The Petrology of Magmatic Rocks, DSDP Leg 38

Kharin, G.N.

doi:10.2973/dsdp.proc.38.110.1976

Cited by 11 publications

(7 citation statements)

References 6 publications

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“…The basalt is composed of plagioclase (labradorite) 35-40%, clinopyroxene 35-50%, magnetite 9-12%, and altered volcanic glass 5-15%, minor amounts of olivine and orthoclase, and secondary minerals such as chlorite, montmorillonite, goethite and calcite. Our results of chemical analyses of two samples of basalt shown in Tables 1 and 2 are in agreement with those of and Kharin (1976).…”

Section: Petrography and Geochemistrysupporting

confidence: 89%

“…DSDP Leg 38 basalts were compared petrochemically with other basalts in the North Atlantic region by Kharin (1976), , Ridley, Perfit & Adams (1976) and Schilling (1976) to determine if they were typical of mid-ocean ridge or mantle-plume-derived basalts. The first three studies, based on bulk samples, concluded that Site 336 basalts are of the mid-ocean ridge type.…”

Section: Petrography and Geochemistrymentioning

confidence: 99%

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Paleoclimatic and paleogeographic implications of a lower Tertiary laterite (latosol) on the Iceland—Faeroe Ridge, North Atlantic region

Nilsen¹,

Kerr²

1978

Geol. Mag.

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SummaryA lower Tertiary lateritic paleosol resting on a plateau basalt was penetrated by drilling at DSDP Site 336 on the NE flank of the Iceland—Faeroe Ridge. The sea floor at the site is about 800 m below sea level and about 400 m below the generally smooth, flat and largely sediment-free top of the ridge. The paleosol is approximately 30 m thick and can be divided into four subunits, in ascending order, basaltic rubble, red clay with altered basaltic clasts, interlayered red and pale-orange clay, and red clay. The paleosol is overlain by about 300 m of marine mudstone of medial Eocene to medial late Oligocene age that was deposited in progressively deeper water through time. About 170 m of Pliocene and Pleistocene glacio-marine sediments unconformably overlie the Paleogene deposits.In the lowest subunit of the paleosol, feldspar, pyroxene, magnetite and chlorite decrease in abundance abruptly upward and are replaced by montmorillonite and small amounts of hematite and goethite. At the contact between the second and third subunits of the paleosol, kaolinite becomes an important constituent and increases greatly in abundance upward. In the uppermost red clay subunit, kaolinite has completely replaced montmorillonite and the amount of hematite and goethite increases markedly. Within the paleosol subunits, the relative amounts of silicon, ferrous iron, magnesium, calcium, sodium, and potassium decrease upward, whereas the amounts of aluminum, ferric iron, and titanium increase upward. The red and pale-orange clay subunit contains layers characterized by veinlet-like structures alternating with more massive layers. The veinlet network is thought to have developed by segregation of ferric iron and alumina as a result of chemical weathering of basalt and possibly thin overlying airfall tuffs.The paleosol indicates a humid, warm climate and demonstrates that the Iceland-Faeroe Ridge was above sea level during the early Tertiary. The ridge formed the main part of the Thulean land bridge that permitted free migration of land mammals between North America-Greenland and Europe prior to late Eocene time. It developed during the early Tertiary break-up and rifting apart of North America-Greenland and Europe. Formerly situated over an active mantle plume or hot spot, the ridge subsequently subsided in late Eocene and Oligocene time, eventually permittingfree interchange of marine waters between the Norwegian-Greenland Sea and the North Atlantic Ocean. Basalts of the Iceland-Faeroe Ridge are simijar in age and character to other basalts of the North Atlantic early Tertiary igneous province on the Rockall and Voring Plateaus, northern Ireland, Scotland, the Faeroe Islands, East and West Greenland, and Baffin Island. Bauxite, lignite, and laterite associated with some of these basalt sequences, as well as vertebrate, plant, and microfossil remains, suggest a relatively uniform, warm, humid climate in the early Tertiary throughout the North Atlantic area and into the region of the Arctic Ocean.

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Section: Petrography and Geochemistrysupporting

confidence: 89%

Section: Petrography and Geochemistrymentioning

confidence: 99%

Paleoclimatic and paleogeographic implications of a lower Tertiary laterite (latosol) on the Iceland—Faeroe Ridge, North Atlantic region

Nilsen¹,

Kerr²

1978

Geol. Mag.

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“…Instead we used magnetic anomaly data from ship tracks near the profile and the gridded data of Verhoef et al (1996). In addition, we use the adjacent DSDP drill sites 336 and 337 which both reported basaltic basement ages (Kharin et al 1976). The basaltic basement radiometric age of site 337 is in error and we consider the oldest sediment age above the basement to be a better indication of the basement age here.…”

Section: A G E O F O C E a N I C C Ru S Tmentioning

confidence: 99%

Influence of the Iceland mantle plume on oceanic crust generation in the North Atlantic

