共查询到20条相似文献，搜索用时 593 毫秒
1.
Abundant natural gas inclusions were found in calcite veins filled in fractures of Central Fault Belt across the centre of Ordos Basin. Time of the calcite veins and characteristics of natural gas fluid inclusion were investigated by means of dating of thermolum luminescence (TL) and analyzing stable isotope of fluid inclusion. Results show that natural gas inclusion formed at 130–140°C with salinity of 5.5 wt%–6.0 wt% NaCl. It indicates that natural gas inclusion is a kind of thermal hydrocarbon fluid formed within the basin. Method of opening inclusion by heating was used to analyze composition of fluid inclusion online, of which the maximal hydrocarbon gas content of fluid inclusion contained in veins is 2.4219 m3/t rock and the maximal C1/ΣC i ratio is 91%. Laser Raman spectroscopy (LRS) was used to analyze chemistry of individual fluid inclusion in which the maximal hydrocarbon gas content is 91.6% compared with little inorganic composition. Isotope analysis results of calcite veins show that they were deposited in fresh water, in which the δ 13CPDB of calcite veins is from ?5.75‰ to 15.23‰ and δ 18OSMOW of calcite veins is from 21.33‰ to 21.67‰. Isotope results show that δ 13C1 PDB of natural gas fluid inclusion is from ?21.36‰ to ?29.06‰ and δDSMOW of that is from ?70.89‰ to ?111.03‰. It indicates that the gas of fluid inclusion formed from coal source rocks and it is the same as that of natural gas of Mizhi gas reservoir. Results of TL dating show that time of calcite vein is (32.4±3.42)×104 a, which is thought to be formation time of gas inclusion. It indicated that natural gas inclusion contained in calcite veins recorded natural gas leakage from Mizhi gas reservoir through the Central Fault Belt due to Himalayan tectonic movement. 相似文献
2.
Abundant natural gas inclusions were found in calcite veins filled in fractures of Central Fault Belt across the centre of Ordos Basin. Time of the calcite veins and characteristics of natural gas fluid inclusion were investigated by means of dating of thermolum luminescence (TL) and analyzing stable isotope of fluid inclusion. Results show that natural gas inclusion formed at 130–140°C with salinity of 5.5 wt%–6.0 wt% NaCl. It indicates that natural gas inclusion is a kind of thermal hydrocarbon fluid formed within the basin. Method of opening inclusion by heating was used to analyze composition of fluid inclusion online, of which the maximal hydrocarbon gas content of fluid inclusion contained in veins is 2.4219 m3/t rock and the maximal C1/ΣC i ratio is 91%. Laser Raman spectroscopy (LRS) was used to analyze chemistry of individual fluid inclusion in which the maximal hydrocarbon gas content is 91.6% compared with little inorganic composition. Isotope analysis results of calcite veins show that they were deposited in fresh water, in which the δ 13CPDB of calcite veins is from −5.75‰ to 15.23‰ and δ 18OSMOW of calcite veins is from 21.33‰ to 21.67‰. Isotope results show that δ 13C1 PDB of natural gas fluid inclusion is from −21.36‰ to −29.06‰ and δDSMOW of that is from −70.89‰ to −111.03‰. It indicates that the gas of fluid inclusion formed from coal source rocks and it is the same as that of natural gas of Mizhi gas reservoir. Results of TL dating show that time of calcite vein is (32.4±3.42)×104 a, which is thought to be formation time of gas inclusion. It indicated that natural gas inclusion contained in calcite veins recorded natural gas leakage from Mizhi gas reservoir through the Central Fault Belt due to Himalayan tectonic movement.
相似文献3.
