Reconstruction and break-out model for the Falkland Islands within Gondwana

Storey, B. C.; Curtis, Michael L.; Ferris, Julie; Hunter, M. A.; Livermore, Roy

doi:10.1016/s0899-5362(99)00086-x

Cited by 49 publications

(50 citation statements)

References 23 publications

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“…In the Gondwana reconstruction, this Mesoproterozoic Eastern Falkland basement lies south of the CFB front and the West Falkland a bit further north (e.g. Figure 6 in Storey et al, 1999), supporting our interpretation that a Mesoproterozoic basement occurs well south of the BMA and CFB.…”

Section: Extent Of the Nnmb Mid-crustsupporting

confidence: 80%

“…Such a fault plane is not imaged in the IyA-200501 seismic data and mineralized shear zones in the NNMB fail to explain the extent or source of the BMA feature. We therefore propose an alternative explanation: Jacobs et al (1997), Thomas et al (1997) and Storey et al (1999). Namaqua-Natal metamorphic terranes (NNMB): R = Richtersveld; G = Gordonia; B= Bushmanland of the Namaqua province; N = Natal province.…”

Section: Deep Crustal Profile Southern Karoo Basin and Beattie Magnementioning

confidence: 93%

“…Many Gondwana reconstructions place the Falkland Islands and surrounding plateau against the south coast of South Africa, conterminous with the Cape-Karoo basin (e.g. Grantham et al, 1997;Jacobs et al, 1997;Thomas et al, 1997;Storey et al, 1999; Figure 11). The basement to the Cape Supergroup equivalent rocks on the Falkland Islands are the ~1 Ga Mesoproterozoic amphibolite grade meta-volcanic and mafic sequences of the Cape Meredith Complex (Thistlewood et al, 1997;.…”

Section: Extent Of the Nnmb Mid-crustmentioning

confidence: 99%

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Deep Crustal Profile Across the Southern Karoo Basin and Beattie Magnetic Anomaly, South Africa: An Integrated Interpretation With Tectonic Implications

Lindeque

Wit

Ryberg

et al. 2011

South African Journal of Geology

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Two geophysical onshore-offshore lines on the southern margin of Africa form the Agulhas-Karoo Geophysical Transect (AKGT) and cross prominent geological features such as the Karoo Basin, Cape Fold Belt (CFB) and the Beattie Magnetic Anomaly (BMA). Geophysical data acquired along this AKGTransect between 2004 and 2007 within the Inkaba yeAfrica (lyA) framework, provide the platform for constructing a deep crustal section (IyA-200501) for the centre 100 km of the western AKGT-transect in order to resolve these features at depth. We present a detailed deep crustal model constructed from the joint interpretation of: i. archive data comprising surface geology, aeromagnetic data, nearby deep boreholes, teleseismic receiver functions and regional seismic reflection profiles, and ii. line coincident newly acquired high-resolution geophysical data consisting of near vertical seismic reflection data, shallow P-and S-wave velocity data, wide-angle refraction data, high resolution magnetotelluric data and impedance spectroscopy measurements on borehole samples. Our model differentiates four components in the up to 45 km thick crust: 1. a ~2 to 5 km thick folded Karoo Supergroup, disrupted by low-angle thrust faults rooted in a zone of local décollements in the lower Ecca Group and resting paraconformably on 2. a continuous undeformed sub-horizontal ~1.5 to 10 km thick wedge of the Cape Supergroup (CSG). This CSG wedge stretches from the Escarpment in the north to the tectonic front of the CFB in the south, and rests on an unconformity that dips about three degrees to the south. The angular unconformity is interpreted as an erosional peneplain that separates the CSG wedge from component 3. the ~13 to 21 km mid-crust basement below. The mid-crust contains a distinct north-dipping seismic fabric, here interpreted as 1.4 to 1.0 Ga Mesoproterozoic Namaqua-Natal Metamorphic Belt (NNMB) crust. A south-dipping mid-crustal detachment, interpreted as a ductile thrust zone, separates the mid-crust from component 4. a highly reflective ~10 to 24 km thick lower crust. The latter is interpreted as an older Palaeoproterozoic section of the NNMB (or even Archean cratonic basement), and bounded by a ~2 to 5 km thick, highly reflective bottom layer below that lies subparallel to a clear Moho. This bottom layer is interpreted as a mafic underplate, metasomatic reaction zone, or lower-crust to mantle transition zone. Collectively the seismic reflection and wide-angle refraction data support an interpretation that the NNMB mid-crustal layer contains the BMA source, possibly connected to two zones of strong reflectivity: a ~10 to 12 km wide northern zone and a ~5 to 7 km wide southern zone, both about 5 km thick and 7 to 8 km below surface. We interpret the BMA source to be at least in part, a Namaqua-like massive to disseminated, deformed/metamorphosed stratiform sulphide-magnetite ore body with metasomatic overprint.

