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1.
With its amplification simultaneously emerging in cryospheric regions, especially in the Tibetan Plateau, global warming is undoubtedly occurring. In this study, we utilized 28 global climate models to assess model performance regarding surface air temperature over the Tibetan Plateau from 1961 to 2014, reported spatiotemporal variability in surface air temperature in the future under four scenarios (SSP1-2.6, SSP2-4.5, SSP3-7.0, and SSP5-8.5), and further quantified the timing of warming levels (1.5, 2, and 3 °C) in the region. The results show that the multimodel ensemble means depicted the spatiotemporal patterns of surface air temperature for the past decades well, although with differences across individual models. The projected surface air temperature, by 2099, would warm by 1.9, 3.2, 5.2, and 6.3 °C relative to the reference period (1981–2010), with increasing rates of 0.11, 0.31, 0.53, and 0.70 °C/decade under the SSP1-2.6, SSP2-4.5, SSP3-7.0, and SSP5-8.5 scenarios for the period 2015–2099, respectively. Compared with the preindustrial periods (1850–1900), the mean annual surface air temperature over the Tibetan Plateau has hit the 1.5 °C threshold and will break 2 °C in the next decade, but there is still a chance to limit the temperature below 3 °C in this century. Our study provides a new understanding of climate warming in high mountain areas and implies the urgent need to achieve carbon neutrality.  相似文献   

2.
This study investigates the variability of extreme rainfall (temperature) events in the twenty-first century based on 18 (24)-member multimodel simulations of models participating in phase 5 of the Couple Model Intercomparison Project (CMIP5). The study employed extreme indices defined by the WMO’s Experts Team on Climate Change Detection Indices, under two radiative forcing scenarios: RCP4.5 and RCP8.5. Two 30-year time periods, mid- (2021–2050) and end (2071–2100) of the twenty-first century, are considered for investigation of extremes, relative to the baseline period (1961–1990). Mann–Kendall test statistic and Sen’s slope estimator are used to investigate trend. Temperature shows a remarkable increase with an increase in radiative forcing. A sharp augmentation in temperature is projected towards the end of the twenty-first century. There will be almost zero cool days and cold nights by the end of the century. Very wet and extremely very wet days increase, especially over Uganda and western Kenya. Variation in maximum 1-day precipitation (R × 1 day) and maximum 5-day precipitation amount shows a remarkable increase in variance towards the end of the twenty-first century. Although the results are based on relatively coarse resolution data, they give likely conditions that can be utilized in long-term planning and be relied on in advanced studies.  相似文献   

3.
Feng  Yuannan  Lan  Tingguang  Pan  Lichuan  Liu  Tingting  Dong  Shaohua 《中国地球化学学报》2019,38(4):530-540

The Nanling Range in South China is well known for its rich granite-related W–Sn deposits. To elucidate the controls of different granite-related W–Sn metallogenesis in the region, we chose five representative ore-related granites (Yanbei, Mikengshan, Tieshanlong, Qianlishan, and Yaogangxian intrusions) in the Hunan–Jiangxi region, and studied their magmatic zircon ages and trace element geochemistry. Our new zircon data showed the differences in ages, temperatures and oxygen fugacity of the ore-forming magmas. Zircon U–Pb ages of the Yanbei and Mikengshan intrusions are characterized by 142.4 ± 2.4 and 143.0 ± 2.3 Ma, respectively, whereas the Tieshanlong and Qianlishan intrusions are 159.5 ± 2.3 and 153.2 ± 3.3 Ma, respectively. The Sn-related intrusions were younger than the W-related intrusions. The Ti-in-zircon thermometry showed that there was no systematic difference between the Sn-related Yanbei (680–744 °C) and Mikengshan (697–763 °C) intrusions and the W-related Tieshanlong (730–800 °C), Qianlishan (690–755 °C) and Yaogangxian (686–751 °C) intrusions. However, the zircon Ce4+/Ce3+ ratios of the Yanbei (averaged at 18.3) and Mikengshan (averaged at 18.8) intrusions are lower than those of the Tieshanlong (averaged at 36.9), Qianlishan (averaged at 38.4) and Yaogangxian (averaged at 37) intrusions, indicating that the Sn-related granitic magmas might have lower oxygen fugacities than those of the W-related. This can be explained by that, in more reduced magmas, Sn is more soluble than W and thus is more enriched in the residual melt to form Sn mineralization. The difference in source materials between the Sn-related and the W-related granites seems to have contributed to the different redox conditions of the melts.

