|
|
 |
|||||||||||||||||
|
|||||||||||||||||
 |
|||||||||||||||||
| JOURNAL HOME | HELP | CONTACT PUBLISHER | SUBSCRIBE | ARCHIVE | SEARCH | TABLE OF CONTENTS |
1 Departamento de Geología, Universidad Nacional de Río Cuarto, 5800 Río Cuarto, Argentina
2 Departamento de Geología, Universidad de Huelva, 21819 Palos de La Frontera, Spain
3 Department of Geology, University of Georgia, Athens, Georgia 30602, USA
4 Departamento de Geología, Universidad de Huelva, 21819 Palos de La Frontera, Spain
We present laser-ablation microprobe inductively coupled–mass spectrometry analyses of Y, Yb, Er, Dy, and Gd in garnet crystals from high-grade metamorphic and migmatitic rocks from the Sierras Pampeanas of Argentina. These rocks contain large garnet porphyroblasts (
4 mm) that are compositionally zoned. Rare earth element concentrations in the rims are typically one order of magnitude lower than those in the cores. A notable feature of this zonation is the inversion of Yb/Er and Yb/Dy ratios, from >1 in the cores to <1 in the rims. We show quantitatively that the spatial distribution of these trace elements in garnet can be most simply and effectively explained as arising from Rayleigh fractionation during garnet growth. We also analyzed a small garnet crystal (<2 mm) representative of a garnet population that is associated with migmatitic leucosomes. This crystal displays uniformly low concentrations of all trace elements that are virtually identical in both absolute and relative magnitudes to those in the rims of the larger garnet porphyroblasts. The small crystals, and perhaps part of the porphyroblast rims, are likely to be peritectic products of incongruent melting reactions. We argue that melts formed from garnet-bearing sources may generally be unable to equilibrate with metamorphic garnet cores and may thus be more strongly depleted in heavy rare earth elements and Y than modeling based on bulk source-rock abundances of these elements would indicate.
Key Words: Rayleigh fractionation • garnet • heavy rare earth elements • melting
This article has been cited by other articles:
|
|
 |
|
  M. J. Dorais, T. K. Pett, and M. Tubrett Garnetites of the Cardigan Pluton, New Hampshire: Evidence for Peritectic Garnet Entrainment and Implications for Source Rock Compositions J. Petrology, November 4, 2009; (2009) egp058v1. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 S. R. Mulcahy, R. L. King, and J. D. Vervoort Lawsonite Lu-Hf geochronology: A new geochronometer for subduction zone processes Geology, November 1, 2009; 37(11): 987 - 990. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
C. J. Gregory, I. S. Buick, J. Hermann, and D. Rubatto Mineral-scale Trace Element and U-Th-Pb Age Constraints on Metamorphism and Melting during the Petermann Orogeny (Central Australia) J. Petrology, February 3, 2009; (2009) egn077v1. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 H. Cheng, E. Nakamura, K. Kobayashi, and Z. Zhou Origin of atoll garnets in eclogites and implications for the redistribution of trace elements during slab exhumation in a continental subduction zone American Mineralogist, July 1, 2007; 92(7): 1119 - 1129. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
D. RUBATTO, J. HERMANN, and I. S. BUICK Temperature and Bulk Composition Control on the Growth of Monazite and Zircon During Low-pressure Anatexis (Mount Stafford, Central Australia) J. Petrology, October 1, 2006; 47(10): 1973 - 1996. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
A. C. STORKEY, J. HERMANN, M. HAND, and I. S. BUICK Using In Situ Trace-Element Determinations to Monitor Partial-Melting Processes in Metabasites J. Petrology, June 1, 2005; 46(6): 1283 - 1308. [Abstract] [Full Text] [PDF]
|
|
| JOURNAL HOME | HELP | CONTACT PUBLISHER | SUBSCRIBE | ARCHIVE | SEARCH | TABLE OF CONTENTS |
