RECURRENT ERUPTION AND SUBSIDENCE AT THE PLATORO-CALDERA COMPLEX, SOUTHEASTERN SAN-JUAN VOLCANIC FIELD, COLORADO - NEW TALES FROM OLD TUFFS

Citation
Pw. Lipman et al., RECURRENT ERUPTION AND SUBSIDENCE AT THE PLATORO-CALDERA COMPLEX, SOUTHEASTERN SAN-JUAN VOLCANIC FIELD, COLORADO - NEW TALES FROM OLD TUFFS, Geological Society of America bulletin, 108(8), 1996, pp. 1039-1055
Citations number
61
Language
INGLESE
art.tipo
Article
Categorie Soggetti
Geosciences, Interdisciplinary
ISSN journal
0016-7606
Volume
108
Issue
8
Year of publication
1996
Pages
1039 - 1055
Database
ISI
SICI code
0016-7606(1996)108:8<1039:REASAT>2.0.ZU;2-T
Abstract
Reinterpretation of a voluminous regional ash-flow sheet (Masonic Park Tuff) as two separate tuff sheets of similar phenocryst-rich dacite e rupted from separate source calderas has important implications for ev olution of the multicyclic Platoro caldera complex and for caldera-for ming processes generally, Masonic Park Tuff in central parts of the Sa n Juan held, including the type area, was erupted from a concealed sou rce at 28.6 Ma, but widespread tuff previously mapped as Masonic Park Tuff in the southeastern San Juan Mountains is the product of the youn gest large-volume eruption of the Platoro caldera complex at 28.4 Ma. This large unit, newly named the ''Chiquito Peak Tuff,'' is the last-e rupted tuff of the Treasure Mountain Group, which consists of at least 20 separate ash-flow sheets of dacite to low-silica rhyolite erupted from the Platoro complex during a 1 m.y, interval (29.5-28.4 Ma). Two Treasure Mountain tuff sheets have volumes in excess of 1000 km(3) eac h, and five more have volumes of 50-150 km(3). The total volume of ash -flow tuff exceeds 2500 km(3), and caldera-related lavas of dominantly andesitic composition make up 250-500 km(3) more, A much greater volu me of intermediate-composition magma must have solidified in subcalder a magma chambers, Most preserved features of the Platoro complex-inclu ding postcollapse asymmetrical trap-door resurgent uplift of the ponde d intracaldera tuff and concurrent infilling by andesitic lava flows-p ostdate eruption of the Chiquito Peak Tuff, The numerous large-volume pre-Chiquito Peak ash-flow tuffs document multiple eruptions accompani ed by recurrent subsidence; early-formed caldera walls nearly coincide with margins of the later Chiquito Peak collapse, Repeated syneruptiv e collapse at the Platoro complex requires cumulative subsidence of at least 10 km. The rapid regeneration of silicic magmas requires the su stained presence of an andesitic subcaldera magma reservoir, or its ra pid replenishment, during the 1 m.y. life span of the Platoro complex, Either case implies large-scale stoping and assimilative recycling of the Tertiary section, including intracaldera tuffs.