Dissertation•
Deformation and metamorphism of the Aileu formation, East Timor
01 May 1979-
TL;DR: The Aileu Formation as discussed by the authors is composed of metamorphosed shales, sedimentary blocks and arenites with minor limestones and basites, and it syn-and post-dates the prograde metamorphic event, produced tight conformations and early cleavage on all scales.
Abstract: A 10 km wide coastal strip of the Aileu Formation was mapped in
detail. This section of the north coast of Timor lies 70 km south of
a recently active island arc and was chosen as a potential type
example of the deformation style in an arc-continent collision zone.
In addition a brief study was made of the petrography and chemistry of
altered igneous rocks from this coastal strip and igneous rocks of a
similar age from other regions in East Timor.
The Aileu Formation is composed of metamorphosed shales,
siltstones and arenites with minor limestones and basites. The metamorphic
grade of this formation is zoned from lower greenschist facies
in the southwest to upper almandine-amphibolite facies in the east.
Five structural phases are recognised. The first generation isa
cleavage or schistosity which predates the single prograde metamorphism.
No folds were found associated with this foliation and its significance
is unknown. The second deformation phase occurred in the Late Miocene.
It syn- and post-dates the prograde metamorphic event, produced tight
folds and transposed the compositional layering and early cleavage on
all scales. The last three deformation phases produced open to gentle
macroscopic folds. Correlations with structural data from other
formations suggest the third and fourth phases occurred in the Late
Miocene and the fifth deformation occurred in the Early Pleistocene.
The major high angle faults, which form the boundaries of the Aileu
Formation, were also active in the Early Pleistocene.
The amphibolites and altered dolerites of the Aileu Formation are
transitional, in composition, between alkaline and tholeiitic basalts.
Permian and Mesozoic basalts and dolerites from other regions in East
Timor include both alkaline and tholeiitic compositions. All these igneous rocks are characteristic of continental rift valleys and ocean
islands. However the associated sedimentary rocks were deposited on a
continental shelf or slope. There is no evidence that the Aileu
Formation or the Permian and Mesozoic formations were not formed on
the Australian continental margin.
The geology of Timor is consistent with its evolution as a rift
valley in the Late Palaeozoic and Early Mesozoic, and a trailing margin
from the Cretaceous to the Early Miocene. Structural data suggests a
Late Miocene arc-continent collision. There has been post-orogenic
uplift and minor additional deformation in the Plio-Pleistocene.
Comparison of Papua New Guinea with Timor suggests that the mobile belt
in arc-continent collisions is characterised by medium pressure metamorphism,
relatively coherent deformation style, and a short history of
orogenic activity. Little evidence of thrusting or imbrication has
been uncovered and their importance as deformation processes in this
environment remains speculative.
Citations
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TL;DR: A detailed study of the structure and metamorphic history of 400 km2 of the Aileu Formation showed it has a complex history of penetrative deformation but the structure is coherent.
58 citations
TL;DR: In this paper, structural mapping in East Timor (Timor-Leste) reveals that duplexing of a 2-km-thick package of Australian continental strata has built the majority of the structural elevation of the Timor orogen.
Abstract: Models of arc-continent accretion often assume that the period of subduction of continental lithosphere before plate boundary reorganization is fairly short lived, yet the timescale of this period is poorly constrained by observations in the geologic record. The island of Timor is the uplifted accretionary complex resulting from the active collision of the Banda volcanic arc with the Australian continental margin. The exposure of underplated and exhumed Australian strata on Timor allows for the characterization of the structural history of accretion of uppermost Australian crust and the quantification of subduction of its original continental lithospheric underpinnings. New structural mapping in East Timor (Timor-Leste) reveals that duplexing of a 2-km-thick package of Australian continental strata has built the majority of the structural elevation of the Timor orogen. Coupling new structural observations with previous thermochronology results reveals the sequence of deformation within the orogen, the presence of subsurface duplexing below the hinterland slate belt, and motion along a foreland subsurface thrust ramp. Construction of balanced cross sections allows for the quantification of the amount of shortening in the orogen, and from that, the length of the subducted Australian continental lithosphere. Two balanced cross sections in East Timor reveal 326–362 km of shortening and that 215–229 km of Australian continental lithosphere have been subducted below the Banda forearc. These results highlight the fact that considerable amounts of continental lithosphere can be subducted while accreting only a thin section of uppermost crust. Continental subduction may have been favorable at Timor because of fast subduction rates, old oceanic crust at the consumed Australian margin, and subduction of some length of transitional crust. These results provide quantitative constraints for future numerical modeling of the geodynamics of continental subduction and arc-continent collision.
52 citations
Cites background from "Deformation and metamorphism of the..."
