nivia_2002_pervasive mantle plume head heterogeneity evidence from the late cretaceous...

Pervasive mantle plume head heterogeneity: Evidence from the late Cretaceous Caribbean-Colombian oceanic plateau Andrew C. Kerr, 1 John Tarney, 2 Pamela D. Kempton, 3 Piera Spadea, 4 Alvaro Nivia, 5 Giselle F. Marriner, 6 and Robert A. Duncan 7 Received 10 July 2001; revised 8 January 2002; accepted 13 January 2002; published 24 July 2002. [1] In SW Colombia picritic pillow lavas and tuffs, as well as breccias composed of picritic clasts, occur interspersed with basalts of the Central Cordillera and represent accreted portions of the $90 Ma Colombian/Caribbean oceanic plateau (CCOP). We present new geochemical data for these picrites and high-MgO basalts from SW Colombia, along with new data from Deep Sea Drilling Project Leg 15 drill sites. The 40 Ar/ 39 Ar ages for the CCOP in the Central Colombian Cordillera range from 87 to 93 Ma. Both SW Colombia picrites and Leg 15 basalts are compositionally diverse and range from reasonably enriched ((La/Nd) n > 1 and (e Nd ) i < +4.1) to relatively depleted ((La/Nd) n < 1 and (e Nd ) i > +8.0). Nb/Y and Zr/Y systemat ics suggest that the deple ted componen t is not depleted MORB mantle, but is an intrinsic part of the plume. The bulk of the CCOP compositions can be explained by mixing between this depleted mantle and a HIMU component. However, radiogenic isotope systematics indicate the presence of an EM2 (or possibly EM1) component within the plume. Mantle melt modeling suggests that the enriched magma types are the product of deeper, small degree melting of a pervasively heterogeneous plume comprising a refractory matrix with enriched streaks/blobs, whereas shallower, more extensive melting, results in the formation of relatively depleted magmas. I NDEX T ERMS : 8121 T ectonop hysics: Dynamics, convectio n currents and mantle plumes; 1040 Geochemistry: Isotopic composition /chemi stry; 3640 Minera logy and Petrol ogy: Igneous petrology; 1025 Geochemistry: Composition of the mantle; 3670 Mineralogy and Petrology: Minor and trace element composition; K EYWORDS : mantle plume, mantl e melti ng, oceani c plate au, picrit e, komati ite, Colombia 1. Introducti on [2] Our knowl edg e of ocean ic pl ateaus comes mai nl y from three Cretaceous age plateaus: the Ontong Java plateau in the wes te rn Pa cif ic [e. g., Mahone y et al. , 1993], the Kerguelen plateau in the Indian Ocean [ Weis et al. , 1989; Fr ey et al. , 200 0] and the Cari bbea n-Co lombi an plat eau [ Donnelly et al. , 1990; Kerr et al. , 1996a, 1996b, 1997a, 1997b]. With the exception of small obducted fragments the former two plateaus have only been sampled in a few Ocean Drill ing Program (ODP) dril l hol es. In the Ontong Java, compositional variability is quite limited [ Mahoney et al. , 1993]. Howev er, Kerguele n plat eau is compo sitionall y diverse, and recent drilling results [ Frey et al., 2000] have confirmed suggestions that part of the plateau is underlain by ancient continental lithosphere. In contrast, the Carib- bean-Colombian oceanic plateau is well exposed around the margins of the Caribbean and in accreted fragments in NW South America [ Kerr et al., 1997a, 1997b]. It is not underlain by any known continental lithospheric fragments, yet has been shown to locally display significant compositional diversity [ Kerr et al. , 1996a, 1997a; Hauff et al., 2000a, 2000b]. [3] In this pape r we pres ent new eleme ntal , isotop ic (Sr, Nd, and Pb), and 40 Ar/ 39 Ar age data for comp osit ion ally hete rog eneous picr ites and basalts from the Central Cor- dil le ra of Col ombia . Add iti onall y , we rep or t new tra ce element data from basalt s dril led during Deep Sea Drill- ing Pro jec t (DS DP) Le g 15. All the se sa mpl es exten d bot h the geoc hemi cal rang e and the geo grap hica l exte nt of hete roge neit y disp laye d by the plateau lavas [ Kerr et al., 199 6a, 199 6b; Sinton et al., 199 8] . We wil l de mon- strate that this heterogeneity is not localized but seems to be ubiquito us thr oug hou t the whole pro vin ce, usu ally where high-MgO lavas occur. We will explore the nature, possible origin, and partial melting of these plume source components. 1.1. Caribb ean-Co lombi an Ocean ic Plat eau (CCOP) [4] Rec ent geoc hemica l wor k ha s sho wn tha t the vast majority of accreted oceanic material in western Colombia are frag ments of mant le plume-de rive d, obd ucte d ocea nic JOURNAL OF GEOPHYSICAL RESEARCH, VOL. 107, NO. B7, 10.1029/2001 JB0007 90, 2002 1 Department of Earth Sciences, Cardiff University, Cardiff, UK. 2 Department of Geology, University of Leicester, Leicester, UK. 3 NERC Isotope Geosciences Laboratory, Nottingham, UK. 4 Dipa rtime nto di Geor isorse E T errito rio, Unive rsita ` Degli Studi di Udine, Udine, Italy. 5 Ingeominas–Regional Pacifico, Cali, Colombia. 6 Depa rtmen t of Geolo gy , Roya l Hollo way Unive rsity of Lond on, Egham, UK. 7 College of Oceanography, Oregon State University, Corvallis, Oregon, USA. Copyright 2002 by the American Geophysical Union. 0148-0227/02/2001JB000790$09.00 ECV 2 - 1

nivia_2002_pervasive mantle plume head heterogeneity evidence from the late cretaceous...

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