HR: 0800h
AN: V11A-1411 [Abstracts]
TI: Retrograde Processes of Eclogite from 100-2000m in the Main hole of Chinese Continental Scientific
Drilling Project,Eastern China
AU: Su, S
EM: susg@cugb.edu.cn
AF: School of the Earth Sciences and Resources,China University of Geosciences,Beijing, Xueyuan Rd. #29,
Beijing, 100083
China
AU: Liang, F
EM: lfh@ccsd.org.cn
AF: Key Laboratory for Continental Dynamics of MLR,Institute of Geology,CAGS, Baiwanzhuang Rd. #26,
Beijing, 100037
China
AU: * You, Z
EM: zdyou@263.net
AF: Faulty of Earth Sciences,China University of Geosciences, Lumo Rd. #388, Wuhan, 430074
China
AU: Zhang, Z
EM: zzm@ccsd.org.cn
AF: Key Laboratory for Continental Dynamics of MLR,Institute of Geology,CAGS, Baiwanzhuang Rd. #26,
Beijing, 100037
China
AB:
The Chinese Continental Scientific Drilling (CCSD) Project is located in the Maobei Village, Donghai County, Jiangsu
Province, Eastern China. Based on the detailed study on mineralogy, petrology, and geochemistry of eclogite from 100 to 2000m
of the main borehole, the major achievements are as following:
1. Four retrograde processes have been identified. That is: weakly retrograde stage, partially retrograde stage, retrograde
stage and strongly retrograde stage.
During the weakly retrograde stage, only a few symplectitic coronas of amphiboles and plagioclases distributed along the
boundry of garnet and omphacite. Rutile is stable.
During the partially retrograde stage, the rate of omphacite disappear is rapid, omphacite exist only as a relict. Aegirine
rim exist along the boundry of quartz and omphacite. Rutile retrograde into ilmenite.
During the retrograde stage, garnets were gradually replaced by pargasite or epidote+biotite. omphacite disappear totally,
and It is replaced by symplectitic coronas of amphiboles and plagioclases, but the pseudomorph of omphacites preserved.
Aegirine rim become wider and sometimes exist as a lump.
During the strongly retrograde stage, Aegirine almost disappear. Amphibolite replaced Aegirine, and It distributes along
the boundry of quartz.
2. From fresh eclogites to strongly retrograde eclogites, MgO, CaO and FeO of the whole rock gradually decrease, SiO2, K2O
and Na2O gradually increase, and Al2O3 almost keep constant. The Pb value increase obviously from weakly retrograde stage to
strong retrograde stage.
3. The peak P-T condition of eclogites: 697-831‘ and 3.0GpaA; partially retrograde phase: 629-776‘ and 1.2-1.6Gpa;
retrograde phase: 550-650‘ and 0.5-0.7Gpa (Xu, Z Q et al., 2004); strongly retrograde phase: 300-400‘ and 0.30-0.35Gpa (Xu,
Z Q et al., 2004).
4. The UHP metamorphic rocks had undergone two-phase exhumation: first, nearly isothermal and decompression, suggested that
fast exhumation occurred before the completely retrograde of the omphacite (during this phase, eclogites had undergone
weakly and partially retrograde); second, decreasing temperature and decreasing pressure by slow uplifting after omphacites
being completely replaced by symplectite (during this phase, eclogites have undergone retrograde phase and strongly
retrograde phase).
Acknowledgement: This work is sponsored by the Major State Key Project to CCSD: 2003CB716501 and major project from NSFC:
40399142
DE: 8100 TECTONOPHYSICS
DE: 3660 Metamorphic petrology
DE: 1020 Composition of the crust
DE: 1025 Composition of the mantle
DE: 0330 Geochemical cycles
SC: Volcanology, Geochemistry, Petrology [V]
MN: 2004 AGU Fall Meeting