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1.
The Luikonlahti Cu-Co-Zn sulphide ore deposit is hosted by metasediments associated with serpentinites in the 1.97 Ga old Outokumpu assemblage in the Svecokarelides of eastern Finland. Polyphase deformation of the host rocks, a history shared by the ore body, includes a phase of sheath fold propagation. A modified vergence rule, utilizing only the intersection geometry of planar fabric elements, permits recognition of these extremely curvilinear folds in poorly exposed terrain. The detailed geometry of these rocks is independently resolved from borehole and underground stope records. Sheath fold propagation occurred during D2, the second phase of regional deformation. In the Kaavi district D2 major structures are either thrusts or thrust-related. The Luikonlahti sheaths are located in a steeply dipping shear zone formed during this deformation episode.  相似文献   

2.
Blasband  B.  Brooijmans  P.  Dirks  P.  Visser  W.  White  S. 《Geologie en Mijnbouw》1997,76(3):247-266
In the late Precambrian history of the Wadi Kid area in the Sinai, Egypt, two deformation phases are clearly recognized. The first phase, D1 (pre-620 Ma), produced a steep regional foliation, axial planar to upright F1 folds, in rocks of a lower-greenschist grade. This compressional phase of deformation is interpreted in terms of subduction in an island-arc setting. The second phase, D1 (post-620 Ma), is mainly expressed by the widespread development of sub-horizontal mylonitic zones with a total thickness of 1.5 km. Shear sense indicators give a consistent regional transport direction to the northwest, with local indications of reversal to the southeast. This event is associated with regional LP/HT metamorphism, indicative of high thermal gradients. Because of the LP/HT metamorphism, the change in geochemical nature of the granitoids, and the orientation of the dykes, we interpret the mylonitic zones as low-angle normal shear zones related to core-complex development during an extensional event with the transport reversal being induced by doming. We postulate that orogenic collapse was responsible for the transition from the D1 compressional phase to the D1 extensional phase.  相似文献   

3.
Massif type anorthosites at Bolangir, eastern India are emplaced at the vicinity of the proto-Indian craton—Eastern Ghats Granulite belt contact. Micro- and meso-structural evidences indicate that the emplacement of the anorthosite pluton and the adjoining granitoids was syn-tectonic with respect to the D3 deformation phase (950–1,000 Ma) in the host gneiss. Anisotropy of magnetic susceptibility confirms that magnetic fabrics within anorthosite were dominantly developed during D3 deformation. Emplacement of felsic melts in the N-S trending dilatant shear zones in the granitoids, Fe-Ti-Zr-REE rich melt bands along N-S trending shear zones and localized N-S magnetic foliation in anorthosite near the Fe-Ti-Zr-REE rich melt bands indicate change in the stress field from NNW-SSE (D3) to E-W (D4). Available geochronological and paleogeographic data coupled with the structural analyses of the intrusive and the host gneiss indicate that the emplacement of massif type anorthosite in the EGP is not related to the accretion of Eastern Ghats Granulite Belt over proto-Indian continent during late Neoproterozoic.  相似文献   

4.
Gold mineralisation in classic Australian slate belt gold deposits at Ballarat, Bendigo, St. Arnaud and Inglewood occurred very late in the orogenic history of these rocks rather than during formation of the main slaty cleavage. This has been revealed through the examination of microstructural relationships in gold-bearing quartz veins and their host rocks from these deposits, which has established a D1 to D4 deformation-stage history and consistent timing for gold mineralisation over a wide area. The gold was deposited synorogenically but during the fourth deformation stage (D4) of the orogeny, a relatively weak event occurring two deformations after the main slaty cleavage producing event, D2. Previously, D2 had been regarded as both the source and control of gold mineralisation as most of the quartz veins that occur in these deposits formed before or during this deformation event. However, most gold is hosted in breccia veins that formed during D4. The wallrock clasts within these breccia veins contain a young rotated foliation and the breccia veins are spatially associated with a paragenetically consistent alteration of the host rocks in the deposits. This alteration both crosscuts and preferentially mineralises wallrock S4 allowing the timing of the breccia veins, alteration and gold deposition to be defined as syn-D4 in age.  相似文献   

