共查询到20条相似文献，搜索用时 47 毫秒
1.
Previously studied thermosequences of wood (chestnut) and grass (rice straw) biochar were subjected to hydrogen pyrolysis (hypy) to evaluate the efficacy of the technique for determining pyrogenic carbon (CP) abundance. As expected, biochar from both wood and grass produced at higher temperature had higher CP amount. However, the trend was not linear, but more sigmoidal. CP/CT ratio values (CT = total organic carbon) for the wood thermosequence were ⩽0.03 at biochar production temperature (TCHAR) ⩽ 300 °C. They increased dramatically until 600 °C and remained relatively constant and near unity at higher biochar production temperature. Grass biochar was similar in profile, but CP/CT values rose dramatically after 400 °C. The findings are consistent with the hypothesis that hypy residues contain polycyclic aromatic hydrocarbons (PAHs) with a degree of condensation above at least 7–14 fused rings, with labile organic matter and pyrogenic PAHs below this degree of condensation removed by hypy.Both wood and grass thermosequences displayed δ13CP values that decreased with increased TCHAR, indicating that recalcitrant carbon compounds (pyrogenic aromatic PAHs with a relatively high degree of condensation) were first formed from structural components with relatively high δ13C values (e.g. cellulose). Relatively constant δ13C values at TCHAR ⩾ 500 °C suggested the dominant pyrolysis reaction was condensation of PAHs with no additional fractionation. Comparison of hypy with benzene polycarboxylic acid (BPCA), ‘ring current’ NMR and pyrolysis gas chromatography–mass spectrometry (GC–MS) results from the same suite of samples indicated a consistent overview of the structure of CP, but provided unique and complimentary information. 相似文献
2.
Future climatic conditions may coincide with an increased potential for wildfires in grassland and forest ecosystems, whereby charred biomass would be incorporated into soils. Molecular changes in biomass upon charring have been frequently analysed with a focus on black carbon. Aliphatic and aromatic hydrocarbons, known to be liberated during incomplete combustion of biomass have been preferentially analysed in soot particles, whereas determinations of these compounds in charred biomass residues are scarce. We discuss the influence of increasing charring temperature on the aliphatic and aromatic hydrocarbon composition of crop grass combustion residues. Straw from rye, representing C3 grasses and maize, representing C4 grasses, was charred in the presence of limited oxygen at 300, 400 and 500 °C. Typical n-alkane distribution patterns with a strong predominance of long chain odd-numbered n-alkanes maximising at C31 were observed in raw straw. Upon combustion at 300 °C aliphatic hydrocarbons in char were dominated by sterenes, whereas at 400 °C sterenes disappeared and medium chain length n-alkanes, maximising around n-C20, with a balanced odd/even distribution were present. At a charring temperature of 500 °C n-alkane chain length shifted to short chain homologues, maximising at C18 with a pronounced predominance of even homologues. Even numbered, short chain n-alkanes in soils may thus serve as a marker for residues of charred biomass. Aromatic hydrocarbons indicate an onset of aromatization of biomass already at 300 °C, followed by severe aromatization upon incomplete combustion at 400–500 °C. The diagnostic composition of aliphatic and aromatic hydrocarbons from charred biomass affords potential for identifying residues from burned vegetation in recent and fossil soils and sediments. 相似文献
3.
Biochar application in a tropical,agricultural region: A plot scale study in Tamil Nadu,India 总被引：1，自引：0，他引：1
A plot-scale evaluation of biochar application to agricultural soils was conducted in Tirunelveli, Tamil Nadu, India, to investigate the potential of biochar to improve soil fertility and moisture content. Biochar feedstocks need to be sustainably sourced: several locally available feedstocks (rice husk, cassia stems, palm leaves and sawdust) were analysed as proposed soil amendments so that no single biomass material is depleted to maintain biochar addition. The biochars from different biomass feedstock contained >20% C and were high in macro- and micronutrients. The results suggest that an application rate of 6.6 metric tonnes ha?1 cassia biochar was enough to initiate C-accumulation, which is reflected in an increase in OM and a net reduction in soil bulk density. 相似文献
4.
