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991.
Mesozoic metallogeny in East China and corresponding geodynamic settings — An introduction to the special issue 总被引:6,自引:0,他引:6
The giant East China Mesozoic metallogenic province hosts some of the World’s largest resources of tungsten, tin, molybdenum, antimony and bismuth. Ores of gold, silver, mercury, lead, zinc, copper, uranium and iron are also of major importance. The province and its constituent metallogenic belts or regions (South China; Middle–Lower Yangtze River Valley; East Qinling–Dabie; Interior of North China Craton; Yan-Liao and North-east China) are the products of several pulses of igneous activity and mineralisation between ~240 and ~80 Ma. Each successive stage has produced a distinctive suite of deposits that can be readily related to the geodynamic evolution of the region during the Mesozoic. This geodynamic evolution is linked to a complex series of tectonic events, involving far-field-subduction, plate collisions, crustal thickening, post-collision collapse and rifting. 相似文献
992.
A natural datolite CaBSiO4(OH) (Bergen Hill, NJ, USA), before and after gamma-ray irradiation (up to ~70 kGy), has been investigated by single-crystal
and powder electron paramagnetic resonance (EPR) spectroscopy from 10 to 295 K. EPR spectra of gamma-ray-irradiated datolite
show the presence of a boron-associated oxygen hole center (BOHC) and an atomic hydrogen center (H0), both of which grow with increasing radiation dose. The principal g and A(11B) values of the BOHC at 10 K are: g
1 = 2.04817(3), g
2 = 2.01179(2), g
3 = 2.00310(2), A
1 = −0.401(7) mT, A
2 = −0.906(2) mT, A
3 = −0.985(2) mT, with the orientations of the g
1 and A
1 axes approximately along the B–OH bond direction. These experimental results suggest that the BOHC represents hole trapping
on the hydroxyl oxygen atom after the removal of the proton (i.e. a [BO4]0 center): via a reaction O3BOH → O3BO· + H0, where · denotes the unpaired electron. Density functional theory (DFT) calculations (CRYSTAL06, B3PW, all-electron basis
sets, and 1 × 2 × 2 supercell) support the proposed structural model and yield the following 11B hyperfine coupling constants: A
1 = −0.429 mT, A
2 = −0.901 mT, A
3 = −0.954 mT, in excellent agreement with the experimental results. The [BO4]0 center undergoes the onset of thermal decay at ~200°C and is completely annealed out at 375°C but can be restored readily
by gamma-ray irradiation. Isothermal annealing experiments show that the [BO4]0 center exhibits a second-order thermal decay with an activation energy of 0.96 eV. The confirmation of the [BO4]0 center (and its formation from the O3BOH precursor) in datolite has implications for not only understanding of BOHCs in alkali borosilicate glasses but also their
applications to nuclear waste disposal. 相似文献
993.
本文根据钻井、地层剖面等资料,利用Surfer8.0软件编制出晚三叠世以来龙门山前陆盆地各构造层序的残留地层等厚图,计算出6个构造层序地层的沉积总量、沉积通量.沉积通量分别为:300.2g/(m2·ka)、66.5g/(m2·ka)、71.7 g/(m2 ·ka)、38.5 g/(m2·ka)、113.0 g/(m2·ka)、1204.6 g/(m2·ka).利用物质平衡法将各阶段沉积物回剥至物源区,计算各阶段物源区剥蚀速率分别为:167.3 mm/ka、22.5 mm/ka、22.9 mm/ka、9.8mm/ka、22.9 mm/ka、319.4 mm/ka.计算结果表明,晚三叠世以来,物源区的剥蚀速率和沉积区的沉积速率均具有先减小后增大的变化规律,晚三叠世和晚新生代是剥蚀一沉积过程最强烈的两个阶段,可能对应了龙门山强烈隆升的两个时期.根据对盆地沉积物总量的估算,利用物质平衡的原理,可以推算出龙门山自晚三叠世开始隆升到现在,龙门山冲断带的地壳隆升幅度大于10 ~ 12km,平均剥蚀厚度超过7.05km. 相似文献
994.
995.
Ages and geochemistry of Laojunshan granites in southeastern Yunnan, China: implications for W-Sn polymetallic ore deposits 总被引:4,自引:0,他引:4
The Southeastern Yunnan region is one of the most important polymetallic ore districts in South China. Located in the southern margin of the South China Block, these ore districts are part of a wider granite-related magmatic-hydrothermal system. Laojunshan granite intrusions, located in the western part of the Southeastern Yunnan, are closely related to W-Sn mineralisation. In this paper we report zircon U-Pb ages, geochemical and petrological characteristics for the ore-related granites in Laojunshan area. Three samples from three intrusive suites of the granitic rocks in Laojunshan intrusion have been analyzed by the LA-ICPMS zircon U-Pb techniques, yielding ages of 86.66?±?0.42 Ma, 86.72?±?0.47 Ma and 86.02?±?0.48 Ma, respectively. Bulk analysis reveals that three intrusive suites are strongly-peraluminous, silica-rich, aluminum-rich and alkali-rich granites and their ACNK values fall mainly into a small range of 1.10–1.38. Moreover, all granites show enriched Rb, La and Zr and depleted Ba, Sr and Ti, as well as a uniformly flat REE-pattern with a marked negative Eu anomaly. The granites and polymetallic W–Sn mineralization possibly both occurred during the Late Coniacian. 相似文献
996.
