Response of U‐Pb Zircon and Rb‐Sr total‐rock and mineral systems to low‐grade regional metamorphism in proterozoic igneous rocks,mount Isa,Australia

A detailed Rb‐Sr total‐rock and mineral and U‐Pb zircon study has been made on suites of Proterozoic silicic volcanic rocks and granitic intrusions, from near Mt Isa, northwest Queensland. Stratigraphically consistent U‐Pb zircon ages within the basement igneous succession show that the oldest recognized crustal development was the outpouring of acid volcanics (Leichhardt Metamorphics) 1865 ± 3 m.y. ago, which are intruded by coeval, epizonal granites and granodiorites (Kalkadoon Granite) whose pooled U‐Pb age is 1862 ⁺²⁷ _‐21 m.y. A younger rhyolitic suite (Argylla Formation) within the basement succession has an age of 1777 ± 7 m.y., and a third acid volcanic unit (Carters Bore Rhyolite), much higher again in the sequence, crystallized 1678 ± 1 m.y. ago.

All of these rocks are altered in various degrees by low‐grade metamorphic events, and in at least one area, these events were accompanied by, and can be partly related to, emplacement of a syntectonic, foliated granitic batholith (Wonga Granite) between 1670 and 1625 m.y. ago. Rocks that significantly predate this earliest recognized metamorphism, have had their primary Rb‐Sr total‐rock systematics profoundly disturbed, as evidenced by 10 to 15% lowering of most Rb‐Sr isochron ages, and a general grouping of many of the lowered ages (some of which are in conflict with unequivocal geological relationships) within the 1600–1700 m.y. interval. Such isochrons possess anomalously high initial ⁸⁷Sr/⁸⁶Sr ratios, and some have a slightly curved array of isotopic data points. Disturbance of the Rb‐Sr total‐rock ages is attributed primarily to mild hydrothermal leaching, which resulted in the loss of Sr (relatively enriched in ⁸⁷Sr in the Sr‐poor (high Rb/Sr) rocks as compared with the Sr‐rich rocks).     

Volcanism on a Proterozoic continental margin in northwestern Queensland

The oldest rocks exposed in northwestern Queensland are metamorphosed calc-alkaline volcanics (Leichhardt Metamorphics), which are intruded by elongate tonalitic to granitic batholiths (Kalkadoon Granite). These rocks are overlain by a less metamorphosed sequence containing basic lavas (Magna Lynn Metabasalt) overlain by extensive ignimbritic rhyolite and dacite (Argylla Formation). Sequences of basalt and psammite overlie the rhyolite unconformably and are overlain in turn unconformably by psammitic, pelitic, carbonate and possibly evaporitic sediments and minor volcanics. Younger granites intrude these rocks.The mineral assemblages of the Leichhardt Metamorphics, Magna Lynn Metabasalt and Argylla Formation indicate greenschist and lower amphibolite facies of metamorphism. The rocks contain no glass and some are obviously recyrstallized; however, phenocrysts, lithic fragments, spherulites, amygdales and flow-top breccias are still recognizable.Sixty-nine of the least deformed volcanic and sub-volcanic rocks were analysed for major elements and up to twenty trace elements. Element dispersion in these analyses indicated that metasomatism was probably of limited extent. The Magna Lynn Metabasalt is similar to low-potassium tholeiite, as it has less than 0.5% potash, high normative hypersthene, some normative quartz and typical Ti/Zr/Y ratios. The acid volcanics have calc-alkaline affinities although andesite is not common and the alumina content is relatively low. They have high K/Na ratios and their trace elements (especially Ba, Sr, Rb, Zr and Ce) are similar to Andean volcanics. The tholeiitic sequences that overlie the calc-alkaline volcanics in northwestern Queensland resemble the basaltic sequences of western U.S.A. that also overlie calc-alkaline volcanics.The predominantly calc-alkaline volcanics of northwestern Queensland are believed to have formed at a continental margin similar to that in the Andean region. The younger tholeiitic lavas and minor continental acid volcanism possibly accompanied crustal tension. Later regional metamorphism and intrusion of large granite batholiths stabilized the region.     

