Petrogenesis of Neoarchean dyke swarms and dispersed volcanic successions in the Singhbhum craton can potentially constrain mantle heterogeneity. Their arc-like trace element contents, that have a mismatch with their intracratonic extensional setting, were interpreted to propose widely varied genesis from either an enriched mantle (EM I) or wholly from a metasomatised subcontinental lithospheric mantle (SCLM). In order to test the type of enriched source(s) of magma to the dykes swarms and volcanics, geochemical modeling, Sr and Nd isotopic analyses and geochronology were conducted. The Jagannathpur amygdular volcanics, one such unmetamorphosed volcanic succession, yielded an SmNd isochron age of 2799 ± 67 Ma (2σ) with Ndi = 0.50895 ± 0.00006, MSWD = 0.36 ( = 16) and ε = −1.12 ± 0.50. As the eruptive age is indistinguishable within error to the Ghatgaon (2762.4 ± 2.0 Ma, 2752.0 ± 0.9 Ma) and the Keshargaria (2800.2 ± 0.7 Ma) dyke swarms, the dykes are interpreted as coeval feeder conduits to the volcanics. Enriched LILE and LREE, Nb/Th and Zr/Th ratios coupled with highly radiogenic present-day Sr isotopic ratios which have mantle-like Sr/Sr ratios (0.7031–0.7055) and negative ε values (between −1.8 and − 5.6 for the dykes and − 1.3 and − 1.4 for the Jagannathpur volcanics) indicate that the source mantle components underwent enrichment processes likely by pre-2800 Ma subduction. The primitive mantle-normalized trace element patterns for these dykes and volcanics have pronounced negative Nb-Ta-Ti anomalies and their arc-like geochemistry suggest interaction with metasomatised SCLM. Generation of primitive magmas has been modeled by two end member components involving 18% partial melt from enriched-DMM (depleted MORB mantle) [100–70%] and interaction with low degree (5%) partial melt of metasomatised SCLM [0–30%]. These magmas ponded at Moho depths and underwent assimilation-fractional crystallization (AFC) forming the diverse dykes and basaltic andesitic-andesitic volcanics. We link the geophysically imaged Mid Lithospheric Discontinuity to depth of metasomatised SCLM beneath the Singhbhum craton that formed ≥2800 Ma ago.

中文翻译：

---

印度东部 Singhbhum 克拉通新太古代 (2.80–2.75 Ga) Jagannathpur 火山以及 Ghatgaon 和 Keshargaria 岩脉群的岩石成因：地球化学、Sr[sbnd]Nd 同位素和 Sm[sbnd]Nd 年代学约束对富集 DMM 衍生岩浆与交代化的次大陆岩石圈地幔

Singhbhum 克拉通中新太古代岩脉群和分散火山序列的岩石成因可能会限制地幔的异质性。它们的弧状微量元素含量与其克拉通内伸展背景不匹配，被解释为来自富集地幔（EM I）或完全来自交代化的次大陆岩石圈地幔（SCLM）。为了测试岩脉群和火山岩浆富集源的类型，进行了地球化学模拟、Sr和Nd同位素分析和地质年代学。Jagannathpur 杏仁火山岩是一种未变质的火山序列，其 SmNd 等时线年龄为 2799 ± 67 Ma (2σ)，其中 Ndi = 0.50895 ± 0.00006，MSWD = 0.36 (= 16)，ε = -1.12 ± 0.50。由于 Ghatgaon（2762.4 ± 2.0 Ma、2752.0 ± 0.9 Ma）和 Keshargaria（2800.2 ± 0.7 Ma）岩脉群的喷发年龄在误差范围内无法区分，因此这些岩脉被解释为同时代的火山喷发管道。富集的 LILE 和 LREE、Nb/Th 和 Zr/Th 比率以及高放射性的当今 Sr 同位素比率，具有类地幔 Sr/Sr 比率 (0.7031–0.7055) 和负 ε 值（对于对于 Jagannathpur 火山岩脉和 − 1.3 和 − 1.4）表明，源地幔成分可能在 2800 Ma 之前的俯冲作用中经历了富集过程。这些岩脉和火山岩的原始地幔标准化微量元素模式具有明显的 Nb-Ta-Ti 负异常，其弧状地球化学表明与交代的 SCLM 存在相互作用。原始岩浆的生成通过两个端元成分进行建模，涉及来自富集 DMM（贫化 MORB 地幔）[100–70%] 的 18% 部分熔融以及与交代化 SCLM 的低度 (5%) 部分熔融的相互作用 [0–30 %]。这些岩浆在莫霍面深度积聚并经历同化-部分结晶（AFC），形成各种岩脉和玄武安山岩-安山岩火山岩。我们将地球物理成像的岩石圈中部不连续面与 Singhbhum 克拉通下方交代化 SCLM 的深度联系起来，该 SCLM 形成于 ≥ 2800 Ma 之前。