The Gulf of Mannar and adjoining Cauvery basin to the north between India and Sri Lanka are associated with a failed rift, which initiated during the late Jurassic to early Cretaceous as a precursor to the breakup of East Gondwana. Despite the occurrence of igneous rocks that can be noted in seismic profiles, offshore, and deep seated occurrence of those have lead only to the limited understanding of igneous activity in the Mannar basin. Rock cuttings recovered in the Barracuda exploratory well in the Mannar basin shows approximately 700 m thick basalt rock sequence interlayered with sediments at a depth of 3500–4200 m below mean sea level. Here, we analyzed samples recovered from the Barracuda well for major and trace element composition. Major and trace element data suggest that the basalts were crystallized from two different degrees of partial melts from a similar source. Chondrite normalized rare earth element (REE) patterns indicate that the basalts are similar to continental flood basalt, though they show a distinct Ba positive anomaly. Importantly, supported with previously available K–Ar data, we decipher that these basalts are contemporaneous with the Deccan traps. Rifting between Seychelles and India which had occurred at ~62 Ma approximately 3.5 Ma after the main Deccan eruption is synchronous with the Barracuda volcanism suggesting coeval rifting between Seychelles–India and India–Sri Lanka. Thus, our data suggest simultaneous rifting between Seychelles–India and India–Sri Lanka. Large plate reorganizations that took place during this time period in the Indian Ocean have likely caused consequent passive rifting in the Mannar basin.

中文翻译：

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斯里兰卡近海马纳尔盆地与德干圈闭同时期的大陆溢流玄武岩岩浆作用

马纳尔湾和毗邻的印度和斯里兰卡之间北部的 Cauvery 盆地与断裂的裂谷有关，裂谷开始于侏罗纪晚期至白垩纪早期，是东冈瓦纳大陆分裂的前兆。尽管可以在地震剖面中注意到火成岩的出现，但这些火成岩的近海和深部发生仅导致对马纳尔盆地火成岩活动的有限了解。在 Mannar 盆地 Barracuda 探井中回收的岩屑显示约 700 m 厚的玄武岩层序与沉积物夹在平均海平面以下 3500-4200 m 的深度。在这里，我们分析了从 Barracuda 井中回收的样品的主要和微量元素组成。主要和微量元素数据表明，玄武岩是由来自相似来源的两种不同程度的部分熔体结晶而成的。球粒陨石归一化稀土元素 (REE) 模式表明玄武岩与大陆泛滥玄武岩相似，但它们显示出明显的 Ba 正异常。重要的是，在先前可用的 K-Ar 数据的支持下，我们破译这些玄武岩与德干圈闭同时存在。塞舌尔和印度之间的裂谷发生在约 62 Ma，在德干主要喷发后约 3.5 Ma 与梭鱼火山活动同步，表明塞舌尔-印度和印度-斯里兰卡之间存在同期裂谷。因此，我们的数据表明塞舌尔-印度和印度-斯里兰卡之间同时存在裂痕。