The Grayback Pluton: Magmatism in a Jurassic Back-Arc Environment, Klamath Mountains, Oregon

The Jurassic Grayback pluton was emplaced in a back-arc settingbehind a contemporaneous oceanic arc. Th\alphae main stage ofthe pluton consists of an early, reversely zoned tonalite togabbro that was intruded by synplutonic noritic and gabbroicmagmas. Late-stage activity was characterized by intrusion oftonalitic and granitic dikes, many of which contain mafic enclavesand hybrid zones. Most mafic rocks in the pluton are calc-alkaline,with characteristic magnesian clinopyroxene, calcic cores inplagioclase, and elemental abundances similar to H₂O-rich arcbasalts. However, some mafic rocks contain relatively Fe-richclinopyroxene, lack calcic cores in plagioclase, and are compositionallysimilar to evolved high-alumina tholeiite. Compositional variation in the main stage can be modeled inpart by fractional crystallization and crusted assimilationduring which parental calc-alkaline basalt evolved to graniticcompositions. Cumulates related to this process are representedby modally variable melagabbro and pyroxenite. Mixing of basalticand tonalitic magmas accounts for the compositions of most main-stageintermediate rocks, but mixing of basaltic and granitic magmaswas uncommon until late in the pluton's history. Oxygen, Sr and Nd isotopic data indicate that virtually allmain-stage magmas in the pluton contain a crustal component.Isotopic and trace element data further suggest that late-stagetonalitic dikes represent melts derived from older, metavolcanicarc crust Deep crustal contamination of main-stage rocks tookplace below the level of emplacement, probably in a magma-richzone where basalts ponded and mixed with crustal melts. The Grayback pluton illustrates the diversity of Jurassic back-arcmagmatism in the Klamath province and demonstrates that ancientmagmatism with arc-like features need not be situated in anarc setting. KEY WORDS: Grayback Pluton; Klamath Mountains; Oregon; back arc; crustal contamination ^*Corresponding author     

Ecophysiological studies on arthropods from Spitsbergen

The cold-hardiness, high temperature tolerance and metabolic activity of summer specimens of staphylinid beetles ( Atheta graminicola ), collembolans ( Onichiurus groenlandicus ), spiders ( Erigone arctica ), and prostigmatid mites ( Molgus littoralis ) from Spitsbergen were investigated. The animals displayed cold-hardiness and haemolymph melting points within the normal ranges for summer insects from temperate regions, but were less tolerant to high temperatures. Haemolymph from spiders and from one species of collembolans ( Isotoma sp.) was found to contain thermal hysteresis factors. The beetles, collembolans, and mites were found to have oxygen consumption rates above the values of their relatives in other climatic zones, whereas the spiders had values within the range of temperate arachnoids. The study supports the view that polar arthropods have activation energy values lower than those of temperate animals.     

Thermal hysteresis antifreeze agents in fishes from Spitsbergen waters

The occurrence of macromolecular antifreeze agents (so-called Thermal Hysteresis Factors) in blood plasma of fishes from Spitsbergen waters was investigated in August 1983, October 1984, and January 1986.
Thermal hysteresis was found in the plasma of three species of Spitsbergen fishes: shorthorn sculpin (Myoxocephalus scorpius) , polar cod (Boreogadus saida) , and sea snail (Liparis liparis) . This is the first time thermal hysteresis is reported from the sea snail. Seasonal changes in the amount of thermal hysteresis were observed in blood plasma of the shorthorn sculpin and the sea snail.
With the exception of the polar cod, blood plasma of deep water fishes displays no thermal hysteresis. The reason for this is probably that the polar cod also occurs in shallow ice laden sea water, where an'antifreeze'would be needed to protect against inoculative freezing.
No thermal hysteresis was observed in blood plasma of the saithe (Pollachius virens) , despite the fact that the saithe was observed swimming in ice laden sea water at a temperature of -1 to – 1.5°C under natural conditions, and was rapidly killed when it came into contact with ice in the laboratory. It is not known how the saithe survives in ice laden water under natural conditions.