Rb-Sr and Sm-Nd Isochron Ages of the Dongmozhazhua and Mohailaheng Pb-Zn Ore Deposits in the Yushu area, southern Qinghai and Their Geological Implications

Located on the northeast margin of the Qiangtang terrane between the Jinshajiang suture zone and Bangonghu-Nujiang suture zone,the Dongmozhazhua and Mohailaheng Pb-Zn deposits in the Yushu area of Qinghai Province are representative Pb-Zn deposits of the Pb-Zn-Cu polymetallic mineralization belt in the northern part of the Nujiang-Lancangjiang-Jinshajiang area,which are in the front belt of the Yushu thrust nappe system.The formed environments of these two deposits are different from those of sediment-hosted base metal deposits elsewhere in the world.The authors hold that they were formed during the Indian-Asian continental collision and developed within the fold-thrust belt combined with thrust and strike-slip-related Cenozoic basins in the interior of the collisional zone.Studying on the metallogenic epochs of these two deposits is helpful to the understanding of ore-forming regularity of the regional Pb-Zn-Cu mineralization belt and also to the search for new deposits in this region.The age of the Dongmozhazhua deposit has been determined by the Rb-Sr isochron method for sphalerite residues,whereas the age of the Mohailaheng deposit has been determined by the Rb-Sr isochron method for sphalerite residues and the Sm-Nd isochron method for fluorite.The age of the Dongmozhazhua deposit is 35.0-±0.0 Ma （（87Sr/86Sr）0=0.708807） for sphalerite residues.The age of the Mohailaheng deposit is 32.2±0.4 Ma （（87Sr/86Sr）o=0.708514） for sphalerite residues and 31.8±0.3 Ma （（143Nd/144Nd）o=0.512362） for fluorite with an average of 32.0 Ma.Together with the regional geological setting during mineralization,a possible tectonic model for metallogeny of the Dongmozhazhua and Mohailaheng Pb-Zn deposits has been established.These two ages are close to the ages of the Pb-Zn deposits in the Lanping and Tuotuohe basins,indicating that it is possible that the narrow 1000-kilometer-long belt controlled by a thrust nappe system on the eastern and northern margins of the Tibetan plateau could be a giant Pb-Zn mineralized belt.

ISOCHRONOUS STRESS-STRAIN CURVES OF LOW ALLOY STEEL CROSS-WELD-SPECIMEN AT HIGH TEMPERATURE

In this work, a parametric approach is presented and utilized to determine the creep properties of weldments; then the model of creep strain for cross weld specimen is given. On the basis of the experimental results, attempt has been made to establish equations of the isochronous stress-strain for weld joint that can predict the function of loading and service time in use of the creep data of base metal and weld metal.

Charge resolution in the isochronous mass spectrometry and the mass of ^(51)Co

Isochronous mass spectrometry(IMS)of heavyion storage rings is a powerful tool for the mass measurements of short-lived nuclei.In IMS experiments,masses are determined through precision measurements of the revolution times of the ions stored in the ring.However,the revolution times cannot be resolved for particles with nearly the same mass-to-charge(m/q)ratios.To overcome this limitation and to extract the accurate revolution times for such pairs of ion species with very close m/q ratios,in our early work on particle identification,we analyzed the amplitudes of the timing signals from the detector based on the emission of secondary electrons.Here,the previous data analysis method is further improved by considering the signal amplitudes,detection efficiencies,and number of stored ions in the ring.A sensitive Z-dependent parameter is introduced in the data analysis,leading to a better resolution of ^(34)Ar^(18+) and ^(51)Co^(27+) with A/Z=17/9.The mean revolution times of ^(34)Ar^(18+) and ^(51)Co^(27+) are deduced,although their time difference is merely 1.8 ps.The uncorrected,overlapped peak of these ions has a full width at half maximum of 7.7 ps.The mass excess of ^(51)Co was determined to be-27;332e41T keV,which is in agreement with the previous value of-27;342e48T keV.

The Cyclicity of the Period Annulus Around the Quadratic Isochronous Center

The number of the limit cycles bifurcating in small quadratic perturbations of quadratic systems with an ischronous center is studied, it turns out that the cyclicity of the period annulus around one kind of quadratic isochronous center is two.

