Re–Os Age of Molybdenite from the Daheishan Mo Deposit in the Eastern Central Asian Orogenic Belt,NE China     

Chunming Han  Wenjiao Xiao  Brian F. Windley  Guochun Zhao  Bexun Su  Songjian Ao  Jien Zhang  Zhiyong Zhang  Bo Wan  Bin Cui  Wenjun Qu  Andao Du 《Resource Geology》2014,64(4):379-386

The Daheishan Mo deposit is located in the eastern part of the Central Asian Orogenic Belt, NE China. Rhenium and osmium isotopes of molybdenites from the Daheishan deposit were used to determine the age of mineralization. Rhenium concentrations in molybdenite samples are between 17 and 30μg g^?1. Analysis of seven molybdenite samples yields an isochron age of 168.0 ± 4.4 Ma (2σ). Based on the geological history and spatial‐temporal distribution of the granitoids, it is proposed that the Mo deposits in eastern China were related to the subduction of the Paleo‐Pacific plate during Jurassic time.  相似文献   

Geochronology of the Xiaodonggou Porphyry Mo Deposit in Northern Margin of North China Craton     

Qingdong Zeng  Jianming Liu  Feng Qin  Zuolun Zhang 《Resource Geology》2010,60(2):192-202

The Xiaodonggou porphyry Mo deposit is located in the Mesozoic calc-alkaline Xiaodonggou granitoid within a Palaeozoic fold zone of northern China. The mineralization mainly occurred in an area of 0.54 km² at the south-eastern part of the Xiaodonggou granitoid. The mineralization includes disseminated molybdenite, pyrite, chalcopyrite, magnetite and pyrrhotite and stockwork quartz-sulfide veins. A molybdenite-rich inner core is surrounded by a concentric zone of the sulfide mineral assemblage of pyrite, galena and sphalerite. Intense potassic alteration is overprinted by sericitization and silicification in the mineralized zone. SHRIMP U-Pb data of zircon indicate that the granitoid crystallized at 142 ± 2 Ma (2σ). Re–Os age dating for six molybdenite samples from underground galleries of the deposit constrains the age of porphyry-style Mo mineralization to be 138.1 ± 2.8 Ma (2σ). These data suggest that porphyry-style mineralization was associated with the Xiaodonggou granitoid intrusion and support an Early Cretaceous porphyry-type metallogenic epoch along the northern margin of North China Craton.  相似文献   

Precise Re–Os mineral isochron and Pb–Nd–Os isotope systematics of a mafic–ultramafic sill in the 2.0 Ga Onega plateau (Baltic Shield)     

I.S Puchtel  G.E Brügmann  A.W Hofmann 《Earth and Planetary Science Letters》1999,170(4):602-461

We present Re–Os, Sm–Nd and Pb–Pb isotope and trace element data for the Konchozero sill, a layered mafic–ultramafic intrusion in the Early Proterozoic Onega plateau, one of the oldest continental flood basalt provinces on Earth. The Sm–Nd and Pb–Pb combined mineral and whole-rock isochron ages of 1988±34 and 1985±57 Ma for the sill coincide with the age of ferropicrites from Pechenga (the Kola Peninsula). The lithostratigraphic, chemical and isotope evidence suggest the derivation of Pechenga lavas and the Onega plateau volcanics from a single mantle plume. Peridotite and gabbro whole-rock samples, and primary ulvospinel and ilmenite mineral separates from the sill yield a Re–Os isochron with a slope corresponding to an age of 1969±18 Ma, γ_Os(T) =−0.61±5.9. This age is consistent with the other isotope data, and indicates the closed-system behavior of Re and Os in the rocks. The peridotites and ulvospinel have high Os concentrations (2.5–14 ppb) and low ¹⁸⁷Re/¹⁸⁸Os ratios (0.35–1.1), thus allowing a more accurate determination of the weighted average initial ¹⁸⁷Os/¹⁸⁸Os of 0.1144±0.0019 (2σ_pop), γ_Os(T) =+0.77±1.7. This value is lower than that determined by Walker et al. (Geochim. Cosmochim. Acta 61 (1997) 3145–3160) for the Pechenga lavas (γ_Os(T) =+6.1±0.7), and implies a substantial Os-isotope heterogeneity in this ancient plume. Compared to the Onega plateau primary basalt magma, Pechenga ferropicrites are relatively enriched in iron and Ni, have lower (Nb/Th)_N ratios (2.1 vs 1.1) and less radiogenic Nd-isotope compositions (_Nd(T) = +3.1 and +1.4, respectively), but share similar low-radiogenic Pb-isotope characteristics (μ₁=8.57 and 8.60). Incorporation of small amounts (1.5%) of outer core material into the hotter central part of the plume and subsequent contamination of the Pechenga ferropicritic magmas with the 2.9 Ga Belomorian gneisses can explain the observed chemical and isotope variations in the two provinces provided that the core had <0.25 ppm of Pb.  相似文献   

