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<p>Diabase and porphyritic diabase dykes were emplaced in Late Mesozoic igneous rocks of the Dalat zone, Vietnam. The dykes are exposed with visible thicknesses varying from tens to 200&#xa0;m, extending a few km long, and are oriented mainly NE–SW. Geochemically, the mafic dykes are of subalkaline to alkaline affinity, and most of them belong to the high-K, calc-alkaline series. They are characterized by fractionated chondrite-normalized rare earth element patterns with (La/Yb)cn = 7.30–19.30 and have slightly negative to no Eu anomalies (Eu/Eu* = 0.75–1.02), similar to ocean island basalts. The primitive mantle-normalized trace element patterns show that the studied mafic dykes are enriched in large-ion lithophile elements (Rb, K, and Pb), while depleted in high field strength elements (Nb, Ta, and Ti), indicating that they were formed in a subduction-related tectonic setting. These dykes have (<sup>87</sup>Sr/<sup>88</sup>Sr)i ratios of 0.7052–0.7062 and ε<sub>Nd</sub>(t) values varying from -0.5 to + 1.6, suggesting a mantle source region influenced by crustal materials or sedimentary melt. The magnesium number (Mg#) of the dykes ranges from 41.01 to 60.54 and does not reflect the primitive mantle source. New U–Pb zircon age data indicate that the emplacement ages of the dykes clustered at approximately 90.5–90.2&#xa0;Ma, which is 30–40 Myrs older than previously thought. These findings suggest that rapid extension over a short period produced concentrated dyke swarms, which took place during the late phase of Paleo-Pacific subduction in the context of transitional to extensional regimes.</p> Graphical abstract <p></p>

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New geochronological evidence for Late Mesozoic mafic dykes in the Dalat zone (Vietnam): implications for Late Cretaceous lithospheric extension in eastern Indochina

  • 期刊论文

  • 发表日期：

    2025年10月19日

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  • Pham Trung Hieu,
  • Nong Thi Quynh Anh,
  • Pham Minh,
  • Nguyen Thi Bich Thuy,
  • Kenta Kawaguchi,
  • Nguyen Thi Truong Giang,
  • Truong Chi Cuong

摘要

Diabase and porphyritic diabase dykes were emplaced in Late Mesozoic igneous rocks of the Dalat zone, Vietnam. The dykes are exposed with visible thicknesses varying from tens to 200 m, extending a few km long, and are oriented mainly NE–SW. Geochemically, the mafic dykes are of subalkaline to alkaline affinity, and most of them belong to the high-K, calc-alkaline series. They are characterized by fractionated chondrite-normalized rare earth element patterns with (La/Yb)cn = 7.30–19.30 and have slightly negative to no Eu anomalies (Eu/Eu* = 0.75–1.02), similar to ocean island basalts. The primitive mantle-normalized trace element patterns show that the studied mafic dykes are enriched in large-ion lithophile elements (Rb, K, and Pb), while depleted in high field strength elements (Nb, Ta, and Ti), indicating that they were formed in a subduction-related tectonic setting. These dykes have (87Sr/88Sr)i ratios of 0.7052–0.7062 and εNd(t) values varying from -0.5 to + 1.6, suggesting a mantle source region influenced by crustal materials or sedimentary melt. The magnesium number (Mg#) of the dykes ranges from 41.01 to 60.54 and does not reflect the primitive mantle source. New U–Pb zircon age data indicate that the emplacement ages of the dykes clustered at approximately 90.5–90.2 Ma, which is 30–40 Myrs older than previously thought. These findings suggest that rapid extension over a short period produced concentrated dyke swarms, which took place during the late phase of Paleo-Pacific subduction in the context of transitional to extensional regimes.

Graphical abstract