In order to understand the melting processes that occur within recycled oceanic crust and mantle in a heterogeneous plume (e.g., that beneath the Hawaiian Islands), a series of high-pressure-high-temperature layered experiments were performed at 2.9 GPa, 5 GPa, and 8 GPa, from 1300 °C to 1650 °C, using a fertile peridotite KLB-1 and N-MORB. Our experiments at conditions below the dry peridotite solidus produced melt compositions that ranged from basaltic andesite to tholeiite. An Opx reaction band formed between eclogite and peridotite layers, likely via chemical reaction between a silica-rich eclogite-derived partial melt and olivine in the peridotite matrix. At temperatures at or above the dry peridotite solidus, substantial melting occurred in both basalt and peridotite layers, and fully molten basalt melt and melt pockets from the peridotite layer combined. In our layered experiments, major and minor element contents in reacted melts closely matched those of Hawaiian tholeiite and picrite, except for Fe. Partial melts of anhydrous run products had ~55 - 57 wt% SiO2 at low temperature ( i.e., were andesitic) and had ~50 - 53 wt% SiO 2 at high temperatures, slightly below the dry peridotite solidus ( i.e., were tholeiitic, and similar to those that occur during the Hawaii shield-building stage). Based on the Fe- and LREE-enriched signature in Hawaiian tholeiites, we propose that recycled components in the Hawaiian plume are not modern N-MORB, but are Fe-rich tholeiite; a lithology that was common in the Archaean and early Proterozoic. We have demonstrated that the entire compositional spectrum of Hawaiian tholeiites (basalt to picrite) can be formed by basalt-peridotite reactive melting near the dry solidus of peridotite. Based on these results, we propose that the potential temperature of the sub-Hawaiian plume may be much lower than previously estimated.
The mantle plume beneath the Hawaiian Islands is the largest known example in the Earth today [
Sobolev et al. [
N-type MORB sample NAM-7 [
Our melting experiments were performed at pressures of 2.9 GPa, 5 GPa, and 8 GPa, temperatures from 1300˚C to 1650˚C, and for durations of 1 - 24 hours (
All experiments were carried out at the Magma Factory in the Tokyo Institute of Technology, Japan [
KLB-1 | NAM-7 (wt%) | |||||
---|---|---|---|---|---|---|
Bulk (wt%) | Oliv (wt%) | Opx (wt%) | Cpx (wt%) | Sp (wt%) | ||
SiO2 | 44.48 | 39.64 | 54.24 | 51.13 | 0.06 | 49.71 |
TiO2 | 0.16 | 0 | 0.11 | 0.58 | 0.11 | 1.71 |
Al2O3 | 3.59 | 0.03 | 4.97 | 7.4 | 58.48 | 15.68 |
FeO (t) | 8.1 | 10.52 | 6.57 | 3.11 | 10.68 | 9.46 |
MnO | 0.12 | 0.16 | 0.16 | 0.1 | -- | 0.18 |
MgO | 39.22 | 48.25 | 32.16 | 14.7 | 21.61 | 8.43 |
CaO | 3.44 | 0.08 | 0.85 | 19.54 | 0 | 11.73 |
Na2O | 0.3 | 0.01 | 0.12 | 1.72 | 0 | 2.76 |
K2O | 0.02 | 0 | 0 | 0.01 | 0 | 0.23 |
P2O5 | 0.03 | - | - | - | - | 0.02 |
Cr2O3 | 0.31 | 0.01 | 0.34 | 0.78 | 7.82 | - |
NiO | 0.25 | 0.39 | 0.11 | 0.11 | 0.43 | - |
Total | 100.02 | 99.09 | 99.63 | 99.18 | 99.19 | 99.91 |
MgO# | 0.896 | 0.891 | 0.897 | 0.894 | 0.783 | 0.614 |
Run No. | P/GPa | T/˚C | Durations/h | Mineral Modes (Weight Fraction) | |
---|---|---|---|---|---|
MORB Layer | KLB-1 Layer | ||||
P948 | 2.9 | 1300 | 3 | Cpx + Pl + Grt + Rt | Ol + Opx + Cpx + Sp + Grt (tr) |
P951 | 2.9 | 1300 | 24 | Cpx + Grt + Coe | Ol + Opx + Cpx + Grt (tr) |
P928 | 2.9 | 1460 | 1 | Cpx + Grt + M | Ol + Opx + Cpx + Sp + Grt (tr) |
P937 | 2.9 | 1460 | 9 | M | Ol + Opx + Cpx + M (tr) |
