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1.
A basin evolution synthesis and an integration of geological and geophysical data, relevant as guides to the exploration of gold and lead–zinc deposits in the Itajaí Basin, are presented in this paper. The Itajaí Basin is interpreted as a collision-related foreland basin consisting of weakly metamorphosed sediments deposited between the structural front of the Dom Feliciano fold and thrust belt and the proximal flank of the cratonic forebulge. Its sediments represent a second-order depositional sequence deposited during a foreland transgression–regression cycle related to flexural subsidence. After deposition, the basin underwent a main late-collisional compressional deformation phase followed by an extensional post-orogenic relaxation. Known gold and lead–zinc deposits are associated with late-orogenic faulting of the Itajaí Basin sediments. The gold-bearing quartz veins are of filonean hydrothermal affiliation, while the lead–zinc deposits were formed by solution-remobilization in a meteoric–connate–magmatic mineralizing fluid. Major trends of favourability for such deposits are recognized. The most favourable sites for lead–zinc deposits are near known mineralized areas and also along a NE-orientated fault at the margin adjacent to the Dom Feliciano metamorphic belt. The higher favourability for gold deposits is assigned to an area along the same NE trend, and also around a small known deposit near the cratonic margin.  相似文献   

2.
The effectiveness of detrital zircon thermochronology as a means of linking hinterland evolution and continental basin sedimentation studies is assessed by using Mesozoic continental sediments from the poorly understood Khorat Plateau Basin in eastern Thailand. New uranium lead (U‐Pb) and fission‐track (FT) zircon data from the Phu Kradung Formation identify age modes at 141 ± 17 and 210 ± 24 Ma (FT) and 2456 ± 4, 2001 ± 4, 251 ± 3, and 168 ± 2 Ma (U‐Pb), which are closely similar to data from the overlying formations. The FT data record post‐metamorphic cooling, whereas the U‐Pb data record zircon growth events in the hinterland. Comparison is made between detrital zircon U‐Pb data from ancient and modern sources across Southeast Asia. The inherent stability of the zircon U‐Pb system means that 250 Myr of post‐orogenic sedimentary recycling fails to change the regional zircon U‐Pb age signature and this precludes use of the U‐Pb approach alone for providing unique provenance information. Although the U‐Pb zircon results are consistent with (but not uniquely diagnostic of) the Qinling Orogenic Belt as the original source terrane for the Khorat Plateau Basin sediments, the zircon FT cooling data are more useful as they provide the key temporal link between basin and hinterland. The youngest zircon FT modes from the Khorat sequence range between 114 ± 6 (Phra Wihan Formation) and 141 ± 17 Ma (Phu Kradung Formation) that correspond to a Late Jurassic/Early Cretaceous reactivation event, which affected the Qinling Belt and adjacent foreland basins. The mechanism for regional Early Cretaceous erosion is identified as Cretaceous collision between the Lhasa Block and Eurasia. Thus, the Khorat Plateau Basin sediments might have originated from a reactivation event that affected a mature hinterland and not an active orogenic belt as postulated in previous models.  相似文献   

3.
Mineral provinces in southern and central Africa are strongly controlled by major structural trends, the alignment of sedimentary basins and metamorphically induced thermal regimes deep in the crust. Ore deposits are preferentially located on cooler margins of orogenic belts and are ultimately end-products of fluid expulsion out of the deeper parts of orogenic axes. Metamorphic and structural vectors within orogenic belts adjacent to major cratons show a trend of high-grade thermal overprinting in the cores of axes and lower metamorphic regimes acting on the distal margins of orogens (e.g. foreland basins). This apparent pattern is considered to have importance in the expulsion of at least three generations of mineralizing fluids beginning with exhalative migration during diagenesis and culminating much later in thrust-controlled expulsion onto adjacent craton margins. Fluids within the hydrosphere that accumulate initially through topographic gradients in the sediments mixed with components of the mantle (CO2). After storage within the crust, migration, enforced by metamorphic processes, transferred fluids out of, and away from, high thermal regimes in the axes of belts, leading to their present preservation around the margins of the major cratonic nuclei.  相似文献   

