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Major Late Miocene cooling of the middle crust associated with extensional orogenesis in the Funeral Mountains, California
Author(s) -
Holm Daniel K.,
Dokka Roy K.
Publication year - 1991
Publication title -
geophysical research letters
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.007
H-Index - 273
eISSN - 1944-8007
pISSN - 0094-8276
DOI - 10.1029/91gl02079
Subject(s) - geology , metamorphic core complex , detachment fault , canyon , late miocene , paleontology , cretaceous , zircon , fission track dating , geomorphology , tectonics , extensional definition , structural basin
The Funeral Mountains of the Death Valley region consist of a metamorphic core complex that underlies the Miocene Boundary Canyon detachment fault. Fissiontrack age determinations on sphene, zircon, and apatite from the highest grade portions of the Funeral Mountains (collected in Monarch Canyon) indicate rapid cooling from above ∼285°C at 9–10 Ma. The steep dT / dt slope implied by the cooling path envelope as well as its synchroneity with development of the Boundary Canyon detachment suggests tectonic unroofing of between 9.5 and 17 km since ∼10 Ma (assuming typical geothermal gradients prior to detachment development of between ∼20–30°C/km). Previous studies report muscovite 40 Ar/ 39 Ar plateau ages from the same area indicating that the Funeral Mountains core may have cooled below ∼350°C between 110‐55 Ma. These data, when combined with the fission track ages, suggest residence of the metamorphic terrain at 285–350°C from Late Cretaceous to late Miocene time. Recent studies, using petrologic constraints, have suggested that much of the unroofing of the Funeral Mountains, as well as development of tectonite fabrics, occurred during Mesozoic extension. Recognition of temperatures in the 300°C range during Miocene time suggests some of the ductile extensional fabrics may be late Miocene in age.