Magma storage and ascent during the 1995 eruption of Fogo, Cape Verde Archipelago

The 1995 eruption of Fogo (Cape Verde Islands) differed from previous eruptions by the occurrence of evolved lavas, the SW-orientation of vents, and pre-eruptive seismicity between Fogo and the adjacent (~20 km) island of Brava. We have conducted a thermobarometric and chemical study of this eruption in order to reconstruct its magma plumbing system and to test for possible connections to Brava. The bimodal eruption produced basanites (5.2–6.7 wt% MgO) and phonotephrites (2.4–2.8 wt% MgO) that are related by fractional crystallization. Clinopyroxene-melt-barometry of phenocrysts yields pressure ranges of 460–680 MPa for the basanites and 460–520 MPa for the phonotephrites. Microthermometry of CO2-dominated fluid inclusions in olivine and clinopyroxene phenocrysts yields systematically lower pressure ranges of 200–310 MPa for basanites and 270–470 MPa for phonotephrites. The combined data indicate pre-eruptive storage of the 1995 magmas within the lithospheric mantle between 16 and 24 km depth. During eruption, the ascending magmas stalled temporarily at 8–11 km depth, within the lower crust, before they ascended to the surface in a few hours as indicated by zonations of olivine phenocrysts. Our data provide no evidence for magma storage at shallow levels (<200 MPa) or lateral magma movements beneath the Fogo-Brava platform. Sr–Nd–Pb isotope ratios of samples from Brava differ significantly from those of the 1995 and older Fogo lavas, which rules out contamination of the 1995 magmas by Brava material and indicates different mantle sources and magma plumbing systems for both islands.

[1]  K. Putirka.  Magma transport at Hawaii: Inferences based on igneous thermobarometry , 1997 .

[2]  S. Chakraborty,et al.  Experimental determination of the diffusion coefficient for calcium in olivine between 900°C and 1500°C , 2005 .

[3]  B. Evans,et al.  Mechanical re-equilibration of fluid inclusions in San Carlos olivine by power-law creep , 1989 .

[4]  T. Hansteen,et al.  The magmatic plumbing system beneath El Hierro (Canary Islands): constraints from phenocrysts and naturally quenched basaltic glasses in submarine rocks , 2009 .

[5]  S. Chakraborty,et al.  Fe–Mg diffusion in olivine II: point defect chemistry, change of diffusion mechanisms and a model for calculation of diffusion coefficients in natural olivine , 2007 .

[6]  E. Neumann,et al.  Carbonatite melt–CO2 fluid inclusions in mantle xenoliths from Tenerife, Canary Islands: a story of trapping, immiscibility and fluid–rock interaction in the upper mantle , 2002 .

[7]  A. V. D. Kerkhof,et al.  Isochoric phase diagrams in the systems CO2CH4 and CO2N2: Application to fluid inclusions , 1990 .

[8]  A. Klügel,et al.  Melt extraction pathways and stagnation depths beneath the Madeira and Desertas rift zones (NE Atlantic) inferred from barometric studies , 2004 .

[9]  R. Bakker,et al.  Experimental post-entrapment water loss from synthetic CO2-H2O inclusions in natural quartz , 1991 .

[10]  J. Duke.  Distribution of the Period Four Transition Elements among Olivine, Calcic Clinopyroxene and Mafic Silicate Liquid: Experimental Results , 1976 .

[11]  W. Wagner,et al.  A New Equation of State for Carbon Dioxide Covering the Fluid Region from the Triple‐Point Temperature to 1100 K at Pressures up to 800 MPa , 1996 .

[12]  T. Hansteen,et al.  Fluid Inclusion Thermobarometry as a Tracer for Magmatic Processes , 2008 .

[13]  Dimitris Sakellariou,et al.  Submarine Mass Movements and Their Consequences , 2003 .

[14]  K. Haase,et al.  On- and off-axis chemical heterogeneities along the South Atlantic Mid-Ocean-Ridge (5–11°S): Shallow or deep recycling of ocean crust and/or intraplate volcanism? , 2011 .

[15]  T. Hansteen,et al.  Changing depths of magma fractionation and stagnation during the evolution of an oceanic island volcano: La Palma (Canary Islands) , 2006 .

[16]  F. Stuart,et al.  Cosmogenic 3He exposure dating of the Quaternary basalts from Fogo, Cape Verdes: Implications for rift zone and magmatic reorganisation , 2009 .

[17]  Claude J. Allègre,et al.  Os isotope systematics in Fogo Island: Evidence for lower continental crust fragments under the Cape Verde Southern Islands , 2005 .

[18]  George Helffrich,et al.  Hydroacoustic detection of volcanic ocean-island earthquakes , 2006 .

[19]  M. Moreira,et al.  Pb-Sr-He isotope and trace element geochemistry of the Cape Verde Archipelago , 2003 .

[20]  S. Day,et al.  Fogo Volcano, Cape Verde Islands: seismicity-derived constraints on the mechanism of the 1995 eruption , 1999 .

[21]  Michael O. Garcia,et al.  Petrologic constraints on rift-zone processes , 1989 .

[22]  F. Costa,et al.  Decadal time gaps between mafic intrusion and silicic eruption obtained from chemical zoning patterns in olivine , 2004 .

[23]  T. Hansteen,et al.  Multi-stage magma ascent beneath the Canary Islands: evidence from fluid inclusions , 1998 .

