Ross-Delamerian Orogen Research Articles

Zircon U-Pb Dating of the Irizar Granite in the Central Victoria Land, Antarctica: Insights into the Tectonic Evolution along the Ross Orogen

It has been accepted that granitoids of the Irizar unit in the Central Victoria Land (Antarctica), as an important part of the Granite Harbour Intrusives, were formed in a post-collisional setting during the Ross orogeny along the margin of east Gondwana. However, the emplacement ages of the Irizar unit remain poorly constrained, making it difficult to form a more complete picture of the geodynamic evolution of the Ross orogen and its counterpart (Delamerian orogen) in southeast Australia. In this work, four syenogranite samples from the Irizar unit were chosen for SHRIMP zircon U-Pb dating, which yielded ages of 507.8–489.7 Ma. The new geochronological data indicate that the post-collisional extension in the Central Victoria Land had begun by ~508 Ma, much earlier than previously thought (i.e., 490–480 Ma). Integrated with U-Pb ages for Early Paleozoic granitoids from the literature, the Ross–Delamerian orogen shows that the post-collisional granitic magmatism initiated at ~515 Ma in the Central Transantarctic Mountains and northward systematically decreased to ~508 Ma in the Victoria Land, and then to ~487 Ma in southeast Australia. This can be explained well by the propagating northward transition from pre- and syn-collisional compression to post-collisional extension.

Zealandia and Australia at Ordovician continental margins: reconciling their similar and differing detrital zircon provenances within Rodinia

ABSTRACT New detrital zircon ages from biostratigraphically well-controlled Ordovician sandstones in southeast Australia are compared with published counterparts in southern Zealandia. During Rodinia supercontinent assembly (RA), Australia and Zealandia age patterns are similar, everywhere with ubiquitous late Mesoproterozoic magmatic zircon sources. However, during earliest Gondwana supercontinent assembly (GA), the age patterns have different sediment sources: (1) those of late Neoproterozoic age are more strongly represented in Zealandia but of uncertain location, but (2) those of late Cambrian-Ordovician age are more prominent in eastern Australia, having probable origins in the Ross-Delamerian Orogen. In particular, a distinctive zircon component, ca. 600–650 Ma, is ubiquitous in Zealandia but rare in Australia. Early Paleoproterozoic and Archean (Nuna, NU) zircon sources (2000–3200 Ma) become important (and locally up to 25% total) in Zealandia but not in Australia. It is difficult to reconcile all these sediment source requirements within disparate and distant Australian-Antarctic Precambrian complexes. Instead, it is proposed that, through the early Palaeozoic, Zealandia had only local sediment sources in a discrete Rodinia basement continental block outcropping in South Zealandia that was formerly adjacent to South China.

The amalgamation of Gondwana: calcite twinning and finite strains from the early–late Paleozoic Buzios, Ross, Kurgiakh and Gondwanide orogens

Abstract Orientated carbonate (calcite twinning strains; n = 78 with 2414 twin measurements) and quartzites (finite strains; n = 15) were collected around Gondwana to study the deformational history associated with the amalgamation of the supercontinent. The Buzios orogen (545–500 Ma), within interior Gondwana, records the high-grade collisional orogen between the São Francisco Craton (Brazil) and the Congo–Angola Craton (Angola and Namibia), and twinning strains in calc-silicates record a SE–NW shortening fabric parallel to the thrust transport. Along Gondwana's southern margin, the Saldanian–Ross–Delamerian orogen (590–480 Ma) is marked by a regional unconformity that cuts into deformed Neoproterozoic–Ordovician sedimentary rocks and associated intrusions. Cambrian carbonate is preserved in the central part of the southern Gondwana margin, namely in the Kango Inlier of the Cape Fold Belt and the Ellsworth, Pensacola and Transantarctic mountains. Paleozoic carbonate is not preserved in the Ventana Mountains in Argentina, in the Falkland Islands/Islas Malvinas or in Tasmania. Twinning strains in these Cambrian carbonate strata and synorogenic veins record a complex, overprinted deformation history with no stable foreland strain reference. The Kurgiakh orogen (490 Ma) along Gondwana's northern margin is also defined by a regional Ordovician unconformity throughout the Himalaya; these rocks record a mix of layer-parallel and layer-normal twinning strains with a likely Himalayan (40 Ma) strain overprint and no autochthonous foreland strain site. Conversely, the Gondwanide orogen (250 Ma) along Gondwana's southern margin has three foreland (autochthonous) sites for comparison with 59 allochthonous thrust-belt strain analyses. From west to east, these include: finite strains from Devonian quartzite preserve a layer-parallel shortening (LPS) strain rotated clockwise in the Ventana Mountains of Argentina; frontal (calcite twins) and internal (quartzite strains) samples in the Cape Fold Belt preserve a LPS fabric that is rotated clockwise from the autochthonous north–south horizontal shortening in the foreland strain site; Falkland Devonian quartzite shows the same clockwise rotation of the LPS fabric; and Permian limestone and veins in Tasmania record a thrust transport-parallel LPS fabric. Early amalgamation of Gondwana (Ordovician) is preserved by local layer-parallel and layer-normal strain without evidence of far-field deformation, whereas the Gondwanide orogen (Permian) is dominated by layer-parallel shortening, locally rotated by dextral shear along the margin, that propagated across the supercontinent.

