董家山隧道小净距段爆破控制的数值模拟   总被引：11，自引：1，他引：11  

姚勇  何川  晏启祥  李玉文 《岩土力学》2004,25(Z2):501-506

结合都-汶高速公路董家山隧道小净距段的实际情况,应用数值模拟方法,对小净距段在爆破荷载作用下的相互影响问题进行了研究.结果表明在隧道爆破施工中应对迎爆侧进行重点监控,采用合理的开挖和加固方式将有效降低爆破施工对先建隧道的不利影响.研究结论可为类似小净距段隧道的爆破设计、施工及现场监控量测提供参考.  相似文献   

长江三峡深槽沉积的研究     

杨达源  李徐生  任黎秀  张建新  葛兆帅  王爱军  陈可锋 《第四纪研究》2004,24(4):501-505

文章研究长江三峡两个基岩深槽沉积岩砾的岩性组成与粒度特征,深槽底部的砾石成分以深槽基岩崩落蚀余物质为主,深槽的中上部则以长江底流搬运沉积物为主。¹⁴C测年数据显示,深槽的发育在3.5万年以前,以侵蚀深切为主,没有留下蚀余堆积;3.5万年以后,仍以侵蚀为主,但已有蚀余为主的岩块堆积;大约2.4万年以来,逐渐有缓慢的冲积砾石堆积;至葛洲坝建成以后,该地发育了比较稳定的冲积砾石层和砂层。看来大约35kaB.P.前后,该地水动力强度发生过重大变化,与施雅风等关于3～4万年前长江上游多雨期研究成果相吻合。  相似文献   

Preliminary study on the occurrence of geothermal systems in the tectonic compressional regions: an example from the Derman geothermal field in the Biga Peninsula, Turkey     

Zeynel Demirel  Talat Yildirim  Musa Burak 《Journal of Asian Earth Sciences》2004,22(5):495

There are numerous hot springs with temperatures ranging from 30 to 100 °C in Biga peninsula and they occur throughout the peninsula. The result of this study shows that the region is under a tectonic compressional regime. The investigation of the faults and fractures in the region indicates that the region has been affected first by N–S and then E–W compression since the Middle Miocene. Opening fractures and antithetic and synthetic faults due to the compressional movements provide paths for the deep circulation of water. In addition, the tectonic movements, granitic intrusion and volcanic activity have also played important roles as heat sources for the geothermal systems.  相似文献   

Nation states, ideological power and globalisation: can geographers catch the boat?     

Martin Jones  Rhys Jones 《Geoforum》2004,35(4):409-424

After a period of considerable and sustained hegemony, many commentators have argued that contemporary processes of globalisation are acting as a challenge to nation state sovereignty. The paper argues that geographers need to focus on the ways in which the nation state continues to act, albeit in a modified manner, within the era of globalisation. This might help to position geography within globalisation debates, which--according to Dicken [Geographers and `globalization': (yet) another missed boat? forthcoming, Transactions of the Institute of British Geographers, 2004]--we have not been centrally involved in. Drawing on the work of Michael Mann, we focus on a neglected dimension of state power--namely, its ideological form--as a means of exploring how the nation state is being differentially re-engineered under globalisation. Using Mann's classification of forms of ideological organisation, we deploy three vignettes in order to demonstrate the evolving nature of ideological power within the contemporary UK State.  相似文献   

U-Pb Zircon Calendar for Namaquan (Grenville) Crustal Events in the Granulite-facies Terrane of the O'okiep Copper District of South Africa     

CLIFFORD  TOM N.; BARTON  ERIKA S.; STERN  RICHARD A.; DUCHESNE  JEAN-CLAIR 《Journal of Petrology》2004,45(4):669-691

The O'okiep Copper District is underlain by voluminous 1035–1210Ma granite gneiss and granite with remnants of metamorphosedsupracrustal rocks. This assemblage was intruded by the 1030Ma copper-bearing Koperberg Suite that includes jotunite, anorthosite,biotite diorite and hypersthene-bearing rocks ranging from leuconoriteto hypersthenite. New sensitive high-resolution ion microprobeage data demonstrate the presence of 1700–2000 Ma zirconas xenocrysts in all of the intrusive rocks, and as detritalzircon in the metasediments of the Khurisberg Subgroup. Thesedata are consistent with published Sm–Nd model ages ofc. 1700 Ma (T_CHUR) and c. 2000 Ma (T_DM) of many of the intrusivesthat support a major crust-forming event in Eburnian (Hudsonian)times. In addition, U–Th–Pb analyses of zirconsfrom all major rock units define two tectono-magmatic episodesof the Namaquan Orogeny: (1) the O'okiepian Episode (1180–1210Ma), represented by regional granite plutonism, notably theNababeep and Modderfontein Granite Gneisses and the Concordiaand Kweekfontein Granites that accompanied and outlasted (e.g.Kweekfontein Granite) regional tectonism [F₂(D₂)] and granulite-faciesmetamorphism (M₂); (2) the Klondikean Episode (1020–1040Ma), which includes the intrusion of the porphyritic RietbergGranite and of the Koperberg Suite that are devoid of regionalplanar or linear fabrics. Klondikean tectonism (D₃) is reflectedby major east–west-trending open folds [F₃(D_3a)], andby localized east–west-trending near-vertical ductilefolds [‘steep structures’; F₄(D_3b)] whose formationwas broadly coeval with the intrusion of the Koperberg Suite.A regional, largely thermal, amphibolite- to granulite-faciesmetamorphism (M₃) accompanied D₃. This study demonstrates, interalia, that the complete spectrum of rock-types of the KoperbergSuite, together with the Rietberg Granite, was intruded in ashort time-interval (<10 Myr) at c. 1030 Ma, and that therewere lengthy periods of about 150 Myr of tectonic quiescencewithin the Namaquan Orogeny: (1) between the O'okiepian andKlondikean Episodes; (2) from the end of the latter to the formalend of Namaquan Orogenesis 800–850 Ma ago. KEY WORDS: U–Pb, zircon; O'okiep, Namaqualand; granite plutonism; granulite facies; Koperberg Suite; Namaquan (Grenville) Orogeny  相似文献   

