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Magnetic properties of ultrahigh-pressure eclogites controlled by retrograde metamorphism: a case study from the ZK703 drillhole in Donghai, eastern China

Magnetic properties of ultrahigh-pressure eclogites controlled by retrograde metamorphism: a case study from the ZK703 drillhole in Donghai, eastern China
Magnetic properties of ultrahigh-pressure eclogites controlled by retrograde metamorphism: a case study from the ZK703 drillhole in Donghai, eastern China
Parallel studies on rock magnetic properties, petrology and mineralogy were conducted on 16 eclogite samples from the ZK703 hole and magnetic susceptibilities and densities of 41 eclogite samples with different degree of retrograde metamorphism (from fresh eclogite to fully-retrograded eclogite) from the Chinese Continental Scientific Drilling (CCSD) near the ZK703 hole, located at Donghai, southern Sulu ultrahigh-pressure metamorphic belt, eastern China. Results show: (1) that the high-field slopes obtained from the hysteresis loops (the paramagnetic fraction ?para) and density have a positive correlation with the volume concentration of garnet + omphacite, a typical mineral assemblage used to semi-quantify the degree of retrograde metamorphism. The low-field slopes obtained from hysteresis loops (the ferrimagnetic susceptibility fraction ?ferri), saturation isothermal remanent magnetization Mrs and saturation magnetization Ms have a positive correlation with the volume concentration of symplectite, a mineral related to retrograded metamorphism. Therefore they could be potential indicators for quickly semi-quantifying the degree of retrograde metamorphism of the eclogite units. (2) The dominant magnetic carriers in retrograded eclogites are magnetite particles in pseudo-single domain grain size region. (3) The P–T conditions during the retrograde (decompressional) process could first increase the concentration of magnetite, which can reach up to 3% for extensively retrograded eclogite and then was dissolved for fully-retrograded eclogite. Therefore, change in the magnetite contents during the retrograde process is the major factor controlling the magnetism of retrograde eclogites.
Rock magnetism, Retrograde metamorphism, Ultrahigh-pressure eclogite, Sulu orogen
0031-9201
181-191
Liu, Q.S.
9890d7f1-dde6-4842-ba93-5895b0f7520b
Liu, Q-S.
e94c4753-4337-4495-8812-9f5af2514dd4
Zhang, Z.M.
d73fc9ec-b4d8-4f5a-8b4b-a10b22bca8df
Xu, H.J.
bf27bab5-3aec-4f5d-88cc-39c5a681a921
Chan, L.S.
68b87dd3-6945-469e-b3c4-acd5f6b61381
Yang, T.
4c66e85c-7c09-48ea-9f67-ccc4e0d1449a
Jin, Z.M.
c55155de-18f1-41d0-9133-0772cc163308
Liu, Q.S.
9890d7f1-dde6-4842-ba93-5895b0f7520b
Liu, Q-S.
e94c4753-4337-4495-8812-9f5af2514dd4
Zhang, Z.M.
d73fc9ec-b4d8-4f5a-8b4b-a10b22bca8df
Xu, H.J.
bf27bab5-3aec-4f5d-88cc-39c5a681a921
Chan, L.S.
68b87dd3-6945-469e-b3c4-acd5f6b61381
Yang, T.
4c66e85c-7c09-48ea-9f67-ccc4e0d1449a
Jin, Z.M.
c55155de-18f1-41d0-9133-0772cc163308

Liu, Q.S., Liu, Q-S., Zhang, Z.M., Xu, H.J., Chan, L.S., Yang, T. and Jin, Z.M. (2007) Magnetic properties of ultrahigh-pressure eclogites controlled by retrograde metamorphism: a case study from the ZK703 drillhole in Donghai, eastern China. Physics of the Earth and Planetary Interiors, 160 (3-4), 181-191. (doi:10.1016/j.pepi.2006.10.001).

Record type: Article

Abstract

Parallel studies on rock magnetic properties, petrology and mineralogy were conducted on 16 eclogite samples from the ZK703 hole and magnetic susceptibilities and densities of 41 eclogite samples with different degree of retrograde metamorphism (from fresh eclogite to fully-retrograded eclogite) from the Chinese Continental Scientific Drilling (CCSD) near the ZK703 hole, located at Donghai, southern Sulu ultrahigh-pressure metamorphic belt, eastern China. Results show: (1) that the high-field slopes obtained from the hysteresis loops (the paramagnetic fraction ?para) and density have a positive correlation with the volume concentration of garnet + omphacite, a typical mineral assemblage used to semi-quantify the degree of retrograde metamorphism. The low-field slopes obtained from hysteresis loops (the ferrimagnetic susceptibility fraction ?ferri), saturation isothermal remanent magnetization Mrs and saturation magnetization Ms have a positive correlation with the volume concentration of symplectite, a mineral related to retrograded metamorphism. Therefore they could be potential indicators for quickly semi-quantifying the degree of retrograde metamorphism of the eclogite units. (2) The dominant magnetic carriers in retrograded eclogites are magnetite particles in pseudo-single domain grain size region. (3) The P–T conditions during the retrograde (decompressional) process could first increase the concentration of magnetite, which can reach up to 3% for extensively retrograded eclogite and then was dissolved for fully-retrograded eclogite. Therefore, change in the magnetite contents during the retrograde process is the major factor controlling the magnetism of retrograde eclogites.

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More information

Published date: 16 March 2007
Keywords: Rock magnetism, Retrograde metamorphism, Ultrahigh-pressure eclogite, Sulu orogen

Identifiers

Local EPrints ID: 49756
URI: http://eprints.soton.ac.uk/id/eprint/49756
ISSN: 0031-9201
PURE UUID: 0ab9e222-38d1-40d5-b796-b88dfe52cca3

Catalogue record

Date deposited: 28 Nov 2007
Last modified: 15 Mar 2024 09:59

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Contributors

Author: Q.S. Liu
Author: Q-S. Liu
Author: Z.M. Zhang
Author: H.J. Xu
Author: L.S. Chan
Author: T. Yang
Author: Z.M. Jin

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