《Gondwana Research》2014,25(3):1120-1138
Phosphatized microfossils from ca. 580 Ma from the Doushantuo Formation in the Weng'an region of South China were analyzed by Fourier transform infrared (FTIR) microspectroscopy for their chemical characterization. Two morpho-types of phosphatized embryo-like fossils (Megasphaera and Megaclonophycus) were analyzed, together with algal fossils. Transmission IR spectra of the microfossils have absorption bands of around 2960 cm− 1 and 2925 cm− 1, indicating the presence of aliphatic hydrocarbon (anti-symmetric aliphatic CH3 and aliphatic CH2), and have an additional band of around 1595 cm− 1, probably derived from aromatic moieties (aromatic CC). In addition, IR microscopic mapping shows that aliphatic hydrocarbon and aromatics are distributed inside the embryo-like fossils. The embryo-like fossils appear to show three types of CH3/CH2 peak height ratios (R3/2) and aromatic CC/CH2 peak height ratios (RCC/2 values): (1) high-R3/2/low-RCC/2 type (R3/2 = ~ 0.2–1.0 and RCC/2 ~ 0–2), (2) low-R3/2/medium-RCC/2 type (R3/2 = ~ 0.2–0.6 and RCC/2 = ~ 1–4); and (3) low-R3/2/high-RCC/2 type (R3/2 = ~ 0.2–0.6 and RCC/2 ~ 1–8). All three types are contained in both Megasphaera and Megaclonophycus. Raman spectra for the carbonaceous matter within the rock sample show a similar degree of thermal alteration, indicating that the organics were embedded in situ prior to thermal maturation. The IR spectroscopic differences might reflect differences in original organic compositions of microorganisms, and/or immediate post-mortem alteration. This suggests that the origins of phosphatized embryo-like fossils are more diverse than was previously recognized on the basis of their morphology. A comparison of R3/2 and RCC/2 values in the embryo-like fossils with those of the algal fossils and the extant microorganisms indicates the possible interpretation that some of the embryo-like fossils belong to animal embryo, others are algae, but none of them originate from bacteria. 相似文献
5.
The Chorukh-Dairon deposit is part of the metallogenic belt of WMo, CuMo, AuW, and Au deposits along the Late Paleozoic active continental margin of the Tien Shan. It is related to the Late Carboniferous multiphase pluton, with successive intrusive phases of early monzogabbro through monzonite-quartz monzonite to monzogranite and leucogranite, and the latest lamprophyre dikes. The deposit is an example of complex W–Mo–Cu magmatic-hydrothermal system related to magnetite-series shoshonitic igneous suite. It contains zones of W–Cu–Mo oxidized prograde and retrograde skarns, with abundant scapolite, plagioclase, K-feldspar, andradite garnet, magnetite, as well as molybdoscheelite and minor chalcopyrite, and molybdenite. Skarns are overprinted by hydrosilicate alteration assemblages, with amphibole, chlorite, epidote, quartz, calcite, scapolite, albite, scheelite, and chalcopyrite, and are cut by quartz-carbonate-barite-fluorite-sulfide veins.The fluid evolution included a release of high temperature (~ 400–500 °C), high pressure (900–1100 to 700–800 bars), high salinity magmatic-hydrothermal aqueous chloride fluid, with its direct separation from crystallizing magma and formation of prograde and retrograde skarns. Fluid enrichment in Ca (up to 15–22 wt.% CaCl2) at the retrograde skarn stage was possibly related to magmatic differentiation and provided intense molybdoscheelite deposition from a homogenous fluid. In contrast, hydrosilicate alteration assemblages were formed at lower temperatures (~ 350–400 °C) initially from a homogenous and then from a boiling Ca-rich (20–22 wt.% CaCl2) magmatic-hydrothermal fluid, with the latter contributing to the most intense scheelite deposition. The stable isotope data (δ13CCO2 = − 3.0 ± 0.5‰ and δ18ОH2O = + 6.5 ± 0.5‰, δ34S = + 7.5 to + 7.7‰) obtained for the hydrosilicate stage minerals suggest significant fluid sourcing from magmatic and meteoric waters as well as from sedimentary rocks enriched in seawater sulfate, possibly evaporites, although a strongly homogenous character of the isotopic composition reveals intense isotope homogenization in a magmatic chamber. Some light sulfur isotope enrichment of sulfides from the quartz-carbonate-barite-fluorite-sulfide veins (δ34S = + 6.0 to + 6.1‰) may be linked to the evolution of the magmatic source toward more mantle-related sulfur species, as these veins were formed after emplacement of the late mafic (lamprophyre) dikes. 相似文献
6.
