Stable isotope paleoaltimetry of Eocene core complexes in the North American Cordillera

Abstract

The hydrogen isotope composition of Eocene muscovite in mylonitic quartzite from the Kettle and Shuswap metamorphic core complexes (Washington and British Columbia) permits estimates of paleoaltimetry of the North American Cordillera at the onset of post‐collisional lithospheric extension. Coupled oxygen, hydrogen, and 40Ar/39Ar isotope data indicate that meteoric water penetrated to significant depths during normal faulting along the Columbia River Detachment bounding both Kettle and Shuswap metamorphic core complexes. Synkinematic muscovite attains δDmuscovite values as low as −135‰ and −157‰, respectively, consistent with δDwater values of −115 ± 5‰ and −135 ± 5‰. In context with stable isotope data from Eocene sedimentary basins of continental North America, these data constrain the isotopic composition of precipitation from which paleoelevation estimates can be made. Stable isotope paleoaltimetry indicates that during detachment formation (49–47 Ma), orogen‐parallel variations in topography existed, and mean elevations decreased from ≥4000 m at the latitude of the Shuswap core complex to ≥3000 m in the Kettle core complex. In addition, these data indicate a net decrease in mean surface elevation by ∼1000 m since the Eocene. Our results for the Kettle core complex are consistent with paleoelevation estimates based on fossil floral physiognomy in the Eocene Republic basin (Washington), indicating that high elevations characterized not only the frontal escarpment near the crustal‐scale detachment but continued into the Okanogan highlands further west. Collectively, the stable isotope, geochronological, and paleofloral data support tectonic models of high Eocene surface elevations contemporaneous with magmatism and lithospheric extension.

Mountain uplift explains differences in Palaeogene patterns of mammalian evolution and extinction between North America and Europe

“…56-50 Ma) extensive regions of western North America were still fairly humid (blue and green colour code in figure 2); the first indication of less humid environments occurs in the southwest (figure 2a; see also table 1). During this time, high elevation (more than 3000 m, most probably accompanied by significant topographic relief) already characterized central British Columbia [14,15,31,32], the Colorado Plateau region [33,34] and the Sierra Nevada (e.g. [35]), while the orogenic front was active in Idaho-Utah-Arizona (e.g.…”

Paleogene landscape evolution of the central North American Cordillera: Developing topography and hydrology in the Laramide foreland

“…In general these two independent approaches arrive at the same interpretation, calling for a spatially and temporally evolving pattern of high elevations from north to south in the Sevier hinterland. Stable isotopic studies of metamorphic core complexes show evidence of high elevations (~4 km) in British Columbia and Washington in the early Eocene at 49-47 Ma (Mulch et al, 2004;Mulch et al, 2007). Oxygen isotopic studies of intermontane Geological Society of America Bulletin, January/February 2009 basins suggest increased peak elevations and development of relief occurring between 50 and 47 Ma in southwestern Montana (Kent-Corson et al, 2006), between 40 and 35 Ma in northern Nevada , and by ca.…”

Central Anatolian Plateau, Turkey: incision and paleoaltimetry recorded from volcanic rocks

“…There are numerous paleoaltimetric proxies that provide information on the topographical evolution of mountain belts (Mulch et al 2007). The major advantage of using various hydrous silicate minerals originates from the fact that multiple (oxygen and hydrogen) isotope systems can be applied and used for stable isotope paleoaltimetry (Mulch et al 2007).…”

“…The major advantage of using various hydrous silicate minerals originates from the fact that multiple (oxygen and hydrogen) isotope systems can be applied and used for stable isotope paleoaltimetry (Mulch et al 2007). The use of hydrous silicates (such as smectite, kaolinite, and chert, as well as metamorphic minerals that grow in the presence of meteoric waters) in paleoclimate and paleoaltimetry studies has important additional advantages (Mulch et al 2007).…”