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4.
The validity of the thermodynamic cBΩ model is tested in terms of the experimentally determined diffusion coefficients of He in a natural Fe-bearing olivine (Fo90) and a synthetic end-member forsterite (Mg2SiO4) over a broad temperature range (250–950 °C), as reported recently by Cherniak and Watson (Geochem Cosmochim Acta 84:269–279, 2012). The calculated activation enthalpies for each of the three crystallographic axes were found to be (134 ± 5), (137 ± 13) and (158 ± 4) kJ mol?1 for the [100], [010] and [001] directions in forsterite, and (141 ± 9) kJ mol?1 for the [010] direction in olivine, exhibiting a deviation of <1 % with the corresponding reported experimental values. Additional point defect parameters such as activation volume, activation entropy and activation Gibbs free energy were calculated as a function of temperature. The estimated activation volumes (3.2–3.9 ± 0.3 cm3 mol?1) of He diffusion in olivine are comparable with other reported results for hydrogen and tracer diffusion of Mg cations in olivine. The pressure dependence of He diffusion coefficients was also determined, based on single experimental diffusion measurements at 2.6 and 2.7 GPa along the [001] direction in forsterite at 400 and 650 °C.  相似文献   

5.
人类活动和气候变化严重改变了黄河水文情势和生态径流,分析未来气候变化对河流生态的影响对流域水资源管理和长期规划意义重大。本文对第六次国际耦合模式比较计划（CMIP6）的13个全球气候模式数据进行偏差订正,驱动水文模型进行径流模拟,应用流量历时曲线方法分析SSP1-2.6、SSP2-4.5、SSP5-8.5情景下2026年至21世纪末年、季节尺度的花园口生态径流变化。结果表明:订正能明显降低降水、气温模拟偏差;人类活动严重影响了1986-2010年花园口生态径流;2026-2100年年均气温和年降水量增加趋势显著,低排放情景增速慢,高排放情景增速快;气候变化可在一定程度上缓解水库调控、水土保持等人类活动对生态径流的负面影响,SSP5-8.5情景缓解程度最高,冬季缓解程度最高,夏、秋季最低。  相似文献   

6.
利用第六次国际耦合模式比较计划（CMIP6）提供的5个气候模式,并结合基于地面气象站的CN05.1气象资料,评估了CMIP6模式对黄河上游地区1961—2014年气温变化的模拟能力。基于7个共享社会经济路径及代表性浓度路径（SSP-RCP）组合情景,结合多模式集合平均预估了2015—2100年黄河上游地区年均气温和季平均气温的时空变化规律。结果表明：多模式集合平均能较好地模拟黄河上游地区历史平均气温的空间分布格局与年变化。7个未来情景一致表明,2015—2100年黄河上游地区年平均气温呈现波动上升趋势［0.03～0.82 ℃?（10a）-1］。其中,低辐射强迫情景下（SSP1-1.9、SSP1-2.6及SSP4-3.4）气温先呈现增加趋势,21世纪中期到达增幅峰值,之后增温呈现放缓趋势;而中、高辐射强迫情景下（SSP2-4.5、SSP3-7.0、SSP4-6.0及SSP5-8.5）气温表现为持续上升态势。空间上,未来气温增幅显著的区域位于黄河上游西部地区;时间上,呈现夏季增温快,春季增温慢。四季增温的空间分布呈现出一致特征,表现为西部增温强于东部,北部增温强于南部。研究结果可为黄河流域水资源管理及气候变化的适应性研究提供科学依据。  相似文献   

