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Geochemistry of basalts from IODP site U1365: Implications for magmatism and mantle source signatures of the mid-Cretaceous Osbourn Trough

Geochemistry of basalts from IODP site U1365: Implications for magmatism and mantle source signatures of the mid-Cretaceous Osbourn Trough
Geochemistry of basalts from IODP site U1365: Implications for magmatism and mantle source signatures of the mid-Cretaceous Osbourn Trough
The Integrated Ocean Drilling Program site U1365 drilled into the basement of the southwest Pacific crust formed from the mid-Cretaceous Osbourn Trough that rifted apart the Manihiki and Hikurangi Plateaus (the Greater Manihiki). The basalt geochemistry at this site is crucial for understanding the magmatic processes and mantle source of the mid-Cretaceous Osbourn Trough. The recovered fresh basalts were low-K tholeiitic normal (N) and depleted (D) mid-ocean ridge basalt (MORB). Their trace element and Sr–Nd isotope compositions indicate a Pacific-type mantle source rather than any significant influences from the nearby Louisville Seamount Chain or from the Greater Manihiki Plateau. Despite the presence of a plume head underneath the Osbourn Trough at its initial stage, the insignificance of a plume head could be explained by the long-distance (> 1000 km) southward migration of the Osbourn Trough. Lavas at site U1365 vary from low-MgO (< 6.9 wt.%) N-MORB at the bottom to high-MgO (8 wt.% to 9.5 wt.%) D-MORB and, then, to medium-MgO (7.3 wt.% to 8.2 wt.%) N-MORB according to their eruption sequences, which was accompanied by magma mixing in the magma reservoir. The D-MORB group lavas have higher melting degrees than those of N-MORB group based on their concentrations of TiO2, Na2O and CaO corrected for crystallization relative to MgO = 7.8 wt.%. The major element compositions of the high-MgO D-MORB lavas were consistent with partial melting in the spinel–peridotite zone over a pressure interval from ~ 3.1 GPa to 2 GPa in the mantle. The significant overlap of N-MORB and D-MORB in Sr–Nd isotopes suggests that chemical differences between the two groups were derived from the mantle melting processes. Based on comparison with lavas from the East Pacific Rise where a positive correlation of mantle melting degree vs. spreading rate is shown, we suggest that the Osbourn Trough might have a full spreading rate of ~ 140 mm/yr. Thus, the slow ridge-like axial morphology of the Osbourn Trough should be a character of an extinct fast ridge.
Mid-ocean ridge basalt, Cretaceous, Mantle source, U1365, Osbourn Trough
0024-4937
73-87
Zhang, Guoliang
5f63e6ae-a821-4d31-a940-64b4e321995c
Smith-Duque, Christopher
f1385032-8c67-40ca-bc6d-6dd3e6c5b013
Tang, Suohan
b93a4be3-7634-4013-940e-8d7803767bdc
Li, He
dbb1fd4a-b116-4e9d-b1e4-51b26deea215
Zarikian, Carlos
5c2a6f18-1cef-4316-8aee-3eb294520c3f
D'Hondt, Steven
06530267-4061-4f9b-b8ec-3e6009d4ac6e
Inagaki, Fumio
5d3c4487-d645-4a4c-83f0-ff43f319650b
IODP Expedition 329 Scientists,
b59aae5c-5bfe-48d9-804c-a80d22dd7fe1
Zhang, Guoliang
5f63e6ae-a821-4d31-a940-64b4e321995c
Smith-Duque, Christopher
f1385032-8c67-40ca-bc6d-6dd3e6c5b013
Tang, Suohan
b93a4be3-7634-4013-940e-8d7803767bdc
Li, He
dbb1fd4a-b116-4e9d-b1e4-51b26deea215
Zarikian, Carlos
5c2a6f18-1cef-4316-8aee-3eb294520c3f
D'Hondt, Steven
06530267-4061-4f9b-b8ec-3e6009d4ac6e
Inagaki, Fumio
5d3c4487-d645-4a4c-83f0-ff43f319650b
IODP Expedition 329 Scientists,
b59aae5c-5bfe-48d9-804c-a80d22dd7fe1

Zhang, Guoliang, Smith-Duque, Christopher, Tang, Suohan, Li, He, Zarikian, Carlos, D'Hondt, Steven, Inagaki, Fumio and IODP Expedition 329 Scientists, (2012) Geochemistry of basalts from IODP site U1365: Implications for magmatism and mantle source signatures of the mid-Cretaceous Osbourn Trough. Lithos, 144-145, 73-87. (doi:10.1016/j.lithos.2012.04.014).

Record type: Article

Abstract

The Integrated Ocean Drilling Program site U1365 drilled into the basement of the southwest Pacific crust formed from the mid-Cretaceous Osbourn Trough that rifted apart the Manihiki and Hikurangi Plateaus (the Greater Manihiki). The basalt geochemistry at this site is crucial for understanding the magmatic processes and mantle source of the mid-Cretaceous Osbourn Trough. The recovered fresh basalts were low-K tholeiitic normal (N) and depleted (D) mid-ocean ridge basalt (MORB). Their trace element and Sr–Nd isotope compositions indicate a Pacific-type mantle source rather than any significant influences from the nearby Louisville Seamount Chain or from the Greater Manihiki Plateau. Despite the presence of a plume head underneath the Osbourn Trough at its initial stage, the insignificance of a plume head could be explained by the long-distance (> 1000 km) southward migration of the Osbourn Trough. Lavas at site U1365 vary from low-MgO (< 6.9 wt.%) N-MORB at the bottom to high-MgO (8 wt.% to 9.5 wt.%) D-MORB and, then, to medium-MgO (7.3 wt.% to 8.2 wt.%) N-MORB according to their eruption sequences, which was accompanied by magma mixing in the magma reservoir. The D-MORB group lavas have higher melting degrees than those of N-MORB group based on their concentrations of TiO2, Na2O and CaO corrected for crystallization relative to MgO = 7.8 wt.%. The major element compositions of the high-MgO D-MORB lavas were consistent with partial melting in the spinel–peridotite zone over a pressure interval from ~ 3.1 GPa to 2 GPa in the mantle. The significant overlap of N-MORB and D-MORB in Sr–Nd isotopes suggests that chemical differences between the two groups were derived from the mantle melting processes. Based on comparison with lavas from the East Pacific Rise where a positive correlation of mantle melting degree vs. spreading rate is shown, we suggest that the Osbourn Trough might have a full spreading rate of ~ 140 mm/yr. Thus, the slow ridge-like axial morphology of the Osbourn Trough should be a character of an extinct fast ridge.

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Published date: 2012
Keywords: Mid-ocean ridge basalt, Cretaceous, Mantle source, U1365, Osbourn Trough
Organisations: Geochemistry

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Local EPrints ID: 347107
URI: http://eprints.soton.ac.uk/id/eprint/347107
ISSN: 0024-4937
PURE UUID: 0e1471d7-5f11-4118-9b36-85586342c128

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Date deposited: 16 Jan 2013 14:36
Last modified: 20 Dec 2018 17:31

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