Isotopic and geochronologic investigation of authigenic, K‐bearing clays in the Appalachian Plateau of the northeastern U.S. Midcontinent yields new insights about the tectonic and diagenetic history of the North American sedimentary cover sequence. In situ texture analysis by High Resolution X‐ray Texture Goniometry indicates preservation of bedding‐parallel diagenetic fabrics with burial depths of 2–5 km, and illite mineralization temperatures are spatially variable, ranging from 80 to 190 °C, correlating to similar depths of 3–6 km. The mineralizing geofluid is surface derived, with δD values ranging from −48‰ to −72‰ (in the range of predicted Pangea meteoric fluid). In addition, we find that mineralizing fluid δD values increase away from the orogenic front, consistent with a rain shadow effect from the high elevation Appalachian orogen. The age of authigenic illite is constrained by40Ar/39Ar geochronology to 308–318 Ma, reflecting Upper Carboniferous diagenesis. We postulate that far‐field stress transmission from continent‐continent collision created regional permeability pathways for surface fluids, altering the hydrologic architecture of the brittle crust and allowing meteoric fluid infiltration into upper crustal rocks. This interpretation challenges the popular view of tectonically forced, lateral fluid flow from the Appalachian orogen (squeegee hypothesis).
Infiltration of meteoric water in the South Tibetan Detachment (Mount Everest, Himalaya): When and why?: Meteoric Fluid Infiltration in the STD
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null (Ed.)Abstract. Meteoric 10Be (10Bemet) concentrations insoil profiles have great potential as a geochronometer and a tracer of Earthsurface processes, particularly in fine-grained soils lacking quartz thatwould preclude the use of in situ produced 10Be (10Bein situ). Oneprerequisite for using this technique for accurately calculating rates anddates is constraining the delivery, or flux, of 10Bemet to a site.However, few studies to date have quantified long-term (i.e., millennial)delivery rates, and none have determined a delivery rate for an erodingsoil. In this study, we compared existing concentrations of 10Bein situ with new measurements of 10Bemet in eroding soils sampledfrom the same depth profiles to calibrate a long-term 10Bemetdelivery rate. We did so on the Pinedale (∼ 21–25 kyr) and BullLake (∼ 140 kyr) glacial moraines at Fremont Lake, Wyoming(USA), where age, grain sizes, weathering indices, and soil properties areknown, as are erosion and denudation rates calculated from 10Bein situ. After ensuring sufficient beryllium retention in each profile,solving for the delivery rate of 10Bemet, and normalizing forpaleomagnetic and solar intensity variations over the Holocene, we calculate10Bemet fluxes of 1.46 (±0.20) × 106 atoms cm−2 yr−1 and 1.30 (±0.48) × 106 atoms cm−2 yr−1 tothe Pinedale and Bull Lake moraines, respectively, and compare these valuesto two widely used 10Bemet delivery rate estimation methods thatsubstantially differ for this site. Accurately estimating the 10Bemetflux using these methods requires a consideration of spatial scale andtemporally varying parameters (i.e., paleomagnetic field intensity, solarmodulation) to ensure the most realistic estimates of10Bemet-derived erosion rates in future studies.more » « less