7.
《Applied Geochemistry》1998,13(6):707-714
The properties of fluorapatite, both a useful radiochronometer and a potential storage matrix specific for minor actinides produced by the reprocessing of spent nuclear fuel, have been investigated with emphasis to its response to alpha decay. Exfoliation, which occurs after implantation of high doses of 1.6-MeV He-ions (>1.4×1017 ions cm−2, corresponding to 5% atomic proportion), could set an upper limit to the concentration of imbedded actinides (about 2 atoms % corresponding to 20 wt. %) or storage age unless significant diffusion of radiogenic He intervenes. This process has been studied by combining He implantation, thermal treatments in the temperature range 124–250°C and measurement of the resulting He profile by an ion beam technique (ERDA) using 8.5-MeV C ions. The diffusion coefficient follows an Arrhenius' law with an activation energy of 120 (±2) KJ/mole and a frequency factor of 14.5 (±7)×10−3 cm2 sec−1 in agreement with literature data. The inferred closure temperature which validates the U,Th–He radiochronological method also fits previous values: 97 (±10)°C for grain size 165 μm. With respect to radwaste disposal. He volume diffusion is too small to exclude the occurrence of exfoliation unless diffusion at grain boundary is much higher and a fine-grain matrix is deliberately chosen.  相似文献   

8.
The present study examines the temporal variability of air–water CO2 fluxes (FCO2) and seawater carbonate chemistry in a Baja California coastal lagoon during an exceptionally warm anomaly that was developed in Northeast Pacific coasts during 2014. This oceanographic condition led to a summer-like season (weak upwelling condition) during the study period, which reached a maximum surface temperature anomaly of 2 °C in September 2014. San Quintín Bay acts as a source of CO2 to the atmosphere in 2014 (3.3 ± 4.8 mmol C m?2 day?1) with the higher positive fluxes mainly observed in summer months (9.0 ± 5.3 mmol C m?2 day?1). Net ecosystem production (NEP) switched seasonally between net heterotrophy and net autotrophy during the study period, with an annual average of 2.2 ± 7.1 mmol C m?2 day?1, which indicates that San Quintín Bay was a net autotrophic system during the atypical warm oceanographic condition in 2014. This pattern of seasonal variations in the carbon balance at San Quintín Bay appears to be linked to the life cycle of benthic communities, which play an important role in the whole-ecosystem metabolism. Under the limited input from external sources coupled with an increase in seawater temperatures, the recycled benthic carbon and nutrient fluxes play a major role to sustain water-column processes within the bay. Since the upwelling condition may influence the magnitude of the air–water CO2 fluxes, our results clearly indicated that San Quintín Bay is a net source of carbon to the atmosphere regardless of the adjacent oceanic conditions. Our study sheds light on the carbon dynamics and its metabolic implications in a shallow coastal ecosystem under a regional warm anomaly and contributes potentially relevant information in view of the likely future scenario of global climate change.  相似文献   

