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20 December 1998, Volume 4 Issue 4

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Article

COMPLEXITY AND SELF－ORGANIZED CRITICALITY 0F SOLID EARTH SYSTEM

Yu Chong-wen

1998, 4(4):  361-368. 

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The trend of development of natura1 sciences in this century is from the very small (particle physics)—the very large (cosmology)—the very complex (science of complexity). The studies of “complexity” are characterized by the trend of the times of scientific development and belong to fundamental researches with foreseeing, exploring and innovation. The author puts foreward the proposition of “Complexity and Self-Organized Criticality of Solid Earth System” in the light of: (1)the science of complexity studies the mechanisms of emergence of complexity and is the science of 21st century，and in combination with (2) the inherent fundamental attributes of complexity and self-organized criticality of the solid earth system. By the proposition we try to cogitate from a new viewpoint the ancient yet even-new solid earth system. The author abstracts the fundamental problem of the solid earth system from the essence of the generalized geological systems and processes，advances its three major basic theoretical problems and proposes the methodology of researches on the complexity of the earth system in which holism is dominant and reductionism is subordinate and macrophysics complemented with microphysics. “Complexity and Self-Organized Criticality of Solid Earth System” is one of the great scientific problems underlying our national economic increase, social progress and geosciences development. The study of this problem would become a growing point in the development of geosciences in the 21st century, causing it to make breakthrough in its advance and bringing along the development of many related disciplines concurrently.

GEOCHEMICAL EVIDENCE FOR NORTH QINLING BEING A PART OF YANGTZE PLATE PRIOR TO THE NEOPR0TEROZOIC

Zhang Ben-ren1, Han Yin-wen1, Oayang Jian-ping1, Xu Jifeng2

1998, 4(4):  369-382. 

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Qinling Orogenic Belt represents the composite convergence gone with two sutures between the North China and Yangtze blocks (NCB and YB). The northern Neoproterozoic to Early Paleozoic Shang-Dan megasuture, in which were tectonically emplaced ophiolite fragments including the well known Songshugou ophiolite(1000 Ma±), is the boundary between North Qinling (NQ)and South Qinling(SQ). The southern Late Paleozoic Mian-Lue suture with ophiolite fragments is situated between SQ and the northern margin of Yangtze block (NYB), and thereby is considered to represent an ocean basin opened and closed within the Yangtze plate. The regional continental growth has been studied based oil Nd model ages and the chemieal characteristics, depletion degree and evolution tendency of the regional upper mantle have been revealed by trace element and isotopic tracers. The results indicate that NQ is basically similar to SQ and NYB in the continental growth mainly during the Paleo-and Meso-Proterozoic, the higher depletion degree (εNd(t) up to +7.5)of the Proterozoic upper mantle, and the Proterzoic mantle chemical features of relative enrichment in Nb, Ta and Cu, and higher Rb/Sr, Ba/Sr, Ba/La, Th/La and Nb/Ta ratios. In contrast, the continental crust of NCB and its southern margin (SNCB) grew mainly during the Archean and Paleoproterozic, their upper mantle was almost steady in its εNd(t) values of about +3 during the same time interval, and the mantle source of the Paleoproterzoic basalts of SNCB was characterized by relative enrichment in Fe and Mo and higher Zr/Hf ratio. The Pb isotopic thee dimensional topological plot and the 206Pb/204Pb-εNd(t) plot for the basement basic rocks from the region consistently show an outstanding geochemical boundary in coincidences with the geological boundary between NQ and NCB, and a subordinate geochemical boundary at the Shang-Dan megasuture. In the Songshugou ophiolite fragment, the discovery of metatholeiites, exhibiting the chemical features peculiar to both N-MORB and E-MORB implies that coexisted the depleted mantle source and mantle plume source beneath the Shang-Dan ocean basin represented by the ophiolite. The N-MORB-type metatholeiite of Songshugou ophiolite is comaparable to the N-MORB-type metatholeiite of Mian-Lue ophiolite in Ba/La, Nb/Ta, Yb/Hf, Y/Tb, Ti/Zr and Ti/V ratios, and Nd and Pb isotopic composition. This infers that the Shang-Dan oceanic crust, like the Mian -Lue oceanic crust, was formed within the Yangtze plate via the lithospheric break-up. In addition, the Qinling region was dominated by the rifting series during the Paleo-and Meso-Proterozoic and no sutured boundary of that time has be en discovered. Therefore, NQ should be a part of the Yangtze plate before the Neoproterozoic. The metatholeiites of Qinling Group(2000 Ma±)and Kuanping Group(1 142 Ma±)are similar to the Songshugou metatholeiites of both the E-MORB and N-MORB types in higher Nb/Ta, Ba/La, Nb/La, Th/La, Sc/Th and Yb/Hf ratios, and are comparable to the E-MORB-type metatholeiite in higher Nb, Ta, U and Th contents. This result not only may be in support of the supposition that NQ was originally a microcontinent formed on an ocean is1and base, but also can give a reasonable interpretation for that the crust and mantle of NQ are characterized by the highest Th/La, Sc/Th and Yb/Hf ratios, the highest Nb,Ta, U and Th contents and the highest Pb isotopic ratios in the region. Finally, the implications of this study for the developing dynamics of Qinling Orogen are also discussed.

