Metallogeny and tectonic development of the Tasman Fold Belt System in Queensland

The northern part of the Tasman Fold Belt System in Queensland comprises three segments, the Thomson, Hodgkinson- Broken River, and New England Fold Belts. The evolution of each fold belt can be traced through pre-cratonic (orogenic), transitional, and cratonic stages. The different timing of these stages within each fold belt indicates differing tectonic histories, although connecting links can be recognised between them from Late Devonian time onward. In general, orogenesis became younger from west to east towards the present continental margin. The most recent folding, confined to the New England Fold Belt, was of Early to mid-Cretaceous age. It is considered that this eastward migration of orogenic activity may reflect progressive continental accretion, although the total amount of accretion since the inception of the Tasman Fold Belt System in Cambrian time is uncertain.The Thomson Fold Belt is largely concealed beneath late Palaeozoic and Mesozoic intracratonic basin sediments. In addition, the age of the more highly deformed and metamorphosed rocks exposed in the northeast is unknown, being either Precambrian or early Palaeozoic. Therefore, the tectonic evolution of this fold belt must remain very speculative. In its early stages (Precambrian or early Palaeozoic), the Thomson Fold Belt was probably a rifted continental margin adjacent to the Early to Middle Proterozoic craton to the west and north. The presence of calc-alkaline volcanics of Late Cambrian Early Ordovician and Early-Middle Devonian age suggests that the fold belt evolved to a convergent Pacific-type continental margin. The tectonic setting of the pre-cratonic (orogenic) stage of the Hodgkinson—Broken River Fold Belt is also uncertain. Most of this fold belt consists of strongly deformed, flysch-type sediments of Silurian-Devonian age. Forearc, back-arc and rifted margin settings have all been proposed for these deposits. The transitional stage of the Hodgkinson—Broken River Fold Belt was characterised by eruption of extensive silicic continental volcanics, mainly ignimbrites, and intrusion of comagmatic granitoids in Late Carboniferous Early Permian time. An Andean-type continental margin model, with calc-alkaline volcanics erupted above a west-dipping subduction zone, has been suggested for this period. The tectonic history of the New England Fold Belt is believed to be relatively well understood. It was the site of extensive and repeated eruption of calc-alkaline volcanics from Late Silurian to Early Cretaceous time. The oldest rocks may have formed in a volcanic island arc. From the Late Devonian, the fold belt was a convergent continental margin above a west-dipping subduction zone. For Late Devonian- Early Carboniferous time, parallel belts representing continental margin volcanic arc, forearc basin, and subduction complex can be recognised.A great variety of mineral deposits, ranging in age from Late Cambrian-Early Ordovician and possibly even Precambrian to Early Cretaceous, is present in the exposed rocks of the Tasman Fold Belt System in Queensland. Volcanogenic massive sulphides and slate belt-type gold-bearing quartz veins are the most important deposits formed in the pre-cratonic (orogenic) stage of all three fold belts. The voicanogenic massive sulphides include classic Kuroko-type orebodies associated with silicic volcanics, such as those at Thalanga (Late Cambrian-Early Ordovician. Thomson Fold Belt) and at Mount Chalmers (Early Permian New England Fold Belt), and Kieslager or Besshi-type deposits related to submarine mafic volcanics, such as Peak Downs (Precambrian or early Palaeozoic, Thomson Fold Belt) and Dianne. OK and Mount Molloy (Silurian—Devonian, Hodgkinson Broken River Fold Belt). The major gold—copper orebody at Mount Morgan (Middle Devonian, New England Fold Belt), is considered to be of volcanic or subvolcanic origin, but is not a typical volcanogenic massive sulphide.The most numerous ore deposits are associated with calc-alkaline volcanics and granitoid intrusives of the transitional tectonic stage of the three fold belts, particularly the Late Carboniferous Early Perman of the Hodgkinson—Broken River Fold Belt and the Late Permian—Middle Triassic of the southeast Queensland part of the New England Fold Belt. In general, these deposits are small but rich. They include tin, tungsten, molybdenum and bismuth in granites and adjacent metasediments, base metals in contact meta somatic skarns, gold in volcanic breccia pipes, gold-bearing quartz veins within granitoid intrusives and in volcanic contact rocks, and low-grade disseminated porphyry-type copper and molybdenum deposits. The porphyry-type deposits occur in distinct belts related to intrusives of different ages: Devonian (Thomson Fold Belt), Late Carboniferous—Early Permian (Hodgkinson—Broken River Fold Belt). Late Permian Middle Triassic (southeast Queensland part of the New England Fold Belt), and Early Cretaceous (northern New England Fold Belt). All are too low grade to be of economic importance at present.Tertiary deep weathering events were responsible for the formation of lateritic nickel deposits on ultramafics and surficial manganese concentrations from disseminated mineralisation in cherts and jaspers.     