9.
Phase equilibria modeling of the pressure–temperature (P–T) path of regional metamorphism and associated fluid expulsion, combined with constraints on the timescale of garnet growth by Sm–Nd geochronology, elucidates the fluid production rate and fluid flux during Barrovian metamorphism of pelitic rocks from Townshend Dam, VT, USA. This modeling builds on a published companion study that utilized Sm–Nd geochronology of concentric growth zones in multiple garnet grains, to constrain the duration of garnet growth in a large sample of schist at Townshend Dam to 3.8?±?2.2 million years (Gatewood et al., Chem Geol 401:151–168, 2015). P–T pseudosections combined with observed mineral compositions constrain garnet growth conditions, and were utilized to construct P–T path-dependent thermodynamic forward models. These models determine that garnet growth was initiated at ~?0.6 GPa and ~?525 °C, with a roughly linear loading and heating P–T trajectory to >?0.8 GPa and ~?610 °C. Loading and heating rates of 2.4 km·Myear?1 (with a range of 1.6 to 5.8 km·million year?1) and 23 °C·million year?1 (with a range of 14 to 54 °C·million year?1), respectively, are consistent with model estimates and chronologic constraints for tectono-metamorphic rates during orogenesis. Phase equilibria modeling also constrains the amount of water release during garnet growth to be ~?0.7 wt% (or >?2 vol%), largely resulting from the complete consumption of chlorite. Coupling this estimate with calculated garnet growth durations provides a fluid production rate of 5.2 kg·m?3·million year?1 (with a range of 3.2 to 12.2 kg·m?3·million year?1) and when integrated over the overlying crustal column, a regional-scale fluid flux of 0.07–0.37 kg·m?2·million year?1. This range of values is consistent with those derived by numerical models and theory for regional-scale, pervasive fluid flow. This study signifies the first derivation of a fluid production rate and fluid flux in regional metamorphism using a direct chronology of water-producing (garnet-forming) reactions and can provide a framework for future studies on elucidating the nature and timescales of fluid release.  相似文献   

10.
The Weihai migmatite in the Sulu ultra-high-pressure (UHP) metamorphic terrane, eastern China, underwent partial melting in the Late Triassic during its exhumation. The primary partial melts experienced a decompressional fractional crystallization (DFC) process to produce plagioclase (Pl)-rich leucosome crystallized under eclogite to granulite facies conditions and K-feldspar (Kfs)-rich pegmatitic veins crystallized under amphibolite-facies conditions. In this study, our results demonstrate that the DFC process can cause decoupling between whole-rock Sr and Nd isotopes. The Pl-rich leucosome has εNd(t) values (–10.4 to ?15.0) and initial (87Sr/86Sr) ratios (0.708173–0.712476) very similar to those of the melanosome, but the Kfs-rich pegmatitic veins have homogeneous εNd(t) values (?14.8 to ?15.2) and significantly high initial (87Sr/86Sr) ratios (0.713882–0.716284). Our results also suggest that the DFC process can change zircon 176Yb/177Hf and 176Lu/177Hf isotopic ratios, with no effect on 176Hf/177Hf ratios or εHf (t) values. Zircon 176Yb/177Hf and 176Lu/177Hf ratios increase dramatically from the Pl-rich leucosome to the Kfs-rich pegmatitic veins, but zircon 176Hf/177Hf ratios (Pl-rich leucosomes = 0.282330 ± 0.000017; Kfs-rich pegmatitic veins = 0.282321 ± 0.000026) and εHf (t) values (Pl-rich leucosomes = ?10.9 ± 0.6; Kfs-rich pegmatitic veins = ?11.6 ± 0.8) remain almost unchanged. We propose that the isotopic decoupling between the Pl-rich leucosome and Kfs-rich pegmatitic vein might be caused by melt fractional crystallization occurring too rapidly to allow complete equilibrium between them.  相似文献   

11.
The Flinton Group is a greenschist to upper amphibolite facies package of metasediments in southeastern Ontario that was metamorphosed during the Ottawan Orogeny. Thermodynamic modeling of metapelitic mineral assemblages suggests an increase in peak conditions of metamorphism across the 40 km wide study area from 3.5 to 7.9 kbar and 540 to 715 °C. Garnet isopleth thermobarometry applied to the cores of compositionally zoned porphyroblasts reveals remarkably similar P-T conditions of initial crystallization at approximately 3.7–4.0 kbar and 512–520 °C, corresponding to a relatively high geothermal gradient of ca. 34–45 °C km?1. It is inferred from modeling and reaction textures that metamorphism was along Barrovian P-T paths. Major and trace element zoning in garnet from one sample records a complex growth history as evidenced by major and trace element zoning and the distribution of xenotime, allanite and monazite inclusions. High-resolution (6 μm) LA-ICP-MS U-Pb geochronology performed on monazite in the rock matrix and included in the outer 150 μm of garnet rim-ward of a Y annulus revealed an age of 976?±?4 Ma. The age is interpreted to reflect monazite growth at the expense of allanite and apatite late in garnet’s growth history over the P-T interval 4.5–6.8 kbar and 540–640 °C. This new age estimate for near peak metamorphism fits well into the regional framework but is significantly younger than previously reported ages for Ottawan metamorphism. Based on microstructures this new age suggests that compressional tectonics were operating much later in the history of the Grenville of southeastern Ontario than previously thought.  相似文献   

12.

