地图矢量数据计算机内存管理方法   总被引：3，自引：0，他引：3  

魏代永  郝向阳  巩学美 《测绘学院学报》1999,(2)

文中提出了复式链表的概念, 讨论了用复式链表对地图矢量数据进行内存管理的原理与方法, 有效地解决了地图属性数据与图形数据的内存管理及内存连接问题, 大大提高了地图矢量数据存取速度, 为各种地理信息系统和地图数据库的矢量数据管理提供了一条有效的途径。  相似文献   

苏北桃林岩基与苏胶造山带燕山期隆升机制的探讨   总被引：1，自引：1，他引：0  

樊金涛  潘明宝 《江苏地质》1999,23(2):65-70

苏北桃林岩基主要单元角闪石、黑云母的矿物化学研究揭示,苏胶造山带在印支期陆内双向对冲碰撞造山后,于燕山期末Ａ型花岗岩体侵位之前,由挤压向拉伸转化时期,曾发现急剧隆升。早期隆升快,为０１３９ｍｍ／ａ,中期隆升变慢,为００２３ｍｍ／ａ。山根拆沉,均衡抬升,地幔上隆,上地壳伸展造盆成山,是造就苏胶造山带现今盆山构造和（超）高压带燕山期折返的主要原因  相似文献   

鄂西黄陵背斜地区前南华纪古构造格架及主要地质事件   总被引：10，自引：1，他引：9  

熊成云  韦昌山  金光富  谭文清  李文羡 《地质力学学报》2004,10(2):97-112

主要运用构造筛分与成生联系解析的综合研究方法,在鄂西黄陵背斜地区,进一步厘定了阜平、吕梁(兴山)、四堡(神农)、晋宁(花山)等构造运动及相关的岩浆、变质事件。建立了黄陵(崆岭)杂岩时序以及由近东西向、北东向、北西向三类古构造带复合的前南华纪古构造格架,提出了定型于四堡期的圈椅淌滑脱构造系。   相似文献   

Thermal modelling in shallow subduction: an application to low P/T metamorphism of the Cretaceous Shimanto Accretionary Complex, Japan     

K. Miyazaki  K. Okumura 《Journal of Metamorphic Geology》2002,20(4):441-452

This paper presents the results of numerical modelling to investigate the regional occurrence of prehnite‐bearing metamorphic rocks at shallow levels in subduction zones. The modelling assumes a simple geometrical configuration in which the thermal structure in a prism is controlled by boundary conditions at the top and base of the prism. It is expected that the predominant metamorphic facies in a prism will change with decreasing age of the descending slab. The results of thermal modelling show that the facies boundary between pumpellyite–actinolite and prehnite–actinolite facies (including prehnite–pumpellyite facies) overlaps with an array of P–T conditions in the prism when the age of a descending slab is younger than 10 Myr. This implies that the change of the predominant metamorphic facies from pumpellyite–actinolite to prehnite–actinolite facies will switch drastically. The critical age of the switch depends on subduction parameters. In particular, the critical age of the descending slab is <5 Myr in the case of no shear heating, with a subduction rate of v=75–200 mm y^?1 and subduction angle of θ=5–15°. For shear heating (constant shear stress=30 MPa) with a subduction rate of v=75 mm y^?1 and subduction angle of θ=10° the critical age is 7 Myr. To test this switching behaviour in the development of prehnite–actinolite facies in the prism, petrologic data from the Cretaceous Shimanto Accretionary Complex (CSAC) in Kyushu, Japan were compiled. The regional occurrence and mineral assemblages of prehnite‐bearing metamorphic rocks suggest that the most of CSAC was metamorphosed under prehnite–actinolite facies. This conclusion is consistent with subduction of a young, hot slab, as has been proposed based on other geological observations. This suggests that the regional extent of the prehnite–actinolite facies metamorphic rocks may be a unique evidence for the subduction of a young, hot slab.  相似文献   

Large-ion lithophile element characteristics of an amphibolite facies to granulite facies transition at Gruinard Bay, North-west Scotland   总被引：1，自引：0，他引：1  

