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Magnetic model studies, rock magnetization, and major element chemical analyses show that unusually large amplitude magnetic anomalies found along the easternmost segment of the Southeast Indian Ridge [zone A] are caused by the high intensities of magnetization of basalts intruded at the ridge axis. In turn, these high magnetizations are caused by a threefold increase in weight percent of titanomagnetites from normal midocean ridge basalts intruded in the west [zones B and C] to ferrobasalts intruded in the high magnetic anomaly zone to the east. The Fe-Ti increase in the opaques reflects a major elemental enrichment in Fe and Ti caused by extensive shallow fractionation of plagioclase, clinopyroxene, and olivine. This shallow fractionation appears related to unusually cold magma crystallization temperatures, perhaps caused by proximity to a postulated downwelling zone in the asthenosphere south of Australia. However, examination of these correlations in greater detail points to several ambiguities: although the entire region is deep, and therefore the lithosphere is integrally colder than normal plates, zone A is shallower than zones B and C, but geothermometrically, its axial magmas are colder. We do not know how cold magmas directly relate to ferrobasalt generation. Also, plumelike geochemical signatures are also seen in some of the analyses. It appears that plume mantle sources are mixing with MORB sources and then undergoing extensive shallow fractional crystallization in zone A.

Three rock units from southern Nova Scotia were sampled for a paleomagnetic study of the relationship of the Meguma terrane to the Atlantic-bordering continents during the Paleozoic. These include the Siluro-Ordovician White Rock Formation volcanics, sandstones of the Lower Devonian Torbrook Formation and red beds of the Lower Carboniferous Cheverie Formation. Progressive thermal and alternating field demagnetization of the White Rock basalts and rhyolites reveal a single component magnetization with a mean direction of D = 149.1°, I = 24.3°, α₉₅ = 10°, for N = 13 sites. Rotation of the site mean directions about the axis of the Torbrook Syncline suggest a post-folding (post Middle Devonian) age for this magnetization, which corresponds to a pole at 21.9° N Lat., 147.7° E Long. after correction for post-Triassic regional tilting. The magnetization of the Torbrook Formation (D = 15.8°, I = 29.6°, a 95 = 11.7°) is clearly a secondary magnetization whose pole (55.5° N Lat., 90.7° E. Long.) lies near Triassic poles from both North America and southern Nova Scotia. The age of the Cheverie Formation magnetization (D = 146°, I = 25°, α₉₅ = 6°, tilt corrected) appears to pre-date folding in the area (pre-Westphalian) and the corresponding pole (24° N Lat., 152° E Long.) lies near to the White Rock pole, suggesting a similar age of magnetization. The White Rock and Cheverie poles, which are constrained to have Early Carboniferous ages, are 30° or more away from the North American APW path over the same age range, a discrepancy which can be explained by a 15 - 19° northward motion of Meguma with respect to the North American craton along with a 20 - 25° counter - clockwise rotation. There is no paleolatitude discrepancy between these results and paleomagnetic results from the adjacent Avalon Zone although a similar rotational discrepancy is evident. These inferred motions of the Meguma terrane most likely took place during the Carboniferous, prior to the formation of Pangea.

Our primary objective at Site 503 (Fig. 1) was to re- cover a complete, undisturbed Neogene and Quaternary section in the eastern equatorial Pacific. Site 503 is located near Site 83 in an area that contains an almost continuous pelagic record of the past 10 m.y. (Hays et al., 1972). Unfortunately, Site 83 was only spot-cored, and the recovered sediment is so badly disturbed by rotary drilling that most of the detailed record is lost. The section has an average sedimentation rate of 2.0 to 2.5 cm/k.y. with good-to-moderate preservation of all the major microfossil groups. We returned to Site 83 to core the same section, using the Hydraulic Piston Corer (HPC) to obtain an undisturbed, continuous section for high-resolution stratigraphic studies.

The ability of the hydraulic piston corer (HPC) to recover virtually undisturbed sections of semi-consolidated deep-sea sediments suitable for paleomagnetic study was first demonstrated on Leg 64 and Leg 68 of the Glomar Challenger . Reported here is a complete magnetostratigraphy for a 150 m section of Plio-Pleistocene pelagic deposits recovered at Site 502 in the Caribbean. Correlation of the magnetic polarity zones to the well-dated standard sequence of geomagnetic polarity reversals provides a precise geochronological framework for age-calibration of calcareous plankton fossil datums and which, combined with the moderate to high sedimentation rates (24–38 m/m.y.), present an opportunity to study paleoenvironmental variations in the Early Pleistocene and the Pliocene with a time control and resolution heretofore possible only in Late Pleistocene deep-sea sediment cores.

Leg 68 of the Deep Sea Drilling Project used the newly developed Hydraulic Piston Corer (HPC) to recover two virtually continuous, undisturbed sections of late Neogene and Quaternary sediment. The sites are located in the western Caribbean (Site 502, 4 holes) and in the eastern equatorial Pacific (Site 503, 2 holes). The sediment of Site 502 is primarily forambearing nanno marl which accumulated at about 3 to 4 cm/thousand yr. The bottom of Site 502 (228.7 m) is ~ 8 m.y. old. The sediment of Site 503 is primarily siliceous calcareous ooze which accumulated at about 2 to 3 cm/thousand yr. The bottom of Site 503 (235.0 m) is ~ 8 m.y. old. The magnetostratigraphy of both sites was determined on the R.V. Glomar Challenger with a long-core spinner magnetometer. All paleomagnetic boundaries through the Gilbert were identified in Site 502; most of them were identified in Site 503. The sediment at both sites shows a distinct cyclicity of calcium carbonate content. These relatively high accumulation rate, continuous, undisturbed HPC cores will enable a wide variety of high-resolution biostratigraphic, paleoclimatic, and p a l e o c e a n o g r a p h ic studies heretofore not feasible.

A suite of felsic extrusive rocks from the Lower Devonian Traveler Felsite, north-central Maine (46.1°N lat., 68.9°W long.) was collected for paleomagnetic study: 28 samples from 5 sites in the (lower) Pogy member, 56 samples from 10 sites in the (upper) Black Cat member, and 13 samples from 10 cobbles in the basal conglomerate of the overlying Trout Valley Formation. Characteristic magnetizations based on AF demagnetization analyses and supported by thermal studies give a formation mean direction, after simple correction for bedding tilt, of D = 25.2°, I = − 20.2°, α 95 = 10.6° for 13 sites in the Traveler Felsite. The occurrence of normal and reversed magnetozones under stratigraphic control and the antiparallel directions of the polarity units following the tilt correction indicate an acquisition of remanence near the time of formation of the rock units. The mean direction corresponds to a (south) paleopole position of 29°S lat., 262°E long. (δ p , δm = 6°, 11°) for the Traveler Felsite. This pole position is in close agreement with poles from two other rock units of similar age from the same lithostratigraphic belt in the northern Appalachians. The mean of these three poles is distinct from Late Silurian and Middle Devonian poles from cratonic North America (Laurentia) and from Early Devonian results from the Acadia displaced terrane, suggesting that this area constituted a separate tectonic unit during the Early Devonian. We propose a tectonic model in which a “Traveler terrane” is rotated 20° to 30° while converging with Laurentia and undergoing deformation during the Early to Middle Devonian Acadian orogeny.