4.
Sedimentary basins in the interior of orogenic plateaus can provide unique insights into the early history of plateau evolution and related geodynamic processes. The northern sectors of the Iranian Plateau of the Arabia–Eurasia collision zone offer the unique possibility to study middle–late Miocene terrestrial clastic and volcaniclastic sediments that allow assessing the nascent stages of collisional plateau formation. In particular, these sedimentary archives allow investigating several debated and poorly understood issues associated with the long‐term evolution of the Iranian Plateau, including the regional spatio‐temporal characteristics of sedimentation and deformation and the mechanisms of plateau growth. We document that middle–late Miocene crustal shortening and thickening processes led to the growth of a basement‐cored range (Takab Range Complex) in the interior of the plateau. This triggered the development of a foreland‐basin (Great Pari Basin) to the east between 16.5 and 10.7 Ma. By 10.7 Ma, a fast progradation of conglomerates over the foreland strata occurred, most likely during a decrease in flexural subsidence triggered by rock uplift along an intraforeland basement‐cored range (Mahneshan Range Complex). This was in turn followed by the final incorporation of the foreland deposits into the orogenic system and ensuing compartmentalization of the formerly contiguous foreland into several intermontane basins. Overall, our data suggest that shortening and thickening processes led to the outward and vertical growth of the northern sectors of the Iranian Plateau starting from the middle Miocene. This implies that mantle‐flow processes may have had a limited contribution toward building the Iranian Plateau in NW Iran.  相似文献   

5.
Changes in sediment flux to continental margins are commonly interpreted in terms of tectonic growth of topography or climatic change. Here, we show that variations in sediment yield from orogenic systems, previously considered as resulting from climate change, drainage reorganisation or mantle processes can be explained by intrinsic mechanisms of mountain belt/foreland basin systems naturally evolving during post-orogenic decay. Numerical modelling indicates an increase of sediment flux leaving the orogenic system synchronous with the cessation of deposition in the foreland basin and the transition from late syn- to post-orogenesis. Experiments highlight the importance of lithospheric flexure that causes the post-orogenic isostatic rebound of the foreland basin. Erosion of the rebounding foreland basin combined with continued sediment flux from the thrust wedge drives an acceleration in sediment outflux towards continental margins. Sediment budget records in natural settings such as the Northern Pyrenees or Western European Alps also indicate accelerated post-orogenic sediment delivery to the Bay of Biscay and Rhône Delta respectively. These intrinsic processes that determine sediment yield to continental margins must be accounted for prior to consideration of additional external tectonic or climatic controls.  相似文献   

6.
Evolution of the late Cenozoic Chaco foreland basin, Southern Bolivia   总被引：3，自引：1，他引：3  
Eastward Andean orogenic growth since the late Oligocene led to variable crustal loading, flexural subsidence and foreland basin sedimentation in the Chaco basin. To understand the interaction between Andean tectonics and contemporaneous foreland development, we analyse stratigraphic, sedimentologic and seismic data from the Subandean Belt and the Chaco Basin. The structural features provide a mechanism for transferring zones of deposition, subsidence and uplift. These can be reconstructed based on regional distribution of clastic sequences. Isopach maps, combined with sedimentary architecture analysis, establish systematic thickness variations, facies changes and depositional styles. The foreland basin consists of five stratigraphic successions controlled by Andean orogenic episodes and climate: (1) the foreland basin sequence commences between ～27 and 14 Ma with the regionally unconformable, thin, easterly sourced fluvial Petaca strata. It represents a significant time interval of low sediment accumulation in a forebulge‐backbulge depocentre. (2) The overlying ～14–7 Ma‐old Yecua Formation, deposited in marine, fluvial and lacustrine settings, represents increased subsidence rates from thrust‐belt loading outpacing sedimentation rates. It marks the onset of active deformation and the underfilled stage of the foreland basin in a distal foredeep. (3) The overlying ～7–6 Ma‐old, westerly sourced Tariquia Formation indicates a relatively high accommodation and sediment supply concomitant with the onset of deposition of Andean‐derived sediment in the medial‐foredeep depocentre on a distal fluvial megafan. Progradation of syntectonic, wedge‐shaped, westerly sourced, thickening‐ and coarsening‐upward clastics of the (4) ～6–2.1 Ma‐old Guandacay and (5) ～2.1 Ma‐to‐Recent Emborozú Formations represent the propagation of the deformation front in the present Subandean Zone, thereby indicating selective trapping of coarse sediments in the proximal foredeep and wedge‐top depocentres, respectively. Overall, the late Cenozoic stratigraphic intervals record the easterly propagation of the deformation front and foreland depocentre in response to loading and flexure by the growing Intra‐ and Subandean fold‐and‐thrust belt.  相似文献   