Zhuming Yang Kuishou Ding Jeffrey de Fourestier Qian Mao He Li 《Mineralogy and Petrology》2013,107(2):163-169
The Fe-rich Li-bearing magnesionigerite-6N6S occurs in the Xianghualing tin-polymetallic ore field, Linwu County, Hunan Province, Peoples Republic of China. It was found near the outer contact zone of the Laizhiling granite body and in the Middle-Upper Devonian carbonate rocks of Qiziqiao Formation. The mineral formed during the skarn stage. Its empirical formula is Sn1.81Li0.67(Fe1.43Zn1.19 Mn0.41)Σ3.03(Al14.89Mg1.46 Ti0.11Si0.01)Σ16.47O30(OH)2. The structure for magnesionigerite-6N6S was solved and refined in space group R-3?m, with a?=?5.7144(8), c?=?55.446(11) Å, V?=?1568.0(4) Å3, to R1?=?0.0528. Based on the structural refinement of single crystal diffraction data the formula of magnesionigerite-6N6S is Sn1.80Li0.97(Fe1.89Zn0.91) Σ2.80 (Al14.60Mg1.63 Ti0.20)Σ16.43O30(OH)2 with Z?=?3. Fe-rich Li-bearing magnesionigerite-6N6S contains 0.74 wt.% Li2O. The idealized charge-balanced composition of magnesionigerite-6N6S may be expressed by bivalent and trivalent cations: (Mg2+)4(Al3+)18O30(OH)2. The simplified general formula for the 6N6S polysomes in the nigerite and högbomite groups can be given as A x B18-x O30(OH)2, x?=?~4, where A?=?Mg2+, Fe2+, Zn2+; B?=?Al3+, Sn4+, Ti4+, Li+, □. 相似文献
997.
998.
Humification degree of peat and its implications for Holocene climate change in Hani peatland, Northeast China 总被引:2,自引:0,他引:2
The humification degree of peat is a significant climatic proxy for paleoclimate change.Using the alkali-extraction method,a time series of absorbance values of the Hani peatland,Northeast China,was determined,which is used as an indicator for the humification degree of peat.Combined with14C dating data of peat cellulose,and compared withδ18O andδ13C time series of the cellulose in the Hani peatland,the evidence for the existence of14 ka paleoclimate was provided.Higher humification degrees hint a warmer-wetter climate,and vice versa.It also reconstructs the four stages of Holocene climate evolution in this region:11.5–9.8 cal ka B.P.,warm and wet period;9.8–9.0 cal ka B.P.,cold and dry period;9.0–4.8 cal ka B.P.,warm and wet period;and 4.8–0 cal ka B.P.,warm-wet and dry-cold alternation period.Meanwhile,it is revealed that the abrupt climate shifts signals such as the "8.2 ka" event and the "4.2 ka" event.Results showed that the Hani peat humification degree is of sensitive response to paleoclimate change.Therefore,it is a feasible method to analyze the relationship between paleoclimate change and peat humification degree. 相似文献
999.
Guangxuan Han Liqiong Yang Junbao Yu Guangmei Wang Peili Mao Yongjun Gao 《Estuaries and Coasts》2013,36(2):401-413
Using the Eddy Covariance (EC) technique, we analyzed temporal variation in net ecosystem CO2 exchange (NEE) and determined the effects of environmental factors on the balance between ecosystem photosynthesis and respiration in a reed (Phragmites australis) wetland in the Yellow River Delta, China. Our results indicated that diurnal and seasonal patterns of NEE and its components (ecosystem respiration (R eco), gross primary production (GPP)) varied markedly among months for the growing season (May to October). The cumulative CO2 emission was 1,657 g CO2 m?2, while 2,612 g CO2 m?2 was approximately accumulated as GPP, which resulted in the reed wetland being a net sink of 956 g CO2 m?2. The ratio of R eco to GPP in reed wetland was 0.68, which was close to other temperate wetlands. Soil temperature and soil moisture exerted the primary controls on R eco during the growing season. Daytime NEE values during the growing season were strongly correlated with photosynthetically active radiation. Aboveground biomass showed significant linear relationships with 24-h average NEE, daytime GPP, and R eco, respectively. Thus, we conclude that the coastal wetland acted as a carbon sink during the growing season despite the variations in environmental conditions, and long-term flux measurements over these ecosystems are undoubtedly necessary. 相似文献
1000.