P931 | 2.9 | 1460 | 24 | Cpx + Grt + M | Ol + Opx + Sp + Grt (tr) |
P929 | 2.9 | 1500 | 1 | Cpx + Grt + M | Ol + Opx + Cpx + Sp + Grt (tr) |
P938 | 2.9 | 1500 | 9 | M | Ol + Opx + M |
P935 | 2.9 | 1500 | 24 | Cpx + Grt + M | Ol + Opx + Cpx |
P932 | 2.9 | 1540 | 1 | Cpx + M | Ol + Opx + Cpx + Grt + M (tr) |
P939 | 2.9 | 1540 | 9 | M | Ol + Opx + Cpx + M |
P936 | 2.9 | 1540 | 24 | M | Ol |
S1813 | 5 | 1300 | 3 | Cpx + Grt + Coe | Ol + Opx + Cpx + Grt(tr) + Sp (tr) |
S1797 | 5 | 1450 | 3 | Cpx + Grt + M | Ol + Cpx + Opx + Grt + Sp (tr) |
S1802 | 5 | 1450 | 20 | Cpx + Grt + M | Ol + Cpx + Opx + Grt + Sp (tr) |
S1799 | 5 | 1500 | 3 | Cpx + Grt + M | Ol + Opx + Cpx + Grt + Sp (tr) |
S1788 | 5 | 1550 | 3 | M | Ol + Cpx + Opx + Grt + Sp (tr) |
S1790 | 5 | 1650 | 3 | M | Opx |
S1808 | 8 | 1300 | 3 | Cpx + Grt + Coe | Ol + Opx + Cpx + Grt + Sp (tr) |
S1812 | 8 | 1500 | 3 | Cpx + Grt + Coe | Ol + Opx + Cpx + Grt + Sp (tr) |
“tr” represents for trace amount of minerals or melts which cannot be analyzed by EPMA.
Experiments performed at 2.9 GPa were conducted using a Boyd-England-type piston-cylinder apparatus, and were based on a half-inch calibration of talc/Pyrex- glass/graphite assembly [
Run products were collected, mounted in epoxy, polished, and carbon-coated for electron microprobe analysis (EPMA). Textures and chemical compositions were analysed with a JEOL-JXA8530F electron microprobe housed at the ELSI, Tokyo Institute of Technology. The acceleration voltage, beam current, and peak measurement time were 15.0 kV, 1 × 10−8 A and 20 s, respectively. Na was analysed for 10 s in order to avoid count loss. Mineral grains were analysed using a focused electron beam, while a defocused beam (~5 - 30 μm) was used for silicate melt.
All run conditions and the phases produced in each lithology are listed in
of olivine (Oliv), orthopyroxene (Opx), Cpx, and Grt. An additional Al-rich phase (Cr-rich spinel) was present in 2.9-GPa run products, though this transformed to garnet at higher pressures. Significant melting took place in runs conducted at temperatures above the peridotite solidus―particularly near the basalt melt layer―with Oliv and Opx present as restitic phases in the suprasolidus regime. Melt pockets spread along matrix Opx-Oliv grain boundaries, while Cpx, Grt, and spinel were consumed.
Cpx and Grt produced at subsolidus basalt temperatures were mostly subhedral to euhedral (
Since partial melt formed in eclogite at pressure?temperature conditions below the peridotite solidus would not have been in chemical equilibrium with Oliv, thin Opx reaction bands formed between both rock types via chemical reaction between silica-rich partial melt of eclogite and Oliv in the peridotite matrix. At subsolidus peridotite conditions, the thickness of the Opx reaction band positively correlated with the run temperature and durations. As partially melted eclogite layers were separated from peridotite by thin Opx bands, chemical reactions between each basalt and peridotite layer were thus hindered and could only proceed via solid-state diffusion. At higher temperatures, substantial melting occurred both in basalt and peridotite layers, and fully molten basalt melts merged with molten pockets in peridotite. Extensive chemical mass transport was able to take place through chemical diffusion and liquid percolation under these conditions, and so basalt melting consistently allowed chemical equilibrium to be established with ambient peridotite, even in short runs.
