Colorado Mineral Belt

Summary and Conclusions

Stretching southwest to northeast through central Colorado, the Colorado Mineral Belt displays a unique and broadly misunderstood swath of igneous rocks. For years geologists have tried to solve the petrogenetic mysteries surrounding these rocks, yet through all the effort no conclusive result has been agreed upon.

CMB magmatism is undoubtedly related in some way to the Laramide orogeny, but to what extent? Did compression facilitate magmatism, or could sub-crustal processes stimulate magmatism which in turn contributed to regional uplift? Was the so-called ‘flat slab’ involved in any of it? Some of these questions may never be answered, but let’s have a review of what we do know:

• the CMB follows an ancient lineament in Colorado
• alkaline and calc-alkaline volcanic rocks occur within the CMB
• there is no obvious age progression within the Laramide CMB
• CMB magmatism coincided temporally with other western North American magmatism
• CMB magmatism may or may not have coincided with the leading edge of the flat slab that may or may not have been present during the Laramide
• isotopic evidence allows mantle melts, crustal melts, and slab derived element enrichments
• everyone has an opinion, no one has the answer

At this point it is virtually impossible to know where these rocks came from and why, but there are a few things we can postulate from what we do know:

• without a clear temporal progression (regionally as well as within the CMB), the CMB can not definitively be linked to a flat slab
• until an irrefutable mantle source is recognized, we can’t rule out a flat slab
• the sub-CMB crust had at least some involvement in the production of the Laramide CMB rocks
• everyone has an opinion, no one has the answers

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