UNIVERSITÀ DEGLI STUDI DI ROMA TRE SCUOLA DOTTORALE IN GEOLOGIA DELL’AMBIENTE E DELLE RISORSE (SDIGAR) Ciclo XXVI THE EVOLUTION OF TURRIALBA VOLCANO PLUMBING SYSTEM (COSTA RICA) Andrea Di Piazza A.A. 2012/2013 Tutors: Dott.ssa Claudia Romano Coordinatore: Prof. Claudio Faccenna Prof. Franco Barberi Co-Tutor: Dott. Gianfilippo De Astis “The future belongs to those who believe in the beauty of their dreams” Eleanor Roosvelt III Content 1. Introduction …………………………………………………………................................... 1 2. Turrialba Volcano ................................................................................................................. 5 2.1. Geodynamical background .............................................................................................. 5 2.1.1. Regional setting ........................................................................................................ 5 2.1.2. Local setting: the Turrialba volcanic system …..................................................... 9 2.2. Volcanological evolution of Turrialba Volcano ............................................................. 11 2.2.1. Chronicles of the 1864-1866 AD eruption .............................................................. 12 2.2.2. The unrest phase (1996-2013) .................................................................................. 12 2.3. Field sampling ............................................................................................................... 13 2.4. Whole rock geochemistry: results ................................................................................... 16 2.4.1. Analytical methods ................................................................................................. 16 2.4.2. Nomenclature and classification ........................................................................... 17 2.4.3. Petrography and mineral chemistry ..................................................................... 18 2.4.4. Major and trace elements chemistry ...................................................................... 20 2.4.5. Sr and Nd isotope geochemistry .............................................................................. 26 2.5. Turrialba volcano in the geochemical framework of the volcanic front of Central America ....................................................................................................................................... 27 2.5.1. Bulk rock geochemistry insights: trace elements variations along the arc …..….. 27 2.5.2. Isotope geochemistry evidences .............................................................................. 30 2.5.3 The occurrence of andesites with primitive geochemical characteristics ................ 33 3. Mantle source feeding the plumbing system of Turrialba volcano: insights from noble gas geochemistry ....................................................................................................................... 38 3.1. Noble gas geochemistry background .............................................................................. 39 3.1.1 Helium isotopes ........................................................................................................ 41 3.2. Sample preparation and analytical methods .................................................................... 43 3.3. Results: fluid inclusions composition .............................................................................. 46 3.3.1. The effect of air contamination ............................................................................... 49 3.4. Inferences on the local mantle source ............................................................................. 51 3.5. Features of magma degassing at present day and inferences on the recent unrest phase IV ....................................................................................................................................................... 55 4. Geochemical study of the degassing system of Turrialba volcano ……………………… 59 4.1. The Turrialba fumarolic discharge .................................................................................. 59 4.2. Previous studies ............................................................................................................... 60 4.3. Methodology and sampling strategy ............................................................................... 62 4.4. Results ............................................................................................................................. 64 4.4.1. The CO2 soil flux surveys ....................................................................................... 65 4.4.2. Soil gases concentration .......................................................................................... 68 4.4.3. Chemical composition of fumaroles ........................................................................ 70 4.5. Discussion ....................................................................................................................... 72 4.6. Constraints on the Turrialba unrest phase ....................................................................... 77 5. Textural analysis on two explosive eruptions of the last 2ka of Turrialba Volcano …... 83 5.1. Crystal and Vescle Size Distributions: brief background theory .................................. 83 5.1.1. Crystal Size Distribution ......................................................................................... 84 5.1.2. Vesicle Size Distribution ......................................................................................... 88 5.2. Methodology .................................................................................................................. 93 5.3. 1.9 ka eruption of Turrialba Volcano .............................................................................. 95 5.3.1. Field observations ................................................................................................... 95 5.3.2. Petrographic observations ...................................................................................... 98 5.3.3. Density and vesicularity ......................................................................................... 100 5.3.4. Vesicle textural observations .................................................................................. 102 5.3.5. Vesicle Volume Distribution .................................................................................. 103 5.3.6. Vesicle Number Density .......................................................................................... 104 5.3.7. Crystal Size Distribution ......................................................................................... 106 5.4. 1864-1866 eruption ........................................................................................................ 108 5.4.1. Field observations ................................................................................................... 108 5.4.2. Petrographic observations ...................................................................................... 110 5.4.3. Density and vesicularity ......................................................................................... 111 5.4.4. Vesicle textural observations .................................................................................. 112 5.4.5. Vesicle Volume Distribution .................................................................................. 113 5.4.6. Vesicle Number Density .......................................................................................... 113 5.4.7. Crystal Size Distribution ......................................................................................... 115 V 5.5. Discussion ...................................................................................................................... 117 5.5.1. The 1.9 ka andesitic eruption ................................................................................. 117 5.5.2. The 1864-1866 basaltic eruption ............................................................................ 124 5.6 Volcanological implications ........................................................................................... 126 6. The multiphase rheology of magmas from Turrialba 1.9 ka eruption ........................... 128 6.1. The rheology of magmatic suspensions .......................................................................... 129 6.1.1. Crystal-bearing magma rheology ............................................................................ 130 6.1.2. Bubble-bearing magma rheology ............................................................................ 137 6.1.3. Three phase mixtures .............................................................................................. 139 6.2. Methods .......................................................................................................................... 140 6.2.1. Sample selection and preparation .......................................................................... 140 6.2.2. Textural characterization ........................................................................................ 141 6.2.3. Density and porosity measurements ....................................................................... 142 6.2.4. The Volcanology Deformation Rig (VDR) ............................................................ 145 6.3. Experimental Results ....................................................................................................