A primordial, solar He–Ne signature in crustal fluids of a stable continental region

Primordial He and Ne have been historically regarded as signatures of mantle plumes that are expressions of a largely undegassed lower mantle. A complementary degassed upper mantle is widely invoked to explain low He with high heat flow at mid-ocean ridges, but recent work demonstrates that this is not required. Here, we report He and Ne data from deep Michigan Basin brines that clearly reveal a primordial solar-like component in this stable continental region, where the presence of mantle plumes is highly unlikely. We suggest that this primordial signature can be accounted for by a shallow refractory reservoir in the Archean subcontinental lithospheric mantle and that primordial He and Ne does not necessarily reflect the presence of mantle plumes, with their associated undegassed lower mantle reservoir.