In-Chang Ryu 《Island Arc》2003,12(4):398-410
Abstract Sandstone petrography considered within a sequence stratigraphic framework provides a better understanding of the characteristics of the Eocene Tyee Basin, an accretionary and forearc sequence, southern Oregon Coast Range. Detailed comparison of the relative abundance of major framework grains documents a marked difference in the sandstone composition of each depositional sequence. Such a difference is mainly due to an abrupt change in provenance, from a local Klamath Mountains metasedimentary source to a more distant extrabasinal Idaho Batholith‐Clarno volcanic arc source. Furthermore, the composition of framework grains varies systematically from the lowstand systems tract to the highstand systems tract within a depositional sequence. This suggests that relative sea level change in the depositional basin, and tectonics in the source area, can affect the patterns of sedimentation and sandstone composition. In addition, the Eocene Tyee Basin sandstones have a down‐section distribution of authigenic minerals, consisting of early formed zeolites and late‐stage quartz, as well as a change in the abundance of smectite to mixed‐layer chlorite/smectite with increasing burial depth. The down‐section distribution of authigenic minerals is also causally linked to the compositional variation of framework grains in each depositional sequence with increasing burial temperature. Much primary porosity has been filled with these authigenic minerals, which diminishes the permeability of potential reservoir rocks. Reservoir‐quality porosities and permeabilities, however, are present locally in the basin. The development of these reservoir‐quality sandstones within the Eocene Tyee Basin sequence is due to a complex burial diagenesis, which is directly related to temporal and spatial variations in original detrital mineralogy, in sedimentation pattern, and in burial temperature in the basin. 相似文献
4.
In connection with the future Seine-North Europe Canal (Seine-Scheldt), a large-scale rescue archaeological survey was conducted at Havrincourt (northern France) between 2008 and 2011. The discovery of several levels of Palaeolithic flint artefacts embedded in a relatively thick loess sequence (ca 6–7 m) preserved on a gentle slope facing North-East, resulted in a 6000 m2 excavation. This opened the opportunity for a detailed pedosedimentary and interdisciplinary geochronological survey (14C, optically stimulated luminescence, thermoluminescence, ESR/U-series) that has allowed us date the sequence reliably. On the basis of these results we propose this sequence as a new pedostratigraphic and archaeological reference sequence for northern France. We present here the optical dating of the sequence performed on fine (4–11 μm) quartz grains extracted from 17 samples. The luminescence characteristics of these extracts indicate that the single-aliquot regenerative dose optically stimulated luminescence (SAR-OSL) procedure that was applied is well suited. A consistent set of optical ages was obtained for the loess deposited up to around 70 ka ago. Independent age control (pedostratigraphy, 14C, ESR/U-series dates) allowed us to apply a Bayesian approach to build a chronometric model. This in turn enabled a regional chronostratigraphic framework to be built, to constrain the correlations with neighboring regions (northern France and Belgium) and to calculate a precise age for the four Palaeolithic levels discovered, including a unique occupation related to the early Upper Palaeolithic which was previously unknown in the area. 相似文献
5.
The Qinghai-Tibetan Plateau is an important area for the study of Quaternary glaciation. Optically stimulated luminescence (OSL) dating has the potential to contribute to the chronology of glaciation in this region, but it is important to assess the accuracy of OSL dating of these glacial sediments. In this study, single grain quartz OSL signals are examined for five glacial samples collected from the moraines outside the Baiyu Valley, southeastern Tibet. The quartz grains exhibit poor luminescence characteristics, with a small proportion of grains passing the screening criteria. Grains which pass the screening criteria have relatively low signal intensity, leading to De values with large uncertainties. MAM and CAM were used to determine De values for these samples. The OSL ages are consistent with the sequence of events derived from the geomorphological relationship of the samples, and also with previous published radiocarbon ages. However, it is more difficult to reconcile the OSL ages and the terrestrial cosmogenic nuclide (TCN) 10Be ages. Analysis of both single grain quartz OSL data and TCN 10Be data is complex in this area. Further work is required to increase confidence in the OSL ages generated for the glacial sediments from this region. 相似文献
6.
