https://www.geomar.de/fileadmin/personal/fb1/p-oz/mfrank/Georg_et_al_2006_Chem_Geol.pdf

New sample preparation techniques for the determination of Si isotopic compositions using MC-ICPMS

...................................................... Introduction...................................................................^ Basic Concepts ................................................................................................................................................2 Aclmowledgements...........................................^ Hydrogen...............................................................................................................................................^ Reference materials and reporting of isotope ratios......................................................................................5 Ranges in isotopic composition......................................................................................................................5 Water...................................................................................................................................... Silicates............................................................................................................................................^ Hydroxides...........:...............................................................................^ Organic hydrogen....................................................................................................................................8 Methane .................................................................................................................................................10 Hydrogen gas......................................................................................................................................... 10 Lithium................................................^ Reference materials and reporting of isotope ratios.................................................................................... 11 Ranges in isotopic composition.................................................................................................................... 11 Marine sources ......................................................................................................................................11 Non-marine sources............................................................................................................................... 13 Lithium in rocks.................................................................................................................................... 13 Phosphates............................................................................................................................................. 13 Silicates....... ... . ........... . .... . .. .. . . .... . ....... .._ Reagents............................ .. ..... ... . ... .. ... . . ..............J^ Boron......................................................................... Reference materials and reporting of isotope ratios.................................................................................... 15 Ranges in isotopic composition.................................................................................................................... 15 Marine sources ......................................................................................................................................15 Non-marine sources............................................................................................................................... 16 Igneous rocks......................................................................................................................................... 19 Metamorphic rocks................................................................................................................................ 19 Sediments............................................................................^ Organic boron........................................................................................................................................19 Carbon ......................................................................................20 Reference materials and reporting of isotope ratios....................................................................................20 Ranges in isotopic composition....................................................................................................................20 Carbonate and bicarbonate ...................................................................................................................20 Carbon dioxide......................................................................................................................................25 Oxalates...............................................................................26 Carbon monoxide..................................................................................................................................26 Organic carbon ......................................................................................................................................26 Elemental carbon...................................................................................................................................28 Ethane ....................................................................................................................................................28 Methane .................................................................................................................................................28 Nitrogen............................................................ Reference materials and reporting of isotope ratios....................................................................................29 Ranges in isotopic composition....................................................................................................................29 Nitrate................................................................................................................................ Nitrite............................................................................................ Nitrogen oxide gases.......................................................................................30 Nitrogen gas ................................................................................................30 Organic nitrogen....................................................................................................................................32 Nitrogen in rocks...................................................................................................................................34 Ammonium.................................................................................................................................^ Oxygen ........................................................... Reference materials and reporting of isotope ratios....................................................................................36 Ranges in isotopic composition....................................................................................................................37 Oxygen gas.............................................................................................................................................39 Water........................................................^ Carbon monoxide..................................................................................................................................41 Carbon dioxide ......................................................................................................................................41 Carbonates .............................................................................................................................................41 Nitrogen oxides.....................................................................................................................................42 Other Oxides..........................................................................................................................................42 Phosphates .............................................................................................................................................42 Silicates...................................................... Sulfates..................................................................................^ Plants and animals.................................................................................................................................43 Magnesium.....................................................................................................................................^ Reference materials and reporting of isotope ratios....................................................................................44 Ranges in isotopic composition....................................................................................................................44 Marine sources ......................................................................................................................................44 Elemental magnesium...........................................................................................................................46 SiHcon..............................................................^ Reference materials and reporting of isotope ratios....................................................................................46 Ranges in isotopic composition....................................................................................................................46 Igneous rocks.........................................................................................................................................47 Metamorphic rocks................................................................................................................................47 Vein quartz and silicified rocks ............................

/pdf/compilation-of-minimum-and-maximum-isotope-ratios-of-4zh3ha1cap.pdf

Compilation of minimum and maximum isotope ratios of selected elements in naturally occurring terrestrial materials and reagents

In contrast to many other stable isotopes of the elements discussed in this book, those of silicon are not strictly speaking “Non-Traditional Stable Isotopes” because they have been studied for more than 60 years. After the pioneering works of Reynolds and Verhoogen (1953) and Allenby (1954), a steady increase in silicon isotope studies of geological materials has led to a substantial corpus of data. These data were compiled by Ding et al. (1996) alongside new measurements that, collectively, included over a thousand samples of rocks, minerals, waters and biological materials. Most of these data were produced using the well established method of gas source mass spectrometry after sample decomposition and silicon purification via fluorination techniques.

As for many non-traditional stable isotopes, silicon isotope research has flourished with the advent of second generation of multicollector plasma source mass spectrometers (MC–ICP–MS). These instruments eliminated the requirement of hazardous gaseous fluorine sample preparation methods while permitting improved analytical precision in both wet plasma (De La Rocha 2002) and in dry plasma (Cardinal et al. 2003). Subsequent analytical developments involving high mass resolution MC–ICP–MS combined with improved silicon purification methods (Georg et al. 2006) made this analytical technique more robust and precise enough to study even the subtle silicon isotope variations produced during high temperature geological processes (Savage et al. 2014).