5.
Detailed field-structural mapping of Neoproterozoic basement rocks exposed in the Wadi Yiba area, southern Arabian Shield, Saudi Arabia illustrates an important episode of late Neoproterozoic transpression in the southern part of the Arabian-Nubian Shield (ANS). This area is dominated by five main basement lithologies: gneisses, metavolcanics, Ablah Group (meta-clastic and marble units) and syn- and post-tectonic granitoids. These rocks were affected by three phases of deformation (D1–D3). D1 formed tight to isoclinal and intrafolial folds (F1), penetrative foliation (S1), and mineral lineation (L1), which resulted from early E-W (to ENE-WSW) shortening. D2 deformation overprinted D1 structures and was dominated by transpression and top-to-the-W (?WSW) thrusting as shortening progressed. Stretching lineation trajectories, S-C foliations, asymmetric shear fabrics and related mylonitic foliation, and flat-ramp and duplex geometries further indicate the inferred transport direction. The N- to NNW-orientation of both “in-sequence piggy-back thrusts” and axial planes of minor and major F2 thrust-related overturned folds also indicates the same D2 compressional stress trajectories. The Wadi Yiba Shear Zone (WYSZ) formed during D2 deformation. It is one of several N-S trending brittle-ductile Late Neoproterozoic shear zones in the southern part of the ANS. Shear sense indicators reveal that shearing during D2 regional-scale transpression was dextral and is consistent with the mega-scale sigmoidal patterns recognized on Landsat images. The shearing led to the formation of the WYSZ and consequent F2 shear zone-related folds, as well as other unmappable shear zones in the deformed rocks. Emplacement of the syn-tectonic granitoids is likely to have occurred during D2 transpression and occupied space created during thrust propagation. D1 and D2 structures are locally overprinted by mesoscopic- to macroscopic-scale D3 structures (F3 folds, and L3 crenulation lineations and kink bands). F3 folds are frequently open and have steep to subvertical axial planes and axes that plunge ENE to ESE. This deformation may reflect progressive convergence between East and West Gondwana.  相似文献   

6.
The metasedimentary rocks of the area around Mangpu constitute a portion of the hinge zone of the northern limb of the major synform of Lower Darjeeling Himalaya. The rocks display evidences of multiple deformation and at least three major phases of deformation have been recognized. The time relations between the phases of deformation (D1, D2, D3) and metamorphic crystallization reveal a single major prograde metamorphic event that initiated with the D1 deformation and finally outlasted it. The earlier phase of this metamorphism is essentially regional syn-tectonic lowgrade (greenschist facies) which may be designated (M1, early). This was followed by regional static metamorphism (M1, late) in the post-tectonic phase between D1 and D2 deformations (upper green schist and amphibolite facies). This M1 metamorphism is superposed by later retrogressive metamorphism (M2) during the D2 and D3 deformations (lower greenschist facies). Within the study area four isograds have been delineated by the first appearance of index minerals in the pelitic schists and gneiss which display Barrovian type of metamorphism.  相似文献   

7.
The Hutti gold mine is located in a high-angle, NNW–SSE-trending shear zone system, which hosts nine discrete auriferous shear zones (reefs). On a clockwise, retrograde PT path two separate stages of deformation/metamorphism (D2/M2 and D3/M3) occurred synchronous with two distinct stages of gold mineralization, both of which were associated with different fluid types. Stage 1 mineralization developed during D2/M2, where the amphibolite host rocks were altered by a metamorphic fluid with a $ {{\delta }^{{18}}}{{O}_{{{{H}_2}O}}} $ of 7.5–10.1?‰, rich in K, S, As, and Au at pressure and temperature conditions of around 3 kbar and 530?+?20/?30°C, respectively. The stage 1 auriferous shear zones are enveloped by a zoned alteration consisting of a distal biotite–chlorite and proximal biotite–plagioclase assemblage. Subsequently, D2/M2 was overprinted by D3/M3 deformation and metamorphism at 300–400°C and <2 kbar that formed the stage 2 mineralization. The stage 2 mineralizing fluid which originated from outside the greenstone belt (δ18Ofluid of 3.2–6.8?‰) was rich in Si, Au, and W. This mineralization stage is distinct by the emplacement of laminated quartz veins central to the shear zone, containing locally visible gold at concentrations of up to 1 kg Au/t. The laminated quartz veins are surrounded by a millimeter-scale chlorite2–K-feldspar alteration halo, which replaced the stage 1 biotite–plagioclase assemblage. The oxygen isotopic composition of the stage 2 fluid suggests a mixture of a magmatic fluid with an oxygen isotopic composition in the range of 6 to 10?‰ and an isotopically light formation fluid that resulted from fluid–rock interaction in the greenstone pile. The two fluid fluxes at stages 1 and 2 both contributed to the overall gold mineralization; however, it was the second fluid pulse, which gave the Hutti mine its status as the largest gold mine in India. The metamorphic evolution was thereby important for the first stage, whereas the second stage was controlled by tectonism and intrusion of the high-heat production Yellagatti granite that re-established the fluid plumbing and mineralizing system.  相似文献   