7.
We have constrained the time‐space migration of the Zagros foredeep basin by performing Sr isotope stratigraphy on 31 samples of marine macrofossils from Neogene sediments now exposed in the Zagros mountain belt in southwest Iran. Our results show that these deposits (represented mainly by the Mishan Formation) are strongly diachronous, with ages ranging between 17.2 ± 0.2 and 1.1 ± 0.1 Ma. These deposits are older in the west (Dezful region) and become progressively younger towards the south and the south‐east (Fars region). Our results show that the marine foredeep was replaced by a fluvial sedimentary environment between ca. 14 and 12 Ma in the western sector, while this occurred between ca. 8 and 1 Ma in the eastern sector, becoming younger towards the south. These results enable us to show that the foreland basin migrated perpendicular to the orogen at rates of between 17.5 and 50 mm year?1 throughout the Neogene, exceeding migration rates in the Alps, Pyrenees, Apennines and Himalayan foreland basins. The sporadically elevated rates in the Zagros appear to be related to times when major widely spaced pre‐existing basement faults became reactivated. Finally, our results, when combined with published data, have enabled us to establish a new chronostratigraphic diagram for the Neogene portion of the Zagros foreland basin. Our study highlights that foreland basins are extremely dynamic settings where depocentres and palaeoenvironments may change rapidly in both time and space in relation to migrating deformation.  相似文献   

8.
The Paradox Basin is a large (190 km × 265 km) asymmetric basin that developed along the southwestern flank of the basement‐involved Uncompahgre uplift in Utah and Colorado, USA during the Pennsylvanian–Permian Ancestral Rocky Mountain (ARM) orogenic event. Previously interpreted as a pull‐apart basin, the Paradox Basin more closely resembles intraforeland flexural basins such as those that developed between the basement‐cored uplifts of the Late Cretaceous–Eocene Laramide orogeny in the western interior USA. The shape, subsidence history, facies architecture, and structural relationships of the Uncompahgre–Paradox system are exemplary of typical ‘immobile’ foreland basin systems. Along the southwest‐vergent Uncompahgre thrust, ～5 km of coarse‐grained syntectonic Desmoinesian–Wolfcampian (mid‐Pennsylvanian to early Permian; ～310–260 Ma) sediments were shed from the Uncompahgre uplift by alluvial fans and reworked by aeolian‐modified fluvial megafan deposystems in the proximal Paradox Basin. The coeval rise of an uplift‐parallel barrier ～200 km southwest of the Uncompahgre front restricted reflux from the open ocean south and west of the basin, and promoted deposition of thick evaporite‐shale and biohermal carbonate facies in the medial and distal submarine parts of the basin, respectively. Nearshore carbonate shoal and terrestrial siliciclastic deposystems overtopped the basin during the late stages of subsidence during the Missourian through Wolfcampian (～300–260 Ma) as sediment flux outpaced the rate of generation of accommodation space. Reconstruction of an end‐Permian two‐dimensional basin profile from seismic, borehole, and outcrop data depicts the relationship of these deposystems to the differential accommodation space generated by Pennsylvanian–Permian subsidence, highlighting the similarities between the Paradox basin‐fill and that of other ancient and modern foreland basins. Flexural modeling of the restored basin profile indicates that the Paradox Basin can be described by flexural loading of a fully broken continental crust by a model Uncompahgre uplift and accompanying synorogenic sediments. Other thrust‐bounded basins of the ARM have similar basin profiles and facies architectures to those of the Paradox Basin, suggesting that many ARM basins may share a flexural geodynamic mechanism. Therefore, plate tectonic models that attempt to explain the development of ARM uplifts need to incorporate a mechanism for the widespread generation of flexural basins.  相似文献   

