Recycling of continental crust into the deep mantle in orogens: Constraints from zircon U-Pb-Hf-O and whole-rock Mg-Fe isotopes of Baihua complex, North Qinling Orogen

IF 3.6 2区地球科学 Q1 GEOCHEMISTRY & GEOPHYSICS

Chemical Geology Pub Date : 2025-07-25 DOI:10.1016/j.chemgeo.2025.122982

Gang Yang , Juan Zhang , Hong-fu Zhang , An-Ping Chen , A-Bing Lin

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Abstract

Mafic magmatism in the orogenic belt acts as an invaluable repository for exploring the intricate dynamics of crust-mantle interactions. It meticulously preserves measurable signatures of recycled oceanic lithosphere and subducted continental materials within the orogenic mantle domains. This study employs an integrated approach, combining zircon U-Pb-Hf-O isotopic analyses and whole-rock geochemistry to investigate the Baihua metamorphosed magmatic complex in the North Qinling orogen, with the aim of deciphering the crustal recycling mechanisms.

Zircon U-Pb dating indicates the emplacement of mafic magma occurred between 441.6 ± 2.9–428.3 ± 2.2 Ma. Amphibolites have arc-like trace element signatures, tholeiitic differentiation trends, and a dual-source origin from mantle-derived melts (ε_Hf(t): +0.10 to +12, δ¹⁸O: 5.61 ± 0.05 ‰) and inherited crustal components (ε_Hf(t): −10.9 to −8.6, δ¹⁸O: 5.75 ± 0.15 ‰), highlighting ancient crustal components in the mantle source. Their δ²⁶Mg values range from −0.28 ± 0.01 ‰ to −0.12 ± 0.01 ‰, and δ⁵⁶Fe values from 0.06 ± 0.02 ‰ to 0.31 ± 0.04 ‰, likely due to mid-lower continental crust involvement in the mantle source.

Mafic microgranular enclaves (MMEs) and host diorites also have arc-like trace element signatures but show calc-alkaline affinities. They have uniform ε_Hf(t) values (−0.1 to +5.1) and δ¹⁸O values from 4.51 ‰ to 6.77 ‰, suggesting a cognate cumulate-residual melt relationship during magma evolution. Their δ²⁶Mg values range from −0.66 ‰ to −0.17 ‰ and δ⁵⁶Fe values from 0.11 ‰ to 0.17 ‰. Light δ²⁶Mg values suggest carbonate metasomatism, and variable Fe isotope signatures are due to fractional crystallization of olivine, clinopyroxene and ilmenite.

Consequently, the ∼433 Ma mafic rock suite likely originated from lithospheric mantle metasomatized by ancient mid-lower crustal and carbonate-rich melts. These mafic rocks preserve a geochemical signature of continental crust recycled into the deep mantle.

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造山带陆壳向深部地幔的再循环：来自北秦岭造山带白花杂岩锆石U-Pb-Hf-O和全岩Mg-Fe同位素的约束

造山带的基性岩浆活动为探索壳幔相互作用的复杂动力学提供了宝贵的资源。它一丝不苟地保留了可测量的海洋岩石圈和造山带地幔域中俯冲的大陆物质的特征。本文采用锆石U-Pb-Hf-O同位素分析和全岩地球化学相结合的综合方法，对北秦岭造山带白花变质岩浆杂岩进行了研究，旨在破解地壳再循环机制。锆石U-Pb测年表明，基性岩浆侵位在441.6±2.9 ~ 428.3±2.2 Ma之间。角闪岩具有弧状微量元素特征，呈拉斑分异趋势，具有幔源熔体（εHf(t): +0.10 ~ +12, δ18O: 5.61±0.05‰）和继承地壳成分（εHf(t):−10.9 ~−8.6,δ18O: 5.75±0.15‰）的双源性，突出了幔源中的古地壳成分。δ26Mg值在- 0.28±0.01‰~ - 0.12±0.01‰之间，δ56Fe值在0.06±0.02‰~ 0.31±0.04‰之间，可能与中-下陆壳参与地幔源有关。基性微颗粒包体和寄主闪长岩也具有弧状微量元素特征，但具有钙碱性亲和力。它们的εHf(t)值一致（−0.1 ~ +5.1），δ18O值一致（4.51‰~ 6.77‰），表明岩浆演化过程中存在同源的堆积—残余熔体关系。δ26Mg值为−0.66‰~−0.17‰，δ56Fe值为0.11‰~ 0.17‰。轻δ26Mg值提示碳酸盐交代作用，而变化的Fe同位素特征是由橄榄石、斜辉石和钛铁矿分馏结晶所致。因此，~ 433 Ma基性岩组可能起源于古代中下地壳和富碳酸盐熔体交代的岩石圈地幔。这些基性岩石保存了大陆地壳循环进入深部地幔的地球化学特征。

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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.