Oxygen isotope compositions were measured in quartz grains extracted from a 7.0 Ma red clay-loess sequence at Lingtai and
six late Pleistocene loess sediments (Malan loess). Results show that the changes in oxygen isotope compositions of Malan
loess are basically controlled by the geochemical characteristics of the source materials, while the effect of weathering
process after dust deposition could be minor. The oxygen isotope distribution of quartz grains from red clay at Lingtai is
similar to that of the overlying loess-paleosol sequence, thus indicating that the red clay at Lingtai has the same eolian
origin as the loess-paleosol deposits. Furthermore, the oscillations of the isotope compositions in 4–16 μm-sized quartz grains
may reflect the changes, to some extent, of the climatic systems of the source region. 相似文献
7.
The carbon isotopic composition of individual oxide grains from Murchison HF—HCl acid residue CFOc has been measured in the ion microprobe. Many grains (Mg-spinel, Cr-spinel, and Fe-oxide) contain carbon with large13C excesses ranging to 7000‰ (corresponding to12C/13C= 11). In most cases the carbon is present as micron-sized subgrains. The association of silicon with the anomalous carbon points towards SiC as carrier. If this tentative identification is correct then the SiC grains most likely originated in the circumstellar atmospheres of red giants. Oxide grains in which the 18O/16O ratio has also been measured show variable16O excesses which are not correlated with the13C excesses. This indicates that the sources of the anomalous carbon and oxygen isotopic compositions of the oxide grains are unrelated. 相似文献
8.
Chondrules are the major high temperature components of chondritic meteorites which accreted a few millions years after the oldest solids of the solar system, the calcium–aluminum-rich inclusions, were condensed from the nebula gas. Chondrules formed during brief heating events by incomplete melting of solid dust precursors in the protoplanetary disk. Petrographic, compositional and isotopic arguments allowed the identification of metal-bearing Mg-rich olivine aggregates among the precursors of magnesian type I chondrules. Two very different settings can be considered for the formation of these Mg-rich olivines: either a nebular setting corresponding mostly to condensation–evaporation processes in the nebular gas or a planetary setting corresponding mostly to differentiation processes in a planetesimal. An ion microprobe survey of Mg-rich olivines of a set of type I chondrules and isolated olivines from unequilibrated ordinary chondrites and carbonaceous chondrites revealed the existence of several modes in the distribution of the ?17O values and the presence of a large range of mass fractionation (several ‰) within each mode. The chemistry and the oxygen isotopic compositions indicate that Mg-rich olivines are unlikely to be of nebular origin (i.e., solar nebula condensates) but are more likely debris of broken differentiated planetesimals (each of them being characterized by a given ?17O). Mg-rich olivines could have crystallized from magma ocean-like environments on partially molten planetesimals undergoing metal–silicate differentiation processes. Considering the very old age of chondrules, Mg-rich olivine grains or aggregates might be considered as millimeter-sized fragments from disrupted first-generation differentiated planetesimals. Finally, the finding of only a small number of discrete ?17O modes for Mg-rich olivines grains or aggregates in a given chondrite suggests that these shattered fragments have not been efficiently mixed in the disk and/or that chondrite formation occurred in the first vicinity of the breakup of these planetary bodies. 相似文献
9.
This work is devoted to the problem of localizing the 14C cosmogenic radionuclide in a firn layer covering glaciers. The data on 14C in ice samples from the GISP2 ice core drilled on a Greenland ice dome (Summit) are analyzed. It has been indicated that
experimental values of the 14C concentration are systematically smaller than theoretically calculated values, which indicates that firn grains partially
lose 14C. Diffusion of cosmogenic 14C in firn grains and hydration of 14CO2 in a disordered ice layer, which is formed on a firn grain surface and at the boundary between ice monocrystals, are considered.
It has been indicated that these processes are among the main ones responsible for the level of radiocarbon concentration
in firn and ice samples. 相似文献
10.