Zircon geochronology and Hf isotopic study from the Leo Pargil Dome, India: implications for the palaeogeographic reconstruction and tectonic evolution of a Himalayan gneiss dome

AbstractU–Pb geochronology, Hf isotopes and trace-element chemistry of zircon grains from migmatite of the upper Sutlej valley (Leo Pargil), Northwest Himalaya, reveal a protracted geological evolution and constrain anatexis and tectonothermal processes in response to Himalayan orogenesis. U–Pb geochronology and ϵHf record separate clusters of ages on the concordia plots in the migmatite (1050–950 Ma, 850–790 Ma and 650–500 Ma). The 1050–950 Ma zircon population supports a provenance from magmatic units related to the assembly of Rodinia. A minor amount of Palaeoproterozoic grains were likely derived from the Indian craton. The potential source rock of the 930–800 Ma detrital zircons may be granitoid present in Greater Himalayan rocks themselves and the Aravalli Range, which has 870–800 Ma granitic rocks. The arc-type basement within the Himalayan–Tibet orogen recorded (900–600 Ma) igneous activity, which may depict a northeasterly extension of juvenile terranes in the Arabian–Nubian Shield. The granitoid of 800 Ma may be a potential source for 790 Ma detrital zircons owing to scatter in 206/238 dates. The 650–500 Ma zircon population suggests their derivation from the East African Orogen and Ross–Delamerian Orogen of Gondwana. The Cambrian–Ordovician magmatism during the Bhimphedian Orogeny and observed late Neoproterozoic to Ordovician detrital zircons have been derived to some extent from Greater Himalayan magmatic sources. We found no detrital zircon grains that cannot be explained as coming from local sources. One sample yielded a discordia lower intercept age of 15.6 ± 2.2 Ma, the age of melt crystallization.

Correlation and Late-Stage Deformation of Liv Group Volcanics in the Ross-Delamerian Orogen, Antarctica, from New U-Pb Ages

We present new zircon U-Pb isotopic data for volcanic rocks from deformed metavolcanic-sedimentary successions of the widespread Ross Supergroup in the Queen Maud Mountains, Antarctica. Zircon U-Pb analyses of Liv Group volcanic rocks thought to be Neoproterozoic in age instead have early Paleozoic ages. Zircon U-Pb analyses of five samples assigned to the Fairweather Formation have yielded 524±9 to 514±9 Ma (2σ) crystallization ages, whereas six samples assigned to the Taylor Formation have yielded 510±12 to 490±6 Ma (2σ) crystallization ages. Although these ages imply that the Fairweather Formation is generally older than the Taylor Formation, the age uncertainties show a 17-My overlap that is consistent with previous suggestions for temporal correlation of these formations. On a regional scale, Liv Group volcanism overlapped with the emplacement of ∼535–490 Ma plutonic rocks associated with the early Paleozoic Queen Maud batholith as well as igneous rocks found elsewhere along the early Paleozoic Pacific-Gondwana margin. Collectively, these igneous rocks provide plausible zircon sources for similar age detrital zircon populations found in outboard siliciclastic rocks belonging to the Leverett, Taylor, Fairweather, Greenlee, and Starshot Formations of the Queen Maud Mountains. The youngest crystallization age yielded by the deformed Taylor Formation (∼490 Ma) assumes regional significance because it represents the youngest volcanic rock yet identified within the Ross orogen in Antarctica and provides important new evidence for latest Cambrian or younger deformation, possibly associated with orogenic collapse during slab rollback at the terminal stages of the Ross orogeny.

