SHRIMP U-Pb zircon dating was undertaken on two samples of Dokhan Volcanics from the type area at Gebel Dokhan, north Eastern Desert, Egypt. A quartz andesite from the Imperial Porphyry unit has a weighted 206Pb/238U age of 593 f 13 Ma (20). A sample of grey andesite, from 450 m lower in the succession, has a weighted 206Pb/23*U age of 602 + 9 Ma (20). These ages are interpreted to record the t...

Oliverian Magma Series gneisses (442–454 Ma) in the cores of domes in southwestern New Hampshire have an igneous mineralogy that crystallized at pressures (P) of 9–11 kbar and temperatures (T) of 650–775 °C, whereas the cover (Ammonoosuc Volcanics) has the same formation age (453 ± 2 Ma) yet is clearly extrusive. A significant crustal section, ~30 km thick, must have originally separated the tw...

A field-mapping and crystal-chemical study of two aluniteand halloysite-rich deposits in the Turplu area, situated northwest of Balıkesir on the Biga Peninsula of northwest Turkey reveals a mineralogically diverse and a potentially economic clay deposit. The mineral assemblage along fault zones is dominated by halloysite and sometimes alunite. The alunite is nearly end-member in composition (a ...

Boninites are unusual island arc volcanic rocks with high MgO (>9%), high Si0 2 (>55%) contents, and exceptionally low TiO 2 (<0.4%) contents. High MgO contents, MgO/(MgO + EFeO), Ni, Cr and Co contents indicate that boninites have equilibrated with mantle peridotite. Experimental petrologic studies and high Cr/(Cr + Al) in spinels in boninites suggest that they have separated from extremely re...

An array of variometers across south-east Australia has recorded natural magnetic variations having power in a frequency band of 0.04-10 cycles/hr. The set data have outlined two major regions of high terrestrial electrical conductivity (c); the first beneath the sea floor off the Australian southeast coast; the second in the vicinity of the most recent eruptive centres of the ‘ Newer Volcanics...

Late Precambrian to early Cambrian sediments of the Amadeus Basin, Central Australia, contain two stable directions of magnetization. Lithologies are diverse and include red beds, green beds, and carbonates, all of which respond to thermal cleaning. Positive fold and unconformity tests, and a well-defined polarity zonation reveal the primary component and direction of magnetization. This direct...