Low-Temperature Alteration and Subsequent Reheating of Shallow Oceanic Crust at Hole 765D, Argo Abyssal Plain

Gillis, K. M.; Ludden, John; Plank, Terry; Hoy, Lawrence D.

doi:10.2973/odp.proc.sr.123.157.1992

Cited by 9 publications

(2 citation statements)

References 29 publications

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“…; Gillis et al . ). The temperature of crystallization of Chl accompanied by enrichment in MgO is estimated to be more than 150°C based on experimental studies (e.g.…”

Section: Discussionmentioning

confidence: 97%

Low‐ and high‐temperature alterations of volcanic rocks in the northwestern Philippine Sea, and association with volcanic settings

et al. 2014

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Petrological and geochemical characteristics of low‐ and high‐temperature alterations were investigated in volcanic rocks from the northern Philippine Sea. The assemblage of secondary minerals is divided into two groups based on microprobe and XRD analyses. The first group, comprising samples from the Kyushu‐Palau Ridge and Urdaneta Plateau, includes calcite, phillipsite, clay minerals and Fe‐oxyhydroxides, reflecting low‐temperature alteration. The content of secondary deposition is high in the Kyushu‐Palau Ridge, but low in the Urdaneta Plateau. The second group, consisting of samples from the Amami Plateau, includes secondary alkali feldspar, analcime, and chlorite, reflecting high‐temperature hydrothermal alteration. As groundmass alteration is dominant in the studied volcanic rocks, the alteration index, defined as the ratio of secondary minerals in voids to the total material count, is useful for estimating alteration degree when precise identification of secondary materials is difficult in highly vesicular rocks. Alteration indexes correlate with bulk H2O+ and loss on ignition (LOI) contents, and bulk major and trace element compositions of the studied volcanic rocks change with alteration. The difference of alteration types in three regions may depend on the tectonic setting of volcanism. That is: (i) the Kyushu‐Palau Ridge is covered with the last lava flow of rifting volcanism associated with spreading of the Shikoku Basin, and the volcanics reacted with circulating seawater under low temperatures and oxidative conditions; (ii) the Urdaneta Plateau was formed as a result of intra‐plate volcanism, and the volcanics were under seafloor weathering without seawater circulation associated with volcanic activity; and (iii) the Amami Plateau was produced by Cretaceous arc volcanism, which suffered high‐temperature alteration associated with intrusive activity of tonalite.

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“…; Gillis et al . ). The temperature of crystallization of Chl accompanied by enrichment in MgO is estimated to be more than 150°C based on experimental studies (e.g.…”

Section: Discussionmentioning

confidence: 97%

Low‐ and high‐temperature alterations of volcanic rocks in the northwestern Philippine Sea, and association with volcanic settings

et al. 2014

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“…Based on basement rocks from Hole 504B and other basement sites with sufficient penetration, the upper oxidative zone of alteration, which contains the lion's share of some element budgets (e.g., K, B, etc. ), lies in the upper 200-300 m of the basaltic crust (e.g., Alt et al, 1986;Gillis et al, 1992). The objectives of coring and logging at this site were to 1.…”

Section: Site 801mentioning

confidence: 99%

Leg 185 Summary: Inputs to the Izu-Mariana Subduction System

Plank¹,

Ludden²,

Escutia³

2000

Proceedings of the Ocean Drilling Program

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Subduction zones are the primary regions on Earth today where crust recycling takes place, and through geologic time they have been sites of continent formation. Many key chemical elements important for understanding crustal growth are subducted in the sedimentary column (e.g., Th, rare earth elements, Ba, and Be) and in the uppermost oxidized portions of the volcanic section of oceanic basement (e.g., K, B, U, CO 2 , and H 2 O). The principal objective of Leg 185 was to core two sites in Mesozoic crust in the west Pacific, which is being subducted into the Mariana and Izu-Bonin subduction systems, in order to determine the inputs into the "west Pacific subduction factory." Hole 801C was first drilled in the oldest (~170 Ma) crust in the Pacific Ocean during Ocean Drilling Program (ODP) Leg 129. During Leg 185 the hole was deepened to 936 meters below seafloor (mbsf), and at Site 1149, located on magnetic Anomaly M11 (~132 Ma) 100 km east of the Izu-Bonin Trench, the complete sedimentary sequence (410 m) and an additional 133 m of highly altered volcanic basement were drilled. Using the recovered core and the logging results, it is possible to reconstruct the volcanic section for Hole 801C. Eight volcanic sequences have been defined by the combined efforts of Legs 129 and 185, some with massive lava flows up to 20 m thick and others with thin pillows and sheet flows of <1 m. The uppermost unit is a ~60-m sequence of alkali basalts drilled during Leg 129 and radiometrically dated at ~157 Ma. This unit is separated from the underlying tholeiites of normal oceanic crust by an ~20-m-thick ocherous Si-Fe-rich hydrothermal deposit. A similar deposit is present 100 m lower in the hole. These hydrothermal deposits and numerous interpillow sediments observed in the upper volcanic sequences define the alteration character of the basement, 1 Examples of how to reference the whole or part of this volume. 2 Shipboard Scientific Party addresses.

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