Melt Generation in Heterogeneous Mantle Sources: A Three-Legged Stool Approach
Abstract
The compositions and volumes of basalts generated by adiabatic decompression melting are primarily a function of three factors: mantle potential temperature, the style of mantle upwelling, and source composition. Attempts to use basalts to infer the relative importance of these three factors in specific localities are made difficult because even for homogeneous mantle sources, basalts are aggregates of melts generated over a range of pressures and temperatures within the melting regime. When source heterogeneity and differences in the melting behavior of source lithologies are accounted for, the complexity of relating basalts to the conditions of melt generation increases substantially. Advances in our understanding of mid - ocean ridge basalt petrogenesis have demonstrated the utility of creating geochemical models for melt generation that are constrained by experimental petrology [e.g. 1]. To better relate basalt compositions to the melting processes within a heterogeneous mantle source, we have developed a forward polybaric melting model that simulates the melting of a source comprised of pyroxenite and peridotite. The model uses thermodynamically - derived polybaric melting functions based on parameterizations of pyroxenite and peridotite melting [2, 3]. The model takes into account mantle potential temperature, style of mantle upwelling and variable amounts of pyroxenite, and outputs the isotopic and trace element compositions and volumes of pooled melts using the residual mantle column method [4]. We propagate uncertainties in model input parameters to assess robustness and compare our results with previous models [5-7]. We apply our model to ocean island and large igneous province environments to constrain potential temperature, upwelling rate and abundance of pyroxenite in the mantle source from observed basalt compositions and volumes. [1] Longhi 2002, G-cubed, doi:10.1029/2001/GC000204; [2] Katz et al. 2003, G-cubed, doi:10.1029/2002GC000433; [3] Pertermann and Hirschmann 2003, JGR, v 108, doi:10.1029/2000JB000118 ; [4] Plank and Langmuir 1992, JGR, v 97, p 19749-119770; [5] Ito and Mahoney 2005, EPSL, v 230, p 29-46; [6] Sobolev et al 2005, Nature, v. 434, p 590-597; [7] Stracke and Bourdon 2008, GCA, v. 73, p 218-238.
- Publication:
-
AGU Spring Meeting Abstracts
- Pub Date:
- May 2009
- Bibcode:
- 2009AGUSM.V11A..06B
- Keywords:
-
- 8410 Geochemical modeling (1009;
- 3610);
- 8411 Thermodynamics (0766;
- 1011;
- 3611);
- 8415 Intra-plate processes (1033;
- 3615);
- 8416 Mid-oceanic ridge processes (1032;
- 3614)