Discussion on Rb-Sr Isochron Ages of Granitoids in the Hengduan Mountains

Based on the Rb-Sr isotopic study of the granitoids in the Hengduan Mountains, the classification andgeologic significance of whole-rock Rb-Sr isochrons as well as the factors influencing homogenization of theisotopic systems are discussed. Usually. there is no good linear correlation of isochrons for diorites andalkali-rich intrusive rocks (including alkaline rock and alkalic granite). But by means of the external isochron ofmonominerals from the rocks. isochrons with good linear correlation as well as ages and Sr initial ratios with ahigh confidence can be obtained. In order to obtain a satisfactory isochron, the discriminant parameters shouldbe calculated from the Rb/Sr ratios and estimated ages of samples. Only those that meet the requirements canbe used as the Rb-Sr isochrons. The quality of an isochron should be judged from three factors, i.e. correlationcoefficient. MSWD and homogenization degree.

Dating Model of Illite Grain Rb-Sr Isochron and Its Application to Precambrian Stratigraphy

This paper discusses the Rb-Sr geochemical behaviour of illites in the sedimentary process, and points out that illites of the lmd and lm types could reach Sr-isotopic equilibrium with its environmental medium during the sedimentary process and initial stage of diagenesis, and illite grains of different sizes have various Rb contents. A new dating method for sedimentary rocks----a dating model of illite grain Rb-Sr isochron----is established, in consideration of the geochemical process of Sr-isotopic homogenization and differentiation in the course of their formation and evolution. In addition, the paper concerns the application of the dating model to the Precambrian unmetamorphosed sedimentary rocks in western Henan Province, which gives satisfactory results coincident with the geological facts.

Effects of Solution Atoms and Precipitates on Isochronal Annealing Behavior of Cold-Rolled Squeeze-Cast SiCw/Al Composites

SiCw/Al and SiCw/6061Al composites, which contained 15 vol pct of whiskers, were fabricated through a squeeze cast route followed by cold rolling and isochronal annealing. Effects of whicker, solution atoms and precipitates on isochronal annealing behavior of cold rolled composites were investigated by comparing the isochronal annealing behavior between pure Al, SiCw/Al, solution-treated SiCw/6061Al and aged SiCw/6061Al. It was found that the recrystallization of SiCw/Al composite occurs earlier than that of pure Al, indicating SiCw has a role of particle stimulated nucleation. Solution atoms have no significant influence on the isochronal annealing behavior of SiCw/6061Al composite, while precipitates have such a strong retarding effect on the recrystallization of SiCw/6061Al composite that the isochronal annealing curve of aged SiCw/6061 composite loses the definable recrystallization step.

Adaptive Isochronal Synchronization in Mutually Coupled Chaotic Systems

This paper studies the problem of isochronal synchronization of chaotic systems with time-delayed mutual coupling. Based on the invariance principle of differential equations, an adaptive feedback scheme is proposed for the stability of isochronal synchronization between two identical chaotic systems. Unlike the usual linear feedback, the variable feedback strength is automatically adapted to isochronally synchronize two identical chaotic systems with delay-coupled, so this scheme is analytical, and simple to implement in practice. Simulation results show that the isochronal synchronization behavior is determined by time delay.

2-6 First Isochronous Mass Measurements with Two Time-of-Flight Detectors at CSRe

In conventional isochronous mass spectrometry (IMS), single time-of-flight (TOF) method is adopted to measurethe ions' revolution times in a storage ring which can then be used to calculate the ions' masses. However, themass-to-charge ratio (m=q) is only related to the revolution time (T) under the condition that is equal to taccording to the following equation:

2-7 Charge and Frequency Resolved Isochronous Mass Spectrometry in Storage Rings: First Direct Mass Measurement of the Short-lived Neutron-de cient 51Co Nuclide

Isochronous mass spectrometry in storage rings is a successful technique for the precision mass measurements ofthe nuclides with half-lives down to tens of microseconds[1]. Since the isochronous condition =t greatly reducesthe influence of the velocity difference on the ion revolution periods, the revolution period difference ΔT =T ??TRof a stored ion with respect to a reference time TR is directly related to its mass-to-charge ratio difference Δ(m=q),written in the first order as:

2-4 Principle of Isochronous Mass Spectrometry Using Two Time-of-flight Detectors

Isochronous mass spectrometry (IMS) in storage rings is a powerful tool for mass measurements of exotic nucle with very short half-lives down to several tens of microseconds, using a multicomponent secondary beam separated in-ight without cooling. However, the inevitable momentum spread of secondary ions limits the precision of nuclear masses determined by using IMS.