Tectonics and geodynamics of Gorny Altai and adjacent structures of the Altai–Sayan folded area

Packages of Late Paleozoic tectonic nappes and associated major NE-trending strike-slip faults are widely developed in the Altai–Sayan folded area. Fragments of early deformational phases are preserved within the Late Paleozoic allochthons and autochthons. Caledonian fold-nappe and strike-slip structures, as well as accompanying metamorphism and granitization in the region, are typical of the EW-trending suture-shear zone separating the composite Kazakhstan–Baikal continent and Siberia. In the Gorny Altai region, the Late Paleozoic nappes envelop the autochthon, which contains a fragment of the Vendian–Cambrian Kuznetsk–Altai island arc with accretionary wedges of the Biya–Katun’ and Kurai zones. The fold-nappe deformations within the latter zones occurred during the Late Cambrian (Salairian) and can thus be considered Salairian orogenic phases. The Salairian fold-nappe structure is stratigraphically overlain by a thick (up to 15 km) well-stratified rock unit of the Anyui–Chuya zone, which is composed of Middle Cambrian–Early Ordovician fore-arc basin rocks unconformably overlain by Ordovician–Early Devonian carbonate-terrigenous passive-margin sequences. These rocks are crosscut by intrusions and overlain by a volcanosedimentary unit of the Devonian active margin. The top of the section is marked by Famennian–Visean molasse deposits onlapping onto Devonian rocks. The molasse deposits accumulated above a major unconformity reflects a major Late Paleozoic phase of folding, which is most pronounced in deformations at the edges of the autochthon, nearby the Kaim, Charysh–Terekta, and Teletskoe–Kurai fault nappe zones. Upper Carboniferous coal-bearing molasse deposits are preserved as tectonic wedges within the Charysh–Terekta and Teletskoe–Kurai fault nappe zones.Detrital zircon ages from Middle Cambrian–Early Ordovician rocks of the Anyui–Chuya fore-arc zone indicate that they were primarily derived from Upper Neoproterozoic–Cambrian igneous rocks of the Kuznetsk–Altai island arc or, to a lesser extent, from an Ordovician–Early Devonian passive margin. A minor age population is represented by Paleoproterozoic grains, which was probably sourced from the Siberian craton. Zircons from the Late Carboniferous molasse deposits have much wider age spectra, ranging from Middle Devonian–Early Carboniferous to Late Ordovician–Early Silurian, Cambrian–Early Ordovician, Mesoproterozoic, Early–Middle Proterozoic, and early Paleoproterozoic. These ages are consistent with the ages of igneous and metamorphic rocks of the composite Kazakhstan–Baikal continent, which includes the Tuva-Mongolian island arc with accreted Gondwanan blocks, and a Caledonian suture-shear zone in the north. Our results suggest that the Altai–Sayan region is represented by a complex aggregate of units of different geodynamic affinity. On the one hand, these are continental margin rocks of western Siberia, containing only remnants of oceanic crust embedded in accretionary structures. On the other hand, they are represented by the Kazakhstan–Baikal continent composed of fragments of Gondwanan continental blocks. In the Early–Middle Paleozoic, they were separated by the Ob’–Zaisan oceanic basin, whose fragments are preserved in the Caledonian suture-shear zone. The movements during the Late Paleozoic occurred along older, reactivated structures and produced the large intracontinental Central Asian orogen, which is interpreted to be a far-field effect of the colliding East European, Siberian, and Kazakhstan–Baikal continents.     

东北地区前中生代构造演化及其与晚中生代盆地发育的关系

摘　 要　 东北地区前中生代构造演化可大致分为如下阶段：（1） 中、新元古代阶段;（2） 早古 生代加里东阶段;（3） 泥盆纪—早石炭世早华力西阶段;（4） 晚石炭世—三叠纪晚华力西—印 支阶段。多旋回构造演化使该区形成由多期褶皱带和多中间或边缘地块组成的 “镶嵌构造 区”‚并为晚中生代大型含油气盆地的发育奠定了基础。     

The eastern part of the Tasman Orogenic Zone

The eastern part of the Tasman Orogenic Zone (or Fold Belt System) comprises the Hodgkinson—Broken River Orogen (or Fold Belt) in the north and the New England Orogen (or Fold Belt) in the centre and south. The two orogens are separated by the northern part of the Thomson Orogen.The Hodgkinson—Broken River Orogen contains Ordovician to Early Carboniferous sequences of volcaniclastic flysch with subordinate shelf carbonate facies sediments. Two provinces are recognized, the Hodgkinson Province in the north and the Broken River Province in the south. Unlike the New England Orogen where no Precambrian is known, rocks of the Hodgkinson—Broken River Orogen were deposited immediately east of and in part on, Precambrian crust.The evolution of the New England Orogen spans the time range Silurian to Triassic. The orogen is orientated at an acute angle to the mainly older Thomson and Lachlan Orogens to the west, but the relationships between all three orogens are obscured by the Permian—Triassic Bowen and Sydney Basins and younger Mesozoic cover. Three provinces are recognized, the Yarrol Province in the north, the Gympie Province in the east and the New England Province in the south.Both the Yarrol and New England Provinces are divisible into two zones, western and eastern, that are now separated by major Alpine-type ultramafic belts. The western zones developed at least in part on early Palaeozoic continental crust. They comprise Late Silurian to Early Permian volcanic-arc deposits (both island-arc and terrestrial Andean types) and volcaniclastic sediments laid down on unstable continental shelves. The eastern zones probably developed on oceanic crust and comprise pelagic sediments, thick flysch sequences and ophiolite suite rocks of Silurian (or older?) to Early Permian age. The Gympie Province comprises Permian to Early Triassic volcanics and shallow marine and minor paralic sediments which are now separated from the Yarrol Province by a discontinuous serpentinite belt.In morphotectonic terms, a Pacific-type continental margin with a three-part arrangement of calcalkaline volcanic arc in the west, unstable volcaniclastic continental shelf in the centre and continental slope and oceanic basin in the east, appears to have existed in the New England Orogen and probably in the Hodgkinson—Broken River Orogen as well, through much of mid- to late Palaeozoic time. However, the easternmost part of the New England Orogen, the Gympie Province, does not fit this pattern since it lies east of deepwater flysch deposits of the Yarrol Province.     