Deformation history of the Naraku Batholith,Mt Isa Inlier,Australia: Implications for pluton ages and geometries from structural study of the Dipvale Granodiorite and Levian Granite

Plutons of the Naraku Batholith were emplaced into Proterozoic metasediments of the northern portion of the Eastern Fold Belt of the Mt Isa Inlier during two intrusive episodes approximately 200 million years apart. Structural relationships and geochronological data suggest that the older plutons (ca 1750 Ma) are contemporaneous with granites of the Wonga Batholith to the west. The Dipvale Granodiorite and the Levian Granite represent these older intrusive phases of the Naraku Batholith, and both contain an intense tectonic foliation, S₁, which is interpreted to have formed during the north‐south shortening associated with D₁ of the Isan Orogeny. The geometry of S₁ form surfaces at the southern end of the Dipvale Granodiorite, and of the previously unrecognised sheeted contact, defines a macroscopic, steeply south‐southwest‐plunging antiform, which was produced by the regional D₂ of the Isan Orogeny. S₁ form surfaces in the Levian Granite define open F₂ folds with wavelengths of several hundred metres. The structural age of emplacement of the Dipvale Granodiorite and the Levian Granite is interpreted to be pre‐ or syn‐ the regional D₁. An intense foliation present in some of the younger (ca 1505 Ma) granites that comprise the bulk of the Naraku Batholith is interpreted to represent S₃ of the Isan Orogeny. Foliations commonly have similar styles and orientations in both the pre‐D₁ and younger plutons. This emphasises the simplicity with which regional fabrics can be, and probably have been, miscorrelated in the Eastern Fold Belt, and that the classification of granites in general on the basis of structural and geometric criteria alone is fraught with danger.     

Potassium‐argon ages on micas from the Precambrian region of North‐Western Queensland

Potassium‐argon measurements have been carried out on the separated micas of 27 samples, principally granites, from the Mount Isa‐Cloncurry region of north‐western Queensland. There is evidence for at least two tectonic periods within the “Lower Proterozoic” of the area. The first is represented only in the north‐western portion, with ages greater than 1,770 m.y. on the Ewen Granite, and on the granites of the Nicholson River area to the far north‐west. The second at 1,400–1,450 m.y. is manifested only to the south and east of the Kalkadoon‐Leichhardt complex, and including the Sybella Granite. The results may be further interpreted as lending support to the concept of a possible “metamorphic discontinuity” along the western flank of the Kalkadoon‐Leichhardt complex, postulated by Carter, Brooks and Walker; as suggesting possible contemporaneity of the Cliffdale Volcanics and the Argylla Formation; and as giving further evidence for the antiquity of stromatolites. Comparison with earlier work suggests that some deposits in this region may be contemporaneous with some of the Agicondian sediments of the Katherine‐Darwin area, and that the second tectonic period corresponds with the K‐Ar ages obtained on the Davenportian granites of Central Australia.     

Mary Kathleen metamorphic‐hydrothermal uranium — rare‐earth element deposit: Ore genesis and numerical model of coupled deformation and fluid flow

The Mary Kathleen U‐REE orebody of the Proterozoic Mt Isa Block was the product of chemical and physical interaction between regional metamorphic/hydrothermal fluids and preexisting calcic skarns. The deposit provides excellent examples of mechanical control on ore localisation and of the complexity of ores in rocks with protracted thermal histories. Host skarns were produced by contact metasomatism around the 1740 Ma Burstall Granite, whereas the allanite‐uraninite ore formed under amphibolite‐facies conditions, late during the D₂ phase of the ca 1550–1500 Ma Isan orogeny. Observations of ore geometry are consistent with previous geochronologic data demonstrating a large time gap between skarn formation and ore genesis. Numerical modelling of coupled deformation and fluid flow suggests that veins at the core of ore shoots may have formed as tensile or shear fractures during coupling of the competent skarn host with the late‐D₂ Mary Kathleen Shear Zone, allowing a change of orientation of ore shoots with distance from the shear zone. Mineral chemistry and petrographic observations suggest the possible role of a redox control on chemical localisation of ore by conversion of Fe²⁺‐rich clinopyroxene‐rich skarn host to Fe³⁺‐rich secondary garnet ‘skarn’ and uraninite‐allanite ore. Alternately, fluid pressure drops as a consequence of fracturing of the host skarn may have triggered fluid unmixing, or fluid mixing, leading to ore precipitation. Available data do not allow clear definition of the ultimate source of the U and REE, nor of the specific chemical ore‐forming mechanism. However, regional constraints, previous Sm–Nd modelling, and our numerical models suggest a combination from proximal skarn hosts and from distal sources accessed by flow of metamorphic and/or late tectonic igneous‐derived fluids. The deposit has some similarities with ironstone‐hosted Cu–Au ± U deposits found in the nearby Cloncurry Belt.     