In recent years, the researches of inland Asia aridification since late Cenozoic have attracted much attention in the paleoclimate community. Rea et al.[1] studied a 12 Ma eolian record in North Pacific and associated it with the aridification of northwes… 相似文献
11.
Magnetite in the oxidized CV chondrite Allende mainly occurs as spherical nodules in porphyritic-olivine (PO) chondrules, where it is associated with Ni-rich metal and/or sulfides. To help constrain the origin of the magnetite, we measured oxygen isotopic compositions of magnetite and coexisting olivine grains in PO chondrules of Allende by an in situ ion microprobe technique. Five magnetite nodules form a relatively tight cluster in oxygen isotopic composition with delta 18O values from -4.8 to -7.1% and delta 17O values from -2.9 to -6.3%. Seven coexisting olivine grains have oxygen isotopic compositions from -0.9 to -6.3% in delta 18O and from -4.6 to -7.9% in delta 17O. The delta 17O values of the magnetite and coexisting olivine do not overlap; they range from -0.4 to -2.6%, and from -4.0 to -5.7%, respectively. Thus, the magnetite is not in isotopic equilibrium with the olivine in PO chondrules, implying that it formed after the chondrule formation. The delta 17O of the magnetite is somewhat more negative than estimates for the ambient solar nebula gas. We infer that the magnetite formed on the parent asteroid by oxidation of metal by H2O which had previously experienced minor O isotope exchange with fine-grained silicates. 相似文献
12.
To constrain the timing of the tectonothermal events and formation process of a plutonic suite, U–Pb dating was carried out by laser ablation inductively coupled plasma mass spectrometry combined with cathodoluminescence imaging on zircon grains extracted from the Bato pluton, northern Yamizo Mountains, Japan. The Bato pluton consists of gabbro and diorite. Zircon grains separated from a gabbro sample had a unimodal 238U–206Pb age (105.7 ±1.0 Ma). It was interpreted as the solidification age of the gabbro. Cathodoluminescence observation showed that the zircon grains from a diorite sample were characterized by anhedral cores, oscillatory zoned mantles, and dark rims. The 238U–206Pb age of the anhedral cores ranged from 2 165 Ma to 161 Ma, indicating the assimilation of surrounding sedimentary rocks. The 238U–206Pb ages of the oscillatory zoned mantles and dark rims are 109.0 ±1.3 Ma and 107.7 ±1.3 Ma, respectively. Observation under polarizing microscopy suggests that the anhedral cores occurred before plagioclase and hornblende, and the oscillatory zones around the anhedral cores had crystallized at the same time as the crystallization of biotite. Moreover, the dark rims formed at the same time as the crystallization of quartz and K‐feldspar. The formation process of the gabbro‐diorite complex in the Bato pluton was inferred as follows. (i) A mafic initial magma intruded into Mesozoic sedimentary rocks, and the assimilation of these sedimentary rocks led to geochemical variation yielding a dioritic composition. Subsequently, plagioclase and hornblende of the diorite were crystallized before 109.0 ±1.3 Ma. (ii) Biotite crystallized in the middle stage around 109.0 ±1.3 Ma. (iii) Quartz and K‐feldspar of the diorite were crystallized at 107.7 ±1.3 Ma. The gabbroic magma solidified (105.7 ±1.0 Ma) after solidification of the diorite. 相似文献
13.
Karleen E. Davis 《Earth and Planetary Science Letters》1981,55(1):190-198
The ubiquitous occurrence of magnetite rods in plagioclase may account for the stable, intense magnetization of ocean floor gabbros. These single-domain grains are formed by the subsolidus exsolution of Fe2+ and Fe3+ incorporated into the plagioclase at higher temperatures. We expect that this process will be particularly important in the upper portions of the oceanic gabbro unit because of the relative paucity of femic minerals at these levels. The geometry of accretion prohibits a constructive contribution to marine magnetic anomalies by the lower olivine-rich gabbros. As a result of the presence of these rods, ocean floor gabbros may constitute an important source for marine magnetic anomalies. 相似文献
14.
