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81.
82.
Paul Jacob Hancock Paul Roberts Michael J. Kesteven Ronald D. Ekers Elaine M. Sadler Tara Murphy Marcella Massardi Roberto Ricci Mark Calabretta Gianfranco de Zotti Philip G. Edwards Jennifer A. Ekers Carole A. Jackson Mark Leach Chris Phillips Robert J. Sault Lister Staveley-Smith Ravi Subrahmanyan Mark A. Walker Warwick E. Wilson 《Experimental Astronomy》2011,32(2):147-177
The Australia Telescope 20 GHz (AT20G) survey is a large area (2?? sr), sensitive (40 mJy), high frequency (20 GHz) survey of the southern sky. The survey was conducted in two parts: an initial fast scanning survey, and a series of more accurate follow-up observations. The follow-up survey catalog has been presented by Murphy et al. (MNRAS 402:2403, 2010). In this paper we discuss the hardware setup and scanning survey strategy as well as the production of the scanning survey catalog. 相似文献
83.
The Abbott Unit (∼508 Ma) and the Vegetation Unit (∼475 Ma) of the Terra Nova Intrusive Complex (northern Victoria Land,
Antarctica) represent the latest magmatic events related to the Early Paleozoic Ross Orogeny. They show different emplacement
styles and depths, ranging from forcible at 0.4–0.5 GPa for the Abbott Unit to passive at ∼0.2 GPa for the Vegetation Unit.
Both units consist of mafic, felsic and intermediate facies which collectively define continuous chemical trends. The most
mafic rocks from both units show different enrichment in trace element and Sr-Nd isotopic signatures. Once the possible effects
of upper crustal assimilation-fractional crystallisation (AFC) and lower crustal coupled AFC and magma refilling processes
have been taken into account the following features are recognised: (1) the modelled primary Abbott Unit magma shows a slightly
enriched incompatible element distribution, similar to common continental arc basalts and (2) the modelled primary Vegetation
Unit magma displays highly enriched isotope ratios and incompatible element patterns. We interpreted these major changes in
magmatic affinity and emplacement style as linked to a major change in the tectonic setting affecting melt generation, rise
and emplacement of the magmas. The Abbott Unit mafic melts were derived from a mantle wedge above a subduction zone, with
subcontinental lithospheric mantle marginally involved in the melting column. The Vegetation Unit mafic melts are regarded
as products of a different source involving an old layer of subcontinental lithospheric mantle. The crustal evolution of both
types of mafic melts is marked by significant compositional contrasts in Sr and Nd isotopes between mafic and associated felsic
rocks. The crustal isotope signature showed an increase with felsic character. Geochemical variations for both units can be
accounted for by a similar two-stage hybridisation process. In the first stage, the most mafic magma evolved mainly by fractional
crystallisation coupled with assimilation of metasedimentary rocks having crustal time-integrated Sr and Nd compositions similar
to those of locally exposed metamorphic basement. The second stage involves contaminated products mixing with independently
generated crustal melts. Petrographic, geochemical and isotope data also provide evidence of significant compositional differences
in the felsic end-members, pointing to the involvement of metaigneous and metasedimentary source rocks for the Abbott granite
and Vegetation leucogranite, respectively.
Received: 31 March 1998 / Accepted: 3 May 1999 相似文献