Continuation of the Ross–Delamerian Orogen: insights from eastern Australian detrital-zircon data

Information on the Paleozoic tectonic evolution of the Tasmanides in eastern Australia is limited due to the presence of an extensive younger sedimentary cover. Based on the spatio-temporal distribution of deformation and magmatism, the Tasmanides have traditionally been subdivided into five domains (Delamerian, Thomson, Lachlan, Mossman and New England). To test the relationships between these domains, we compiled over 10000 published detrital-zircon ages from basement rocks of the Tasmanides. We split the dataset spatially to test postulated connectivity between domains, and temporally to isolate corresponding age populations that can highlight subtle variations between domains. Results show that the Delamerian and Thomson domains originated as a single orogenic belt that likely received detritus from an early Paleozoic continental-scale drainage system. We also recognise a remarkably similar pattern of Paleoproterozoic and Archean ages in the Delamerian, Thomson and New England domains. This similarity indicates that the late Paleozoic development of the New England domain involved recycling of rocks from the Delamerian–Thomson domain(s). These findings shed new light on the crustal architecture of eastern Australia, and the nature of Paleozoic drainage and sediment recycling in eastern Gondwana.

Deformation correlations, stress field switches and evolution of an orogenic intersection: The Pan-African Kaoko-Damara orogenic junction, Namibia

Age calibrated deformation histories established by detailed mapping and dating of key magmatic time markers are correlated across all tectono-metamorphic provinces in the Damara Orogenic System. Correlations across structural belts result in an internally consistent deformation framework with evidence of stress field rotations with similar timing, and switches between different deformation events. Horizontal principle compressive stress rotated clockwise ∼180° in total during Kaoko Belt evolution, and ∼135° during Damara Belt evolution. At most stages, stress field variation is progressive and can be attributed to events within the Damara Orogenic System, caused by changes in relative trajectories of the interacting Rio De La Plata, Congo, and Kalahari Cratons. Kaokoan orogenesis occurred earliest and evolved from collision and obduction at ∼590 Ma, involving E–W directed shortening, progressing through different transpressional states with ∼45° rotation of the stress field to strike-slip shear under NW–SE shortening at ∼550–530 Ma. Damaran orogenesis evolved from collision at ∼555–550 Ma with NW–SE directed shortening in common with the Kaoko Belt, and subsequently evolved through ∼90° rotation of the stress field to NE–SW shortening at ∼512–508 Ma. Both Kaoko and Damara orogenic fronts were operating at the same time, with all three cratons being coaxially convergent during the 550–530 Ma period; Rio De La Plata directed SE against the Congo Craton margin, and both together over-riding the Kalahari Craton margin also towards the SE. Progressive stress field rotation was punctuated by rapid and significant switches at ∼530–525 Ma, ∼508 Ma and ∼505 Ma. These three events included: (1) Culmination of main phase orogenesis in the Damara Belt, coinciding with maximum burial and peak metamorphism at 530–525 Ma. This occurred at the same time as termination of transpression and initiation of transtensional reactivation of shear zones in the Kaoko Belt. Principle compressive stress switched from NW–SE to NNW–SSE shortening in both Kaoko and Damara Belts at this time. This marks the start of Congo-Kalahari stress field overwhelming the waning Rio De La Plata-Congo stress field, and from this time forward contraction across the Damara Belt generated the stress field governing subsequent low-strain events in the Kaoko Belt. (2) A sudden switch to E–W directed shortening at ∼508 Ma is interpreted as a far-field effect imposed on the Damara Orogenic System, most plausibly from arc obduction along the orogenic margin of Gondwana (Ross-Delamerian Orogen). (3) This imposed stress field established a N–S extension direction exploited by decompression melts, switch to vertical shortening, and triggered gravitational collapse and extension of the thermally weakened hot orogen core at ∼505 Ma, producing an extensional metamorphic core complex across the Central Zone.

A continental arc tempo discovered in the Pacific-Gondwana margin mudpile?

