Metamorphic P-T evolution of high-pressure eclogites from garnet growth and reaction textures: insights from the Kaghan Valley transect, northern Pakistan

<jats:title>Abstract</jats:title><jats:p>The <jats:styled-content style="fixed-case">H</jats:styled-content>imalayan <jats:styled-content style="fixed-case">M</jats:styled-content>etamorphic <jats:styled-content style="fixed-case">B</jats:styled-content>elt of the <jats:styled-content style="fixed-case">K</jats:styled-content>aghan <jats:styled-content style="fixed-case">V</jats:styled-content>alley transect in northern <jats:styled-content style="fixed-case">P</jats:styled-content>akistan is a key area where rocks of the <jats:styled-content style="fixed-case">I</jats:styled-content>ndian <jats:styled-content style="fixed-case">P</jats:styled-content>late have been subducted to greater depths >100 km beneath the <jats:styled-content style="fixed-case">A</jats:styled-content>sian <jats:styled-content style="fixed-case">P</jats:styled-content>late and experienced high‐ to ultrahigh‐pressure metamorphism. At least three distinct metamorphic events can be recognized in the metamorphosed mafic rock units (eclogites and amphibolitized eclogites) of the <jats:styled-content style="fixed-case">K</jats:styled-content>aghan <jats:styled-content style="fixed-case">V</jats:styled-content>alley: (i) prograde; (ii) peak; and (iii) retrograde stages. Chemical composition, zoning pattern and inclusions in garnet, and metamorphic reactions among major mineral assemblage (garnet + clinopyroxene + quartz + amphibole + epidote) show that core portions of garnet grew under the prograde stage, whereas most of the middle portions were developed or recrystallized under the high‐pressure stage with <jats:styled-content style="fixed-case">P</jats:styled-content>–<jats:styled-content style="fixed-case">T</jats:styled-content> conditions at 2.3 ± 0.4 <jats:styled-content style="fixed-case">GP</jats:styled-content>a and 766 ± 107°<jats:styled-content style="fixed-case">C</jats:styled-content>. The rim portions of garnet in association with amphibole and presence of symplectites indicate amphibole‐eclogite to amphibolite‐facies (retrograde) stage with average <jats:styled-content style="fixed-case">P</jats:styled-content>–<jats:styled-content style="fixed-case">T</jats:styled-content> conditions at 1.5 ± 0.2 <jats:styled-content style="fixed-case">GP</jats:styled-content>a and 710 ± 75°<jats:styled-content style="fixed-case">C</jats:styled-content>. Zoning in garnet shows <jats:styled-content style="fixed-case">C</jats:styled-content>a‐poor wider cores, <jats:styled-content style="fixed-case">C</jats:styled-content>a‐rich thin middle portions, and chlorite and amphibole development along the outermost rims, suggesting prograde growth at cores and homogenous middle portions and retrogressive formation at rims during the amphibolite‐facies stage. These features suggest that most of the garnet grew during subduction of the <jats:styled-content style="fixed-case">I</jats:styled-content>ndian <jats:styled-content style="fixed-case">P</jats:styled-content>late lithosphere before the <jats:styled-content style="fixed-case">I</jats:styled-content>ndia–<jats:styled-content style="fixed-case">A</jats:styled-content>sia collision, whereas rim portions developed during rapid exhumation in the post‐collision stage.</jats:p>