THE CAMP MAGMA SOURCE

The ongoing debate pertaining to the source of CAMP has not abated. However, evidence supporting a passive (non-plume) model is accumulating. The plume model is consistent with a plume component mixed to varying degrees with a lithospheric component to generate CFB. However, CAMP is not typical CFB. Well established evidence includes the fact that CAMP magma types clearly show depletions in high field strength elements and a distinct negative Nb-Ta anomaly on spider diagrams indicating a major subduction zone component in the mantle source. Indeed CAMP magmatism was preceded and stratigraphically overlaps arc magmatism and was extruded out of rifts located close to convergent Paleozoic sutures. More recent evidence of subduction enrichment is provided by mineralogical evidence. Dorais and Tubrett (2008) analyzed Cr-rich pyroxenes from ENA CAMP tholeiites and calculated corresponding equilibrium magma compositions with subduction enriched characteristics. This subduction association is not predicted by a plume model but is consistent with some passive models. This association is true of the entire CAMP province, not just local portions, and must be an integral part of any genetic model. As summarized by Salters et al. (2003) plume models predict that as plume heads impinge the base of the lithosphere the initial average depth of melting is relatively deep but decreases as the degree of melting increases. They showed, however, that initial ITi CAMP magmas were derived from shallower depths than subsequent LTi magma. In addition, Herzberg and Gazel (2009) calculated mantle potential temperatures for several LIPs including CAMP and found most melted at > 1500 ^oC consistent with the melting region of mantle plume heads. However, CAMP was an exception and melted at < 1500^oC. Our calculations using PRIMEMELT2 (Herzberg and Asimow, 2008) yield mantle potential temperatures for the mean ITi and LTi primary magma compositions (Salters et al. 2003) of 1394 ° C and 1449° C, respectively. These temperatures are lower than the melting region of the mantle plume model. Important forthcoming evidence bearing on a CAMP source awaits ongoing studies utilizing Sr, Nd, Pb, and Os isotopic systematics.