TRACE ELEMENT GEOCHEMISTRY AND TECTONIC SETTING OF GREENSCHISTS IN THE CENTRAL PART OF FUJIAN PROVINCE

Wang He-nian, Sun Cheng-yuan,

1998, 4(4):  383-392. 

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The Precambrian greenschists of the Longbeiqi Group in the central part of Fujian province are distributed along the Zhenghe-Daipu fult belt. Major chemical compositions of the greenschists indicate that they were originated from picrite-basalt and basalt. The Precambrian metamorphic acidic volcanics are generally associated with the basic ones, and demonstrate a “biomode” feature of the continental rift volcanic rocks. The geochemical characteristics of trace elements of the greenschists are different from MORB and VAB in higher contents of LILE，such as K, Rb，Ba, Zr and Ti；The chondrite-normalized REE patterns are enriched in LREE with a small Eu anomaly. Based on the Ti-Zr-Y and Ti-Zr-Nb diagrams, the grecnschist is identified as within plate tholeiite (WPT). Consequently，the greenshists in the central Fuijan province are considered to be derived from the continental tholeiite formed in a continental rift tectonic setting. Our results may have important significance for further studies of Zhenghe-Daipu fault belt, as well as the tectonic evolution of South East China.

CHARACTERISTICS AND LATITUDINAL COMPARATIVE RESEARCH ON THE EARLY PALAEOZOIC VOLCANIC ROCKS OF RIFTED OROGENIC BELT AND SMALL OCEAN BASIN OPHIOLITE SUIT FROM NORTHERN QINLING MOUNTAINS AND SOUTHERN QILIAN MOUNTAINS

Qiu Jia-xiang1, Zeng Guang-ce1, Zhu Yun-hai1, Su Shang-guo2

1998, 4(4):  393-405. 

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Northern Qinling Mountains and southern Qilian Mountains are located in the middle part of the famous latitudinal Qinling mega-orogenic belt. It belongs to rifted orogenic belt of the Cambrian-Ordovician period. It underwent a series of tectonic opening-closing including intraplate continental rift--intercontinetal rift--volcanic arc--orogenic belt. During the Cambrian, the alkaline and tholeiitie basalt, and also small Ocean basin ophiolite suit were formed under an extension environment. In the Ordovician, the tectonic setting was closing. The intermediate-acidic volcanic rocks of calc-alkaline and shoshonite series, as well as the volcanic are suit rocks were formed. The boninites were also formed at this time. Southem Qilian belongs to the single rift system; however, northern Qinling belongs to the double rift system. In northern Qinling rift system, from east to west and from south to north, the distance of extension decreased, the velocity of closing increased, and the intensity of volcanic eruptions, acidity, K content, crustal materials of volcanic rocks we gradually getting larger. The distance of extension was similar to the Red sea’s; however, the velocity of closing was similar to the Andes type. The characteristics of old mantle ware superimposed. In the Cambrian period the mantle was depleted in crustal materials; however, in the Ordovician period the mantle was enriched in crustal materials. Through the latitudinal comparative research between Dabei Mountains--northem Qinlng--southern Qilian--northern margin of the Chaidamu Basin, we found that the basic and acidic magmas of northern Qinling and southern Qilian were mainly formed through partial melting of mantle and crustal respectively; whereas the intermediate reeks were formed through assimilation- fractional crystallization(AFC)of the basic magama. From east to west, the rift opened gradually; The ages of volcanic eruptions were getting younger; the duration of volcanic eruptions was getting shorter; the rift system changed from single to double character; the distance of extension was getting larger; the velocity of extension and closing Was becoming larger; the alkalinity of volcanic rocks was getting smaller. There was no ophiolite suit in the east, whereas it appeared in the west; The sources of old mantle were changed from mixed DMM and EM-I to mixed EMM and EM-Ⅱ.

