Mechanical models of fracture reactivation and slip on bedding surfaces during folding of the asymmetric anticline at Sheep Mountain, Wyoming     

Pablo F. Sanz  David D. Pollard  Patricia F. Allwardt  Ronaldo I. Borja 《Journal of Structural Geology》2008,30(9):1177-1191

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中甸红山矽卡岩铜矿稳定同位素特征及其对成矿过程的指示   总被引：9，自引：7，他引：2  

王守旭  张兴春  冷成彪  秦朝建  王外全  赵茂春 《岩石学报》2008,24(3)

红山铜矿床位于三江地区义敦岛弧南端的中甸弧,是在晚三叠世甘孜-理塘洋盆向西俯冲过程中形成的一个中型规模的矽卡岩矿床.通常,矽卡岩体就是铜矿体或铜矿化体,主要呈似层状、层状、脉状及透镜体状产于大理岩与角岩接触带或局部在角岩中,未见其与侵入岩直接接触.通过对不同成矿阶段所形成的石榴石、磁铁矿、磁黄铁矿、黄铁矿、黄铜矿、方解石等典型矿物以及大理岩的稳定同位素特征研究,发现矽卡岩的最主要组成矿物石榴石的δ18OSHOW范围为6.2～8.3‰,反映了矽卡岩可能直接继承隐伏斑岩体的氧同位素组成.根据磁铁矿的氧同位素组成(5.5～7.1‰)所计算的磁铁矿化阶段成矿流体的δ18OSHOW为13.1～14.7‰(400℃)或12.5～14.1‰(500℃),暗示有富集δ18O的CO2溶入到成矿流体中.硫化物的δ18SCDT范围4.45～6.20‰,说明矿床具有高度均一的硫源,并且在硫化物的结晶沉淀过程中,流体中硫同位素分馏很弱.由此推测主成矿期成矿流体的δ18S∑S为5.6±0.6‰.矿床中的大理岩的δ13CPDB为2.0～2.2‰,δ18OSMOW为24.0～24.8‰,说明大理岩是由海相碳酸盐岩经重结晶作用而成.成矿晚期阶段形成的方解石脉的δ13C范围是-2.4～1.7‰,δ18OSMOW范围是16.3～22.4%o,表明其C和O主要来源于大理岩.总之,我们推测红山矽卡岩很可能主要是由中酸性岩浆浅成侵位时局部同化碳酸盐围岩所形成的一种富含钙质成分的次生岩浆就位于碎屑岩与碳酸盐岩之间的构造薄弱带冷凝固结而成,矽卡岩型矿化与深部斑岩型矿化具有共同的成矿物质和成矿流体来源.  相似文献   

The sequence of sediment behaviour during wave-induced liquefaction   总被引：4，自引：0，他引：4  

B. MUTLU SUMER  FIGEN HATIPOGLU  JØRGEN FREDSØE  S. KAAN SUMER 《Sedimentology》2006,53(3):611-629

This paper presents the results of an experimental investigation of the complete sequence of sediment behaviour beneath progressive waves. The sediment was silty with d ₅₀ = 0.060 mm. Two kinds of measurements were carried out: pore-water pressure measurements (across the sediment depth), and water-surface elevation measurements. The process of liquefaction/compaction was videotaped from the side simultaneously with the pressure and water-surface elevation measurements. The video records were then analysed to measure: (i) the time development of the mudline, (ii) the time development of liquefaction and compaction fronts in the sediment and (iii) the characteristics of the orbital motion of the liquefied sediment including the motion of the interface between the water body and the sediment. The ranges of the various quantities in the tests were: wave height, H  = 9–17 cm, wave period, T  = 1.6 sec, water depth = 42 cm, and the Shields parameter = 0.34–0.59. The experiments reveal that, with the introduction of waves, excess pore pressure builds up, which is followed by liquefaction during which internal waves are experienced at the interface of the water body and the liquefied sediment, the sequence of processes known from a previous investigation. This sequence of processes is followed by dissipation of the accumulated excess pore pressure and compaction of the sediment which is followed by the formation of bed ripples. The present results regarding the dissipation and compaction appear to be in agreement with recent centrifuge wave-tank experiments. As for the final stage of the sequence of processes (formation of ripples), the ripple steepness (normalized with the angle of repose) for sediment with liquefaction history is found to be the same as that in sediment with no liquefaction history.  相似文献   