Yanjun Wang Weiguang Zhu Hong Zhong Zhongjie Bai Junhua Yao Chong Xu 《Acta Geochimica》2019,(3):376-390
The Pingchuan iron deposit, located in the Yanyuan region of Sichuan Province, SW China, has an ore reserve of 40 Mt with ~60 wt% Fe. Its genesis is still poorly understood. The Pingchuan iron deposit has a paragenetic sequence of an early Fe-oxide–Pyrite stage(Ⅰ) and a late Fe-oxide–pyrrhotite stage(Ⅱ). Stage Ⅰ magnetite grains are generally fragmented, euhedral–subhedral, largesized crystals accompanying with slightly postdated pyrite.Stage Ⅱ magnetite grains are mostly unfragmented, anhedral, relatively small-sized grains that co-exist with pyrrhotite. Combined with micro-textural features and previously-obtained geochronological data, we consider that these two stages of iron mineralization in the Pingchuan deposit correspond to the Permian ELIP magmatism and Cenozoic fault activity event. Both the Stage Ⅰ and Ⅱ magnetites are characterized with overall lower contents of trace elements(including Cr, Ti, V, and Ni) than the ELIP magmatic magnetite, which suggests a hydrothermal origin for them. ‘‘Skarn-like' enrichment in Sn, Mn, and Zn in the Stage Ⅰ magnetite grains indicate significant material contributions from carbonate wall-rocks due to water–rock interaction in ore-forming processes. Stage Ⅱ magnetite grains contain higher Mn concentrations than Stage Ⅰ magnetite grains, which possibly implies more contribution from carbonate rocks. In multiple-element diagrams, the Stage Ⅰ magnetite shows systematic similarities to Kiruna-type magnetite rather than those from other types of deposits. Combined with geological features and previous studies on oxygen isotopes, we conclude that hydrothermal fluids have played a key role in the generation of the Pingchuan low-Ti iron deposit. 相似文献
15.
Graphite comprises about 2% of some of the 3.8-AE metamorphosed sedimentary rocks of Isukasia, west Greenland. δ13CPDB of carbon in this graphite ranges from ?16.0 to ?9.3‰. For those samples that contain both graphite and siderite, Δcarbonate-graphite is about 6; this fractionation is consistent with an inorganic equilibrium between siderite and graphite at roughly 400–500°C. It is likely that graphite found in these rocks formed by the reaction: 6FeCO3 = 2Fe3O4 + 5CO2 +C in which case it is of little help in determining whether or not organisms were active 3.8 AE ago. The presence of quartz-magnetite-cummingtonite-iron formation in the Isukasia metasedimentary sequence may, ultimately, be one of the most powerful environmental indicators remaining in these rocks. 相似文献
16.
U-Pb dating of early Mesozoic granodioritic intrusions in southeastern Hunan Province, South China and its petrogenetic implications 总被引：12，自引：0，他引：12
The NE-trended Mesozoic granodioritic intrusions are spatially and temporally associated with the copper multi-metal mineralization
in southeastern Hunan Province, South China. U-Pb dating result of single-grained zircons of four samples respectively from
Shuikoushan, Baoshan, western Tongshanling and eastern Tongshanling intrusions reveals that their crystallization age spans
a range from 172 Ma to 181 Ma, which also represents the oldest age of the regional copper multi-metal mineralization. Some
of the zircon grains give an upper intercept age of about 1753 Ma and 207Pb/206Pb apparent age of (1752 ± 4) Ma, implying the involvement of the pre-Cambrian metamorphic (possible Middle Proterozoic) basement
in their genesis. The presence of such a kind of zircon grains in these granodiorites indicates either that the parental magmas
were assimilated by basement rocks during magma ascent or that lower/middle crustal rocks were one of the important components
during the melting process. 相似文献
17.
