Origin
Due to the presence of the olivine-rich zone, the normally difficult task of determining the history of an igneous body becomes even tougher.
- The original studies concluded that the sill was the result of a single injection of magma. The variety in mineralogy was credited to simple crystal fractionation.
- The next model introduced whole rock geochemistry data and determined that there were at least two separate injections; an olivine-rich magma was followed by normal tholeiitic basalt.
- The third hypothesis instead proposed at least three, but probably four separate pulses, with the olivine-rich magma being the final one. This was also conjectured through the use of whole-rock chemistry.
Each of these theories supported the idea of crystal fractionation playing a significant, if not total, role in the differentiation of the sill. A single source for the magma was assumed.
- The latest conclusion reached for the origin of the intrusion was that the olivine in the olivine-rich zone could not have been in equilibrium with the rest of the body, indicating more than one source for the magma. This was determined through mass balance equations. It was also suggested that lateral flow within the still-liquid body played as important a role in differentiation as fractionation.
Due to the interest in the subject, and a lack of a satisfactory conclusion, research on the Palisades Sill is currently ongoing.
Read more about this topic: Palisades Sill
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