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| Titel |
Partially Melted UHP Eclogite in the Sulu Orogenic Belt, China and its rheological significance to deep continental subduction: Micro- to Macro-scale Evidence |
| VerfasserIn |
Lu Wang, Timothy Kusky, Ali Polat, Songjie Wang, Xingfu Jiang, Keqing Zong, Junpeng Wang, Hao Deng, Jianmin Fu |
| Konferenz |
EGU General Assembly 2015
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 17 (2015) |
| Datensatznummer |
250103790
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| Publikation (Nr.) |
 EGU/EGU2015-3206.pdf |
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| Zusammenfassung |
| Partially Melted UHP Eclogite in the Sulu Orogenic Belt, China and its rheological
significance to deep continental subduction: Micro- to Macro-scale Evidence
Numerous studies have described partial melting processes in low-high pressure
meta-sedimentary rocks, some of which may generate melts that coalesce to form plutons.
However, migmatized ultrahigh pressure (UHP) eclogite has never been clearly described
from the microscale to macroscale, though experimental studies prove dehydration partial
melting of eclogite at high pressure condition1 and low degrees of partially melted
eclogite have been reported from the Qaidam UHP orogenic belt in NW China2,3 or
inferred from multiphase solid (MS) inclusions within eclogite4 in the Sulu UHP
belt.
We present field-based documentation of decompression partial melting of UHP eclogite
from Yangkou and General’s Hill, Sulu Orogen. Migmatized eclogite shows successive stages
of anatexis, initially starting from intragranular and grain boundary melt droplets, which grow
into a 3D interconnected intergranular network, then segregate and accumulate in pressure
shadow areas, and finally merge to form melt channels and dikes that transport melts to
upper lithospheric levels. In-situ phengite breakdown-induced partial melting is
directly identified by MS inclusions of Kfs+ barium-bearing Kfs + Pl in garnet,
connected by 4-10 μm wide veinlets consisting of Bt + Kfs + Pl next to the phengite.
Intergranular veinlets of plagioclase + K-feldspar first form isolated beads of melt
along grain boundaries and triple junctions of quartz, and with higher degrees of
melting, eventually form interconnected 3D networks along grain boundaries in the
leucosome, allowing melt to escape from the intergranular realm and collect in low-stress
areas.
U-Pb (zircon) dating and petrological analyses on residue and leucocratic rocks shows
that partial melting occurred at 228-219 Ma, shortly after peak UHP metamorphism (~230
Ma), and at depths of 30-90 km. Whole-rock trace element analyses show that the leucocratic
rocks, residue and peak metamorphic stage eclogite (no decompression partial melting) show
well matched mass balance relationships. Melts derived from eclogite partial melting
lubricated the subducted eclogite slices and facilitated their buoyant rise from mantle depths
to crustal levels.
Partial melting of deeply subducted eclogite is an important process in determining the
rheological structure and mechanical behavior of subducted lithosphere and its rapid
exhumation, controlling flow of deep lithospheric material, and for generation of melts from
the upper mantle, potentially contributing to arc magmatism and growth of continental crust.
Deeply subducted, partially melted eclogite from General’s Hill show that eclogites can
develop regularly spaced melt channels, a meter or two thick, that would act as significant
seismic anomalies5. This may provide direct evidence for the nature of enigmatic
“bright zones” presented in some deep-crustal seismic reflection profiles which
have been interpreted to represent areas of melt, high fluid content or unusual rock
compositions6.
Hermann, J. & Green, D. H. (2001). Earth Planet. Sci. Lett. 188, 149–168.
Song, S.G., et al. (2014). Geochim. Cosmochim. Acta 130 42–62.
Zhang, G.B., et al. (2014). Lithos, doi: 10.1016/j.lithos.2014.12.009
Gao, X. Y., et al. (2012). J. Metamorph. Geol. 30, 193-212.
Wang, L., et al. (2014). Nature Communications. 5:5604 doi:
10.1038/ncomms6604.
Brown, L. et al. (1996). Science 274, 1688–1690. |
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