Metallogeny and tectonic development of the tasman fold belt system in tasmania

In western Tasmania, Precambrian sedimentary sequences form the basement for narrow trough accumulations of Eocambrian and younger sequences. The main trough, the meridional Dundas Trough, is flanked to the west by the Rocky Cape region of Precambrian rocks within which major, apparently stratiform, exhalative magnetite-pyrite deposits are intercalated with metabasaltic volcanics and ultramafic bodies.The Eocambrian-Cambrian troughs apparently developed during extension of Precambrian continental crust. Early shallow-water deposition includes thick dolomite units in some troughs. Deepening of the troughs was accompanied by turbidite sedimentation, with minor limestone, and submarine basaltic volcanism with associated minor disseminated native copper. Ultramafic and related igneous rocks were tectonically emplaced in some troughs during a mild compressional phase. They contain only minor platinoids, copper-nickel sulphides and asbestos, but are source rocks for Tertiary secondary deposits of platinoids, chromite and lateritic nickel.In the Dundas Trough, Eocambrian-Early Cambrian rocks are separated by an inferred erosional surface from structurally conformable overlying Middle to Late Cambrian fossiliferous turbidite sequences. The structural conformity continues through overlying Ordovician to Early Devonian terrestrial and shallow-marine stable shelf deposits.A considerable pile of probable Middle Cambrian felsic volcanics accumulated between the sedimentary deposits of the Dundas Trough and the Tyennan region of Precambrian rocks to the east. A lava-dominated belt within the volcanics hosts major volcanogenic massive sulphide deposits, including those of the exhalative type, which in the south are enriched in copper, gold and silver, whereas in the north they are rich in zine, lead, copper, gold and silver. Cambrian movements along faults near the margin of the Tyennan region resulted in erosion of the mineralized volcanics, locally exposing sub-volcanic granitoids. Above the local unconformities occur unmineralized volcaniclastic sequences that pass conformably into Ordovician to Early Devonian shelf deposits. Ordovician limestone locally hosts stratabound disseminated and veined base metal sulphide deposits.Pre-Middle Devonian rocks of western Tasmania differ, for most part, from those in the northeast where deeper marine turbidite quartz-wacke sequences were deposited during the Ordovician and Early Devonian.The Eocambrian to Early Devonian rocks of Tasmania were extensively deformed in the mid-Devonian. The Precambrian regions of western Tasmania behaved as relatively competent blocks controlling early fold patterns. In northeastern Tasmania, folding is of similar age but resulted from movements inconsistent with those affecting rocks of equivalent age in western Tasmania.The final metallogenic event is associated with high-level granitoid masses emplaced throughout Tasmania during the Middle to Late Devonian. In northeastern Tasmania, extensive I-type granodiorite and S-type granite, with alkali-feldspar granites, are associated with mainly endogranitic stanniferous grelsens and wolframite ± cassiterite vein deposits. In contrast, scheelite-bearing skarns and cassiterite stannite pyrrhotite carbonate replacement deposits are dominant in western Tasmania, associated mainly with S-type granites. Several argentiferous lead-zinc vein deposits occur in haloes around tin-tungsten deposits. A number of gold deposits are apparently associated with I-type granodiorite, but some have uncertain genesis.The contrasting regions of western and northeastern Tasmania have probably been brought together by lateral movement along an inferred fracture. Flat-lying, Late Carboniferous and younger deposits rest on the older rocks, and the only known post-Devonian primary mineralization is gold associated with Creta ceous syenite.     

Lithospheric Structure of the Southeast Australian Lachlan Orogen along the Victorian Global Geoscience Transect

Upper-crustal elements of the ～35 km thick crust of the southern portion of the Lachlan Orogen consist of a chevron-folded and faulted turbidite package (15 to 17 km structural thickness) overlying imbricated Cambrian metabasites and cherts (～5 km structural thickness). These are intruded by both Early and Late Devonian granites and are overlain by Upper Silurian (?) marine to continental clastics (Grampians Group) in the west, and Upper Devonian-Early Carboniferous silicic volcanics and continental redbed elastics in the east. The turbidites show a general younging to the east, as well as eastward vergence apart from a local reversal (Tabberabbera zone). The region has been relatively stable since the mid-Paleozoic with apatite fission-track data recording cooling below ～100°C at 340-330 Ma in the west and 300 to 280 Ma in the east. Younger fission-track ages to the south, approaching the present coastline, reflect denudation during the opening of Bass Strait and the formation of the Cretaceous Otway and Gippsland basins. The major crustal discontinuities, the Woorndoo-Moyston and Mount Wellington fault zones, show significant Mesozoic reactivation and juxtapose regions of younger against older apatite fission-track ages. The nature of the lower crust remains unclear, but there is increasing evidence that it is not underlain by thinned Proterozoic continental crust. The Lachlan Orogen is an example of mid-Paleozoic tectonic accretion in a Southwest Pacific-style oceanic setting. Subduction-related oceanic thrusting produced the deformed and imbricated turbidite packages, and subduction-related magmatic underplating (perhaps during “rollback”) produced the large volumes of granite and volcanic rocks, and the localized high-T/low-P metamorphism.     