8.
Large-scale structures, textures and mineral assemblages in the Precambrian rocks of the Banded Gneissic Complex and the overlying Delhi Group in north-central Aravalli Mountain reveal a complex deformational-crystallization history. In the basement Gneissic Complex at least three deformational events, D0, D1 and D2, and two separate episodes of metamorphism, M1 and M2, are recognized. The supracrustal Delhi Rocks display only two phases of deformation, D1 and D2, associated with a single protracted period of metamorphism, M2.The first phase of deformation (D1) of the Delhi orogeny (1650-900 m.y.) produced large isoclinal folds that are overturned towards the southeast and have gentle plunges in NE and SW directions. The second phase of deformation (D2) gave rise to tight open folds on the limbs and axial-plane surfaces of the D1 folds. These folds generally plunge towards the N and NNW at 30°–80°. In the Basement Complex one more deformation (D0) of the Pre-Delhi orogeny (> 2000 m.y.) is recorded by the presence of reclined and recumbent folds with W to WNW trending fold axes. The D0 folds were superimposed by D1 and D2 folds during the Delhi orogeny.The three deformational events have been correlated with the crystallization periods of minerals in the rocks and a setting in time is established for this part of the Aravalli range.  相似文献   

9.
In Kameng Valley of Arunachal Pradesh, the crystalline rocks of Se La Group of Higher Himalaya are thrust over the Lesser Himalayan rocks of Dirang Formation, Bomdila Group along the Main Central Thrust and exhibit well preserved structures on macro- to microscopic scales. Detailed analysis of structures reveals that the rocks of the area have suffered four phases of deformation D1, D2, D3 and D4. These structures have been grouped into (i) early structures (ii) structures related to progressive ductile thrusting and (iii) late structures. The early structures which developed before thrusting formed during D1 and D2 phases of deformation, synchronous to F1 and F2 phases of folding respectively. The structures related to progressive ductile shearing developed during D3 phase of deformation, when the emplacement of the crystalline rocks took place over the rocks of Dirang Formation along the Main Central Thrust. Different asymmetric structures/kinematic indicators developed during this ductile/brittle-ductile regime suggest top-to-SSW sense of movement of the crystalline rocks of the area. D4 is attributed to brittle deformation. Based on satellite data two new thrusts, i.e. Tawang and Se La thrusts have been identified parallel to Main Central Thrust, which are suggestive of imbricate thrusting. Strain analysis from the quartz grains of the gneissic rocks reveals constriction type of strain ellipsoid where k value is higher near the MCT, gradually decreases towards the north. Further, the dynamic analysis carried out on the mesoscopic ductile and brittle-ductile shear zones suggest a NNE-SSW horizontal compression corresponding to the direction of northward movement of Indian Plate.  相似文献   