COMPARISION BETWEEN THE GEOLOGICAL STRUCTURAL FEATURES OF FELSIC CRYPT0EXPLOSIVE BRECCIA 0F NO.6722 URANIUM DEPOSIT IN SOUTH JIANGXI PROVINCE AND THE GEOLOGICAL EFFECTS OF UNDERGR0UND NUCLEAR EXPLOSION

Zhang Bang-tong1, Wang Xiang-yun1, Rao Bing2, Zhang Fusheng3

1998, 4(4):  406-412. 

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Based on a comparision between the geological structural features of felsic cryptoex-plosive breccia within granitic basement of No.6722 uranium deposit and the geological effects of underground nuclear explosion, the explosion equivalent of TNT for cryptoexplosive breccia of No.6722 uranium deposit is calculated by a comparision method. The microfissuring optic features, and ultramicrostructure of quartz for cryptoexplosive breccia and basement granite have been studied respectively under the polarization microscope and transmision electron microanalyzer (TEM). The densely parallel directional microfissuring, similar to impact microfoliation (shock lamellae), is observed in quartz grains of cryptoexplosive breccia for No.6722 uranium deposit, but undulatory extinction is not found. It has been found under the TEM that the free dislocations and dislocation walls are sparsely distributed in quartz grains of basement granite, but sharply reduced and even disappeared in quartz grains of granite breccia. The results of a comprehensive study suggest that the cryptoexplosion-forming mechanism of No.6722 uranium deposit is attributed to a brittle deformation due to instantaneous explosion which simultaneously caused the annealing of dislocations; U quartz.

STUDY ON VOLCANIC ACTIVITIES 0F MESOZOIC YIXIAN CYCLE, WESTERN LIAONING

Shi Bu-qing, Wu Zhi-ping, Zhou Yao-qi, Zhang Da-gang, Xu Xiu-cai

1998, 4(4):  413-422. 

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Mesozoic volcanic rocks are widely distributed in Western Liaoning Province. They can be mainly divided into three eruption cycles, i.e. the Xinglonggou, the Lanqi and the Yixian cycles, among which the Yixian cycle is most importantly developed. Based on a high precision sampling on Yixian cycle, this paper made a particular study on the geochemical characteristics of trace elements in volcanic rocks of Yixian cycle. We found that all volcanic rocks in Yixian cycle were derived from a common source, which seems to be an admixture of crust and mantle materia1s. All of them were formed through several eruption pulses in a prolonged geodynamic process. Each eruption cycle had pulsation character and the, volcanic activity weakened gradually. The variation of trace element parameters shows a quite coincidence with the lithology and eruption cycle subdivision, and provides a sensitive indicator on volcanic activities. This paper also discusses the structure background of Yixian volcanic cycle. which should be affected by the lithosphere delamination at K3-J1 in this area.

STUDY 0N THE ORE-FORMING FLUID OF THE JINDUICHENG PORPHYRY MOLYBDENUM DEPOSIT, SHANXI PR0VINCE

Xu Zhao-wen, Yang Rong-yong, Liu Hong-ying, Lu Xian-cai, Xu Wen-yi, Ren Qi-jiang

1998, 4(4):  423-431. 

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The Jinduicheng Porphyry Molybdenum Deposit, Shanxi Province is one of the largest molybdenum deposits in China. Base on the observation of the cross-cutting sequence of veins, the whole ore-forming process can be divided into two periods and ten stages. The analysis of fluid inclusions in quartz indicates that the ore-forming hydrothermal system is rich in CO2. The average homogenization temperature ranges from 83 to 412℃. The salinty of metallogenetic fluid manifests bimodal distribution pattern with two ranges from 27.5 to 42.5 wt％ NaCl and from 0.61 to 17 wt％ NaC1 equiv. The values of oxygen and hydrogen isotope show that the major source of metallogantic element is magmatic fluid. At the last stage large amount of meteoric water was mixed into the hydrothermal system, leading to decrease of temperature, salinity, δ18OH2O andδD, and to precipitation of molybodnite which formed the main body of the super-large Jinduicheng molybdenum deposit.