Representative chemical compositions of individual solid and melt phases are listed in
Run No. | P (GPa) | T (˚C) | Duration (h) | Layer | Phase | SiO2 | TiO2 | Al2O3 | FeO | MnO | MgO | CaO | Na2O | K2O | P2O5 | V2O3 | Cr2O3 | NiO | Total |
---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
P948 | 2.9 | 1300 | 3 | MORB | Cpx1 | 52.46 | 0.80 | 5.64 | 10.44 | 0.19 | 15.99 | 10.91 | 2.12 | 0.00 | 0.09 | 0.00 | 0.00 | 0.03 | 98.68 |
Opx | 53.17 | 0.45 | 2.96 | 12.14 | 0.18 | 26.58 | 2.61 | 0.41 | 0.00 | 0.00 | 0.00 | 0.00 | 0.12 | 98.61 | |||||
Grt | 38.00 | 0.88 | 20.50 | 22.20 | 0.41 | 7.39 | 8.92 | 0.13 | 0.01 | 0.16 | 0.00 | 0.00 | 0.01 | 98.60 | |||||
Pl | 51.55 | 0.09 | 29.73 | 0.60 | 0.00 | 0.10 | 12.51 | 3.92 | 0.62 | 0.09 | 0.00 | 0.00 | 0.02 | 99.24 | |||||
Rt | 5.75 | 79.85 | 3.46 | 5.24 | 0.06 | 1.54 | 1.63 | 0.05 | 0.01 | 0.00 | 7.91 | 0.00 | 0.01 | 105.51 | |||||
KLB-1 | Ol | 39.98 | 0.01 | 0.04 | 10.22 | 0.14 | 48.32 | 0.13 | 0.02 | 0.00 | 0.02 | 0.00 | 0.00 | 0.37 | 99.25 | ||||
Opx | 53.70 | 0.12 | 4.95 | 6.52 | 0.14 | 32.36 | 0.86 | 0.12 | 0.00 | 0.01 | 0.00 | 0.00 | 0.10 | 98.88 | |||||
Cpx | 51.02 | 0.58 | 7.09 | 3.31 | 0.09 | 15.16 | 19.47 | 1.66 | 0.00 | 0.00 | 0.00 | 0.00 | 0.05 | 98.42 | |||||
Sp | 0.12 | 0.14 | 56.69 | 10.22 | 0.12 | 20.53 | 0.06 | 0.00 | 0.00 | 0.00 | 0.00 | 4.52 | 0.32 | 92.72 | |||||
P951 | 2.9 | 1300 | 24 | MORB | Cpx | 50.56 | 1.64 | 13.97 | 6.99 | 0.09 | 7.65 | 13.93 | 3.83 | 0.01 | 0.07 | 0.00 | 0.00 | 0.04 | 98.76 |
Grt | 39.16 | 0.86 | 21.45 | 18.63 | 0.40 | 9.01 | 9.15 | 0.18 | 0.01 | 0.21 | 0.00 | 0.00 | 0.01 | 99.09 | |||||
Coe | 93.75 | 0.07 | 1.49 | 0.89 | 0.01 | 0.45 | 0.53 | 0.02 | 0.00 | 0.00 | 0.00 | 0.00 | 0.00 | 97.20 | |||||
P928 | 2.9 | 1460 | 1 | MORB | Cpx1 | 50.60 | 0.95 | 13.18 | 8.00 | 0.16 | 8.96 | 13.47 | 3.34 | 0.02 | 0.01 | 0.00 | 0.00 | 0.03 | 98.73 |
Cpx2 | 49.15 | 1.06 | 16.51 | 7.23 | 0.12 | 7.57 | 13.45 | 3.50 | 0.02 | 0.01 | 0.00 | 0.00 | 0.02 | 98.63 | |||||
Cpx3 | 52.51 | 0.78 | 7.26 | 9.75 | 0.18 | 14.81 | 10.60 | 2.32 | 0.00 | 0.03 | 0.00 | 0.00 | 0.04 | 98.28 | |||||
Grt | 38.75 | 0.92 | 21.17 | 18.44 | 0.42 | 9.75 | 8.32 | 0.18 | 0.01 | 0.09 | 0.00 | 0.00 | 0.02 | 98.07 | |||||
M | 54.39 | 3.63 | 14.70 | 9.30 | 0.11 | 2.21 | 7.39 | 3.23 | 1.12 | 0.44 | 0.00 | 0.00 | 0.01 | 96.53 | |||||
KLB-1 | Ol | 40.31 | 0.03 | 0.11 | 10.52 | 0.14 | 47.40 | 0.21 | 0.03 | 0.00 | 0.02 | 0.00 | 0.00 | 0.36 | 99.13 | ||||
Opx | 54.41 | 0.13 | 4.94 | 6.59 | 0.15 | 31.92 | 0.86 | 0.12 | 0.01 | 0.04 | 0.00 | 0.00 | 0.11 | 99.28 | |||||
