Late Neoarchean–Paleoproterozoic granitoid basement serves as an effective helium source rock in cratonic basins

The growing shortage of helium reserves presents a pressing worldwide concern. However, it remains ambiguous that how, when, and which type of tectonic environment the helium source rocks were formed. Recently, several helium-enriched gas fields have been discovered in the northern Ordos Block and confirmed to be crust-derived. Why late Neoarchean–Paleoproterozoic effective helium source rocks are distributed in the northern Ordos Block are still not clear. Detailed petrological, geochemical, geochronology, Sr-Nd isotopic and in-situ EPMA of U,-Th rich minerals studies were analyzed on the outcrops and drill cores of the basement of the northern Ordos Block to investigate the helium source rocks. The results show that (1) Late Neoarchean–Paleoproterozoic A-type granite and S-type granitoids are effective helium source rock types, and a large amount of U-Th rich accessory minerals (e.g., phosphate minerals, zircon, magnetite et al.) are preserved in alkaline feldspar and quartz. (2) The helium source rocks are classified into distinct temporal intervals: 2.60–2.45 Ga, 2.45–2.30 Ga and 1.95–1.80 Ga, respectively. 2.60–2.45 Ga granitoids exhibit compositional signatures of I-type granites, consistent with magmatic arc tectonic settings linked to subduction zones. 2.45–2.30 Ga granitoids display both A-type and I- type granitic affinities, indicating long live continental magmatic arc environment characteristics.1.95–1.80 Ga granitoids exhibit both A-type and S-type characteristics, suggesting formation in an extensional tectonic regime following continental collision. (3) 2.60–2.45 Ga period is late Archean subduction-accretion and arc magmatism, followed by arc-continent collision; 2.45–2.30 Ga period is a long-time arc-continental accretion process with multiple arc magmatism; 1.95–1.80 Ga period represents continent-continent collision to post-collisional extension setting. Thus, the long-term arc-continental accretion and multistage crustal recycling of terrigenous sediments with high U and Th content, comparable to Phanerozoic subduction-accretionary orogens, explain why effective helium source rocks are enriched in the northern Ordos Block. By the comparison of Khondalite Belts in North China Craton with global Khondalite Belts, global Khondalite belts could be favorable areas for predicting the worldwide distribution of helium source rocks.