Microstructural evidence for an epigenetic origin of a Proterozoic zinc-lead-silver deposit, Dugald River, Mount Isa Inlier, Australia

The Zn-Pb-Ag deposit contained in the metasediments of middle Proterozoic age at Dugald River forms one of a number of significant zones of sulphide mineralization within the Eastern Fold Belt of the Mount Isa Inlier. It is characterized by its high Zn + Pb grade, high Zn/(Zn+Pb) ratio and strong structural controls with the present resource standing at 38 million tons averaging 13% Zn, 2.1% Pb and 42 g/t Ag. Microstructural timing relationships and a variety of microscopic ore textures indicate that the deposit resulted from replacement and partial infill of carbonaceous and pyritic host rocks by hydrothermal ore-forming fluids during the D₄ deformation event. This genesis is contrary to earlier syngenetic-based interpretations, but accords with the discordant nature and structural controls on emplacement of the mineralization. Key timing criteria include (1) truncation of S₂ and/or S₃ by the late ore minerals, (2) replacement textures in undeformed mineral paragenesis, (3) slightly preferred dimensional orientation and undulating extinction of quartz and muscovite that are intergrown but which crystallized earlier than sulphide minerals in veins. The presence of these microstructural relationships throughout the deposit and the complete absence of any syngenetic stratiform precursor to zinc-lead-silver mineralization indicates that the zinc, lead and silver at Dugald River were epigenetically introduced rather than just having undergone syngenetic deposition during sedimentation and remobilization during deformation. The regional distribution of the mineralization in a specific stratigraphic zone is most likely due to the partitioning of deformation between different rock types. This caused the weaker lithology to accommodate significantly higher strain than adjacent more competent units, resulting in fracturing and localization of the syntectonic mineralization. Received: 8 September 1995 / Accepted: 12 April 1996     

Structural geology of the Dugald River Zn---Pb---Ag deposit, Mount Isa Inlier, Australia

The sediment-hosted Zn---Pb---Ag deposit at Dugald River is situated 87 km northeast of Mount Isa, NW Queensland. It is a mid-scale base metal accumulation restricted to a black slate sequence of low metamorphic grade. The orebody is tabular and consists of fine- to medium-grained sulphides with a dominant mineralogy of sphalerite, pyrrhotite, pyrite, galena, quartz and muscovite. Three different ore types have been recognized based on mineralization textures; laminated, banded and brecciated. The present reserve stands at 38 million tons of ore averaging 13.0% Zn, 2.1% Pb and 42 g/t Ag. A structural investigation has revealed that six stages of deformation have affected the metasediments in the Dugald River area. The first four (D₁, D₂, D₃ and D₄) are characterized by the extensive development of folds and associated axial plane cleavage. They were all generated in a ductile regime and are of considerable significance for the structural evolution of this region as well as for the emplacement and localization of the sulphide mineralization. D₅ provides a transition towards brittle deformation developing strong kink folds with subhorizontal axial planes. D₆ was a brittle event, producing E-W-trending open folds and major NE and NW strike-slip faults crosscutting all the pre-existing structural elements plus segmenting the orebody. Correlation between the development of deformation and the formation of mineralization can be observed from macro- to microscales. Relationships of mineralization with folds and cleavage indicate a post-D₂ (dominant deformation event) and probably syn-D₄ deformation timing for the Zn---Pb---Ag mineralization at Dugald River, as suggested by the ubiquitous truncations of D₂ fabrics by ore mineral assemblages throughout the deposit.     

