Influence of igneous processes and serpentinization on geochemistry of the Logatchev Massif harzburgites (14 degrees 45' N, Mid-Atlantic Ridge), and comparison with global abyssal peridotites Journal Article


Authors: Chen, Zhi-qiang; Zhou, Huai-yang; Liu, Yang; Yang, Qun-hui; Li, Ji-wei; Dick, Henry J. B.
Article Title: Influence of igneous processes and serpentinization on geochemistry of the Logatchev Massif harzburgites (14 degrees 45' N, Mid-Atlantic Ridge), and comparison with global abyssal peridotites
Abstract: We acquired bulk-rock analyses of Mid-Atlantic Ridge (MAR) harzburgites in order to understand the influence of submarine igneous and metamorphic processes on the distribution of incompatible elements (especially rare Earth elements or REEs) in abyssal peridotites. The geochemical characteristics of these Logatchev Massif serpentinized and talc-altered harzburgites, and spatially associated metagabbros were then compared with a compilation of global abyssal peridotites. The Logatchev harzburgites show light rare earth element (LREE) enrichments (average La-N/Yb-N = 2.81), positive correlations between LREEs (e. g. La, Ce, Pr, and Nd) and high field strength elements (HFSEs; e. g. Nb and Zr), and positive correlations between HFSEs and Th. Most global abyssal peridotites show similar trends. We suggest that the systematic enrichment of incompatible elements probably reflects a post-partial fusion magmatic refertilization. The compositional scatter exhibited by some serpentinized peridotites in Nb-LREE diagrams is probably due to the elimination of diopside during partial melting and significant impregnation by a melt produced in the Opx-Ol-Sp melting field rather than to later hydrothermal alteration. The correlation between Pb and Nd observed for most global abyssal peridotites, including the Logatchev harzburgites, indicates magmatic generation. The scatter of Pb in some rocks suggests that lead is likely mobile during serpentinization or weathering. Low to moderate water/rock (W/R) ratios in the harzburgites calculated from Sr isotopic compositions (5.98-26.20 for a close system and 1.66-2.72 for an open system), and the low abundance of REEs in Logatchev hydrothermal fluids indicate that the REE contents of abyssal peridotites probably were little influenced by hydrothermal alteration. Compared to this later alteration, the presence of small proportions of gabbroic melt (from 1:30 to 1:3 in our sample) that crystallized in the residual harzburgites modified their REE patterns significantly by elevating the LREEs.
Keywords: MIDOCEAN RIDGES; BENEATH; hydrothermal field; ocean island basalts; EXTRACTION; MANTLE; MELT; 15-20 FRACTURE-ZONE; SLOW-SPREADING RIDGE; SR; REFERTILIZATION; Logatchev Massif; serpentinized abyssal peridotites; LREE enrichment; mixing model of melt refertilization; mid-ocean ridge serpentinization; partial melting and diopside exhaustion
Journal Title: International Geology Review
Volume: 55
Issue: 1
ISSN: 0020-6814
Publisher: Taylor & Francis  
Publication Place: PHILADELPHIA; 325 CHESTNUT ST, SUITE 800, PHILADELPHIA, PA 19106 USA
Date Published: 2013
Start Page: 115
End Page: 130
DOI/URL:
Notes: PT: J; TC: 0; UT: WOS:000311555600005