9.
The wedge‐top depozone in the southern Taiwan foreland basin system is confined by the topographic front of the Chaochou Fault to the east and by a submarine deformation front to the west. The Pingtung Plain, Kaoping Shelf and Kaoping Slope constitute the main body of the wedge‐top depozone. In a subaerial setting, the alluvial and fluvial sediments accumulate on top of the frontal parts of the Taiwan orogenic wedge to form the Pingtung Plain proximal to high topographic relief. In a submarine setting, fine‐grained sediments accumulate on the Kaoping Shelf and dominant mass‐wasting sediment forms the Kaoping Slope. Wedge‐top sediments are deformed into a series of west‐vergent imbricated thrusts and folds and associated piggyback basins. A major piggyback basin occurs in the Pingtung Plain. Four smaller piggyback basins appear in the shelf–slope region. Many small‐sized piggyback basins developed over ramp folds in the lower slope region. Pliocene–Quaternary deep marine to fluvial sediments about 5000 m thick have been deposited on top of the frontal orogenic wedge in southern Taiwan. Sedimentary facies shows lateral variations from extremely coarse fluvial conglomerates proximal to the topographic front (Chaochou Fault) to fine‐grained deep marine mud close to the deformation front near the base of the slope. The stratigraphic column indicates that offshore deep‐water mud is gradationally overlain by shallow marine sands and then fluvial deposits. The transverse cross‐section of the wedge‐top depozone in the southern Taiwan is a doubly tapered prism. The northern boundary of the wedge‐top depozone in southern Taiwan is placed along the southern limit of the Western Foothills where the frontal orogenic wedge progressively changes southward to a wedge‐top depozone (Pingtung Plain), reflecting ongoing southward oblique collision between the Luzon Arc and the Chinese margin. The wedge‐top depozone is bounded to the south by the continent–ocean crust boundary. The deep slope west of the Hengchun Ridge can be viewed as an infant wedge‐top depozone, showing initial mountain building and the beginning of wedge‐top depozone.  相似文献   

10.
Apatite fission‐track (AFT) thermochronology and (U‐Th)/He (AHe) dating, combined with paleothermometers and independent geologic constraints, are used to model the thermal history of Devonian Catskill delta wedge strata. The timing and rates of cooling determines the likely post‐orogenic exhumation history of the northern Appalachian Foreland Basin (NAB) in New York and Pennsylvania. AFT ages generally young from west to east, decreasing from ~185 to 120 Ma. AHe single‐grain ages range from ~188 to 116 Ma. Models show that this part of the Appalachian foreland basin experienced a non‐uniform, multi‐stage cooling history. Cooling rates vary over time, ~1–2 °C/Myr in the Early Jurassic to Early Cretaceous, ~0.15–0.25 °C/Myr from the Early Cretaceous to Late Cenozoic, and ~1–2 °C/Myr beginning in the Miocene. Our results from the Mesozoic are broadly consistent with earlier studies, but with the integration of multiple thermochronometers and multi‐kinetic annealing algorithms in newer inverse thermal modeling programs, we constrain a Late Cenozoic increase in cooling which had been previously enigmatic in eastern U.S. low‐temperature thermochronology datasets. Multi‐stage cooling and exhumation of the NAB is driven by post‐orogenic basin inversion and catchment drainage reorganization, in response to changes in base level due to rifting, plus isostatic and dynamic topographic processes modified by flexure over the long (~200 Myr) post‐orogenic period. This study compliments other regional exhumation data‐sets, while constraining the timing of post‐orogenic cooling and exhumation in the NAB and contributing important insights on the post‐orogenic development and inversion of foreland basins along passive margins.  相似文献   

11.
The main Karoo Basin of South Africa is a Late Carboniferous–Middle Jurassic retroarc foreland fill, developed in front of the Cape Fold Belt (CFB) in relation to subduction of the palaeo-Pacific plate underneath the Gondwana plate. The Karoo sedimentary fill corresponds to a first-order sequence, with the basal and top contacts marking profound changes in the tectonic setting, i.e. from extensional to foreland and from foreland to extensional, respectively. Sedimentation within the Karoo Foreland Basin was closely controlled by orogenic cycles of loading and unloading in the CFB. During orogenic loading, episodes of subsidence and increase in accommodation adjacent to the orogen correlate to episodes of uplift and decrease in accommodation away from the thrust-fold belt. During orogenic unloading the reverse occurred. As a consequence, the depocentre of the Karoo Basin alternated between the proximal region, during orogenic loading, and the distal region, during orogenic unloading. Orogenic loading dominated during the Late Carboniferous–Middle Triassic interval, leading to the accumulation of thick foredeep sequences with much thinner forebulge correlatives. The Late Triassic–Middle Jurassic interval was dominated by orogenic unloading, with deposition taking place in the distal region of the foreland system and coeval bypass and reworking of the older foredeep sequences. The out of phase history of base-level changes generated contrasting stratigraphies between the proximal and distal regions of the foreland system separated by a stratigraphic hinge line. The patterns of hinge line migration show the flexural peripheral bulge advancing towards the craton during the Late Carboniferous–Permian interval in response to the progradation of the orogenic front. The orogenward migration of the foreland system recorded during the Triassic–Middle Jurassic may be attributed to piggyback thrusting accompanied by a retrogradation of the centre of weight within the orogenic belt during orogenic loading (Early Middle Triassic) or to the retrogradation of the orogenic load through the erosion of the orogenic front during times of orogenic unloading (Late Triassic–Middle Jurassic).  相似文献   