Recognition of the Cambrian Timan–Severnaya Zemlya orogen and timing of geological evolution of the North Kara sedimentary basin based on detrital zircon dating

New data on the ages of detrital zircons from folded basement rocks and cover sediments of the Severnaya Zemlya archipelago and Izvestiy TSIK islands have been obtained. The basement age is defined as Cambrian (pre-Ordovician). The Ordovician and Silurian sandstones were mainly formed by erosion of the basement rocks. The Devonian sandstones were formed by debris sourced from the Caledonian orogen. The Carboniferous–Early Permian molasse was formed simultaneously with the erosion of the Carboniferous granitoids and weathering of the Ordovician volcanic arc rocks and the Cambrian basement. The North Kara basin was formed in the Ordovician as a back-arc basin. It experienced its main compression deformations at the boundary of the Devonian and Carboniferous and in the Carboniferous.     

Isotopic age determinations on granitic rocks from Tasmania

Potassium‐argon and rubidium‐strontium isotopic age measurements show that emplacement of granitic rocks in Tasmania occurred during the Late Devonian and Early Carboniferous and in pre‐Devonian times, possibly in the Cambrian. In addition, a Precambrian granite, dated at about 750 m.y., has been recognized on the west coast of King Island.

The granitic bodies of pre‐Devonian age include the Murchison River Granite, the Dove River Granite and its correlatives, and the adamellite on the southwest coast of Tasmania at Elliott Bay. These rocks were deformed during the Devonian Tabberabberan Orogeny with the result that leakage of radiogenic daughter products has occurred from minerals. Hence the indicated ages are younger than the true ages. Possibly these granitic rocks were emplaced during the Jukesian Movement of the Tyennan Orogeny, in the Late Cambrian, although a Precambrian age cannot be excluded for some of the bodies.

As recognized by earlier workers the most important period of emplacement of granitic rocks in Tasmania was in the Middle Palaeozoic. The measured dates for this group of rocks range from 375 to 335 m.y., and indicate that intrusion occurred over an extended period from the Late Devonian to the Early or possibly Middle Carboniferous. There are distinct concentrations of measured ages at about 370 and 340 m.y. The granitic bodies of northeast Tasmania mainly yield the older age, whereas those of northwest Tasmania give the younger age. As the granites are post‐tectonic bodies the older age of about 375 m.y. provides a younger limit to the time of completion of the main folding in the Tabberabberan Orogeny, and this is consistent with the stratigraphic evidence.

The evidence suggests that generation of granitic magma was initiated during the main folding associated with the Tabberabberan Orogeny, but that emplacement of the granites into the upper crust continued over a long period subsequently to the main folding phase. Alternatively, the younger granitic bodies, dated at about 340 m.y., may indicate that these rocks are related to the Early Carboniferous Kanimblan Orogeny recognized in Victoria and New South Wales; however, there is no field evidence to support such a proposition.     

Evolution of geochemistry and depositional settings of Early Palaeozoic siliciclastics of the Barrandian (Teplá-Barrandian Unit,Bohemian Massif,Czech Republic)

Cambrian and Ordovician-Middle Devonian sequences of two successive Early Palaeozoic basins of the Barrandian unconformably overlie Cadomian basement in the Bohemian Massif NW interior (Teplá-Barrandian unit) which is the easternmost peri-Gondwanan remnant within the Variscides. Correlation of stratigraphy and geochemistry of the Early Palaeozoic siliciclastic rocks elucidated sediment provenances. Sandstones of the Middle Cambrian Píbram-Jince Basin were derived from a Cadomian Neoproterozoic island arc. The source area of the Ordovician shallow-marine siliciclastics of the successor Prague Basin is a dissected Cadomian orogen. Late Cambrian acid volcanics of the Barrandian and Cambrian (meta)granitoids emplaced in the W part of the Teplá-Barrandian Cadomian basement are also discernible in these sediments. Old sedimentary component increased during the Ordovician. Early Llandovery siliciclastic rocks show characteristics of an abruptly weakened supply of terrigenous material and an elevated proportion of synsedimentary basic volcanics as a result of Silurian transgression. Emsian siliciclastics (intercalated in the Late Silurian to Early Devonian limestone suite) presumably comprise an addition of coeval basic/ultrabasic volcaniclastics. Middle Devonian flysch-like siliciclastics indicate reappearance of Cadomian source near the Barrandian during early Variscan convergences of Armorican microplates that preceeded accretion of the Teplá-Barrandian unit within the Bohemian Massif terrane mosaic.Dr. Patoka deceased in July 2004.     