洪山预测区煤层赋存的可能性分析     

尚洪田 《中国煤田地质》2006,18(4):25-26,52

分析了洪山预测区西部洪山岩体地质特征及其向外围扩散的范围和程度，研究了北掌勘查区和焦窑煤矿两邻区煤层受岩浆岩影响的程度，认为洪山岩体对预测区煤系及煤层赋存的影响较小，岩体外围仍有煤系赋存。为下一步找煤指明了方向。  相似文献   

甜水海微陆块上二叠系地层的厘定及其特征     

边小卫  王炬川  罗乾周  杨克俭  朱海平  杨运军 《陕西地质》2005,23(2):44-49,75

笔者在《岔路口》等四幅1：25万区域地质调查工作中，在红山湖一带从前人所划的石炭系地层中解体出一套二叠系地层，并对其进行了详细的岩石地层、生物地层和层序地层研究，拟新命名为红山湖组，时代为中二叠世。该地层为甜水海微陆块上稳定型的碳酸盐岩建造，与陆块南北两侧二叠系特征截然不同。该套地层的发现填补了微陆块上二叠系地层的空白，对古特提斯多岛洋研究具有重要意义。  相似文献   

滇中震旦系碳酸盐岩破碎地层的钻探护孔新技术   总被引：1，自引：1，他引：1  

毛毓坤 《云南地质》2003,22(2):206-210

破碎地层中钻探，采用有效的护孔技术是避免孔内事故发生的重要手段，同时也是保证完成钻探各项技术经济指标的先决条件。本文阐述了在具代表性的磷矿破碎地层中钻进所遇到的护孔难题及其所采用的护孔新技术、新方法。  相似文献   

Late Pliocene to late Pleistocene environments preserved at the Palisades Site, central Yukon River, Alaska     

Paul Matheus  James BegétOwen Mason  Carol Gelvin-Reymiller 《Quaternary Research》2003,60(1):33-43

The Palisades Site is an extensive silt-loam bluff complex on the central Yukon River preserving a nearly continuous record of the last 2 myr. Volcanic ash deposits present include the Old Crow (OCt; 140,000 yr), Sheep Creek (SCt; 190,000 yr), PA (2.02 myr), EC (ca. 2 myr), and Mining Camp (ca. 2 myr) tephras. Two new tephras, PAL and PAU, are geochemically similar to the PA and EC tephras and appear to be comagmatic. The PA tephra occurs in ice-wedge casts and solifluction deposits, marking the oldest occurrence of permafrost in central Alaska. Three buried forest horizons are present in association with dated tephras. The uppermost forest bed occurs immediately above the OCt; the middle forest horizon occurs below the SCt. The lowest forest bed occurs between the EC and the PA tephras, and correlates with the Dawson Cut Forest Bed. Plant taxa in all three peats are common elements of moist taiga forest found in lowlands of central Alaska today. Large mammal fossils are all from common late Pleistocene taxa. Those recovered in situ came from a single horizon radiocarbon dated to ca. 27,000 ¹⁴C yr B.P. The incongruous small mammal assemblage in that horizon reflects a diverse landscape with both wet and mesic environments.  相似文献   

ADVANCES IN MEASURING TECHNIQUES OF BED LOAD     

ZHOU Gangyan ZOU Jiazhong 《国际泥沙研究》1997,(1)

