The timing and nature of the formation of the Himalayan Orogeny remains unclear (Donaldson et al., 2013). The original theory is that these mountains were formed during a continent-continent collision (Liou et al., 2005) but recent finding of coesite (evidence of ultrahigh pressures greater than ~26 kb) in some eclogites in the Himalayas indicates that continental subduction was also involved in their formation (O’Brian et al., 2001; Sachan et al, 2004). Many studies have been done on the Himalayan rocks to identify the pressures and temperatures the rocks experienced during formation; most of these have focused on traditional major element thermobarometric techniques. However, new research (Skora et al., 2006) shows the importance of trace elements (elements that make up less than 1 weight percent of a mineral) in recording the intricate details of rock pressure–temperature histories.
This research investigates the trace element patterns of garnets from an eclogite from Tso Morari, India (Western Himalaya). I used a laser-ablation inductively-coupled mass spectrometer to measure twenty-nine trace elements across five garnets from one rock. My results show a unique pattern across each garnet for the heavy, medium, and light rare earth elements. For example, Eu shows core and mantle peaks across garnet #4, but Tm records only a core peak. At the same time, patterns vary between garnets. This may be due to garnet core location (not in the center of the garnet, for instance), the differing garnet age (growth during different mineral reactions), or varied local geochemistry.
John McElroy, ’14
Sponsor: Emily Walsh