Progressive developments in industrial and agricultural activities are causing a critical stress on groundwater quality in developing countries. The objective of this paper is to assess and evaluate the contamination level of groundwater caused by leachate in 11 villages of the Gautam Budh Nagar district in Uttar Pradesh, India. We systematically sampled 22 groundwater samples and 13 leachate samples to ascertain the source of pollution on groundwater quality. The standard analytical methods given by the American Public Health Association (APHA) (Standard methods for examination of water and wastewater, 23rd edn. APHA, AWWA, WPCF, Washington, 2017) were used for quantitative estimation of hydrochemical parameters of collected samples. The results of the analysis of groundwater samples indicate that pH values range from 7.31 to 8.97. The mean magnesium concentration in groundwater samples is 58.93 ± 21.44 mg/L. Out of the groundwater samples taken, approximately 41% and 73% of samples analysis results have been found beyond the acceptable limit with respect to the parameters of turbidity and total dissolved solids, respectively, according to the Bureau of Indian Standards (Indian standard specification for drinking water (IS:10500). BIS, Manak Bhawan, New Delhi, 2012) for drinking water. Around 95.4% of groundwater samples and 92.3% of leachate samples have high nitrate concentrations above the standard limit of BIS (45 mg/L), respectively. The Piper plot shows that 50% of the samples belong to the Ca2+–Mg2+–HCO3− type. Ternary and Durov’s diagrams indicate that the mean concentrations of ions are in the order of Na+ > Mg2+ > Ca2+ > K+ (for cations) and HCO3−> NO3− > Cl− > SO42− > CO32− > F− (for anions) in groundwater of the study area. The spatial variation of the hydrochemical parameters shows that groundwater is heavily contaminated with respect to nitrate. Analytical results indicate that the groundwater of villages Achheja, Bisrakh road, Dujana, Badalpur and Sadopur is not suitable for drinking.

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13.
The Yaochong porphyry Mo deposit in Xinxian County, Henan Province, China, is located in the Hong’an terrane, that is, the western part of the Dabie orogen. The Dabie orogen is part of a >1,500 km long, Triassic continental collision belt between the North China Block and the South China Block. Four types of vein are present. Paragenetically, from early to late, they are as follows: stage 1 quartz + K-feldspar ± pyrite ± magnetite vein; stage 2 quartz + K-feldspar + molybdenite ± pyrite vein; stage 3 quartz + polymetallic sulfides ± K-feldspar vein; and stage 4 quartz ± carbonate ± fluorite vein. Four compositional types of fluid inclusion, pure CO2, CO2 bearing, aqueous, and solid bearing, are present in quartz from the first three stages; only low-salinity aqueous fluid inclusions occur in quartz from the last stage. All the estimated salinities are ≤13.1 wt% NaCl eq., and no halite crystals were identified. Homogenization temperatures for the fluid inclusions from stages 1 to 4 are in the ranges of 262–501, 202–380, 168–345, and 128–286 °C, respectively, and estimated depths decrease from 6.9 to 8.9 km, through 6.2–7.2, to ~4.7 km. Quartz separates from the veins yielded a δ18O value of 7.7–11.2 ‰, corresponding to δ18OH2O values of ?1.3 to 6.9 ‰ using temperature estimates from fluid inclusion data; δDH2O values of fluid inclusion vary from ?80 to ?55 ‰, and δ13CCO2 from ?2.3 to 2.7 ‰, suggesting that the ore-fluids evolved from magmatic to meteoric sources. We conclude that the ore-forming fluid system at Yaochong was initially high temperature, high salinity, and CO2-rich and then progressively evolved to CO2-poor, lower salinity, and lower temperature, by mixing with meteoric water, which results in ore precipitation.  相似文献   