10.
The ore deposits of The Granites goldfield are shear-hosted within Palaeoproterozoic amphibolite facies metasedimentary rocks in the Tanami Region, Northern Territory, Australia. The ore bodies are located within a 5- to 35-m thick sequence of steeply dipping unit of metamorphosed iron-rich metasedimentary rocks. Deformation at The Granites was complex and is characterized by five successive deformation phases (D1–5). Shear veins (central and oblique) are the dominant type of vein geometry, with minor development of extensional veins and reverse-fault related veins. Four generations of syn-tectonic veins, corresponding to D1, D3, D4, and D5, have been recognized and are comprised of quartz, quartz-carbonate, calc-silicate, and calcite. In addition, two generations of disseminated sulfide–arsenide mineralization, dominated by pyrrhotite, arsenopyrite, and loellingite, with minor pyrite, chalcopyrite and rare marcasite, formed syn-D1 and syn- to post-D3. Textural and structural evidence indicates deposition of gold was contemporaneous with the syn-D1 veins and sulfide–arsenide mineralization. Four hydrothermal phases are proposed for the formation of the veins and disseminated sulfide–arsenide assemblages. The first phase (D1) was responsible for transport and deposition of the majority of the gold. Minor remobilization and deposition of gold occurred during the D3 and D4 phases. Little is known about the nature of the D1 ore fluid, although a relatively low sulfur content is indicated by the assemblage pyrrhotite–arsenopyrite–loellingite+rare pyrite. The growth of amphibolite facies metamorphic minerals andalusite and almandine garnet during D1 indicates a high temperature for the fluid. The D3 hydrothermal phase coincided with peak metamorphism. D4 fluids were hypersaline, high temperature, CO2-poor, and H2S-poor. Editorial handling: L. Meinert  相似文献   

11.
The Paleoproterozoic Liaohe assemblage and associated Liaoji granitoids represent the youngest basement in the Eastern Block of the North China Craton. Various structural elements and metamorphic reaction relations indicate that the Liaohe assemblage has experienced three distinct deformational events (D1 to D3) and four episodes of metamorphism (M1 to M4). The earliest greenschist facies event (M1) is recognized in undeformed or weakly deformed domains wrapped by the S1 schistosity, suggesting that M1 occurred before D1. The D1 deformation produced small, mostly meter-scale, isoclinal and recumbent folds (F1), an associated penetrative axial planar schistosity (S1), a mineral stretching lineation (L1) and regional-scale ductile shear zones. Concurrent with D1 was M2 metamorphism, which occurred before D2 and produced low- to medium-pressure amphibolite facies assemblages. Regionally divergent motion senses reflected by the asymmetric F1 folds and other sense-of-shear indicators, together with the radial distribution of the L1 lineation surrounding the Liaoji granitoids, imply that D1 represents an extensional event. The D2 deformation produced open to tight F2 folds of varying scales, S2 axial crenulation cleavages and ENE-NE-striking thrust faults, involving broadly NW–SE compression. Following D2 was M3 metamorphism that led to the formation of sillimanite and cordierite in low-pressure type rocks and kyanite in medium-pressure rocks. The last deformational event (D3) formed NW-WNW-trending folds (F3), axial planar kink bands, spaced cleavages (S3), and strike–slip and thrust faults, which deflect the earlier D1 and D2 structures. D3 occurred at a shallow crustal level and was associated with, or followed by, a greenschist facies retrograde metamorphic event (M4).The Liaohe assemblage and associated Liaoji granitoids are considered to have formed in a Paleoproterozoic rift, the late spreading of which led to the occurrence of the early extensional deformation (D1) and the M1 and M2 metamorphism, and the final closing of which was associated with the D2 and D3 phases of deformation and M3 and M4 metamorphism.  相似文献   

