Al‐Mg systematics of hibonite‐bearing Ca,Al‐rich inclusions from Ningqiang

Abstract– Hibonite‐bearing Ca,Al‐rich inclusions (CAIs) usually occur in CM and CH chondrites and possess petrographic and isotopic characteristics distinctive from other typical CAIs. Despite their highly refractory nature, most hibonite‐bearing CAIs have little or no ²⁶Mg excess (the decay product of ²⁶Al), but do show wide variations of Ca and Ti isotopic anomalies. A few spinel‐hibonite spherules preserve evidence of live ²⁶Al with an inferred ²⁶Al/²⁷Al close to the canonical value. The bimodal distribution of ²⁶Al abundances in hibonite‐bearing CAIs has inspired several interpretations regarding the origin of short‐lived nuclides and the evolution of the solar nebula. Herein we show that hibonite‐bearing CAIs from Ningqiang, an ungrouped carbonaceous chondrite, also provide evidence for a bimodal distribution of ²⁶Al. Two hibonite aggregates and two hibonite‐pyroxene spherules show no ²⁶Mg excesses, corresponding to inferred ²⁶Al/²⁷Al < 8 × 10^?6. Two hibonite‐melilite spherules are indistinguishable from each other in terms of chemistry and mineralogy but have different Mg isotopic compositions. Hibonite and melilite in one of them display positive ²⁶Mg excesses (up to 25‰) that are correlated with Al/Mg with an inferred ²⁶Al/²⁷Al of (5.5 ± 0.6) × 10^?5. The other one contains normal Mg isotopes with an inferred ²⁶Al/²⁷Al < 3.4 × 10^?6. Hibonite in a hibonite‐spinel fragment displays large ²⁶Mg excesses (up to 38‰) that correlate with Al/Mg, with an inferred ²⁶Al/²⁷Al of (4.5 ± 0.8) × 10^?5. Prolonged formation duration and thermal alteration of hibonite‐bearing CAIs seem to be inconsistent with petrological and isotopic observations of Ningqiang. Our results support the theory of formation of ²⁶Al‐free/poor hibonite‐bearing CAIs prior to the injection of ²⁶Al into the solar nebula from a nearby stellar source.     

基于下一代四星转轮式编队系统精确和快速反演FSCF地球重力场

第一,由于重力卫星编队轨道的稳定性设计是建立下一代高精度和高空间分辨率地球重力场模型的关键,因此为保证下一代四星转轮式编队系统的稳定性,轨道根数的最优设计如下:(1)轨道半长轴a、轨道偏心率e、轨道倾角i和升交点赤经Ω保持不变;(2)每对卫星的近地点幅角ω和平近点角M分别相差180°;(3)初始近地点辐角ω设置于赤道处,初始平近点角M设计于极点处;(4)卫星编队系统椭圆轨道的半长轴和半短轴之比为2:1. 第二,基于下一代四星转轮式编队系统,利用星间速度插值法,通过相关系数(激光干涉测量系统的星间速度0.85、GPS接收机的轨道位置和轨道速度0.95、星载加速度计的非保守力0.90)、观测时间30天和采样间隔10 s,反演了120阶FSCF-1/2/3/4(Four-Satellite Cartwheel Formation)地球重力场,在120阶处累计大地水准面精度为1.162×10^-4 m,较目前GRACE地球重力场精度至少提高一个数量级. 第三,下一代四星转轮式编队系统具有低轨道高度、高精度测量、全张量观测、弱混频效应和强时变信号的优点.     

测高-重力边值问题的局部剪裁解

给出了基于最小方差原理的测高-重力超定边值问题解的局部建模剪裁解法,并采用由卫星测高资料计算的6′×6′海洋重力异常和30′×30′大地水准面数据,计算了展开到1 800阶次的中国南海及邻近海域的测高-重力试验模型.与其他模型比较表明,这种由超定剪裁法解得到的局部模型能够较好地改善重力场模型中波长部分的精度.     