Cpx | 51.78 | 0.54 | 7.08 | 3.44 | 0.08 | 15.21 | 19.06 | 1.49 | 0.00 | 0.01 | 0.00 | 0.00 | 0.06 | 98.75 | |||||
Sp | 0.069 | 0.12 | 56.76 | 9.86 | 0.12 | 20.83 | 0.03 | 0.00 | 0.01 | 0.00 | 0.00 | 5.22 | 0.35 | 93.36 | |||||
P931 | 2.9 | 1460 | 24 | MORB | Cpx | 49.83 | 0.87 | 13.95 | 7.24 | 0.15 | 9.84 | 14.14 | 3.13 | 0.01 | 0.03 | 0.00 | 0.00 | 0.01 | 99.20 |
Grt | 39.68 | 0.76 | 22.08 | 15.95 | 0.41 | 11.94 | 8.24 | 0.11 | 0.00 | 0.04 | 0.00 | 0.00 | 0.01 | 99.23 | |||||
M | 52.66 | 2.83 | 15.12 | 10.40 | 0.14 | 4.19 | 8.66 | 3.22 | 0.68 | 0.27 | 0.00 | 0.00 | 0.00 | 98.18 | |||||
KLB-1 | Ol | 40.55 | 0.01 | 0.12 | 10.44 | 0.12 | 48.15 | 0.25 | 0.03 | 0.00 | 0.02 | 0.00 | 0.00 | 0.36 | 100.06 | ||||
Opx | 54.72 | 0.15 | 4.99 | 6.55 | 0.13 | 32.03 | 1.06 | 0.16 | 0.01 | 0.05 | 0.00 | 0.00 | 0.12 | 99.98 | |||||
Sp | 0.37 | 0.34 | 57.31 | 9.39 | 0.12 | 21.31 | 0.04 | 0.02 | 0.00 | 0.00 | 0.00 | 4.98 | 0.32 | 94.18 | |||||
P929 | 2.9 | 1500 | 1 | MORB | Cpx | 49.50 | 0.71 | 13.37 | 6.70 | 0.16 | 10.32 | 14.61 | 2.95 | 0.01 | 0.02 | 0.00 | 0.00 | 0.03 | 98.38 |
Grt | 39.22 | 0.79 | 21.39 | 16.17 | 0.39 | 11.92 | 7.98 | 0.16 | 0.01 | 0.07 | 0.00 | 0.00 | 0.04 | 98.15 | |||||
M | 51.21 | 2.62 | 15.34 | 11.38 | 0.17 | 3.72 | 8.45 | 2.93 | 0.62 | 0.26 | 0.00 | 0.00 | 0.01 | 96.70 | |||||
KLB-1 | Ol | 39.88 | 0.01 | 0.15 | 10.73 | 0.14 | 47.56 | 0.29 | 0.03 | 0.00 | 0.06 | 0.00 | 0.00 | 0.39 | 99.22 | ||||
Opx | 53.89 | 0.15 | 4.95 | 6.71 | 0.13 | 32.10 | 0.88 | 0.13 | 0.01 | 0.02 | 0.00 | 0.00 | 0.11 | 99.07 | |||||
Cpx | 50.95 | 0.61 | 7.13 | 3.28 | 0.08 | 15.21 | 19.12 | 1.63 | 0.01 | 0.04 | 0.00 | 0.00 | 0.06 | 98.12 | |||||
Sp | 0.07 | 0.12 | 56.76 | 9.86 | 0.12 | 20.83 | 0.03 | 0.00 | 0.01 | 0.00 | 0.00 | 5.22 | 0.35 | 93.36 | |||||
P935 | 2.9 | 1500 | 24 | MORB | Cpx | 52.53 | 0.42 | 8.29 | 5.47 | 0.14 | 18.30 | 12.38 | 1.86 | 0.00 | 0.02 | 0.00 | 0.00 | 0.04 | 99.45 |
Grt | 41.16 | 0.56 | 22.39 | 10.21 | 0.31 | 17.85 | 6.57 | 0.04 | 0.01 | 0.03 | 0.00 | 0.00 | 0.01 | 99.14 | |||||
M | 47.49 | 2.01 | 12.87 | 8.98 | 0.16 | 12.21 | 8.68 | 2.78 | 0.42 | 0.24 | 0.00 | 0.00 | 0.01 | 95.83 |
KLB-1 | Ol | 40.58 | 0.02 | 0.15 | 10.32 | 0.14 | 48.17 | 0.30 | 0.03 | 0.00 | 0.01 | 0.00 | 0.00 | 0.34 | 100.07 | ||||
---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
Opx | 54.64 | 0.15 | 4.99 | 6.38 | 0.14 | 31.97 | 1.08 | 0.17 | 0.00 | 0.03 | 0.00 | 0.00 | 0.13 | 99.69 | |||||
P932 | 2.9 | 1540 | 1 | MORB | Cpx | 50.35 | 0.70 | 11.99 | 6.27 | 0.16 | 13.43 | 14.64 | 2.10 | 0.01 | 0.02 | 0.00 | 0.00 | 0.01 | 99.67 |
