Comprehensive modification of cratonic lithospheric mantle beneath the central North China Craton: Insights from Li isotope systematics of olivine xenocrysts in Cenozoic basalts

IF 3.6 2区地球科学 Q1 GEOCHEMISTRY & GEOPHYSICS

Chemical Geology Pub Date : 2025-03-03 DOI:10.1016/j.chemgeo.2025.122721

Yao Xu , Hong-Fu Zhang , Yan-Jie Tang , A-Bing Lin , Juan Zhang , Ming-Jie Zhang

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Abstract

The flat subduction and subsequent rollback of the Paleo-Pacific plate played a critical role in the destruction of the eastern North China Craton (NCC), manifested by a drastic transformation of the subcontinental lithospheric mantle (SCLM) in physico-chemical properties. However, the nature of the SCLM beneath the central NCC remains poorly defined. This study presents in situ major element compositions and Li systematics (concentrations and δ⁷Li) of olivine xenocrysts from Cenozoic Xiyang–Pingding basalts to investigate the impacts of circum-craton plate subduction on the SCLM. Olivine grains from the basalts are classified into four types based on core forsterite (Fo) contents and mineralogical traits. Types 1–3 xenocrysts show sub-rounded shapes, kink bands, and geochemical affinities with xenolithic olivines, distinct from Type 4 phenocrysts. Xenocrystic zoned textures resulted from re-equilibration with host magma, while large xenocrystic cores retain the SCLM composition. Type 1 cores (Fo = 92.1–93.5) exhibit Li contents (1.0–1.7 ppm) comparable to mantle olivines and δ⁷Li values within or slightly above the normal mantle range (2–6 ‰), representing relicts of ancient refractory SCLM enriched by Paleo-Pacific slab-derived silicate melts. Type 2 (Fo = 90.0–92.0) and high-Fo (88.6–89.9) Type 3 xenocrysts display Li enrichment (1.3–3.5 ppm) and δ⁷Li depletion (down to −20 ‰). Positive relationships between δ⁷Li and both Fo and 1/Li indicate their formation through interaction between Archean refractory SCLM and asthenospheric carbonated silicate melts. Low-Fo (84.7–88.2) Type 3 cores record the highest Li (1.7–4.9 ppm) and δ⁷Li (9 ‰ to 14 ‰), marking the recent refertilization by asthenospheric silicate melts. Combined with previous studies, these Li-δ⁷Li variations reflect the most comprehensive record of SCLM modification beneath the NCC, offering crucial insights into the dynamics of cratonic evolution.

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华北克拉通中部克拉通岩石圈地幔的综合改造——来自新生代玄武岩橄榄石杂晶Li同位素系统的启示

古太平洋板块的平俯冲及其后的回滚对华北克拉通（NCC）东部的破坏起了关键作用，表现为次大陆岩石圈地幔（SCLM）物理化学性质的剧烈变化。然而，中央NCC下的SCLM的性质仍然不明确。本文通过对新生代西阳-平定玄武岩橄榄石异种结晶的原位主元素组成和Li分系统（浓度和δ7Li）的研究，探讨了环克拉通板块俯冲对SCLM的影响。根据岩心橄榄石（Fo）含量和矿物学特征，将玄武岩橄榄石颗粒划分为4种类型。1-3型异晶与4型异晶不同，呈亚圆形、扭结带，与异石器时代橄榄石具有地球化学亲和性。异晶带织构是与寄主岩浆重新平衡形成的，而大的异晶岩心则保留了scm成分。1型岩心（Fo = 92.1 ~ 93.5）的Li含量（1.0 ~ 1.7 ppm）与地幔橄榄石相当，δ7Li值在正常地幔范围（2 ~ 6‰）以内或略高于正常地幔范围（2 ~ 6‰），代表古太平洋板块衍生硅酸盐熔体富集的古难熔SCLM遗迹。2型（Fo = 90.0 ~ 92.0）和高Fo(88.6 ~ 89.9) 3型异晶表现为Li富集（1.3 ~ 3.5 ppm）和δ7Li亏缺（- 20‰）。δ7Li与Fo和1/Li均呈正相关，表明它们是太古宙难熔SCLM与软流圈碳酸盐硅酸盐熔体相互作用形成的。低fo(84.7 ~ 88.2) 3型岩心的Li值最高（1.7 ~ 4.9 ppm）， δ7Li值最高（9‰~ 14‰），表明软流圈硅酸盐熔体在近期发生了再成矿作用。结合前人的研究，这些Li-δ7Li变化反映了NCC下最全面的SCLM改造记录，为克拉通演化动力学提供了重要的见解。

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来源期刊

Chemical Geology 地学-地球化学与地球物理

CiteScore

7.20

自引率

10.30%

发文量

374

审稿时长

3.6 months

期刊介绍： Chemical Geology is an international journal that publishes original research papers on isotopic and elemental geochemistry, geochronology and cosmochemistry. The Journal focuses on chemical processes in igneous, metamorphic, and sedimentary petrology, low- and high-temperature aqueous solutions, biogeochemistry, the environment and cosmochemistry. Papers that are field, experimentally, or computationally based are appropriate if they are of broad international interest. The Journal generally does not publish papers that are primarily of regional or local interest, or which are primarily focused on remediation and applied geochemistry. The Journal also welcomes innovative papers dealing with significant analytical advances that are of wide interest in the community and extend significantly beyond the scope of what would be included in the methods section of a standard research paper.