2009 Vol. 15, No. 4

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INFLUENCE OF STRENGTH PARAMETERS ON OVERALL DEFORMATIONS OF ROCK SPECIMENS WITH INITIALLY RANDOM MATERIAL IMPERFECTIONS
WANG Xue-bin
2009, 15(4): 321-329.
Abstract (164) HTML (77) PDF (690KB)(12)
Abstract:
For heterogeneous rock specimen with smooth ends and initially random material imperfections in uniaxial plane strain compression, the effects of initial cohesion and internal friction angle on the overall deformational characteristics (such as the axial, lateral and volumetric strains as well as the calculated Poisson's ratios) are modeled using FLAC. A few written FISH functions are used to set the random imperfections and to calculate the overall deformational characteristics. For intact rock, the failure criterion is a combined Mohr-Coulomb criterion with tension cut-off, exhibiting linear strain-softening and then ideal plastic behavior beyond the occurrence of failure. Imperfection undergoes ideal plastic behavior beyond the occurrence of failure. As strength parameters (such as initial cohesion and internal friction angle) increase, the peak stress and related lateral strain increase, and the peak volumetric strain increases also, and the calculated Poisson's ratio corresponding to the peak stress increases slightly. At post-deformational stage, the volume of the specimen can dilate although the dilation angle is zero, as is in agreement with the analytical solution proposed by Wang (2006). This is attributable to the relative sliding between adjacent rock blocks separated by shear zones. With lower strength parameters, the nonlinear pre-peak portions of lateral strain-axial strain curve, volumetric strain-axial strain curve and calculated Poisson's ratio-axial strain curve become shorter. The numerically predicted upper bound of shear band inclination is lower than that predicted by Coulomb theory, and the lower bound approaches that predicted by Roscoe theory. The predicted results by Arthur theory are closer to the present numerical shear band inclination.
STRENGTH ESTIMATION OF COLUMNAR JOINTED BASALTIC MASS BASED ON GEOLOGICAL STRENGTH INDEX
ZHENG Wen-tang, WANG Hua-an, GE Jun-hui
2009, 15(4): 330-335.
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The strength parameters of jointed rock mass are important to rock engineering design.The columnar jointed basaltic mass is special with columnar mosaic structure and the similar engineering case la cks.The strength of columnar jointed basaltic mass currently becomes an advanced research hotspot in hydropower project.This paper reviews domestic and international researches on strength of columnar jointed basaltic mass.Taking the columnar jointed basaltic at Baihetan Hydropower Station as an example, the GSI and Hoek-Brown Criterion are applied to estimate strength parameters of columnar mosaic blocky and cataclastic basaltic masses under different blasting damages.The result is proved by in situ tests at Baihetan Hydropower Station.It is concluded that the GSI-based Hoek-Brown Criterion can better reflect real strength parameters of columnar jointed basaltic masses.
MESOZOIC-CENOZOIC TECTONIC MAGMATIC PORTFOLIO ANALYSIS IN CUOQIN AREA OF THE MIDDLE GANGDISE
JIANG Yuan-sheng, XU Tian-de, ZHAO You-nian
2009, 15(4): 336-348.
Abstract (113) HTML (38) PDF (1040KB)(5)
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On the basis of 1:250000 regional geological mapping in the blank areas of the Qinghai-Tibet Plateau, the magmatic rocks in Cuoqin area are divided into six kinds of petrotectonic assemblage through their time-spatial distribution, occurrence, petrology, geochemistry and tectonic settings as follows: (1) the combination of inter-arc dilated, (2) the Oceanic-island ophiolite portfolio, (3) the portfolio of island and margin arcs, (4) the combination of collision-type, (5) the inland subduction and collision-type combination, and (6) the intracontinental extensional type combination. Then, the geodynamic mechanism of tectono-magmatic portfolios, especially the mid-Himalayan magmatism, is discussed. It is proposed that the Gangdise tectono-magmatic belt is comprised by the subduction-, collision- and uplift-type magmatic rocks clearly zoned in space and evolution from base to acidic in time.
