板块构造理论研究新进展

本文评述了80年代以来板块构造理论的重要研究成果,就板块划分与板块运动学研究,大洋中脊与板块的扩张,活动边缘与板块的俯冲,板块再造和造山研究等方面的进展,展示板块构造的许多概念已更趋复杂化,板块构造理论变得更加成熟了。     

华北地台北侧的古板块构造演化

在华北地台北侧原兴蒙华力西褶皱带内相继确立了加里东褶皱带和中晚元古代褶皱带,并划分了早、晚华力西褶皱带,探讨了定位于中亚—蒙古古大洋中的微大陆。本文概述了华北地台北侧古板块构造格局、各板块构造单元的地质构造特征以及华北地台北侧元古代—古生代岩石圈的形成与演化。     

褶皱—冲断构造的动力学研究现状和力学分析初探

综述了褶皱—冲断构造的几何特征,造山带的岩石物理性质以及临界锥体力学分析研究现状,认为运用临界锥体力学原理可以很好地解释褶皱—冲断构造发育和发展动力学机制。     

Possible geothermal resources in the Coast Plutonic Complex of southern British Columbia,Canada

In southern British Columbia the terrestrial heat flow is low (44 mW m^–2) to the west of the Coast Plutonic Complex (CPC), average in CPC (50–60 mW m^–2),and high to the east(80–90 mW m^–2). The average heat flow in CPC and the low heat generation (less than 1 W m^–3) indicate that a relatively large amount of heat flows upwards into the crust which is generally quite cool. Until two million years ago the Explorer plate underthrust this part of the American plate, carrying crustal material into the mantle. Melted crustal rocks have produced the inland Pemberton and Garibaldi volcanic belts in the CPC.Meager Mountain, a volcanic complex in the CPC 150 km north of Vancouver, is a possible geothermal energy resource. It is the product of intermittent activity over a period of 4 My, the most recent eruption being the Bridge River Ash 2440 y B.P. The original explosive eruption produced extensive fracturing in the granitic basement, and a basal explosion breccia from the surface of a cold brittle crust. This breccia may be a geothermal reservoir. Other volcanic complexes in the CPC have a similar potential for geothermal energy.Earth Physics Contribution No. 704.     

Late Mesozoic extensional tectonics in the North China Craton and its adjacent regions: a review and synthesis

ABSTRACT

The late Mesozoic tectonics of the North China Craton (NCC) and its adjacent regions were characterized by a general lithospheric extension and remarked by extensional dome structures, such as the metamorphic core complexes, syn-tectonic plutons, rolling-hinge structures, and widespreadgraben/half graben basins. According to our own field observations, laboratory work, and previous results of other groups, from north to south, five extensional domains have been delineated, namely Transbaikalia–Mongol–Okhotsk, western part of NCC, eastern part of NCC and Korea, Qinling–Dabie and its neighbouring, and the interior of South China Block, respectively. As the largest crustal scale extensional tectonic realm in the world, these domains are featured by a NW–SE extensional direction with strong extensional exhumation of middle to lower crust rocks to the surface along detachment faults. Geochronological work on these ductile detachment faults constrain a narrow activity period around 130 Ma except several extensive structures along the Tan–Lu fault, which documents a relative longer extensional period. The foundering of the lower part of the lithosphere could be a possible mechanism of this continent-scale extensional tectonics. This geodynamic model could help us to enhance the knowledge of the time, scale, and mechanism of the NCC destruction from the view of structural analysis.     

