The Influence of Source Heterogeneity on Melt Production in OIBs and LIPs
Abstract
The role of eclogite in the genesis of ocean island basalts (OIB) and large igneous provinces (LIP) remains controversial. While it is generally agreed that eclogite is required as a mantle source component to explain the compositional variability of basalts erupted in these settings, the extent to which eclogite contributes to anomalous melt productivity remains poorly quantified. This problem stems from the fact that melt productivity is also dependent on mantle temperature and upwelling rate. To evaluate the influence of these factors on melt productivity we have developed a forward polybaric melting model that simulates the melting of a heterogeneous source comprised of eclogite and peridotite. This model takes into account mantle potential temperature, upwelling rate and amount of eclogite and outputs the compositions and volumes of modeled pooled melts. Comparison of model results with the compositions and volumes of OIB and LIP basalts allows us to constrain a family of possible solutions for potential temperature, upwelling rate and abundance of eclogite in the mantle source. As a case study, we apply this model to the genesis and evolution of the North Atlantic large igneous province (NAIP). Based on our modeling, we find that the compositions and volumes of Tertiary basalts erupted along the central east Greenland rifted margin and in Iceland can be explained by potential temperatures ranging from 1400-1450° C, with an upwelling rate of ~5-10 times passive. The compositions and volumes of modern Icelandic basalts from Theistareykir and Tertiary basalts from the southeast Greenland rifted margin are consistent with potential temperatures ranging from 1400-1500° C, and an upwelling rate of ~1-2.5 times passive. In all cases, the mantle source is constrained to contain less than 7% eclogite and will be positively buoyant (rise) for these mantle potential temperatures. Based on density considerations, the NAIP mantle source cannot contain more than ~13% eclogite. These results indicate that the predominant factors enhancing melt productivity are moderate temperature anomalies (relative to ambient mid-ocean ridge mantle) and active upwelling, whereas eclogite is a relatively minor component in the source of NAIP basalts. To better understand the relationships between these parameters in other tectonic environments, we extend this analysis to OIB settings in which the compositions and volumes of basalts are well characterized.
- Publication:
-
AGU Fall Meeting Abstracts
- Pub Date:
- December 2008
- Bibcode:
- 2008AGUFM.V52A..05B
- Keywords:
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- 1009 Geochemical modeling (3610;
- 8410);
- 1037 Magma genesis and partial melting (3619);
- 1040 Radiogenic isotope geochemistry;
- 1065 Major and trace element geochemistry