volcanic complex 2M. HALL, 2M. JIMENEZ, 1,2M. 'ORSTOM, UR A.P. 17-01-2 - PDF document

volcanic complex 2M. HALL, 2M. JIMENEZ,
volcanic complex 2M. HALL, 2M. JIMENEZ, 1,2M. 'ORSTOM, UR A.P. 17-01-2759, Fig. 1. Ecuador, from Litherland Egiiez (1993), modified. volcanics, proximal distal deposits. Mojanda-Fuya Fuya Regional tectonic sketch NAZ=Nazca Plate; G=Galapagos Depression; Q=Quito. fieldwork shows that it adjacent volcanic centres contemporaneous but

different histories. eruptive dynamics
different histories. eruptive dynamics stratigraphic control of forty-six sections, twenty-two of which whole-rock analyses paper. Here, only petrographic nature AND STRUCTURE volcanic complex by 30 m at Cerro Fuya Fuya. Its base m to the north, m to the has a wide, presently lake, the Laguna upon thick detrital deposits pyroclast

ic deposits, the intermediate to the sum
ic deposits, the intermediate to the summit area many peaks between These peaks to the the eastern Cerro Yanaurcu, Fig. western side, are the convergence shown the intermediate surrounding pyroclastic deposits indicates two volcanoes. whose Simplified geological possible relation- this caldera. followed by their deposits travelled

down activity filled wide, which the so
down activity filled wide, which the south descended only to the a thick They began representative of summit caldera. breccia sequence. bed showing overlain by surge deposits. 5b). In these breccia facies consisting vitric blocks Fig. 5d). they reach in size. these breccias. vitric clasts a granular, dark palagonitized matrix. Ju

venile clasts platy in shape, vitric cla
venile clasts platy in shape, vitric clasts, incipiently Houghton and these deposits structures (Fig. Dark colored falls (andesitic) ... ... ... Stratigraphic columns pyroclastic deposits from Mojanda the avalanche event. Note the rhyolitic pumice related vol.%,) of altered lithic Its thick- m at Jerusalen (Fig. the north Laguna S

an interpreted as from block contains te
an interpreted as from block contains ten deposits associated with and R2 lesser thickness series of deposits, commonly fractures, characteristic a dome blocks in Cerro San wt%) of represents the and the avalaache event (unit Fuya Fuya followed valleys westwards, deep Guayllabamba canyon. proximal deposits consist flows whose dist

urbed during Atahualpa appear de Minas m
urbed during Atahualpa appear de Minas many outcrops. the Puellaro and dammed -, -, Subsequently, ash traveled in following the declivity between the Mojanda westwards, following Rio Piganta columns, sites the north, deposits are from Otavalo m. They wt%) in andesitic material age �35,000 OBDY 13 deposits are flank deposits

Weathered ash columns showing post-avala
Weathered ash columns showing post-avalanche vesicularities (Wohletz, shaped clasts (Honnorez and complex in Houghton and Wilson, 1989). basaltic hyaloclastite are more varied, lithic blocks, lapilli and ash (Furnes Schmincke, 1984). Given deposits found the andesitic the formation these breccias. show a magmatism following activi

ty declined shortly thereafter andesitic
ty declined shortly thereafter andesitic fallout was probably destroyed great influence and lahar Plinian events dispersion as 30 km some of these explo- After the contemporaneous with activity broke edifice which lahars at the Jerusalen section (Fig. this eruptive Plinian deposits such as during the acid extru- shallow, gas-rich m

agma chamber. ,the course that are large
agma chamber. ,the course that are large Plinian eruption, that of rhyolitic composition (R1 three episodes Plinian episodes probably associated with were filled presence of (the largest, Plinian activity cone represents tion stage the Fuya Fuya in the avalanche to the south 10). Before collapse event, the adjacent edifice. Associa

ted and ash that this experienced explos
ted and ash that this experienced explosive episodes. the greater cone left a surges (units immediately followed avalanche event, forming a St Helens Popocatepetl (Robin Most of also carried to the Late Pleistocene, lava flows flows were flows, of lesser volume, southwards (Cochasqui ash flows). deposits accumulated summit area vol

canic complex. Whereas Cochasqui ash the
canic complex. Whereas Cochasqui ash the Colangal similar compositions ash flows also the most charcoal date a Cochasqui ash (Centre for Isotope Research, 22435). As and are domes occurred shortly associated volcanic centres was previously the solitary Although no radiometric dates are phases of and at the older the cessation after

the the south the avalanche exposes bas
the the south the avalanche exposes basic layers of FUYA FUYA summit domes - - Generalized stratigraphy volcanic complex. Fuya Fuya Fuya Fuya A=basalts, BA=basic andesites, D=dacites; and LK affinity (Fig. causal relation- magmatic episode and the Fuya Fuya if any, Fuya sector At least magma batches triggered the Fuya Fuya, larg

e avalanche. joint program carried Resea
e avalanche. joint program carried Research for Cooperation) and authors thank Dunkley (British Geological Survey) for the manuscript. Coltelli, M. and Ferrara, of young subducted Schmincke, H.U. the formation of acid hyaloclastites. Geothermal Research, Hall, M.L. el Ecuador. Publ. del Nacional del Hall, M.L. volcanismo Plio-quate

rnario Boletin del Colegio Geografos del
rnario Boletin del Colegio Geografos del Ecuador, M.L. and Simposio “Suelos and Kirst, basaltic volcanism: discriminating hyaloclastites from (1989). A vesicularity Kay, R.W. Aleutian magnesian andesites: melts from subducted Pacific Ocean Volcanology and Geothermal Research, pyroclastic deposits. 986). Magma-water subaqueous

and emergent basaltic la Republica del E
and emergent basaltic la Republica del Ecuador, and CODIGEM (Quito, Ecuador). (1996). Le volcan son activité au cours des 5 années et qui en résultent. Etudes Andines, Mayon volcano, Philippines. Robin, C., de Colima volcano. Geotliermal Research, Robin, C. A gigantic Bezymianny-type event at Journalpf Volcanology and Geothermal