Facies architecture, emplacement mechanisms and eruption style of the submarine andesite El Barronal complex, Cabo de Gata, SE Spain

El Barronal complex consists of a succession of andesite lavas and andesite volcaniclastic facies interbedded with carbonate and siliciclastic sedimentary rocks. Carbonate and siliciclastic rocks were deposited in a shallow-marine environment during periods of volcanic quiescence. Lavas consist of an inner coherent core grading outward into hyaloclastite breccia made of dense clasts that in turn grade into hyaloclastite breccia made of vesicular clasts, in massive to layered zones. Volcaniclastic facies contain clasts produced during explosive eruptions and reworked clasts from sources above wave base. Volcaniclastic facies were deposited from cold granular flows with different grain size populations. Stratigraphy and facies architecture at El Barronal suggest that a succession of several discrete eruptive events occurred with a similar cyclic pattern made of an initial explosive phase followed by effusive emplacement of lavas, in turn followed by a period of quiescence of volcanic activity. Hyaloclastic fragmentation of magma took place in the final stages of lava emplacement, allowing only for local disorganization of the jigsaw-fit texture. © 2013 Elsevier B.V.This research has been funded by projects CGL2005-03511/BTE and HI2006-0073Peer Reviewe

Nonadditivity of critical Casimir forces

In soft condensed matter physics, effective interactions often emerge due to the spatial confinement of fluctuating fields. For instance, microscopic particles dissolved in a binary liquid mixture are subject to critical Casimir forces whenever their surfaces confine the thermal fluctuations of the order parameter of the solvent close to its critical demixing point. These forces are theoretically predicted to be nonadditive on the scale set by the bulk correlation length of the fluctuations. Here we provide direct experimental evidence of this fact by reporting the measurement of the associated many-body forces. We consider three colloidal particles in optical traps and observe that the critical Casimir force exerted on one of them by the other two differs from the sum of the forces they exert separately. This three-body effect depends sensitively on the distance from the critical point and on the chemical functionalisation of the colloid surfaces

Textural analysis of strongly altered kimberlite : examples from the Ekati diamond mine, Northwest Territories, Canada

Two massive, poorly sorted pyroclastic kimberlite deposits from the Fox and Koala pipes at the Ekati diamond mine, Northwest Territories, Canada present different styles of alteration. The first, at Fox, has an interstitial medium-alteration assemblage dominated by saponite, serpentine (lizardite), and microlitic diopside. The second, at Koala, has an alteration assemblage of serpentine (antigorite), carbonate, and minor saponite. They share the following sequence of events. Fine-grained matrix material has been serpentinized and replaced to varying degrees within each deposit, and the proportions of the preserved mineralogy of the interstitial medium reflect the nature and degree of alteration. Fine kimberlite ash is likely to have been hydrated and serpentinized soon after deposition by volcanic fluids percolating through the kimberlite vent fill deposits. Replacement, dissolution, and infilling of primary and secondary pore space are commonly observed textural features, and indicate that several phases of alteration have occurred, either as distinct episodes or, more likely, as part of a progressive sequence. The proportion of accessory lithic fragments contained within the deposits is much greater at Fox (15 to 35%) than at Koala (<10%) and has influenced the style of alteration in two ways. First, a greater proportion of cold lithic clasts acted as heat sinks and decreased the emplacement temperature of the Fox deposit as a whole. Second, a greater proportion of granodioritic lithic clasts, especially of smaller grain sizes, provided accessible sources of silica, aluminum, and calcium to the system, thus influencing the resulting alteration mineral assemblage.17 page(s

Base surge deposits, eruption history, and depositional processes of a wet phreatomagmatic volcano in Central Anatolia (Cora Maar)

