The genesis of the Caribbean Large Igneous Province (CLIP) has been associated to the melting of the Galapagos plume head at ~90 Ma or to the interaction between the plume and the Caribbean slab window. Gorgona Island, offshore western Colombia, is an accreted fragment of the CLIP and its highly heterogeneous igneous suite, ranging from enriched basalts to depleted komatiites and picrites, was assumed to have formed at ~89 Ma from different part of the plume. Herewepresent new geologic, geochronologic and geochemical data ofGorgona with significant implications for the formation of the CLIP. A new set of 40Ar???39Ar ages documents a magmatic activity spanning the whole Late Cretaceous (98.7±7.7 to 64.4±5 Ma) followed by a shallower, picritic pyroclastic eruption in the Paleocene. Trace element and isotope geochemistry confirm the existence of an enriched (EDMM: La/SmN ???1 and ??Ndi of 5.7 to 7.8) and a depleted (DMM: La/SmNb1 and ??Ndi of 9.5 to 11.3) mantle sources. A progressive increase in the degree of melting and melt extraction with time occurred in both groups. Petrologic modelling indicates that low but variable degrees of wet melting (b5%) of an EDMM can produce the LREEenriched rocks. Higher degree of melting (N10%) of a mixedDMM+EDMM(40 to 60%) may reproduce themore depleted rocks with temperatures in the range of ambient mantle in absence of plumes. Our results contradict the notion that the CLIP formed by melting of a plume head at ~90Ma.Multiple magmatic pulses over several tens of Ma in small areas like Gorgona, also recognised in other CLIP areas, suggest a long period of diffuse magmatism without a clear pattern of migration. The age span of this magmatism is broadly concurrent with the Caribbean slab window. During this time span the Farallon oceanic lithosphere (later becoming the Caribbean plate) advanced eastward ~1500 km, overriding the astenosphere feeding the proto-Caribbean spreading ridge. This hotter mantle flowed westward into, and mixed with, the opening mantle wedge, promoting increasing melting with time. The fortuitous occurrence of a plume passing through the slab gap area cannot be excluded but not required to produce the observed composition and degree of melting.
An integrative geologic, geochronologic and geochemical study of Gorgona Island, Colombia: Implications for the formation of the Caribbean Large Igneous Province
SERRANO DURAN, LINA MARIA;
2011
Abstract
The genesis of the Caribbean Large Igneous Province (CLIP) has been associated to the melting of the Galapagos plume head at ~90 Ma or to the interaction between the plume and the Caribbean slab window. Gorgona Island, offshore western Colombia, is an accreted fragment of the CLIP and its highly heterogeneous igneous suite, ranging from enriched basalts to depleted komatiites and picrites, was assumed to have formed at ~89 Ma from different part of the plume. Herewepresent new geologic, geochronologic and geochemical data ofGorgona with significant implications for the formation of the CLIP. A new set of 40Ar???39Ar ages documents a magmatic activity spanning the whole Late Cretaceous (98.7±7.7 to 64.4±5 Ma) followed by a shallower, picritic pyroclastic eruption in the Paleocene. Trace element and isotope geochemistry confirm the existence of an enriched (EDMM: La/SmN ???1 and ??Ndi of 5.7 to 7.8) and a depleted (DMM: La/SmNb1 and ??Ndi of 9.5 to 11.3) mantle sources. A progressive increase in the degree of melting and melt extraction with time occurred in both groups. Petrologic modelling indicates that low but variable degrees of wet melting (b5%) of an EDMM can produce the LREEenriched rocks. Higher degree of melting (N10%) of a mixedDMM+EDMM(40 to 60%) may reproduce themore depleted rocks with temperatures in the range of ambient mantle in absence of plumes. Our results contradict the notion that the CLIP formed by melting of a plume head at ~90Ma.Multiple magmatic pulses over several tens of Ma in small areas like Gorgona, also recognised in other CLIP areas, suggest a long period of diffuse magmatism without a clear pattern of migration. The age span of this magmatism is broadly concurrent with the Caribbean slab window. During this time span the Farallon oceanic lithosphere (later becoming the Caribbean plate) advanced eastward ~1500 km, overriding the astenosphere feeding the proto-Caribbean spreading ridge. This hotter mantle flowed westward into, and mixed with, the opening mantle wedge, promoting increasing melting with time. The fortuitous occurrence of a plume passing through the slab gap area cannot be excluded but not required to produce the observed composition and degree of melting.
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