12.
Evolution of the Himalayan foreland basin, NW India   总被引：3，自引：0，他引：3  
This paper provides new information on the evolution of the Himalayan foreland basin in the under‐reported region of the Kangra and Subathu sub‐basins, NW India. Comparisons are made with the better documented co‐eval sediments of Nepal and Pakistan to build up a broader picture of basin development. In the Subathu sub‐basin, shallow marine sediments of the Palaeocene–lower Lutetian Subathu Formation are unconformably overlain by the continental alluvial Dagshai and Kasauli Formations and Siwalik Group. The start of continental deposition is now dated at younger than 31 Ma from detrital zircon fission track data, thereby defining the duration of this major unconformity, which runs basin‐wide along strike. Final exhumation of these basin sediments, as thrusting propagated into the basin, occurred by 5 Ma constrained from detrital apatite fission track data. In the Kangra sub‐basin, the Subathu Formation is not exposed and the pre‐Siwalik sediments consist of the Dharamsala Group, interpreted as the deposits of transverse‐draining rivers. In this area, there is no evidence of westerly axial drainage as documented for coeval facies in Nepal. Similar to data reported along strike, facies analysis indicates that the sediments in NW India represent the filled/overfilled stages of the classic foreland basin evolutionary model, and the underfilled stage is not represented anywhere along the length of the basin studied to date.  相似文献   

13.
Fission track analyses of detrital components in the Permo-Triassic Karoo Basin (South Africa), highlight the potency of tectono-magmatically driven fluids to penetrate wide and far in foreland basins. The data, together with the data published on Karoo tectonics and magmatism, support a model which requires that fluids were driven north out of the Cape-Karoo orogen during the Cape Orogeny (270–200 Ma). Later fluids were redistributed and aquifers rejuvenated during (and after) the final break-up of Gondwana (<200 Ma). The fission track data indicate that thermal annealing of fission tracks in zircon occurs non-uniformly between individual zircon grains. This model is in agreement with recent models applied to deformed foreland basins and implicates tectonic fluids in U metallogenesis.  相似文献   

14.
Magnetostratigraphy from the Kashi foreland basin along the southern margin of the Tian Shan in Western China defines the chronology of both sedimentation and the structural evolution of this collisional mountain belt. Eleven magnetostratigraphic sections representing ～13 km of basin strata provide a two‐ and three‐dimensional record of continuous deposition since ～18 Ma. The distinctive Xiyu conglomerate makes up the uppermost strata in eight of 11 magnetostratigraphic sections within the foreland and forms a wedge that thins southward. The basal age of the conglomerate varies from 15.5±0.5 Ma at the northernmost part of the foreland, to 8.6±0.1 Ma in the central (medial) part of the foreland and to 1.9±0.2, ～1.04 and 0.7±0.1 Ma along the southern deformation front of the foreland basin. These data indicate the Xiyu conglomerate is highly time‐transgressive and has prograded south since just after the initial uplift of the Kashi Basin Thrust (KBT) at 18.9±3.3 Ma. Southward progradation occurred at an average rate of ～3 mm year?1 between 15.5 and 2 Ma, before accelerating to ～10 mm year?1. Abrupt changes in sediment‐accumulation rates are observed at 16.3 and 13.5 Ma in the northern part of the foreland and are interpreted to correspond to southward stepping deformation. A subtle decrease in the sedimentation rate above the Keketamu anticline is determined at ～4.0 Ma and was synchronous with an increase in sedimentation rate further south above the Atushi Anticline. Magnetostratigraphy also dates growth strata at <4.0, 1.4±0.1 and 1.4±0.2 Ma on the southern flanks the Keketamu, Atushi and Kashi anticlines, respectively. Together, sedimentation rate changes and growth strata indicate stepped migration of deformation into the Kashi foreland at least at 16.3, 13.5, 4.0 and 1.4 Ma. Progressive reconstruction of a seismically controlled cross‐section through the foreland produces total shortening of 13–21 km and migration of the deformation front at 2.1–3.4 mm year?1 between 19 and 13.5 Ma, 1.4–1.6 mm year?1 between 13.5 and 4.0 Ma and 10 mm year?1 since 4.0 Ma. Migration of deformation into the foreland generally causes (1) uplift and reworking of basin‐capping conglomerate, (2) a local decrease of accommodation space above any active structure where uplift occurs, and hence a decrease in sedimentation rate and (3) an increase in accumulation on the margins of the structure due to increased subsidence and/or ponding of sediment behind the growing folds. Since 5–6 Ma, increased sediment‐accumulation (～0.8 mm year?1) and gravel progradation (～10 mm year?1) rates appear linked to higher deformation rates on the Keketamu, Atushi and Kashi anticlines and increased subsidence due to loading from both the Tian Shan and Pamir ranges, and possibly a change in climate causing accelerated erosion. Whereas the rapid (～10 mm year?1) progradation of the Xiyu conglomerate after 4.0 Ma may be promoted by global climate change, its overall progradation since 15.5 Ma is due to the progressive encroachment of deformation into the foreland.  相似文献   

