Editing Eclogite (section)

=== Surface versus mantle origin ===
The broad range in composition has led a longstanding debate on the origin of eclogite xenoliths as either mantle or surface derived, where the latter is associated with the [[gabbro]] to eclogite transition as a major driving force for [[subduction]].<ref name=":12">{{Cite journal|last=Jacob|first=D. E.|date=2004-09-01|title=Nature and origin of eclogite xenoliths from kimberlites|url=https://www.sciencedirect.com/science/article/pii/S0024493704001045|journal=Lithos|series=Selected Papers from the Eighth International Kimberlite Conference. Volume 2: The J. Barry Hawthorne Volume|language=en|volume=77|issue=1|pages=295–316|doi=10.1016/j.lithos.2004.03.038|issn=0024-4937|access-date=2021-11-30|archive-date=2022-02-12|archive-url=https://web.archive.org/web/20220212025749/https://www.sciencedirect.com/science/article/abs/pii/S0024493704001045|url-status=live|url-access=subscription}}</ref><ref name="O'Hara 69–133">{{Cite journal|last=O'Hara|first=M. J.|date=1968-01-01|title=The bearing of phase equilibria studies in synthetic and natural systems on the origin and evolution of basic and ultrabasic rocks|url=https://dx.doi.org/10.1016/0012-8252%2868%2990147-5|journal=Earth-Science Reviews|language=en|volume=4|pages=69–133|doi=10.1016/0012-8252(68)90147-5|issn=0012-8252|url-access=subscription}}</ref><ref>{{Cite journal|last1=Ringwood|first1=A. E.|last2=Green|first2=D. H.|date=1966-10-01|title=An experimental investigation of the Gabbro-Eclogite transformation and some geophysical implications|url=https://dx.doi.org/10.1016/0040-1951%2866%2990009-6|journal=Tectonophysics|language=en|volume=3|issue=5|pages=383–427|doi=10.1016/0040-1951(66)90009-6|issn=0040-1951|url-access=subscription}}</ref>

Group A eclogite xenoliths remain the most enigmatic in terms of their origin due to [[Metasomatism|metasomatic]] overprinting of their original composition.<ref>{{Cite journal|date=1980-07-24|title=Chemical variations in upper mantle nodules from southern African kimberlites|url=https://royalsocietypublishing.org/doi/10.1098/rsta.1980.0215|journal=Philosophical Transactions of the Royal Society of London. Series A, Mathematical and Physical Sciences|language=en|volume=297|issue=1431|pages=273–293|doi=10.1098/rsta.1980.0215|s2cid=123640184 |issn=0080-4614|access-date=2021-11-30|archive-date=2021-11-04|archive-url=https://web.archive.org/web/20211104080455/https://royalsocietypublishing.org/doi/10.1098/rsta.1980.0215|url-status=live|url-access=subscription}}</ref><ref name=":13"/> Models proposing a primary surface origin as seafloor [[protolith]]s strongly rely on the wide range in [[Isotopes of oxygen|oxygen isotope]] composition, which overlaps with obducted oceanic crust, such as the Ibra section of the [[Semail Ophiolite|Samail ophiolite]].<ref name="onlinelibrary.wiley.com">{{Cite journal|last1=MacGregor|first1=Ian D.|last2=Manton|first2=William I.|date=1986|title=Roberts victor eclogites: Ancient oceanic crust|url=https://onlinelibrary.wiley.com/doi/abs/10.1029/JB091iB14p14063|journal=Journal of Geophysical Research: Solid Earth|language=en|volume=91|issue=B14|pages=14063–14079|doi=10.1029/JB091iB14p14063|issn=2156-2202|url-access=subscription}}</ref><ref>{{Cite journal|last1=Gregory|first1=Robert T.|last2=Taylor|first2=Hugh P.|date=1981|title=An oxygen isotope profile in a section of Cretaceous oceanic crust, Samail Ophiolite, Oman: Evidence for δ18O buffering of the oceans by deep (>5 km) seawater-hydrothermal circulation at mid-ocean ridges|url=https://onlinelibrary.wiley.com/doi/abs/10.1029/JB086iB04p02737|journal=Journal of Geophysical Research: Solid Earth|language=en|volume=86|issue=B4|pages=2737–2755|doi=10.1029/JB086iB04p02737|s2cid=46321182 |issn=2156-2202}}</ref> The variation found in some eclogite xenoliths at the Roberts Victor kimberlite pipe are a result of [[hydrothermal alteration]] of basalt on the seafloor.<ref name="onlinelibrary.wiley.com"/> This process is attributed to both low- and high-temperature seawater exchange, resulting in large fractionations in oxygen isotope space relative to the upper mantle value typical of mid ocean ridge basalt glasses.<ref>{{Cite journal|last=Muehlenbachs|first=Karlis|date=1998-04-15|title=The oxygen isotopic composition of the oceans, sediments and the seafloor|url=https://www.sciencedirect.com/science/article/pii/S0009254197001472|journal=Chemical Geology|language=en|volume=145|issue=3|pages=263–273|doi=10.1016/S0009-2541(97)00147-2|issn=0009-2541|url-access=subscription}}</ref><ref>{{Cite journal|last1=Mattey|first1=David|last2=Lowry|first2=David|last3=Macpherson|first3=Colin|date=1994-12-01|title=Oxygen isotope composition of mantle peridotite|url=https://dx.doi.org/10.1016/0012-821X%2894%2990147-3|journal=Earth and Planetary Science Letters|language=en|volume=128|issue=3|pages=231–241|doi=10.1016/0012-821X(94)90147-3|issn=0012-821X|url-access=subscription}}</ref> Other mechanisms proposed for the origin of Group A eclogite xenoliths rely on a [[cumulate]] model, where garnet and clinopyroxene bulk compositions derive from residues of [[partial melting]] within the mantle.<ref name="O'Hara 69–133"/> Support of this process is result of metasomatic overprinting of the original oxygen isotope composition, driving them back towards the mantle range.<ref>{{Cite journal|last1=Huang|first1=Jin-Xiang|last2=Gréau|first2=Yoann|last3=Griffin|first3=William L.|last4=O'Reilly|first4=Suzanne Y.|last5=Pearson|first5=Norman J.|date=2012-06-01|title=Multi-stage origin of Roberts Victor eclogites: Progressive metasomatism and its isotopic effects|url=https://www.sciencedirect.com/science/article/pii/S002449371200093X|journal=Lithos|language=en|volume=142-143|pages=161–181|doi=10.1016/j.lithos.2012.03.002|issn=0024-4937|url-access=subscription}}</ref>