Cl-36 production rate from K-spallation in the European Alps (Chironico landslide, Switzerland)

The abundant production of in situ cosmogenic Cl-36 from potassium renders Cl-36 measurements in K-rich rocks or minerals, such as K-feldspars, potentially useful for precisely dating rock surfaces, either in single-nuclide or in multi-nuclide studies, for example combined with Be-10 measurements in quartz. However, significant discrepancies in experimentally calibrated Cl-36 production rates from spallation of potassium (36P(K-sp)), referenced to sea-level/high-latitude (SLHL), limit the accuracy of Cl-36 dating from K-rich lithologies. We present a new Cl-36 calibration using K-feldspars, in which K-spallation is the most dominant Cl-36 production pathway (>92% of total Cl-36), thus minimizing uncertainties from the complex multi-pathway Cl-36 production systematics. The samples are derived from boulders of an similar to 13.4 ka-old landslide in the Swiss Alps (similar to 820 m, 46.43 degrees N, 8.85 degrees E). We obtain a local 36P(K-sp) of 306 +/- 16 atoms Cl-36 (gK)(-1) a(-1) and an SLHL 36P(K-sp) of 145.5 +/- 7.7 atoms Cl-36 (gK)(-1) a(-1), when scaled with a standard scaling protocol ('Lm'). Applying this SLHL 36P(K-sp) to determine Cl-36 exposure ages of K-feldspars from Be-10-dated moraine boulders yields excellent agreement, confirming the validity of the new SLHL 6P(K-sp) for surface exposure studies, involving Cl-36 in K-feldspars, in the Alps. Copyright (C) 2014 John Wiley & Sons, Ltd.