Tasman Fold Belt System in Tasmania

In western Tasmania Eocambrian and Cambrian rock sequences accumulated in narrow troughs between and within Precambrian regions which became geanticlines. The largest trough is meridional and is flanked by the Tyennan Geanticline to the east and the Rocky Cape Geanticline to the west. Within this trough ultramafic and mafic igneous masses, some of which are dismembered ophiolites, occur below a structurally conformable but erosional surface. This surface is at the base of an early-Middle Cambrian turbidite sequence, which grades upward into a probable correlate of the Owen Conglomerate that ranges into the Ordovician. Fault-bounded areas of Rocky Cape strata occur at the eastern boundary of the sedimentary trough deposits. A considerable pile of mineralized calcalkalic volcanic material, in which granite was emplaced, accumulated between the sedimentary trough deposits and the Tyennan Geanticline. Movements along Cambrian faults near and parallel to the margin of the Tyennan Geanticline caused angular unconformities. Above the unconformities occur volcaniclastic sequences that pass conformably upward into shallow marine and terrestrial Owen Conglomerate, derived from the Tyennan Geanticline.The transgressive Owen Conglomerate and its correlates are followed conformably by shallow marine limestone, of Early to Late Ordovician age. These limestone deposits covered much of western Tasmania and are succeeded conformably by Silurian to Early Devonian beds of shallow-marine quartz sandstone and mudstone.Pre-Middle Devonian rocks of western Tasmania extend to the Tamar Tertiary trough. In the northeast of Tasmania, immediately to the east of the Tamar trough, are sequences of interbedded mudstone and turbidite quartz-wacke of the Mathinna Beds, ranging in age from Early Ordovician to Early Devonian.The Cambrian to Early Devonian rocks of Tasmania are extensively deformed and show flattened parallel folds. In western Tasmania the folds are dated as late-Early to early-Middle Devonian because fragments of the deformed rocks occur in undisturbed Middle Devonian terrestrial cavern fillings. Folds of the northeastern Tasmania Mathinna Beds are probably of the same age. This widespread Devonian deformation is correlated with the Tabberabberan Orogeny of eastern Australia.In western Tasmania the geanticlines of Cambrian times behaved as relatively competent blocks during the Devonian folding, which is of two main phases. In the earlier phase the competent behaviour of the Tyennan Block determined the fold patterns. In the north the dominantly later folds resulted from movement from the northeast. During this later Devonian phase the Tyennan Block yielded in a northwesterly trending narrow zone of folding.In northeast Tasmania the Mathinna Beds exhibit folds which indicate a tectonic transportation opposite in direction to that which resulted in the folds of similar age in western Tasmania.Granitic rocks, dated 375-335 m.y., were emplaced within the folded rocks of Tasmania with usually sharp, discordant contacts. Foliations in the batholiths of northeast Tasmania suggest post-intrusion deformations involving east—west flattening. The late deformations may be related to lateral movements along a fracture zone which brought the Mathinna Beds of northeast Tasmania into juxtaposition with the rocks of contrasting stratigraphical and structural characteristics of western Tasmania.Flat-lying Late Carboniferous and younger deposits rest unconformably on the older rocks.     

Geologists: And their contribution to Australia

Abstract

Eight sets of stratigraphic layers and igneous rocks are the basis for the recognition of eight tectonic periods, TP1‐TP8, in the history of the New England and Yarrol Orogens from the Devonian to the opening of the Tasman Sea in the Late Cretaceous. The opening of the Tasman Sea caused the removal of an eastern section of the New England Orogen to form parts of the Lord Howe Rise and Norfolk Ridge. The Gwydir‐Calliope and Kuttung volcanic arc systems of TP1 and TP2 in the Devonian and Carboniferous were possibly W‐facing, and probably formed far to the NE of their present positions relative to the Lachlan Orogen. They moved SW as they developed, and in the latest Carboniferous or earliest Permian were cut obliquely by the Mooki Fault on which there was a dextral strike‐slip of about 500 km before the Kuttung volcanic arc became extinct. In the Late Carboniferous a narrow region on the E side of the Peel Fault was elevated to form the Campbell High which was intruded by the Bundarra Plutonic Suite and has probably remained elevated since then. Plutons of similar ages were intruded into a high to the E of the Bowen Basin (and the northern part of the Mooki Fault). The two highs and the intrusives in them divided the Yarrol Belt of the Yarrol Orogen from the Tamworth Belt of the New England Orogen, and the two belts have developed in different ways since the Visean. In Latest Carboniferous to Early Permian there was a major tectonic change and the Gympie‐Brook Street volcanic arc developed. The New England Orogen was in a back arc setting and broke into a mosaic of microplates, the relative motions between them being accompanied by deposition of diamictites, by metamorphism, by folding on W to NW trending axes, and by the intrusion of the Hillgrove Plutonic Suite. Further W, sediments of the Sydney, Gunnedah and Bowen basins were deposited above the Mooki Fault System and above the two segments of the Kuttung arc system that had been displaced along the Mooki Fault System.     

Tectonics and geodynamics of the western Central Asian Fold Belt (Kazakhstan Paleozoides)

On the basis of stratigraphical and geological data, paleogeographical and palinspastic reconstructions of the Kazakhstan Paleozoides were done; their multistage geodynamic evolution was considered; their tectonic zoning was proposed. The main stages are described: the initiation of the Cambrian and Ordovician island arcs; the development of the Kazakhstan accretionary–collisional composite continent in the Late Ordovician as a result of continental subduction and the amalgamation of Gondwana blocks with the island arcs (a long granitoid collisional belt also formed in this period); the development of the Devonian and Carboniferous–Permian active margins of the composite continent and its tectonic destruction in the Late Paleozoic.In the Late Ordovician, compensated terrigenous and volcanosedimentary complexes formed within Kazakhstania and developed in the Silurian. The Sakmarian, Tagil, Eastern Urals, and Stepnyak volcanic arcs formed at the boundaries with the Ural, Turkestan, and Junggar–Balkhash Oceans. In the late Silurian, Kazakhstania collided with the island arcs of the Turkestan and Ob'–Zaisan Oceans, with the formation of molasse and granite belts in the northern Tien Shan and Chingiz. This was followed by the development of the Devonian and Carboniferous–Permian active margins of the composite continent and the inland formation of the Early Devonian rift-related volcanosedimentary rocks, Middle–Late Devonian volcanic molasse, Late Devonian–Early Carboniferous rift-related volcanosedimentary rocks, terrigenous–carbonate shelf sediments, and carbonaceous lake–bog sediments, and the Middle–Late Carboniferous clastic rocks of closed basins. In the Permian, plume magmatism took place on the southern margin of the Kazakhstan composite continent. It was simultaneous with the formation of red-colored molasse and the tectonic destruction of the Kazakhstan Paleozoides as a result of a collision between the East European and Kazakhstan–Baikal continents.     