Abstract The integration of detrital zircon age and trace element analyses provides a powerful tool with which to reconstruct continental arc evolution. Detrital zircons from the Ross-Delamerian orogen along the Pacific-Gondwana margin in north Victoria Land in Antarctica yield a broad 700–500 Ma U-Pb age population that shows a prominent period of activity centered at ca. 630–550 Ma. This activity is well correlated with the highest zircon Th/U and U/Yb ratios, suggesting an increase in lithospheric contribution coincident with fluid input from oceanic slab subduction, respectively. A low Yb/Gd ratio over this same period also suggests crustal thickening. Determination of zircon parent rock types using trace element proxies reveals the presence of previously unrecognized distinct pulses of granitoid activity that occur over tens of millions of years. Lulls between granitoid flare-ups overlap with increases in mafic-carbonatite-alkaline magma production, suggesting an influx of mantle or lower crustal melts during syn-subduction extension. A concomitant increase in the number of metamorphic zircons (U/Th > 10) and 40Ar/39Ar white mica cooling ages found during these extensional episodes suggest that significant thermal perturbations of the crust coincided with orogenic cooling, which was possibly influenced by uplift and exhumation.

Protracted (~ 30 Ma) eclogite-facies metamorphism in northern Victoria Land (Antarctica): Implications for the geodynamics of the Ross/Delamerian Orogen

Northern Victoria Land, Antarctica, plays a key role in any geodynamic reconstructions of the paleo-Pacific margin of Gondwana because it represents the along-strike continuation of Australia in Antarctica and hosts the only Paleozoic eclogites known along the Transantarctic Mountains. The architecture and evolution of the early Cambrian to Early Ordovician Ross–Delamerian Orogen in northern Victoria Land, however, remain controversial. Accurate geodynamic reconstructions have been hindered by a dearth of temporal metamorphic constraints. This study reports laser-ablation split-stream ICP-MS data on zircon in newly recognized eclogite, that preserves a memory of the prograde evolution, and on zircon from its country rock from the Lanterman Range of northern Victoria Land. Geochronological data are supplemented for the eclogite by whole-rock geochemical and petrological constraints, that indicate an E-MORB protolith derived from a depleted mantle source, and P–T conditions for the eclogite-facies stage of ~700°C and 1.7–2.4GPa. U–Pb ages, trace-element contents, cathodoluminescence imaging and textural/inclusion relationships testify to protracted zircon growth/recrystallization history under eclogite-facies conditions, that also included (re)crystallization during part of the prograde path. Results extend the onset of eclogite-facies metamorphism in northern Victoria Land back to ~530Ma and, together with geochronological evidence for the emplacement of calc-alkaline granitoids at ~530–520Ma, suggest that UHP–HP rocks formed by accretion of material beneath an active continental margin. Regionally, this interpretation implies that burial of mafic rocks and associated siliciclastic sequences to mantle depths commenced significantly earlier than previously believed (~500Ma), thereby contrasting with the common belief that high-pressure metamorphism was linked to arc–continent collision. New and old results reveal the coexistence along the same ridge of two eclogite types: (1) medium-grained, “colder” and undeformed eclogites, that recorded both prograde and peak conditions, and (2) finer-grained, “hotter” and slightly deformed eclogites, that recorded only metamorphic peak conditions with hints of the subsequent retrogression. We propose that “prograde/peak” eclogites formed during an active continental margin stage and “peak” eclogites during the subsequent island arc–continental arc collision.

Detrital zircon ages from the Ross Supergroup, north Victoria Land, Antarctica: Implications for the tectonostratigraphic evolution of the Pacific-Gondwana margin

We present new U–Pb isotopic age data for detrital zircons from 16 deformed sandstones of the Ross Supergroup in north Victoria Land, Antarctica. Zircon U/Th ratios primarily point to dominantly igneous parent rocks with subordinate contributions from metamorphic sources. Comparative analysis of detrital zircon age populations indicates that inboard stratigraphic successions (Wilson Terrane) and those located outboard of the East Antarctic craton (the Bowers and Robertson Bay terranes) have similar ~1200–950Ma (Mesoproterozoic–Neoproterozoic) and ~700–490Ma (late Neoproterozoic–Cambrian, Furongian) age populations. The affinity of the age populations of the sandstones to each other, as well as Gondwana sources and Pacific-Gondwana marginal stratigraphic belts, challenges the notion that the outboard successions form exotic terranes that docked with Gondwana during the Ross orogeny and instead places the terranes in proximity to each other and within the peri-Gondwana realm during the late Neoproterozoic to Cambrian. The cumulative zircon age suite from north Victoria Land yields a polymodal age spectra with a younger, primary 700–480Ma age population that peaks at ~580Ma. Cumulative analysis of zircons with elevated U/Th ratios (>20) indicating metamorphic heritage yield ~657–532Ma age probability peaks, which overlap with the younger dominantly igneous zircon population. The data are interpreted to give important new evidence that is consistent with ongoing convergent arc magmatism by ~626Ma, which provided the dominant zircon-rich igneous rocks and subordinate metamorphic rocks. Maximum depositional ages as young as ~493–481Ma yielded by deformed sequences in the outboard Bowers and Robertson Bay terrane samples provide new support for late Cambrian to Ordovician deformation in outboard sectors of the orogen, consistent with tectonic models that call for cyclic phases of contraction along the north Victoria Land sector of the Ross–Delamerian orogen.