The link between hydrothermal epigenetic copper mineralization and the Caçapava Granite of the Brasiliano Cycle in southern Brazil

Base-metal deposits in the Caçapava do Sul Copper Province are hosted by both volcanosedimentary rocks of the Bom Jardim Group and by metamorphic rocks of the Passo Feio Formation, and show a spatial relationship to the Caçapava Granite. These associations have led to much controversy about the genesis of the base-metal deposits, which has been at least partly resolved by precise dating using SHRIMP (Sensitive High Resolution Ion Microprobe) U/Pb zircon studies combined with S, Pb, and Sr isotope trace studies.The Passo Feio Formation is Neoproterozoic in age and was derived from a complex continental source, as shown by the presence of xenocryst zircons of Archaean, Paleoproterozoic, and Neoproterozoic ages. It was metamorphosed at ca. 700 Ma. The syntectonic Caçapava Granite that intruded the supracrustal rocks of the Passo Feio Formation at 562 Ma was derived from an old sialic basement.Lead-isotope data are consistent with a 562 Ma age for the base-metal sulphide deposits sited in the Passo Feio Formation. The least-radiogenic compositions lie between the field of the isotopic compositions of the Caçapava Granite and rocks of the Passo Feio Formation, suggesting that Pb in the sulphide deposits may have been derived from both sources. The Pb, like that in the Caçapava Granite and Passo Feio Formation, was derived from a primitive crustal source. Sulphur isotope data from the base-metal sulphide deposits in the Passo Feio Formation are compatible with a mixed sedimentary and magmatic source.The most logical model for ore genesis, based on the isotopic data and spatial relationships, is that magmatic metal-bearing fluids from Caçapava Granite leached metals from the Passo Feio Formation and that the deposited sulphides therefore show mixed isotopic signatures. However, there is also some isotopic evidence from the Caçapava Granite itself that suggests assimilation of S-bearing rocks of the Passo Feio Formation during emplacement. Thus, isotopic signatures could have been inherited from assimilated metal sulphides at this stage, and deposition could have been entirely from Caçapava Granite-derived magmatic fluids.Importantly, the inferred 562±8 Ma age for the deposits in the Passo Feio Formation is younger than the well-constrained age of 594±5 Ma for the Camaquã/Santa Maria deposits. Thus, the epigenetic sulphides in the Passo Feio Formation cannot be the source of these deposits as previously suggested. Other isotopic data also argue against such a model.     

Post‐Late Paleozoic Collisional Framework of Southern Great Altai

We outline the post-Late Paleozoic (latest Permian to Cenozoic) collisional framework of the southern Great Altai (Central Asia) produced by the convergence between the Tuva-Mongolia and Junggar continental terranes (microplates). The collisional structures in the region classified on the basis of their geometry and deformation style, dynamic metamorphism, and compositions of tectonites are of three main types: (1) mosaic terranes made up of large weakly deformed Paleozoic blocks separated by younger shear zones; (2) contractional deformation systems involving structures formed in post-Late Paleozoic time, parallel faults oriented along collisional deformation systems, and relict lenses of Paleozoic orogenic complexes; and (3) isolated zones of dynamic metamorphism composed mostly of collisional tectonites different in composition and alteration grade.     

