Medium: Taschenbuch, Einband: Kartoniert / Broschiert, Titel: Potassium Dating of Iron Meteorites, Autor: Shankar, Nirmala, Verlag: LAP Lambert Academic Publishing, Sprache: Englisch, Rubrik: Wirtschaft // Wirtschaftsratgeber, Seiten: 252, Informationen: Paperback, Gewicht: 392 gr, Verkäufer: averdo
Felsic is a term used in geology to refer to silicate minerals, magma, and rocks which are enriched in the lighter elements such as silicon, oxygen, aluminium, sodium, and potassium. The term combines the words "feldspar" and "silica." Felsic minerals are usually light in color and have specific gravities less than 3. Common felsic minerals include quartz, muscovite, orthoclase, and the sodium-rich plagioclase feldspars. The most common felsic rock is granite. On the opposite side of the rock spectrum are the iron and magnesium-rich mafic and ultramafic minerals and rocks. In modern usage, the term acid rock, although sometimes used as a synonym, refers to a high silica content (greater than 63% SiO2 by weight) volcanic rock such as rhyolite. The term was used more broadly in older geologic literature. It is considered archaic as the terms acidic and basic rock were based on an incorrect idea dating from the 1800s that silicic acid was the chief form of silicon occurring in rocks. The term felsic is related to but not derived from the German adjective felsig ("rocky").
This research involves the determination of the cosmic ray exposure ages of iron meteorites using 39K-40K-41K dating. Potassium was separated from nickel using ~ 4 mL of Chelex-100 resin and 15 mL of ammonium acetate (a mixture of equal volumes of 2 M acetic acid and 3 M aqueous ammonia) as eluent. Nickel was retained as a complex and potassium elutes out. The method is effective because of a low value for the blanks (~ 50 ng of potassium) that could be achieved. The concentration of the separated K, measured using Graphite furnace atomic absorption spectrometry (GFAAS), inductively coupled mass spectrometry (ICPMS) and isotope dilution mass spectrometry (IDMS) and will be used for the calculation of 39K-40K-41K exposure ages of iron meteorites. Potassium was successfully separated from multiple samples of 8 iron meteorites. The calculated CRE age (378 Ma) agrees for the meteorite Brownfield (355 Ma, Voshage and Feldmann, 1979) with the literature value. The literature value (645 Ma, Voshage and Feldmann, 1979) is ~3 times the value calculated (190 Ma, this work) for Picacho.
Perhaps no dating method has the wide range of applicability as does the potassium argon dating method from either consideration of the ranges of ages which can be dated or the availability of suitable material to date. Minerals as young as tens of thousands of years to minerals billions of years old have been successfully dated. Many minerals retain for times of the order of billions of years the daughter, Ar40, and many minerals contain as a component K40 the parent element, potassium being a common element in the earth's crust. As a result, most rock contains at least one mineral which can be successfully dated by the potassium argon method. Even though this method has been applied for over fifteen years, there is as yet no work which summarizes the experimental techniques and the results available. The sixtieth birthday ofW. GENTNER, one of the pioneers in this field of research, is a suitable time to present such a summary.