Paleo-geomorphology of the Sierra Nevada, California, from (U-Th)/He ages in apatite

Citation
Ma. House et al., Paleo-geomorphology of the Sierra Nevada, California, from (U-Th)/He ages in apatite, AM J SCI, 301(2), 2001, pp. 77-102
Citations number
61
Language
INGLESE
art.tipo
Article
Categorie Soggetti
Earth Sciences
Journal title
AMERICAN JOURNAL OF SCIENCE
ISSN journal
0002-9599 → ACNP
Volume
301
Issue
2
Year of publication
2001
Pages
77 - 102
Database
ISI
SICI code
0002-9599(200102)301:2<77:POTSNC>2.0.ZU;2-V
Abstract
New apatite (U-Th)/He ages from the central Sierra Nevada, California, plac e limits on the morphology and evolution of longitudinal profiles of major transverse river drainages developed in the Late Cretaceous, Helium ages fr om a new orogen-parallel, constant-elevation sample transect are relatively uniform (similar to 60 Ma) and not correlated with topography, unlike thos e from a similar, lower elevation transect approx 15 km to the west. We int erpret the marked difference in the two orogen-parallel profiles to reflect a headward decrease in long-wavelength, transverse relief at the time of c ooling, consistent with either a concave-up stream gradient, typical of tho se observed near the headwaters of modern Sierran trunk streams, or a conve x gradient like those found along slope breaks of eroding plateau edges. Fr om the San Joaquin drainage we obtained a new helium age-versus-elevation p rofile, which has a comparable slope to those previously reported for the Y osemite Valley, Kings Canyon, and Mt. Whitney areas. This new profile yield s slightly older ages at a given elevation as expected from its position ad jacent to the largest major drainage. The age versus elevation profiles imp ly that the mean denudation rate of the region in the Cenozoic was about 0. 04 to 0.05 mm/yr, We show that long-wavelength (lambda = 70 km) relief infe rred from longitudinal helium age variations is a strong function of erosio n rate, such that even relatively subdued relief is detectable with helium age profiling provided that denudation rates were low. Using the rate impli ed by Sierran age-versus-elevation profiles, we infer long-wavelength relie f of 1500 +/- 500 m in the Late Cretaceous, By analogy with modern orogenic plateaus, this value of long-wavelength relief suggests a Cretaceous inter ior Cordilleran plateau lay at an elevation of at least 3000 m.