12.
The New Consort Gold Mine in the Palaeo- to Mesoarchaean Barberton greenstone belt, South Africa is one of the oldest recognized orogenic gold deposits on Earth. The gold mineralization is hosted by discrete mylonitic units that occur at, or close to, the contact between the mafic and ultramafic volcanic rocks of the c. 3,280 Ma Onverwacht Group and the mainly metasedimentary rocks of the overlying c. 3,260–3,230 Ma Fig Tree Group. This contact, locally referred to as the Consort Bar, formed during ductile D1 imbrication of the metavolcanosedimentary sequence and predates the main stage of the gold mineralization. The imbricate stack is situated in the immediate hanging wall of the basal granitoid–greenstone contact along the northern margin of the greenstone belt. It is characterized by a condensed metamorphic profile in which the metamorphic grade increases from upper greenschist facies conditions (510–530°C, 4 kbar) in rocks of the Fig Tree Group to upper amphibolite facies grades (600–700°C, 6–8 kbar) in the basal Onverwacht Group. Detailed structural and petrological investigations indicate that the Consort Bar represents a major structural break, which is largely responsible for the telescoping of metamorphic isograds within the structural sequence. Two stages of mineralization can be distinguished. Loellingite, pyrrhotite, and a calc–silicate alteration assemblage characterize an early high-T mineralization event, which is restricted to upper amphibolite facies rocks of the Onverwacht Group. This early mineralization may correlate with the local D1 deformation. The second and main stage of gold mineralization was associated with renewed ductile shearing during D2. The D2 deformation resulted in the reactivation of earlier structures, and the formation of a NNW trending, steeply dipping shear zone system, the Shires Shear Zone, which separates two regional SE plunging D1 synclines. The mineralized shear zones are intruded by abundant syn-kinematic pegmatite dykes that have previously been dated at c. 3040 Ma. Petrological and geothermobarometric data on ore and alteration assemblages indicate that the main stage of gold mineralization, which affected a crustal profile of ca. 1.5 km, was characterized by increasing temperatures (c. 520 to 600°C) with increasing structural depth. Sulfide assemblages in the ore bodies change progressively with metamorphic grade, ranging from arsenopyrite + pyrite + pyrrhotite in the structurally highest to arsenopyrite + pyrrhotite + chalcopyrite + loellingite in the structurally deepest part of the mine. The main stage of gold mineralization was broadly syn-peak metamorphic with respect to the Fig Tree Group, but postdates the peak of metamorphism in upper amphibolite facies rocks of the structurally underlying Onverwacht Group. This indicates that the mineralization coincided with the juxtaposition of the two units. As the footwall rocks were already on their retrograde path, metamorphic devolatilisation reactions within the greenstone sequence can be ruled out as the source of the mineralizing fluids.  相似文献   

13.
The Bardoc Tectonic Zone (BTZ) of the late Archaean Eastern Goldfields Province, Yilgarn Craton, Western Australia, is physically linked along strike to the Boulder-Lefroy Shear Zone (BLSZ), one of the richest orogenic gold shear systems in the world. However, gold production in the BTZ has only been one order of magnitude smaller than that of the BLSZ (∼100 t Au vs >1,500 t Au). The reasons for this difference can be found in the relative timing, distribution and style(s) of deformation that controlled gold deposition in the two shear systems. Deformation within the BTZ was relatively simple and is associated with tight to iso-clinal folding and reverse to transpressive shear zones over a <12-km-wide area of high straining, where lithological contacts have been rotated towards the plane of maximum shortening. These structures control gold mineralisation and also correspond to the second major shortening phase of the province (D2). In contrast, shearing within the BLSZ is concentrated to narrow shear zones (<2 km wide) cutting through rocks at a range of orientations that underwent more complex dip- and strike-slip deformation, possibly developed throughout the different deformation phases recorded in the region (D1–D4). Independent of other physico-chemical factors, these differences provided for effective fluid localisation to host units with greater competency contrasts during a prolonged mineralisation process in the BLSZ as compared to the more simple structural history of the BTZ.  相似文献   

14.
The NE to ENE trending Mesozoic Xingcheng-Taili ductile shear zone of the northeastern North China Craton was shaped by three phases of deformation. Deformation phase D1 is characterized by a steep, generally E–W striking gneissosity. It was then overprinted by deformation phase D2 with NE-sinistral shear with K-feldspar porphyroclasts forming a subhorizontal low-angle stretching lineation on a steep foliation. During deformation phase D3, lateral motion accommodated by ENE sinistral strike-slip shear zones dominated. Associated fabrics developed at upper greenschist metamorphic facies conditions and show the deformation characteristics of middle- to shallow crustal levels. In some parts, the older structures have been in turn overprinted by late-stage sinistral D3 shearing. Finite strain and kinematic vorticity in all deformed granitic rocks indicate a prolate ellipsoid (L-S tectonites) near plane strain. Simple shear-dominated general shear during D3 deformation is probably of general significance. The quartz c-axis textures indicate prism-gliding with a dominant rhomb <a> slip and basal <a> slip system formed mainly at low-middle temperatures. Mineral deformation behavior, quartz c-axis textures, quartz grain size and the Kruhl thermometer demonstrate that the ductile shear zone developed under greenschist facies metamorphic conditions at deformation temperatures ranging from 400 to 500 °C. Dislocation creep is the main deformation mechanism at a shallow crustal level. Fractal analysis showed that the boundaries of recrystallized quartz grains had statistically self-similarities. Differential stresses deduced from dynamically recrystallized quartz grain size are at around 20–39 MPa, and strain rates in the order of 10−12 to 10−14 s−1. This indicates deformation of granitic rocks in the Xingcheng-Taili ductile shear zone at low strain rates, which is consistent with most other ductile shear zones. Hornblende-plagioclase thermometer and white mica barometer indicate metamorphic conditions of medium pressures at around ca. 3–5 kbar and temperatures of 400–500 °C within greenschist facies conditions. The main D3 deformation of the ENE-trending sinistral strike-slip ductile shearing is related to the roll-back of the subducting Pacific plate beneath the North China Craton.  相似文献   

