Details
| Original language | English |
|---|---|
| Pages (from-to) | 206-217 |
| Number of pages | 12 |
| Journal | Precambrian research |
| Volume | 231 |
| Early online date | 21 Mar 2013 |
| Publication status | Published - Jul 2013 |
Abstract
The felsic continental crust formed in the early Earth most likely resulted from melting of basaltic protoliths, but the geodynamic processes leading to partial melting are still debated. Attempts to reconcile geochronological data, thermal modeling and experimental results have led to two major alternative scenarios: (1) partial melting of subducted oceanic slabs and (2) dehydration melting at the base of thick (or thickened) oceanic/simatic protocrusts. Existing experimental data on melting of metabasalt suggest that garnet only becomes an important residual phase (>10wt%) at depths >50-60km, which has been seen as difficulty for model 2. We present results of amphibolite dehydration-melting experiments at pressures of 5-15kbar and provide constraints on melting reactions of a hydrated metabasalt with SiO2 of 47.5wt% and Al2O3 of 16.4wt%. Our experiments demonstrate that felsic melts and complementary restites with ~20wt% garnet can form at ca. 900°C and 12kbar, conditions corresponding to the base of a 40-km thick basaltic protocrust that might be prevalent in the Early Archean. Based on phase proportions determined experimentally and trace element partitioning data, our modeling suggests that such partial melts resemble the Early Archean tonalite-trondhjemite-granodiorite (TTG) suites, including high Al2O3 and low MgO contents, and modestly high La/Yb and Sr/Y ratios. The garnet-rich restite is calculated to be denser than the underlying Early Archean lherzolitic upper mantle and would have the potential to delaminate. Our experimental results and combined geochemical modeling are consistent with models where the initial growth of continental crust on the Archean Earth occurred in non-subduction settings by anatexis of the base of basaltic plateaus.
Keywords
- Continental crust, Experimental petrology, Oceanic plateau, Partial melting, Subduction, TTG
ASJC Scopus subject areas
- Earth and Planetary Sciences(all)
- Geology
- Earth and Planetary Sciences(all)
- Geochemistry and Petrology
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In: Precambrian research, Vol. 231, 07.2013, p. 206-217.
Research output: Contribution to journal › Article › Research › peer review
}
TY - JOUR
T1 - Constraints from experimental melting of amphibolite on the depth of formation of garnet-rich restites, and implications for models of Early Archean crustal growth
AU - Zhang, Chao
AU - Holtz, Francois
AU - Koepke, Jürgen
AU - Wolff, Paul Eric
AU - Ma, Changqian
AU - Bédard, Jean H.
N1 - Funding Information: This work was funded by the German Research Council (DFG) grants to F. Holtz and J. Koepke. C. Zhang appreciates the financial supports from the China Scholarship Council (CSC) and the German Academic Exchange Service (DAAD). C. Ma acknowledges National Nature Science Foundation of China (NSFC Grants 41272079 & 90814004 ) and China Geological Survey (Grant 1212011121270 ) for supporting related studies. This paper benefited from the insightful and helpful reviews of Editor-in-chief Guochun Zhao and two anonymous reviewers, and Elis Hoffmann's review on an earlier version. This is NRCAN/ESS/GSC contribution no. ( 20130001 ). Copyright: Copyright 2013 Elsevier B.V., All rights reserved.
PY - 2013/7
Y1 - 2013/7
N2 - The felsic continental crust formed in the early Earth most likely resulted from melting of basaltic protoliths, but the geodynamic processes leading to partial melting are still debated. Attempts to reconcile geochronological data, thermal modeling and experimental results have led to two major alternative scenarios: (1) partial melting of subducted oceanic slabs and (2) dehydration melting at the base of thick (or thickened) oceanic/simatic protocrusts. Existing experimental data on melting of metabasalt suggest that garnet only becomes an important residual phase (>10wt%) at depths >50-60km, which has been seen as difficulty for model 2. We present results of amphibolite dehydration-melting experiments at pressures of 5-15kbar and provide constraints on melting reactions of a hydrated metabasalt with SiO2 of 47.5wt% and Al2O3 of 16.4wt%. Our experiments demonstrate that felsic melts and complementary restites with ~20wt% garnet can form at ca. 900°C and 12kbar, conditions corresponding to the base of a 40-km thick basaltic protocrust that might be prevalent in the Early Archean. Based on phase proportions determined experimentally and trace element partitioning data, our modeling suggests that such partial melts resemble the Early Archean tonalite-trondhjemite-granodiorite (TTG) suites, including high Al2O3 and low MgO contents, and modestly high La/Yb and Sr/Y ratios. The garnet-rich restite is calculated to be denser than the underlying Early Archean lherzolitic upper mantle and would have the potential to delaminate. Our experimental results and combined geochemical modeling are consistent with models where the initial growth of continental crust on the Archean Earth occurred in non-subduction settings by anatexis of the base of basaltic plateaus.
AB - The felsic continental crust formed in the early Earth most likely resulted from melting of basaltic protoliths, but the geodynamic processes leading to partial melting are still debated. Attempts to reconcile geochronological data, thermal modeling and experimental results have led to two major alternative scenarios: (1) partial melting of subducted oceanic slabs and (2) dehydration melting at the base of thick (or thickened) oceanic/simatic protocrusts. Existing experimental data on melting of metabasalt suggest that garnet only becomes an important residual phase (>10wt%) at depths >50-60km, which has been seen as difficulty for model 2. We present results of amphibolite dehydration-melting experiments at pressures of 5-15kbar and provide constraints on melting reactions of a hydrated metabasalt with SiO2 of 47.5wt% and Al2O3 of 16.4wt%. Our experiments demonstrate that felsic melts and complementary restites with ~20wt% garnet can form at ca. 900°C and 12kbar, conditions corresponding to the base of a 40-km thick basaltic protocrust that might be prevalent in the Early Archean. Based on phase proportions determined experimentally and trace element partitioning data, our modeling suggests that such partial melts resemble the Early Archean tonalite-trondhjemite-granodiorite (TTG) suites, including high Al2O3 and low MgO contents, and modestly high La/Yb and Sr/Y ratios. The garnet-rich restite is calculated to be denser than the underlying Early Archean lherzolitic upper mantle and would have the potential to delaminate. Our experimental results and combined geochemical modeling are consistent with models where the initial growth of continental crust on the Archean Earth occurred in non-subduction settings by anatexis of the base of basaltic plateaus.
KW - Continental crust
KW - Experimental petrology
KW - Oceanic plateau
KW - Partial melting
KW - Subduction
KW - TTG
UR - http://www.scopus.com/inward/record.url?scp=84876959493&partnerID=8YFLogxK
U2 - 10.1016/j.precamres.2013.03.004
DO - 10.1016/j.precamres.2013.03.004
M3 - Article
AN - SCOPUS:84876959493
VL - 231
SP - 206
EP - 217
JO - Precambrian research
JF - Precambrian research
SN - 0301-9268
ER -