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Diagenetic character of the Tertiary basin between Los Angeles and Osorno, southern Chile

1994; National Geology and Mining Service; Volume: 21; Issue: 2 Linguagem: Inglês

10.5027/andgeov21n2-a07

0718-7092

Ursula Kelm, María Eugenia Cisternas, Sonia Helle, David Méndez,

Geochemistry and Geologic Mapping

ABSTRACT. The diagenetic character of the sedimentary rocks 01 the Tertiary basin between Los Angeles and Osorno has been assessed according to its clay mineralogy and coal rank. Illite/smectite mixed layering varies between more than 90% and more than 70% on the western basin margin. 30% smectite interlayering is found on the eastern margin at 1,000 m, the maximum depth sampled. Ro values vary between 0.42% and 0.52%. The role of contemporaneous volcanism in basin diagenesis is analyzed and dated, and its importance in the diagenetic development of the basin is discussed. Oligocene-early Miocene volcanism changes from rhyolitic to basaltic compositions from north to south. K-Ar ages vary from 28 to 18 Ma for the Los Angeles and Temuco areas. Volcanism is considered to be a producer of abundant sediment rather than a source of permanent elevated heatflow. 70°C is proposed as the burial temperature reached in the western sector of the basin. RESUMEN. Caracter diagenetico de la cuenca Terciaria entre Los Angeles y Osorno, sur de Chile. Se evaluo el caracter diagenetico de las rocas sedimentarias de la cuenca terciaria entre Los Angeles y Osorno con referencia a su mineralogia de arcillas y la madurez de su materia carbonosa. La intercalacion illita/esmectita varia entre mayor que 90% y mayor que 70%, en la margen occidental de la cuenca; en la margen oriental, a la profundidad maxima del muestreo (1 .000 m), se detecto una intercalacion de esmectita de 30%. Los valores Ro varian entre 0,42% y 0,52%. Se discute el rol del vulcanismo contemporaneo en la diagenesis de la cuenca. El vulcanismo del Oligoceno-Mioceno temprano cambia su composicion de norte a sur, pasando esta de riolitica a basaltica. Las edades K-Ar varian entre 28 Ma y 18 Ma, en las areas de Los Angeles y Temuco. Se toma al vulcanismo como un productor de abundante sedimentacion mas que como una IU3nte permanente de flujo calorico elevado. Se propone que la temperatura de diagenesis alcanzo 70C en el sector occidental de la cuenca.