[24]  F. Hauff,et al.  Flow of Canary mantle plume material through a subcontinental lithospheric corridor beneath Africa to the Mediterranean: Reply , 2009 .

[25]  N. Chatterjee,et al.  Depth of alkalic magma reservoirs below Kolekole cinder cone, Southwest rift zone, East Maui, Hawaii , 2005 .

[26]  J. Dixon.  Degassing of alkalic basalts , 1997 .

[27]  A. Peccerillo,et al.  Modeling the magma plumbing system of Vulcano (Aeolian Islands, Italy) by integrated fluid-inclusion geobarometry, petrology, and geophysics , 2006 .

[28]  R. Batiza,et al.  Mid‐ocean ridge magma chamber processes: Constraints from olivine zonation in lavas from the East Pacific Rise at 9°30′N and 10°30′N , 2002 .

[29]  Kenneth S. Pitzer,et al.  An equation of state for carbon dioxide valid from zero to extreme pressures , 1994 .

[30]  T. Elliott,et al.  Melt evolution beneath thick lithosphere: a magmatic inclusion study of La Palma, Canary Islands , 2002 .

[31]  K. Hoernle,et al.  The chemically zoned 1949 eruption on La Palma (Canary Islands): Petrologic evolution and magma supply dynamics of a rift zone eruption , 2000 .

[32]  J. M. Rhodes,et al.  Geochemical evidence for invasion of Kilauea's plumbing system by Mauna Loa magma , 1989, Nature.

[33]  T. L. Bas,et al.  Slope Failures Of The Flanks Of The Southern Cape Verde Islands , 2007 .

[34]  R. S. J. Sparks,et al.  Effect of degassing on rheology of basaltic lava , 1978, Nature.

[35]  B. Wood,et al.  Thermodynamics of minerals and melts , 1981 .

[36]  Youxue Zhang,et al.  Toward a general viscosity equation for natural anhydrous and hydrous silicate melts , 2007 .

[37]  E. Neumann,et al.  Fluid inclusions in mantle xenoliths , 2001 .

[38]  John Crank,et al.  The Mathematics Of Diffusion , 1956 .

[39]  R. Bodnar,et al.  Statistical microthermometry of synthetic fluid inclusions in quartz during decompression reequilibration , 1998 .

[40]  I. Samson,et al.  Fluid inclusions : analysis and interpretation , 2003 .

[41]  A. Barker,et al.  An 40Ar-39Ar study of the Cape Verde hot spot: Temporal evolution in a semistationary plate environment , 2008 .

[42]  T. Hansteen,et al.  Magma storage and underplating beneath cumbre vieja volcano, la palma (canary islands) , 2005 .

[43]  J. Baker,et al.  Geochemical Stratigraphy of Submarine Lavas (3^5 Ma) from the Flamengos Valley, Santiago, Southern Cape Verde Islands , 2009 .

[44]  L. Hollister.  Enrichment of CO2 in fluid inclusions in quartz by removal of H2O during crystal-plastic deformation , 1990 .

[45]  K. Cashman.  Textural constraints on the kinetics of crystallization of igneous rocks , 1990 .

[46]  P. Richet,et al.  High-pressure and temperature equation of state and calculation of the thermodynamic properties of gaseous carbon dioxide , 1981 .

[47]  D. Hoffmann,et al.  Volcano-stratigraphic and structural evolution of Brava Island (Cape Verde) based on 40Ar/39Ar, U-Th and field constraints , 2010 .

[48]  K. Putirka.  Clinopyroxene + liquid equilibria to 100 kbar and 2450 K , 1999 .

[49]  D. Kohlstedt,et al.  Diffusion of hydrogen in olivine: Implications for water in the mantle , 1990 .

[50]  J. Holloway.  Volatile Interactions in Magmas , 1981 .

[51]  F. Ryerson,et al.  New clinopyroxene-liquid thermobarometers for mafic, evolved, and volatile-bearing lava compositions, with applications to lavas from Tibet and the Snake River Plain, Idaho , 2003 .

[52]  S. Hart.  A large-scale isotope anomaly in the Southern Hemisphere mantle , 1984, Nature.

[53]  Simon Day,et al.  A past giant lateral collapse and present-day flank instability of Fogo, Cape Verde Islands , 1999 .

[54]  W. Strauch,et al.  Arc-parallel flow in the mantle wedge beneath Costa Rica and Nicaragua , 2008, Nature.

[55]  I. Carmichael,et al.  The compressibility of silicate liquids containing Fe2O3 and the effect of composition, temperature, oxygen fugacity and pressure on their redox states , 1991 .

[56]  W. McDonough,et al.  Chemical and isotopic systematics of oceanic basalts: implications for mantle composition and processes , 1989, Geological Society, London, Special Publications.

[57]  A. Krabbenhoeft,et al.  Crustal structure and origin of the Cape Verde Rise , 2008 .

[58]  M. Schnabel,et al.  Seismic activity at Cadamosto seamount near Fogo Island, Cape Verdes—formation of a new ocean island? , 2010 .

[59]  D. M. Kerrick,et al.  A modified Redlich-Kwong equation for H 2 O, CO 2 , and H 2 O-CO 2 mixtures at elevated pressures and temperatures , 1981 .

[60]  Falk Amelung,et al.  InSAR observations of the 1995 Fogo, Cape Verde, eruption: Implications for the effects of collapse events upon island volcanoes , 2002 .

[61]  G. Helffrich,et al.  Depleted swell root beneath the Cape Verde Islands , 2006 .