15.
Burgess  & Moresi 《Basin Research》1999,11(4):305-314
Dynamic topography formed over subducting oceanic lithosphere has been proposed as a mechanism to explain certain otherwise anomalous long-wavelength patterns of subsidence inferred from ancient strata. Forward modelling of mantle flow in response to a subducting slab predicts amplitudes and distributions of dynamic topography that may occur due to various subducting slab geometries and histories. Plotting calculated dynamic topographies at a point against time produces tectonic subsidence curves. These subsidence curves show features such as evolution from convex to concave shape, amplitudes up to ~2000 m, subsidence rates up to ~220 m Myr−1, and a general decrease in subsidence amplitude away from the subduction zone, over a distance of ~2000 km. On many convergent continental margins, dynamic topography is likely to be superimposed on other subsidence mechanisms. In back-arc basins, subsidence due to dynamic topography should be distinguishable from that due to extensional tectonics based simply on the temporal subsidence evolution expressed in the subsidence curve shapes. In a foreland basin setting, comparing dynamic topography models with forward models of flexural loading suggest the two processes can generate similar temporal subsidence patterns, but that dynamic topography causes subsidence over significantly greater wavelengths. Matches between calculated subsidence due to dynamic topography and backstripped subsidence patterns from Upper Cretaceous strata of the Western Interior Basin, USA, support the hypothesis that a long-wavelength 'background subsidence' was caused by dynamic topography.  相似文献   

16.
Detrital zircon geochronology of Neoproterozoic to Devonian sedimentary rocks from the Georgina and Amadeus basins has been used to track changes in provenance that reflect the development and inversion of the former Australian Superbasin. Through much of the Neoproterozoic, sediments appear to have been predominantly derived from local sources in the Arunta and Musgrave inliers. Close similarities between the detrital age signatures of late Neoproterozoic sedimentary rocks in the two basins suggests that they were contiguous at this time. A dominant population of 1.2–1.0 Ga zircon in Early Cambrian sediments of the Amadeus Basin reflects the uplift of the Musgrave Inlier during the Petermann Orogeny between 560 and 520 Ma, which shed a large volume of detritus northwards into the Amadeus Basin. Early Cambrian sedimentary rocks in the Georgina Basin have a much smaller proportion of 1.2–1.0 Ga detritus, possibly due to the formation of sub‐basins along the northern margin of the Amadeus Basin which might have acted as a barrier to sediment transfer. An influx of 0.6–0.5 Ga zircon towards the end of the Cambrian coincides with the transgression of the Larapintine Sea across central Australia, possibly as a result of intracratonic rifting. Detrital zircon age spectra of sedimentary rocks deposited within this epicontinental sea are very similar to those of coeval sedimentary rocks from the Pacific Gondwana margin, implying that sediment was transported into central Australia from the eastern continental margin. The remarkably consistent ‘Pacific Gondwana’ signature of Cambro‐Ordovician sediments in central and eastern Australia reflects a distal source, possibly from east Antarctica or the East African Orogen. The peak of the marine incursion into central Australia in the early to mid Ordovician coincides with granulite‐facies metamorphism at mid‐crustal depths between the Amadeus and Georgina basins (the Larapinta Event). The presence of the epicontinental sea, the relative lack of a local basement zircon component in Cambro‐Ordovician sedimentary rocks and their maturity suggest that metamorphism was not accompanied by mountain building, consistent with an extensional or transtensional setting for this tectonism. Sediments deposited at ～435–405 and ～365 Ma during the Alice Springs Orogeny have detrital age signatures similar to those of Cambro‐Ordovician sedimentary rocks, reflecting uplift and reworking of the older succession into narrow foreland basins adjacent to the orogen.  相似文献   

