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Heterogeneity of the Caribbean plateau mantle source: Sr, O and He isotopic compositions of olivine and clinopyroxene from Gorgona Island

Heterogeneity of the Caribbean plateau mantle source: Sr, O and He isotopic compositions of olivine and clinopyroxene from Gorgona Island
Heterogeneity of the Caribbean plateau mantle source: Sr, O and He isotopic compositions of olivine and clinopyroxene from Gorgona Island
The composition of the mantle plumes that created large oceanic plateaus such as Ontong Java or the Caribbean is still poorly known. Geochemical and isotopic studies on accreted portions of the Caribbean plateau have shown that the plume source was heterogeneous and contained isotopically depleted and relatively enriched portions. A distinctive feature of samples from the Caribbean plateau is their unusual Sr isotopic compositions, which, at a given Nd isotopic ratio, are far higher than in samples from other oceanic plateaus. Sr, O and He isotopic compositions of whole rocks and magmatic minerals (clinopyroxene or olivine) separated from komatiites, gabbros and peridotites from Gorgona Island in Colombia were determined to investigate the origin of these anomalously radiogenic compositions. Sequentially leached clinopyroxenes have Sr isotopic compositions in the range 87Sr/86Sr = 0.70271–0.70352, systematically lower than those of leached and unleached whole rocks. Oxygen isotopic ratios of clinopyroxene vary within the range δ18O = 5.18–5.35 ‰, similar to that recorded in oceanic island basalts. He isotopic ratios are high (R/Ra = 8–19). The lower 87Sr/86Sr ratios of most of the clinopyroxenes shift the field of the Caribbean plateau in Nd–Sr isotope diagrams toward more 'normal' values, i.e. a position closer to the field defined by mid-ocean ridge basalts and oceanic-island basalts. Three clinopyroxenes have slightly higher 87Sr/86Sr ratios that cannot be explained by an assimilation model. The high 87Sr/86Sr and variations of 143Nd/144Nd are interpreted as a source characteristic. Trace-element ratios, however, are controlled mainly by fractionation during partial melting. We combine these isotopic data in a heterogeneous plume source model that accounts for the diversity of isotopic signatures recorded on Gorgona Island and throughout the Caribbean plateau. The heterogeneities are related to old recycled oceanic lithosphere in the plume source; the high 3He/4He ratios may indicate that the source material once resided in the lower mantle.
Caribbean oceanic plateau, Sr, O, He, clinopyroxenes, plumes
0012-821X
91-106
Revillon, S.
58bd2948-077d-436b-ba95-76ff59186db3
Chauvel, C.
f7ca5d63-7263-4f9e-8523-6a5ad4231aa4
Arndt, N.T.
b4f52052-cabf-4376-bd4b-23897fe2b9de
Pik, R.
52522cfc-45d4-4fae-870d-63c6fe12967d
Martineau, F.
776c7dae-0a6c-40d3-bca1-6594d0a5416d
Fourcade, S.
53780cd1-0900-4809-b4d6-939849b471d9
Marty, B.
36bcc290-a7e8-4ed8-ae91-cabd2d64342a
Revillon, S.
58bd2948-077d-436b-ba95-76ff59186db3
Chauvel, C.
f7ca5d63-7263-4f9e-8523-6a5ad4231aa4
Arndt, N.T.
b4f52052-cabf-4376-bd4b-23897fe2b9de
Pik, R.
52522cfc-45d4-4fae-870d-63c6fe12967d
Martineau, F.
776c7dae-0a6c-40d3-bca1-6594d0a5416d
Fourcade, S.
53780cd1-0900-4809-b4d6-939849b471d9
Marty, B.
36bcc290-a7e8-4ed8-ae91-cabd2d64342a

Revillon, S., Chauvel, C., Arndt, N.T., Pik, R., Martineau, F., Fourcade, S. and Marty, B. (2002) Heterogeneity of the Caribbean plateau mantle source: Sr, O and He isotopic compositions of olivine and clinopyroxene from Gorgona Island. Earth and Planetary Science Letters, 205 (1-2), 91-106. (doi:10.1016/S0012-821X(02)01003-8).

Record type: Article

Abstract

The composition of the mantle plumes that created large oceanic plateaus such as Ontong Java or the Caribbean is still poorly known. Geochemical and isotopic studies on accreted portions of the Caribbean plateau have shown that the plume source was heterogeneous and contained isotopically depleted and relatively enriched portions. A distinctive feature of samples from the Caribbean plateau is their unusual Sr isotopic compositions, which, at a given Nd isotopic ratio, are far higher than in samples from other oceanic plateaus. Sr, O and He isotopic compositions of whole rocks and magmatic minerals (clinopyroxene or olivine) separated from komatiites, gabbros and peridotites from Gorgona Island in Colombia were determined to investigate the origin of these anomalously radiogenic compositions. Sequentially leached clinopyroxenes have Sr isotopic compositions in the range 87Sr/86Sr = 0.70271–0.70352, systematically lower than those of leached and unleached whole rocks. Oxygen isotopic ratios of clinopyroxene vary within the range δ18O = 5.18–5.35 ‰, similar to that recorded in oceanic island basalts. He isotopic ratios are high (R/Ra = 8–19). The lower 87Sr/86Sr ratios of most of the clinopyroxenes shift the field of the Caribbean plateau in Nd–Sr isotope diagrams toward more 'normal' values, i.e. a position closer to the field defined by mid-ocean ridge basalts and oceanic-island basalts. Three clinopyroxenes have slightly higher 87Sr/86Sr ratios that cannot be explained by an assimilation model. The high 87Sr/86Sr and variations of 143Nd/144Nd are interpreted as a source characteristic. Trace-element ratios, however, are controlled mainly by fractionation during partial melting. We combine these isotopic data in a heterogeneous plume source model that accounts for the diversity of isotopic signatures recorded on Gorgona Island and throughout the Caribbean plateau. The heterogeneities are related to old recycled oceanic lithosphere in the plume source; the high 3He/4He ratios may indicate that the source material once resided in the lower mantle.

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More information

Published date: 2002
Keywords: Caribbean oceanic plateau, Sr, O, He, clinopyroxenes, plumes

Identifiers

Local EPrints ID: 1310
URI: http://eprints.soton.ac.uk/id/eprint/1310
ISSN: 0012-821X
PURE UUID: 0a235181-f3ea-4565-8191-951e8ab33a4b

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Date deposited: 23 Apr 2004
Last modified: 09 Nov 2021 06:04

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Contributors

Author: S. Revillon
Author: C. Chauvel
Author: N.T. Arndt
Author: R. Pik
Author: F. Martineau
Author: S. Fourcade
Author: B. Marty

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