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Typically these ages correspond to crystallization and exhumation or eruption ages, and their combination can be used to more confidently resolve candidate source terrains, establish maximum depositional ages, and constrain the thermal histories of orogenic source regions. In this paper we describe a method and case-studies of measurement of both U/Pb and (U-Th)/He ages on single crystals of zircon that improves the robustness of constraints in each of these areas by establishing both formation and cooling ages of single detrital grains.The lab will be capable of measuring U and Th concentrations for (U-Th)/He dating and the isotopic compositions of all five noble gases will sufficient mass resolution to completely resolve He thermochronometry.The laboratory will consist of: (i) A calibrated binocular microscope and camera system for preparing and measuring the geometry of samples, (ii) An automated ultra high vacuum (UHV) noble gas extraction, purification and calibrated standard and spiking system, (iii) A gas-source quadrupole mass spectrometer (QMS) for measuring NG abundances using isotope dilution, (iv) An MAP-215 sector-field NG mass spectrometer for high-precision isotope ratio measurements, and (v) An inductively coupled plasma-source quadrupole mass spectrometer (ICPQMS) for measuring U and Th (and Sm).is specifically designed for high-precision and high-accuracy thermochronometry and is currently under construction at BGC.The lab will simultaneously and accurately measure nuclide abundances and temperatures during stepwise thermal extraction of noble gases from minerals and glasses over a wide range of temperatures.
In this paper we describe a method and case-studies of measurement of both U/Pb and (U-Th)/He ages on single crystals of zircon that improves the robustness of constraints in each of these areas by establishing both formation and cooling ages of single detrital grains. Important results include the fact that detritus from ancient orogens may dominate sediments thousands of kilometers away, crustal melting and exhumation appear to be spatially-temporally decoupled in at least two orogens, and first-cycle volcanic zircons older than depositional age are surprisingly rare in most settings except in the continental interior.Accurate temperature control is essential for noble gas thermochronology.The design of the NGTL is optimized for He molar abundances, and (e) total U, Th and Sm molar abundances.The NGTL will be capable of simultaneously performing multiple and automated high-accuracy stepwise degassing analyses and diffusion experiments.
Complete system automation and instrument communications will be achieved using software written in Lab View.
In the case of the Kamchatkan, and possibly Olympic, turbidites, zircon He ages are partially reset.