基于ADCIGS预测地层孔隙压力的方法研究          下载免费PDF全文

张冰  徐嘉亮 《地球物理学报》2020,63(1):313-319

工业界计算孔隙压力系数普遍应用的Eaton和Fillippone方法都需要构建能够准确表征低速层的层速度模型,层速度模型精度及效率成为制约孔隙压力预测的关键参数,但目前工业界层速度建模的精度及效率很难满足孔隙压力预测的要求.本文由正常压实情况下的背景速度场出发,基于时距曲线公式及角道集抽取公式,创新推导了以角度域共成像点道集(ADCIGS)剩余曲率为自变量的孔隙压力系数计算公式,该公式完全由去噪后的地震数据进行驱动,不需要构建层速度模型,该方法大幅提高了计算孔隙压力系数的效率.由模型测试及实际数据应用证明,利用本文提出方法进行孔隙压力预测是有效可行的,该方法可以有效提高预测孔隙压力精度,还可以有效提高预测孔隙压力效率.  相似文献   

Did boninite originate from the heterogeneous mantle with recycled ancient slab?          下载免费PDF全文

Susumu Umino  Kyoko Kanayama  Keitaro Kitamura  Akihiro Tamura  Osamu Ishizuka  Ryoko Senda  Shoji Arai 《Island Arc》2018,27(1)

Boninites are widely distributed along the western margin of the Pacific Plate extruded during the incipient stage of the subduction zone development in the early Paleogene period. This paper discusses the genetic relationships of boninite and antecedent protoarc basalt magmas and demonstrates their recycled ancient slab origin based on the T–P conditions and Pb–Hf–Nd–Os isotopic modeling. Primitive melt inclusions in chrome spinel from Ogasawara and Guam islands show severely depleted high‐SiO₂, MgO (high‐silica) and less depleted low‐SiO₂, MgO (low‐silica and ultralow‐silica) boninitic compositions. The genetic conditions of 1 346 °C at 0.58 GPa and 1 292 °C at 0.69 GPa for the low‐ and ultralow‐silica boninite magmas lie on adiabatic melting paths of depleted mid‐ocean ridge basalt mantle with a potential temperature of 1 430 °C in Ogasawara and of 1 370 °C in Guam, respectively. This is consistent with the model that the low‐ and ultralow‐silica boninites were produced by remelting of the residue of the protoarc basalt during the forearc spreading immediately following the subduction initiation. In contrast, the genetic conditions of 1 428 °C and 0.96 GPa for the high‐silica boninite magma is reconciled with the ascent of more depleted harzburgitic source which pre‐existed below the Izu–Ogasawara–Mariana forearc region before the subduction started. Mixing calculations based on the Pb–Nd–Hf isotopic data for the Mariana protoarc basalt and boninites support the above remelting model for the (ultra)low‐silica boninite and the discrete harzburgite source for the high‐silica boninite. Yb–Os isotopic modeling of the high‐Si boninite source indicates 18–30 wt% melting of the primitive upper mantle at 1.5–1.7 Ga, whereas the source mantle of the protoarc basalt, the residue of which became the source of the (ultra)low‐Si boninite, experienced only 3.5–4.0 wt% melt depletion at 3.6–3.1 Ga, much earlier than the average depleted mid‐ocean ridge basalt mantle with similar degrees of melt depletion at 2.6–2.2 Ga.  相似文献   

