Petrologic study of the eclogite xenoliths in fengzhen carbonatite, North China Craton: Evidence for the start of modern-style plate tectonic regime in Paleoproterozoic

článek v časopise ve Web of Science, Jimp

angličtina

The onset of modern plate tectonic regime on Earth became increasingly controversial in recent years because of the lack of continuously newly found records of subduction and collision. Here, we present the study of the ultra-high pressure eclogite xenoliths in the Paleoproterozoic Fengzhen carbonatite complex, including the garnet-rich (Fz-2) and the omphacite-rich (Fz-16) samples. All samples are collected from the same site and exhibit identical mineral chemistry and textures. The xenoliths display whole-rock compositions indicative of the protoliths of oceanic gabbro. At least two metamorphic stages are recognized in these eclogites epidote/amphibole-eclogite stage M1 and lawsonite-eclogite stage M2. Coesite pseudomorph within radial cracks occurs as inclusions in garnet and omphacite. Columnar lawsonite pseudomorph as aggregates of coexisted kyanite and zoisite occasionally present as inclusion in garnet. The porphyroblastic garnet exhibits an inclusion-rich core and an inclusion-poor rim. The garnet displays compositional zoning, with the increasing pyrope and decreasing almandine content from core to rim. The phase equilibria modeling records the prograde path from amphibole-eclogite phase to lawsonite eclogite phase, at pressure and temperature of 2.6 similar to 3.7GPa and 655 similar to 670 degrees C, recorded from garnet zonation. The garnet-omphacite-phengite-kyanite-quartz thermobarometry yields a pressure and temperature of 3.0GPa and 734 degrees C. The Zr-in-rutile thermometer also gives a similar temperature range of 601 similar to 685 degrees C at 2.6 similar to 3.7GPa. The coesite and lawsonite pseudomorphs within the garnet and omphacite support the existence of the lawsonite-eclogite stage, representing the oldest record of low temperature ultra-high pressure metamorphic rock in the world. With a thermal gradient of 216 +/- 35 degrees C/GPa, the eclogite rocks supports the onset of modern-style cold subduction prior to similar to 1.8Ga.

Paleoproterozoic cold subduction; Eclogite xenolith; UHP metamorphism; Modern plate tectonics

LI, Y.; ZHANG, LF.; XU,C.; KYNICKÝ, J.; FEI, YW.;

1. 2. 2021

SCIENCE PRESS

BEIJING

1000-0569

ACTA PETROLOGICA SINICA

37

2

Čínská lidová republika

391

416

26

https://www.researchgate.net/publication/350819645_Petrologic_study_of_the_eclogite_xenoliths_in_fengzhen_carbonatite_North_China_Craton_Evidence_for_the_start_of_modern-style_plate_tectonic_regime_in_Paleoproterozoic