摘要:

The foliation developed in parts of the Bega Batholith is related to the mode of granite emplacement and the regional tectonic setting. In the Cape Conran area in Victoria, folding and metamorphism coincide with the intrusion of the granite. During emplacement and cooling, a primary homogeneous syntectonic foliation (S) was developed and deformed by ductile shear bands (C), the S C fabric suggesting a minimum easterly displacement of approximately 3 km within the granite body. Quartzc‐axis fabrics in the granite define girdle patterns lying at high angles to an eastward shear direction and these are characteristic of a subsolidus deformation in the granite. These observations are compatible with plutonism during east‐west compression in an eastward shear regime. Similar examples in east Gippsland suggest that eastward shearing was a characteristic kinematic element of this part of the Lachlan Fold Belt during the late Middle Devonian.

ISSN:0812-0099    

DOI:10.1080/08120098808729435

出版商:Taylor & Francis Group    

年代:1988

数据来源: Taylor

摘要:

The Namatjira Formation is a newly recognized mixed carbonate and clastic sequence from the eastern Gardiner Range in the Amadeus Basin, central Australia. The formation grades from clastic at the base to carbonate at the top, and contains three distinct lithofacies. Numerous small cycles, 1–5 m thick, are of tempestite origin. Detailed sedimentological and facies analysis indicates that the Namatjira Formation was deposited in a tidal flat to coastal lagoon environment, with periods of emergence and hypersalinity. The formation interfingers with, and is time equivalent to, the Arumbera Sandstone, which in the Gardiner Range has previously been assigned a Proterozoic age. This interpretation is now in question as the Namatjira Formation contains abundant vertical burrows and horizontal tracks, which in the Arumbera Sandstone elsewhere in the basin have been used to assign that unit to the Early Cambrian.

ISSN:0812-0099    

DOI:10.1080/08120098808729436

出版商:Taylor & Francis Group    

年代:1988

数据来源: Taylor

摘要:

The geochemistry of two deerite‐bearing meta‐ironstones from the Emo Metamorphics of Papua New Guinea suggests that they were deposited as metalliferous cherts enriched in manganese and iron by hydrothermal exhalative activity in an ocean ridge system. Subsequent blueschist facies metamorphism resulted in the formation of the assemblage deerite‐quartz‐albite‐iron oxides‐alkali amphiboles‐spessar‐tine‐stilpnomelane‐apatite, with calcium‐manganese carbonates in one specimen. Assemblages in associated metabasites suggest P‐T conditions of 7 kb at 320°C, which overlap with the P‐T field defined by one of the meta‐ironstones. Oxygen fugacity was probably an important control in determining variations in mineralogy and mineral chemistry. Preliminary data on the trace element geochemistry of associated metabasites are consistent with an ocean ridge environment for the formation of the meta‐ironstones.

ISSN:0812-0099    

DOI:10.1080/08120098808729437

出版商:Taylor & Francis Group    

年代:1988

数据来源: Taylor

摘要:

Late Palaeozoic biotite granites from the Emuford district of the Herberton tinfield form part of the Emu Suite, a group of fluorine‐rich, high‐silica, ilmenite series granites associated with extensive tin mineralization in the eastern Tate Batholith. The Emu Suite granites are enriched in F, Rb, U, Th, Y and Sn and depleted in TiO2, MgO, MnO, CaO, P2O5, Ba, Sr and Eu compared with many other silicic granites. Fractionation trends from early coarse grained to later medium and fine grained granites include increases in Al2O3, Na2O, F, Rb, Th, U, Hf, Y, Nb, W, Sn, Ga and HREE, and decreases in TiO2, MgO, Ba, Sr, Eu, La and Ce. These trends are compatible with an evolution via fractionation of a fluorine‐rich magma involving mainly separation of plagioclase and minor zircon and monazite. The Emu Suite granites form part of a much more extensive group of high‐Si granites associated with tin mineralization in the region. These tin‐bearing granites are amongst the earliest intrusions of a major Late Palaeozoic magmatic episode which extended from approximately 315 to 270 Ma. Modelling the evolution of the Emu Suite granites indicates that the high LREE and Rb and the extremely low Ba, Sr and Eu are not compatible with an origin via partial melting and fractionation of average or depleted crustal sources unless very small degrees of partial melting over a wide area are proposed. The strongly fractionated chemistry of the Emu Suite granites could have resulted from their derivation from a relatively fractionated, crustal source. Heat and volatiles required to promote partial melting were probably supplied by mantle outgassing which homogenized Sr isotope ratios in the region in the early stages of Late Palaeozoie magmatism.

ISSN:0812-0099    

DOI:10.1080/08120098808729438

出版商:Taylor & Francis Group    

年代:1988

数据来源: Taylor

摘要:

The initial application of depositional sequence analysis to selected stratigraphic sections through outcropping Late Proterozoic strata of the Adelaide Geosyncline in South Australia has identified major depositional sequences within the several‐kilometre‐thick Wilpena Group. Sharp facies shifts in vertical stratigraphic sections are proposed as actual sequence boundaries which, provided they are the result of eustatic sea level variations, may be key elements for future attempts at inter‐regional chronostratigraphic correlation.

