Some of the most important, rapid, and enigmatic changes in our Earth’s environment and biota occurred during the Neoproterozoic Era (1000540 million years ago; Ma). Paramount among these changes are the rapid evolution of eukaryotes and appearance of metazoa (Knoll 1992, Conway Morris 1993), major episodes of continental glaciation that may have extended to low latitudes (Hambrey & Harland 1985), marked increases in the oxygen concentration of the atmosphere and hydrosphere (Derry et al 1992), the reappearance of sedimentary banded iron formations (BIF; James 1983), and striking temporal variations in the isotopic composition of C and Sr (Asmerom et al 1991, Derry et al 1992). Understanding the causes of and relationships between these changes is a challenging focus of interdisciplinary research, and there are compelling indications that the most important causes were tectonic (Des Marais et al 1992, Veevers 1990). For example, development of ocean basins may have been accompanied by the development of seafloor hydrothermal systems, which lowered the 87Sr/S6Sr of seawater, led to the development of BIF, and formed anoxic basins where organic carbon could be buried, thus leading to an increase in O~. Continental collision and formation of a supercontinent may have led to continental glaciation and an increase in the 87Sr/86Sr of seawater,

http://www.utdallas.edu/~rjstern/egypt/PDFs/General/SternEAO-AREPS94.pdf

ARC Assembly and Continental Collision in the Neoproterozoic East African Orogen: Implications for the Consolidation of Gondwanaland

A synopsis of events related to the assembly of eastern Gondwana

https://www.adelaide.edu.au/directory/alan.collins?dsn=directory.file;field=data;id=2241;m=view

Amalgamating eastern Gondwana: The evolution of the Circum-Indian Orogens

Terra Australis Orogen: Rodinia breakup and development of the Pacific and Iapetus margins of Gondwana during the Neoproterozoic and Paleozoic

Experimental and natural partitioning of Th, U, Pb and other trace elements between garnet, clinopyroxene and basaltic melts

An isotopic dating investigation (66 K-Ar and 34 Rb-Sr analyses) provided the geochronological framework for the Alpine events of metamorphism and granitic magmatism on Naxos. The oldest phase of high-pressure/medium-temperature metamorphism, M1, was dated by Rb-Sr and K-Ar analyses of paragonites, phengitic muscovites and muscovites at 45±5 Ma (Middle Eocene). Most of the record of the M1 phase has been eraded by a second phase of medium-pressure/high-temperature metamorphism, M2, which induced a metamorphic zonation with anatectic melting in the highest-grade part, the migmatite dome. Most K-Ar dates of M2 hornblendes, muscovites, biotites and tourmalines range from about 21 Ma in the lower-grade part (biotite-chloritoid zone) to about 11 Ma in the migmatite dome. From the pattern of K-Ar mineral dates it is concluded that the M2 phase took place 25±5 Ma ago (Late Oligocene/Early Miocene) and was followed by a prolonged cooling history until about 11 Ma ago (Late Miocene), when the ambient temperature in the migmatite dome had decreased to below 400−360 °C. A Rb-Sr whole-rock isochron analysis of a granodioritic mass dated the intrusion (and the associated M3 phase of contact-metamorphism) at 11.1±0.7 Ma (Late Miocene), with an initial 87Sr/86Sr ratio of 0.7112 ±0.0001. A local phase of low-grade retrograde metamorphism, M4, probably related to Late Alpine overthrusting, was dated at about 10 Ma (Late Miocene).

Dating the events of metamorphism and granitic magmatism in the Alpine orogen of Naxos (Cyclades, Greece)

Isotopic dating of older elements (including the Cabo Ortegal mafic-ultramafic complex) in the Hercynian orogen of NW Spain: Manifestations of a presumed Early Paleozoic mantle-plume

The Caledonian orogeny has imposed a zone of greenschist facies metamorphism on the high-grade Sveconorwegian basement along the front of the Caledonian nappe system in S.W. Norway. In this zone a Caledonian generation of green biotite (ca 400 Ma old) has developed, indicating a metamorphic temperature of about 400° C. This Caledonian biotite occurs side by side with relicts of a Sveconorwegian generation of brown biotite (ca 870 Ma old). The somewhat younger ages obtained from a number of brown biotites can be related to a partial transformation of the old biotite to titanite+green biotite during the Caledonian metamorphic recrystallization. Loss of radiogenic Ar and Sr from the biotite by volume diffusion apparently has not been operative, even at a temperature as high as 400° C. The Sveconorwegian biotite appears to have remained virtually closed to K-Ar and Rb-Sr up to the break-down due to metamorphic recrystallization.

On the thermal stability of Rb-Sr and K-Ar biotite systems: Evidence from coexisting Sveconorwegian (ca 870 Ma) and Caledonian (ca 400 Ma) biotites in SW Norway

A Rb-Sr analysis of suites of samples from a small intrusion of cordierite-bearing alkali granite into the peridotite of the Sierra Bermeja (Serrania de Ronda) yields an age of 22± 4 Ma (λ = 142×10−11 a−1): Late Oligocene/Early Miocene It is believed that the intrusion was derived from contact-anatectic melts produced along the hot ultramafic mass during and/or directly following its tangential, tectonic dislocation from a mantle diapir Its age can thus be taken as dating the termination of the hot emplacement of the ultramafic masses K-Ar dates of biotites and Rb-Sr dates of biotite/whole-rock pairs in contact-metamorphic wall rocks along the ultramafics mostly lie between 195 and 185 Ma This probably indicates that about 19 Ma ago the contact-zones of the ultramafic masses had cooled down to the blocking temperature of biotite to Rb-Sr and K-Ar

H.N.A. Priem

Papers

Dating the events of metamorphism and granitic magmatism in the Alpine orogen of Naxos (Cyclades, Greece)

Isotopic dating of older elements (including the Cabo Ortegal mafic-ultramafic complex) in the Hercynian orogen of NW Spain: Manifestations of a presumed Early Paleozoic mantle-plume

On the thermal stability of Rb-Sr and K-Ar biotite systems: Evidence from coexisting Sveconorwegian (ca 870 Ma) and Caledonian (ca 400 Ma) biotites in SW Norway

Isotopic dating of the emplacement of the ultramafic masses in the Serrania de Ronda, southern Spain

Possible zircon UPb evidence for Pan-African granulite-facies metamorphism in the Mozambique belt of southern Tanzania