14.
Soil organic carbon (SOC) storage and erosion in South China at the regional scale in the past decades remains far from being understood. This paper calculated the SOC density, storage and erosion in 14 soil classes in Guangdong Province, South China, based on statistical data from the soil survey and soil erosion survey of Guangdong, which was performed in the 1990s. The purpose of this study is to understand the relationships between soil classes and SOC erosion at the regional scale. The results indicated that the SOC density in the soils of Guangdong varied from 12.7 to 144.9 Mg ha?1 over the entire profile and from 12.6 to 68.4 Mg ha?1 in the top 20-cm soil layer. The average area-weighted SOC density in the topsoil (0–20 cm) and the entire profile was 32 ± 3 and 86 ± 4 Mg ha?1, respectively. The total SOC storage was 1.27 ± 0.06 Pg, with 35.6 % (0.46 ± 0.04 Pg) located in the topsoil. The average area-weighted strength of the SOC erosion in the 1990s was 20.6 ± 0.8 Mg km?2 year?1. The results indicated that SOC erosion was strongly related to soil class.  相似文献   

15.
基于第六次国际耦合模式比较计划（CMIP6）的22个地球气候/系统模式模拟数据,分析了1961—2100年期间青藏高原年均地表气温在不同情景下的时空变化。结果表明,多模式集合平均的模拟结果优于大多数单个模式。由于共享社会经济路径（SSP）和辐射强迫的不同,在SSP1-2.6、SSP2-4.5、SSP3-7.0和SSP5-8.5四种情景下,2015—2100年间青藏高原年均地表气温的增温趋势分别为0.10 ℃·（10a）-1、0.29 ℃·（10a）-1、0.53 ℃·（10a）-1和0.69 ℃·（10a）-1,帕米尔高原、藏北高原中西部和巴颜喀拉山区为三个升温中心。相对于1995—2014年参考时段,到本世纪中期（2041—2060年）,青藏高原区域年均地表气温将分别增加1.37 ℃、1.72 ℃、1.98 ℃和2.30 ℃,而到本世纪末期（2081—2100年）,年均地表气温将分别增加1.42 ℃、2.65 ℃、4.28 ℃和5.38 ℃。与《巴黎协定》提出的到本世纪末全球平均气温升高不超过2 ℃目标相比,无论在哪种情景下,到本世纪中期时青藏高原年均地表气温相对于工业革命前均升高超过2 ℃,这会造成极大的气候生态环境问题。  相似文献   

16.
Li  Songtao  Xia  Yong  Liu  Jianzhong  Xie  Zhuojun  Tan  Qinping  Zhao  Yimeng  Meng  Minghua  Tan  Lijin  Nie  Rong  Wang  Zepeng  Zhou  Guanghong  Guo  Haiyan 《中国地球化学学报》2019,38(4):587-609