Predicting pyrogenic carbon (PyC) or biochar stability from its precursor properties is critical for evaluating and managing terrestrial C stocks. Transmission mode Fourier transform infrared spectroscopy (FTIR) spectroscopy was compared with proximate analysis data and H/C and O/C for predicting C mineralization. PyC produced at 7 different temperatures from 6 different feedstocks, in addition to the original feedstock materials, was incubated for 3 yr at 30 °C in a sand matrix. A C debt or credit ratio was calculated by comparing the C remaining in the incubated PyC sample (accounting for the measured C lost during initial PyC production) to the C remaining in the incubated original feedstock. A value > 1 indicates that more C remains in the PyC than in the original feedstock (credit), while a value < 1 indicates a debt. After 3 yr, PyC produced at 300 °C lost significantly more C than higher temperature PyC material, but significant differences in C loss between PyC produced at temperatures ⩾ 350 °C were not detectable. The best predictor of C loss was a multiple linear regression model using the fractional FTIR signals at 816, 1048, 1374, 1424, 1460, 1590, 1700 and 2925 cm−1 as parameters (R2 0.80, p < 0.0001). After 3 yr, the C debt or credit ratio reached values significantly > 1 for all corn PyC samples and some bull, dairy and poultry PyC samples, resulting in net C credit, while all pine and oak PyC samples remained in debt. This C debt or credit ratio reveals that, depending on the timeline of interest, producing relatively low temperature PyC with less initial C loss can result in greater C savings than producing higher temperature PyC, even though the C remaining after exposure to higher pyrolysis temperatures is more stable. 相似文献
7.
Seafloor sediment containing biogenic amino acids was heated with NaCl solutions at 50–200 °C for 240 h to investigate the dissolution process of amino acids and evaluate their stabilities under hydrothermal conditions. Dissolved amino acids in the combined phase (dissolved combined amino acids, DCAAs) and free phase (dissolved free amino acids, DFAAs) were rapidly released into the solution during heating. The amount of DCAAs in the solutions was 4–9 times higher than the amount of DFAAs at each temperature. When heated at ⩽ 100 °C, most of the total dissolved hydrolyzable amino acids (TDHAAs) were in the combined form (DCAAs/TDHAAs ratios > 0.9). The compositions of the DCAAs in solutions heated at ⩽ 100 °C were similar to that of the total hydrolyzable amino acids (THAAs) of the initial sediment, indicating that the DCAAs, which are derived from organisms and biodebris in the sediment, are barely altered during the hydrothermal reaction at these temperatures. On the other hand, the DCAAs/TDHAAs ratios were 0.72 and 0.57 at 150 and 200 °C, respectively, and the compositions of the DCAAs at 150 and 200 °C were significantly different from that of the initial THAAs. In addition, non-protein amino acids (β-alanine and γ-aminobutyric acid), which are sensitive biochemical indicators of the diagenetic alteration of natural organic matter, drastically increased to 80.9% of the DCAAs after heating at 200 °C. These results suggests that DCAAs are thermally unstable in the hydrothermal solutions at ⩾ 150 °C. These DCAA would be transformed into thermally stable geo-polymers such as humic-like substances and hydrolyzable kerogens. 相似文献
8.
9.