GEOCHEMISTRY AND GENESIS OF SHENGMIKENG LEAD-ZINC DEPOSIT IN NORTHERN WUYI, EASTERN CHINA
LUO Ping, WU Gan-guo, ZHANG Da, DI Yong-jun, WANG Chang-min, WANG Yong-qin
2009, 15(4): 349-362.
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The Shengmikeng vein-type lead-zinc deposit is located in Huanggangshan volcano-tectonic depression of the Mesozoic volcanic belt in Northern Wuyi.The ore featured by veinlets and disseminations is hosted both inside the fault zone in the upper Jurassic Ehuling ignimbrite and the potassic trachyte porphyry. Geochemical characteristics indicate S-type granites and volcanic rocks depleted in sodium and enriched in potassium, with 62.42%~78.02% w(SiO2), 7.66%~9.13% w(K2O+Na2O), 1.18~2.62 w(K2O)/w(Na2O), and Rittmann index δ of 1.67~3.78. They are enriched in LREE with an average LREE/HREE ratio of 10.94×10-6, and generally depleted Eu with an minimum δEu less than 0.31 especially in the ignimbrite and biotite granite, which have experienced a significant process of separation and crystallization of plagioclases. ΣREE at the main stage of the magmatic activity decreases with time. From the point of the ΣREE, δEu, geochemical parameters and standard REE distribution patterns, lead-zinc mineralization altered rocks in the Shengmikeng deposit have close genetic relationship with the potassic trachyte porphyry with SHRIMP zircon age of 138.3±1.4 Ma. It is suggested that the deposit was formed in the early Cretaceous period during Yanshanian and is of sub-volcanic hydrothermal type.
GEOCHEMICAL CHARACTERS OF BAND IRON FORMATIONS FROM XINGSHAN IRON DEPOSIT IN QIAN'AN AREA, HEBEI PROVINCE: IMPLICATION FOR THEIR ORIGIN
DING Wen-jun, CHEN Zheng-le, CHEN Bo-lin, DONG Fa-xian, CUI Ling-ling
2009, 15(4): 363-373.
Abstract (148) HTML (88) PDF (1511KB)(9)
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The origin of Qian'an BIFs remains unclear, although plenty of efforts have been done in this area (especially on the Precambrian geology, petrology and geochemistry). In the early stage of "Exploring Mines Facing A Resourse Crisis" project, large and high-grade iron ores were discovered. The ma\or and trace element analyses reported in this paper provide new insights on the origin and formation environment of Qian'an BIFs. The average bulk compositions of the BIFs are rich in total Fe and Sio2, and very low in Al2o3 and Tio2 contents, indicating that a minor terrigenous component input. Their PASS-normalized REE patterns show strongly enriched HREE and positive anomalies of La, Eu and Y. All of the geochemistry fingerprints, in combination with Co/Zn, Ni/Zn, Y/Ho (> 44), La/La* and LaN/YbN (< 1) ratios, strongly suggest a combined origin of hydrothermal water and marine for Qian'an BIFs > consistent with BIFs otherwhere. There are no distinct differences between High-Grade and normal ores, which have apparently similar original sedimentary belts, in ma\or and trace element content, PASS-normalized REE pattern and Fe-bearing mineral assemblage (mainly magnetite), demonstrating that they might have the same origin. It is suggested that the high-grade ores were probably formed at locally Fe-rich environment during volcanic-sedimentary activity.
RESERVOIR DIAGENESIS AND DIAGENETIC EVOLUTION HISTORY OF 4th + 5th-6th MEMBERS IN YANCHANG FORMATION, WESTERN MAHUANGSHAN, ORDOS BASIN
LI Shun-li, LI Sheng-li, YU Xing-he, DU Wei-wei
2009, 15(4): 374-384.
Abstract (135) HTML (52) PDF (3492KB)(4)
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The reservoirs of 4th + 5th-6th Members of Yanchang Formation in west Mahuangshan were fine sandstone of delta front. The diagenesis in this area had reached A-period of middle diagenetic stage. The mechanical compaction and cementation had resulted in the poor physical property of the reservoir and that was the reason of reservoir lacking primary pores. However, the eluviation by atmospheric water and corrosion by organic acid were helpful to the local reservoir with induced pore. The next step of petroleum exploration and development should be focused on the forecast of favorable areas with induced pore.