...The Aileu Complex has been previously described as a wide metamorphic belt with slates, phyllites, metavolcanics, quartzites, marbles, and amphibo lites (AudleyCharles, 1968; Berry and Grady, 1981; Charlton et al., 2002)....
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TL;DR: In this article, an analysis of the relatively immobile elements, particularly Ti, Zr, Y, Nb, P and rare earths, from both units revealed that the basalts vary from tholeiitic to mildly alkaline but are all consistent with emplacement in a rift-valley or ocean-floor setting.
Abstract: Metamorphosed basic volcanic rocks of Permo-Triassic age occur in several distinct geological formations on Timor. Some are found in para-autochthonous units, which have been correlated with similar sequences on the Australian continental shelf; and some occur in apparently allochthonous units, which have been correlated with similar sequences in Malaya and Sumatra. Analyses of the relatively immobile elements, particularly Ti, Zr, Y, Nb, P and the rare earths, from both units revealed that the basalts vary from tholeiitic to mildly alkaline but are all consistent with emplacement in a rift-valley or ocean-floor setting. No difference was detected between the units based on basalt geochemistry, no calc-alkaline basalts similar to those reported in Malaya and Sumatra were found. and the basaltic suites are regionally distributed so as to cross-cut boundaries between the para-autochthonous and allochthonous units. The geochemistry is consistent with the evolution of all the Permo-Triassic units now on Timor as a part of the Australian continental margin but requires revision of detailed interpretations in order to be compatible with an exotic origin for the ‘allochthonous’ units.
24 citations
TL;DR: A spinel lherzolite body outcrops as a fault block on the north coast of East Timor as discussed by the authors, where the dominant mineral assemblage is olivine, orthopyroxene, clinopyroxenes, spinel and calcic amphibole.
Abstract: A spinel lherzolite body outcrops as a fault block on the north coast of East Timor The most common rock‐type in this body is a clinopyroxene‐poor lherzolite, but there are smaller proportions of clinopyroxene‐rich lherzolite and harzburgite The dominant mineral assemblage is olivine, orthopyroxene, clinopyroxene, spinel and calcic amphibole Low‐temperature hydrous minerals are restricted in distribution The chemical composition of the peridotite is closely similar to mantle‐derived spinel lherzolite nodules and some alpine peridotites The internal variation of the peridotite suggests variable depletion by some combination of partial melting and liquid contamination of the residua, in a CO2‐rich system at 10–15 kb (1000–1500 MPa) Three solid‐state events are indicated by geothermometry The earliest event is recorded by coarse exsolution lamellae of orthopyroxene in clinopyroxene porphyro‐clasts These grains formed at 1250°C A later granoblastic texture equilibrated at 1100°C, and finally
24 citations
TL;DR: In particular, the wide range in Nd and Sr isotopic compositions, overlapping that of arc volcanics from the Sunda-Banda Island arc, and highly fractionated Nb/Ta values indicate a supra-subduction setting for the Hili Manu peridotite as discussed by the authors.
Abstract: The Hili Manu peridotite occupies a key position at the outer limit of continental crust on the north coast of East Timor. Most models for the tectonic evolution of the Outer Banda Arc interpret peridotite bodies on Timor, such as Hili Manu, as fragments of young oceanic lithosphere from the Banda Arc (upper plate). However, recent workers have used major-element geochemistry to argue that the peridotite bodies on Timor were derived from the Australian subcontinental lithosphere. Our major, trace and isotopic geochemical study of the Hili Manu peridotite body supports a supra-subduction origin from either a forearc or backarc position for the Hili Manu peridotite. In particular, the wide range in Nd and Sr isotopic compositions, overlapping that of arc volcanics from the Sunda – Banda Island arc, and highly fractionated Nb/Ta values indicate a supra-subduction setting. As there is no evidence for subduction beneath the rifted Australian continental margin, it is unlikely that the Hili Manu peridotite is A...
21 citations
Cites background or methods from "Deformation and metamorphism of the..."
...Isotope analyses (Table 3) were performed at the Max Planck-Institut für Chemie in Mainz by thermal ionisation mass spectrometry (TIMS) following methods outlined by Rampone et al. (1995). Both leached and unleached aliquots of whole-rock powders were analysed....
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...hot 6 N HCl, and the residue was thoroughly washed in H2O. During the period of analyses (1995), the La Jolla Nd standard and SRM-NBS 987 Sr standards yielded (143)Nd/(144)Nd1⁄4 0....
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...depletion by some combination of partial melting and liquid contamination of the residua. Berry (1981) recognised three solid-state events from...
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...For this project, we have reanalysed the original samples reported by Berry (1981). These samples have been moved to the University of Tasmania (UTAS) and...
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...the east, there is also a small block of amphibolite of ambiguous association (Berry 1979; Harris & Long 2000), but the nature of this eastern contact is unknown. Berry and McDougall (1986) suggested that this massive...
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