17.
We present the first fission‐track (FT) thermochronology results for the NW Zagros Belt (SW Iran) in order to identify denudation episodes that occurred during the protracted Zagros orogeny. Samples were collected from the two main detrital successions of the NW Zagros foreland basin: the Palaeocene–early Eocene Amiran–Kashkan succession and the Miocene Agha Jari and Bakhtyari Formations. In situ bedrock samples were furthermore collected in the Sanandaj‐Sirjan Zone. Only apatite fission‐track (AFT) data have been successfully obtained, including 26 ages and 11 track‐length distributions. Five families of AFT ages have been documented from analyses of in situ bedrock and detrital samples: pre‐middle Jurassic at ～171 and ～225 Ma, early–late Cretaceous at ～91 Ma, Maastrichtian at ～66 Ma, middle–late Eocene at ～38 Ma and Oligocene–early Miocene at ～22 Ma. The most widespread middle–late Eocene cooling phase, around ～38 Ma, is documented by a predominant grain‐age population in Agha Jari sediments and by cooling ages of a granitic boulder sample. AFT ages document at least three cooling/denudation periods linked to major geodynamic events related to the Zagros orogeny, during the late Cretaceous oceanic obduction event, during the middle and late Eocene and during the early Miocene. Both late Cretaceous and early Miocene orogenic processes produced bending of the Arabian plate and concomitant foreland deposition. Between the two major flexural foreland episodes, the middle–late Eocene phase mostly produced a long‐lasting slow‐ or nondepositional episode in the inner part of the foreland basin, whereas deposition and tectonics migrated to the NE along the Sanandaj‐Sirjan domain and its Gaveh Rud fore‐arc basin. As evidenced in this study, the Zagros orogeny was long‐lived and multi‐episodic, implying that the timing of accretion of the different tectonic domains that form the Zagros Mountains requires cautious interpretation.  相似文献   

18.
A multidisciplinary approach, combining sediment petrographic, palynological and thermochronological techniques, has been used to study the Miocene‐Pliocene sedimentary record of the evolution of the Venezuelan Andes. Samples from the Maracaibo (pro‐wedge) and Barinas (retro‐wedge) foreland basins, proximal to this doubly vergent mountain belt, indicate that fluvial and alluvial‐fan sediments of similar composition were shed to both sides of the Venezuelan Andes. Granitic and gneissic detritus was derived from the core of the mountain belt, whereas sedimentary cover rocks and uplifted foreland basin sediments were recycled from its flanks. Palynological evidence from the Maracaibo and Barinas basins constrains depositional ages of the studied sections from late Miocene to Pliocene. The pollen assemblages from the Maracaibo Basin are indicative of mountain vegetation, implying surface elevations of up to 3500–4000 m in the Venezuelan Andes at this time. Detrital apatite fission‐track (AFT) data were obtained from both stratigraphic sections. In samples from the Maracaibo basin, the youngest AFT grain‐age population has relatively static minimum ages of 5 ± 2 Ma, whereas for the Barinas basin samples AFT minimum ages are 7 ± 2 Ma. With exception of two samples collected from the Eocene Pagüey Formation and from the very base of the Miocene Parángula Formation, no evidence for resetting and track annealing in apatite due to burial heating in the basins was found. This is supported by rock‐eval analyses on organic matter and thermal modelling results. Therefore, for all other samples the detrital AFT ages reflect source area cooling and impose minimum age constraints on sediment deposition. The main phase of surface uplift, topography and relief generation, and erosional exhumation in the Venezuelan Andes occurred during the late Miocene to Pliocene. The Neogene evolution of the Venezuelan Andes bears certain similarities with the evolution of the Eastern Cordillera in Colombia, although they are not driven by exactly the same underlying geodynamic processes. The progressive development of the two mountain belts is seen in the context of collision of the Panama arc with northwestern South America and the closure of the Panama seaway in Miocene times, as well as contemporaneous movement of the Caribbean plate to the east and clock‐wise rotation of the Maracaibo block.  相似文献   

