Abstract
Mineralogy, geochemistry, and magmatic inclusions in minerals were investigated from represen tative samples of major volcanic series, and magmatic processes were numerically simulated to determine the compositions, formation conditions, and evolution of the primary melts of intraplate magmatism in the Hawai ian Islands and Reunion Island. It is demonstrated that the primary melts of the Hawaiian tholeiitic series and the Hawaiian and Reunion transitional series had an ultramafic composition (18.5- 21 wt% MgO- tholeiitic series and 16 - 20 wt % MgO- transitional series) and were generated by the melting of mantle peridotite at 30- 40 kbar and 1650- 1500°C. The primary melts of the Hawaiian basanite and nephelinite series approx
{ imate the composition of alkalic picrites (15.5 and 13.2 wt % MgO, respectively) and originated as a result
' of the partial melting of mantle peridotite at 30- 40 kbar and 1595 - 1485°C and 1575- 1465°C, respectively.
The early crystallization of primary magma occurred in shallow, intermediate reservoirs. The depth at which the primary magma separated from peridotite was controlled by an oceanic lithosphere thickness of 100 ± 20 km. The successive temperature decrease of the Hawaiian primary magma formation in the sequence of the tholeii tic-transitional-basanite-nephelinitic series corresponds, considering the approximately similar depth of their formation (100- 130 km), to the model of lateral zoning of the Hawaiian mantle plume. It is demonstrated that
the P-T conditions of intraplate magma formation are considerably higher than the values of tholeiites from oceanic rifts. This indicates that the mantle is, on a global scale, vertically heterogeneous and that intraplate magmas are generated in deeper mantle reservoirs as compared to MORB magmas.The pressure and temperature values obtained in this study for the primary magma generation suggest that the Hawaiian and Reunion mantle plumes originated in the lower mantle at a depth below 900 km. This is direct and independent evidence in sup port of the hotspot concept.
{ imate the composition of alkalic picrites (15.5 and 13.2 wt % MgO, respectively) and originated as a result
' of the partial melting of mantle peridotite at 30- 40 kbar and 1595 - 1485°C and 1575- 1465°C, respectively.
The early crystallization of primary magma occurred in shallow, intermediate reservoirs. The depth at which the primary magma separated from peridotite was controlled by an oceanic lithosphere thickness of 100 ± 20 km. The successive temperature decrease of the Hawaiian primary magma formation in the sequence of the tholeii tic-transitional-basanite-nephelinitic series corresponds, considering the approximately similar depth of their formation (100- 130 km), to the model of lateral zoning of the Hawaiian mantle plume. It is demonstrated that
the P-T conditions of intraplate magma formation are considerably higher than the values of tholeiites from oceanic rifts. This indicates that the mantle is, on a global scale, vertically heterogeneous and that intraplate magmas are generated in deeper mantle reservoirs as compared to MORB magmas.The pressure and temperature values obtained in this study for the primary magma generation suggest that the Hawaiian and Reunion mantle plumes originated in the lower mantle at a depth below 900 km. This is direct and independent evidence in sup port of the hotspot concept.
| Original language | English |
|---|---|
| Article number | No.2 |
| Pages (from-to) | 111- 144 |
| Journal | Petrology |
| Volume | 2 |
| Issue number | 2 |
| Publication status | Published - 1994 |