TECTONICS AND GEOLOGICAL EVOLUTION OF XUEFENG INTRA-CONTINENTAL OROGENE, SOUTH CHINA

Qiu Yuan-xi1, Zhang Yi-chang2, Ma Wen-pu3

1998, 4(4):  432-443. 

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The Xuefeng Mountains are located in the southeastern margin of the Yangtze Block, South China. The tectonics and geological evolution of this region have been studied and compared with the orogene and allochthonous nappes of Alpine and Appalachian types. The following features are recognized： 1. The development of inter-layer gliding is one of the major features of the Xuefeng Mountains. The glide structures have a regional scale and are of multi-layer and polycyclic characteristics. Discordant folds were well developed. in which the upper layers are usually more intensively deformed than the lower layers. Thrust or overthrust developed in the earlier stages, while gravity slide or extensional detachment in the later stages. The basement WSS thrusted rflore intensively in its front edge and detached from the cover, forming Jura-type folds, extended anticlines, imbricated thrusts, and foredeep depressions. A sequence of progressive deformations developed: inter-layer gliding-- inter-layer folding--imbricated thrusting--overthrusting(1ayer-cutting)gravity sliding or extensional detachment. Recoil structures formed on the hanging side of the thrusts. 2. Although imbrcated thrusts developed in the Xuefeng Mountains, klippes, structure windows, duplex and recoil structures, mega-recumbent folds or nappe sheets do not exist in this area. The displacement of thrust or glide does not exceed 50km. The hanging side of the thrusts is allochthonous in the relatively sense, as it resided in the same paleobiogeographic division with the downthrown side. The thrusting has narrowed the sedimentary facies, belts of original formations, but did not distort their sedimentary framework(platform facies’ continental facies’ abyssal facies). The Banxi, Xiajiang, and Danzhou groups are synchronous formations with different sedimentary facies and are not melanges. The outcrops of Early Paleozoic in southeast Guizhou Province are not in the structural windows but in synclines. The Proterozoic Banxi Group does not overlay on the Early Paleozoic strata. No Alpine-type allochthonous nappe has been found in the Xuefeng Mountains. 3. The tectonic evolution of the Xuefeng Mountains has been proceeded on the background of continental crust. Since the Late Caledonian orogene, intra-continental subduction had replaced the B-type subduction as the major geodynamic process in the area. Inter-layer gliding became the dominant form of deformation. When the rifts closed, the micro-continental blocks collided (soft collision), and inter-layer gliding occurred.

GEOMETRY AND MECHANICS OF ZHANGBALING NAPPE IN EAST OF TANLU FAULT ZONE, EASTERN CHINA

Zhang yong-jun Huang zhong-jin

1998, 4(4):  444-451. 

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The Zhangbaling nappe lies in the northern margin of the South China block, east of the Tanlu fault zone. It belongs to the western part of fold and thrust tectonics of the Lower Yangzi area with a trend of NNE. The Dabie belt is to its northwest and Chuxian-Susong tight fold and thrust belt is to its southeast. It covers an area of about 1100 km2. According to the 1evels of thrusts and types of folds, the Zhangbaling nappe can be divided into the Feidong rappe and the Shiji rappe. Based on data of field observation, drills and geophysics, the authors demonstrated that the Zhangbaling thrust rappe is a complex thrust structure with a movement more than 16km southeastward. The isotope age of its granites and metamorphic belts is commonly 165～240Ma. This suggests that it was shaped during the early Mesozoic time when the North and South China blocks co11ided. After it was fomred, the Tanlu fault, which is 1eft-lateral slip, destroyed its integrity. Therefore, the Tanlu fault zone is not its northwest boundary It is suggested that the western houndary of the Zhengbaling rappe is located in the south of Dabie block.

