Petrogenesis of calcic plagioclase megacrysts in Archean rocks

Anorthositic complexes with large equidimensional plagioclase grains of highly calcic composition occur in nearly all Archean cratons. Similar plagioclase occur as megacrysts in many Archean sills, dikes, and volcanic flows. In the Canadian Shield these units occur throughout the Archean portions of the entire shield and are particularly common as dikes over an area of a few 100,000 sq km in Ontario and Manitoba during a period of at least 100 m.y. in many different rock types and metamorphic grades. The plagioclase generally occurs in three modes: as inclusions in mafic intrusions at various stages of fractionation, as crystal segregations in anorthosite complexes, or as megacrysts in fractionated sills, dikes, and flows. Most occurrences suggest that the plagioclase was formed elsewhere before being transported to its present location. The evidence seems to be quite clear that occurrences of these types of calcic plagioclase require: (1) ponding of a relatively undifferentiated Archean tholeiitic melt at some depth; (2) isothermal crystallization of large, equidimensional homogeneous plagioclase crystals; (3) separation of the plagioclase crystals from any other crystalline phases; (4) further fractionation of melt; (5)transport of various combinations of individual plagioclase crystals and clusters of crystals by variously fractionated melts; and (6) emplacement as various types of igneous intrusions or flows

Delta method, an empirical drag buildup technique

An empirical drag correlation technique was developed from analysis of 19 subsonic and supersonic military aircraft and 15 advanced or supercritical airfoil configurations which can be applied in conceptual and advanced aircraft design activities. The Delta Method may be used for estimating the clean wing drag polar for cruise and maneuver conditions up to buffet onset, and to approximately Mach 2.0. This technique incorporates a unique capability of predicting the off-design performance of advanced or supercritical airfoil sections. The buffet onset limit may also be estimated. The method is applicable to wind tunnel models as well as to full scale configurations. This technique has been converted into a computer code for use on the IBM 360 and CDC 7600 computer facilities at NASA AMES. Results obtained using this method to predict known aircraft characteristics are good and agreement can be obtained within a degree of accuracy judged to be sufficient for the initial processes of preliminary design

Archaean megacrystic plagioclase units and the tectonic setting of greenstones

Large (up to 20 cm), equidimensional, commonly euhedral, plagioclase megacrysts of highly calcic composition (An sub 80-90) occur commonly in all Archean cratons in one or more of three distinct associations: (1) as cumulate crystal segregations of anorthosite or as megacrysts in basaltic dikes, sills, and flows in greenstone belts that vary in metamorphic grade from greenschist to granulite. Throughout 100's of thousands of square kilometers of northwestern Ontario and Manitoba the plagioclase megacrysts occur in pillowed and massive flows, sills, dikes, large inclusions in dikes, and intrusive anorthositic complexes with areas of up to a few 100 sq km and spanning a period of at least 100 m.y. in the 2.7 to 2.8 b.y. time frame; (2) as basaltic dike swarms in stable cratonic areas forming parallel to subparallel patterns over hundreds of thousands of square kilometers intruding both granitic gneisses and supracrustal belts including greenstones. These swams include the Ameralik-Saglek system at 3.1 to 3.4 b.y., the Matachewan system at 2.5 to 2.6 b.y., and the Beartooth-Bighorn system at 2.2 to 2.3 b.y.; and, (3) as anorthositic complexes associated with marbles and quartzites (Sittampundi, India and Messina, South Africa) in granulite grade terrains. Initial attempts to correlate tectonic settings of similar modern crystbearing units with their Archean counterparts were only partially successful

The Petrogenetic significance of Plagioclase megacrysts in Archean rocks

The petrogenetic significance of plagioclase megacryst-bearing Archean rocks was considered. It was suggested that these developed in mid-to upper-crustal magma chambers that were repeatedly replenished. Crystallization of megacrysts from a primitive liquid that evolves to an Fe-rich tholeiite (with LREE enrichment) is nearly isothermal and is an equilibrium process. Cumulates probably form near the margins of the chambers and liquids with megacrysts are periodically extracted and can appear as volcanics. Some flows and intrusives are found in arc-like settings in greenstone belts. Megacrystic dikes represent large volumes of melt and dike swarms such as the Metachawan swarm of Ontario suggest multiple sources of similar compositions. A complex series of melt ponding and migration are probable and involve large amounts of liquid

Tectonic implications of Archean anorthosite occurrences

The occurrences of megacrystic anorthosite and basalt in a variety of geologic settings were reviewed and it was found that these rock types occur in a variety of tectonic settings. Anorthosites and megacrystic basalts are petrogenetically related and are found in oceanic volcanic crust, cratons, and shelf environments. Although megacrystic basalts are most common in Archean terranes, similar occurrences are observed in rocks of early Proterozoic age, and even in young terranes such as the Galapagos hotspot. Based on inferences from experimental petrology, all of the occurrences are apparently associated with similar parental melts that are relatively Fe-rich tholeiites. The megacrystic rocks exhibit a two- (or more)-stage development of plagioclase, with the megacrysts having relatively uniform composition produced under nearly isothermal and isochemical conditions over substantial periods of time. The anorthosites appear to have intruded various crustal levels from very deep to very shallow. The petrogenetic indicators, however, suggest that conditions of formation of the Precambrian examples were different from Phanerozoic occurrences

Linguistic Reflection in Java

Reflective systems allow their own structures to be altered from within. Here we are concerned with a style of reflection, called linguistic reflection, which is the ability of a running program to generate new program fragments and to integrate these into its own execution. In particular we describe how this kind of reflection may be provided in the compiler-based, strongly typed object-oriented programming language Java. The advantages of the programming technique include attaining high levels of genericity and accommodating system evolution. These advantages are illustrated by an example taken from persistent programming which shows how linguistic reflection allows functionality (program code) to be generated on demand (Just-In-Time) from a generic specification and integrated into the evolving running program. The technique is evaluated against alternative implementation approaches with respect to efficiency, safety and ease of use.Comment: 25 pages. Source code for examples at http://www-ppg.dcs.st-and.ac.uk/Java/ReflectionExample/ Dynamic compilation package at http://www-ppg.dcs.st-and.ac.uk/Java/DynamicCompilation

CIR Modulation of the X-ray Flux from the O7.5 III(n)((f)) Star xi Persei?

We analyze a 162 ks HETG Chandra observation of the O7.5 III(n)((f)) star xi Per, together with contemporaneous H alpha observations. The X-ray spectrum of this star is similar to other single O stars, and not pathological in any way. Its UV wind lines are known to display cyclical time variability, with a period of 2.086 days, which is thought to be associated with co-rotating interaction regions (CIRs). We examine the Chandra and H alpha data for variability on this time scale. We find that the X-rays vary by about 15% over the course of the observations and that this variability is out of phase with variable absorption on the blue wing of the H alpha profiles (assumed to be a surrogate for the UV absorption associated with CIRs). While not conclusive, both sets of data are consistent with models where the CIRs are either a source of X-rays or modulate them.Comment: Accepted by MNRAS. 9 pages, 9 figure