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Section: Extent Of the Nnmb Mid-crustsupporting

confidence: 80%

Section: Deep Crustal Profile Southern Karoo Basin and Beattie Magnementioning

confidence: 93%

Section: Extent Of the Nnmb Mid-crustmentioning

confidence: 99%

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Deep Crustal Profile Across the Southern Karoo Basin and Beattie Magnetic Anomaly, South Africa: An Integrated Interpretation With Tectonic Implications

Lindeque

Wit

Ryberg

et al. 2011

South African Journal of Geology

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“…For example, ~ 15 km of such material in the lowermost crust would produce ~2.7 km of permanent uplift assuming a thermal time constant for the lithosphere of ~60 Ma (McKenzie, 1984) The early magmatic event related to the KarooFerrar LIP (Large Igneous Province) occurred between 174-184 Ma during the first breakup between east and west Gondwana, about 20-30 Ma before the initial opening of the Indian Ocean and the Weddell Sea (Cox, 1989;Storey, 1995;Storey and Kyle, 1997;Duncan et al, 1997;Hawkesworth et al, 1999;Storey et al, 1999;2001;Elliot and Fleming, 2000;Reeves and de Wit, 2000;Jokat et al, 2003;Eagles and König, 2007;Jourdan et al, 2007). The large thermal anomaly presumed to underlie the Karoo-Ferrar LIP Elliot and Fleming, 2000) may have initiated substantial uplift and exhumation across southern Africa (Cox, 1989) but this is not recorded in FTA dates of continental rocks or any basin analyses to date.…”

Section: Large Igneous Provinces (Lips) and Basaltic Underplatingmentioning

confidence: 99%

The Kalahari Epeirogeny and climate change: differentiating cause and effect from core to space

Wit

2007

South African Journal of Geology

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Southern Africa's high Kalahari plateau and its flanking mountain ranges formed over an extended period of ~200 million years through vertical tectonic processes different from those at convergent plate boundaries. We refer to this as the Kalahari epeirogeny. Episodic uplift and erosion during the Kalahari epeirogeny is inferred from thermo-chronology and from stratigraphy of sediment accumulated around its continental margin. A total thickness of 2 to 7 km of rock (of which basalt was a major component) was eroded from the subcontinent's surface during two punctuated episodes of exhumation, in the early-Cretaceous and in the mid-Cretaceous. Major exhumation was over by the end of the Cretaceous, and the rate of erosion decreased by more than an order of magnitude to remove less than 1 km thickness of rock during the Cenozoic. Cosmogenic dating shows that erosion rates today are almost an order of magnitude less still.The cause for the Kalahari epeirogeny remains elusive, but three striking observations stand out: (i) major exhumation occurred during the late Mesozoic break-up of Gondwana; (ii) large scale basaltic magmatism closely match two accelerated episodes of exhumation: first along the west coast (~132 Ma, Etendeka large igneous province [LIP], associated with vast amounts of underplating along this entire passive margin), and the second flanking the sheared south coast margin (~90 Ma, Agulhas oceanic LIP). Yet exhumation that might have accompanied the vast Karoo LIP (~180 Ma) is not readily detected; (iii) the two main regional episodes of accelerated exhumation and coastal sediment accumulation are near synchronous with two regional 'spikes' of kimberlite intrusions: >450 kimberlites at ~90 Ma, and >200 kimberlites at ~120 Ma. Southern Africa is underlain by an anomalous warm region in the lowermost ~1500 km of the mantle that is linked to core to mantle heat loss. This warm region was inherited from a large Cretaceous thermo-chemical anomaly in the mantle created during long-lived subduction beneath Gondwana. Associated Mesozoic kimberlite genesis and basaltic magmatism may have been sufficient to cause volatile/heat-induced density changes in the lithospheric mantle of southern Africa to sustain the Kalahari plateau. In addition, such changes may have been induced by tectonic uplift and decompressional melting resulting from far-field collision processes between Africa and Europe, and/or final continental lithosphere decoupling between the Falkland plateau and southern Africa. CO 2 released into the ocean-atmosphere system during the Kalahari epeirogeny contributed to the global mid-Cretaceous hot-house conditions. However, because the CO 2 -consumption rate associated with basalt weathering is about eight times that of granite, atmospheric CO 2 was also efficiently sequestrated during the rapid erosion of Karoo basalt. Thus, the Kalahari epeirogeny also may have catalysed the onset of long-term global Cenozoic cooling.

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“…Adie 1952;Marshall 1994;Storey et al 1999;Trewin et al 2002) in proximity to East Antarctica and the Ellsworth Mountains microplate. One such reconstruction is shown in Fig.…”

Section: In Reconstructions Of Gondwana the Falklands Microplate Is Gmentioning

confidence: 99%

Archaeocyathan limestone blocks of likely Antarctic origin in Gondwanan tillite from the Falkland Islands

Stone

Thomson

2005

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Other qualitative differences are also apparent between the tillites of East and West Falkland, quite apart from the well-defined facies contrast: the lithological and size range of the clasts is much greater in the west than in the east; clasts in the west are generally more rounded than those in the east; in the west there is a much higher proportion of red granite and quartzite, relative to white varieties. Additionally, the apparent concentration of archaeocyathan limestone clasts at a few localities in West Falkland, rather than their being randomly distributed, is a feature that may have broad stratigraphical and palaeogeographical implications. The archaeocyathsArchaeocyaths are extinct organisms with a long history of phylogenetic uncertainty but a current consensus that they were closely related to the sponges (Hill 1972; archaeocyaths then diversified rapidly into hundreds of species that were important contributors to the construction of early marine reefs. Despite their success they were a relatively short-lived group and were extinct before the end of the Cambrian, less than 25 million years after their first appearance. In contrast, other families of sponges that also appeared in the Cambrian are still represented today, over 500 million years later.

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Reconstruction and break-out model for the Falkland Islands within Gondwana

Cited by 49 publications

References 23 publications

Deep Crustal Profile Across the Southern Karoo Basin and Beattie Magnetic Anomaly, South Africa: An Integrated Interpretation With Tectonic Implications

Deep Crustal Profile Across the Southern Karoo Basin and Beattie Magnetic Anomaly, South Africa: An Integrated Interpretation With Tectonic Implications

The Kalahari Epeirogeny and climate change: differentiating cause and effect from core to space

Archaeocyathan limestone blocks of likely Antarctic origin in Gondwanan tillite from the Falkland Islands

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