Recent Tectonic Structures in a Transect of the Central Betic Cordillera

—The Betic Cordillera has undergone recent Alpine deformations related to the Eurasian-African plate interaction boundary. Most of the present-day relief has been built up since Tortonian times, and is related to the development of folds and faults that are overprinted on older deformations, and some of the faults may be considered as out-of-sequence. The combination of geophysical and geological data makes it possible to determine the main features of the recent tectonic structures, or those recently active, in its central transect. The main fault is a crustal detachment that separates a footwall constituted by the Iberian Massif and a hanging wall formed by the rocks of the Betic Cordillera. While the footwall is practically undeformed, the hanging wall has been folded and faulted. The folds are mainly E-W to NE-SW and have larger sizes and higher related relieves towards the South. The reverse faults are mainly concentrated in the northern mountain front. However, normal faults affect the southern part of the Cordillera and are associated with the development of large asymmetrical basins such as the Granada Depression. In this setting, the slip along the crustal detachment is variable and should increase southwards. The model of the recent tectonics in the central transect of the Cordillera is compatible with the presence of an active subduction in the Alboran Sea, and contrasts notably with the setting of the eastern Betic Cordillera, mainly deformed by transcurrent faults.     

Duration Magnitude Scale and Site Residuals for Northern Morocco

— The first empirical duration magnitude (M_D) formula is developed and tested for the Northern Morocco Seismic Network (NMSNET). This relationship is obtained by relating the IGN (Instituto Geografico National, Madrid) body-waves mbLg^IGN to the duration (), and the epicentral distance (), at 25 analogue stations of the NMSNET for 479 earthquakes with 2.5 mb 5.4, from March 1992 to February 2001. M_D estimates are significantly more precise while introducing a correction term for each of these stations, cSta_j. The magnitude for the i^th event (M_D)_i is the mean value of individual M_Dij=–0.14+1.63log₁₀(_ij)+0.031(_ij)+cSta_j. The cSta_j corrections reduce considerably the local site effects which influence the recorded durations and cause stations to either overestimate, or underestimate M_D up to 0.5 magnitude units. Average station M_D residuals (–cSta_j) are found to be independent of the distance from the epicenter to at least 10 degrees. It seems evident that regional geological features in the immediate behavior of stations have a systematic effect on the corresponding obtained residuals: older well-consolidated Precambrian crystalline rocks produce high negative residuals (shorter durations), younger unconsolidated sediments produce high positive residuals (longer durations), whereas, intermediate M_D site residuals appear to be the result of the effect of various factors, principally age and state of consolidation of the bedrock, combined with the local tectonic.     

Transcurrent continental tectonics model for the Ossa-Morena Zone Neoproterozoic–Paleozoic evolution,SW Iberian Massif,Portugal

The Ossa-Morena Zone (SW Iberian Massif) was affected by continuous orogen-parallel transcurrent continental tectonics from the Neoproterozoic to the Carboniferous times, involving transtension (TT) and transpression (TP) processes that co-existed together, occurred separately in neighbouring regions by the means of strain partitioning or even worked diachronically. A first stage of transpression TP1 took place during the Late Neoproterozoic–Lower Cambrian as a result of Cadomian arc-continent collisional processes. Structures generated by transtension TT1 from Cambrian to Lower Devonian were related to strong lithosphere stretching responsible for the development of basins controlled by major detachments, tilting, rifting and important tectono–thermal diachronic processes. Denudation phenomena and inhibition of sedimentation related with thermal uplift (asthenosphere upwelling) and consequent subsidence caused by isostatic equilibrium, involving generalized transgressions, were processes responsible for major unconformities. The Variscan TP2-TT2 episodes that followed diachronically TP1-TT1, by maintaining the orogen-parallel transport direction, were concomitant with syntectonic deposition of continental basins in the OMZ and foreland basins in the SPZ. TT2 local transtension and tectonic exhumation of deep crustal rocks along major shear zones, favoured the opening of tectonic troughs filled up by sediments and volcanism. TP2 shortening have generated fold axes parallel to the orogen-strike and composite dissymmetric flower structures.     