Black carbon decomposition under varying water regimes 总被引：1，自引：0，他引：1
The stability of biomass-derived black carbon (BC) or biochar as a slow cycling pool in the global C cycle is an important property and is likely governed by environmental conditions. This study investigated the effects of water regimes (saturated, unsaturated and alternating saturated–unsaturated conditions) and differences in BC materials, produced by carbonizing corn residues and oak wood at two temperatures (350 °C and 600 °C) on BC degradation at 30 °C over 1 year in a full factorial experiment. Effects of water regime on C loss and potential cation exchange capacity (CECp at pH 7) significantly depended on biomass type. Corn BC was both mineralized (16% C loss for the first year) and was oxidized [1000 mmole(+) kg?1 C] significantly faster under unsaturated conditions than under other water regimes, whereas oak BC mineralized most rapidly (12%) under alternating saturated–unsaturated conditions with similar oxidation, irrespective of water regime. Over 1 year of saturated incubation, the O/C ratio values did not significantly (P > 0.05) increase even though BC was mineralized by 9% and CECp increased by 170 mmole(+) kg?1 C, in contrast to unsaturated and alternating saturated–unsaturated conditions. While mineralization and oxidation significantly decreased at higher charring temperature for corn, no difference was observed for oak (P > 0.05). Unsaturated and alternating conditions increased carboxylic and OH functional groups, while they decreased aliphatic groups. The pH increased by about one unit for corn BC, but decreased by 0.2 units for oak BC, indicating strong mineral dissolution of corn BC. Carbon loss strongly correlated with changes in O/C values of both corn BC and oak BC, indicating that oxidation of BC was most likely the major mechanism controlling its stability. However, under saturated conditions, additional mechanisms may govern BC degradation and require further investigation. 相似文献
10.
11.
The age and origin of the past-producing Nanisivik carbonate-hosted ZnPb deposit in Nunavut, Canada, have been controversial for decades. Various direct and indirect dating methods have produced results ranging from Mesoproterozoic to Ordovician in age, and previous studies of the mineralising fluids have suggested that the fluids were anomalously hot (> 150 °C). This study combines ReOs (pyrite) geochronology, in-situ sulphur isotope analysis, and fluid inclusion analysis to refine both the timing of mineralisation and the nature of mineralising fluids. ReOs pyrite analysis shows that the Nanisivik deposit formed ca. 1.1 Ga, broadly similar to the depositional age of the host rock and with the Grenville orogeny, making it one of few known Precambrian carbonate-hosted ZnPb deposits. In-situ sulphur isotope measurements from Nanisivik show a narrow δ34S range of 27.54 ± 0.72, very similar to what has been reported before in bulk sample analyses. New fluid inclusion data show that the mineralising fluids were ~ 100 °C, which is not anomalous in the context of carbonate-hosted base-metal deposits. The fluids exhibit no significant spatial variation in homogenisation temperature in the 2-km-long ‘upper lens’ of the ore deposit, but recrystallisation and modification of fluid inclusions took place in the immediate vicinity of the cross-cutting ~ 720 Ma “mine dyke”. The deposit is broadly inferred to have formed during late Mesoproterozoic assembly of supercontinent Rodinia, when regional hydrostatic head developed under the influence of far-field stresses originating in the developing Grenville orogen. The Nanisivik deposit remains anomalous only in its age; most other aspects of this ore deposit are now shown to be quite typical for carbonate-hosted ore deposits. 相似文献
12.