The Archaean Nucleus of Singhbhum: The Present State of Knowledge

The supracrustal rocks of the Older Metamorphic Group (OMG), consisting of metasediments and ortho-amphibolite, constitute the oldest unit in the Archaean nucleus of Singhbhum. However, there are indications that still older (3.4–3.8 Ga) crust of both sialic and mafic composition existed in this region. The OMG ortho-amphibolites were formed by partial melting of mantle with near chondritic composition ca. 3.3 Ga ago, probably as a result of plume activity. Shortly afterwards, partial melting of the underplated mafic material produced a tonalitic melt (Older Metamorphic Tonalitic Gneiss — OMTG), which intruded the OMG supracrustals and the entire suite was deformed and metamorphosed to upper amphibolite facies. Subsequent to this, melting of the OMG ortho-amphibolites and the lower crustal material of probable andesitic composition produced melts varying in composition from tonalite to granite and these intruded in different phases to produce plutons of Singhbhum Granite, Bonai Granite and Kaptipada Granite, which together form volumetrically the major part of the Archaean nucleus. The older OMG and OMTG occur as enclaves within these younger granitoids. The time difference between the emplacements of the OMTG and the early phases of younger granitic intrusion was of the order of 100–200 Ma. Thus, serial additions of juvenile material led to the formation of a stable microcontinent by 3.2 Ga. Thermally triggered stretching in this microcontinent produced basins peripheral to the present day Singhbhum Granite pluton, and in these basins the younger supracrustal rocks of the Iron Ore Group (IOG), consisting of BIF, associated argillaceous and subordinate arenaceous rocks, and mafic lavas were laid down. There is inadequate field or geochronological evidence to resolve the issue of whether the different iron ore basins were coeval or not. Meagre geochronological data suggest that some of the BIFs are older than ca. 3.1 Ga. Post-IOG activity is confined to the intrusion of mafic dyke swarms and formation of intracratonic basins, the ages of both being uncertain.     

Transposed high-pressure granulite fabrics (Cabo Ortegal, NW Spain): Implications on the scales of deformation localization

High-pressure granulite facies rocks of the Bacariza Formation (Cabo Ortegal, NW Spain) were syn-metamorphically deformed at the contacts with the bounding units (peridotite and eclogite massifs). This enabled the formation of meter-thick, spectacular shear zones with reworked and transposed foliations and lineations. The texturally stable mineral assemblage of the new fabrics records an intense, ductile deformation of the mineral aggregate at temperatures of 700–800 °C associated with amalgamation of eclogite, high-pressure granulitic rocks and ultramafic sheets in deep portions of a subduction channel. The lattice preferred orientation of the main constituent minerals (garnet, augite, amphibole, plagioclase, quartz and biotite) discloses the active deformation mechanisms at the scale of the mineral grains and the relationships with the deformation at larger scales. Overprinting relationships of the metamorphic assemblages demonstrates that partitioning and deformation localization occurred at different scales under similar high-grade conditions. Complete macroscopic transposition in the shear zones was complementary to meso and microscopic partitioning of deformation intensity and mechanisms between different lithological layers and mineral species.     

Molar tooth structures of the Neoarchean Monteville Formation, Transvaal Supergroup, South Africa. II: A wave-induced fluid flow model

Sedimentological, morphological, and geochemical characteristics of molar tooth (MT) structures in the ca 2·6 Ga Monteville Formation suggest a new fluid flow model for MT formation: (i) intercalated shales and carbonate sands were deposited near to above storm wave base; (ii) sediments cracked, forming an interconnected network of MT cracks that were also open to pores in sand lenses; (iii) storm waves pumped sea water into open MT crack networks, causing rapid microcrystalline carbonate nucleation, Ostwald ripening of nuclei, and growth of granular carbonate cores; some of these cores were transported by water flowing through the cracks; (iv) unfilled MT cracks collapsed, and filled MT ribbons deformed plastically as host sediments compacted and dewatered; (v) carbonate cores were overgrown by polygonal rims; and (vi) MT structures deformed brittlely with additional compaction and produced pebbly lags if reworked. MT cracks may have formed by multiple mechanisms; however, expansion of gas from organic decay and sediment heaving due to wave loading best explain MT crack morphology and are most consistent with the fluid flow model for MT CaCO₃ presented here.     

Barry Granodiorite and Sunset Hills Granite: Wyangala‐style intrusion at the margin of a regional ductile shear zone,northern Lachlan Fold Belt,New South Wales

The Barry Granodiorite is a weakly deformed I‐type, and the Sunset Hills Granite is a moderately deformed S‐type, granite. Both granites were passively intruded into an already foliated greywacke and volcanic sequence. Emplacement may have been facilitated by faults related to the oblique opening of the late Early Silurian Hill End Trough. The granites display a dominant foliation which formed during the late Middle Devonian and subsequently was reoriented during the Early Carboniferous. The Barry Granodiorite and Sunset Hills Granite are on the margin of north‐south ductile shear zones related to the Wyangala Batholith. These granites and the adjacent Carcoar Granodiorite have undergone reorientation during movement on ductile shear zones either due to megakinking during late‐stage north‐south shortening, or southeastward movement of the southern margin of the west‐northwest‐trending Lachlan Transverse Zone.     