The metamorphic sole of the western Tasmanian ophiolite: New insights into the Cambrian tectonic setting of the Gondwana Pacific margin

The Cambrian Ross–Delamerian Orogeny records the first phase of accretional tectonics along the eastern margin of Gondwana following breakup of the supercontinent Rodinia. Western Tasmania represents a key area for understanding the Cambrian tectonic setting of the eastern margin of Gondwana as it is one of the few places where a Tethyan-type ophiolite is preserved and contains the only known exposures of a sub-ophiolitic metamorphic sole associated with the Ross–Delamerian Orogen. This paper presents an integrated study of the field, petrographic, geochemical, and metamorphic characteristics of the metamorphic sole to the western Tasmanian ophiolite. The structurally highest levels of the metamorphic sole consist of granulite–upper amphibolite facies metacumulates and metagabbros. A transition to amphibolite and epidote–amphibolite facies conditions is recorded by metadolerites and metabasalts towards the base of the metamorphic sole. Kinematic indicators in mylonitic amphibolites suggest the metamorphic sole formed in an east-dipping subduction zone located to the east of the Proterozoic continental crust of Tasmania. Major and trace element whole rock and relict igneous spinel geochemistry indicates that the protoliths to the metamorphic sole formed at a back arc basin spreading centre. Our new data supports a model in which east-dipping subduction in Tasmania was driven by collapse of a back arc basin developed above an earlier west-dipping subduction zone outboard of the eastern margin of Gondwana. The proposed model may help to resolve a controversy related to apparent along-strike variations in subduction zone polarity during the Ross-Delamerian Orogeny and suggests a complex geodynamic setting had developed along the eastern margin of Gondwana by the Middle Cambrian. This study highlights the importance of considering the role of multiple subduction zones in generating metamorphic soles and emplacing ophiolites, which are key events associated with the construction of many orogenic belts worldwide.

Time–space focused intrusion of genetically unrelated arc magmas in the early Paleozoic Ross–Delamerian Orogen (Morozumi Range, Antarctica)

The growth of continental crust in accretionary orogenic belts takes place through repeated cycles of subduction–accretion of rock units from continental and oceanic magmatic arcs, supra-subduction zone backarcs and forearcs loaded with continent-derived materials. An ancient example relevant to magmatic arc accretion models is represented by the remnants of the Cambrian–Ordovician Ross Orogen in the Morozumi Range, Victoria Land (Antarctica). There, late Neoproterozoic phyllites host an intrusive complex which preserves a remarkably uncommon record of genetically unrelated magma pulses emplaced under a variable stress regime in a short time span: (1) a dominant K-feldspar–phyric granite, (2) fine-grained dioritic stocks and dykes, (3) a peraluminous granite; and (4) a tonalitic–granodioritic dyke swarm. Laserprobe U–Pb zircon dates cluster at late Cambrian times for all these units, yet they carry differential cargoes of relict cores. Unique geochemical–isotopic signatures for both the less evolved magmas (diorite and dyke tonalite) and the most acidic ones (granite and peraluminous granite) indicate that each one of them originated from distinct sources at depth. Additionally, field relationships and chemical evolutionary trends testify for a variety of shallow level open-system processes, such as magma mingling/mixing between diorite and main granite magmas, as well as progressive incorporation of the host schists by the dyke tonalite magma. In summary, crustal growth in the Morozumi intrusive complex was contributed by fresh mantle magma issuing from the metasomatised mantle wedge, while the production of other melts did recycle different crustal portions/layers: the main granite derived from Grenville-age granulitic lower crust; the peraluminous granite from late Proterozoic upper crust, and the tonalite magmas derived from subduction erosion-enriched subarc mantle and evolved by ingestion of local metasedimentary rocks. Overall, the Morozumi intrusive complex yields evidence for emplacement in the same site at the same time of magmas issuing from different sources that are usually found at a different depth in the arc lithospheric section. A likely scenario to activate this specific mechanism of melt production is a subduction zone affected by subduction erosion.

