Remnants of Older Crustal Component in Mafic Magmas: Compelling Evidence From the Whole‐Rock Geochemistry and Heterochronous Zircons of Mafic Dyke From Karimnagar Granulite Belt, Eastern Dharwar Craton, Southern India

The rarity of zircon occurrence in ultramafic‐mafic systems offers valuable insights into the geological processes related to its formation, mixing of heterogeneous magmas, assimilation of surrounding wall rock, or the combination of various source materials apart from the conventional geochronology. This study reports an undocumented mafic dyke of picritic affinity from the Karimnagar Granulite Belt (KGB) of southern India, characterised by olivine, two pyroxenes, chrome spinel, plagioclase, and high MgO (16 wt.%), Cr (2624 ppm), and Ni (815 ppm). Prominent negative Nb, Ta, and Ti, positive Zr, and Hf anomalies, along with enriched LILE and LREE, indicate that the dyke has undergone crustal contamination. However, the Th/Yb and Nb/Yb ratios suggest that mantle metasomatism preceded crustal contamination, significantly contributing to the mildly alkaline character of the studied rocks. Most recovered zircons show clear signs of a magmatic origin, reflected in their REE profiles and Th/U ratios (> 0.5), although some exhibit evidence of post‐crystallisation processes. The dating results show an age range from the Neoarchean to the Paleoproterozoic (2.7–1.9 Ga), making it unlikely to represent the intrusion age of the dyke. This age range indicates that ancient crustal material has significantly influenced the mafic magma, emphasising the zircon's xenocrystic nature and suggesting a source from continental granitoids with arc affinity. The age coherence between the studied zircon and the zircons of KGB charnockites indicates that 2.5 Ga was the major crustal growth episode. This study reveals that heterochronous zircons, paired with traditional geochemical proxies, are crucial for understanding ancient crustal components within mafic magmas, highlighting the complex dynamics of the cryptic mixing process.