Sp | 0.12 | 0.42 | 57.43 | 10.09 | 0.08 | 20.73 | 0.09 | 0.02 | 0.01 | 0.00 | 0.00 | 5.59 | 0.38 | 94.95 | |||||
M | 48.76 | 1.60 | 13.93 | 9.79 | 0.18 | 9.45 | 10.95 | 2.59 | 0.24 | 0.11 | 0.00 | 0.00 | 0.01 | 97.62 | |||||
KLB-1 | Ol | 40.57 | 0.01 | 0.16 | 10.33 | 0.14 | 48.13 | 0.30 | 0.04 | 0.01 | 0.00 | 0.00 | 0.00 | 0.35 | 100.04 | ||||
Opx | 54.73 | 0.14 | 4.94 | 6.57 | 0.15 | 32.30 | 0.92 | 0.11 | 0.01 | 0.02 | 0.00 | 0.00 | 0.09 | 99.96 | |||||
Cpx | 52.73 | 0.28 | 6.86 | 5.31 | 0.12 | 23.02 | 9.88 | 0.86 | 0.01 | 0.02 | 0.00 | 0.00 | 0.11 | 99.20 | |||||
Grt | 42.34 | 0.66 | 21.75 | 6.84 | 0.20 | 21.25 | 5.46 | 0.08 | 0.04 | 0.12 | 0.00 | 0.00 | 0.03 | 98.76 | |||||
P936 | 2.9 | 1540 | 24 | MORB | M | 48.14 | 1.09 | 11.00 | 6.44 | 0.17 | 19.90 | 8.64 | 1.81 | 0.18 | 0.06 | 0.00 | 0.00 | 0.01 | 97.43 |
KLB-1 | Ol | 41.59 | 0.01 | 0.17 | 5.95 | 0.11 | 52.60 | 0.23 | 0.02 | 0.01 | 0.04 | 0.00 | 0.00 | 0.01 | 100.74 | ||||
S1813 | 5 | 1300 | 3 | MORB | Cpx | 51.61 | 1.25 | 15.46 | 5.93 | 0.08 | 6.87 | 12.69 | 4.53 | 0.16 | 0.09 | 0.00 | 0.00 | 0.03 | 98.70 |
Grt | 39.85 | 1.10 | 20.99 | 18.03 | 0.37 | 8.84 | 10.08 | 0.31 | 0.08 | 0.22 | 0.00 | 0.00 | 0.02 | 99.89 | |||||
Coe | 97.54 | 0.11 | 0.52 | 0.48 | 0.02 | 0.11 | 0.24 | 0.01 | 0.01 | 0.00 | 0.00 | 0.00 | 0.00 | 99.05 | |||||
KLB-1 | Ol | 40.11 | 0.02 | 0.04 | 10.23 | 0.14 | 48.92 | 0.11 | 0.01 | 0.00 | 0.04 | 0.00 | 0.00 | 0.35 | 99.97 | ||||
Opx | 54.04 | 0.13 | 4.88 | 6.52 | 0.15 | 32.58 | 0.88 | 0.11 | 0.01 | 0.05 | 0.00 | 0.00 | 0.11 | 99.45 | |||||
Cpx | 51.44 | 0.58 | 6.80 | 3.36 | 0.08 | 15.65 | 19.22 | 1.66 | 0.00 | 0.05 | 0.00 | 0.00 | 0.07 | 98.93 | |||||
Sp | 0.14 | 0.15 | 57.44 | 10.50 | 0.11 | 20.92 | 0.05 | 0.01 | 0.00 | 0.04 | 0.00 | 4.64 | 0.40 | 94.37 | |||||
S1797 | 5 | 1450 | 3 | MORB | Cpx | 52.68 | 1.01 | 13.42 | 6.75 | 0.11 | 9.50 | 13.16 | 3.91 | 0.04 | 0.01 | 0.15 | 0.05 | 0.02 | 100.82 |
Grt | 41.34 | 0.80 | 22.39 | 15.04 | 0.36 | 12.53 | 8.55 | 0.11 | 0.00 | 0.07 | 0.10 | 0.09 | 0.01 | 101.39 | |||||
M | 51.78 | 2.38 | 14.59 | 9.96 | 0.15 | 5.91 | 8.95 | 3.37 | 0.60 | 0.16 | 0.27 | 0.01 | 0.02 | 98.14 | |||||
KLB-1 | Ol | 41.35 | 0.02 | 0.08 | 11.72 | 0.12 | 48.64 | 0.20 | 0.05 | 0.01 | 0.01 | 0.01 | 0.07 | 0.38 | 102.66 | ||||
Opx | 55.88 | 0.12 | 4.79 | 6.68 | 0.13 | 33.12 | 0.81 | 0.16 | 0.00 | 0.01 | 0.02 | 0.27 | 0.13 | 102.13 | |||||
Cpx | 53.35 | 0.56 | 7.66 | 4.31 | 0.09 | 16.27 | 15.65 | 2.26 | 0.01 | 0.00 | 0.07 | 0.38 | 0.07 | 100.67 | |||||
