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921.
The Taparko gold deposit, located in the eastern branch of the Proterozoic Birimian Bouroum-Yalogo greenstone belt (Burkina
Faso) consists of a network of quartz veins developed in a N 170° trending shear zone (250 m wide, 4 km long) superimposed
on the regional Birimian structural pattern. The quartz vein network is composed of: (a) a dominant array of quartz veins
(type 1), parallel to the shear zone and comprising strongly deformed dark quartz exhibiting foliation, layering, ribbon,
tension gashes, etc.; (b) oblique and subparallel related veins (type 2) of gray to white weakly deformed quartz crosscutting
the dominant quartz veins resulting in breccia structures; and (c) shallow dipping veins (type 3), cross-cutting veins types
1 and 2 and filled by undeformed white buck structure quartz. Cross-cutting relationships and different quartz types in different
veins and within individual veins imply a concomitant filling of the veins during the progressive deformation. Initial sinistral
transcurrent shearing evolved with time to sinistral reverse shearing. Metallic minerals occur only in type 1 and 2 veins
and were deposited in two stages, with native gold being related to second stage sulfides. Gold (and chalcopyrite) precipitated
preferentially upon the surfaces of fractured pyrite grains in low-pressure sites (pressure shadow zones) around and/or within
the sulfide grains (along subsequently annealed fractures). The formation of the South Taparko deposit can be divided into
a succession of events: (a) during the first event, N 170°-directed sinistral transcurrent shearing resulted in a N 20° mylonitic
foliation and fractured rock which allowed H2O-, CO2- and SiO2-rich fluids to circulate and deposit quartz with buck texture; (b) during the second event, type 1 quartz was strongly deformed
and type 2 veins formed with sigmoidal shapes as viewed on a horizontal plane; and (c) during the third event, the sinistral
transcurrent shearing evolved to sinistral reverse shearing and the deformation style evolved correspondingly from ductile
to brittle-ductile. During the last phase of deformation gold nucleated and deposited in low-pressure zones.
Received: 9 July 1997 / Accepted: 23 March 1998 相似文献
922.
湘赣边区NNE向走滑断裂-流体-铀成矿动力学分析 总被引:7,自引:0,他引:7
以湘赣边区NNE向走滑断裂系统构造解析及其演化和动力学分析为主线,结合含矿流体的运动学过程研究,进行热液铀成矿动力学分析,以探讨成矿作用的动力来源、作用机制和演化过程。 相似文献
923.
924.
储层裂缝特征测井解释方法综述 总被引:20,自引:0,他引:20
为了更好地研究裂缝性砂砾岩储层和其它裂缝性储层裂缝的测井解释问题,综述了目前在裂缝性储层裂缝测井解释中主要采用的常规评价、人工神经网络和斯通利波3类方法在识别裂缝带和定量计算储层裂缝参数两个方面的应用原理和研究现状,并指出了今后的一些研究方向。 相似文献
925.
RayequationmigrationofwideanglereflectionsinDabieorogeniczoneXU-YAOZHENG1)(郑需要)CHUN-YONGWANG2)(王椿镛)XIAO-LINGLAI1)(赖晓玲)XIAN... 相似文献
926.
The Izu–Ogasawara arc contains, from east to west, a volcanic front, a back-arc extensional zone (back-arc knolls zone), and a series of across-arc seamount chains that cross the extensional zone in an east-northeast and west-southwest direction and extend into the Shikoku Basin. K–Ar ages of dredged volcanic rocks from these across-arc seamount chains and extension-related edifices in the back-arc region of the Izu–Ogasawara arc were measured to constrain the volcanic and tectonic history of the arc since the termination of spreading in the Shikoku Basin. K–Ar ages range between 12.5 and 1 Ma. Andesitic to dacitic rocks of 12.5–2.9 Ma occur mainly on the western part of the chains. The western part of the chains are the locus of volcanism behind the front which erupted mainly calc-alkaline andesitic lavas. The youngest rocks (< 2.8 Ma), characterized by cpx-ol basalt, occur along the western margin of the back-arc knolls zone. Basaltic rocks of 12.5–2.9 Ma have relatively high concentrations of Na2 O (> 2.0 wt%), Zr (> 50 p.p.m.) and Y (> 20 p.p.m.) and low CaO (< 12 wt%). On the other hand, basalts of 2.8–1 Ma have lower Na2 O (< 1.8 wt%), Zr (< 50 p.p.m.) and Y (< 20 p.p.m.), but significantly higher CaO (> 12 wt%). The age inferred for the initiation of back-arc rifting (∼ 2.35–2.9 Ma: Taylor 1992 ) behind the current volcanic arc coincides with the time that basalt chemistry changed drastically (eruption of the low-Na2 O and high-CaO basalt). This implies that post-2.8 Ma volcanism in the back-arc knolls zone is associated with rifting. Similarly, the change in chemical composition might be explained by a different type of source mantle following rift initiation. Volcanism in the western seamounts ceased after the onset of rifting at ∼ 2.8 Ma. 相似文献
927.