ISSN:0812-0099    

DOI:10.1080/08120098808729439

出版商:Taylor & Francis Group    

年代:1988

数据来源: Taylor

摘要:

Acid extraction of microfossils from siliceous rocks of the New England Fold Belt has yielded radiolarians, and less commonly conodonts, that are of biostratigraphic value. Rock units, the ages of which have until now been only indirectly estimated, are directly dated, and although some earlier argued ages are confirmed others are younger than previously supposed. Thus the Woolomin Formation, an accretionary subduction complex, has elements of Silurian age but also includes rocks as young as Carboniferous. The Wisemans Arm Formation, once considered to be Late Devonian, contains chert olistoliths as young as Namurian, and a Late Devonian age is indicated for the Watonga Formation, a sequence of ocean floor rocks previously correlated with the Woolomin Formation. These results suggest that some ideas on provenance linkage and terrane amalgamation in the New England Fold Belt need to be reassessed. Several Early Devonian radiolarian assemblages have been identified in the western part of the Hastings Block. Together with a fauna from near Taree in the southeast of the Tamworth Belt they confirm earlier lithological correlations, and support the idea of major strike‐slip displacement of the southern part of the Tamworth Belt.

ISSN:0812-0099    

DOI:10.1080/08120098808729440

出版商:Taylor & Francis Group    

年代:1988

数据来源: Taylor

摘要:

The chemical composition of a stratigraphically controlled sequence of volcanic conglomerate clasts in the Palaeozoic forearc sequence of the New England Fold Belt has been used to deduce characteristics of their source. Basaltic lithologies are absent, and compatible element concentrations indicate that the suite has undergone low pressure fractionation, producing a continuum from andesite to rhyolite. A discrimination diagram based on immobile elements from modern arc lavas, originally constructed for basaltic rocks, can be used for intermediate rocks and shows that the clasts were derived from a calc‐alkaline volcanic arc. A new plot utilizing Ce/Yv. Sr/Y distinguishes between volcanic arc rocks erupted through oceanic, continental and thinned continental crust. This plot shows that the magmatic arc bordering the forearc basin in New England was floored by thin continental crust (intermediate in thickness to oceanic and continental crust), in accord with a significant proportion of granitic and recycled sedimentary clasts.

ISSN:0812-0099    

DOI:10.1080/08120098808729441

出版商:Taylor & Francis Group    

年代:1988

数据来源: Taylor

摘要:

Igneous‐textured and recrystallized amphibolite or pyroxene granulite dykes cut Proterozoic granitoid gneisses in the Port Lincoln area of South Australia. The igneous‐textured dykes are largely Ol‐normative, and the amphibolites Qz‐normative, tholeiites. The igneous‐textured dykes comprise norites, gabbronorites and plagioclase‐phyric dolerites which may be readily distinguished by their different Hy/Di ratios. All three igneous‐textured groups are LREE enriched, but they are further distinguished by their different degrees of HREE fractionation, distinct Zr/Ti and Zr/Y ratios and different combinations of normalized negative Ti, Nb, P, Sr and V anomalies. The compositional variation within the three groups may be modelled by crystal fractionation of opx + cpx + plag and cpx + plag dominated assemblages.

ISSN:0812-0099    

DOI:10.1080/08120098808729442

出版商:Taylor & Francis Group    

年代:1988

数据来源: Taylor

摘要:

Chemical sediments of the Thorntonia Limestone were deposited during a major, gradually transgressive, but rapidly regressive sea level cycle that spanned the Ordian Stage of the early Middle Cambrian. In the northeastern parts of the Georgina Basin the Cambrian sea invaded an irregular landscape and proceeded to drown basement rocks with a series of small scale transgressive pulses, represented by repeating sets of three generalized shallowing‐upward cycles. Sediments deposited within the cycles are represented by seven lithofacies within two mineralogical suites of rocks. One, a mixed mineralogy suite (Suite A), contains: (1) the mud dominant, peloid and bioclast lithofacies, (2) a coated peloid, phosphate pavement lithofacies, and (3) the skeletal particle dominant lithofacies. The other, a calcareous mineralogy suite (Suite B), comprises: (1) the peloid and oncolite grainstone dominant lithofacies, (2) the peloid boundstone dominant lithofacies, (3) the thin bedded and fenestrate mudstone lithofacies, and (4) a flat and domal laminate stromatolite lithofacies. Generalized cycles mP and gP contain phosphatic carbonates of the mixed mineralogy suite and where complete culminate in emergence and the formation of phosphatic hardgrounds, phoscrete profiles, desiccated mudstone phosphorites and stromatolitic phosphorites. These phosphatic sediments accumulated in peritidal environments where the sea floor geometry was influenced by the irregular palaeotopography of the basement. Generalized cycle gC is characterized by rocks of the calcareous suite that accumulated in peritidal environments above a sea floor of negligible relief. Although the two mineralogical suites are spatially separated, they may be temporally equivalent. The coexistence of similar peritidal environments characterized by a different suite of chemical sediments provides a model for palaeotopographic controls on processes of phosphogenesis.

ISSN:0812-0099    

DOI:10.1080/08120098808729443

出版商:Taylor & Francis Group    

年代:1988

数据来源: Taylor

ISSN:0812-0099    

DOI:10.1080/08120098808729444

出版商:Taylor & Francis Group    

年代:1988

数据来源: Taylor