Time Series Correlated Error''''s Simulation Scheme with the Application to Simulate the Ephemerides Error of CHAMP

Computer simulation experiment is very important in the phase of project design, the availability of simulated result highly depends on the scheme of error simulation. Time series observations are normally correlated. This paper first discusses the formula of correlated error propagation, then derives the formula of simulating time series correlated errors. This formula is then used to simulate correlated ephemerides errors of CHAMP, then the ephemerides are used to recover the gravity vector at satellite altitude with finite differential formula. The formulae derived in this paper are verified with the difference between the recovered gravity vectors and the `true values' which are directly computed with the same gravity model as that generating the ephemerides.     

A Petrographic and Mineralogical Study of Volcanic Rocks from the Mayaxueshan Area, North Qilian Fold Belt, NW China

The Ordovician volcanic rocks in the Mayaxueshan area have been pervasively altered or metamorphosed and contain abundant secondary minerals such as albite, chlorite, epidote, prehnite, pumpellyite, actinolite, titanite, quartz, and/or calcite. They were denoted as spilites or spilitic rocks in terms of their petrographic features and mineral assemblages. The metamorphic grades of the volcanic rocks are equivalent to that of the intercalated metaclastic rocks. This indicates that both the spilitic volcanic rocks and metaclastic rocks in the Mayaxueshan area have formed as a result of Caledonian regional metamorphism. We suggest that the previously denoted spilitic rocks or altered volcanic rocks should be re-denoted as metabasalts or metabasaltic rocks. The metamorphic grade of the volcanic rocks increases with their age: prehnite-pumpellyite facies for the upper part of the Middle Ordovician volcanic rocks, prehnite-pumpeilyite to lower greenschist facies for the lower part of the Middle Ordovician vol     

Accurate determination of calibration factor for tidal gravity observation of a GWR-superconducting gravimeter

Introduction The superconducting gravimeters (SGs) are widely used to observe the change in temporal and spatial gravity field by many countries along the world, considering their characteristics as of the high-precision, good continuity and stability. By using the temporal variation of the tidal grav-ity obtained from the global network of SGs, the Global Geophysics Project (GGP) aims at some hot problems in geophysics and geodynamics (SUN, HSU, 1997). The original observations of the c…     

On the Range of Validity and Accuracy of Boussinesq-Type Models

In this paper the range of validity and comparison of accuracy of three Boussinesq-type models (Madsen and Sφrensen, 1992; Nwogu, 1993; Wei et al., 1995; referred to as MS, NW and WKGS, respectively) are analyzed and discussed. The governing equations are extended to the second-order approximations to keep higher-order nonlinear terms. Two key parameters ε and μ representing wave nonlinear and frequency dispersive properties are used to demarcate the limit of applicability for these three models. The accuracy of predictions by each model is compared by the relative errors with and without hlgher-order nonlinear terms in Boussinesq equations. A numerical model is developed based on one-dimensional Boussinesq equations and applied to the case of waves propagating over a submerged bar. The performance and feasibility of each model are tested against laboratory data.     

Numerical Model of Internal Solitary Wave Evolution on Impermeable Variable Seabed in A Stratified Two-Layer Fluid System

1.IntroductionIn mathematics and physics,a soliton is a self-reinforcing solitary wave caused by nonlinear ef-fectsinthe medium.Solitons are found in many physical phenomena(Chou and Shih,1996;Chouand Quyang,1999;Chouet al.,2003;Chenet al.,2004;Wang,2004;…     

On the Occurrence of Triassic Fauna in the Pemo-Trlassic Succession of Leiyanghsien,South Hunan

The valley of the Leiho in South Hunan has long been famous for itsnumerous coal-fields.It was Ferdinand von Richthofen~1 who first studiedthe geology of the region and discovered the well-known Gigantopterisflora in the coal measures,which was named by him the Lui-Pa-Kou     

A Third Note on the Statigraphical Unconformities in Kuangsi

正 As stratigraphical data regarding breaks between the Triassic formations have accumulated as a consequence of recent research in the southern and western parts of Kuangsi, the appearance of a third note on the stratigraphical unconformities in this province to supplement previous papers on the sub