Parkin¹,

White²

2008

Geophysical Journal International

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SUMMARY When a mantle plume with elevated temperature underlies an oceanic spreading centre it affects the generation of oceanic crust by creating thicker crust. We map the variation in crustal thickness and seismic velocity along three long‐offset seismic profiles acquired over oceanic crust generated shortly after continental breakup in the North Atlantic: a 212‐km‐long flowline from the Faroes rifted continental margin across crust of 51–42 Ma age, where oceanic spreading developed close to the inferred centre of the Iceland mantle plume; a 256 km flowline extending from the Hatton rifted continental margin across crust of 52–40 Ma age, about 800 km south of the presumed centre of the mantle plume; and a 99 km strike line over oceanic crust formed at 43 Ma in the Iceland Basin off the Hatton continental margin. The crustal velocity structure along each profile is constrained by multichannel seismic reflection data, which is used primarily to map the sediments, and by densely spaced ocean‐bottom seismometers, which recorded wide‐angle reflections and refractions to offsets of more than 100 km. Over 56 000 crustal diving wave and Moho wide‐angle reflection arrivals were used in joint crustal refraction and reflection tomographic inversions. Quantitative error analysis shows that the seismic velocity of the crust is mostly constrained to within 0.1 km s−1 and the depth of the Moho to within ±250 m. We interpret the crustal thickness and velocity changes along the profiles as caused primarily by changes in the mantle temperature at the time of crustal formation. If all the oceanic crustal thickness variations are ascribed to mantle temperature changes, we infer that as mature seafloor spreading developed following continental breakup, the mantle cooled by ca. 75 °C over a 10 Myr period, although it still remained hotter than the global average of normal oceanic crust. The crust formed close to Iceland is at all times thicker than that formed further away, which we interpret as reflecting higher temperatures close to the centre of the thermal anomaly created by the mantle plume. Currently at the Reykjanes Ridge, south of Iceland, we interpret thicker than normal oceanic crust as being caused by the presence of hotter mantle, modulated by thickness variations of 1.5–2.0 km which are attributed to temporal variations in the mantle plume temperature of about 25 °C on a 3–6 Myr timescale. A 1.5 km increase in thickness of oceanic crust generated between 48 and 45 Ma on the Faroes line is similar in magnitude and duration to those occurring on the present day Reykjanes Ridge, which we suggest is due to a temperature pulse of ∼25 °C. Gravity lineations in the northern North Atlantic suggest that the oceanic crust has exhibited small thickness fluctuations of similar size throughout its history, interpreted as due to small fluctuations in the temperature of the Iceland mantle plume.

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“…A 30-m-thick, mid-to upper Eocene lateritic paleosol, correlative to laterites developed on basalt in northern Ireland, was recovered at DSDP Site 336 on the northeast flank of the Iceland-Faeroe Ridge, east of Iceland in the North Atlantic (Nilsen and Kerr, 1978). The lower part of this weathering horizon retains relict internal structures of the original lava flows and volcanic tuffs (Kahrin, 1976). The lower 8.5-m overlying basalt comprises highly altered basaltic rubble dominated mineralogically by montmorillonite.…”

Section: Previous Studiesmentioning

confidence: 94%

Pedogenic Alteration of Basalts Recovered during Leg 144

Holmes¹

1995

Proceedings of the Ocean Drilling Program, 144 Scientific Results

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Basalts erupted to form the atolls and guyots of the Western Pacific have been altered in various ways, ranging from hydrothermal alteration to subaerial weathering by meteoric waters in a tropical environment. Subaerial weathering has been moderate to extreme. Moderate subaerial weathering is expressed by dissolution or replacement of primary minerals (olivine, pyroxenes, plagioclase feldspar) and alteration of glassy or aphanitic matrix to clay minerals, goethite, and hematite. The clay minerals are kaolinite or a brown smectite. Kaolinite concentrations decrease downhole and smectite concentrations increase. Although primary minerals are generally not preserved, primary structures, such as vesicles (generally filled by secondary or tertiary minerals), flow structure, or relict breccia structure, remain evident. Extreme subaerial weathering is expressed by the loss of all primary minerals as well as all traces of primary structures, presumably by plant root and soil infaunal bioturbation, resulting in recognizable soil. Kaolinite, goethite, and hematite have replaced all primary components. Hydrothermal alteration is expressed by the presence of analcime and delicate zonation in vesicles and veins of secondary minerals. The hydrothermal clay in this case is a green smectite; analcime and other zeolites are present.Soil development has occurred at Sites 871 (28.6 m thick), 873 (22.5 m), 874 (15 m), 877 (5 m), and possibly 878 (9.6 m) and 879 (40.2 m). Sites 871 and 873 exhibit the most extreme weathering and pedogenesis, expressed by soil horizonation, loss of parent relict structure, and distinct vertical zonations of mineral and chemical compositions, from kaolinitic at the surface to smectitic at the base. B horizons were identified from these paleosols, and a possible reworked A horizon occurs at Site 871. The relict parent structure is still very evident in the clays at Sites 874, 877, 878, and 879 as well as in the deeper parts of Sites 871 and 873. These are interpreted as C horizons. The parent materials-lava flows and epiclastic volcanic deposits-are completely altered to clay: to kaolinite at Site 874 and to kaolinite and smectite at the others. The clays at Site 877 are vertically zoned; they are not vertically zoned at Sites 878 or 879. The clays at Sites 878 and 879 may have been altered by groundwater, are very deep parts of soil profiles, or else are the products of multiple deposition and pedogenic events.The depth of soil development and the mineral composition (absence of gibbsite) suggest that at Site 871 on Limalok Guyot, soils developed in upland areas were subjected to annual rainfall of less than 1 m. Relief was at least tens of meters and possibly more. The presence of a drab mottled horizon at Site 873 indicates it formed in a poorly drained, possibly low-lying area on Wodejebato Island. Rainfall here was also insufficient to generate gibbsite. Similar depths of weathering mantles and the degree of soil development that occurs on older land surfaces of the older Hawaiian Islands...

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The Petrology of Magmatic Rocks, DSDP Leg 38

Cited by 11 publications

References 6 publications

Paleoclimatic and paleogeographic implications of a lower Tertiary laterite (latosol) on the Iceland—Faeroe Ridge, North Atlantic region

Paleoclimatic and paleogeographic implications of a lower Tertiary laterite (latosol) on the Iceland—Faeroe Ridge, North Atlantic region

Influence of the Iceland mantle plume on oceanic crust generation in the North Atlantic

Pedogenic Alteration of Basalts Recovered during Leg 144

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