Open Access Repository

LIMA U–Pb ages link lithospheric mantle metasomatism to Karoo magmatism beneath the Kimberley region, South Africa

Downloads

Downloads per month over past year

Giuliani, A and Phillips, D and Maas, R and Woodhead, JD and Kendrick, MA and Greig, A and Armstrong, RA and Chew, D and Kamenetsky, VS and Fiorentini, ML (2014) LIMA U–Pb ages link lithospheric mantle metasomatism to Karoo magmatism beneath the Kimberley region, South Africa. Earth and Planetary Sciences Letters, 401. pp. 132-147. ISSN 0012-821X

[img] PDF
EPSL-2014-LIMA...pdf | Document not available for request/download
Full text restricted
Available under University of Tasmania Standard License.

Abstract

The Karoo igneous rocks (174–185 Ma) of southern Africa represent one of the largest continental flood basalt provinces on Earth. Available evidence indicates that Karoo magmas either originated in the asthenosphere and were extensively modified by interaction with the lithospheric mantle prior to emplacement in the upper crust; or were produced by partial melting of enriched mantle lithosphere. However, no direct evidence of interaction by Karoo melts (or their precursors) with lithospheric mantle rocks has yet been identified in the suites of mantle xenoliths sampled by post-Karoo kimberlites in southern Africa. Here we report U–Pb ages for lindsleyite–mathiasite (LIMA) titanate minerals (crichtonite series) from three metasomatised, phlogopite and clinopyroxene-rich peridotite xenoliths from the ∼84 Ma Bultfontein kimberlite (Kimberley, South Africa), located in the southern part of the Karoo magmatic province. The LIMA minerals appear to have formed during metasomatism of the lithospheric mantle by fluids enriched in HFSE (Ti, Zr, Hf, Nb), LILE (K, Ba, Ca, Sr) and LREE. LIMA U–Pb elemental and isotopic compositions were measured in situ by LA-ICP-MS methods, and potential matrix effects were evaluated by solution-mode analysis of mineral separates. LIMA minerals from the three samples yielded apparent U–Pb ages of 177±12 Ma, 178±29 Ma and 190±24 Ma(±2σ). A single zircon grain extracted from the ∼190 Ma LIMA-bearing sample produced a similar U–Pb age of 184±6 Ma, within uncertainty of the LIMA ages. These data provide the first robust evidence of fluid enrichment in the lithospheric mantle beneath the Kimberley region at ∼180–190 Ma, and suggest causation of mantle metasomatism by Karoo melts or their precursor(s). The results further indicate that U–Pb dating of LIMA minerals provides a new, accurate tool for dating metasomatic events in the lithospheric mantle.

Item Type: Article
Keywords: crichtonite-series LIMA titanate U–Pb geochronology mantle metasomatism Kimberley Karoo magmatism
Journal or Publication Title: Earth and Planetary Sciences Letters
Page Range: pp. 132-147
ISSN: 0012-821X
Identification Number - DOI: 10.1016/j.epsl.2014.05.044
Additional Information:

Copyright 2014 Elsevier

Date Deposited: 07 Jul 2014 06:38
Last Modified: 18 Nov 2014 05:02
Item Statistics: View statistics for this item

Actions (login required)

Item Control Page Item Control Page
TOP