《Chemie der Erde / Geochemistry》2014,74(3):343-351
The formation of solid bituminous matter (SBM) on surfaces of microporous silicates was experimentally studied at pressure and temperature conditions typical of late-stage magmatic and hydrothermal processes. Aliquots of microporous silicate minerals (zorite and kuzmenkoite-Mn, Lovozero Alkaline Massif, Kola Peninsula, Russia) were exposed to solid or liquid organic carbon sources (natural brown coal and liquid 1-hexene for synthesis purposes) in a 0.1 M NaCl-solution for 7 days, at constant pressure (50 MPa), and at three individual temperatures (200, 275, and 300 °C). No thermal decomposition of the solid organic sources happened at 200 °C and only a thin film of brown coal derivatives on the silicates’ surfaces and no formation of SBM were observed at 275 °C and 300 °C. But solid bituminous matter on the surfaces of both microporous silicates were detected in experiments with liquid 1-hexene as organic carbon source and at temperatures of 275 °C and 300 °C with a more pronounced formation of SBM at 300 °C compared to 275 °C. The aromatic and aliphatic hydrocarbons, as well as alcoholic compounds of the experimentally produced SBM are similar, if not even partly identical, with natural SBM occurrences of the Khibiny and Lovozero Massifs, Kola Peninsula, Russia, and from the Viitaniemi granitic pegmatite, Finland, as shown by FT-IR and 1H NMR spectroscopy. This strengthens the hypothesis of formation of natural solid bituminous matter by catalytic reactions between microporous Ti-, Nb- and Zr-silicates and hydrocarbons at postmagmatic hydrothermal conditions. 相似文献
13.
Biochar is charcoal made from waste biomass and intended to be added to soil to improve soil function and reduce emissions from the biomass caused by natural degradation to CO2. Nitrogen (N) forms in biochar can be complex and their lability likely to be influenced by pyrolysis temperature which, together with the nature of carbon (C), will influence N mineralisation or immobilisation. These complex relationships are poorly understood, yet impact strongly on the potential agronomic value of biochar. In this study, N in different biochar samples produced from human and animal waste streams (biosolids and cow manure; each mixed with eucalyptus wood chips in a 1:1 dry wt. ratio) at different pyrolysis conditions (highest heating temperature 250, 350, 450 and 550 °C) was extracted with 6 M HCl. The acid hydrolysable, extractable N (THN) was fractionated into ammonia N (AN), amino acid N (AAN), amino sugar N (ASN) and uncharacterisable hydrolysable N (UHN). Biochar samples were also treated with 0.167 M K2Cr2O7 acid to determine N potentially available in the long term. An incubation study of the different biochar samples mixed with acid washed sand was conducted at 32 °C for 81 days to study both C and N turnover. During incubation, the CO2 released was trapped in NaOH and quantified. Hydrolysable N decreased as pyrolysis temperature increased from 250 to 550 °C. Fractionation into AN, AAN, ASN and UHN revealed progressive structural rearrangement of N with pyrolysis temperature. Based on HCl hydrolysis and dichromate oxidation results, C and N in biochar became more stable as pyrolysis temperature increased. The ratio of volatile C to THN was a useful indicator of whether net N mineralisation or immobilisation of N in biochar occurred. THN thus seems a sound estimate of the labile N fraction in biochar in the short term; however, dichromate-oxidisable N is probably more meaningful in the long run. Further studies using different types of biochar need to be conducted under more realistic conditions to obtain more information on N availability in biochar once in soil. 相似文献
14.
Stable Zn isotopes may be applied to trace the source of ore-forming metals in various types of PbZn deposits. To test this application, Zn and Pb isotope systematics for sulfides and associated basement rocks as well as FeMn carbonates (gangue) from the Zhaxikang PbZn deposit in South Tibet have been analyzed. The basement in this region includes metamorphosed mafic to felsic rocks (dolerite, quartz diorite, rhyolite porphyry, pyroclastics and porphyritic monzogranite). These rocks have similar δ66Zn values of 0.33 to 0.37‰, with an average value of 0.36 ± 0.03‰ (2σ), except for the more evolved porphyritic monzogranite that has a heavier value of 0.49‰. FeMn carbonates are present as hydrothermal veins and were probably precipitated from magmatic fluids. They have an average δ66Zn value of 0.27 ± 0.05‰, which is slightly lighter than the basement rocks, possibly representing δ66Zn isotopic compositions of the hydrothermal fluids. Sphalerite and galena have similar Zn isotopic compositions with δ66Zn ranging from 0.03 to 0.26‰ and 0.21 to 0.28‰, respectively. Considering the Zn isotope fractionation factor between sphalerite and fluids of − 0.2‰ at ~ 300 °C as reported in literature, hydrothermal fluids from which these sulfides precipitated will have δ66Zn values of ca. 0.39 ± 0.10‰, which are consistent with the values of basement rocks and the FeMn carbonates. This similarity supports a magmatic-hydrothermal origin of the Zhaxikang PbZn deposit. Both Pb and S isotopes in these sphalerite and galena show large variations and are consistent with being derived from a mixture of basement and sedimentary rocks in various proportions. Zn isotopic compositions of the sulfides significantly extend the range of regional basement rocks, suggesting that sedimentary rocks (e.g., shales) are also a significant source of Zn. However, the Zn isotopic compositions of sphalerite and galena differ from those of marine carbonates and those of typical SEDEX-type deposits (e.g. Kelley et al., 2009), confirming a magmatic-hydrothermal model. Combined with regional geological observations and the age constraints of ~ 20 Ma (Zheng et al., 2012, 2014), the results of our investigation indicate that the Zhaxikang PbZn deposit is most likely a magmatic-hydrothermal deposit. 相似文献
15.