ROTATIONAL SHEAR TECTONIC SYSTEMS IN DIFFERENT LEVELS AND THEIR RELATION TO HYDROCARBON ENRICHMENT RULES IN HEBEI, SHANDONG AND HENAN PROVINCES
LI Hong-nan, LIU Wei, CAI Chuan-qiang, LIU Ze-rong
2009, 15(4): 385-395.
Abstract (142) HTML (61) PDF (3286KB)(13)
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With the effect of stress and stress field in Tanlu fault in Meso-Cenozoic, tectonic systems of various rotational shear structures are developed extensively in Huabei depression area in the second depression zone of new Cathaysian, which controls the generation and distribution of duplex hydrocarbon accumulation zones in different degrees. Oil and gas are concentrated in the inner cycle bed, divergent places, inner part of the arc faults and the lower-order twisting structures formed in tectonic movement active phase, which has important guiding significance in oil and gas exploration and development.
CARBONATE RESERVOIR COMPARISON BETWEEN TAHE OIL FIELD AND PUGUANG GAS FIELD
LI Hui-jun, ZHOU Xin-gui, ZHANG Lin-yan, ZHANG Wen-cai
2009, 15(4): 396-408.
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Great breakthroughs have been made in ChinaGs carbonate rocks exploration for oil and gas in recent years with the discoveries of such large-scale oil and gas fields as Tahe oilfield and Puguang gasfield. Basic features of reservoirs, diagenesis, and controlling factors of Tahe oilfield and Puguang gasfield are discussed and compared systemically in this paper. Reef (shoal) reservoirs on the platform margin are usually in good quality as porous or fractured-porous reservoir type with low heterogeneity. Weathering crust karst reservoirs are usually in bad quality, as pore-hole-fracture complex reservoir type with high heterogeneity. Dolomitization is an important mechanism for the forming of super-deep (> 6000 m) carbonate reservoirs, resulting an average porosity increase of 3.5%~4.0%. Thermochemical sulfate reduction (TSR) reactor plays an active role in alteration of reservoir, but it may not meliorate reservoir properties greatly. Tectonism and depositional facies are the main factors controlling the reservoir physical properties of Tahe oil field and Puguang gas field. Depositional facies controlled reservoir quality by affecting rock solubility and water permeability in weathering crust karst reservoir, or by affecting lithology and physical properties in reef (shoal) reservoir on the platform margin. Tectonism controlled the distribution and intensity of weathering crust karst reservoir, while multi-stage structural fractures improved the reservoir physical properties of reef (shoal) reservoir on the platform margin.
STUDY ON QUATERNARY TECTONIC-SEDIMENTARY EVOLUTION OF LUJIAO AREA, EAST EDGE OF YUANJIANG SAG, DONGTING BASIN
BAI Dao-yuan, ZHOU Ke-jun, MA Tie-qiu, WANG Xian-hui, PENG Yun-yi, LI Gang, CHEN Du-ping
2009, 15(4): 409-402.
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Quaternary Yuanjiang sag is an eastern one of the secondary tectonic units of the Dongting basin. Detailed geologic mapping and bore data were taken to reveal the Quaternary tectonic, sedimentary and geomorphic characteristics and tectonic-sedimentary evolution of Lujiao area, northeast Yuanjiang sag. The Honghu-Xiangyin fault and Rongjiawan fault formed in succession during Early Pleistocene, which caused that the west walls of the faults subsided and received alluvial and lacustrine deposits, while the east walls rose and were denuded. Eastern area of the sag uplifted and was denuded in the end of Early Pleistocene. The sag subsided and received alluvial and lacustrine deposits during early-middle Middle Pleistocene. The study area rose as a whole and was denuded during late Middle Pleistocene. The western main depressional area was stable or subsided weakly and formed clay deposits in Late Pleistocene, when east area rose by fits. In the same time of above tectonic uplift since late Middle Pleistocene, east of the area tilted westward and northward. The area was under tectonic stable state in Holocene, forming alluvial-lacustrine deposits in western Dongting lake area.