Titanian Clinohumite-Bearing Peridotite from the Ulamertoq Ultramafic Body in the 3.0 Ga Akia Terrane of Southern West Greenland

Geosciences

Graham Pearson¹  Kristofer Szilas²  Akihiro Tamura³  Tomoaki Morishita³  JuanMiguel Guotana⁴  Ikuya Nishio⁴  Yumiko Harigane⁵  Ken-Ichiro Tani⁶ 

[1] Department of Earth and Atmospheric Science, Univesity of Alberta, Edmonton, AB T6G 2B4, Canada;Department of Geosciences and Natural Resource Management, University of Copenhagen, 10, 1165 Copenhagen, Denmark;Faculty of Geosciences and Civil Engineering, Institute of Science and Engineering, Kanazawa University, Kanazawa, Ishikawa 920-1192, Japan;Graduate School of Natural Science and Technology, Kanazawa University, Kanazawa, Ishikawa 920-1192, Japan;Institute of Geology and Geoinformation Geological Survey of Japan/AIST, Tsukuba, Ibaraki 305-8560, Japan;National Museum of Nature and Science, Tokyo 110-8718, Japan;

关键词: titanian clinohumite-bearing ultramafic rock;    Archaean terrane;    West Greenland;    serpentinite;    dehydration;   

DOI  :  10.3390/geosciences9040153

来源: DOAJ

【 摘 要 】

A titanian clinohumite-bearing dunite was recently found in the Ulamertoq ultramafic body within the 3.0 Ga Akia Terrane of southern West Greenland. Titanian clinohumite occurs as disseminated and discrete grains. Titanian clinohumite contains relatively high amounts of fluorine, reaching up to 2.4 wt.%. The high-Fo content of olivine (Fo₉₃) coupled with low Cr/(Cr + Al) ratio of orthopyroxene implies that the dunite host is not of residual origin after melt extraction by partial melting of the primitive mantle. Olivine grains are classified into two types based on abundances of opaque mineral inclusions: (1) dusty inclusion-rich and (2) clear inclusion-free olivines. Opaque inclusions in coarse-grained olivines are mainly magnetite. Small amounts of ilmenite are also present around titanian clinohumite grains. The observed mineral association indicates partial replacement of titanian clinohumite to ilmenite (+magnetite) and olivine following the reaction: titanian clinohumite = ilmenite + olivine + hydrous fluid. The coexistence of F-bearing titanian clinohumite, olivine, and chromian chlorite indicates equilibration at around 800–900 °C under garnet-free conditions (<2 GPa). Petrological and mineralogical characteristics of the studied titanian clinohumite-bearing dunite are comparable to deserpentinized peridotites derived from former serpentinites. This study demonstrates the importance of considering the effects of hydration/dehydration processes for the origin of ultramafic bodies found in polymetamorphic Archaean terranes.

【 授权许可】

Unknown