Grt | 42.41 | 0.73 | 22.88 | 10.86 | 0.27 | 16.95 | 7.23 | 0.12 | 0.00 | 0.00 | 0.11 | 0.02 | 0.01 | 101.58 | |||||
Sp | 0.15 | 0.53 | 58.35 | 9.54 | 0.09 | 22.06 | 0.07 | 0.00 | 0.00 | 0.00 | 0.11 | 7.88 | 0.41 | 99.18 | |||||
S1802 | 5 | 1450 | 20 | MORB | Cpx | 52.90 | 1.09 | 14.07 | 7.09 | 0.11 | 8.04 | 11.43 | 4.17 | 0.01 | 0.02 | 0.15 | 0.03 | 0.02 | 99.13 |
Grt | 40.58 | 0.98 | 22.05 | 17.68 | 0.39 | 9.77 | 8.12 | 0.19 | 0.01 | 0.02 | 0.13 | 0.01 | 0.03 | 99.94 | |||||
M | 54.84 | 3.57 | 12.93 | 8.62 | 0.10 | 3.29 | 6.55 | 2.89 | 1.13 | 0.09 | 0.39 | 0.01 | 0.01 | 94.43 | |||||
KLB-1 | Ol | 41.12 | 0.03 | 0.08 | 10.55 | 0.10 | 48.90 | 0.17 | 0.02 | 0.01 | 0.00 | 0.00 | 0.05 | 0.41 | 101.45 | ||||
Opx | 55.07 | 0.18 | 4.32 | 6.57 | 0.11 | 32.40 | 1.01 | 0.19 | 0.00 | 0.00 | 0.04 | 0.30 | 0.13 | 100.32 | |||||
Cpx | 52.48 | 0.52 | 6.56 | 3.58 | 0.08 | 16.19 | 16.87 | 1.56 | 0.01 | 0.01 | 0.09 | 0.61 | 0.08 | 98.64 | |||||
Grt | 41.97 | 0.61 | 21.24 | 7.10 | 0.20 | 21.18 | 4.54 | 0.01 | 0.01 | 0.00 | 0.09 | 2.27 | 0.02 | 99.23 | |||||
S1799 | 5 | 1500 | 3 | MORB | Cpx | 51.05 | 0.88 | 15.09 | 6.57 | 0.13 | 8.18 | 13.53 | 3.97 | 0.01 | 0.00 | 0.00 | 0.00 | 0.04 | 99.44 |
Grt | 39.26 | 0.91 | 21.77 | 16.74 | 0.39 | 10.33 | 9.53 | 0.15 | 0.01 | 0.06 | 0.00 | 0.00 | 0.01 | 99.16 | |||||
M | 56.00 | 4.52 | 13.05 | 9.44 | 0.10 | 2.22 | 7.23 | 2.70 | 1.40 | 0.41 | 0.42 | 0.01 | 0.01 | 97.49 | |||||
KLB-1 | Ol | 41.32 | 0.03 | 0.09 | 10.33 | 0.12 | 49.17 | 0.21 | 0.04 | 0.01 | 0.01 | 0.00 | 0.06 | 0.37 | 101.74 | ||||
Opx | 55.84 | 0.20 | 4.10 | 6.86 | 0.13 | 32.23 | 1.34 | 0.23 | 0.01 | 0.01 | 0.04 | 0.25 | 0.13 | 101.36 |
Cpx | 53.20 | 0.46 | 5.95 | 3.73 | 0.11 | 17.76 | 17.16 | 1.43 | 0.01 | 0.02 | 0.08 | 0.58 | 0.07 | 100.54 | |||||
---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
Grt | 44.76 | 0.39 | 21.19 | 7.15 | 0.25 | 21.51 | 5.70 | 0.06 | 0.01 | 0.00 | 0.05 | 1.23 | 0.03 | 102.31 | |||||
Sp | 4.78 | 0.48 | 50.17 | 10.35 | 0.12 | 22.07 | 0.48 | 0.00 | 0.01 | 0.02 | 0.16 | 11.09 | 0.40 | 100.13 | |||||
S1788 | 5 | 1550 | 3 | MORB | M | 49.79 | 1.73 | 14.00 | 9.64 | 0.18 | 9.64 | 9.85 | 2.85 | 0.32 | 0.17 | 0.19 | 0.04 | 0.01 | 98.41 |
KLB-1 | Ol | 40.44 | 0.03 | 0.14 | 11.00 | 0.12 | 49.74 | 0.28 | 0.06 | 0.01 | 0.05 | 0.00 | 0.07 | 0.31 | 102.24 | ||||
Opx | 55.21 | 0.11 | 4.86 | 6.54 | 0.15 | 33.31 | 0.87 | 0.16 | 0.01 | 0.00 | 0.05 | 0.27 | 0.10 | 101.62 | |||||
Cpx | 54.33 | 0.31 | 4.68 | 5.61 | 0.15 | 25.00 | 9.49 | 0.84 | 0.01 | 0.01 | 0.07 | 0.46 | 0.06 | 101.02 | |||||