APPLICATION OF THE PROBABILISTIC ENERGY METHOD TO EVALUATE THE ULTIMATE LOAD CAPACITY OF CAST-IN-SITU PILE

Lou Zhong-lian, Luo Guo-yu

1998, 4(4):  452-458. 

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The feasibility of using probabilistic energy method to evaluate the ultimate load capacity of cast-in-situ pile has been investigated with the data derived from the results of CAPWAP hack-analytic and static pile load test of 200 pile cases in the urban district of Nanjing city. The dynamic soil-pile interaction model, similar to that used in the CAPWAP method, is adopted in this method. The energies delivered and transformed during the high strain dynamic tests is comprehensively analyzed, and the formulas calculating pile capacity are derived based on the principle of energy balance. The model parameters, including the shaft dam ping factor Js, the tip damping factor Jt, shaft quake Qs, and tip quake Qt are treated as random variables with mean values, standard deviations and probability distribution functions determined by a statistical analysis. The statistics of regional experiments, such as the means and standard deviations of the model parameters, are used as given values in the calculation of pile capacity. The other required values, including the energy delivered to the pile head during each hammer blow, the pile penetration of each blow, the maximum velocity at the pile head, and the pile dimensions and elastic properties, are easi1y measured. The distribution of pile capacity is determined through a Monte Carlo simulation. Furthermore, the authors proposed here a formula to calculate the probability of the evaluated pile capacity exceeding certain design load. The rationality and accuracy of this method are demonstrated in a comparison of the pile capacity calculated with this method and the results of static pile1oad test.

COMPREHENSIVE EVALUATION OF FRACTURES IN DAAN OIL FIELD

Zeng Lian-buo1, Gao Shao-qing2

1998, 4(4):  459-464. 

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Based on the core description and three-dimensional finite-element numerical simulation, the authors comprehensively evaluated the distribution characteristics, development rule and effect on exploitation of different fracture groups. There are four group fractures which were controlled by sedimentary microfacies and structure in Daan oil field. Under the effect of modern stress field, the permeability of the EW fracture is the best, then the NW and NE fractures, the NS fracture is the worst. The mudstone partings absorb water seriously and have important influence on exploitation effect because both hig-dip tectonic fracture and low-dip bedding detachment fracture are developed wel1.

SEDIM ENTARY ENVIRONM ENT OF 11# AND 9# COALS OF TAIYUAN FORMATION AT PINGSUO OPEN-PIT MINE

Cheng Dong1, Shen Fang1, Chai Dong-hao2, Cheng Bao-zhou2

1998, 4(4):  465-472. 

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The 11# and 9# coals, exposed and mined at Pingsuo open-pit mine, occur in Ⅱ-Ⅲ intervals of the Taiyuan Formation, Upper Carboniferous. They were accumulated in environment of fan delta-1agoon and fan delta-tidal flat. The 4m thick 11# coal was formed in an environment of fan delta-tidal flat and the 15m thick 9# coal in all environment of fan deltaic plain, fan delta front and lagoon revering with deep water.

GR0UNDWATER CLASSIFICATION AND BASIC C0NCEPTS OF FRACTURE WATER

Liao Zi-sheng

1998, 4(4):  473-477. 

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Two important concepts in hydrogeology, groundwater type and bed rock fracture water, have been systematically reviewed, and the different groundwater classifications have been compared in this paper. There are two groundwater classification plans in the world now. The classification based on groundwater dynamic properties of the aquifer is widely agreed among hydrogeologists all around the world.Another classification is based on the rock media, which included two different plans: the classification according to the types of openings in water-bearing media, and the classification according to the rock type. Since the classification according to the type of openings (i.e., porous water, fracture water and karst water) has a good representation on the relationship among rock type, opening type and groundwater type, therefore, it has been adopted by many hydrogeolgists in China, Russia and many other countries. Based on recent data of groundwater survey in many countries, the author pointed out that although the classification according to the opening type of water-bearing media has many advantages, sortie problems still existed, such as: (1)there is no absolute co-relations among rock type, opening type and groundwater type; (2)sortie transitional rock type and the rocks with two opening types are not included in the classification; and (3)the classification does not cover all types of the groundwater. Here, the author proposed a modified classification plan, in which the transitional type, rock type and opening type have been considered together. Based on this classification, the basic concepts of bed rock fracture water have been discussed.