Proterozoic low-pressure/high-temperature metamorphism and an anticlockwise P–T–t path for the Hazeldene area, Mount Isa Inlier, Queensland, Australia

In the Hazeldene area, situated in the Mount Isa Inlier, Queensland, the metamorphic grade changes from chlorite zone, through biotite and cordierite zones, to sillimanite/K-feldspar zone.
Microstructural studies of rocks near the sillimanite isograd demonstrate that cordierite grew early during the development of a steep foliation (S2), was replaced by biotite, andalusite and sillimanite at the metamorphic peak late in S2, and in turn by kyanite + chlorite adjacent to localized small post-D2 shear zones. Although the anticlockwise P–T–t path is well defined, the precise P–T conditions are uncertain because of problems with experimental and thermodynamic data. The best estimate for the metamorphic peak for rocks close to the sillimanite isograd is around 600° C at 4 kbar.
The metamorphism has been dated at 1544 Ma, and was synchronous with a major crustal shortening event. Because proposed extensional events occurred more than 60 Ma earlier, their contribution to the peak metamorphic thermal perturbation would have been insignificant. The syn-metamorphic Mica Creek Pegmatites, the abundance of high heat-producing elements in the nearby pre-D2 Sybella Granite, and advective heat by fluids which caused considerable metasomatism in the Hazeldene area, may have each contributed to the thermal budget. However, the metamorphic thermal gradient may be 80°C km^-1 or higher, strongly suggesting a local magmatic control. As none are known in the area, such syn-metamorphic plutons would have to lie beneath the exposed high-grade rocks.     

Structural geology of the Dugald River ZnPbAg deposit, Mount Isa Inlier, Australia

The sediment-hosted ZnPbAg deposit at Dugald River is situated 87 km northeast of Mount Isa, NW Queensland. It is a mid-scale base metal accumulation restricted to a black slate sequence of low metamorphic grade. The orebody is tabular and consists of fine- to medium-grained sulphides with a dominant mineralogy of sphalerite, pyrrhotite, pyrite, galena, quartz and muscovite. Three different ore types have been recognized based on mineralization textures; laminated, banded and brecciated. The present reserve stands at 38 million tons of ore averaging 13.0% Zn, 2.1% Pb and 42 g/t Ag. A structural investigation has revealed that six stages of deformation have affected the metasediments in the Dugald River area. The first four (D₁, D₂, D₃ and D₄) are characterized by the extensive development of folds and associated axial plane cleavage. They were all generated in a ductile regime and are of considerable significance for the structural evolution of this region as well as for the emplacement and localization of the sulphide mineralization. D₅ provides a transition towards brittle deformation developing strong kink folds with subhorizontal axial planes. D₆ was a brittle event, producing E-W-trending open folds and major NE and NW strike-slip faults crosscutting all the pre-existing structural elements plus segmenting the orebody. Correlation between the development of deformation and the formation of mineralization can be observed from macro- to microscales. Relationships of mineralization with folds and cleavage indicate a post-D₂ (dominant deformation event) and probably syn-D₄ deformation timing for the ZnPbAg mineralization at Dugald River, as suggested by the ubiquitous truncations of D₂ fabrics by ore mineral assemblages throughout the deposit.     

Occurrence and composition of sphene from eastern fold belt, Mount Isa Inlier, Cloncurry, northwestern Queensland, Australia

Sphene is very common in rocks including albitized granite, dioritic porphyrite, calcsilicate rock and breccia from the eastern fold belt of Mount Isa Inlier, Cloncurry. Two stages of sphenes are present in these rocks. First-staged sphene is relatively fine, euhedral, some grains show round or patchy zoning; second-staged sphene is relatively large, anhedral to subhedral, some grains show patchy zoning;both possibly contain rutile, ilmenite and magnetite inclusions. All sphenes are of low-Al type. The second-staged sphene has lesser Fe apfu than the first-staged sphene. Light-color part of the sphene has bigger Fe apfu than the dark-color part, as observed on one individual grain of sphene with patchy zoning, the average Xro of the sphene with patchy zoning is greater than that of the sphene without patchy zoning. Because the sphenes are taken from different types of rocks, Si, Ti, and Al have variable relations with F OH apfu. Si and Ti are not correlated with OH F in all analyzed samples ; Fe is correlated with OH F in the sphene just from granite and dioritic porphyrite; Al is correlated with OH F in the sphene fromgranite and breccia and is not correlated with OH F in the sphene from the dioritic porphyrite and calcsilicate rocks. The first-staged sphenes were possibly formed in the processes of magmatism and metamorphism. The second-staged sphenes were formed as a result of the breakdown of hornblendes and biotites in the process of Na (Ca) -metasomatism.     