Significant amounts of sulfuric acid (H2SO4) rich saline water can be produced by the oxidation of sulfide minerals contained in inland acid sulfate soils (IASS). In the absence of carbonate minerals, the dissolution of phyllosilicate minerals is one of very few processes that can provide long-term acid neutralisation. It is therefore important to understand the acid dissolution behavior of naturally occurring clay minerals from IASS under saline–acidic solutions. The objective of this study was to investigate the dissolution of a natural clay-rich sample under saline–acidic conditions (pH 1–4; ionic strengths = 0.01 and 0.25 M; 25 °C) and over a range of temperatures (25–45 °C; pH 1 and pH 4). The clay-rich sample referred to as Bottle Bend clay (BB clay) used was from an IASS (Bottle Bend lagoon) in south-western New South Wales (Australia) and contained smectite (40%), illite (27%), kaolinite (26%) and quartz (6%). Acid dissolution of the BB clay was initially rapid, as indicated by the fast release of cations (Si, Al, K, Fe, Mg). Relatively higher Al (pH 4) and K (pH 2–4) release was obtained from BB clay dissolution in higher ionic strength solutions compared to the lower ionic strength solutions. The steady state dissolution rate (as determined from Si, Al and Fe release rates; RSi, RAl, RFe) increased with decreasing solution pH and increasing temperature. For example, the highest log RSi value was obtained at pH 1 and 45 °C (−9.07 mol g−1 s−1), while the lowest log RSi value was obtained at pH 4 and 25 °C (−11.20 mol g−1 s−1). A comparison of these results with pure mineral dissolution rates from the literature suggests that the BB clay dissolved at a much faster rate compared to the pure mineral samples. Apparent activation energies calculated for the clay sample varied over the range 76.6 kJ mol−1 (pH 1) to 37.7 kJ mol−1 (pH 4) which compare very well with the activation energy values for acidic dissolution of monomineralic samples e.g. montmorillonite from previous studies. The acid neutralisation capacity (ANC) of the clay sample was calculated from the release of all structural cations except Si (i.e. Al, Fe, K, Mg). According to these calculations an ANC of 1.11 kg H2SO4/tonne clay/day was provided by clay dissolution at pH 1 (I = 0.25 M, 25 °C) compared to an ANC of 0.21 kg H2SO4/tonne clay/day at pH 4 (I = 0.25 M, 25 °C). The highest ANC of 6.91 kg H2SO4/tonne clay/day was provided by clay dissolution at pH 1 and at 45 °C (I = 0.25 M), which is more than three times higher than the ANC provided under the similar solution conditions at 25 °C. In wetlands with little solid phase buffering available apart from clay minerals, it is imperative to consider the potential ANC provided by the dissolution of abundantly occurring phyllosilicate minerals in devising rehabilitation schemes. 相似文献
16.
