Zirconium in rutile thermometry of the Himalayan ultrahigh-pressure eclogites and their retrogressed counterparts, Kaghan Valley, Pakistan

Abstract

Abstract This study reports zirconium-in-rutile thermometry data from the Himalayan ultrahigh-pressure eclogites and their retrogressed counterparts. The Zr contents of three textural varieties of rutile i.e. matrix rutile, inclusion phase, and overgrown by ilmenite/titanite from coesite-bearing eclogites, slightly retrogressed eclogites, highly retrogressed eclogites, and amphibolites were analyzed for Zr contents using the electron probe micro-analyser. Majority of the rutile grains exhibited homogeneous chemical compositions in all the aforementioned textural varieties; however, some of grains were relatively heterogeneous. Average temperature values of 729\u202f°C, 727\u202f°C, and 706\u202f°C were obtained for the matrix, inclusion, and overgrown rutiles from UHP eclogites and of 705\u202f°C, 699\u202f°C, and 707\u202f°C for those from HP eclogites, respectively. Slightly retrogressed eclogites yielded similar average T values of 703\u202f°C, 706\u202f°C, and 706\u202f°C, respectively, whereas highly retrogressed eclogites resulted in relatively low average temperatures, ca. 690\u202f°C, 691\u202f°C, and 679\u202f°C, respectively. When compared with these eclogites, lower average T values of 672\u202f°C, 630\u202f°C, and 656\u202f°C were obtained from garnetites, and of 665\u202f°C, 658\u202f°C, and 640\u202f°C from garnet amphibolites, respectively. The relatively homogeneous Zr contents and higher temperature values from the matrix rutile in HP and UHP eclogites suggest peak or near-peak metamorphic crystallization, whereas grains with low Zr contents, yielding low temperature values, were likely to be affected by the late-stage retrogression.