Evolution of the Mount Woods Inlier, northern Gawler Craton, Southern Australia: an integrated structural and aeromagnetic analysis

Structural mapping integrated with interpretation and forward modelling of aeromagnetic data form complimentary and powerful tools for regional structural analysis because both techniques focus on architecture and overprinting relationships. This approach is used to constrain the geometry and evolution of the sparsely exposed Mount Woods Inlier in the northern Gawler Craton. The Mount Woods Inlier records a history of poly-phase deformation, high-temperature metamorphism, and syn- and post-orogenic magmatism between ca. 1736 and 1584 Ma. The earliest deformation involved isoclinal folding, and the development of bedding parallel and axial planar gneissic foliation (S₁). This was accompanied by high-temperature, upper amphibolite to granulite facies metamorphism at ca. 1736 Ma. During subsequent north–south shortening (D₂), open to isoclinal south–southeast-oriented F₂ folds developed as the Palaeoproterozoic successions of the inlier were thrust over the Archaean nuclei of the Gawler Craton. The syn-D₂ Engenina Adamellite was emplaced at ca. 1692 Ma. The post-D₂ history involved shear zone development and localised folding, exhumation of metamorphic rocks, and deposition of clastic sediments prior to the emplacement of the ca. 1584 Ma Granite Balta Suite. The Mount Woods Inlier is interpreted as the northern continuation of the Kimban Orogen.     

Attenuated basin‐margin sequence stratigraphy of the Palaeoproterozoic Calvert and Isa Superbasins: The Fickling Group,southern Murphy Inlier,Queensland

Sedimentary rocks of the Palaeoproterozoic Calvert and Isa Superbasins are exposed across a large area of northern Australia. Despite the extent of the exposures there is little to indicate the nature of the basin margins as most outcrop boundaries are structurally or erosionally defined, or the margins, where preserved, are concealed beneath younger basins. The Murphy Inlier, which forms the boundary between the Mt Isa and McArthur Basins, is unique in that on its southern flanks a basin‐margin succession is well‐preserved as the Fickling Group. A detailed sequence‐stratigraphic analysis of outcrop sections and well logs, supplemented by seismic reflection profiles and SHRIMP U–Pb zircon ages, shows that all seven supersequences of the Isa Superbasin and one supersequence from the older Calvert Superbasin are represented in the Fickling Group. Through this high‐resolution sequence‐stratigraphic framework, it is possible to accurately correlate chronostratigraphically equivalent strata from the McNamara Group on the central Lawn Hill Platform to the Fickling Group on the southern Murphy Inlier. Each supersequence thins substantially from the McNamara Group (～11 km thick) to the Fickling Group (<1 km thick). The combined effects of truncation and onlap of sequences over the Murphy Inlier basement high are responsible for the thinning. Major time breaks of up to 25 million years occur between supersequences in the Fickling Group. Erosional hiatuses are often manifested at the base of supersequences as conglomerate beds composed of silicified detritus from older strata. Sequences in the Fickling Group were generally deposited in a proximal basin‐margin setting, while sequences in the McNamara Group were deposited in distal basin depocentres. The proximal depositional setting of Fickling Group sequences reduces the number of thick carbonaceous shale and siltstone intervals, which often host Zn–Pb–Ag and Cu deposits in the McNamara Group. Many host sequences from the McNamara Group are also absent in the Fickling Group due to truncation and onlap pinchout. Consequently, the economic potential of Palaeoproterozoic strata on the southern Murphy Inlier is less than equivalent strata from the central Lawn Hill Platform. Despite this, potential does exist for future discoveries of economic mineral deposits in the Mt Les Siltstone and Walford Dolomite units of the Fickling Group.     

