|
|
 |
|||||||||||||||||
|
|||||||||||||||||
 |
|||||||||||||||||
| JOURNAL HOME | HELP | CONTACT PUBLISHER | SUBSCRIBE | ARCHIVE | SEARCH | TABLE OF CONTENTS |
1 Key Laboratory for Metallogenic Dynamics, Guangzhou Institute of Geochemistry, Chinese Academy of Sciences, Guangzhou 510640, China
The early continental crust is composed dominantly of Archean tonalite-trondhjemite-granodiorite (TTG) gneisses and is generally explained as the product of melting of metabasalts in the subducted crust. However, whether the melting occurs in shallow-level amphibolite facies or in relatively deep eclogite facies is debated. Here I present experimental partition coefficients (Ds) for 27 trace elements between garnet/amphibole and tonalitic melts. They are used together with published mineral/melt trace element Ds to model the melting of metabasalt in order to delimit the conditions for TTG production. The results clearly show that model melts with trace element characteristics that completely mimic the TTG are in equilibrium with rutile-bearing anhydrous and hydrous (amphibole bearing) eclogitic residues, but not rutile-free, amphibole-dominated residues. Rutile appears to be a necessary residual phase to account for the characteristic negative Nb-Ta anomaly in the TTG. These results thus suggest that the early continental material was produced under eclogite facies conditions. Based on the modeling results obtained using appropriate partition coefficients and the Archean geotherm, the preferred process for the TTG production is the melting of rutile-bearing hydrous eclogite, triggered by the release of H2O from the progressive breakdown of amphibole. The pressure-temperature (P-T) conditions for TTG production via this process are constrained to 1.5–2.5 GPa (
50– 80 km) and 850–1050 °C by the P-T stability boundaries of amphibole and rutile in the basalt system.
Key Words: tonalite-trondhjemite-granodiorite melt • trace element partitioning • amphibolite melting • eclogite melting.
This article has been cited by other articles:
|
|
 |
|
  X. Xiong, H. Keppler, A. Audetat, G. Gudfinnsson, W. Sun, M. Song, W. Xiao, and L. Yuan Experimental constraints on rutile saturation during partial melting of metabasalt at the amphibolite to eclogite transition, with applications to TTG genesis American Mineralogist, August 1, 2009; 94(8-9): 1175 - 1186. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 M.-X. Ling, F.-Y. Wang, X. Ding, Y.-H. Hu, J.-B. Zhou, R. E. Zartman, X.-Y. Yang, and W. Sun CRETACEOUS RIDGE SUBDUCTION ALONG THE LOWER YANGTZE RIVER BELT, EASTERN CHINA Economic Geology, March 1, 2009; 104(2): 303 - 321. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 F. Nehring, S. F. Foley, P. Holtta, and A. M. Van Den Kerkhof Internal Differentiation of the Archean Continental Crust: Fluid-Controlled Partial Melting of Granulites and TTG-Amphibolite Associations in Central Finland J. Petrology, January 7, 2009; (2009) egn070v1. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 R. Nair and T. Chacko Role of oceanic plateaus in the initiation of subduction and origin of continental crust Geology, July 1, 2008; 36(7): 583 - 586. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 W.-X. LI, X.-H. LI, and Z.-X. LI Middle Neoproterozoic syn-rifting volcanic rocks in Guangfeng, South China: petrogenesis and tectonic significance Geological Magazine, July 1, 2008; 145(4): 475 - 489. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
E. Bali, Z. Zajacz, I. Kovacs, CS. Szabo, W. Halter, O. Vaselli, K. Torok, and R. J. Bodnar A Quartz-bearing Orthopyroxene-rich Websterite Xenolith from the Pannonian Basin, Western Hungary: Evidence for Release of Quartz-saturated Melts from a Subducted Slab J. Petrology, March 1, 2008; 49(3): 421 - 439. [Abstract] [Full Text] [PDF]
|
|
| JOURNAL HOME | HELP | CONTACT PUBLISHER | SUBSCRIBE | ARCHIVE | SEARCH | TABLE OF CONTENTS |