S1790 | 5 | 1650 | 3 | MORB | M | 48.83 | 0.88 | 9.54 | 7.22 | 0.14 | 23.03 | 7.04 | 1.70 | 0.15 | 0.05 | 0.10 | 0.18 | 0.02 | 98.88 |
KLB-1 | Opx | 57.43 | 0.09 | 3.86 | 4.03 | 0.07 | 34.45 | 1.38 | 0.24 | 0.00 | 0.01 | 0.01 | 0.28 | 0.02 | 101.87 | ||||
S1808 | 8 | 1300 | 3 | MORB | Cpx | 54.28 | 0.75 | 11.10 | 5.14 | 0.06 | 8.73 | 12.77 | 5.31 | 0.27 | 0.01 | 0.00 | 0.00 | 0.01 | 98.42 |
Grt | 40.92 | 1.09 | 20.05 | 16.30 | 0.31 | 9.90 | 9.78 | 0.74 | 0.07 | 0.20 | 0.00 | 0.00 | 0.01 | 99.38 | |||||
Coe | 96.14 | 0.06 | 0.65 | 0.52 | 0.01 | 0.28 | 0.44 | 0.22 | 0.02 | 0.00 | 0.00 | 0.00 | 0.01 | 98.33 | |||||
KLB-1 | Ol | 40.46 | 0.03 | 0.16 | 9.98 | 0.10 | 48.38 | 0.12 | 0.02 | 0.01 | 0.01 | 0.00 | 0.00 | 0.39 | 99.65 | ||||
Opx | 53.79 | 0.12 | 4.65 | 6.53 | 0.16 | 32.60 | 0.88 | 0.16 | 0.00 | 0.00 | 0.00 | 0.00 | 0.11 | 98.99 | |||||
Cpx | 51.46 | 0.49 | 6.54 | 3.36 | 0.07 | 15.86 | 19.17 | 1.59 | 0.01 | 0.01 | 0.00 | 0.00 | 0.10 | 98.66 | |||||
Grt | 43.74 | 0.60 | 18.70 | 8.46 | 0.29 | 21.07 | 6.40 | 0.24 | 0.01 | 0.00 | 0.00 | 0.00 | 0.00 | 99.50 | |||||
S1812 | 8 | 1500 | 3 | MORB | Cpx | 53.89 | 1.16 | 11.53 | 5.21 | 0.07 | 8.40 | 13.02 | 4.97 | 0.22 | 0.03 | 0.00 | 0.00 | 0.02 | 98.52 |
Grt | 38.98 | 1.52 | 20.66 | 14.91 | 0.29 | 7.73 | 13.76 | 0.47 | 0.03 | 0.10 | 0.00 | 0.00 | 0.00 | 98.45 | |||||
Coe | 98.78 | 0.05 | 0.12 | 0.37 | 0.01 | 0.05 | 0.11 | 0.04 | 0.00 | 0.00 | 0.00 | 0.00 | 0.03 | 99.57 | |||||
KLB-1 | Ol | 39.95 | 0.02 | 0.04 | 10.22 | 0.10 | 48.66 | 0.11 | 0.03 | 0.00 | 0.02 | 0.00 | 0.00 | 0.38 | 99.54 | ||||
Opx | 54.11 | 0.18 | 4.64 | 6.43 | 0.14 | 32.33 | 0.96 | 0.21 | 0.01 | 0.03 | 0.00 | 0.00 | 0.09 | 99.12 | |||||
Cpx | 51.03 | 0.52 | 7.04 | 3.31 | 0.10 | 15.46 | 19.53 | 1.65 | 0.00 | 0.00 | 0.00 | 0.00 | 0.10 | 98.75 | |||||
Grt | 41.10 | 1.11 | 20.18 | 7.52 | 0.26 | 21.64 | 4.48 | 0.08 | 0.01 | 0.19 | 0.00 | 0.00 | 0.04 | 96.60 | |||||
Sp | 0.09 | 0.55 | 56.01 | 10.52 | 0.11 | 21.06 | 0.09 | 0.00 | 0.00 | 0.00 | 0.00 | 5.46 | 0.34 | 94.22 |
Si-rich tholeiitic melts dominated at temperatures near the dry peridotite solidus, the compositions of which were buffered by the aforementioned Opx reaction band along the interface of each rock type.
The relative K2O and TiO2 contents of melts formed within each starting material (yellow star in
Because of the different starting materials used for layered experiments, our melt compositions (e.g., Ti, Na, Ca, and Fe) were systematically different from those reported by Mallik and Dasgupta [
A schematic model for melting processes in a heterogeneous Hawaiian plume is shown in