Switching bulk horizontal shortening directions and regional-scale partitioning of deformation during the Isan Orogeny in the Eastern Fold Belt,Mount Isa Inlier,Australia

Prolonged deformation for ca 150 Ma along the Eastern Fold Belt, Mount Isa Inlier, differentially partitioned into three distinct Mesoproterozoic tectonic domains. NW–SE-trending structures dominate the northern domain, whereas E–W- and N–S-trending structures dominate the central and southern domains, respectively.

Changing the direction of bulk horizontal shortening from NE–SW to N–S to E–W shifted the locus of maximum tectono-metamorphic effect. This accounts for the different generations of structures preserved in these three domains. Overprinting relationships and geochronological data reveal a component of deformation partitioning in time as well as space.

Rheological contrasts in the Soldiers Cap Group between a thick interlayered pelitic, psammitic and volcanic units on the one hand, and ca 1686 Ma, competent mafic intrusives and genetically related metasomatic albitite bodies present in its lower part, on the other, enhanced strain localisation during the long-lived Isan Orogeny (ca 1670–1500 Ma).     

Facies analysis and high-resolution sequence stratigraphy of the Lower Eocene shallow marine Ametlla Formation, Spanish Pyrenees

The Lower Eocene Ametlla Formation of the Ager Basin, Spanish Pyrenees, is a rapidly deposited shallow marine unit formed in a setting characterized by syn-sedimentary tectonic activity. Mapping of the formation over a distance of 25 km was conducted according to sequence stratigraphical principles with emphasis on facies analysis. Twelve facies, grouped in five facies associations, have been recognized in the Ametlla Formation. The studied succession records a vertical transition from deltaic systems prograding onto a sediment-starved shelf, via estuarine deposits associated with incised valleys, to sandbar complexes in a tidal seaway. In terms of sequence stratigraphy, three scales of genetic sedimentary units were recognized. (1) At the regional scale, elements of two 3rd-order composite sequences (sensu Exxon) have been recognized. These include a 3rd-order highstand sequence set encompassing the lowermost part of the Ametlla Formation and the underlying Passarella Formation, and a 3rd-order transgressive sequence set that constitutes the middle parts of the Ametlla Formation. The sequence sets are separated by an unconformity with up to 35 m of incision that is interpreted as a major sequence boundary. It is argued that the incised valleys associated with this unconformity were infilled during landward-stepping of the shelfal depositional system. Basinwards, the unconformable surface becomes subhorizontal and is overlain by a 2 m thick oyster bed formed in a sediment-starved setting subsequent to flooding of the incised valleys (which still acted as sediment conduits). Sandstones dominate the transgressive sequence set, whereas the highstand sequence set is dominated by siltstones, particularly in the lower part. In the transgressive sequence set, an upward increase in sand content and calibre is observed, relatable to punctuations of the transgressive trend by high-frequency sea-level fluctuations, and to downslope redistribution of sand. (2) At the subregional scale, detailed mapping indicates the presence of five 4th-order sequences. The 4th-order sequence boundaries are associated with sediment bypassing and minimal erosional relief, and were created by forced regressions during periods of relative sea-level fall. Sharp-based sandstones overlying these unconformities are believed to have accumulated during subsequent rise of relative sea-level. Where 4th-order maximum flooding surfaces can be recognized, the sequences may be subdivided into a sandstone-dominated transgressive systems tract and a siltstone-dominated highstand systems tract. (3) At the local scale, 2–9 5th-order parasequences are present within the 4th-order sequences. Superimposed parasequences are separated by flooding surfaces characterized by bioclastic accumulations, pervasive burrowing and extensive calcite cementation. The parasequences are commonly stacked in a landward-stepping manner.     