A Sequence of Pan-African and Hercynian Events Recorded in Zircons from an Orthogneiss from the Hercynian Belt of Western Central Iberia--an Ion Microprobe U-Pb Study   总被引：1，自引：0，他引：1  

ZECK  H. P.; WINGATE  M. T. D.; POOLEY  G. D.; UGIDOS  J. M. 《Journal of Petrology》2004,45(8):1613-1629

Sensitive high-resolution ion microprobe U–Pb dating showsthat a biotite orthogneiss from the Hercynian belt of westerncentral Iberia contains 1000–300 Ma zircon. Older, 1000–570Ma ages within this range represent inherited, detrital materialamong which four age components may be recognized:  相似文献   

Tectonic evolution of the Intra-Pontide suture zone in the Armutlu Peninsula, NW Turkey     

Alastair H. F. Robertson  Timur Ustamer 《Tectonophysics》2004,381(1-4):175

The Armutlu Peninsula and adjacent areas in NW Turkey play a critical role in tectonic reconstructions of the southern margin of Eurasia in NW Turkey. This region includes an inferred Intra-Pontide oceanic basin that rifted from Eurasia in Early Mesozoic time and closed by Late Cretaceous time. The Armutlu Peninsula is divisible into two metamorphic units. The first, the Armutlu Metamorphics, comprises a ?Precambrian high-grade metamorphic basement, unconformably overlain by a ?Palaeozoic low-grade, mixed siliciclastic/carbonate/volcanogenic succession, including bimodal volcanics of inferred extensional origin, with a possibly inherited subduction signature. The second unit, the low-grade znik Metamorphics, is interpreted as a Triassic rift infilled with terrigenous, calcareous and volcanogenic lithologies, including basalts of within-plate type. The Triassic rift was unconformably overlain by a subsiding Jurassic–Late Cretaceous (Cenomanian) passive margin including siliciclastic/carbonate turbidites, radiolarian cherts and manganese deposits. The margin later collapsed to form a flexural foredeep associated with the emplacement of ophiolitic rocks in Turonian time. Geochemical evidence from meta-basalt blocks within ophiolite-derived melange suggests a supra-subduction zone origin for the ophiolite. The above major tectonic units of the Armutlu Peninsula were sealed by a Maastrichtian unconformity. Comparative evidence comes from the separate Almacık Flake further east.Considering alternatives, it is concluded that a Mesozoic Intra-Pontide oceanic basin separated Eurasia from a Sakarya microcontinent, with a wider Northern Neotethys to the south. Lateral displacement of exotic terranes along the south-Eurasian continental margin probably also played a role, e.g. during Late Cretaceous suturing, in addition to overthrusting.  相似文献   

U–Pb ages of Neoarchean granitoids from the Black Hills, South Dakota, USA: implications for crustal evolution in the Archean Wyoming province     

James A. McCombs  Peter S. Dahl  Michael A. Hamilton 《Precambrian Research》2004,130(1-4):161-184