Silicon is the fourteenth element of the Periodic Table. Its atomic mass was precisely determined to be 28.08553 ± 0.00039 in atomic mass units (a.m.u.) on a pure silicon reference material (NIST SRM–990, Barnes et al. 1975). This 95% confidence limit error includes the overall natural isotopic variation range for 30Si/28Si known by the time, estimated to be about 5‰ from the analysis of biological, meteoritic and terrestrial materials (Tilles 1961). As detailed below, the current database suggests …

Silicon Isotope Geochemistry

The silicon isotope composition (d30Si) of biogenic opal provides a view of the silica cycle at times in the past. Reconstructions require the knowledge of silicon isotope fractionation during opal biomineralization. The d30Si of specimens of hexactinellid sponges and demosponges growing in the modern ocean ranged from -1.2‰ to -3.7‰ (n=6), corresponding to the production of opal that has a d30Si value 3.8‰ +/- 0.8‰ more negative than seawater silicic acid and a fractionation factor (a) of 0.9964. This is three times the fractionation observed during opal formation by marine diatoms and terrestrial plants and is the largest fractionation of silicon isotopes observed for any natural process on Earth. The d30Si values of sponge spicules across the Eocene- Oligocene boundary at Ocean Drilling Program Site 689 on Maud Rise range from -1.1‰ to -3.0‰, overlapping the range observed for sponges growing in modern seawater.

Silicon isotope fractionation by marine sponges and the reconstruction of the silicon isotope composition of ancient deep water

Late Cretaceous, granitic pegmatite-aplite dikes in southern California have been known for gem-quality minerals and as a commercial source of lithium. Minerals, whole-rock samples, and inclusion fluids from nine of these dikes and from associated wall rocks have been analyzed for their oxygen, hydrogen, and carbon isotope compositions to ascertain the origins and thermal histories of the dikes. Oxygen isotope geothermometry used in combination with thermometric data from primary fluid inclusions enabled the determination of the pressure regime during crystallization. Two groups of dikes are evident from their oxygen isotope compositions (δ18Oqtz≃+10.5 in Group A, and ≃+8.5 in Group B). Prior to the end of crystallization, Group A pegmatites had already extensively exchanged oxygen with their wall rocks, while Group B dikes may represent a closer approximation to the original isotopic composition of the pegmatite melts. Oxygen isotope fractionations between minerals are similar in all dikes and indicate that the pegmatites were emplaced at temperatures of about 730 ° to 700 ° C. Supersolidus crystallization began with the basal aplite zone and ended with formation of “quench aplite” in the pocket zone, nearly to 565 ° C. Subsolidus formation of gem-bearing pockets took place over a relatively narrow temperature range of about 40 ° C (approximately 565–525 ° C). Nearly closed-system crystallization is indicated. Hornblende in gabbroic and noritic wall rocks (δDw.r. = −90 to −130) in the Mesa Grande district crystallized in the presence of, or exchanged hydrogen with, meteoric water (δD≃ −90) prior to the emplacement of the pegmatite dikes. Magmatic water was subsequently added to the wall rocks adjacent to the pegmatites. Groups A and B pegmatites cannot be distinguished on the basis of their hydrogen isotope compositions. A decrease in δD of muscovite inward from the walls of the dikes reflects a decrease in temperature. δD values of H2O from fluid inclusions are: −50 to −73 (aplite and pegmatite zones); −62 to −75 (pocket quartz: Tourmaline Queen and Stewart dikes); and −50 ± 4 (pocket quartz from many dikes). The average δ13C of juvenile CO2 in fluid inclusions in Group B pegmatites is −7.9. In Group A pegmatities, δ13C of CO2 is more negative (−10 to −15.6), due to exchange of C with wall rocks and/or loss of 13C-enriched CO2 to an exsolving vapor phase. Pressures during crystallization of the pockets were on the order of 2,100 bars, and may have increased slightly during pocket growth. A depth of formation of at least 6.8 km (sp. gr. of over burden = 3.0, and P
fiuid=P
load) is indicated, and a rate of uplift of 0.07 cm/yr. follows from available geochronologic data.

Stable isotope and fluid inclusion studies of gem-bearing granitic pegmatite-aplite dikes, San Diego Co., California

Isotopic abundance variations of silicon in quartz and feldspar from the Rose Quartz Pegmatite of the Pala district in Southern California are reported. All feldspar samples are enriched in Si30 with respect to adjacent quartz samples, and the magnitude of enrichment varies from 0.6 to 2.7 per mil in Si30. Feldspar-quartz differences were found to increase from outer zones towards the inner quartz core. All measurements on quartz samples were within a total range of about 0.6 per mil. The feldspars most heavily enriched in Si30 are believed to result from Rayleigh fractionation during crystallization from a vapor phase.

Variations of silicon isotope ratios in a zoned pegmatite

Primordial gas in the Washington County meteorite

Measurements of natural variations in isotopic abundance ratios of silicon are reported. A maximum natural range of 5.3 per mil in Si/sup 30/ is obsenved to date. Coexisting biotite, quartz, and feldspars from some specimens of igneous rock from the Yosemite region differ by as much as 3 per mil; in other grossly similar igneous rocks from the same region the same minerals differ by less than 0.3 per mil. In those rocks with large differences between the minerals, the ratio of STASi/sup 30/!/ STASi/sup 28/ + Si/sup 29/! increases in the order biotite, quartz, feldspar. All granitic rocks studied are enriched in Si/sup 30/ with respect to meteorites and basic rocks. Measurements on some sediments and biologic samples covered a range of approximately 4 per mil. A group of tektites covered a range of less than 0.7 per mil, with isotopic abundances centrally distributed within the observed normal terrestrial range. The results are interpreted, and applications of such studies to problems of geothermometry and formation of igneous rocks are discussed. (auth)

Natural Variations in Isotopic Abundances of Silicon

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Variations of silicon isotope ratios in a zoned pegmatite

Primordial gas in the Washington County meteorite

Natural Variations in Isotopic Abundances of Silicon