Comparing primitive EETA 79001 melts with those from other SNC

Introduction: The shergottite meteorites have been subdivided into three groups based on texture and mineralogy [1]. EETA79001 is a shergottite that contains examples of all three lithologies: lherzolitic (lithology X), olivine-phyric (lithology A), and basaltic (lithology B). Therefore, studying the magmas involved in the petrogenesis of EETA79001 may provide information not only on its own petrogenesis but of the petrogenetic links between the shergottites. This preliminary study involves the rehomogenization of the ground mass and interstitial melts in chips of EETA79001’s lithology A in order to constrain the composition of the parental magma. These melt compositions are then compared to melt compositions determined for ALH 77005, a lherzolitic shergottite [2,3]. Experiments: Experiments were performed in argon-pressurized, TZM pressure vessels. Samples were surrounded with graphite, which reacts with ferric iron to fix the oxidation state of the experiment at QFM2.0. The graphite also prevents sample tube reaction (Fe-loss to Pt tubing). The tubes were pressurized to 800 bars. The temperature of the samples was raised to 1150, 1155, 1160, and 1165oC. Samples were run for durations ranging from 48 to 72 hours. After a rapid quench, polished sections were made for analysis by electron microprobe. Results: The fused ground mass and interstitial melt for lithology A of EETA79001 is plotted (Figure 1) along with the liquid line of descent determined for ALH 77005 from rehomogenized, olivine-hosted melt inclusions. For the major elements SiO2, FeO, and Al2O3, the interstial melt falls near the liquid line of descent defined by ALH 77005 (Figure 1). In addition, K2O and Na2O (not pictured) also fell near the liquid line of descent defined by ALH 77005. However, the CaO, P2O5, and TiO2 contents of the ground mass are lower for comparable MgO contents (Figure 1). The chlorine content of the fused ground mass is considerably lower than that of the rehomogenized melt inclusions from ALH 77005 (Figure 2). In addition, the interstitial melt that was homogenized during experiments on ALH 77005 is plotted for comparison. Although more scatter exists in ALH 77005’s interstitial melts, EETA79001’s ground mass still has significantly lower chlorine content than ALH 77005.