摘要:

The Tia Granodiorite, a Hillgrove Suite pluton in the southern New England Fold Belt, intruded complexly deformed metasediment and metabasite belonging to the Tia Complex, which at the time of intrusion had already been affected by two deformation events at low‐T moderate‐P metamorphic conditions and two overprinting deformation events at high‐T low‐P metamorphic conditions. Emplacement took place during D5thrusting associated with limited uplift as low‐P amphibolite facies metamorphism prevailed. Large‐scale warping during D6was followed by a second penetrative thrusting event (D7) that caused further uplift and was initiated under lower amphibolite facies conditions.

ISSN:0812-0099    

DOI:10.1080/08120099308728067

出版商:Taylor & Francis Group    

年代:1993

数据来源: Taylor

摘要:

Peperite is a non‐genetic term used to describe volcanic breccia in which a texture of dark blocks in a light matrix resembles a mixture of salt and pepper. In the Gold Creek Volcanics, peperite is a mixture of partly vesiculated basalt clasts in a mudstone‐sandstone matrix. It is formed by the buoyant intrusion of basaltic magma into wet unconsolidated sediment. The intruding bodies deform and quench, giving rise to discordant masses of hyaloclastic breccia, confined largely to the subsurface. These basalt masses may remain hot enough to locally superheat pore water and produce convective systems where the basalt clasts and fluidized sediment become mixed, forming the distinctive peperite.

ISSN:0812-0099    

DOI:10.1080/08120099308728068

出版商:Taylor & Francis Group    

年代:1993

数据来源: Taylor

摘要:

Polygenetic mélange is intercalated with multiply deformed Siluro‐Devonian shale, greywacke, clast‐in‐matrix rock, spilite and chert in the Hodgkinson goldfield of northeast Australia. Differing sedimentary facies, fold styles, veining events and mélange units occur in six fault‐bounded domains. Locally coherent stratigraphic units can be traced into the mélange. The chief mechanism of fragmentation in the mélange was an intense domainal cleavage event which formed chlorite‐illite‐vitrinite seams. Multiple tight folding and local shale diapirism pre‐dated cleavage development and greatly contributed to desegregation and mixing. Late brittle shear zones further juxtaposed coherent phacoidal megablocks within zones of clast‐in‐matrix rock. Laminated protolith sequences aided the formation of clast‐in‐matrix rock, whereas more massive units became slabs, blocks and clasts. The rocks are of sub‐greenschist metamorphic facies, based on spilite and sandstone mineral assemblages, textures and illite crystallinity. Sequential genesis of the mélange correlates well with the known progression of Late Palaeozoic deformation, and contains characteristics of both collision and overthrust type margins.

ISSN:0812-0099    

DOI:10.1080/08120099308728069

出版商:Taylor & Francis Group    

年代:1993

数据来源: Taylor

摘要:

Similar slopes of lines connecting δ18O and δ13C plots between co‐existing micrite and dolomite pairs are due to small inheritance effects on δ13C from dissolution of CaCC3and large variations in δ18O in dolomite due to dolomitizing fluids in a marine to mixing zone. The δ13C values of replaced precursor CaCO3were variable due to early meteoric diagenesis. Dolomite is in equilibrium with marine, mixed‐marine and meteoric CaCO3because dolomitization occurred when CaCO3was metastable, simultaneously with or slightly after the transformation of metastable CaCC3to calcite during early diagenesis. Recrystallization of dolomite involved the renewed growth of dolomite on early‐formed dolomite and the replacement of co‐existing CaCO3. This involved negligible depletion in δ13C and a small negative shift in δ18O.

ISSN:0812-0099    

DOI:10.1080/08120099308728070

出版商:Taylor & Francis Group    

年代:1993

数据来源: Taylor

摘要:

Wide‐angle reflection and refraction seismic studies indicate that two velocity models are appropriate for the structure of the crust and upper mantle under the New England Batholith, eastern Australia. Under the southern part of the batholith crustal velocities increase gradually from 5.5–6.03 km/s at the surface to 6.45 km/s near a distinct Moho at 34–35 km depth, suggesting that rocks of granitic composition make up a large part of the crust. Under the northern part there is a (? mafic) sill‐like feature at 21–24 km depth with a velocity maximum of 6.7 km/s. The crustal velocities are significantly less than those of the Lachlan and Thomson Orogens underlying the Bowen‐Gunnedah‐Sydney Basin system just to the west of the New England Orogen (typically > 6.3 km/s at > 10 km depth) and of terranes in the northern New England Orogen. In areas with similar granite geochemistry and inferred to have similar evolutionary process (for example the Peninsular Ranges Batholith, southwestern USA), there are again contrasts with the New England Batholith with high velocity mafic rocks (inferred ophiolite basement) at quite shallow (10 km) depths. Under the southern New England Orogen an upper mantle velocity of 7.7 km/s is determined, the lowest upper mantle velocity yet interpreted for any region of continental Australia. This upper mantle velocity persists down to ∼45 km depth and then increases to 8.08 km/s at 60 km. This again contrasts with upper mantle velocities under the adjacent Lachlan and Thomson Orogens (typically > 8.04–8.15 km/s) and with the batholiths in southwestern USA (∼8.2 km/s). Low velocity material in the mantle under New England could be the residue from geochemical differentiation within the mantle during I‐type plutonism, but our preferred interpretation is that it indicates underplated material emplaced during the formation of the Tasman Sea Basin and the subsequent uplift of eastern Australia.

