Mantle metasomatism and the generation of alkaline lamprophyres in the Spanish Peaks Intrusive Complex, south-central Colorado
Hamil, Arminda Brooke
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The Spanish Peaks Intrusive Complex, Colorado, is composed of compositionally diverse mid-Tertiary igneous rocks. The intrusive stocks of the Spanish Peaks are surrounded by a famous radial dike system as well as subparallel dikes and sills that include lamprophyres. Some of the lamprophyres are relatively sodic (Na2O>K2O) and others are relatively potassic (Na2O<K2O). The lamprophyres are approximately the same age (20-25 Ma; Miggins, 2002), providing a unique opportunity to study the nature of the sources of two highly distinct, contemporaneous alkaline magmas. McGregor (2010) hypothesized the two groups of lamprophyres formed from sequential melting of distinct phase assemblages in the same metasomatic vein. Distinct initial Sr ratios from this study disprove this hypothesis. I hypothesize that the two types of lamprophyres were sourced from separate groups of veins that formed from the same metasomatic event but have distinct phase assemblages because they crystallized at different depths in the upper mantle.