The newly discovered Baogudi gold district is located in the southwestern Guizhou Province, China, where there are numerous Carlin-type gold deposits. To better understand the geological and geochemical characteristics of the Baogudi gold district, we carried out petrographic observations, elemental analyses, and fluid inclusion and isotopic composition studies. We also compared the results with those of typical Carlin-type gold deposits in southwestern Guizhou. Three mineralization stages, namely, the sedimentation diagenesis, hydrothermal (main-ore and late-ore substages), and supergene stages, were identified based on field and petrographic observations. The main-ore and late-ore stages correspond to Au and Sb mineralization, respectively, which are similar to typical Carlin-type mineralization. The mass transfer associated with alteration and mineralization shows that a significant amount of Au, As, Sb, Hg, Tl, Mo, and S were added to mineralized rocks during the main-ore stage. Remarkably, arsenic, Sb, and S were added to the mineralized rocks during the late-ore stage. Element migration indicates that the sulfidation process was responsible for ore formation. Four types of fluid inclusions were identified in ore-related quartz and fluorite. The main-ore stage fluids are characterized by an H2O–NaCl–CO2–CH4 ± N2 system, with medium to low temperatures (180–260 °C) and low salinity (0–9.08% NaCl equivalent). The late-ore stage fluids featured H2O–NaCl ± CO2 ± CH4, with low temperature (120–200 °C) and low salinity (0–7.48% NaCl equivalent). The temperature, salinity, and CO2 and CH4 concentrations of ore-forming fluids decreased from the main-ore stage to the late-ore stage. The calculated δ13C, δD, and δ18O values of the ore-forming fluids range from − 14.3 to − 7.0‰, −76 to −55.7‰, and 4.5–15.0‰, respectively. Late-ore-stage stibnite had δ34S values ranging from − 0.6 to 1.9‰. These stable isotopic compositions indicate that the ore-forming fluids originated mainly from deep magmatic hydrothermal fluids, with minor contributions from strata. Collectively, the Baogudi metallogenic district has geological and geochemical characteristics that are typical of Carlin-type gold deposits in southwest Guizhou. It is likely that the Baogudi gold district, together with other Carlin-type gold deposits in southwestern Guizhou, was formed in response to a single widespread metallogenic event.

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17.
The dehydration kinetics of serpentine was investigated using in situ high-temperature infrared microspectroscopy. The analyzed antigorite samples at room temperature show relatively sharp bands at around 3,655–3,660 cm?1 (band 1), 3,570–3,595 cm?1 (band 2), and 3,450–3,510 cm?1 (band 3). Band 1 corresponds to the Mg–OH bond, and bands 2 and 3 correspond to OH associated with the substitution of Al for Si. Isothermal kinetic heating experiments at temperatures ranging from 625 to 700 °C showed a systematic decrease of the OH band absorbance with heating duration. The one-dimensional diffusion was found to provide the best fit to the experimental data, and diffusion coefficients were determined with activation energies of 219 ± 37 kJ mol?1 for the total water band area, 245 ± 46 kJ mol?1 for band 1, 243 ± 57 kJ mol?1 for band 2, and 256 ± 53 kJ mol?1 for band 3. The results indicate that the dehydration process is controlled by one-dimensional diffusion through the tetrahedral geometry of serpentine. Fluid production rates during antigorite dehydration were calculated from kinetic data and range from 3 × 10?4 to 3 × 10?5  $ {\text{m}}_{\text{fluid}}^{ 3} \,{\text{m}}_{\text{rock}}^{ - 3} \,{\text{s}}^{ - 1} $ . The rates are high enough to provoke hydraulic rupture, since the relaxation rates of rocks are much lower than these values. The results suggest that the rapid dehydration of antigorite can trigger an intermediate-depth earthquake associated with a subducting slab.  相似文献   

18.
Cylinders of synthetic periclase single crystals were annealed at 0.15–0.5 GPa and 900–1200 °C under water-saturated conditions for 45 min to 72 h. Infrared spectra measured on the quenched products show bands at 3,297 and 3,312 cm?1 indicating V OH ? centers (OH-defect stretching vibrations in a half-compensated cation vacancy) in the MgO structure as a result of proton diffusion into the crystal. For completely equilibrated specimens, the OH-defect concentration, expressed as H2O equivalent, was calculated to 3.5 wt ppm H2O at 1,200 °C and 0.5 GPa based on the calibration method of Libowitzky and Rossmann (Am Min 82:1111–1115, 1997). This value was confirmed via Raman spectroscopy, which shows OH-defect-related bands at identical wavenumbers and yields an H2O equivalent concentration of about 9 wt ppm using the quantification scheme of Thomas et al. (Am Min 93:1550–1557, 2008), revised by Mrosko et al. (Am Mineral 96:1748–1759, 2011). Results of both independent methods give an overall OH-defect concentration range of 3.5–9 (+4.5/?2.6) ppm H2O. Proton diffusion follows an Arrhenius law with an activation energy E a = 280 ± 64 kJ mol?1 and the logarithm of the pre-exponential factor logDo (m2 s?1) = ?2.4 ± 1.9. IR spectra taken close to the rims of MgO crystals that were exposed to water-saturated conditions at 1,200 °C and 0.5 GPa for 24 h show an additional band at 3,697 cm?1, which is related to brucite precipitates. This may be explained by diffusion of molecular water into the periclase, and its reaction with the host crystal during quenching. Diffusion of molecular water may be described by logDH2O (m2 s?1) = ?14.1 ± 0.4 (2σ) at 1,200 °C and 0.5 GPa, which is ~ 2 orders of magnitude slower than proton diffusion at identical P-T conditions.  相似文献   

