally unstable thickened crust and mantle lithosphere over a steepening subduction zone. Major and trace element analyses of Cerro Galán ignimbrites (68-71% SiO 2) that include 75 new analyses can be interpreted as reflecting evolution at three crustal levels. AFC modeling and new fractionation corrected δ 18 O values from quartz (+7.63-8.85‰) are consistent with the ignimbrite magmas being near 50:50 mixtures of enriched mantle (87 Sr/ 86 Sr0 .7055) and crustal melts (87 Sr/ 86 Sr near 0.715-0.735). Processes at lower crustal levels are predicated on steep heavy REE patterns (Sm/Yb = 4-7), high Sr contents (>250 ppm) and very low Nb/Ta (9-5) ratios, which are attributed to amphibolite partial melts mixing with fractionating mantle basalts to produce hybrid melts that rise leaving a gravitationally unstable garnet-bearing residue. Processes at mid crustal levels create large negative Eu anomalies (Eu/Eu*=0.45-0.70) and variable trace element enrichment in a crystallizing mush zone with a temperature near 800-850°C. The mush zone is repeatedly recharged from depth and partially evacuated into upper crustal magma chambers at times of regional contraction. Crystallinity differences in the ignimbrites are attributed to biotite, zoned plagioclase and other antecrysts entering higher level chambers where variable amounts of near-eutectic crystallization occurs at temperatures as low as 680°C just preceding eruption. 40 Ar/ 39 Ar single crystal sanidine weighted mean plateau and isochron ages combined with trace element patterns show that the Galán ignimbrite erupted in more than one batch including a~2.13 Ma intracaldera flow and outflows to the west and north at near 2.09 and 2.06 Ma. Episodic delamination of gravitationally unstable lower crust and mantle lithosphere and injection of basaltic magmas, whose changing chemistry reflects their evolution over a steepening subduction zone, could trigger the eruptions of the Cerro Galán ignimbrites. Keywords Cerro Galán. Puna ignimbrite chemistry. 40 Ar/ 39 Ar ages. Delamination. Plateau evolution Editorial responsibility: R. Cas This paper constitutes part of a special issue: Cas RAF, Cashman K (eds) The Cerro Galan Ignimbrite and Caldera: characteristics and origins of a very large volume ignimbrite and its magma system.

Bulletin of Volcanology, 2008

... The least-evolved pumice fragments were collected at San Marco Evangelista (Fig. ... The thre... more ... The least-evolved pumice fragments were collected at San Marco Evangelista (Fig. ... The three analysed samples from San Marco Evangelista are: San Marco OF 3D black pumice (SMs), SanMarco OF 3D black single pumice (SMsp), and San Marco OF 3D light pumice (SMc). ...

Bulletin of Volcanology, 1988

Subduction-related volcanism in the Nevados de Payachata region of the Central Andes at 18 °S com... more Subduction-related volcanism in the Nevados de Payachata region of the Central Andes at 18 °S comprises two temporally and geochemically distinct phases. An older period of