M. B. FOWLER 《Journal of Metamorphic Geology》1986,4(3):345-359

Abstract Lewisian grey gneisses from Gruinard Bay, North-west Scotland retain mineralogical and geochemical evidence for Scourian horn-blende-granulite facies metamorphism, and they may be used to assess current models of elemental depletion at granulite grade. Their 'immobile'major and trace element geochemistry is indistinguishable from that of Lewisian amphibolite and pyroxene-granulite facies counterparts. The K, Rb, Th and U contents of the Gruinard Bay gneisses are depleted relative to amphibolite facies gneisses, but generally the abundances of these elements are above those of comparable pyroxene granulites. U and Th have reached an advanced stage of depletion, but allanite appears to be crucial in maintaining significantly higher U and Th abundances at Gruinard Bay than in pyroxene granulites. K and Rb loss is less extreme, and depends on the stability of the rock-forming minerals: K-feldspar; biotite; and, amphibole. Early removal of K and Rb has resulted in a small rise in K/Rb, but further preferential Rb loss would have been required to generate the characteristically high K/Rb ratios of Lewisian pyroxene granulites.
The residence of U and Th in the accessory minerals of granulite facies gneisses, which are often correlated with the residua of intracrustal partial melting, renders unlikely their extreme incompatibility required by such models. Even if such phases are ignored, high mineral-melt partition coefficients for silicic melts argue against partial fusion as an efficient depletion mechanism. On the other hand, the advanced stage of U and Th depletion reached in Gruinard Bay gneisses, which were still partly hydrous, severely restricts the role played by CO₂-dominated fluids and a hydrous medium is preferred.  相似文献   

The Rayner Complex of East Antarctica: complex isotopic systematics within a Proterozoic mobile belt   总被引：8，自引：0，他引：8  

L. P. BLACK  S. L. HARLEY  S. S. SUN  M. T. McCULLOCH 《Journal of Metamorphic Geology》1987,5(1):1-26

Abstract New isotopic (Rb–Sr, U–Pb zircon and Sm–Nd) and petrological data are presented for part of an extensive Proterozoic mobile belt (locally known as the Rayner Complex) in East Antarctica. Much of the belt is the product of Mid-Proterozoic (∼ 1800–2000 Ma) juvenile crustal formation. Melting of this crust at about 1500 Ma ago produced the felsic magmas from which the dominant orthogneisses of this terrain were subsequently derived. Deformation and transitional granulite-amphibolite facies conditions (which peaked at 750 ± 50°C and 7–8 kbar (0.7–0.8 GPa) produced open to tight folding about E–W axes and syn-tectonic granitoids about 960 Ma ago. Subsequent felsic magmatism occurred at about 770 Ma and not, as has been widely advocated, at 500–550 Ma, which appears to have been a time of widespread upper greenschist facies (400–500°C) metamorphism, localized shearing and faulting. Sm-Nd model ages of 1.65–2.18 Ga disprove a previously favoured hypothesis that the Rayner Complex mostly represents reworked Archaean rocks from the neighbouring craton (Napier Complex). Models that involve rehydration of the Napier Complex are no longer required, since the Rayner Complex was its own source of water. Two episodes of Proterozoic crustal growth are identified, the later of which occurred between about 1200 Ma and 1000 Ma, and was relatively minor. Sedimentation took place only shortly before Late Proterozoic orogenesis. The multiphase history of the Rayner Complex has resulted in complex isotopic behaviour. Three temporally discrete episodes of Pb loss from zircon have been identified, the earliest two of which are responses to the c. 960 Ma and 540 Ma tectonothermal events. Fluid leaching was operative during the later event for there is a good correlation between degree of isotopic discordance and secondary mineral growth. Pb loss during the high-grade event was probably governed by the same process or by lattice annealing. Some zircon suites also document recent Pb loss. Most lower concordia intercepts have no direct geological meaning and are explicable as mixed ages produced by incomplete Pb loss during two or more secondary events. Whereas all zircon separates from the orthogneisses produce U–Pb isotopic alignments, zircons from the only analysed paragneiss produce scattered data, in part reflecting a range of provenance. The 960 Ma event was also associated with the growth of a characteristically low U zircon (∼ 300 μg/g) in rocks of inferred high Zr content. There is ubiquitous evidence for the resetting of Rb–Sr total-rock isochrons. Even samples separated by up to 10 km fail to produce igneous crystallization ages. Minor mineralogical changes produced by the 540 Ma upper greenschist-facies metamorphism were sufficient to almost completely reset some Rb–Sr isochrons and to produce open system conditions on outcrop scale, at least in one location.  相似文献   

Landscape evolution of the Blue Mountains revealed by longitudinal river profiles and Cenozoic basalts and gravels     