15.
Granite plutons of the Whypalla Supersuite in the Butchers Hill — Helenvale region of north Queensland were intruded into the upper crust of the Hodgkinson Formation during contractional deformation associated with the Permian‐Triassic Hunter‐Bowen Orogeny. A four‐stage structural history has been resolved for the area, with fabric overprinting relationships, porphyroblast‐matrix microstructural geometries and isotopic ages being consistent with granite emplacement during D4 shortening at ca 274 Ma. Microstructural relationships suggest the possibility of a minor syn‐D3 phase of granite emplacement. The deformation‐emplacement history of the Butchers Hill — Helenvale area is consistent with that recognised regionally for the Hodgkinson Province, indicating province‐wide synchronous syntectonic granite intrusion during a major phase of contractional deformation. Intense syn‐emplacement deformation partitioning was ongoing in the country rocks during progressive D4 and was associated with upward translation of country rock from the microscale to the macroscale along D4 cleavages and shears. Kinematic indicators show that this progressive uplift, at the scale of the area examined, was east‐side‐up.  相似文献   

16.
Polyphase deformation and metamorphism of pelitic schists of Chorbaoli Formation of Sausar Group in and around Ramtek area, Nagpur district, Maharashtra, India has led to the development of garnet and sataurolite porphyroblasts in a predominantly quartz-mica matrix. Microstructural study of oriented thin sections of these rocks shows that garnet and staurolite have different growth histories and these porphyroblasts share a complex relationship with the matrix. Garnet shows at least two phases of growth — first intertectonic between D1 and D2 (pre-D2 phase) and then syn-tectonic to post-tectonic with respect to D2 deformation. Growth of later phase of garnet on the earlier (pre-D2) garnet grains has led to the discordance of quartz inclusion trails between core and rim portion of the same garnet grain. Staurolite develops only syn-D2 and shows close association with garnet of the later phase. The peak metamorphic temperature thus coincided with D2 deformation, which developed the dominant crenulation schistosity (S2), regionally persistent in the terrain. The metamorphic grade reached up to middle amphibolite facies in the study area, which is higher than the adjoining southern parts of Sausar Fold Belt.  相似文献   

17.
《Geodinamica Acta》2001,14(6):345-360
In the southeastern Ötztal basement remnants of eo-Alpine high-pressure metamorphism as well as deformation related to the emplacement of these eclogites are preserved. The eo-Alpine age of the two main ductile deformation phases is constrained by Ar-Ar and Rb-Sr mica cooling ages of about 80 Ma, providing a lower, and by deformed Permo-Mesozoic rocks, providing an upper time limit. While high-pressure minerals (M1) are aligned along structures of the first deformation phase (D1), subsequently grown amphibolite facies minerals (M2) are late- to post-kinematic with respect to the third phase (D3). D1 is characterized by non-coaxial deformation producing an E-W oriented stretching lineation, the younger phases D2 and D3 by folding, where the older set of folds strikes N-S, the younger one E-W. These results imply a basic change of tectonic movement direction during the eo-Alpine event. Structural and petrological evidences favour a two-stage exhumation model, where tectonic exhumation (D1, D2 and D3) is correlated with the first stage, statically overprinted under amphibolite facies conditions (M2). As there is no evidence of significant deformation after this stage, erosion and surface uplift most probably represent the relevant processes for the last part of the exhumation path. During this stage the high-pressure rocks were exhumed from amphibolite facies conditions to the surface.  相似文献   