The size of the entrained eclogite component plays an essential role in the melting processes that occur within a heterogeneous plume. If the eclogite components were small (such as mafic dyke or mafic bands, which are common in peridotite massifs), partially molten eclogite layers could achieve equilibrium with the surrounding peridotite over geological timescales relevant to plume melting (i.e., 104 - 106 yr). Conversely, if eclogite blocks were large (e.g., km-scale or larger), melt formed in the eclogite blocks would be isolated from surrounding peridotite due to the formation of Opx bands at their interfaces. The timescale of melt segregation from the partially molten eclogite may be faster
than that for reaction rate across the Opx band; thus, melts derived from eclogite domains would have geochemical signatures that record entrainment and would contaminate the surrounding peridotite less extensively.
Takahashi and Nakajima [
Tholeiite to basaltic andesite magmas could be generated in an upwelling mantle plume containing a recycled oceanic component (
We have carried out high-pressure melting experiments using an N-MORB/ peridotite (KLB-1) layered starting material in order to study magma genesis processes in the heterogeneous Hawaiian plume, which has entrained ancient oceanic crust. Major conclusions from this study are as follows:
1) In an upwelling mantle plume with a recycled oceanic component, N-MORB eclogite begins to melt at depth (5 GPa), but peridotite remains entirely solid almost up to the top of plume (~3 GPa).
2) Extensive partial melting occurs in eclogite domains, which produces tho- leiite to basaltic andesite melts. Some chemical reaction occurs at the basalt- peridotite interface.
3) Excluding FeO contents, the major-element composition of melts formed by reactive melting of N-MORB/KLB-1 at temperatures near the dry peridotite solidus are similar to Hawaiian tholeiite and picrite.
4) Relatively Fe- and LREE-enriched geochemical signatures in Hawaiian tholeiite compared with MORB suggest that the source of recycled components in the Hawaiian plume is more enriched in Fe and in incompatible elements than modern MORB.
5) The potential temperature of the Hawaiian plume could be 1450˚C or lower.
Gao, S., Takahashi, E. and Suzuki, T. (2017) High-Pressure Melting Experiments on Basalt-Peridotite Layered Source (KLB-1/N-MORB): Implications for Magma Genesis in Hawaii. In- ternational Journal of Geosciences, 8, 1-15. http://dx.doi.org/10.4236/ijg.2017.81001