Multi-stage reaction history in different eclogite types from the Pakistan Himalaya and implications for exhumation processes

Subduction, peak and multi-stage exhumation metamorphism: Traces from one coesite-bearing eclogite, Tso Morari, western Himalaya

“…It should be pointed out that the eclogite samples studied by St-Onge et al (2013) were taken from the same outcrop as the sample investigated in this study, but remarkably differ in, for example, their lack of kyanite, glaucophane and coesite. Such inhomogeneities could be attributed to compositionally zoned protoliths and/or to higher degrees of retrogression and alteration but the major point is that slightly different paragenesis and mineral compositions can be derived from the same protolith by variations in growth episodes of major, non-equilibrated minerals modifying the available bulk composition (Wilke et al, 2010a).…”

“…Carbonates, especially calcite, oxides (titanite and Fe-oxides), white and dark mica were found in rarely modified source rocks beside greenschist-facies minerals (Vannay and Spring, 1993). The investigated eclogite sample and counterparts in the Kaghan Valley, Pakistan have been interpreted to be metamorphosed equivalents of the Panjal Trap basalts (Honegger et al, 1982;Wilke et al, 2010a). First evidence for high-pressure metamorphism, recognised by Berthelsen (1953), comes from the presence of garnet + omphacite+/− phengite+/− -glaucophane in metabasites, jadeite + garnet + chloritoid + phengite in metapelites and grossular-rich garnet + kyanite + zoisite + rutile + phengite in metagranite (de Sigoyer et al, , 2004Guillot et al, Fig.…”

“…Using the most Mg-rich garnet, the most silicic phengite and the most jadeite-rich omphacite (Wilke et al, 2010a;Table 1; note that Jd-rich omphacite has been found in the Mg-rich outer mantel of the garnet, whereas phengite is only present as relicts in the matrix), temperatures of 560-760°C and pressures of 44-48 kbar were calculated ( Table 2). The results indicate that pressures peaked within the coesite field above the coesite = quartz univariant curve, as already shown by Sachan et al, 2004.…”

“…Due to the very low Na A -content of glaucophane (Table 1), a formation at temperatures around 550°C is most likely (see Fig. 9 in Wilke et al, 2010a for comparison to the UHP Kaghan eclogite in which glaucophane were set to 580-630°C with a Na A -content of 0.10). Amphiboles of sodic-calcic (winchite, barroisite) composition surround the glaucophane cores, large matrix amphiboles are edenites.…”

Phase equilibria modelling of retrograde amphibole and clinozoisite in mafic eclogite from the Tso Morari massif, northwest India: constraining the P–T–M(H2O) conditions of exhumation

“…A common mineralogical feature of exhumed (ultra)high pressure ((U)HP) metabasic eclogite is the occurrence of epidote and/or clinozoisite poikiloblasts associated with compositionally zoned amphibole, the latter typically containing a substantial sodic component (Smulikowski & Smulikowski, ; Messiga et al ., ; Zack et al ., ; Garciá‐Casco et al ., ; Massonne & Kopp, ; Su et al ., ; Wilke et al ., ). These are present in many subduction‐related (U)HP terranes that form during continental collision, although the petrographic significance of this mineralogical pairing is debated (Massonne, ).…”