ISSN:0812-0099    

DOI:10.1080/08120099308728071

出版商:Taylor & Francis Group    

年代:1993

数据来源: Taylor

摘要:

Superimposed contraction, extension and oblique‐slip faulting has juxtaposed and segmented blocks and slices of Precambrian metasedimentary rocks, Cambrian marine sedimentary and ultramafic rocks, and Early‐Middle Palaeozoic strata near the boundary between the East and West Tasmania Terranes in the Badger Head region of northern Tasmania. Of greatest significance was post‐Early Devonian southwest‐directed thrusting which caused thin‐skinned style imbrication and led to juxtaposition of the East and West Tasmania Terranes. Polydeformed Precambrian meta‐turbiditic rocks of the Badger Head massif are part of a fault‐bounded allochthonous slice which was brought to the present structural level at this time. An inferred west‐directed Cambrian thrusting event emplaced ultramafic rocks (Andersons Creek ultramafic complex) and produced a tectonic melange (Port Sorell Formation), possibly within an east‐dipping accretionary wedge. The Cambrian event is considered to have involved an imbricated accretionary complex containing dismembered ophiolitic slices. Superimposed Middle Devonian and post‐Jurassic faulting has masked evidence of this event. Post‐Jurassic deformation caused displacement of the Late Carboniferous to Jurassic cover sequence along northwest‐trending strike‐slip and oblique‐slip faults and along the normal faults that produced northwest‐trending rift basins in northern Tasmania. The normal faults are probably related to the extensional event which separated Tasmania from the mainland. The strike‐slip and oblique‐slip faults may be related to the Tertiary contractional deformation that affected southern Victoria.

ISSN:0812-0099    

DOI:10.1080/08120099308728072

出版商:Taylor & Francis Group    

年代:1993

数据来源: Taylor

摘要:

Palaeocurrents, sandstone compositions and sedimentologic profiles in the turbiditic Mathinna Group of northeastern Tasmania have enabled the geometry and dynamics of the Late Silurian‐Early Devonian part of the depositional basin to be defined. The oldest rocks in the Mathinna Group are Early Ordovician or older, and comprise a thick‐ to thin‐bedded turbiditic arenite succession ∼ 1 km thick (Stony Head Sandstone) overlain by a 1–2 km thick pelite (Turquoise Bluff Slate) containing the only known Ordovician fossil in the succession — an Early Ordovician graptolite. This pelite succession passes conformably upwards by influx of gradually increasing proportions of siltstone and fine‐grained sandstone into a thin‐ to thick‐bedded interval of classical turbidites at least several kilometres thick containing Early Devonian fossils in its upper part. The lower part of this upper turbiditic succession (Bellingham Formation) contains the oldest palaeocurrent pattern measured and indicates lobes on a submarine fan system prograding to the east‐northeast. Dominant sandstone composition is quartzose sublitharenite, consistent with derivation from stable platform areas inferred to have lain to the southwest. The age of this fan system is uncertain, but could be Late Silurian.

ISSN:0812-0099    

DOI:10.1080/08120099308728073

出版商:Taylor & Francis Group    

年代:1993

数据来源: Taylor

摘要:

Benthic foraminifera are abundant in surficial sediment of Gulf St Vincent and the distribution of many species is related to water depth. For example,Nubecularia lucifugais most abundant in shallow northern waters whileAmmobaculites reophaciformisis more common in deeper southern parts of the gulf.Elphidium crispum,a shallow‐water species, andE. macelliforme,favouring deeper water, provide a useful numerical ratio. Their logarithmic relative abundance in the sediment size fraction 0.50–0.25 mm correlates closely with water depth, particularly for southern Gulf St Vincent. Vibrocore SV23 recovered an undisturbed section of Quaternary strata from one of the deepest parts (40 m) of the gulf. Late Pleistocene sediment (oxygen isotope stage 3) was in turn overlain by rapidly deposited lacustrine and restricted marginal marine sediment before development of more open Holocene marine conditions. Using theElphidiumratios and other supporting foraminiferal data on a framework of14C dates, a palaeosea‐level curve was calculated from SV23. Changes in sea‐level so derived for the period 45–30 ka bp agree closely with those previously calculated for Gulf St Vincent and can be correlated with those determined from studies of Huon Peninsula coral reef terraces. For this time‐interval, southern Australian palaeosea‐levels of ‐30 to ‐27 m are indicated from the work reported here.

ISSN:0812-0099    

DOI:10.1080/08120099308728074

出版商:Taylor & Francis Group    

年代:1993

数据来源: Taylor

ISSN:0812-0099    

DOI:10.1080/08120099308728075

出版商:Taylor & Francis Group    

年代:1993

数据来源: Taylor