The tectonostratigraphic history of the Proterozoic Northern Lawn Hill Platform, Australia: an integrated intracontinental basin analysis

The Northern Lawn Hill Platform (NLHP) comprises an area of approximately 16,000 km² in north-central Australia. Thick packages of Proterozoic strata outcrop in the region, although large areas are also covered by younger strata. The packages contain basin sediments and igneous rocks that span 400 m.y. We present a regional synthesis of approximately 150 m.y. of the tectonostratigraphic history of the area which hosts several world-class base metals deposits. The interpretation is based primarily on a sequence stratigraphic and structural interpretation of seismic data, a common approach in the petroleum resource sector, but rare in analyses of mineral resources. Models of subsurface geology and a basement template are provided using observed geopotential data that are iteratively calibrated with other data. Geochronological, palaeomagnetic, geochemical and sequence stratigraphic investigations on outcrop and drill core also are integrated into the history. The seismic data allow separated outcrop belts to be confidently correlated for the first time. Geochronological data control the basin history delineated by this interpretation. Palaeomagnetic data allow the results presented here to be extrapolated regionally and globally. Although considered to be deposited on entirely intracontinental lithosphere, the basin phases record significant fluctuations in the volume and geometry of accommodation space for sedimentation. Multiple pulses of deformation are recorded by changing depositional geometries. We propose a history of re-activation of a basement template and speculate on geodynamical mechanisms for accommodation space fluctuations and geometric variability. The detailed understanding of the basin evolution of the NLHP gained by integrated basin analysis provides a powerful tool for predictive fluid flow models as an aid to resource exploration. It should also provide a useful analogy in understanding tectonic processes and basin evolution of other similar aged intracontinental basins.     

Local to regional scale structural controls on mineralisation and the importance of a major lineament in the eastern Mount Isa Inlier, Australia: Review and analysis with autocorrelation and weights of evidence

Although major crustal lineaments may play an important role in mineralisation, the relationship between lineaments and mineral deposits can be quite cryptic, and structural controls may vary as a function of scale along lineaments. Major lineaments alone may be of limited use for detailed target generation. The Cloncurry Lineament in the Eastern part of the Mount Isa Inlier is a crustal scale structure defined by potential field-derived ‘worms’. Weights-of-evidence quantifies the association between mineral occurrences and this lineament. Autocorrelation is used to recognise structural controls on mineralisation at different scales, by progressively limiting the lengths of the vectors between mineral occurrence points in the autocorrelation plot. The weights-of-evidence analysis shows that Au, Au–Cu, Cu–Au and Cu deposits have a positive spatial correlation to the Cloncurry Lineament, which suggests it that acted as a primary crustal scale control on the localisation of Cu and Au through focussing mineralisation systems on a broad scale. However, autocorrelation defines a variety of local structural controls, which can be interpreted as shear zones, variably oriented fault sets, en echelon fault arrays, and potentially the orientation of bedding and/or iron formations which localise fluid flow and mineral deposition at finer scales. The results suggest that major lineaments defined by geophysical contrasts can be used in conjunction with techniques of spatial analysis for targeting structurally controlled mineralisation in areas under thin cover adjacent to mineralised terrains such as the Mt Isa Inlier.     

Combining fractal analysis of mineral deposit clustering with weights of evidence to evaluate patterns of mineralization: Application to copper deposits of the Mount Isa Inlier, NW Queensland, Australia