Geochronology and geochemistry of the Devonian Gumbardo Formation (Adavale Basin): evidence for cratonisation of the Central Thomson Orogen by the Early Devonian

Abstract

The Devonian subsurface Adavale Basin occupies a central position in the Paleozoic central Thomson Orogen of eastern Australia and records its tectonic setting during this time interval. Here, we have focussed on the basal volcanics of the Gumbardo Formation to clarify the tectonic setting of the basin. The approach has been to undertake stratigraphic logging, LA-ICP-MS U–Pb zircon geochronology and whole-rock geochemical analysis. The data indicate that basin initiation was rapid occurring at ca 401?Ma. The volcanic rocks are dominated by K-feldspar phyric rhyodacitic ignimbrites. The whole-rock geochemical data indicate little evidence for extensive fractional crystallisation, with the volcanic suite resembling the composition of the upper continental crust and exhibiting transitional I- to A-type tectonomagmatic affinities. One new U–Pb zircon age revealed an Early Ordovician emplacement age for a volcanic rock previously interpreted to be part of the Early Devonian Gumbardo Formation, and older basement age is consistent with seismic interpretations of uplifted basement in this region of the western Adavale Basin. Five ignimbrites dated from different stratigraphic levels within the formation yield similar emplacement ages with a pooled weighted age of 398.2?±?1.9?Ma (mean square weighted deviation?=?0.94, n?=?93). Significant zircon inheritance in the volcanic rocks records reworking of Ordovician and Silurian silicic igneous basement from the Thomson Orogen and provides insight into the crustal make-up of the Thomson Orogen. Collectively, the new data presented here suggest the Adavale Basin is a cover-type basin that developed on a stabilised Thomson Orogen after the major Bindian deformation event in the late Silurian.     

思茅地块西缘龙洞河组放射虫动物群及其地质意义

思茅地块西缘的龙洞河组为一套火山—沉积岩系 ,原定时代为晚石炭世 ,被认为属南澜沧江洋弧后盆地沉积。现在龙洞河组层状硅质岩断片中发现了晚泥盆世放射虫化石 ,在细碧角斑岩之硅质岩夹层中发现了早石炭世放射虫动物群 ,表明龙洞河组不全是晚石炭世地层 ,而是由晚古生代的一些地层断片组成。思茅地块西缘深水沉积盆地的演化始于泥盆纪 ,应为滇西南古特提斯多岛洋的一个分支 ,向南可能与泰国难河带对比。     

Metallogeny and tectonic development of the Tasman Fold Belt System in Victoria

Current evidence suggests that most of Victoria is underlain by a relatively thick (20 km +) basement of sialic composition of assumed Proterozoic age. This basement is nowhere exposed and its structural relationship with exposed Palaeozoic rocks is conjectural. This uncertainty has resulted in both ensimatic and ensialic tectonic models being proposed for Victoria during the Cambrian.Mineralization associated with Cambrian igneous activity shows a variety of styles from minor orthomagmatic chromite deposits, through Au and Cu deposits of syngenetic or epigenetic origin, to Fe---Mn, Ba occurrences of exhalative volcanogenic affiliation.Cambrian volcanism and associated sedimentation was followed by the deposition of dominantly quartz-rich turbidites with interbedded shale and siliceous units. Subsequent to the epi-Ordovician Benambran Orogeny, late Silurian crustal extension caused several rifts to open along roughly orthogonal NW and NE aligned fractures. Within these fault-bounded depressions, thick acid volcanic sequences were deposited in close association with shallow-marine sediments. Mineralization in these Upper Silurian rocks comprises polymetallic base-metal sulphide lenses and minor disseminations, at least some of which are of exhalative volcanogenic affiliation.The Silurian rifts were obliterated and their rocks strongly deformed during the Bindian (Bowning) deformation during late Silurian to early Devonian time. This in turn was followed by another episode of crustal extension and rifting, during which the formation of a broad meridional trough marks the Buchan Rift. A very thick sequence of largely subaerial bimodal volcanics is overlain by shelf limestone and mudstone. A variety of minor base metal, barite, manganese, and iron mineralization is hosted by these volcanics and shelf sediments.The mid-Devonian Tabberabberan Orogeny was followed in the Late Devonian by bimodal volcanism and granite intrusion, and “red-bed”-type non-marine sedimentation. In Central Victoria, thick bimodal volcanics were erupted into a series of cauldron subsidences and intruded by comagmatic granites. Bimodal volcanism also occurred in the Mount Howitt Province farther east, but was followed by deposition of extensive fluviatile and lacustrine sediments (mainly mudstone, sandstone, and minor conglomerate). In the Mansfield Basin, these contain minor sedimentary copper occurrences.There are four distinct episodes of granite emplacement in Victoria, namely Late Cambrian -Early Ordovician (Delamerian) in the Glenelg Zone; Early Silurian (Benambran) in the Highlands Zone; Early Devonian (Bindian) in the Grampians, Ararat-Bendigo, Highlands, and Mallacoota Zones; and Middle Devonian-Carboniferous (post Tabberabberan) in the Ararat- Bendigo, Melbourne, Howqua, and Highlands Zones. Data for the Delamerian granitoids are sketchy, but in the remaining groups S-type granitoids predominate with the exception of eastern Victoria, east of the Yalmy Fault (I-S line), where only I- and A-type granitoids occur. A variety of Sn, Mo, W deposits and prospects are associated with the Benambran and younger intrusive phases.Victoria is a major gold province which has produced nearly 2.5 × 10⁶ kg gold. Primary gold occurs in a number of geological settings including veins and disseminations spatially associated with mafic Cambrian volcanism, vein deposits in turbiditic sequences of central and eastern Victoria, veins associated with mafic and intermediate intrusives of Mid to Late Devonian age, and minor amounts associated with a variety of granitoids and porphyry dykes.     

