Determining the cooling history of in situ lower oceanic crust; Atlantis Bank, SW Indian Ridge

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doi: 10.1016/j.epsl.2004.02.014
Author(s): John, Barbara E.; Foster, David A.; Murphy, John M.; Cheadle, Michael J.; Baines, A. Graham; Fanning, C. Mark; Copeland, Peter
Author Affiliation(s): Primary:
University of Wyoming, Department of Geology and Geophysics, Laramie, WY, United States
Other:
University of Florida, United States
Australian National University, Australia
University of Houston, United States
Volume Title: Earth and Planetary Science Letters
Source: Earth and Planetary Science Letters, 222(1), p.145-160. Publisher: Elsevier, Amsterdam, Netherlands. ISSN: 0012-821X CODEN: EPSLA2
Note: In English. 50 refs.; illus., incl. 3 tables, sketch map
Summary: The cooling history and therefore thermal structure of oceanic lithosphere in slow-spreading environments is, to date, poorly constrained. Application of thermochronometric techniques to rocks from the very slow spreading SW Indian Ridge provide for the first time a direct measure of the age and thermal history of in situ lower oceanic crust. Crystallization of felsic veins (∼850°C) drilled in Hole 735B is estimated at 11.93±0.14 Ma, based on U-Pb analyses of zircon by ion probe. This crystallization age is older than the "crustal age" from remanence inferred from both sea surface and near-bottom magnetic anomaly data gathered over Hole 735B which indicate magnetization between major normal polarity chrons C5n.2n and C5An.1n (10.949-11.935 Ma). 40Ar/39Ar analyses of biotite give plateau ages between 11 and 12 Ma (mean 11.42±0.21 Ma), implying cooling rates of >800°C/m.y. over the first 500,00 years to temperatures below ∼330-400°C. Fission-track ages on zircon (mean 9.35±1.2 Ma) and apatite reveal less rapid cooling to <110°C by ∼7 Ma, some 4-5 m.y. off axis. Comprehensive thermochronometric data from the structurally intact block of gabbro between ∼700 and 1100 m below sea floor suggest that crust traversed by ODP Hole 735B mimics conductive cooling over the temperature range ∼900-330°C, characteristic of a 2-D plate-cooling model for oceanic lithosphere. In contrast, lower temperature chronometers (fission track on zircon, titanite, and apatite; T≤280°C) are not consistent with these predictions and record anomalously high temperatures for crust >700 m below sea floor at 8-10 Ma (i.e. 2-4 m.y. off axis). We offer two hypotheses for this thermal anomaly:(i) Off-axis (or asymmetric) magmatism that caused anomalous reheating of the crust preserved in Hole 735B. This postulated magmatic event might be a consequence of the transtension, which affected the Atlantis II transform from ∼19.5 to 7.5 Ma. (ii) Late detachment faulting, which led to significant crustal denudation (2.5-3 km removed), further from the ridge axis than conventionally thought. Abstract Copyright (2004) Elsevier, B.V.
Year of Publication: 2004
Research Program: ODP Ocean Drilling Program
Key Words: 03 Geochronology; 18 Geophysics, Solid-Earth; Absolute age; Ar/Ar; Atlantis II fracture zone; Cenozoic; Cooling; Crust; Dates; Gabbros; Heat flow; Igneous rocks; In situ; Indian Ocean; Lower crust; Magnetization; Neogene; Nesosilicates; ODP Site 735; Ocean Drilling Program; Oceanic crust; Orthosilicates; Paleomagnetism; Plutonic rocks; Remanent magnetization; Silicates; Southwest Indian Ridge; Tertiary; Thermal anomalies; Thermal conductivity; Thermal history; Thermochronology; Thermomechanical properties; U/Pb; Zircon; Zircon group
Coordinates: S324327 S324318 E0571618 E0571557
Record ID: 2006016114
Copyright Information: GeoRef, Copyright 2019 American Geosciences Institute. Reference includes data from CAPCAS, Elsevier Scientific Publishers, Amsterdam, Netherlands