The clustering of mineral occurrences and their spatial associations with particular geological features are critical aspects of mineral distributions for exploration and understanding ore genesis. Variations in the degree of clustering of mineral occurrences or geological features can be measured by fractal dimensions, obtained from a shifting box counting method. Spatial associations between mineral occurrences and geological features can be quantified by the weights of evidence (WofE) method using the contrast value, which increases with the strength of the spatial relationship. A new method is proposed to evaluate mineral occurrence distributions by combining the power of fractal analysis of clustering with the WofE approach. The method compares the correlation between the variation in degree of clustering of mineral occurrences and a geological feature in a study area, with the contrast value of the same feature. The possible outcomes can be simplified into four scenarios, depending on whether the correlation in variation of clustering and the contrast are high or low, respectively. Each outcome has specific exploration implications. If either a high correlation in variation of clustering or a high contrast value is obtained, the geological feature can be used for exploration targeting.The integrated fractal and WofE approach is applied to copper occurrences in the Proterozoic Mount Isa Inlier, NW Queensland, Australia, which hosts large numbers of copper deposits (1,869 occurrences), including the world class Mount Isa copper deposit. Variation in clustering of copper occurrences has a positive correlation with variation in clustering of fault bends (R = 0.823), fault intersections (R = 0.862) and mafic rocks (R = 0.885). WofE results indicate that the copper occurrences are spatially associated with fault intersections and bends and with mafic rocks. Analyses were carried out separately for the two major lithostratigraphic sequences in the Inlier, the Eastern and Western Successions. The Western Succession copper occurrences are apparently more clustered than those of the Eastern Succession, which may reflect a lower degree of exploration and/or geological factors. The association of copper occurrences with mafic rocks compared with fault bends and intersections is greater in the Eastern Succession, which may reflect genetic factors. Correlations in the variation of clustering of mineral occurrences and geological features have a linear relationship with the contrast values, and the spatial association between all geological features and copper occurrences constitute high correlation/high contrast cases. The linear relationship suggests that the geological features that control the clustering of the copper occurrences could be the same features that control their localization.     

Metasomatic albitites and related biotite-rich schists from a low-pressure polymetamorphic terrane, Snake Creek Anticline, Mount Isa Inlier, north-eastern Australia: microstructures and P–T–d paths

Rocks of the Snake Creek Anticline are mainly pelitic schists, psammitic schists and quartzites that were metamorphosed during multiple high‐T/low‐P events extending from D1 to D5, with the metamorphic peak occurring late to post‐D3. Albitites are widespread, but are concentrated in five areas. They are typically fine‐ to medium‐grained, and consist of albite, with or without combinations of quartz, biotite, staurolite, cordierite, garnet, andalusite, sillimanite, kyanite, gedrite and tourmaline. From the presence or absence of albite inclusions in porphyroblasts, the albitites are interpreted as forming early in the D3 event as a result of infiltration of external fluids. Psammitic schists and quartzites were preferentially altered, but pelitic schists were also albitized in localities where the alteration was more extreme, with the replacement of muscovite total and the replacement of quartz and biotite variable. Structural controls on albitization include fracturing and syn‐D3 shear zones in fold hinges. Biotite schists with abundant porphyroblasts (combinations of staurolite, garnet, andalusite and cordierite) occur adjacent to albitites, and it is argued that they formed by the addition of Fe and Mg sourced from the albitites. In several albitite‐rich areas, cordierite grew early in D3 and was partly or entirely replaced during or after D3 by combinations of biotite, andalusite, tourmaline, staurolite and sillimanite. A postulated P–T–d path involved an increase in pressure (with or without a decrease in temperature) subsequent to early D3 albitization, followed by an increase in temperature up to the metamorphic peak (late D3 to early D4. The metamorphism was contemporary in part with the emplacement of the Williams Batholith (c. 1550–1500 Ma), which probably supplied the Na‐rich fluids.     

Two sulphur isotope provinces deduced from ores in the Mount Isa Eastern Succession,Australia