I.m~UCrIONBedloadisthesedimentwhichmovesalongtheriverbedintheformofrolling,slidingandsaltation.BedloadmaycreatemanyproblemsintheoperationandmaintenanceofnavigationchannelandinthedevelOPmentofhydroelectricity.Dataofbedloaddischargearealsorequiredinthedesignofreservoir,inwhichtheinflowbedloadareallactuallytrapped.Thewaysofbedloadmotionaredifferentfordifferentsizes.Thus,itisextremelydifficulttodeterminethebedloaddischargeaccurately.Manyequationshavebeenproposedtocalculatethebedloaddischarge.H…  相似文献   

Long-term bed load transport rate based on aerial-photo and ground penetrating radar surveys of fan-delta growth, Coast Mountains, British Columbia     

Channa P. Pelpola  Edward J. Hickin   《Geomorphology》2004,57(3-4):169-181

Sequential aerial photography, sonar bathymetry, ground-penetrating radar (GPR), and sediment sampling and analysis provide the basis for calculating the volumetric and mass rate of progradation of the delta of Fitzsimmons Creek, a steep, high-energy, debris-flow-dominated channel draining about 100 km² of the southern Coast Mountains of British Columbia. Fitzsimmons Creek is typical of small mountain rivers in the region. GPR imaging is used to define the pre-depositional morphology of the receiving basin, a technique that improves the accuracy of the volumetric survey. The 52-year record (1947–1999) of progradation yielded an average annual volumetric transport rate of 1.00±0.16×10⁴ m³ year⁻¹ for bed load, corresponding to a mass transport rate of 1.60±0.28×10⁴ Mg year⁻¹. Bed load yields are consistent with those obtained in hydrogeomorphically similar basins in the region and elsewhere. Decade-based annual rates, which vary from 0.64±0.11×10⁴ to 2.85±0.38×10⁴ Mg year⁻¹, provide poor estimates of the 52-year average. Indeed, the 52-year record may also not be long enough to fully integrate the significant fluctuations in the sediment efflux from Fitzsimmons Creek. The methodology proposed in this paper can be transferred to other comparable mountain environments worldwide.  相似文献   

Environmental pollution impact on water and sediments of Kumaun lakes, Lesser Himalaya, India: a comparative study     

Brijraj K. Das 《Environmental Geology》2005,49(2):230-239

A study of the water and sediment chemistry of the Nainital, Bhimtal, Naukuchiyatal and Sattal Lakes of Kumaun, has shown that the water of these lakes are alkaline and that electrical conductivity, total dissolved solid and bicarbonate HCO ₃ ⁻ are much higher in Nainital than in the other three lakes. The weathering of limestone lithology and anthropogenic pollution, the latter due to the very high density of population in the Nainital valley, are the primary sources of enhanced parameters. The low pH of Nainital Lake water is due to low photosynthesis and enhanced respiration, increasing CO₂ in the water and the consequent enhancement of Ca²⁺ and HCO ₃ ⁻ . The dissolved oxygen in Nainital Lake is less compared to other lakes, indicating anoxic conditions developing at the mud–water interface at depth. The PO ₄ ³⁻ content in Nainital is higher (124 μg/l), showing an increasing trend over time leading to eutrophic conditions. The trace metals (Cu, Co, Zn, Ni, Mn, and Sr) are present in greater amounts in the water of Nainital Lake than in the other three lakes, though Fe and Cr are high in Bhimtal and Fe in Naukuchiyatal. The higher abundance is derived from the leaching of Fe–Mg from metavolcanic and metabasic rocks. Most of the heavy metals (Cr, Ni, Cu, Mn, Fe, Sr, and Zn) significantly enrich the suspended sediments of the lakes compared to the bed sediments which due to their adsorption on finer particles and owing to multiple hydroxide coating and organic content, except for Fe, which is enriched in the bed sediments. The high rate of sedimentation, 11.5 mm/year in Nainital, compared to Bhimtal with 4.70 mm/year, Naukuchiyatal with 3.72 mm/year, and Sattal with 2.99 mm/year, has resulted in shorter residence time, poor sorting of grains, and lesser adsorption of heavy metals, leading consequently, their depletion in the bed sediments of Nainital Lake.  相似文献