A Reactivated Back-Arc Source for CAMP Magma
John H. Puffer, Department of Geological Sciences, Rutgers University, Newark,
Evidence is presented indicating that CAMP magma is the product of decompression
induced eutectic melting of a back-arc source that had been dormant since
Paleozoic magmatism associated with the assembly of Pangea. The composition
of CAMP basalt is unlike OIB, plume, hot-spot, N-MORB, or E-MORB magma types
but resembles typical arc-related basalt and back-arc basin basalt in particular.
Similarities to arc and back-arc basalts include a distinct negative Nb anomaly
and overlapping lines plotted on silicate earth normalized spider diagrams.
The uniform composition of CAMP basalt indicates that fractionation and contamination
played only minor roles and that CAMP magma was quickly generated and extruded
during the break-up of Pangea. The composition of CAMP basalt also
closely resembles Paleozoic volcanics that stratigraphicafly underlie Eastern
North American CAMP flows including the Ordovician Ammonoosuc and Partridge
Formations and the Silurian Newbury and Lieghton Formations that were extruded
onto arcs and back-arc basins during the assembly of Pangea. The enriched
mantle involved in the Paleozoic magmatism remained trapped under the Laurentian
- Gondwana suture until early Jurassic extentional tectonism forced renewed
melting. A new model is proposed that involves upward migration of
undepleted asthenosphere displaced by the sinking of a detached oceanic lithospheric
slab. The undepleted asthenosphere was enriched in incompatible elements
except Nb as it moved into a backarc tectonic setting and fluxed with water
before it underwent decompression melting.