Calcite veins with fluid and solid bitumen inclusions have been discovered in the south-western shoulder of the Dead Sea rift within the Masada-Zohar block, where hydrocarbons exist in small commercial gas fields and non-commercial fields of heavy and light oils. The gas–liquid inclusions in calcite are dominated either by methane or CO2, and aqueous inclusions sometimes bear minor dissolved hydrocarbons. The enclosed flake-like solid bitumen matter is a residue of degraded oil, which may be interpreted as “dead carbon”. About 2/3 of this matter is soot-like amorphous carbon and 1/3 consists of n-C8C18 carboxylic acids and traces of n-alkanes, light dicarboxylic acids, and higher molecular weight (>C20) branched and/or cyclic carboxylic acids. Both bitumen and the host calcites show genetic relationship with mature Maastrichtian chalky source rocks (MCSRs) evident in isotopic compositions (δ13C, δ34S, and δ18O) and in REE + Y patterns. The bitumen precursor may have been heavy sulfur-rich oil which was generated during the burial compaction of the MCSR strata within the subsided blocks of the Dead Sea graben. The δ18O and δ13C values and REE + Y signatures in calcites indicate mixing of deep buried fluids equilibrated with post-mature sediments and meteoric waters. The temperatures of fluid generation according to Mg–Li-geothermometer data range from 55 °С to 90 °С corresponding to the 2.5–4.0 km depths, and largely overlap with the oil window range (60–90 °С) in the Dead Sea rift (Hunt, 1996; Gvirtzman and Stanislavsky, 2000; Buryakovsky et al., 2005). The bitumen-rich vein calcites originated in the course of Late Cenozoic rifting and related deformation, when tectonic stress triggers damaged small hydrocarbon reservoirs in the area, produced pathways, and caused hydrocarbon-bearing fluids to rise to the subsurface; the fluids filled open fractures and crystallized to calcite with entrapped bitumen. The reported results are in good agreement with the existing views of maturation, migration, and accumulation of hydrocarbons, as well as basin fluid transport processes in the Dead Sea area. 相似文献
17.
Dissolution rates of pressure solution (PS) for quartz aggregates in 0.002 M NaHCO3 solution were experimentally determined under low effective stress conditions of 0.42–0.61 MPa, and low temperatures of 25–45 °C. At temperatures of 25 °C, 35 °C, and 45 °C, the resultant silicon dissolution rates are 4.2 ± 1.2 × 10−15, 6.0 ± 1.0 × 10−15 and 7.8 ± 1.9 × 10−15 mol/cm2/s, respectively. Ratios between these dissolution rates and those of quartz sand at zero effective stress are 4.1 ± 1.2 at 25 °C, 3.0 ± 0.5 at 35 °C, and 2.4 ± 0.6 at 45 °C. As the uniaxial pressure was increased, the dissolution rate of PS also increased, though gradually decreased when the effective stress was kept constant. After the removal of stress, the dissolution rate was observed to increase once again. The activation energy of our PS experiments was determined to be approximately 24 kJ/mol, lower than the amount required for quartz sand dissolution to commence at zero effective stress. Our results clearly show that, even at such low temperature and effective stress, Si released into solution as a result of PS can be detected. This implies that experimental compaction of quartz aggregates can be measured even under such condition. 相似文献
18.
《Gondwana Research》2014,25(3-4):969-983
The Ediacaran–Cambrian Petermann Orogeny, central Australia, is an exceptional example of intraplate orogenesis. It involved sub-eclogite facies metamorphism and extreme basin inversion during the exhumation of Musgrave Province basement from beneath the formerly contiguous Centralian Superbasin. Sensitive High Resolution Ion Microprobe (SHRIMP) U–Pb geochronology of zircon, titanite and rutile, along with Ti-in-zircon thermometry from meta-igneous samples, have been used to determine the timing and duration of high-pressure metamorphism and subsequent cooling associated with this orogenic event. Peak metamorphic temperatures of 720–760 °C were attained at 544 ± 7 Ma (U–Pb zircon). Subsequent cooling to 600–660 °C by ~ 521 Ma occurred at a rate of ~ 2.6–7.0 °C Myr− 1, as recorded by the closure of Pb diffusion in titanite. Further cooling to 585–560 °C by 498–472 Ma occurred at a rate of 0.9–4.8 °C Myr− 1, as recorded by Pb closure in rutile. The duration of tectonism was long-lived (> 40 Myr) across the central and western parts of the orogenic system, and deformation occurred in a comparatively warm and weak portion of crust, characterised by regional thermal gradients of 17–26 °C km− 1. This proposed duration of tectonism is much longer than that permitted by a shear heating mechanism, which requires an exceptionally short duration of tectonism, and additionally, an overall cold lithosphere characterised by geothermal gradients of ~ 9 °C km− 1. 相似文献
19.
