4He behavior in calcite filling viewed by (U–Th)He dating, 4He diffusion and crystallographic studies.pdfVIP

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4He behavior in calcite filling viewed by (U–Th)He dating, 4He diffusion and crystallographic studies.pdf

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4He behavior in calcite filling viewed by (U–Th)He dating, 4He diffusion and crystallographic studies.pdf

Available online at ScienceDirect Geochimica et Cosmochimica Acta 125 (2014) 414–432 /locate/gca 4He behavior in calcite ?lling viewed by (U–Th)/He dating, 4He di?usion and crystallographic studies Alexandre Cros a, Ce′cile Gautheron a,?, Maurice Pagel a, Patrick Berthet b, Laurent Tassan-Got c, Eric Douville d, Rosella Pinna-Jamme a, Philippe Sarda a a Universite′ Paris-Sud, Laboratoire IDES, UMR CNRS-UPS 8145, F-91405 Orsay, France b ICMMO/LPCES, UMR8182, CNRS, Universite′ Paris-Sud, F-91405 Orsay, France c Institut de Physique Nucle′aire, CNRS/IN2P3, Universite′ Paris-Sud, F-91405 Orsay, France d LSCE/IPSL, UMR 8212 CNRS-CEA-UVSQ, 91198 Gif sur Yvette, France Received 28 February 2013; accepted in revised form 26 September 2013; available online 10 October 2013 Abstract Fault-?lling calcite crystals sampled from the Eocene/Oligocene Gondrecourt graben, Paris Basin, Eastern France, have been studied in order to test the potentiality of calcite (U–Th)/He dating, based on recognized He retention behavior in crystal lattice at surface temperature (Copeland et al., 2007). The samples have been selected because of their relatively old Eocene to Oligocene precipitation age and cold thermal history (40 °C since precipitation). They were sorted into three main tectonic and morphological groups in order of precipitation, including (1) micro-fracture calcites, (2) breccia and associated geodic calcites, and (3) vein and associated geodic calcites. (U–Th)/He dating of 63 calcite fragments yields ages dispersed from 0.2 ± 0.02 to 35.8 ± 2.7 Ma, as well as two older dates of 117 ± 10 and 205 ± 28 Ma (1r). These He ages correlate with grain chemistry, such as Sr, RREE concentrations or (La/Yb)N ratios, likely re?ecting parent ?uid evolution. Only the oldest He ages, which correspond to the most recently precipitated crystals, have preserved the total 4He budget since precipitation. To better understand both the age dispersion and why calcites precipitated earlier show younger