CRISPY is a cristobalite-pyroxene assemblage in the L6 chondrite ALHA 76003. It was formed by reaction of a very siliceous inclusion with the surrounding olivine-rich rock. Oxygen isotopes show that the inclusion was derived from a source with non-chondritic isotopic composition. The isotopes also show that the oxygen of the pyroxene reaction product was derived by simple mixing of oxygen from the inclusion and its immediately adjacent surroundings, with exchange with the bulk meteorite limited to a distance of about a millimeter. The persistence of cristobalite in close proximity to olivine, and the lack of isotopic equilibration, show that the metamorphic processes that form petrographic grade 6 chondrites involve transport of major elements over distances only on the order of millimeters. 相似文献
18.
Abstract Characterization of magnetic particles, and magnetostratigraphic dating, of Holocene and Pleistocene shallow-water carbonates (the Ryukyu Group) in the Ryukyu Islands was carried out to infer the age of reef formation. Magnetic particles from these strata are dominated by fine-grained, single-domain magnetite/maghemite (40–140 nm in length). The magnetite crystals exhibit the size and morphologies characteristic of the magnetite formed by magnetotactic bacteria. No large multidomain grains were seen in transmission electron microscopy observations. The widespread presence of single-domain magnetite in the Ryukyu Islands suggests that bacterial magnetites carry depositional remanent magnetization, which is stable enough for magnetostratigraphic dating and thereby for elucidating the evolution of shallow-water carbonates. The polarity-reversal sequence seen in a core taken from the Ryukyu Group correlates with the timescale of the Matuyama chron, including the Jaramillo subchron, Kamikatsura or Santa Rosa Excursions, through the Brunhes chron. These magnetostratigraphic results imply that the time of reef initiation in the Ryukyu Islands of the northwestern Pacific was earlier than in the Great Barrier Reef of the southwestern Pacific, where it started after the Brunhes–Matuyama boundary. 相似文献
19.
Santo Antão, the northernmost island of the Cape Verde Archipelago, consists entirely of silica-undersaturated volcanic products and minor intrusions. 40Ar–39Ar incremental heating experiments have been carried out on 24 samples that cover the entire exposed chronological sequence. The oldest lavas (7.57±0.56 Ma), representing an older volcanic basement, are exposed about 620 m above mean sea level. After an interval of quiescence of up to 4.3 Ma the volcanic activity resumed and continued at low eruption rates. The older basement is unconformably overlain by a ca. 810-m-thick lava sequence that spans an age range from 2.93±0.03 to 1.18±0.01 Ma. This sequence is cut by many dykes and sills. Simultaneous volcanic activity occurred in the northeastern, central and eastern part of the island. A phonolitic pumice deposit that forms a noteworthy feature over most of the island has an estimated age of 0.20 Ma. This predates volcanic activity that formed the highest point of the island (Tope de Coroa) which has an age of 0.17±0.02 Ma. The most recent eruption on the island formed nephelinitic lavas in the Porto Novo region at 0.09±0.03 Ma. The oldest volcanism exposed on Santo Antão, which took place about 7.6 Ma ago, was simultaneous with waning activity on Maio at the eastern end of the Cape Verde Archipelago. 相似文献
20.
Oxygen isotopic data are presented for bulk glacial meltwaters draining the Haut Glacier d'Arolla, Valais, Switzerland and for the sulphate contained within them in an attempt to assess the redox status of the subglacial chemical weathering environment. The sulphate derived from subglacial chemical weathering is so depleted in 18O that it must have formed, at least partially, in an anoxic environment. Under these conditions, Fe3+ can act as an oxidizing agent and oxygen atoms incorporated into sulphate are derived from 18O‐depleted water molecules (by contrast, dissolved O2 is strongly enriched in 18O). These data therefore support the hypothesis that sectors of the glacier bed are anoxic and that Fe3+ may act as a significant oxidizing agent under these conditions. Copyright © 2002 John Wiley & Sons, Ltd. 相似文献