who is tboz dating - What problems are encountered in dating metamorphic rocks

As with other isochron methods, the U-Pb isochron method has been questioned in the open literature, because often an excellent line of best fit between ratios obtained from a set of good cogenetic samples gives a resultant isochron and yields a derived age that has no distinct geological meaning.

what problems are encountered in dating metamorphic rocks-84

Owing to the isoclinal recumbent folding of metasedimentary units of the Cahill Formation, the typical rock sequence encountered at Koongarra is probably a tectono-stratigraphy (from youngest to oldest): muscovite-biotite-quartz-feldspar schist (at least 180m thick) garnet-muscovite-biotite-quartz schist (90-100m thick) sulphide-rich graphite-mica-quartz schist (±garnet) (about 25m thick) distinctive graphite-quartz-chlorite schist marker unit (5-8m thick) quartz-chlorite schist (±illite, garnet, sillimanite, muscovite) (50m thick) the mineralized zone reverse fault breccia (5-7m thick) sandstone of the Kombolgie Formation foliation of the schist sequence, which at Koongarra dips at 55° to the south-east.

The dominant structural feature, however, is the reverse fault system that dips at about 60° to the south-east, sub-parallel to the dominant S There are two discrete uranium orebodies at Koongarra, separated by a 100m wide barren zone. 1) orebody has a strike length of 450m and persists to 100m depth.

The Koongarra uranium deposit occurs in a metamorphic terrain that has an Archean basement consisting of domes of granitoids and granitic gneisses (the Nanambu Complex), the nearest outcrop being 5km to the north.

Some of the lowermost overlying Lower Proterozoic metasediments were accreted to these domes during amphibolite grade regional metamorphism (estimated to represent conditions of 5-8kb and 550-630°C) at 1800-1870Ma.

Yet in the literature these problems are commonly glossed over or pushed aside, but their increasing occurrence from a variety of geological settings does seriously raise the question as to whether U-Th-Pb data ever yields any valid age information.

One such geological setting that yields these false U-Th-Pb isochrons is the Koongarra uranium deposit and the surrounding area (Northern Territory, Australia).

Because no geologically meaningful results can be interpreted from the U-Th-Pb data at Koongarra (three uraninite grains even yield a Pb age of 0Ma), serious questions must be asked about the validity of the fundamental/foundational basis of the U-Th-Pb dating method.

This makes the task of creationists building their model for the geological record much easier, since claims of U-Th-Pb radiometric dating having proven the claimed great antiquity of the earth, its strata and fossils can be safely side-stepped.

Superimposed on the primary prograde metamorphic mineral assemblages of the host schist units is a distinct and extensive primary alteration halo associated, and cogenetic, with the uranium mineralization.

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