初论造山带古地理学

造山带古地理学属构造古地理学 ,是造山带地层学的姐妹学科 ,其核心是活动论构造观。简述了造山带古地理学的形成和内涵 ,重点讨论了地质记录已发生移位、歪曲和混杂的造山带地区 (或经造山作用改造的克拉通地区 )正确地进行构造—古地理重建的三个问题 :一是不能用“将今论古”的方法恢复地史期间的隆起区和堆积区 ,地史期间的物源区并非一成不变 ,要充分认识物源供应的多样性和多重性 ;二是沉积相带的展布受区域构造应力场及基底构造格局控制 ,要特别重视边缘相及其物源区的研究 ;三是辨析原生沉积盆地与构造盆地 ,对盆地进行正确的构造复位是古地理重建的基础。     

Iron oxide-copper-gold deposits: an Andean view

Iron oxide-copper-gold (IOCG) deposits, defined primarily by their elevated magnetite and/or hematite contents, constitute a broad, ill-defined clan related to a variety of tectono-magmatic settings. The youngest and, therefore, most readily understandable IOCG belt is located in the Coastal Cordillera of northern Chile and southern Peru, where it is part of a volcano-plutonic arc of Jurassic through Early Cretaceous age. The arc is characterised by voluminous tholeiitic to calc-alkaline plutonic complexes of gabbro through granodiorite composition and primitive, mantle-derived parentage. Major arc-parallel fault systems developed in response to extension and transtension induced by subduction roll-back at the retreating convergent margin. The arc crust was attenuated and subjected to high heat flow. IOCG deposits share the arc with massive magnetite deposits, the copper-deficient end-members of the IOCG clan, as well as with manto-type copper and small porphyry copper deposits to create a distinctive metallogenic signature.The IOCG deposits display close relations to the plutonic complexes and broadly coeval fault systems. Based on deposit morphology and dictated in part by lithological and structural parameters, they can be separated into several styles: veins, hydrothermal breccias, replacement mantos, calcic skarns and composite deposits that combine all or many of the preceding types. The vein deposits tend to be hosted by intrusive rocks, especially equigranular gabbrodiorite and diorite, whereas the larger, composite deposits (e.g. Candelaria-Punta del Cobre) occur within volcano-sedimentary sequences up to 2 km from pluton contacts and in intimate association with major orogen-parallel fault systems. Structurally localised IOCG deposits normally share faults and fractures with pre-mineral mafic dykes, many of dioritic composition, thereby further emphasising the close connection with mafic magmatism. The deposits formed in association with sodic, calcic and potassic alteration, either alone or in some combination, reveal evidence of an upward and outward zonation from magnetite-actinolite-apatite to specular hematite-chlorite-sericite and possess a Cu-Au-Co-Ni-As-Mo-U-(LREE) (light rare earth element) signature reminiscent of some calcic iron skarns around diorite intrusions. Scant observations suggest that massive calcite veins and, at shallower palaeodepths, extensive zones of barren pyritic feldspar-destructive alteration may be indicators of concealed IOCG deposits.The balance of evidence strongly supports a genetic connection of the central Andean IOCG deposits with gabbrodiorite to diorite magmas from which the ore fluid may have been channelled by major ductile to brittle fault systems for several kilometres vertically or perhaps even laterally. The large, composite IOCG deposits originated by ingress of the ore fluid to relatively permeable volcano-sedimentary sequences. The mafic magma may form entire plutons or, alternatively, may underplate more felsic intrusions, as witnessed by the ore-related diorite dykes, but in either case the origin of the ore fluid at greater, unobserved depths may be inferred. It is concluded that external 'basinal' fluids were not a requirement for IOCG formation in the central Andes, although metamorphic, seawater, evaporitic or meteoric fluids may have fortuitously contaminated the magmatic ore fluid locally. The proposed linkage of central Andean and probably some other IOCG deposits to oxidised dioritic magmas may be compared with the well-documented dependency of several other magmatic-hydrothermal deposit types on igneous petrochemistry. The affiliation of a spectrum of base-metal poor gold-(Bi-W-Mo) deposit styles to relatively reduced monzogranite-granodiorite intrusions may be considered as a closely analogous example.Editorial handling: B. Lehmann