HR: 1400h
AN: GS23B-10    [Abstracts]
TI: Helium and Argon Everywhere in the Earth's Crust
AU: * Solé, J
EM: jsole@geologia.unam.mx
AF: Instituto de Geología Universidad Nacional Autónoma de México, Cd. Universitaria, México, DF 04510, Mexico
AU: Pi, T
EM: tpuig@geologia.unam.mx
AB: Noble gas abundances and isotopic ratios in minerals and rocks are used in many fields of the Earth Sciences. Besides primordial abundance in the solar system, radiogenic ⁴He and ⁴⁰Ar are found in minerals that contain their parent elements, principally K, U, Th and Sm. It is generally supposed that He and Ar are generated and stored in a reduced set of minerals. A systematic study of about 40 common minerals, not investigated previously for radiogenic nobles gases, shows that most contain significant amounts of helium and argon and therefore are potential candidates for noble gas transport and storage. We measured ⁴He and ⁴⁰Ar concentrations and ⁴⁰Ar/³⁶Ar ratios and found that every studied mineral contains measurable He and/or Ar. Argon ratios are variable, from almost 100% radiogenic to entirely atmospheric, but for most minerals a radiogenic component can be measured. At the present stage of the study, we have not yet measured the parent concentrations for age determination, so the role of excess argon is unknown. Nevertheless, with the advent of high reproducibility multicollector noble gas mass spectrometers, the dating of many minerals not considered previously for geochronology will be probably feasible, and direct dating of diverse ore deposits, sedimentary sequences, etc. will become a reality.
DE: 1040 Radiogenic isotope geochemistry
SC: Geochemical Society [GS]
MN: 2007 Joint Assembly