Why are blueschists rare in Precambrian rocks?

Blueschists are rare in Precambrian rocks primarily because the conditions required for their formation—high pressure and low temperature—were difficult to achieve during that time.12

Blueschists typically form in subduction zones, where the descent of cold oceanic lithosphere into the mantle creates a high-pressure, low-temperature environment. Geologists suggest that the Earth’s geothermal gradient was significantly higher during the Precambrian than it is today. This elevated heat flow likely resulted in higher temperatures within early subduction zones, preventing the rocks from reaching the specific low-temperature conditions necessary for the stability of the diagnostic blue mineral glaucophane.132

Consequently, the relative absence of these metamorphic rocks in ancient orogenic belts is often cited by researchers as evidence that tectonic processes or thermal conditions in the early Earth differed from those observed in the modern era.3