19.
Late early–early middle Miocene (Burdigalian–Langhian) time on the island of Corsica (western Mediterranean) was characterized by a combination of (i) postcollisional structural inversion of the main boundary thrust system between the Alpine orogenic wedge and the foreland, (ii) eustatic sealevel rise and (iii) subsidence related to the development of the Ligurian‐Provençal basin. These processes created the accommodation for a distinctive continental to shallow‐marine sedimentary succession along narrow and elongated basins. Much of these deposits have been eroded and presently only a few scattered outcrop areas remain, most notably at Saint‐Florent and Francardo. The Burdigalian–Langhian sedimentary succession at Saint‐Florent is composed of three distinguishing detrital components: (i) siliciclastic detritus derived from erosion of the nearby Alpine orogenic wedge, (ii) carbonate intrabasinal detritus (bioclasts of shallow‐marine and pelagic organisms), and (iii) siliciclastic detritus derived from Hercynian‐age foreland terraines. The basal deposits (Fium Albino Formation) are fluvial and composed of Alpine‐derived detritus, with subordinate foreland‐derived volcanic detritus. All three detrital components are present in the middle portion of the succession (Torra and Monte Sant'Angelo Formations), which is characterized by thin transitional deposits evolving vertically into fully marine deposits, although the carbonate intrabasinal component is predominant. The Monte Sant'Angelo Formation is characteristically dominated by the deposits of large gravel and sandwaves, possibly the result of current amplification in narrow seaways that developed between the foreland and the tectonically collapsing Alpine orogenic wedge. The laterally equivalent Saint‐Florent conglomerate is composed of clasts derived from the late Permian Cinto volcanic district within the foreland. The uppermost unit (Farinole Formation) is dominated by bioclasts of pelagic organisms. The Saint‐Florent succession was deposited during the last phase of the counterclockwise rotation of the Corsica–Sardinia–Calabria continental block and the resulting development of the Provençal oceanic basin. The succession sits at the paleogeographic boundary between the Alpine orogenic wedge (to the east), its foreland (to the west), and the Ligurian‐Provençal basin (to the northwest). Abrupt compositional changes in the succession resulted from the complex, varying interplay of post‐collisional extensional tectonism, eustacy and competing drainage systems.  相似文献   

20.
Reactivation of intraplate structures and weak zones within the foreland lithosphere disrupt the modelled geometry and pattern of migration of the flexural wave in foreland basins. In the southern Appalachians (USA), the Middle Ordovician unconformity, irregular Middle Ordovician distal foreland deposition and backstepping of Middle–lower Upper Ordovician carbonate strata have been related to migration of the flexural wave. However, integration of stratigraphy, tectonic subsidence history and composition of palinspastically restored distal foreland strata, using a map of subsurface basement structures as reference, allows us to distinguish an early event of inversion from two events of flexural migration. Sections restoring at very short distances outside the boundaries of a former basement graben have the youngest passive‐margin strata preserved beneath Middle Ordovician (～466 Ma) peritidal to deep lagoonal carbonates with gravel‐size chert clasts. In contrast, sections restoring inside the graben record >470 m of truncation of pre‐Middle Ordovician passive‐margin strata, late onset of deposition (～456 Ma), and subaerial features in carbonate and siliciclastic strata. The lacuna geometry and early patterns of distal foreland uplift and carbonate deposition indicate that inversion of a basement graben in response to Middle Ordovician convergence, rather than a migrating or semi‐fixed forebulge, was the primary control on the early evolution of the distal foreland. Drowning of the carbonate platform in more proximal settings, northeastward onset of deposition on upthrown blocks, and thick accumulation of carbonates in downthrown blocks record northwestward and northeastward flexural wave migration at the Middle–Late Ordovician boundary. In early Late Ordovician, the overall shoaling of carbonate and siliciclastic depocentres and the rise of tectonic subsidence curves indicate hinterlandward migration of flexural uplift. Both events of flexural migration were accompanied by influx of volcanic ash and synorogenic sediments.  相似文献   

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