P. J. Hatherly 《Australian Journal of Earth Sciences》2020,67(2):243-263

Abstract

For the past 200?years, there have been numerous investigations and much speculation concerning the formation of the dramatic valleys of the Blue Mountains of NSW. In this paper, further evidence for the uplift and erosional history of the Blue Mountains is obtained from longitudinal river profiles, detailed mapping of the Rickabys Creek Gravel on the Lapstone Structural Complex and consideration of the topographical position of Miocene basalts. Knickpoints on the main rivers flowing east from the Great Dividing Range are identified and interpreted to be due to uplift events linked to the northward movement of the Australian continent over mantle inhomogeneities. At the Lapstone Structural Complex on the eastern range front, the occurrence of the Rickabys Creek Gravel and the nature of the over-steepened reaches on the rivers and streams crossing the Complex, suggest a more recent ongoing phase of uplift and antecedent river erosion. The Miocene basalts provide evidence of this landscape 20–15?Ma. Their locations with respect to the current rivers and ridges are interpreted to show additional evidence for recent uplift that has resulted in the formation of the Lapstone Structural Complex. It is suggested that this uplift commenced 10–5?Ma when the contemporary compressive stress field was established.

• KEY POINTS

• Longitudinal profiles for major rivers in the Blue Mountains are consistent with a model of initial Cretaceous uplift followed by further Cenozoic uplift associated with dynamic topography.

• Mapping of Rickabys Creek Gravel within the Lapstone Structural Complex suggests the presence of antecedent rivers.

• Within the Lapstone Structural Complex, stream profiles, gravels and nearby outcrops of Miocene basalts are interpreted to indicate a third phase of uplift, possibly since 10?Ma.

  相似文献   

Single zircon U-Pb dating of the Kongling high-grade metamorphic terrain: Evidence for >3.2 Ga old continental crust in the Yangtze craton   总被引：4，自引：0，他引：4  

Shan Gao  Yumin Qiu  Wenli Ling  McNaughton Neal J.  Groves David I. 《中国科学D辑(英文版)》2001,44(4):326-335

Single zircons from two trondhjemitic gneisses and two clastic metasedimentary rocks without Eu anomaly of the Kongling high-grade metamorphic terrain are dated by thein situSHRIMP U-Pb method. The results show that the trondhjemitic magma emplaced at 2947-2903 Ma. Concordant age of as old as 3.3 Ga is present in the detrital zircons from the clastic metasedimentary rocks. Together with the depleted mantle Nd model age (T_DM =3.2-3.3 Ga) of the clastic metasedimentary rocks, this documents the presence of Paleoarchean continental crust in the Yangtze craton.  相似文献   

对加拿大萨德伯里撞击构造的考察及其启示   总被引：1，自引：0，他引：1  

傅昭仁  李紫金 《地质科技情报》1996,15(4):57-63

简介了近年来萨德伯里撞击构造及超大型铜镍硫化物矿床的研究现状和作者现场考察所得的认识。记述了萨德伯里的撞击构造、陨石撞击事件及其构造效应、岩浆杂岩（SIC）和有关成因争论；叙述了该大陨石坑的变形和邻近格林威尔造山作用导致的NW－SE向缩短和剪切作用；还介绍了萨德伯里铜镍硫化物矿床撞击成矿假说；最后，特别提出在从事地球动力学和成矿作用动力学研究时，应十分注意类似萨德伯里陨石撞击灾变事件及损击成矿作用的研究。  相似文献   

早元古代宽甸杂岩的成因：地球化学证据   总被引：29，自引：1，他引：29  

孙敏  张立飞 《地质学报》1996,70(3):207-222

宽甸杂岩形成于2.3—2.4Ga,是目前较少保留的早元古代火山岩系之一,主要由斜长角闪岩和各类片麻岩、浅粒岩、变粒岩及花岗质岩石组成。岩石学和地球化学研究表明,其原岩建造相当于一套双峰式火山岩和非造山花岗岩石组合,原始岩浆来源于混染了的亏损地幔源(DMM)或者是DMM和Ⅱ型富集地幔(EM2)的混合地幔源,并具有Dupal异常特征。成因过程的理论模拟计算表明,该杂岩中片麻岩和花岗岩来源于角闪质岩石的母岩浆,经强烈的分离结晶作用形成。其原岩建造形成陆壳拉开向洋壳转化的过渡环境。宽甸杂岩所在的中朝克拉通构造演化与北美地盾、欧洲地台和澳洲大陆不同,曾发生强烈的火山喷溢活动而使其增生。宽甸杂岩形成之前(2.3—2.4Ga)就曾经存在过类似现代板块规模的壳幔对流作用发生。  相似文献