Partial melting of zoisite eclogite from the Sanddal area, North-East Greenland Caledonides
<p>Metamorphic textures and a pressure–temperature (<span class="inline-formula"><i>P</i></span>–<span class="inline-formula"><i>T</i></span>) path of zoisite eclogite are presented to better understand the metamorphic evoluti...
| Main Authors: | , , |
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| Format: | Article |
| Language: | English |
| Published: |
Copernicus Publications
2020-07-01
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| Series: | European Journal of Mineralogy |
| Online Access: | https://ejm.copernicus.org/articles/32/405/2020/ejm-32-405-2020.pdf |
| Summary: | <p>Metamorphic textures and a pressure–temperature (<span class="inline-formula"><i>P</i></span>–<span class="inline-formula"><i>T</i></span>) path
of zoisite eclogite are presented to better understand the metamorphic
evolution of the North-East Greenland eclogite province and this particular
type of eclogite. The eclogite contained the mineral assemblage garnet,
omphacite, kyanite, phengite, quartz and rutile at peak pressure. Partial
melting occurred via breakdown of hydrous phases, paragonite,
phengite and zoisite, based on (1) polymineralic inclusions of albite and
K-feldspar with cusps into host garnet, (2) small euhedral garnet with
straight boundaries against plagioclase, (3) cusps of plagioclase into
surrounding phases (such as garnet), and (4) graphic intergrowth of plagioclase
and amphibole next to anhedral zoisite grains. Isochemical phase equilibrium
modeling of a melt-reintegrated composition, along with
<span class="inline-formula"><i>X</i><sub>Na</sub></span>-in-omphacite and Si-in-phengite isopleths, yields a peak pressure
of <span class="inline-formula">2.4±0.1</span> GPa at <span class="inline-formula">830±30</span> <span class="inline-formula"><sup>∘</sup></span>C. A peak temperature
of <span class="inline-formula">900±50</span> <span class="inline-formula"><sup>∘</sup></span>C at <span class="inline-formula">1.9±0.2</span> GPa is determined using
the rim composition of small euhedral garnet, as predicted by modeling a
crystallized melt pocket. Zoisite growth at the expense of kyanite suggests
that the <span class="inline-formula"><i>P</i></span>–<span class="inline-formula"><i>T</i></span> path crossed the fields of zoisite growth at <span class="inline-formula">∼1.9</span> GPa, 800–900 <span class="inline-formula"><sup>∘</sup></span>C on the modeled phase diagram of the bulk rock. A
point on the exhumation path at <span class="inline-formula">∼1.3</span> GPa and 750 <span class="inline-formula"><sup>∘</sup></span>C is derived from hornblende-plagioclase thermometry and
Al-in-hornblende barometry. The study demonstrates that paragonite, phengite
and zoisite could contribute to partial melting of eclogite at near-peak <span class="inline-formula"><i>P</i></span>
and during exhumation.</p> |
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| ISSN: | 0935-1221 1617-4011 |