2nd International Maar Conference -- SEP 21-25, 2004 -- Lajosmizse, HUNGARYWOS: 000243607900012Cora Maar is a Quaternary volcano located to the 20 km northwest of Mount Erciyes, the largest of the 19 polygenetic volcanic complexes of the Cappadocian Volcanic Province in central Anatolia. Cora Maar is a typical example of a maar-diatreme volcano with a nearly circular crater with a mean diameter of c. 1.2 km, and a well-bedded base surge-dominated maar rim tephra sequence up to 40 m in thickness. Having a diameter/depth ratio (D/d) of 12, Cora is a relatively "mature" maar compared to recent maar craters in the world. Cora crater is excavated within the andesitic lava flows of Quaternary age. The tephra sequence is not indurated, and consists of juvenile clasts up to 70 cm, non-juvenile clasts up to 130 cm, accretionary lapilli up to 1.2 cm in diameter, and ash to lapilli-sized tephra. Base surge layers display well-developed antidune structures indicating the direction of the transport. Both progressive and regressive dune structures are present within the tephra sequence. Wavelength values increase with increasing wave height, and with large wavelength and height values. Cora tephra display similarities to Taal and Laacher See base surge deposits. Impact sags and small channel structures are also common. Lateral and vertical facies changes are observed for the dune bedded and planar bedsets. According to granulometric analyses, Cora Maar tephra samples display a bimodal distribution with a wide range of Md-phi values, characteristic for the surge deposits. Very poorly sorted, bimodal ash deposits generally vary from coarse tail to fine tail grading depending on the grain size distribution while very poorly sorted lapilli and block-rich deposits display a positive skewness due to fine tail grading. (c) 2006 Elsevier B.V. All rights reserved.Int Assoc Volcanol & Chem Earth Interior, IAVCEI, Commiss Volcanogen Sediments, Int Assoc Sedimentol, Int Comm Hungarh, Slovak Republic German

Clasts in Archean conglomerates and implications for uplift : Evidence from the 2.7 Ga Agnew Greenstone Belt (Western Australia)

Archean greenstone belts commonly consist of a stratigraphy that records subaqueous deposition capped by subaerial sedimentation, yet it remains unclear if the controls on this change were driven by horizontal or vertical processes. Clasts in conglomerates can provide important constraints on this question because they inform on the changing nature of sources. The 2.7 Ga Agnew Greenstone Belt, Yilgarn Craton, Australia, provides the ideal opportunity for such a study because it contains abundant and diverse conglomerate facies and its basal stratigraphy is well understood. This study focusses on the texture and composition of lithic clasts derived from three stratigraphic conglomerate units and their host successions. The lowermost conglomerate-bearing unit, hosted in the Vivien Formation, unconformably overlies the mafic-ultramafic lavas and intrusions of the Kalgoorlie Group (ca. 2720–2690 Ma) and is dominated by aphyric to porphyritic mafic and felsic volcanic clasts. The conformably overlying Maria Mine Formation conglomerates contain a higher proportion of felsic clasts with medium- and plutonic groundmass textures. The Vivien and Maria Mine Formations (ca. 2690–2670 Ma) are dominated by cherts, turbidites and conglomerates, and represent subaqueous sediments formed in the ring-plain surrounding an emergent volcanic island. The unconformably overlying Scotty Creek Formation (ca. 2665–2655 Ma) contains conglomerates with many plutonic felsic clasts, and is dominated by bedded and cross-bedded sandstones formed in a subaerial environment. Whole-rock geochemistry of mafic and ultramafic clasts matches the local Kalgoorlie Group rocks and indicates progressive erosion of the underlying supracrustal sequence. Undeformed conglomerates lack clasts with metamorphic foliations, indicating uplift by horizontal compression could not have been significant before ca. 2655 Ma, which is considered as the time of the first major compressional event in many published structural frameworks for the region. The systematic erosion of a felsic stratovolcano, its associated plumbing system, and any resultant upwarping of underlying sequences through vertically-driven diapirism, better explains the progressive changes observed in clast texture and composition, as opposed to horizontally-driven uplift, such as compression associated with subduction

Causes of complexity in a fallout dominated plinian eruption sequence: 312ka Fasnia Member, Diego Hernández Formation, Tenerife, Spain

