摘要:

AbstractStudies of the deformation styles, formation types and isotopic age data indicate that the Altaides has successively experienced 5 stages of orogeny: (1) the Kanas orogeny forming the angular unconformity between the Baihaba Formation (O3) and the Habahe Group (Z‐O2); (2) the Daqiao orogeny (S3‐D1‐2) giving rise to the early Hercynian quasi‐aulacogen extensional continental crust of the area; (3) the Altay orogeny (middle‐ late Hercynian) leading to the oblique intracontinental collision and the formation of large shear arc‐shaped thrust system and representing a strong orogeny stage; (4) the pan‐Altay orogeny (latest Hercynian‐Indosinian) resulting in the uplifting and erosion of the mountains as a whole; (5) the Himalayan movement causing the rejuvenation of fault systems and block uplift of the Altaides sin

ISSN:1000-9515    

DOI:10.1111/j.1755-6724.1993.mp6001001.x

出版商:Geological Publishing House    

年代:1993

数据来源: WILEY

摘要:

AbstractBased on the study of folds and related conjugate shear joints, the tectonic stress fields of the Urumqi‐ Usu region to the north of the North Tianshan Mountains have been reconstructed. Furthermore the author discussed the tectonic movements and their dynamic features. The early tectonic movement in the investigated region occurred from the end of the Late Jurassic to the initial stage of the Early Cretaceous, with the maximum (tensile) and minimum (compressional) principal stress trajectories in the tectonic stress field being in E‐ W and S‐ N directions respectively; the late tectogenesis took place from the end of the Early Pleistocene to the initial Middle Pleistocene, with the maximum and minimum principal stress trajectories in the late stress field striking in WNW and NE‐NNE directions respectively. Through computer‐aided simulated calculation by the finite element method and analysis of geological structure, it has been ascertained that the early tectogenesis is a nearly N‐S compressive movement and the late one a NE to nearly N‐ S compressive movement with reverse shear. The dynamic force which caused the tectogeneses came from the movement of the southern major fault, i.e. the North Tians

ISSN:1000-9515    

DOI:10.1111/j.1755-6724.1993.mp6001002.x

出版商:Geological Publishing House    

年代:1993

数据来源: WILEY

摘要:

AbstractManganese minerals in the polymetallic nodules from the Central Pacific Ocean were studied using electron microscopy. The principal Mn minerals, being vernadite and todorokite, exhibit different electron diffraction patterns and morphological features. According to its morphological feature, todorokite shows three phases: fibrous, lamellar and lath‐shaped. Both vernadite and todorokite are authigenic minerals. While vernadite was mainly precipitated directly from the relevant solution by microbiological oxidation, todorokite was separated from the solution chemically without the help of microbe. Hence, these two minerals show a close genetic relatio

ISSN:1000-9515    

DOI:10.1111/j.1755-6724.1993.mp6001003.x

出版商:Geological Publishing House    

年代:1993

数据来源: WILEY

摘要:

AbstractUltramafic rocks of Tibet and Xinjiang are the products of partial melting of the upper mantle. The evolution of their mineral composition is marked by two parallel evolutionary series: one is the progressive increase of the 100 Mg / (Mg+Fe2+) ratio of silicate minerals in order of lherzolite?harzburgite?dunite, i.e. the increase in magnesium; the other is the increase of the 100 Cr/(Cr+Al) ratio of accessory chrome spinel in the same order, i.e. the increase in Chromium. The above‐ mentioned evolutionary trends are contrary to that of magmatic differentiation. The evolution of fabrics of ultramafic rocks is characterized by progressive variation in order of protogranular texture? melted residual texture, symplectic texture and clastophyritic texture? equigranular mosaic texture and tabular mosaic texture. Experiments of partial melting of lherzolite have convincingly shown that the evolution of Alpine ultramafic rocks resulted from the partial melting of pyrolite. Various subtypes of them represent different degrees of partial melting. The vertical zoning marked by more basic rocks in the upper part and more acid rocks in the lower actually belongs to the fusion zoning of pyrolit

ISSN:1000-9515    

DOI:10.1111/j.1755-6724.1993.mp6001004.x

出版商:Geological Publishing House    

年代:1993

数据来源: WILEY

摘要:

AbstractAccording to the kinds of feldspar and rock associations in the Al‐rich gneisses, the low‐pressure metamorphic crust of the Early Proterozoic granulite facies in central Inner Mongolia can be divided into southern and northern belts which are composed of six rock associations. They represent the relevant rock sequences of the layered metamorphic rock series formed under specific metamorphic temperature and pressure conditions as well as tectonic environments. Mineral inclusions and reaction texture have recorded that the medium‐temperature high‐pressure mineral assemblages are replaced by the high‐temperature low‐pressure mineral assemblages, thus, giving rise to: garnet+quartz? hypersthene+plagioclase; kyanite? sillimanite and garnet+ kyanite / sillimanite+quartz? cordierite. The deformation fabrics of the rocks, the change of mineral assemblages and the PTt path of metamorphism indicate that the contempranceous high‐temperature normal‐slip ductile shearing is the main cause of the formation of the low‐pressure metamorphic crust of granulite facies. In the orogenic event, the co‐action of thrusting and extension resulted in the change of a medium‐temperature high‐pressure metamorphic environment into the high‐temperature low‐pres

ISSN:1000-9515    

DOI:10.1111/j.1755-6724.1993.mp6001005.x

出版商:Geological Publishing House    

年代:1993

数据来源: WILEY

摘要:

AbstractBased on studies of the reflectance of Ordovician and Silurian zooclasts from 11 sections around the Huangling Anticline, Hubei, China, combined with determination of the conodont colour alteration indices (CAI) and of infrared spectroscopy of dispersed organic matter from the same or adjacent horizons, it is further proved that reflectances of graptolites, chitinozoans and scolecldonts, like vitrinite and natural bitumen, increase with increasing maturation, but follow different reflectance paths. They may be used, therefore, as thermal maturation indicators. Graptolites display optically strong anisotropy. The maximum reflectance measured from graptolite on polished section cut parallel to the bedding plane is the most suitable for determination of maturation of their host rocks. In polished section chitinozoan and scolecodont show reflectance, but no bireflectance owing to their isotropy. The random reflectance of chitinozoans is higher than that of scolecodonts in the case of the same maturity. By analysing the distribution trends of graptolite, chitionzoan and scolecodont reflectances, the Ordovician and Silurian strata can be subdivided into three areas of maturation in the present region. The potential of oil or gas generation is discussed for each area. The result is basically coincident with the distribution pattern of regional organic maturation presented by CAI and infrared spectroscopic determination of organic matter.

ISSN:1000-9515    

DOI:10.1111/j.1755-6724.1993.mp6001007.x

出版商:Geological Publishing House    

年代:1993

数据来源: WILEY

摘要:

AbstractThe extensive intrusion (covering an area of 83.7‐238.3 km2and accounting for 18.6‐31.5% of the total area of the plain), the presence of a transitional zone 1.5‐6.0 km in width, and the interconnection in distribution between the seawater intrusion district and the region lower than the sea level caused by the strong drop of the groundwater level are major characteristics of the seawater intrusion in the study area. Cation exchange played an important role during the formation of chemical composition of the groundwater in the seawater intrusion dis

ISSN:1000-9515    

DOI:10.1111/j.1755-6724.1993.mp6001008.x

出版商:Geological Publishing House    

年代:1993

数据来源: WILEY