Passive rifting

Goodge (1997, p. 698) summed up the presentation of his model for the tectonic evolution of the passive rift margin of East Antarctic into an active subduction zone which resulted in the prolonged Beardmore + Ross Orogeny with these words ... 

The insights gained by these specialized studies of the central Transantarctic Mountains must be examined critically to determine whether the master hypothesis concerning the formation of the Ross orogen presented by Stump (1995) is still valid and still explains satisfactorily the deposition of detrital sediment along a passive rift margin which later evolved into an active subduction zone that caused the deformation and regional metamorphism of the rocks that now form the basement complex of the central Transantarctic Mountains. 

The study of the structure and tectonic evolution of Antarctica was stimulated by a proposal that the East Antarctic craton was originally connected to North America (Moores 1991 Dalziel 1991 Hoffman 1991). This startling hypothesis was preceded by reports of Hartnady (1986,1991) and was prompted by the work of the Bell and Jefferson (1987) who had previously correlated the late Precambrian rocks of western Canada with similar rocks in South Australia. These authors concluded that a rift had formed between western Canada and Australia at about 1,200 Ma and that both continental fragments had developed complementary passive rift margins by about 750 Ma. 

Robinson and Splettstoesser (1986) also noted that the East and West Antarctic plates did not collide forcefully because the rocks of the Beacon Supergroup and of the Ferrar Group are not folded and thrust-faulted. In addition, the Transantarctic fault zone cannot be a normal fault because the geology of West Antarctica differs profoundly from the Transantarctic Mountains. Robinson and Splettstoesser (1986) also considered that the Transantarctic Mountains cannot be located on the passive margin of a continental rift that split the Antarctic plate because passive rift margins elsewhere do not reach the high elevations of the Transantarctic Mountains. Perhaps other processes have enhanced the elevation of the Transantarctic Mountains. 

Lithospheric stretching, passive upwelling of asthenosphere and variable degrees of decompression melting at various mantle levels in an intracontinental rifting setting ... 

This group includes peridotite massifs dominated by fertile Iherzolites that were exhumed in the early stages of continental rifting and exposed as denuded mantle on the seafloor, along passive continental margins. 

Oceanic arc -Forearc -On-craton Passive margin -Ocean island -Abyssal Ophiolite Coot- intraplate Massif Cont- arc -Cont- rift Pre-ocecmic margin -PUM -... 

Oceanic arc Forearc On-craton Passive margin Ocean island Abyssal Ophiolite Cent- intraplate Massif Cent- arc Cent- rift Pre-oceanic margin... 

The first is stratigraphic in nature and involves the relative abundance, particularly compared with sedimentary rocks, of mafic and ultramafic lavas piled in sequences of 1-10 km thickness, or sometimes multiple sequences, on pre-existing felsic crust. Modern flood basalts, related to mantle plumes, rifts, or both, are the closest analogue but are not nearly as dominant in the modern world relative to sediment-dominated cover sequences and passive margins. 

Bruhn, C.H.L (1993) High-re..solution stratigraphy, reservoir geometry and facies characterization of Cretaceous and Tertiary turhidites from rift and passive margin Brazilian basins. PhD thesis, McMaster University, Hamilton. 

Mauffret, a. Montadert, L. (1987) Rift tectonics of the passive continental margin off Galicia (Spain). Mar. Petrol. Geol., 4, 49-70. 

Tankard, A.J. Welsink, H.J. (1988) Extensional tectonics, structural styles and stratigraphy of the Mesozoic Grand Banks of Newfoundland. In Triassic-Jurassic Rifting Continental Breakup and the Origin of the Atlantic Ocean and Passive Margins, Part A (Ed. Manspeizer, W.). Devel. Geotectonics 22, 129-165. Elsevier, Amsterdam. 

Passive continental margin — rifted continental margins developed on thick continental crust on the edges of continents sedimentaiy basins on the trailing edge of a continent. 

Friedman G. M. (2002) Highest Phanerozoic strontium isotopic ratios of pre-rift late Cambrian passive margin in New York State USA products of continental weathering and orogenesis. Sedim Geol. 147, 143 153. 

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