2-8 SimCSR Program for the Simulation of the Isochronous Mass Spectrometry at the HIRFL-CSR

Until now, several isochronous mass spectrometry (IMS) experiments have been successfully performed usingvarious primary beams at the HIRFL-CSR and masses of both proton-rich and proton-deficient exotic nuclei havebeen measured. In order to improve the performance of the IMS experiments and to provide a reliable tool fordesigning and preparing the future experiments, a simulation code, named SimCSR is developed.Presently, six-dimension phase-space linear transmission theory is applied to simulate the transmission of ionsin the experimental storage ring (CSRe). The basic algorithm is Bf = MBi. The Bi and Bf are six-dimensionphase-space vectors of ions at the entrance and exit of each element of the CSRe lattice, respectively. M is a6-by-6-dimension first-order transfer matrix of each element. M is calculated using formulas described in Ref.[1]. Inthe simulations, the ring lattice is considered in detail, and the same magnetic setting as in our previous experimentwith 58Ni projectile fragments[2] is considered. The ions are assumed to circulate 300 turns inside the CSRe.

2-4 First Isochronous Mass Measurement in Neutron-rich Region at CSRe

Mass is one of the fundamental properties of atomic nuclei. Isochronous mass spectrometry (IMS), using astorage ring combined with an in-flight separator, has been shown to be a powerful tool for mass measurementof exotic nuclei[1]. Recently, masses of many proton-rich nuclides were accurately determined at the HIRFL-CSRfacility[2]. In this paper, we described the first isochronous mass measurement of neutron-rich nuclides at CSRe.This experiment was performed at the end of 2011. In the experiment, the primary beam of 86Kr28+ ions wasaccumulated and accelerated to an energy of 460.65 MeV/u in the synchrotron CSRm. The 86Kr28+ ions were fastextracted and focused on a 15 mm thick beryllium target which was placed at the entrance of the RIBLL2 (anin-flight fragment separator).

Auriferous Quartz Veins from the Dongping Gold Deposit, NW Hebei Province and Metallogenesis—Fluid Inclusion Rb-SrIsochron Evidence

The Dongping gold deposit, situated on the northern margin of the North China Platform, is a composite deposit composed of auriferous quartz vein-type and altered rock-type ore bodies. It is hosted in the inner contact zone of an alkaline intrusion which was intruded into Archean metamorphic rocks and was formed not later than the Hercynian peried. Auriferous quartz veins of the deposit are dated with the fluid inclusion Rb-Sr isochron method at 103 ±4Ma, indicating that the gold deposit was formed in the Yenshanian period. 87Sr/86Sr sourcetracing shows the ore-forming materials came dominantly from alkaline intrusions. These results, combined with other isotope and REE data, suggest that the Dengping gold deposit is not a traditional magmatic hydrothermal deposit, but a reworked hydrothermal deposit related to heated and evoved meteoric water.

Global Phase Portraits of Uniform Isochronous Centers System of Degree Six with Polynomial Commutator

This paper studies the global phase portraits of uniform isochronous centers system of degree six with polynomial commutator.Such systems have the form x=-y+xf(x,y),y=x+yf(x,y),where f(x,y)=a_(1)x+a_(2)xy+a_(3)xy^(2)+a_(4)xy^(3)+a_(5)xy^(4)=xσ(y),and any zero of 1+a_(1)y+a_(2)y^(2)+a_(3)y^(3)+a_(4)y^(4)+a_(5)y^(5),y=y is an invariant straight line.At last,all global phase portraits are drawn on the Poincare disk.

