The relative concentration of oxygen vacancies in granitic quartz was estimated using the ESR signal intensity of E′ centers (an electron at an oxygen vacancy) after γ ray irradiation and subsequent heating at 300°C. The E′ intensity indicative of total oxygen vacancies in granitic quartz is correlated with total absorbed dose from β and γ rays for the geological ages ranging from 12 to 1700 Ma. The amount of oxygen vacancies in natural quartz created by β and γ rays may be comparable in the absorbed dose range of 104 to 107 Gy to the amount by α-recoil effect.
Organic geochemical study on an extremely acid crater lake (Yugama, pH = 1.2) of an active Kusatsu-Shirane Volcano in Japan has been carried out to clarify the features and sources of organic components in relation to biological activity. Generally, n-alkanes ranging from n-C15 to n-C36 with a predominance of long-chain (n-C20–n-C36) n-alkanes maximizing at n-C27, n-C29 or n-C31 were detected in suspended solids (≥0.60 μm), sulfur aggregate and surface sediments of the lake, and soils in the surroundings of the lake, together with pristane, phytane, squalane, steranes and/or triterpanes. A series of n-alkanoic acids ranging from n-C8 to n-C32 with a predominance of even-carbon numbers were found in all the samples, along with cis- and trans-isomers of n-alkenoic acids [n-C16:1 (Δ7 and δ9) and n-C18:1 (Δ9 and Δ11)], iso- and anteiso-alkanoic acids (C14–C17), and cyclopropyl alkanoic acids (C17 and C19). No polyenoic alkenoic acids were, however, found in all the samples. Normal 3-hydroxy acids (n-C10–n-C18) mainly maximizing at n-C14 were detected, together with iso- and anteiso-3-hydroxy acids (C12–C18). The features of organic components in the lake waters and sediments indicate that they can be attributed to bacteria, such as Thiobacillus thiooxidans in addition to certain uncultured bacteria, with some influences of eroded, and/or wind-transported materials containing vascular plant debris from the surroundings of the lake. Low concentrations of fatty acids mainly reflect the paucity of photosynthetic producers and small living biomass in the lake. Relatively high trans/cis-C16:1 alkenoic acid ratios (0.24–0.52) may be caused by unfavorable habitat for microbial activity in the lake. The thermal maturation parameters of (20S/20R)-24-ethyl-5α(H), 14α(H), -17α(H)-cholestane ratios (0.49–0.77) and (22S/22R)-17α(H), 21β(H)-30-homohopane ratios (1.0–1.4) have not reached equilibrium values, but may have been significantly influenced by hydrothermal activity in the past in Lake Yugama and the surroundings of the lake.
Gas chromatographic/mass spectrometric examination of products from laboratory thermal degradation of kerogen from a young marine sediment (Tanner Basin off California), revealed a series of long-chain nitriles whose carbon-chain lengths range from 12 to 26. These compounds appeared after the relatively mild thermal conditions of 310–350°C for 5–116 hrs and disappeared before major n-alkane generation. We hypothesise that n-alkanes are generated at the expense of long-chain fatty nitriles which in turn are formed via fatty acid amide-linked structures in kerogen. Heating of standard long chain (C18) fatty acid amides with kerogen produced n-alkanes with no odd/even predominance. The heating experiments showed that these nitrogen compounds have a strong potential for producing a series of normal hydrocarbons. Consequently, nitrogen-linked long-methylene-chain structures in kerogen analogous to fatty acid amides/fatty nitriles can act as one of the precursors of petroleum hydrocarbons.
Rare earth element (REE) contents and distribution patterns in the major rock-forming minerals (vesuvianite, wollastonite, garnet, pyroxene, hornblende, epidote and fluorite) from the Shizhuyuan W, Sn, Mo and Bi-containing skarn deposit of Hunan Province of South China have been determined. Three types of REE distribution patterns were found: 1) vesuvianite and wollastonite, formed at the expense of carbonates and shales of the Upper Devonian Shetianqiao Formation during thermal metamorphism stage, show linear light REE enrichment and small Eu anomalies; 2) garnet, the most abundant mineral in the skarn deposited at metasomatic stage, exhibits high REE enrichment and considerable negative Eu anomalies; 3) epidote and fluorite, precipitated during retrograde alteration stage, display very strong negative Eu anomalies. Comparison of relative REE abundances in these minerals with those in the carbonates and shales as well as in the Qianlishan Yanshanian granite suggests that REE compositions of the vesuvianite and wollastonite appear to have been inherited from precursor carbonates and shales, whereas REE contents and patterns in the metasomatic and the retrograde alteration products, such as garnet and epidote, seem to have been determined by the interactions between the reacting minerals and hydrothermal solutions originated from Qianlishan granite.
A detailed isotopic and trace element acid-leaching study of “less-altered” and “more-altered” splits of a crystalline MORB (∼12 Ma) and a glassy (∼15 Ma) MORB from NE Pacific has been carried out by collecting two successive acid-leached fractions and residues left after leaching, and analyzing for Sr, Nd and Pb isotopes and related elements. During oxidation of the crystalline basalt, the inferred whole-rock isotope ratios show only a small increase for Sr, a very small insignificant decrease for Nd, but very large increase for Pb. Relative to “fresh” basaltic glass, the whole-rock isotope ratios for palagonitized glass show a very large increase for Sr, a very small decrease for Nd, and small increase for Pb. Most trace elements and their ratios in both types of samples and their splits also show very significant changes related to seawater interaction. During oxidation of the crystalline MORB, the whole-rock Rb/Sr and U/Pb increase by ∼75% and ∼500%, whereas Sm/Nd, Th/Pb and Th/U decrease by ∼4%, ∼30% and ∼90% respectively. On the other hand during palagonitization of the basaltic glass, the whole-rock Rb/Sr increases by ∼275%, whereas Th/Pb and Th/U both decrease by ∼60%. For the first acid-leached fractions, all elements including the REE show high enrichment factors; the highest values are for U and Pb in the crystalline MORB. A viable mechanism to explain these data may be an elemental and isotopic exchange (under seawater-dominated conditions; modified seawater/rock ratios ∼10–400) between basalt and seawater that had interacted earlier with overlying sediments.