Zoned amphibole in an eclogite from the Hida Marginal belt in the Hakuba district, Nagano Prefecture, Japan

A cobble-sized clast of eclogite was recently found in gravels in the bed of the Matsukawa River at Wadano in Hakuba village，Nagano Prefecture．The cobble was probably derived from an area in the Hida Marginal belt，which consists of high-pressure type schists and closely associated serpentinites，and also includes blocks of garnet glaucophane schist and garnet-epidote-glaucophane schist．
The eclogite cobble consists mainly of garnet，omphacite，epidote and amphibole，along with small amounts of quartz，albite，chlorite，phengite，apatite，rutile，titanite and pumpellyite．Amphibole occurs as abmdant subhedral prismatic crystals showing distinct zoning，with bluish cores and greenish rims．The cores of such amphiboles often have resortion texture，and are overgrown by green amphibole at their rims．The boundaries between the cores and rims are sharp and abrupt．The cores ofthe prismatic amphibole are chemically classified as glaucophane，whereas the rims are divided into two parts；inner rims consisting of barroisite，and outer rims of actinolite．
The eclogite described in this paper shows a typical clockwise P-T path of　metamorphism，which is composed of a prograde path from the glaucophane schist facies to form eclogite，and a retrograde path from eclogite through the epidote amphibolite to the greenschist facies．