四川甘洛铅锌矿集区闪锌矿Rb-Sr等时线年龄及其地质意义

四川甘洛铅锌矿集区位于扬子地块西南缘的川滇黔铅锌成矿带北段,是四川主要的铅锌产地,具有重要经济价值。为研究该矿集区铅锌成矿时代、成矿大地构造背景和成矿机制,以支撑区域找矿勘查,在区内选择赤普和尔呷地吉两个典型铅锌矿床开展闪锌矿Rb-Sr同位素体系研究,获得Rb-Sr等时线年龄246±17 Ma(MSWD=2.3),表明区内铅锌矿化作用发生于早三叠世,与古特提斯洋闭合时限吻合;闪锌矿(87Sr/86Sr)i值变化于0.71061~0.71393,高于幔源87Sr/86Sr值0.70355及峨眉山玄武岩87Sr/86Sr值0.704979~0.706938,低于基底岩石87Sr/86Sr值0.7243~0.7288,暗示成矿物质主要来源于地壳。综合前人研究,认为在古特提斯洋闭合背景下,强烈造山运动诱发盆地卤水深循环并萃取基底地层中的成矿物质,在峨眉山玄武岩岩浆活动的热动力条件下,含矿流体沿马拉哈断裂进一步迁移沉淀形成了赤普和尔呷地吉铅锌矿床。马拉哈深大断裂及造山作用派生的层间或断层破碎带、碳酸盐岩地层是甘洛地区主要的控矿要素。

回旋加速器主磁铁非理想磁场垫补方法研究

回旋加速器主磁场的精密测量和误差垫补技术是回旋加速器技术研究的一个重要方向,也是设备建造的关键环节之一。由于受铁材料内部缺陷、机械加工误差等因素的影响,回旋加速器主磁铁所产生非理想磁场通常会偏离所需要的等时性磁场分布,且含有一定幅值的谐波磁场。因此,在研制回旋加速器的过程中需对非理想磁场进行多次垫补,通过修正实际磁场的分布而最终达到使用要求。与传统磁场垫补算法相比,本文提出了一种基于多元线性回归模型的垫补算法,加入对一次谐波磁场的计算,实现对磁场等时性误差与一次谐波误差同时进行定量化垫补,省去了单独针对一次谐波磁场的垫补过程。为避免增加有限元计算量,本文在新算法中使用了基于1/4磁铁模型获取平均磁场、一次谐波磁场的垫补形状函数。最后使用本文所提垫补方法,将中国原子能科学研究院16 MeV回旋加速器主磁场的等时性误差降低至10-4量级、一次谐波磁场降低至6 Gs以内。实验结果表明,本文提出的算法具有形状函数计算量小、垫补精度高、迭代次数少的特点。

吉林省敦化市松江河金(钼)矿床辉钼矿Re-Os年龄及其地质意义

松江河金(钼)矿是近十年来发现的产在韧性变形带内的一座中型金矿床(Au资源储量达9 t)。近年来,在松江河矿区五中段至八中段发现大量辉钼矿分布,至少延深至九中段,从五中至八中段钼矿化具有明显的增强趋势。为确定钼成矿时代,文章利用高精度ICP-MS辉钼矿Re-Os同位素测年技术,首次获得了松江河矿床的辉钼矿Re-Os同位素加权平均模式年龄和等时线年龄分别为(167±2.4) Ma和(158±10)Ma,该年龄与前人报道的松江河矿区黄泥河岩体的年龄(164~162 Ma)和五道溜河岩体的年龄(174~172 Ma)误差范围内基本一致,证实了该矿床成矿与成岩作用近于同时发生,且主要在燕山早期的中、晚侏罗世。结合吉林省中东部地区已发表的成岩与成矿年代学资料,文章认为,区内钼多金属矿床形成于燕山期古太平洋板块向欧亚大陆岩石圈俯冲的活动大陆边缘的地球动力学背景。矿床中辉钼矿的ω(Re)为142.74×10^(-6)~217.67×10^(-6),均值为196.58×10^(-6),结合矿床地质特征和成矿岩体及矿石O、S、Pb同位素等证据,文章认为该矿床的成矿物质主要为地幔来源,来自深部的流体可能对该矿床的成矿作用起了重要作用。