The sulphur isotopic characteristics of ore deposits in the Australian Mount Isa Eastern Succession are not well known, unlike those of the Western Succession. In this study new detailed analyses are provided for recently discovered Eastern Succession mineralisation, such as the Starra and Osborne BIF-hosted Cu-Au ores, the Dugald River sediment-hosted Pb-Zn prospect, and four vein-hosted Cloncurry-style Cu±Au deposits (Hampden, Mt Elliot/Swan, Mt Cobalt, and the Answer Mine). All of the deposits of the Eastern Succession have ³⁴S_sulphide between –8 and +9%., regardless of their genesis. Empirically a moderate (³⁴S range averaging close to 0%. characterises Starra-style Cu-Au and Pegmont Pb-Zn BIF ores, whereas shear and vein-style Cu mineralisation populations are tighter and do not average close to 0%. This is a particularly surprising result for Dugald River, where a larger isotopic variation more typical of stratiform sediment-hosted Pb-Zn ores in the region might have been expected. By comparison, Western Succession stratiform Pb-Zn and vein-style Cu deposits span a huge range of-15 to 51%. Large sulphur isotope ranges typify sulphate evaporite or organic sulphur-rich sedimentary successions. The lack of such variation in the Eastern Succession in turn suggests that primary evaporite sequences there were halite-dominated but sulphate-poor, and/or contained only limited volumes of organic-sulphur-rich sediment. Eastern Succession sequences were therefore less likely hosts for giant stratiform Pb-Zn deposits, because of their paucity of sulphur, although local sulphur sources permitted small deposits such as Dugald River to develop. Sedimentary conditions were more favourable for the development of sulphur-poor synsedimentary hydrothermal systems such as Starra, Osborne, and Pegmont, although sulphur isotope evidence is equivocal about the origin of these. Epigenetic deposits close to the Williams Batholith (Mt Dore, Hampden) owe their clustering around 0%. to their granitic fluid source.     

鹤岗盆地石头河子组高分辨率层序地层与聚煤规律

运用高分辨率层序地层原理,通过岩心和测井资料的综合分析,对鹤岗盆地石头河子组进行了基准面旋回研究,识别出1个长期基准面旋回、5个中期基准面旋回和3种类型的短期基准面旋回。通过对比分析,建立了研究区高分辨率层序地层格架。研究表明,基准面旋回对聚煤演化起着重要的控制作用,在气候和地形条件适宜的情况下,长期基准面上升半旋回晚期和下降半旋回早期为聚煤作用有利时期,厚煤层形成于最大湖泛面附近;此期间持续时间长的中期基准面上升半旋回和较短的中期基准面下降旋回组合,有利于形成厚度大、分布范围广的煤层。研究成果对鹤岗盆地扩大深部煤炭资源勘探提供了依据。     

塔里木盆地克拉通内古隆起的成因机制与构造类型

古隆起是克拉通盆地的重要构造单元。由于盆地边界条件与深部构造背景的变化,古隆起的形成与发育表现为复杂的动力学过程。借助于地震反射剖面与钻探资料,可以刻画不同地质时期古隆起的分布、形态、结构与构造样式,剖析古隆起的成因机制。文中以塔里木盆地为例,对古生代克拉通内古隆起的几何学与运动学特点进行描述,结合周缘大地构造背景的演变,剖析了古隆起的形成机制。在此基础上,将克拉通内古隆起划分为稳定型、活动型、残余型与消亡型4种基本类型。由于运动体制的变革,古隆起经历了形成发育、叠加改造、调整定型与最终埋藏的动力学演变,具有多层叠加的地质结构,并发育断裂带、背斜带、地层剥蚀尖灭带等一系列构造带。古隆起是油气聚集的主要单元,古隆起的动力学演化历史决定了隆起富集油气的关键条件。     

Significance of strain localization and fracturing in relation to hydrothermal mineralization at Mount Isa, Australia

The rheology of layered meta-sedimentary rocks, and their orientation and position relative to major fault systems were the key controls on Proterozoic hydrothermal copper mineralization at Mount Isa, Australia. Compositional layering in the host rock partitioned mechanical behavior and strain, leading to selective permeability generation and the focusing of fluid flow. Shale layers preferentially failed by plastic shearing, whereas meta-siltstones remained elastic or failed in tension depending on magnitude of deformation and fluid pressure. Numerical simulations support the hypothesis that the orientation of layering and the proximity to major fault systems controlled fracturing and permeability increase in the Urquhart shale. The dilating shale provided a pathway for an upward-flowing, reduced basement fluid, from which quartz was precipitated during cooling. During a later event, the reactivation of steep structures provided access to surface derived oxidized metal-bearing brine, causing the precipitation of dolomite followed by chalcopyrite ore in the brecciated silicified shale.