Thanks for the troll comment Bob. There was no workable Crossover solution for Rift beta. Since there was a lot of of Mac users on the rift forums and fansites asking for help I posted this solution at that time.
Rift For Mac
Prydz Bay lies at the seaward end of the Lambert rift graben, which extends 500 km south of Prydz Bay. The adjacent rift-flank mountains (e.g., Prince Charles Mountains) (Fig. F2) are mostly ice covered and have a visible relief of up to 3500 m. Most of the basement rocks of the region are high-grade Precambrian metamorphic and intrusive rocks (Tingey, 1991; Mikhalsky et al., 2001) with isolated onshore exposures of Paleozoic granite, mafic dykes, Permian sediments, Paleogene volcanics, and Oligocene and younger glacial sediments (Tingey, 1991; Hambrey and McKelvey, 2000a, 2000b).
The offshore area is underlain by the Prydz Bay sedimentary basin, which contains as much as 12 km of sediment (Cooper et al., 1991a) and is part of the extensive rift system that also includes the Lambert Graben. The broad pattern of ice and sediment movement in the region is controlled by the Lambert Graben. The rifting history extends back to at least Cretaceous (Truswell, 1991) and probably back to Permo-carboniferous (Arne, 1994). Sediments that probably occupy the Lambert Graben crop out in the Amery Oasis and were described by Fielding and Webb (1995) and McLoughlin and Drinnan (1997a, 1997b). During Leg 119 a pre-Cenozoic sedimentary section was sampled in the Prydz Bay Basin and included an undateable floodplain redbed unit similar to Triassic sediments onshore (Site 740) and a middle Aptian alluvial coal-bearing sequence (Site 741) (Turner and Padley, 1991). Core samples from the Mac.Robertson shelf indicate nearby outcrops of Jurassic and Early Cretaceous sedimentary rocks (Truswell et al., 1999). Cenozoic rocks were found at all Leg 119 shelf sites, and like Leg 188 Site 1166, they include late Neogene glacial diamictites with interbedded diatomaceous muddy units that unconformably overlie early Oligocene glaciomarine rock or pre-Cenozoic units.
The dominant tectonic event in the Lake Superior area was the development of the Keweenawan rift zone at approximately 1110 Ma.;Lithological sequences present within the Nipigon plate and the ages of these rocks are: passive granite and associated sub-aerial rhyolite (1536.7 +10/dollar-2.3dollar Ma); alkali basalt and lamprophyre dikes (ca. 1500 Ma); epicontinental clastic sediments of the Sibley Group (dollardollar1108 Ma); and extensive tholeiitic diabase sills, dikes and cone sheets (1108 +4/dollar-2dollar Ma). These sequences form a shallow basinal structure which overlies Archean crust and is connected to the Lake Superior basin in the south by the Black Sturgeon Graben. An increase in intensity of rifting toward Lake Superior is suggested by the form of the igneous intrusions feeding diabase sills in the Nipigon plate.;The diabase and picritic intrusions both crystallized from fractionated magmas. The picrites are cumulate rocks derived at shallow crustal depths from a magma controlled by olivine fractionation. Picrite chills are in equilibrium with olivine phenocrysts of composition Fodollar\sblcub80rcubdollar and are interpreted to be the least evolved liquids observed. The diabase sills crystallized from an evolved basaltic liquid controlled by cotectic crystallization of plagioclase and lesser olivine and pyroxene.;The diabase sills occur as two 150 to 200 m thick intrusions covering an area of 11,000 kmdollar\sp2dollar. The sills were emplaced under conditions approaching hydrostatic equilibrium near the Archean/Proterozoic unconformity. At the time of emplacement, the lithostatic load was probably less than 0.4 kbars. Crustal loading of the sedimentary sequence with sills enabled later magmas to erupt as basalts. Chemical variation within the sills reflects crystallization from multiple pulses of magma, minor crystal accumulation and movement of volatiles to late crystallizing parts of the sills. Variation in pyroxene crystallization sequences and the persistence of olivine during fractionation are a result of variations in a(SiOdollar\sb2dollar) in the magma. This variation may reflect the degree of contamination with siliceous crustal material.;Pre-Keweenawan passive granites and rhyolites are associated with a zone of ring faulting in northern Lake Nipigon. Partial melting of the lower crust with a heat source provided by mafic magmatism is suggested as a mechanism of producing the granites. (Abstract shortened with permission of author.)
2ff7e9595c
Comments