19.
Authigenic carbonates and seep biota are archives of seepage history and record paleo-environmental conditions at seep sites. We obtained the timing of past methane release events at the northeastern slope of the South China Sea based on U/Th dating of seep carbonates and seep bivalve fragments from three sites located at 22°02′–22°09′N, 118°43′–118°52′E (water depths from 473 to 785 m). Also, we were able to reconstruct the paleo-bottom water temperatures by calculating the equilibrium temperature using the ages, the corresponding past δ18O of seawater (δ18Osw) and the δ18O of the selected samples formed in contact with bottom seawater with negligible deep fluid influence. A criterion consists of mineralogy, redox-sensitive trace elements and U/Th-isotope systematics is proposed to identify whether the samples were formed from pore water or have been influenced by deep fluid. Our results show that all methane release events occurred between 11.5 ± 0.2 and 144.5 ± 12.7 ka, when sea level was about 62–104 m lower than today. Enhanced methane release during low sea-level stands seems to be modulated by reduced hydrostatic pressure, increased incision of canyons and increased sediment loads. The calculated past bottom water temperature at one site (Site 3; water depth: 767–771 m) during low sea-level stands 11.5 and 65 ka ago ranges from 3.3 to 4.0 °C, i.e., 1.3 to 2.2 °C colder than at present. The reliability of δ18O of seep carbonates and bivalve shells as a proxy for bottom water temperatures is critically assessed in light of 18O-enriched fluids that might be emitted from gas hydrate and/or clay dehydration. Our approach provides for the first time an independent estimate of past bottom water temperatures of the upper continental slope of the South China Sea.  相似文献   

20.
The Cenozoic volcanism of western Saudi Arabia extends from southern Yemen to Jordan northward. They cover an area of nearly 180,000 km2. The rocks are dominated by alkali olivine basalts and olivine basalts. Al-Wahbah crater, a part of Harrat Kishb, represents a model occurrence to study the gneisses of these rocks. New mineral chemistry and isotopic data are presented. It aims to follow the isotopic, mineralogical, and thermobarometry variations among these volcanics. Amphiboles of the studied volcanics belong to the monoclinic calcic group. The chemistry of the amphibole crystals shows two ranges of pressure. They are 3.6–5.6 and 0.38–0.78 kbar. The Aliv values of the amphiboles are in the range of 1.202 and 1.407, indicating corresponding temperature condition of 820–920 and 620–720 °C, respectively. The feldspar of the studied samples has the composition of plagioclase, though some grains have sanidine composition. They are formed in temperature range of 975 and 400 °C. The coexisting amphiboles and plagioclases indicate two sets of pressure and temperature. They are 540–575 °C (3.5–4 kbar) and 510–525 °C (~2 kbar), respectively. Rb–Sr isochron of the whole rock yields an age of 0.867 ± 0.160 Ma with initial Sr87/Sr86 of 0.702 ± 0.00086. The low initial ratio of Sr87/Sr86 together with positive values of εNd today implies that the studied volcanics have mantle source. Meanwhile, the present isotopic data suggest extraction of juvenile magma from asthenosphere source. The present study shows that the Al-Wahbah crater rocks belong to Cenozoic basalts and indicate EM-I-like signature.  相似文献   

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