The Palmer Granite--A Study of a Granite within a Regional Metamorphic Environment

The Palmer Granite is a small, regionally conformable body whichoccurs in association with migmatites and high-grade schistsand gneisses in the metamorphic belt flanking the eastern MountLofty Ranges of South Australia. Seven new rock analyses, including some trace element data,are presented. The normative percentages of quartz-orthoclase-albite,and orthoclase-albite-anorthite fall near or within the low-temperaturetroughs for the corresponding synthetic systems and hence itis probable that the granite was produced by crystal-liquidequilibrium. Mineral data on biotites (2 analyses) and potassium feldspars(7 analyses) indicate disequilibrium with the envelope rocks. Initial S7Sr/86Sr ratios for the granite specimens average 0-708,whereas the initial 87Sr/86Sr ratios of the analysed countryrocks are all higher than this. The age is 49015 m.y. Chemical, isotopic, and mineralogical data rule out the possibilityof either granitization, partial melting, or complete meltingof country rocks similar to those analysed. The granite is consideredto have been produced at greater depths. The absence of superimposedcontact aureoles, together with macroscopic and microscopicfabric data, indicates that the Palmer Granite was intrudedduring metamorphism and that it cooled, and in part recrystallized,in the same stress field as that which produced the fabric ofthe country rocks. The metamorphic textures are a result ofthis recrystallization     

REE Abundance and REE Minerals in Granitic Rocks in the Nanling Range,Jiangxi Province,Southern China,and Generation of the REE‐rich Weathered Crust Deposits

Studies of Mesozoic granites associated with rare earth element (REE)‐rich weathered crust deposits in southernmost Jiangxi Province indicate that they have high‐K to shoshonite compositions and belong to ilmenite‐series I‐type granites. Of the studied rocks at 59–292 ppm of bulk REE content, the highest are seen in the biotite granites of Dingnan (358, 429 ppm) and mafic biotite granite of the Wuliting Granite (344 ppm) near the Dajishan tungsten mine, both areas where weathered‐crust REE deposits occur. REE‐bearing accessory minerals in these granites are mainly zircon, apatite and allanite, and REE‐fluorocarbonates are common. REE enrichment occurs in the rims of apatite crystals, and in fluorocarbonates that occur along grain boundaries of and cracks in major silicate minerals, and in fluorocarbonates that replaced altered biotite. It is therefore thought that a major part of the REE content of these granites was concentrated during deuteric activity, rather than during magmatic crystallization. The crack‐filling REE‐fluorocarbonates could subsequently have been easily leached out and deposited in weathered crust developed during a long period of exposure.     

The Harry Creek Deformed Zone,a retrograde schist zone of the Arunta Block,central Australia

The Harry Creek Deformed Zone, a retrograde schist zone of epidote amphibolite facies grade, which separates the granulite facies Utralanama Block from the amphibolite facies Ankala Block in the southeastern Strangways Range, N.T., is typical of the retrograde schist zones transecting the Arunta Block. Associated with the deformed zone is a small deformed granitic pluton and its various offshoots—the Gumtree Granite Suite—which provides structural and geochrono‐logical evidence that the Harry Creek Deformed Zone has had a polyphase deforma‐tional history. Early movements within the deformed zone pre‐dated intrusion of the Gumtree Granite Suite and resulted in the movement of the Utralanama and Ankala Blocks into their present juxtaposition. Reactivation of much of the zone during the Alice Springs Orogeny brought about the schistose character of the zone and the deformation of the granitic rocks. Further minor reactivation of the zone, subsequent to the main phase of the Alice Springs Orogeny, resulted in limited development of pseudotachylytes.

The age of the granite (990 ± 13 m.y.) gives a minimum age for initiation of the zone, and evidence for the nature of the structures associated with the early movements is presented. It is suggested that the Harry Creek Deformed Zone represents a post‐orogenic wrench fault which has been reactivated. Early movements, which were of a brittle transcurrent nature, brought about major uplift (up to 10 km) to the north, and lateral movements may have been of the order of 60 km in a sinistral sense. Comparison with the Redbank Zone indicates many similarities, suggestive of a similar history.     