Detrital zircon ages in Buller and Takaka terranes, New Zealand: constraints on early Zealandia history

Detrital zircon ages are presented for 34 early Palaeozoic sandstones from Buller and Takaka terranes, New Zealand, and formerly adjacent parts of Australia–Antarctica. The Buller–Takaka datasets always have two major groups: Ordovician–late Neoproterozoic, 444–700 Ma (but mainly 540–700 Ma), termed ‘Gondwana Assembly’ (GA), and early Neoproterozoic–Mesoproterozoic, 700–1600 Ma (but mainly 900–1200 Ma), termed ‘Rodinia Assembly’ (RA). In both terranes, significant age components within these groups are strikingly similar and also have RA/GA ratios, 0.6–1.8. The Cambrian volcanic arc of the Takaka Terrane has contributed little to the zircon patterns. Proportions of Late Cambrian–Early Ordovician zircons, characteristic of granitoid sources in the Ross–Delamerian Orogen are low. The zircons are predominantly reworked with contemporary zircons only evident in a few Buller datasets. The zircon patterns suggest that two major sources (late Mesoproterozoic and late Neoproterozoic), enduring over 120 Ma, were widely distributed and it is postulated they form Precambrian basement beneath southern Zealandia.

Paleozoic siliciclastic rocks from northern Victoria Land (Antarctica): Provenance, timing of deformation, and implications for the Antarctica-Australia connection

Paleozoic sequences exposed along the Transantarctic Mountains in Antarctica and in southeastern Australia are segments of a formerly contiguous accretionary orogen that developed along the eastern margin of Gondwana. The margin underwent amalgamation and eastward accretion in the early Cambrian to Early Ordovician Ross-Delamerian orogen and in the Ordovician to Carboniferous Lachlan orogen. Northern Victoria Land plays a key role in many geodynamic reconstructions because it has long been considered the along-strike continuation of Australia in Antarctica; however, the correlation between lithotectonic units in Antarctica (Wilson, Bowers, and Robertson Bay terranes) and those in southeastern Australia (Glenelg, Grampians-Stavely, and Stawell zones), as well as the presence of Lachlan-aged tectono-metamorphic events in northern Victoria Land, are still uncertain. 40 Ar- 39 Ar laser experiments on detrital and syndeformational white micas from low-grade siliciclastic rocks of northern Victoria Land, in conjunction with mineral-textural analysis and whole-rock geochemical and Nd isotope data, are used to constrain provenance and the timing of deformation, and to assess analogies with correlative structural zones in southeastern Australia. Detrital white micas of the western lithotectonic unit (Wilson terrane) yielded an age pattern dominated by late Cryogenian to Ediacaran ages (650–550 Ma), closely matching those of turbidites from the Australian Kanmantoo Group. Detrital white micas from the easternmost lithotectonic units (Bowers terrane and Robertson Bay terrane) yield indistinguishable age patterns, strikingly in agreement with those available for the western subprovince of the Lachlan orogen in Australia, which are dominated instead by younger ages with a dominant Ross orogen fingerprint (550–480 Ma). Deposition of siliciclastic detritus in the three lithotectonic units most likely occurred synchronously in the early–middle Cambrian, and the different signatures suggest that detritus was supplied from different source areas, with sediment supply from the west-southwest (East African orogen or ice-covered regions of East Antarctica) in the Wilson terrane and from the south (Ross orogen) in the Bowers and Robertson Bay terranes. Results also provide evidence for post-Ross orogen (ca. 462 Ma) contractional tectonics at the boundary between the Bowers and the Robertson Bay terranes, suggesting that available Ar data from the literature are variably affected by the presence of detrital micas. This finding establishes a cause-effect relationship between compressional tectonics at the plate margin and Middle–Late Ordovician intraplate reactivation processes in the western Wilson terrane. The accretion of northern Victoria Land was polyphase; it began with the amalgamation of the Bowers and Wilson terranes in the middle–late Cambrian and was followed by the docking of the Robertson Bay and Bowers terranes in the Middle–Late Ordovician. Results further support the link between northern Victoria Land and southeastern Australia. Together with a careful examination of data from the literature, they also suggest that the Bowers terrane and the across-strike contiguous Robertson Bay terrane are correlatives of the whole Stawell zone.