基于独立分量分析的南极半岛GNSS网区域滤波   总被引：1，自引：0，他引：1       下载免费PDF全文

李斐  李文浩  张胜凯  雷锦韬  张卿川  袁乐先 《地球物理学报》2019,62(9):3279-3295

高精度GNSS速度场是研究地壳垂向运动及板块运动的基础,能够为冰川均衡调整（Glacial Isostatic Adjustment,GIA）的建模提供外部检核和新的约束.共性误差（Common Mode Error,CME）是区域连续GNSS时间序列中存在的一种与时空相关的主要误差源,通过空间滤波可有效的降低共性误差的影响,提高坐标时间序列的精度.目前广泛采用的主分量分析法（Principal Component Analysis,PCA）,基于二阶统计量（方差和协方差）进行处理,没有充分利用CME高阶统计信息.而独立分量分析ICA （Independent Component Analysis）,引入高阶统计量,能够分离出统计独立的非高斯信号.以南极半岛地区的15个GNSS站点为例,由于某些站点存在强烈的局部效应,因此引入了因子分析法首先对异常站进行剔除,然后对比分析了PCA和ICA方法在南极半岛地区区域滤波结果.结果显示,ICA的滤波效果要优于PCA,ICA滤波前后E、N、U三个方向RMS平均降低44.69%、26.94%、34.87%,不确定度分别降低37.43%,44.58%,55.86%,有效的降低了GNSS残差序列的发散性和速度的不确定度.  相似文献   

基于多通道奇异谱分析的GNSS坐标时间序列共模误差的提取   总被引：1，自引：0，他引：1       下载免费PDF全文

周茂盛  郭金运  沈毅  孔巧丽  袁佳佳 《地球物理学报》2018,61(11):4383-4395

共模误差是区域连续GNSS网中存在的一种与时空相关的主要误差源.为了有效的剔除共模误差,提高坐标时间序列的精度,本文提出了利用多通道奇异谱分析（Multi-channel Singular Spectrum Analysis,MSSA）提取共模误差的新思路,并利用实验区域18个测站9年（2002年到2010年）的GPS坐标时间序列进行实验,分析了共模误差对时间序列的影响和测站噪声特性的影响,并对共模误差序列进行周期探测,结果显示：通过MSSA能够有效的剔除共模误差,提高坐标时间序列的精度.  相似文献   

Drivers of successful common-pool resource management: A conjoint experiment on groundwater management in Brazil     

《Global Environmental Change》2022

Carefully designed common-pool resource (CPR) management systems can improve water security, but many NGOs and governments do not have the resources and logistical capacity to implement all important features of a system at once. In addition, users’ perception of management features is important to increase buy-in and adoption of a new system. Which aspects of a commons management system do users perceive to be most important? We conduct a conjoint survey experiment about groundwater management with rural residents in the semi-arid region of Northeast Brazil. We randomly vary five features of a water management system: 1) discussion, 2) social sanctions for overuse, 3) rules and penalties, 4) payment, 5) monitoring and dissemination of conditions to users. Each feature increases perceived likelihood of collective well management and individual water conservation. We find that features act as complements or substitutes; in particular, discussion complements monitoring, and payment substitutes for rules. Our results have implications for how to study and prioritize the features of CPR management systems to improve water security in other rural, semi-arid regions with groundwater reliance when it is infeasible to implement all recommended features.  相似文献