Molar tooth structures of the Neoarchean Monteville Formation, Transvaal Supergroup, South Africa. I: Constraints on microcrystalline CaCO3 precipitation

Molar tooth (MT) structures are enigmatic, contorted millimetre‐ to decimetre‐long veins and spheroids of microcrystalline calcite that formed during very early diagenesis in Precambrian sediments. MT structures in the ca 2·6 Ga Monteville Formation are 600–800 Myr older than previously reported occurrences and establish that conditions necessary for MT genesis were met locally throughout much of the Precambrian. In the Monteville Formation, MT structures were formed shallow subtidally, extending to depths near storm wave base, in shale host sediments intercalated with storm‐generated carbonate sand lenses. They are filled with microcrystalline calcite and rare pyrite. Microcrystalline calcite identical to that in MT structures fills other pore space, including porosity between grains in carbonate sand lenses, moldic porosity in sand grains, sheet cracks in columnar stromatolites, and shallow cracks on sandy bedding planes. Relationships in the Monteville Formation demonstrate that microcrystalline CaCO₃ precipitated in fluid‐filled cracks and pores; microcrystalline calcite characteristics, as well as the paucity of carbonate mud in host rocks, are inconsistent with injection of lime mud as the origin of MT structures. Locally, MT cracks were filled by detrital sediment before or during precipitation. Precipitation occurred in stages, and MT CaCO₃ evolved from granular cores to a rigid mass of cores with overgrowths – allowing both plastic and brittle deformation of MT structures, as well as reworking of eroded MT structures as rigid clasts and lime mud. Crystal size distributions and morphology suggest that cores precipitated through nucleation, Ostwald ripening and size‐dependent crystal growth, whereas overgrowths formed during size‐independent crystal growth.     

Origin and terminal architecture of a submarine slide: a case study from the Permian Vischkuil Formation,Karoo Basin,South Africa

Submarine mass movement deposits exposed in the Vischkuil Formation, Laingsburg Karoo Basin, South Africa, provide a rare opportunity to analyse and interpret their emplacement history and deformation processes at a scale comparable to seismic examples. An up to 80 m thick slide deposit, continuously exposed in two 2 km long sub‐parallel sections, passes from extensionally deformed material (clastic dykes and down‐dip facing low‐angle shear surfaces) down‐dip into a compressional toe zone with large (tens of metres amplitude) folds dissected by steep, up‐dip facing thrust planes. The compressional shear planes sole out onto a highly sheared décollement and cross‐cutting relationships indicate an up‐depositional dip younging in the timing of fold dissection. Lithofacies characteristics and detailed correlation of volcanic ash and other marker beds over more than 500 km² in the bounding undeformed stratigraphy indicate a low‐gradient (<0·1°) basin floor setting. The slide is abruptly overlain by an up to 50 m thick debrite with sandy clasts supported by an argillaceous matrix. Shear loading of the debris flow is interpreted to have driven large‐scale deformation of the substrate through the generation of high shear stresses at a rheological interface due to: (i) the abrupt contact between the slide and the debrite; (ii) the coincident thickness distributions of the debrite and slide; (iii) the distribution of the most intense folding and thrusting under the thickest parts of the debrite; (iv) the preservation of fold crests with only minor erosion along fold limbs; (v) the presence of the debrite under overturned folds; (vi) the presence of laterally extensive marker beds directly above deformation units indicating minimal depositional topography; and (vii) the demonstrably local derivation of the slide as individual folded beds are mapped into undeformed strata outside the areas of deformation. The debrite is directly overlain by fine‐grained turbidite sandstone beds that show widespread vertical foundering into the debrite. This case study demonstrates that intensely deformed strata can be generated by negligible amounts of down‐dip movement in a low‐gradient, fine‐grained basin floor setting with the driver for movement and deformation being the mass imbalance resulting from emplacement of episodic debris flows. Simple interpretation of an unstable slope setting based on the presence of such deformed strata should be treated with caution.     

Architecture of a Palaeoproterozoic Rift System: Evidence from the Fiery Creek Dome region,Mt Isa terrane

