Secondary Minerals of Basalts from the Nauru Basin, Deep Sea Drilling Project Leg 61

Kurnosov, Victor B; Kholodkevich, I.V.; Shevchenko, A.Ya.

doi:10.2973/dsdp.proc.61.124.1981

Cited by 2 publications

(2 citation statements)

References 12 publications

(26 reference statements)

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“…A late formation is indicated by a second generation of microscopic okenite crystals rarely occurring on apophyllite in the void spaces of the hyaloclastite breccia. Kurnosov [71] attributed okenite to a group of 'middle-temperature minerals' formed at 100-350 • C. However, Taylor [72] stated that synthesis of okenite is possible only at low temperatures, a little above or perhaps even below 100 • C.…”

Section: Hydrated Calcium Silicate Mineralsmentioning

confidence: 99%

The Secondary Minerals from the Pillow Basalt of Salsette-Mumbai, Deccan Volcanic Province, India

2022

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Secondary minerals occur within the tholeiitic basalts of Salsette Island in the greater Mumbai region, as well as in other localities in the Deccan Volcanic Province (DVP). However, the secondary minerals of Salsette Island show remarkable differences with respect to their mineral speciation and precipitation sequence, which are both due to their unique geological environment. The greater Mumbai region is built up by the Salsette subgroup, which represents the youngest sequence of the DVP. It formed subsequently to the main phase of DVP activity in Danian time (62.5 to 61.5 Ma), in the course of the India–Laxmi Ridge–Seychelles breakup. The main part of the Salsette subgroup consists of tholeiitic basaltic flows with pillows, pillow breccia, and hyaloclastite, which formed in contact with brackish and fresh water in a lagoonal environment. In some places, intertrappeans are represented by fossiliferous shallow water sediments. On the top, trachytic and rhyolitic subaqueous volcaniclastics occur, and some dioritic bodies have intruded nearby. Due to differing fluid rock interactions, several distinctly different secondary minerals developed in the void spaces of the hyaloclastite breccia of the interpillow matrix and in the pillow cavities. The highly permeable hyaloclastite breccia formed an open system, where pronounced precipitation occurred in the early phase and at higher temperatures. In contrast, the pillow cavities were a temporally closed system and contained, for example, more low-temperature zeolites. The genesis of the secondary minerals can be summarized as follows: During initial cooling of the volcanic rocks at about 62 Ma, the first mineralization sequence developed with chlorite, laumontite I, quartz, and calcite I. Ongoing magmatic activity caused reheating and the main phase of precipitation at prehnite–pumpellyite facies conditions. During generally decreasing temperatures, in the range of 270–180 °C, babingtonite, laumontite II, prehnite, julgoldite, yugawaralite, calcite II, ilvaite, pumpellyite, and gryolite developed. The fluid contained SiO2 + Al2O3 +FeO + MgO + CaO, and minor MnO and Na2O, and was predominately mineralized by the decomposition of basaltic glass. Further temperature decreases caused zeolite facies conditions and precipitation of okenite I, scolecite, heulandite, stilbite, and finally chabazite I, in the temperature range of 180 °C to less than 100 °C. As FeO, MgO, and MnO were then absent, an interaction of the fluid with plagioclase is indicated. According to Rb-Sr and K-Ar ages on apophyllite-K, a third phase of precipitation with apophyllite-K, okenite II, and chabazite II occurred in the late Eocene to early Oligocene (30–40 Ma). The new hydrothermal fluid additionally contained K2O, and temperatures of 50–100 °C can be expected.

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Section: Hydrated Calcium Silicate Mineralsmentioning

confidence: 99%

The Secondary Minerals from the Pillow Basalt of Salsette-Mumbai, Deccan Volcanic Province, India

2022

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“…Secondary minerals are developed in the following locations in Leg 89 basalts: glass in quenched flow margins; interstitial glass in hypocrystalline units, phenocrysts, plagioclase-rich interiors of holocrystalline units, as infilling in vesicles, and as vein material in fractures. The distribution and composition of secondary minerals in both rock matrix and veins encountered on Leg 61 have been commented on by Kurnosov et al (1981).…”

Section: Secondary Mineral Distributionmentioning

confidence: 99%

Petrology and Geochemistry of Oceanic Intraplate Sheet-Flow Basalts, Nauru Basin, Deep Sea Drilling Project Leg 89

Floyd¹

1986

Initial Reports of the Deep Sea Drilling Project

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Reentry of Hole 462A during Leg 89 resulted in the penetration of a further 140 m of basalt sheet-flows similar to those found during Leg 61 at the same site. Twelve volcanic units (45 to 56) were recognized, comprising a series of rapidly extruded, interlayered aphyric and poorly clinopyroxene-plagioclase-olivine phyric, nonvesicular basalts. All exhibit variable, mild hydration and oxidation, relative to fresh oceanic basalts, produced under reducing, low-CO 2-activity conditions within the zeolite facies. Secondary assemblages are dominated by smectites, zeolites, and pyrite, produced by low-temperature reaction with poorly oxygenated seawater. No systematic mineralogical or chemical changes are observed with depth, although thin quenched units and more massive hypocrystalline units exhibit slightly different alteration parageneses. Chemically, the basalts are olivine-and quartz-normative tholeiites, characterized by low incompatible-element abundances, similar to mildly enriched MORB (approaching T-type), with moderate, chrondite-normalized, large-ionlithophile-element depletion patterns and generally lower or near-chrondritic ratios for many low-distribution-coefficient (K D) element pairs. In general, relative to cyclic MORB chemical variation, they are uniform throughout, although 3 chemical megagroups and 22 subgroups are recognized. It is considered that the megagroups represent separate low-pressure-fractionated systems (olivine + Plagioclase ± clinopyroxene), whereas minor variations within them (subgroups) indicate magma mixing and generation of near-steady-state conditions. Overall, relatively minor fractionation coupled with magma mixing produced a series of compositionally uniform lavas. Parental melts were produced by similar degrees of partial melting, although the source may have varied slightly in LIL-element content.

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Secondary Minerals of Basalts from the Nauru Basin, Deep Sea Drilling Project Leg 61

Cited by 2 publications

References 12 publications

The Secondary Minerals from the Pillow Basalt of Salsette-Mumbai, Deccan Volcanic Province, India

The Secondary Minerals from the Pillow Basalt of Salsette-Mumbai, Deccan Volcanic Province, India

Petrology and Geochemistry of Oceanic Intraplate Sheet-Flow Basalts, Nauru Basin, Deep Sea Drilling Project Leg 89

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