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ORIGINAL RESEARCH article

Front. Earth Sci.
Sec. Geochemistry
Volume 12 - 2024 | doi: 10.3389/feart.2024.1473101

Petrogenesis and tectonic setting of the Proto-Tethyan Dachaidan ophiolite, North China: Insights from clinopyroxene chemistry and whole-rock Sr-Nd-Pb and zircon Hf isotopes

Provisionally accepted
Yilin QU Yilin QU XIJUN LIU XIJUN LIU *Xiao LIU Xiao LIU Qianwen HUANG Qianwen HUANG Qijun YANG Qijun YANG Rongguo HU Rongguo HU Pengde LIU Pengde LIU Yujia SONG Yujia SONG
  • Guilin University of Technology, Guilin, China

The final, formatted version of the article will be published soon.

    The Dachaidan ophiolites outcrop within an ultrahigh-pressure metamorphic belt along the northern margin of the Qaidam Basin. However, their age, source, and tectonic setting remain still in debate. In this study, we investigated the geochemistry and geochronology of the Dachaidan ophiolitic gabbros. Zircon U-Pb dating yielded a crystallization age of 510.0 ± 2.8 Ma and 510.0 ± 2.9 Ma for the gabbro. The gabbros have low SiO2 contents (47.15-50.10 wt.%) and high MgO contents (6.35-9.04 wt.%) and Mg # values (55-74). The total rare earth element (∑REE) contents are 8.35-28.07 ppm, lower than those of normal-type mid-ocean ridge basalts (MORBs), and the gabbros exhibit light REE depletion or flat REE patterns, with small positive Eu anomalies (Eu/Eu* = 1.06-1.40). Trace element patterns are depleted to enriched in Nb and Ta, similar to island arc rocks and MORB. Clinopyroxene thermobarometry indicates the parental magma of the gabbros formed by high-temperature (1318-1363°C) and medium-pressure (1.27-1.64 GPa) partial melting in a mantle wedge. The gabbros have depleted Sr-Nd-Pb-Hf isotopic compositions, with ( 87 Sr/ 86 Sr)i = 0.704586-0.707441, εNd(t) = 4.7-6.6, and zircon εHf(t) = 7.6-11.4. The age-corrected Pb isotope ratios of these volcanic rocks are variable, with 206 Pb/ 204 Pb(t) = 18.085-18.253, 207 Pb/ 204 Pb(t) = 15.595-15.614, and 208 Pb/ 204 Pb(t) = 37.880-38.148, which are similar to the isotopic compositions of typical Indian MORBs. The source of the Dachaidan ophiolite is inferred to have been depleted mantle. The Dachaidan ophiolite likely formed in a forearc oceanic setting along the northern margin of the Qaidam Basin, during the initial subduction of an oceanic plate.

    Keywords: North Qaidam ultrahigh-pressure metamorphic belt, Early Paleozoic, Gabbro, Petrogenesis, Tectonic setting

    Received: 30 Jul 2024; Accepted: 27 Sep 2024.

    Copyright: © 2024 QU, LIU, LIU, HUANG, YANG, HU, LIU and SONG. This is an open-access article distributed under the terms of the Creative Commons Attribution License (CC BY). The use, distribution or reproduction in other forums is permitted, provided the original author(s) or licensor are credited and that the original publication in this journal is cited, in accordance with accepted academic practice. No use, distribution or reproduction is permitted which does not comply with these terms.

    * Correspondence: XIJUN LIU, Guilin University of Technology, Guilin, China

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