The 312ka Fasnia eruption from the Las Cañadas Caldera on Tenerife, Canary Islands, Spain, produced a complex sequence of twenty-two intercalated units, including 7 pumice fall, 7 ignimbrite and 8 ash surge and fall deposits that define two distinct eruption sequences (Lower and Upper Fasnia sequences). The fallout units themselves are internally complex, reflecting waxing and waning of the eruption column, while many of the ignimbrites reflect multiple intra-plinian partial column collapse events associated with the injection of lithic clasts into the eruption column. The Lower and Upper Fasnia eruption phases were each terminated by caldera collapse and complete column collapse events. Probable blockage of the conduit and vent system during Lower Fasnia caldera collapse event briefly terminated the eruption, resulting in a short-lived period of erosion and sedimentation prior to the onset of the Upper Fasnia phase. The transition to the Upper Fasnia eruption phase coincided with the eruption of more geochemically homogeneous pyroclasts. In total, 62km3 of tephra were erupted, including 49km3 of juvenile clasts and >12km3 of lithic clasts. The DRE volume of magma erupted was 13km3 (Lower Fasnia>5km3, Upper Fasnia>8km3), two thirds of which (~9-10km3) was deposited purely by fallout. The Fasnia Member is one of the most complex plinian sequences known. © 2017 Elsevier B.V.The research was funded by discretionary research funds of Ray Cas, NSF grant EAR-0001013 to John Wolff, and MCyT REN2001-0502/RIES and EC EVG1-CT-2002-00058 grants to Joan Marti.Peer reviewe

Tenerife, a complex end member of basaltic oceanic island volcanoes, with explosive polygenetic phonolitic calderas, and phonolitic-basaltic stratovolcanoes

Tenerife, one of the active oceanic island volcanoes in the Canary Islands, located in the eastern Atlantic Ocean off northwest Africa, is the second largest intraplate oceanic island volcanic system after Hawai'i but is more complex and represents a different and more evolved end-member to Hawai'i in the spectrum of oceanic island volcanic systems. Tenerife began life as a mafic oceanic shield volcano at ~12 Ma, erupting (picro)basalt, basanite, hawaiite, mugearite, benmoreite series lavas of the Older Basaltic Series. These were derived from a spatially variable mantle plume source with varying degrees of magma-lithosphere interaction and fractional crystallisation. At ~3.05 Ma an evolved phonolitic magma system began to develop under the centre of the island. That led to the building of an initial summit effusive and explosive stratovolcano system (the Las Cañadas edifice) represented by the poorly understood Lower Group, followed by development of 3 cycles of explosive phonolitic caldera forming activity (Ucanca, Guajara, Diego Hernández) of the Upper Group, from 1.66 Ma to 0.19 Ma, each cycle separated by ~180 kyr (the recharge interval?). Phonolite genesis is complex, involving fractional crystallisation, partial melting of island crust including syenitic plutons, and recycling of crystal mushes. Three coalesced explosive calderas are preserved at the summit of Tenerife, constituting the Las Cañadas Caldera Complex. Since 0.19 Ma two stratovolcanoes (Teide, Pico Viejo) have been growing along the northern rim of the caldera complex, becoming more phonolitic from basaltic beginnings and more explosive, perhaps heralding the beginning of a new explosive cycle. Simultaneously shield building basaltic volcanism has continued on the flanks to historic times through multiple monogenetic eruptions along the linear northwestern and northeastern rift zones, and a more diffuse southern volcanic zone. Volcanic eruption styles have included fissure fed basaltic shield sheet lava eruptions, monogenetic basaltic cone lava and scoria eruptions, highly explosive plinian phonolitic pumice and ash fallout, and pyroclastic flow forming eruptions. The volumes of the largest explosive eruptions likely caused a component of magma chamber roof block subsidence, with multiple, spaced eruptions during each caldera forming cycle producing incremental caldera collapse and polygenetic calderas. Major landslides coincide with some of the large explosive eruptions, raising the question of cause and effect.Much of this research was undertaken during a collaborative research program between Monash University, Australia, Jaume Almera CSIC, Spain, and Washington State University, USA. Research funding was provided from discretionary research funds of Ray Cas, NSF grant EAR-0001013 to John Wolff, and MCyT REN2001-0502/RIES and EC EVG1-CT-2002-00058 grants to Joan Marti.Peer reviewe