Provenance connections between late Neoproterozoic and early Palaeozoic sedimentary basins of the Ross Sea region, Antarctica, south-east Australia and southern Zealandia

AbstractThick successions of turbidites are widespread in the Ross–Delamerian and Lachlan orogens and are now dispersed through Australia, Antarctica and New Zealand. U-Pb detrital zircon age patterns for latest Precambrian, Cambrian and Ordovician metagreywackes show a closely related provenance. The latest Neoproterozoic–early Palaeozoic sedimentary rocks have major components, at c. 525, 550, and 595 Ma, i.e. about 40–80 million years older than deposition. Zircons in these components increase from the Neoproterozoic to Ordovician. Late Mesoproterozoic age components, 1030 and 1070 Ma, probably originate from igneous/metamorphic rocks in the Gondwanaland hinterland whose exact locations are unknown. Although small, the youngest zircon age components are coincident with estimated depositional ages suggesting that they reflect contemporaneous and minor, volcanic sources. Overall, the detrital zircon provenance patterns reflect the development of plutonic/metamorphic complexes of the Ross–Delamerian Orogen in the Transantarctic Mountains and southern Australia that, upon exhumation, supplied sediment to regional scale basin(s) at the Gondwana margin. Tasmanian detrital zircon age patterns differ from those seen in intra-Ross Orogen sandstones of northern Victoria Land and from the oldest metasediments in the Transantarctic Mountains. A comparison with rocks from the latter supports an allochthonous western Tasmania model and amalgamation with Australia in late Cambrian time.

Extent of the Ross Orogen in Antarctica: new data from DSDP 270 and Iselin Bank

AbstractThe Ross Sea is bordered by the Late Precambrian–Cambrian Ross–Delamerian Orogen of East Antarctica and the more Pacific-ward Ordovician–Silurian Lachlan–Tuhua–Robertson Bay–Swanson Orogen. A calcsilicate gneiss from Deep Sea Drilling Project 270 drill hole in the central Ross Sea, Antarctica, gives a U-Pb titanite age of 437 ± 6 Ma (2σ). This age of high-grade metamorphism is too young for typical Ross Orogen. Based on this age, and on lithology, we propose a provisional correlation with the Early Palaeozoic Lachlan–Tuhua–Robertson Bay–Swanson Orogen, and possibly the Bowers Terrane of northern Victoria Land. A metamorphosed porphyritic rhyolite dredged from the Iselin Bank, northern Ross Sea, gives a U-Pb zircon age of 545 ± 32 Ma (2σ). The U-Pb age, petrochemistry, Ar-Ar K-feldspar dating, and Sr and Nd isotopic ratios indicate a correlation with Late Proterozoic–Cambrian igneous protoliths of the Ross Orogen. If the Iselin Bank rhyolite is not ice-rafted debris, then it represents a further intriguing occurrence of Ross basement found outside the main Ross–Delamerian Orogen.

Precambrian sources of Early Paleozoic SE Gondwana sediments as deduced from combined Lu–Hf and U–Pb systematics of detrital zircons, Takaka and Buller terrane, South Island, New Zealand

Combined U–Pb–Lu–Hf isotope investigations on small detrital zircons (30–120 μm) using solution ID-MC-ICPMS and ID-TIMS were carried out on Cambrian–Ordovician sedimentary rocks from the Buller and Takaka terranes of the northeastern South Island of New Zealand. The sediments in these two terranes are considered correlatives of voluminous sedimentary belts in the Lachlan and Adelaidian fold belts of southeastern Australia and in the Wilson and Bowers terranes of Antarctica (SE Gondwana). In order to constrain the sources of these sediments, we use combined U–Pb and Lu–Hf data from detrital zircons, enabling the calculation of Lu–Hf model ages that date the crustal residence time of the zircon protoliths. The Lu–Hf age information is combined with Nd model ages for the bulk sediments. U–Pb systematics of the detrital zircons show age maxima at 0.5–0.6 Ga, 0.8 Ga, and 1.0–1.2 Ga, with initial εHf values for the New Zealand detrital zircons ranging from + 14.9 to − 27.6. These zircon age populations broadly agree with age patterns for sediments found elsewhere in SE Gondwana, confirming a link between the Paleozoic belts of New Zealand and Australia–Antarctica. Lu–Hf model ages obtained from the detrital zircon populations range from 0.9 to 3.7 Ga with an age maximum at ~ 1.5 Ga. A comparison with average crustal residence ages of potential source regions indicates that the Ross-Delamerian orogen of present day Eastern Australia and Antarctica, and crustal provinces in Western Australia are likely sources. The presence of sources as distant as Western Australia suggests long transport pathways for the zircons, possibly via large river systems. A comparison of model age distributions for sediments from Australia, Antarctica, and New Zealand indicate that the Australian sediments have been fed by an additional Archean source (~ 2.8–3.1 Ga), in contrast to sedimentary rocks from New Zealand and Antarctica that lack an Archean model age peak.

