Architecture and pyroclastic succession of a small Quaternary (?) maar in the Pali Aike Volcanic Field, Santa Cruz, Argentina

MJ HALLER; K NÉMETH

Zeitschrift Der Deutschen Gesellschaft Für Geowissenschaften

E. Schweizerbart'sche Verlagsbuchhandlung

Lugar: Stuttgart; Año: 2006 vol. 157 p. 155 - 164

1860-1804

An approximately 200 m long, 3 m thick continuous outcrop of a near vent crater rim tephra sequence from a young phreatomagmatic volcano of the Pali Aike Volcanic Field (Santa Cruz Province, Argentina) is one of the few outcrops where the eruptive sequence of the phreatomagmatic volcanoes of this field can be studied. Regardless of the large number of morphological features such as lake filled depressions, suggestive of the existence of maar volcanoes in the Pali Aike Volcanic Field, exposed tephra ring sequences are rare. The newly identified tephra ring section documents an eruption history of a maar that erupted through a “soft rock” environment and formed a shallow maar basin, currently filled with saline lake water. The tephra ring is rich in pre-volcanic sedimentary material. A fine grained tephra succession with abundant glassy pyroclasts indicates effective magma/water interaction and the presence of high energy bedforms suggests subsequent transportation and deposition from high energy base surges. Irregularly interbedded accidental lithic fragment rich beds suggest temporal collapse of the volcanic conduit of the active vent. The common appearance of cauliflower and breadcrust bombs together in the coarse grained tephra beds suggest that during magma/water interaction certain part of the uprising melt could have reached the surface without significant contact with the ground water.