Polyphase late Palaeozoic deformation in the southeastern foreland and northwestern Piedmont of the Alabama Appalachians

Late Palaeozoic deformation in the southern Appalachians is believed to be related to the collisional events that formed Pangaea. The Appalachian foreland fold and thrust belt in Alabama is a region of thin-skinned deformed Palaeozoic sedimentary rocks ranging in age from Early Cambrian to Late Carboniferous, bounded to the northwest by relatively undeformed rocks of the Appalachian Plateau and to the southeast by crystalline thrust sheets containing metasedimentary and metaigneous rocks ranging in age from late Precambrian to Early Devonian. A late Palaeozoic kinematic sequence derived for a part of this region indicates complex spatial and temporal relationships between folding, thrusting, and tectonic level of décollement. Earliest recognized (Carboniferous(?) or younger) compressional deformation in the foreland, observable within the southernmost thrust sheets in the foreland, is a set of large-scale, tight to isoclinal upright folds which preceded thrafing, and may represent the initial wave of compression in the foreland. Stage 2 involved emplacement of low-angle far-traveled thrust sheets which cut Lower Carboniferous rocks and cut progressively to lower tectonic levels to the southwest, terminating with arrival onto the foreland rocks of a low-grade crystalline nappe. Stage 3 involved redeformation of the stage 2 nappe pile by large-scale upright folds oriented approximately parallel to the former thrusts and believed to be related to ramping or imbrication from a deeper décollement in the foreland rocks below. Stage 4 involved renewed low-angle thrusting within the Piedmont rocks, emplacement of a high-grade metamorphic thrust sheet, and decapitation of stage 3 folds. Stage 5 is represented by large-scale cross-folding at a high angle to previous thrust boundaries and fold phases, and may be related to ramping or imbrication on deep décollements within the now mostly buried Ouachita orogen thrust belt to the southwest. Superposed upon these folds are stage 6 high-angle thrust faults with Appalachian trends representing the youngest (Late Carboniferous or younger, structures in the kinematic sequence.     

Provenance and deformation history of the Eastern Thomson Orogen and implications for the Paleozoic evolution of the Tasmanides (Eastern Australia)

Abstract

Cambrian deformation associated with the Delamerian Orogeny is most evident in the Delamerian Orogen (southwestern Tasmanides) but has also been documented in the Thomson Orogen (northern Tasmanides). The tectonic evolution of the Thomson Orogen in the context of the Delamerian Orogeny is poorly understood. In particular, tectonostratigraphic relationships between the different parts of the Thomson Orogen (Anakie Inlier, Nebine Ridge, and southern Thomson Orogen) are still unclear. New detrital zircon data from the Nebine Ridge revealed an age spectrum that is consistent with published geochronological data from the Anakie Inlier. These results, in conjunction with petrographic observations and the interpretation of geophysical data, suggest that along the eastern part of the Thomson Orogen, the?～?NNE-trending Nebine Ridge represents the southward continuation of the?～?N–S-trending Anakie Inlier. New detrital zircon geochronological data are also presented for metasedimentary rocks from both sides of the Thomson–Lachlan boundary. The results constrain the maximum age of deposition (Ordovician–Devonian), and show that both sides of the Thomson–Lachlan boundary received detritus from a similar provenance. This might suggest that the Thomson–Lachlan boundary did not play a major role as a crustal-scale boundary prior to the Devonian. We speculate that transpressional deformation along this?～?E–W boundary, during the Early Devonian, was responsible for disrupting the original belt that connected the Delamerian Orogen (Koonenberry Belt) with the eastern Thomson Orogen (Nebine Ridge and Anakie Inlier).

1. Highlights

2. The Nebine Ridge is the southward continuation of the Anakie Inlier.

3. The Anakie Inlier and Nebine Ridge represent a northern segment of the Cambrian Delamerian–Thomson Belt.

4. ～E–W-trending crustal-scale structures at the southern Thomson Orogen were active during Devonian.

     

Insights into the evolution of the Thomson Orogen from geochronology,geochemistry, and zircon isotopic studies of magmatic rocks