The Hengshan massif is an exhumed, mid-crustal, plutonic–metamorphic dome formed during Cretaceous crustal extension in the Jiangnan orogenic belt, central South China. Multiple thermochronometers (mica 40Ar/39Ar, apatite fission track and zircon (U–Th)/He) are applied to its footwall along a slip-parallel transect to quantify its thermal history and cooling rate, and the slip magnitude, rate, initial geometry and kinematic evolution of the low-angle Hengshan detachment fault. Our thermochronological data, in conjunction with previous ages, indicate that (1) footwall rocks cooled from ~ 700 °C to ~ 60 °C in less than 60 Myr (136–80 Ma) at variable rates ranging from ~ 50 °C/Myr to ~ 13 °C/Myr, (2) the Hengshan detachment fault accommodated ~ 8–12 km of total slip at variable slip rates from 0.14 to 1 mm/yr during tectonic exhumation, (3) the footwall has been tilted ~ 26°–50° to the east since slip began, indicating that the low-angle Hengshan detachment fault initiated at a steep dip and was passively rotated to a more gentle orientation during subsequent normal slip. This study provides compelling evidence supporting that the low-angle detachment fault in the extensional dome can be generated by the reactivation and passive rotation of an initially steep reverse fault during normal slip. In addition, our thermochronological data constrain the time of extension in the Hengshan dome between 136 and 80 Ma, which implies that the back-arc extension within South China associated with the rollback of the Paleo-Pacific slab might have lasted until at least 80 Ma. 相似文献
20.
Understanding the formation mechanism of the South China Sea has important implications for research on plate rupture and continent-ocean transition globally. Granitoids dredged from the Xiaozhenzhu Rise provide new perspectives on lithosphere evolution processes of this region. Zircon UPb (127–122 Ma) and amphibole/K-feldspar 40Ar/39Ar (123–115 Ma) ages indicate high cooling rates of 55–64 °C/myr and thus rapid magma emplacement and uplift in the Early Cretaceous. These calc-alkaline granitoids with intermediate Mg# (44–53) and slightly negative Eu anomalies (Eu/Eu* = 0.63–1.00) have highly variable and well-correlated Cr (4.89–531 ppm) and Ni (2.27–258 ppm) contents, which indicate melt mixing. The low CrNi sample (19.4 ppm Ni) displays much higher Sr (847 ppm), Sr/Y (93.4), and overall stronger crustal signatures than the high CrNi samples (107–258 ppm Ni) which have more mantle-like characteristics. Despite these differences, all studied samples show relatively similar and moderately enriched SrNd isotopic compositions ((87Sr/86Sr)i = 0.7055–0.7064, εNd(t) = −0.6 to −1.7) and enriched Pb isotopic compositions that are comparable with those of marine sediments. They also show mantle-like depleted zircon O (δ18O = 4.5–6.3‰) and mostly positive zircon Hf (εHf(t) = −0.4–4.1) isotopic compositions that indicate limited upper crustal contribution in the melt source. Their compositional features are best explained by magma mixing between partial melts of a delaminated lower arc crust and partial melts of a metasomatized arc mantle wedge. Combining our new results with literature studies of magmatism, metamorphism, sedimentary records and crustal structures from the region, we propose a new model of the Late Mesozoic–Early Cenozoic lithosphere deformation of the South China continental margin where lower arc crust delamination generated a tectonic weak zone that is essential for the rifting of the South China Sea. 相似文献