The Coast Range megalineament is a prominent, nearly continuous topographic and structural feature that extends southeastward about 550 km (330 mi) from its junction with the Chatham Strait – Lynn Canal fault at Point Sherman to Tongass Passage near the mouth of Pearse Canal where it leaves southeastern Alaska. It probably extends still further southeastward into British Columbia along Work Channel and Chatham Sound – Grenville Channel.The megalineament is a zone a few hundred metres to 10 km (6 mi) wide in which closely spaced joints, foliation, compositional layering, and small faults define the megalineament trend. The zone usually coincides with topographic depressions apparently caused by selective fluvial and glacial erosion of the less resistant rocks of the zone.Studies in the Juneau, Endicott Arm, and Behm Canal areas indicate that the megalineament (1) is locally the site of lateral and (or) vertical separations of no greater than several kilometres; (2) does not mark a major structural or metamorphic discontinuity in the near-surface rocks; (3) may be located near a pre-metamorphic and pre-intrusive discontinuity; (4) is consistently associated with and parallel to steep gradients in both the gravity and aeromagnetic fields; and (5) probably is the surface expression of the western contact, at depth, of the intrusive rocks and gneisses of the Coast Range batholithic complex with the schists to the southwest.

An inverted metamorphic gradient is preserved in the western metamorphic belt near Juneau, Alaska. The western metamorphic belt is part of the Coast plutonic-metamorphic complex of western Canada and southeastern Alaska that developed as a result of tectonic overlap and/or compressional thickening of crustal rocks during collision of the Alexander and Stikine terranes. Detailed mapping of pelitic single-mineral isograds, systematic changes in mineral assemblages, and silicate geothermometry indicate that thermal peak metamorphic conditions increase structurally upward over a distance of about 8 km. Peak temperatures of metamorphism increase progressively from about 530 "C for the garnet zone to about 705 "C for the upper kyanite-biotite zone. Silicate geobarometry suggests that the thermal peak metamorphism occurred under pressures of 9-11 kbar. The metamorphic isograds are in general parallel to the tonalite sill that is regionally continuous along the east side of the western metamorphic belt, although truncation of the isograds north of Juneau indicates that the sill intrusion continued after the isograds were established. Our preferred interpretation of the cause of the inverted gradient is that it formed during compression of a thickened wedge of relatively wet and cool rocks in response to heat flow associated with the formation and emplacement of the tonalite sill magma. Garnet rim compositions and widespread growth of chlorite suggest partial re-equilibration of the schists under pressures of 5-6 kbar during uplift in response to final emplacement and crystallization of the tonalite sill. The combined results of this study with previous studies elsewhere in the western metamorphic belt indicate that high-T/high-P metamorphism associated with the collision of the Alexander and Stikine terranes was a long-lived event, extending from about 98 Ma to about 67 Ma.

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A variety of mafic igneous bodies, including the unusually large, differentiated, layered gabbroic Dufek intrusion, and basalt and dolerite dikes and sills, intrude a Permian and older sequence in the Pensacola Mountains, near Weddell Sea, Antarctica. K-Ar age determinations show that the sills (179 ± 5 m.y.), the Dufek intrusion (172 ± 4 m.y.), and probably the dikes (minimum age 169 ± 4 m.y.) were emplaced over a narrow time interval in

Calcareous metamorphic rocks of a continental-type crystalline basement were recovered by drilling at Site 270 in the south-central Ross Sea. Calcareous basement gneiss is of amphibolite-facies metamorphic rank and may correlate with calcareous metasedimentary rocks of similar rank in the early Paleozoic(?) Skelton Group near McMurdo Sound. The basement rocks are overlain by 25 meters of coarse, angular, poorly sorted sedimentary breccia, the upper 3 meters of which is a deeply weathered regolith. The regolith is overlain unconformably by a thick sequence of mainly glaciomarine sediments of Oligocene and younger age.The breccia is interpreted as a probable talus or solifluction deposit derived from a nearby topographic high of basement rocks. Abundant fragments of marble and calc-silicate gneiss similar to the cored basement rocks, and numerous fragments of highly varied granitic and other metamorphic rocks in the breccia indicate that the basement terrane near Site 270 is a granitic and metamorphic complex probably similar to that of coastal parts of south Victoria Land near McMurdo Sound. Sedimentary rocks similar to those of the Devonian to Jurassic Beacon Supergroup and mafic-igneous rocks similar to those of the Jurassic Ferrar Dolerite were not observed in the breccia, suggesting that these widespread Victoria Land units do not extend to this region.

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