Abstract

Zircon U–Pb ages, εHf(t), and δ¹⁸O isotopic data together with geochemistry and limited Sm–Nd results from magmatic rocks sampled in deep-basement drill cores from undercover parts of the Thomson Orogen provide strong temporal links with outcropping regions of the orogen and important clues to its evolution and relationship with the Lachlan Orogen. SHRIMP U–Pb zircon ages show that magmatism of Early Ordovician age is widespread across the central, undercover regions of the Thomson Orogen and occurred in a narrow time-window between 480 and 470?Ma. These rocks have evolved εHf(t)_zrn (?12.18 to ?6.26) and εNd (?11.3 to ?7.1), and supracrustal δ¹⁸O_zrn (7.01–8.50‰), which is in stark contrast to Early Ordovician magmatic rocks in the Lachlan Orogen that are isotopically juvenile. Two samples have late Silurian ages (425–420?Ma), and four have Devonian ages (408–382?Ma). The late Silurian rocks have evolved εHf(t)_zrn (?6.42 to ?4.62) and supracrustal δ¹⁸O_zrn (9.26–10.29‰) values, while the younger Devonian rocks show a shift toward more juvenile εHf(t)_zrn, a trend that is also seen in rocks of this age in the Lachlan Orogen. Interestingly, two early Late Devonian samples have juvenile εHf(t)_zrn (0.01–1.92) but supracrustal δ¹⁸O_zrn (7.45–8.77‰) indicating rapid recycling of juvenile material. Two distinct Hf–O isotopic mixing trends are observed for magmatic rocks of the Thomson Orogen. One trend appears to have incorporated a more evolved supracrustal component and is defined by samples from the northern two-thirds of the Thomson Orogen, while the other trend is generally less evolved and from samples in the southern third of the Thomson Orogen and matches the isotopic character of rocks from the Lachlan Orogen. The spatial association of the Early Ordovician magmatism with the more evolved metasedimentary signature suggests that at least the northern part of the Thomson Orogen is underlain by older pre-Delamerian metasedimentary rocks.     

U–Pb zircon geochronology of Late Devonian to Early Carboniferous extension‐related silicic volcanism in the northern New England Fold Belt

Laser ablation‐inductively coupled plasma‐mass spectrometry (LA‐ICP‐MS) analysis of zircons confirm a Late Devonian to Early Carboniferous age (ca 360–350 Ma) for silicic volcanic rocks of the Campwyn Volcanics and Yarrol terrane of the northern New England Fold Belt (Queensland). These rocks are coeval with silicic volcanism recorded elsewhere in the fold belt at this time (Connors Arch, Drummond Basin). The new U–Pb zircon ages, in combination with those from previous studies, show that silicic magmatism was both widespread across the northern New England Fold Belt (>250 000 km² and ≥500 km inboard of plate margin) and protracted, occurring over a period of ～15 million years. Zircon inheritance is commonplace in the Late Devonian — Early Carboniferous volcanics, reflecting anatectic melting and considerable reworking of continental crust. Inherited zircon components range from ca 370 to ca 2050 Ma, with Middle Devonian (385–370 Ma) zircons being common to almost all dated units. Precambrian zircon components record either Precambrian crystalline crust or sedimentary accumulations that were present above or within the zone of magma formation. This contrasts with a lack of significant zircon inheritance in younger Permo‐Carboniferous igneous rocks intruded through, and emplaced on top of, the Devonian‐Carboniferous successions. The inheritance data and location of these volcanic rocks at the eastern margins of the northern New England Fold Belt, coupled with Sr–Nd, Pb isotopic data and depleted mantle model ages for Late Palaeozoic and Mesozoic magmatism, imply that Precambrian mafic and felsic crustal materials (potentially as old as 2050 Ma), or at the very least Lower Palaeozoic rocks derived from the reworking of Precambrian rocks, comprise basement to the eastern parts of the fold belt. This crustal basement architecture may be a relict from the Late Proterozoic breakup of the Rodinian supercontinent.     

Geology of the Severnaya Zemlya Archipelago and the North Kara Terrane in the Russian high Arctic

The Severnaya Zemlya Archipelago is located at 80°N near the continental shelf break, between the Kara and Laptev seas. Sedimentary successions of Neoproterozoic and Palaeozoic age dominate the bedrock geology. Together with Northern Tajmyr, Severnaya Zemlya constitutes the main land areas of the North Kara Terrane (NKT), which is inferred here to have been a part of the Timanide margin of Baltica, i.e. an integral part of Baltica at least since the Vendian. Vendian turbidites derived from the Timanide Orogen are inferred to have been deposited on Neoproterozoic greenschist facies, granite-intruded basement. Shallow-water siliclastic deposition in the Early to Mid-Cambrian was followed by highly organic-rich shales in the Late Cambrian and influx of more turbidites. An episode of folding, the Kan’on River deformation, separates these formations from the overlying Tremadocian conglomerates and sandstones. In the Early Ordovician, rift-related magmatic rocks accompanied the deposition of variegated marls, sandstones, carbonates and evaporites. Dark shales and gypsiferous limestones characterise the Mid-Ordovician. Late Ordovician quartz-sandstones mark a hiatus, followed by carbonate rocks that extend up into and through most of the Silurian. The latter give way upwards into Old Red Sandstones, which are inferred to have been deposited in a Caledonian foreland basin. Deformation, reaching the area in the latest Devonian or earliest Carboniferous and referred to as the Severnaya Zemlya episode, is thought to be Caledonian-related. The dominating E-vergent structure was controlled by décollement zones in Ordovician evaporite-bearing strata; detachment folds and thrusts developed in the west and were apparently impeded by a barrier of Ordovician igneous rocks in the east. Below the décollement zones, the Neoproterozoic to Early Ordovician succession was deformed into open to close folds. The exposed strata in the lower structural level have been juxtaposed with those in the upper structural level along the major N-trending Fiordovoe Lake Fault Zone, which involved several kilometres of dextral strike-slip movement and downthrow to the west. A major Early Carboniferous unconformity separates the folded Mid-Palaeozoic and older rocks from overlying Carboniferous formations, as on Franz Joseph Land and Svalbard. Subsequent latest Palaeozoic to Early Mesozoic orogeny, as on Taimyr, apparently had little influence on the Severnaya Zemlya successions.