The Indian sub-continent was an integral part of the Gondwana supercontinent with multiple magmatic episodes during the Gondwana assembly and break-up events. However, most of these vital records to understand the past magmatism were obliterated during the Himalayan orogeny due to the subduction of the Indian plate. In this contribution, we attempt to tackle this issue by investigating the Abor magmatic rocks from the eastern Himalayan syntaxis, which are likely to represent the leftover fragments of the eastern Gondwana continental margin. This study uses zircon U-Pb dating, whole-rock geochemistry, and Sr-Nd isotopic ratios data of the mafic intrusive and felsic volcanic rocks of the Abor magmatism. The mafic intrusive rocks have zircon ages of 500–473 Ma, while the felsic rocks yield ages of 145–132 Ma, indicating two temporally separated episodes of magmatism. The mafic intrusives are sub-alkaline/tholeiitic (Nb/Y < 0.65), with high TiO₂ (1.63–3.42 wt%) and ocean island basalt to enriched-mid oceanic ridge basalt affinities. A relatively narrow range of initial ⁸⁷Sr/⁸⁶Sr (0.703887–0.705513), ¹⁴³Nd/¹⁴⁴Nd (0.511978–0.512118), and εNd(t) (-0.323–+2.43) of the mafic intrusives suggest fractional crystallization with negligible crustal contamination, generated by low degree (∼3–13 %) partial melting of a primitive mantle (garnet and spinel lherzolite). The felsic rocks display low MgO (0.38–1.17 wt%), CaO (1.06–5.31 wt%), LREE and LILE (Rb, K, Pb) enrichment, depletion in HREE, Sr, Nb, Ti, with strong negative Eu-anomaly (0.48–0.73), high initial ⁸⁷Sr/⁸⁶Sr (0.707878–0.717650), and negative εNd(t) (-14.35 to −9.21), suggesting A-type felsic magmatism. The older mafic intrusions were thus attributed to the events of the Gondwana assembly and were inferred to form in an extensional passive margin during the early Paleozoic. However, the younger felsic rocks were likely to have been generated by the interaction of the upwelling Kerguelen mantle plume and the pre-existing crust during the initiation of the eastern Gondwana break-up during the early Cretaceous. Our new findings reveal that two episodic magmatic events related to the eastern Gondwana assembly and the subsequent Gondwana break-up are responsible for the magmatism in the Siang window of eastern Himalayan syntaxis, northeast India.

印度次大陆是冈瓦纳超大陆不可分割的一部分，在冈瓦纳组装和分裂事件期间发生了多次岩浆事件。然而，由于印度板块的俯冲，在喜马拉雅造山运动期间，这些了解过去岩浆作用的重要记录大部分都被抹杀了。在这篇文章中，我们试图通过调查来自喜马拉雅东部构造层的 Abor 岩浆岩来解决这个问题，这些岩浆岩很可能代表了冈瓦纳东部大陆边缘的剩余碎片。本研究使用了阿博尔岩浆的镁铁质侵入岩和长英质火山岩的锆石 U-Pb 测年、全岩地球化学和 Sr-Nd 同位素比数据。镁铁质侵入岩的锆石年龄为 500-473 Ma，而长英质岩的年龄为 145-132 Ma，表示两个时间上分开的岩浆作用事件。镁铁质侵入体为亚碱性/拉斑沸石（Nb/Y < 0.65），具有高 TiO2₂ (1.63–3.42 wt%) 和大洋岛玄武岩对富集的中洋脊玄武岩的亲和力。镁铁质侵入岩的初始⁸⁷ Sr/ ⁸⁶ Sr (0.703887–0.705513)、¹⁴³ Nd/ ¹⁴⁴ Nd (0.511978–0.512118) 和 εNd(t) (-0.323–+2.43) 范围相对较窄，这表明地壳分馏结晶可忽略不计污染，由原始地幔（石榴石和尖晶石二辉石）的低度（~3-13%）部分熔融产生。长英质岩石表现出低 MgO（0.38-1.17 wt%）、CaO（1.06-5.31 wt%）、LREE 和 LILE（Rb、K、Pb）富集，HREE、Sr、Nb、Ti 贫化，具有强负 Eu-异常（0.48–0.73），初始高⁸⁷ Sr/ ⁸⁶Sr（0.707878-0.717650）和负εNd（t）（-14.35至-9.21），表明A型长英质岩浆作用。因此，较老的镁铁质侵入体归因于冈瓦纳组装事件，并被推断为早古生代在伸展被动边缘形成的。然而，较年轻的长英质岩很可能是在白垩纪早期冈瓦纳东部分裂开始期间，上升的 Kerguelen 地幔柱与先前存在的地壳相互作用产生的。我们的新发现表明，与东部冈瓦纳集会和随后的冈瓦纳分裂有关的两次偶发性岩浆事件是印度东北部喜马拉雅东部构造层 Siang 窗的岩浆活动的原因。