Extraordinary transport and mixing of sediment across Himalayan central Gondwana during the Cambrian-Ordovician

Detrital zircon samples from Cambrian and Lower to Middle Ordovician strata were taken across and along the strike of the Hima- laya from Pakistan to Bhutan (~2000 km). By sampling rocks from one time interval for nearly the entire length of an orogen, and by covering a range of lithotectonic units, we minimize time as a signifi cant source of vari- ance in detrital age spectra, and thus obtain direct assessment of the spatial variability in sediment provenance. This approach was applied to the Tethyan margin of the Hima- laya, which during the Cambrian occupied a central depositional position between two major mountain belts that formed during the amalgamation of Gondwana, the inter- nal East African orogen and the external Ross-Delamerian orogen of East Gondwana. Detrital age spectra from our Lesser and Tethyan Himalayan samples show that well- mixed sediment was dispersed across at least 2000 km of the northern Indian margin. The detrital zircon age spectra for our samples are consistent with sources for most grains from areas outside the Indian craton that record Pan-African events, such as the Ross- Delamerian orogen; East African orogen, in- cluding the juvenile Arabian-Nubian Shield; and Kuunga-Pinjarra orogen. The great dis- tances of sediment transport and high degree of mixing of detrital zircon ages are extraor- dinary, and they may be attributed to a com- bination of widespread orogenesis associated with the assembly of Gondwana, the equa- torial position of continents, potent chemical weathering, and sediment dispersal across a nonvegetated landscape.

Proterozoic metamorphism in Tasmania: Implications for tectonic reconstructions

Tasmania forms an enigmatic province within the Neoproterozoic history of Australia. While now part of Australia, it was closer to East Antarctica in the Cambrian. It also lies at the boundary between Australia and North America in most Rodinia reconstructions. The Tasmanian Proterozoic stratigraphy has some common features with South Australia but there are major differences. New chemical U–Th–Pb monazite dating demonstrates that Tasmania was metamorphosed at 1290 Ma and again at 920 Ma, and intruded by granitoids at 1050 Ma. These results and a compilation of other data relevant to the Proterozoic evolution of Tasmania are used to test several aspects of Rodinia reconstructions. The Mesoproterozoic tectonic history of Tasmania is similar to the Musgrave Block in central Australia. However, the best correlation of Proterozoic history for Tasmania is with the Transantarctic Mountains. We conclude that the Western Tasmanian Terrane rifted from the East Antarctic margin at 580 Ma and was trapped outboard of the Cambrian Ross-Delamerian Orogen. The Victoria Land-Transantarctic Mountains-Western Tasmania block has many similarities to southwest Laurentia and provides additional support for the AUSWUS reconstruction of Rodinia.

A Damara orogen perspective on the assembly of southwestern Gondwana

Abstract The Pan-African Damara orogenic system records Gondwana amalgamation involving serial suturing of the Congo–São Francisco and Río de la Plata cratons (North Gondwana) from 580 to 550 Ma, before amalgamation with the Kalahari–Antarctic cratons (South Gondwana) as part of the 530 Ma Kuunga–Damara orogeny. Closure of the Adamastor Ocean was diachronous from the Araçuaí Belt southwards, with peak sinistral transpressional deformation followed by craton overthrusting and foreland basin development at 580–550 Ma in the Kaoko Belt and at 545–530 Ma in the Gariep Belt. Peak deformation/metamorphism in the Damara Belt was at 530–500 Ma, with thrusting onto the Kalahari Craton from 495 Ma through to 480 Ma. Coupling of the Congo and Río de la Plata cratons occurred before final closure of the Mozambique and Khomas (Damara Belt) oceans with the consequence that the Kuunga suture extends into Africa as the Damara Belt, and the Lufilian Arc and Zambezi Belt of Zambia. Palaeomagnetic data indicate that the Gondwana cratonic components were in close proximity by c. 550 Ma, so the last stages of the Damara–Kuunga orogeny were intracratonic, and led to eventual out-stepping of deformation/metamorphism to the Ross–Delamerian orogen ( c. 520–500 Ma) along the leading edge of the Gondwana supercontinental margin.