The Day Nui Con Voi belt in Vietnam is the southeasternmost part of the Red River shear zone in Asia. It is a narrow high-grade metamorphic core complex consisting of garnet–sillimanite–biotite gneisses, mylonite bands, amphibolite layers and migmatites. Geothermobarometric study of the complex revealed that the peak metamorphism took place under amphibolite-facies conditions of 690−60+30°C and 0.65±0.15 GPa and the subsequent mylonitization occurred under greenschist-facies conditions of 480°C and under 0.3 GPa. Fifteen synkinematic hornblende and biotite separates from gneisses, amphibolites and mylonites were dated with the K/Ar method. Hornblende separates from the Day Nui Con Voi give K–Ar ages of 26.4–28.5 Ma, and the biotite separates do give 24.5–24.7 Ma. Combination of thermobarometric and geochronological data yields the cooling history of 500°C at 28 Ma and 300°C at 24 Ma with a cooling rate of 70–110°C Ma−1, and 23 km post-metamorphic exhumation of the core complex. The first 16 km exhumation from the peak of metamorphism (at probably 31 Ma) to 28 Ma was triggered by the left-lateral strike-slip displacement of the Red River shear zone. 相似文献
928.
Ki-Suk Lee 《GeoJournal》1998,44(3):249-257
Since the Tumen River Area Development Project(TRADP) was launched in 1991, Hunchun city located between North Korea and Russia
along the river corridor, has become an important and unique border city. Hunchun, formerly a strategic military city, is
emerging as an international trade linkage center through Satouz and Quanhe on the North Korea side and through Changlinzi
on the Russian side. Furthermore, the establishment and operation of the Hunchun Border Economic Cooperation Zone (HBECZ)
in the city is becoming the main source of the growth, providing a new role for the border city. Its underlying economic momentum
comes from the combination of the Chinese-Korean labor force and foreign investment and technology transferred from Korea,
Japan, and others.
The most important expected new role for Hunchun is as a new 21st century entrepot connection between the Pacific rim and
Eurasia by rail and trunk lines, and as a new regional center of the border region based on both a newly generated urban subsystem
and the increasing informal sector of cross border business. However, there are many obstacles to overcome in the near future,
such as the possible military tensions among the three border nations, the guarantee of free entries and sailing on the Tumen
river, and agreements concerning environmental conservation.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
929.
The Pleistocene Ashigara Basin and adjacent Tanzawa Mountains, Izu collision zone, central Japan, are examined to better understand the development of an arc–arc orogeny, where the Izu–Bonin – Mariana (IBM) arc collides with the Honshu Arc. Three tectonic phases were identified based on the geohistory of the Ashigara Basin and the denudation history of the Tanzawa Mountains. In phase I, the IBM arc collided with the Honshu Arc along the Kannawa Fault. The Ashigara Basin formed as a trench basin, filled mainly by thin-bedded turbidites derived from the Tanzawa Mountains together with pyroclastics. The Ashigara Basin subsided at a rate of 1.7 mm/year, and the denudation rate of the Tanzawa Mountains was 1.1 mm/year. The onset of Ashigara Basin Formation is likely to be older than 2.2 Ma, interpreted as the onset of collision along the Kannawa Fault. Significant tectonic disruption due to the arc–arc collision took place in phase II, ranging from 1.1 to 0.7 Ma in age. The Ashigara Basin subsided abruptly (4.6 mm/year) and the accumulation rate increased to approximately 10 times that of phase I. Simultaneously, the Tanzawa Mountains were abruptly uplifted. A tremendous volume of coarse-grained detritus was provided from the Tanzawa Mountains and deposited in the Ashigara Basin as a slope-type fan delta. In phase III, 0.7–0.5 Ma, the entire Ashigara Basin was uplifted at a rate of 3.6 mm/year. This uplift was most likely caused by isostatic rebound resulting from stacking of IBM arc crust along the Kannawa Fault which is not active as the decollement fault by this time. The evolution of the Ashigara Basin and adjacent Tanzawa Mountains shows a series of the development of the arc–arc collision; from the subduction of the IBM arc beneath the Honshu Arc to the accretion of IBM arc crust onto Honshu. Arc–arc collision is not the collision between the hard crusts (massif) like a continent–continent collision, but crustal stacking of the subducting IBM arc beneath the Honshu Arc intercalated with very thick trench fill deposits. 相似文献
930.