Composition and structural formulas of ODP Site 200-1224 Eocene ferrobasalt minerals


Autoria(s): Lustrino, Michele
Cobertura

MEDIAN LATITUDE: 27.889428 * MEDIAN LONGITUDE: 141.979250 * SOUTH-BOUND LATITUDE: 27.889380 * WEST-BOUND LONGITUDE: 141.979200 * NORTH-BOUND LATITUDE: 27.889500 * EAST-BOUND LONGITUDE: 141.979280 * DATE/TIME START: 2001-12-26T08:45:00 * DATE/TIME END: 2002-01-13T18:17:00

Data(s)

04/01/2006

Resumo

The ~46-m.y.-old igneous basement cored during Leg 200 in the North Pacific represents one of the few cross sections of Pacific oceanic crust with a total penetration into basalt of >100 m. The rocks, emplaced during the Eocene at a fast-spreading rate (~14 cm/yr; full rate) are strongly differentiated tholeiitic basalts (ferrobasalts) with 7-4.5 wt% MgO, relatively high TiO2 (2-3.5 wt%), and total iron as Fe2O3 (9.1-16.8 wt%). The differentiated character of these lavas is related to unusually large amounts of crystallization differentiation of plagioclase, clinopyroxene, and olivine. The lithostratigraphy of the basement (cored to ~170 meters below seafloor) is divided into three units. The deepest unit (lithologic Unit 3), is a succession of lava flows of no more that a few meters thickness each. The intermediate unit (lithologic Unit 2) is represented by intermixed thin flows and pillows, whereas the shallowest unit (lithologic Unit 1), comprises two massive flows. The rocks range from aphyric to sparsely clinopyroxene-plagioclase-phyric (phenocryst content = <3 vol%) and from holocrystalline to hypohyaline. Chilled margins of pillow fragments show holohyaline to sparsely vitrophyric textures. Site 1224 oxide minerals present a type of alteration not previously seen, where titanomagnetite is only partially destroyed and the pure magnetite component is partially removed from the mineral, leaving, in the most extreme case, a nearly pure ulvöspinel residuum. As a result of this dissolution, iron, mainly in the oxidized state, is added to the circulating solvent fluids. This means that a considerable metal source can result from low-temperature reactions throughout the upper ocean crust. The coarsest-grained lithologic Unit 1 rocks have interstitial myrmekitic intergrowths of quartz and sodic plagioclase (~An12), roughly similar in mineralogy and bulk composition to tonalite/trondhjemite veinlets in abyssal gabbros from the southwest Indian Ocean and Hess Deep, eastern equatorial Pacific. Based on idiomorphic relationships and projections into the simplified Q-Ab-Or-H2O granite ternary system, the myrmekitic intergrowths formed at the same time as, or just after, the oxide minerals coprecipitated and at low water vapor pressure (~0.5 kbar). Their compositions correspond to SiO2-oligoclase intergrowths that are considerably less potassic than dacitic glasses that erupt, although rarely, along the East Pacific Rise or that have been produced experimentally by partial melting of gabbro. Based on the crystallization history and comparison to experimental data, the original interstitial siliceous liquids resulted from late-stage immiscible separation of siliceous and iron-rich liquids. The rare andesitic lavas found along the East Pacific Rise may be hybrid rocks formed by mixing of these immiscible siliceous melts with basaltic magma.

Formato

application/zip, 6 datasets

Identificador

https://doi.pangaea.de/10.1594/PANGAEA.773388

doi:10.1594/PANGAEA.773388

Idioma(s)

en

Publicador

PANGAEA

Direitos

CC-BY: Creative Commons Attribution 3.0 Unported

Access constraints: unrestricted

Fonte

Supplement to: Lustrino, Michele (2006): Composition, petrography, and mineral chemistry of ODP Site 1224 Eocene ferrobasalts (Leg 200; North Pacific Ocean). In: Kasahara, J; Stephen, RA; Acton, GD; Frey, FA (eds.) Proceedings of the Ocean Drilling Program, Scientific Results, College Station, TX (Ocean Drilling Program), 200, 1-36, doi:10.2973/odp.proc.sr.200.008.2006

Palavras-Chave #200-1224A; 200-1224D; 200-1224E; 200-1224F; Ab; Al; Al (M1); Al (T); Al2O3; Albite; Aluminium; Aluminium oxide; An; Anorthite; BaO; Barium oxide; Ca; Calcium; Calcium oxide; Calculated; Calculated based on oxygen number; CaO; Chlorine; Chromium; Chromium(III) oxide; Chromium number; Cl; Cr; Cr/(Cr + Al); Cr# = Cr/(Cr + Al); Cr2O3; Data in this column are the phases intergrown or associated with plagioclase. The number indicates the number of phases in that column.; Description; DRILL; Drilling/drill rig; Electron microprobe; Elements, total; En; Enstatite; Event; Fe2+; Fe3+; Fe3+ (M1); Fe3+ (T); FeO; Ferrosilite; Fs; Ilm; Ilmenite; Iron 2+; Iron 3+; Iron oxide, FeO; Joides Resolution; K; K2O; Label; Label 2; Leg200; Magnesium; Magnesium number; Magnesium oxide; Manganese; Manganese oxide; Mg; Mg/(Mg + Fe); Mg# = Mg/(Mg + Fe2+); MgO; Mn; MnO; Na; Na2O; Name; North Pacific Ocean; Ocean Drilling Program; ODP; ODP sample designation; Or; Orthoclase; P2O5; Phosphorus oxide; Potassium; Potassium oxide; Samp com; Sample code/label; Sample code/label 2; Sample comment; Si; Silicon; Silicon dioxide; SiO2; Sodium; Sodium oxide; Sum; The first number indicates the number of the circle drawn on the thin section, and the second number indicates the sequential number of analyses in that circle.; Ti; TiO2; Titanium; Titanium oxide; total; Type; Ulvöspinel; Usp; Wo; Wollastonite
Tipo

Dataset