Zircons in basement rocks from the eastern Wyoming province (Black Hills, South Dakota, USA) have been analyzed by ion microprobe (SHRIMP) in order to determine precise ages of Archean tectonomagmatic events. In the northern Black Hills (NBH) near Nemo, Phanerozoic and Proterozoic (meta)sedimentary rocks are nonconformably underlain by Archean biotite–feldspar gneiss (BFG) and Little Elk gneissic granite (LEG), both of which intrude older schists. The Archean granitoid gneisses exhibit a pervasive NW–SE-trending fabric, whereas an earlier NE–SW-trending fabric occurs sporadically only in the BFG, which is intruded by the somewhat younger LEG. Zircon crystals obtained from the LEG and BFG exhibit double terminations, oscillatory zoning, and Th/U ratios of 0.6±0.3—thereby confirming a magmatic origin for both lithologies. In situ analysis of the most U–Pb concordant domains yields equivalent ²⁰⁷Pb/²⁰⁶Pb ages (upper intercept, U–Pb concordia) of 2559±6 and 2563±6 Ma (both ±2σ) for the LEG and BFG, respectively, which constrains a late Neoarchean age for sequential pulses of magmatism in the NBH. Unzoned (in BSE) patches of 2560 Ma zircon commonly truncate coeval zonation in the same crystals with no change in Th/U ratio, suggesting that deuteric, fluid-assisted recrystallization accompanied post-magmatic cooling. A xenocrystic core of magmatic zircon observed in one LEG zircon yields a concordant age of 2894±6 Ma (±2σ). This xenocryst represents the oldest crustal material reported thus far in the Black Hills. Whether this older zircon originated as unmelted residue of 2900 Ma crust that potentially underlies the Black Hills or as detritus derived from 2900 Ma crustal sources in the Wyoming province cannot be discerned. In the southern Black Hills (SBH), the peraluminous granite at Bear Mountain (BMG) of previously unknown age intrudes biotite–plagioclase schist. Zircon crystals from the BMG are highly metamict and altered, but locally preserve small domains suitable for in situ analysis. A U–Pb concordia upper intercept age of 2596±11 Ma (±2σ) obtained for zircon confirms both the late Neoarchean magmatic age of the BMG and a minimum age for the schist it intrudes. Taken together, these data indicate that the Neoarchean basement granitoids were emplaced at 2590–2600 Ma (SBH) and 2560 Ma (NBH), most likely in response to subduction associated with plate convergence (final assembly of supercontinent Kenorland?). In contrast, thin rims present on some LEG–BFG zircons exhibit strong U–Pb discordance, high common Pb, and low Th/U ratios—suggesting growth or modification under hydrothermal conditions, as previously suggested for similar zircons from SE Wyoming. The LEG–BFG zircon rims yield a nominal upper intercept date of 1940–2180 Ma, which may represent a composite of multiple rifting events known to have affected the Nemo area between 2480 and 1960 Ma. Together, these observations confirm the existence of a Paleoproterozoic rift margin along the easternmost Wyoming craton. Moreover, the 2480–1960 Ma time frame inferred for rifting in the Black Hills (Nemo area) corresponds closely to a 2450–2100 Ma time frame previously inferred for the fragmentation of supercontinent Kenorland.  相似文献   

The Role of Pre-existing Structures in the Origin, Propagation and Architecture of Faults in the Main Ethiopian Rift     

Tesfaye Korme  Valerio Acocella  Bekele Abebe 《Gondwana Research》2004,7(2):467-479

Four major fault systems oriented N–S to NNE–SSW, NE–SW, E–W and NW–SE are identified from Landsat Thematic Mapper (TM) images and a high resolution digital elevation model (DEM) over the Ethiopian Rift Valley and the surrounding plateaus. Most of these faults are the result of Cenozoic - extensional reactivation of pre-existing basement structures. These faults interacted with each other at different geological times under different geodynamic conditions. The Cenozoic interaction under an extensional tectonic regime is the major cause of the actual volcano-tectonic landscape in Ethiopia. The Wonji Fault Belt (WFB), which comprises the N–S to NNE–SSW striking rift floor faults, displays peculiar propagation patterns mainly due to interaction with the other fault systems and the influence of underlying basement structures. The commonly observed patterns are: curvilinear oblique-slip faults forming lip-horsts, sinusoidal faults, intersecting faults and locally splaying faults at their ends. Fault-related open structures such as tail-cracks, releasing bends and extensional relay zones and fault intersections have served as principal eruption sites for monogenetic Plio-Quaternary volcanoes in the Main Ethiopian Rift (MER).  相似文献   

The magmatic to hydrothermal transition and its bearing on ore-forming systems   总被引：1，自引：0，他引：1  

Werner E. Halter  James D. Webster 《Chemical Geology》2004,210(1-4):1-6

The exsolution of volatile phases from silicate magmas controls physical and chemical magma properties and influences large-scale geologic phenomena and processes having major societal and economic implications including the release of climate-altering gases to the atmosphere, the explosivity of volcanic eruptions, hydrothermal alteration, and the generation of magmatic–hydrothermal mineralization. These volatile phases exsolve from a wide variety of magmas and cover a very broad spectrum of compositions.

The transition from the orthomagmatic to the hydrothermal stages has important bearing on these fundamentally important geologic phenomena, and this report summarizes the published results of a dozen scientific investigations on the magmatic–hydrothermal transition as applied to volcanic eruption and magmatic–hydrothermal mineralization. These studies involve a variety of analytical and experimental methodologies, and many focus on fluid and melt inclusions from mineralized magmatic systems. A primary goal of each study is to better understand the role of magmatic volatiles and the importance of the magmatic–hydrothermal transition on these geologic processes.  相似文献