18.
The Skellefte district in northern Sweden is host to abundant volcanogenic massive sulphide (VMS) deposits comprising pyritic, massive, semi-massive and disseminated Zn–Cu–Au ± Pb ores surrounded by disseminated pyrite and with or without stockwork mineralisation. The VMS deposits are associated with Palaeoproterozoic upper crustal extension (D1) that resulted in the development of normal faults and related transfer faults. The VMS ores formed as sub-seafloor replacement in both felsic volcaniclastic and sedimentary rocks and partly as exhalative deposits within the uppermost part of the volcanic stratigraphy. Subsequently, the district was subjected to deformation (D2) during crustal shortening. Comparing the distribution of VMS deposits with the regional fault pattern reveals a close spatial relationship of VMS deposits to the faults that formed during crustal extension (D1) utilising the syn-extensional faults as fluid conduits. Analysing the shape and orientation of VMS ore bodies shows how their deformation pattern mimics those of the hosting structures and results from the overprinting D2 deformation. Furthermore, regional structural transitions are imitated in the deformation patterns of the ore bodies. Plotting the aspect ratios of VMS ore bodies and the comparison with undeformed equivalents in the Hokuroko district, Japan allow an estimation of apparent strain and show correlation with the D2 deformation intensity of the certain structural domains. A comparison of the size of VMS deposits with their location shows that the smallest deposits are not related to known high-strain zones and the largest deposits are associated with regional-scale high-strain zones. The comparison of distribution and size with the pattern of high-strain zones provides an important tool for regional-scale mineral exploration in the Skellefte district, whereas the analysis of ore body shape and orientation can aid near-mine exploration activities.  相似文献   

19.
《Gondwana Research》2014,26(4):1599-1613
The map-view structure of the southern New England Orogen in the eastern Gondwanan margin is characterised by four tight orogenic-scale curvatures: Texas, Coffs-Harbour, Manning and Nambucca oroclines. Here we focus on the geometry of the Manning Orocline and examine whether the inner-arc area of the oroclinal structure is expressed within the accretionary wedge rocks of the Tablelands Complex. Our observations from the Tablelands Complex (Armidale–Walcha area) show that rocks were subjected to penetrative deformation (D1), which resulted in a regional slaty cleavage (S1) and related isoclinal folds. This was followed by subsequent deformation (D2) associated with minor gentle folds. In a larger scale, the steeply dipping S1 structural fabric shows a continuous map-view curvature, thus defining a macroscopic fold structure. We interpret this macroscopic fold as the expression of the Manning Orocline within the accretionary wedge complex. This interpretation is consistent with the contorted spatial distribution of other tectonic elements (serpentinite belt, forearc basin terranes and early Permian granitoids), which independently define the structure of the Manning Orocline. Our new structural data support the existence of the Manning Orocline and the quadruple oroclinal geometry of the whole southern New England Orogen. The origin of these oroclines is attributed to multiple stages of bending, possibly associated with an earlier phase of curvature during slab rollback (in the early Permian), followed by a subsequent (middle-late Permian) episode of contractional deformation that tightened the oroclinal structure.  相似文献   

20.
The crystallines in the Kumaon Himalaya, India are studied along Goriganga, Darma and Kaliganga valleys and found to be composed of two high-grade metamorphic gneiss sheets i.e. the Higher Himalayan Crystalline (HHC) and Lesser Himalayan Crystalline (LHC) zones. These were tectonically extruded as a consequence of the southward directed propagation of crustal deformation in the Indian plate margin. The HHC and its cover rocks i.e. the Tethyan Sedimentary Zone (TSZ) are exposed through tectonic zones within the hinterland of Kumaon Himalaya. The HHC records history of at least one episode of pre-Himalayan deformation (D1), three episodes of Himalayan deformation (D2, D3, D4). The rocks of the HHC in Kumaon Himalaya are thoroughly transposed by D2 deformation into NW-SE trending Sm (S1+S2). The extent of transposition and a well-developed NE-plunging L2 lineation indicate intense strain during D2 throughout the studied portion of the HHC. Ductile flow continued, resulting in rotation of F1 and F2 folds due NE-direction and NW-SE plunging F3 folds within the HHC. The over thickened crystalline was finally, superimposed by late-to-post collisional brittle-ductile deformation (D4) and exposed the rocks to rapid erosion.  相似文献   

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