The Mt Isa Rift Event is a Palaeoproterozoic intracontinental extension event that defines the beginning of sedimentation into the Isa Superbasin in the Western Fold Belt, Mt Isa terrane. In the mildly deformed Fiery Creek Dome region, on the northwest flanks of the Mt Isa Rift, elements of the Mt Isa Rift Event rift architecture are preserved without being intensely overprinted by later deformation. In this region two discrete generations of northwest‐dipping normal faults have been identified. Early generation normal faults were active during the deposition of fluvial and immature conglomerate and sandstone of the Bigie Formation. Renewed rifting and the development of late‐generation normal faults occurred during deposition of shallow‐marine sandstone and siltstone of the lower Gunpowder Creek Formation. Differential uplift between tilt blocks formed an array of spatially and temporally discontinuous synrift unconformities on the crests of uplifted tilt blocks. Applying the domino model yields ～28% crustal extension for the entire Mt Isa Rift Event. Northwest‐striking transverse faults facilitated differential displacement along normal faults and formed boundaries to normal fault segments, creating smaller depositional compartments along half‐graben axes. Three large domes were formed during laccolith emplacement. These domes produced palaeogeographical highs that divided the region into sub‐basins and were a source for the coarse fluvial synrift sequences deposited during the early Mt Isa Rift Event. The basin architecture in the Fiery Creek Dome region is consistent with northwest‐southeast‐directed extension.     

Syn‐extension leucogranite deformation during convergence in the Eastern Central Alps: example of the Novate intrusion

The Novate intrusion is a Late Alpine leucogranite that intruded the structures related to dextral back‐thrusting along the Periadriatic Fault System in the Eastern Central Alps. The Novate granite was heterogeneously deformed from amphibolite to greenschist facies conditions during cooling of the intrusion. The deformation inside the granite is characterized by strongly localized and anastomosed ductile shear zones surrounding lenses of weakly deformed granite and by late faults formed at the brittle–ductile transition. The fault kinematic analysis of conjugated shear zones suggests that the Novate leucogranite was emplaced at 25 Ma in an extensional regime along the southern tip of the Forcola Fault. A model of extensional jog opening by vertical shearing along the Forcola Fault provided the space for magma accommodation. The Novate granite is the first evidence for orogen‐parallel syn‐extensional leucogranite emplacement during the Oligocene collision in the Alps.     

安徽沿江地区中晚三叠世沉积演化及其与印支早期金子运动关系的探讨

安徽沿江地区古生代—中生代地层发育较为完整,印支构造变形表现最为强烈。印支晚期南象运动已成为公认的事实,而早期金子运动存在与否及其地质界面一直存在较大的争议。本文通过关键界面的考查、角砾岩特征及成因,以及岩相古地理的演化的分析,初步认为安徽沿江地区印支运动早期金子运动确实存在,其构造界面位于周冲村组与黄马青组之间,以平行不整合或微角度不整合接触关系为表现形式,其构造样式以构造抬升为主,盆地边界以宽缓的褶皱变形为辅。该运动与南象运动(大规模的褶皱造山)共同控制了沿江地区构造格架的形成和发展。     

Terrane sutures in the Maine Appalachians,USA and adjacent areas

Terrane sutures in the Maine Appalachians and adjacent areas are recognized as melange dominated, deformed accretionary prisms of Ordovician age, and as a broad synmetamorphic transcurrent fault zone of probable Late Silurian-Early Devonian age. Although the accretionary prisms are associated with present day aeromagnetic and Bouguer gravity anomalies, they are probably not associated with present day crustal penetrating boundaries. The geology of the accretionary prisms indicates subduction-obduction dominated regimes during which (1) the Gander and Boundary Mountain (Dunnage) terranes amalgamated and (2) the composite Boundary Mountain-Gander terrane accreted to the Laurentian margin. The Penobscottian orogeny produced and deformed the older of the two accretionary prisms. This accretionary prism indicates that the Penobscottian was a continuous or perhaps diachronous event which spanned the late Cambrian to early Late Ordovician. The younger accretionary prism was produced and deformed during the Taconian orogeny during late Middle to early Late Ordovician. Initial deformation of this accretionary prism may have overlapped the waning stages of the Penobscottian. Portions of the Taconian arc locally overlie the Penobscottian accretionary prism. A synmetamorphic fault zone lies within Precambrian(?) to Ordovician(?) bimodal metavolcanic and metapelitic rocks assigned here to the Avalon terrane. This zone is several kilometres wide and is interpreted to be the postsubduction suture between the Avalon and Gander terranes, and may, in part, represent a fossil transform fault system. The fault zone contains phyllonites as well as shear zones which generally record dextral motion. The phyllonites were previously interpreted as a stratigraphic unit, whereas the shear zones span or are contained within mappable compositional units. Formation of and movement along these phyllonites and shear zones ceased before the intrusion of Early Devonian plutons. Not all faults in south-western Maine are related to the suture. Younger dip and/or strike-slip and thrust faults are approximately parallel to, or may lie within, the older shear zones and they complicate the recognition of the older faults.