It commonly happens that the less factual information we have on a problem, the more argument is generated. The lower crust is no exception. In fact the main thrust of our review paper on the lower crust was to demonstrate just how little factual data was available on which to construct reliable models for rustal growth, but that the data which was available (largely on Precambrian lower crustal granulites) did not fully support popular concepts that the lower continental crust is predominantly made up of cumulates or the refractory residues from partial melting. We did not set out to criticize Taylor's andesitic model for crustal growth directly, although in view of the important role the model has played over the last decade we could not avoid referring to it. Taylor & McLennan's defence of the andesite model, coupled with their critique of our own paper, nevertheless behoves us to comment on the andesite model both in relation to their specific points and in relation to our further observations since the paper was written. With the andesite model there are basically three components to the equation: island arc = upper crust + lower crust. Knowledge of the geochemical characteristics of each is vital in order to test whether the equation will balance. Of the three, only the upper crust composition is known sufficiently well, and as far as the mean rare-earth distribution is concerned it can be approximated by the average sedimentary pattern given by Taylor (1977). There is much less
The Late Cretaceous Caribbean—Colombian igneous province is one of the world's best-exposed examples of a plume-derived oceanic plateau. The buoyancy of the plateau (resulting from residual heat and thick crust) kept it from being totally subducted as it moved eastward with the Farallon Plate from its site of generation in the eastern Pacific and encountered a destructive plate margin. In effect, the plateau makes up much of the Caribbean Plate; it is well exposed around its margins, but more so in accreted terranes in western Colombia (including the well-known Gorgona komatiites and Bolivar mafic/ultramafic cumulates). Compositionally, the lavas of the plateau form three groups: (a) basalts, picrites, and komatiites with light-rare-earth-element (LREE)-depleted chondrite-normalised patterns; (b) basalts with LREE-enriched patterns; and (c) basalts with essentially flat REE patterns (the most dominant type) similar to many of the basalts from the Ontong Java Plateau. These three types demonstrate the heterogeneous nature of the mantle plume source region. The picrites and the komatiites seem to lie nearer the base of the plateau than the more homogeneous basalts; thus, the more MgO-rich melts may have been erupted before large magma chambers had a chance to develop. A reconstructed crustal cross section through the plateau consists of dunitic and pyroxenitic cumulates near the base which are overlain by layered olivine-rich gabbros and more isotropic gabbros. The lowermost eruptive sequence comprises compositionally heterogeneous picrites/komatiites overlain by more homogeneous pillow basalts. Spectacular hornblende-plagioclase veins cut the Bolivar assemblage and these may represent local partial melts of the plateau's base as it was thrusted onto the continent. Subduction-related batholiths and extrusive rocks found around the margin of the province are of two distinct ages; one suite represents pre-plateau collision-related volcanism whereas the other suite, slightly younger than the plateau, may be associated with obduction.
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 (ε Nd ) i < +4.1) to relatively depleted ((La/Nd) n < 1 and (ε Nd ) i > +8.0). Nb/Y and Zr/Y systematics suggest that the depleted component 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.
Research Article| November 01, 1999 A new plate tectonic model of the Caribbean: Implications from a geochemical reconnaissance of Cuban Mesozoic volcanic rocks Andrew C. Kerr; Andrew C. Kerr 1Department of Geology, University of Leicester, University Road, Leicester LE1 7RH, United Kingdom Search for other works by this author on: GSW Google Scholar Manuel A. Iturralde-Vinent; Manuel A. Iturralde-Vinent 2Museo Nacional de Historia Natural, Obispo No. 61, Plaza de Armas, La Habana Vieja 10100, Cuba Search for other works by this author on: GSW Google Scholar Andrew D. Saunders; Andrew D. Saunders 1Department of Geology, University of Leicester, University Road, Leicester LE1 7RH, United Kingdom Search for other works by this author on: GSW Google Scholar Tanya L. Babbs; Tanya L. Babbs 1Department of Geology, University of Leicester, University Road, Leicester LE1 7RH, United Kingdom Search for other works by this author on: GSW Google Scholar John Tarney John Tarney 1Department of Geology, University of Leicester, University Road, Leicester LE1 7RH, United Kingdom Search for other works by this author on: GSW Google Scholar Author and Article Information Andrew C. Kerr 1Department of Geology, University of Leicester, University Road, Leicester LE1 7RH, United Kingdom Manuel A. Iturralde-Vinent 2Museo Nacional de Historia Natural, Obispo No. 61, Plaza de Armas, La Habana Vieja 10100, Cuba Andrew D. Saunders 1Department of Geology, University of Leicester, University Road, Leicester LE1 7RH, United Kingdom Tanya L. Babbs 1Department of Geology, University of Leicester, University Road, Leicester LE1 7RH, United Kingdom John Tarney 1Department of Geology, University of Leicester, University Road, Leicester LE1 7RH, United Kingdom Publisher: Geological Society of America First Online: 01 Jun 2017 Online ISSN: 1943-2674 Print ISSN: 0016-7606 Geological Society of America GSA Bulletin (1999) 111 (11): 1581–1599. https://doi.org/10.1130/0016-7606(1999)111<1581:ANPTMO>2.3.CO;2 Article history First Online: 01 Jun 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn Email Permissions Search Site Citation Andrew C. Kerr, Manuel A. Iturralde-Vinent, Andrew D. Saunders, Tanya L. Babbs, John Tarney; A new plate tectonic model of the Caribbean: Implications from a geochemical reconnaissance of Cuban Mesozoic volcanic rocks. GSA Bulletin 1999;; 111 (11): 1581–1599. doi: https://doi.org/10.1130/0016-7606(1999)111<1581:ANPTMO>2.3.CO;2 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGSA Bulletin Search Advanced Search Abstract Accreted terranes, comprising a wide variety of Jurassic and Cretaceous igneous and sedimentary rocks, are an important and conspicuous feature of Cuban geology. Although the Mesozoic igneous rocks are generally poorly exposed and badly altered, we have collected and geochemically analyzed 25 samples that place new constraints on plate tectonic models of the Caribbean region. From our recognizance sampling, six main lava types have been identified within the Mesozoic igneous rocks of Cuba: rift basalts, oceanic tholeiites, backarc basin lavas, boninites, island arc tholeiites (IAT), and calc-alkaline lavas. We suggest that the rift-related basalts may have formed during the development of the proto-Caribbean, as the Yucatan block rifted away from northern South America in Jurassic–Early Cretaceous time. The Early Cretaceous oceanic tholeiites have flat rare earth element patterns, and are compositionally similar to Pacific mantle plume–derived oceanic plateaus of similar age. The Early Cretaceous arc-related rocks are either backarc basalts, boninites, or relatively trace element–depleted IAT lavas. A limited amount of geochemical and field evidence hints that two parallel arc systems existed in the western proto-Caribbean area in Early Cretaceous time. This leads us to speculate that in the proto-Caribbean at this time there was a western arc with a northeast-dipping subduction zone erupting IAT lavas (with Farallon plate being consumed), and a more eastern boninitic arc with a southwest-dipping subduction zone (with proto-Caribbean plate being consumed). This latter arc was relatively short lived and after being aborted was mostly eroded away. The Cretaceous primitive (IAT) arc survived and, later in Cretaceous time, as this arc system moved into the widening gap between North and South Americas, calc-alkaline lavas began to be erupted. The evidence suggests that the change from IAT to calc-alkaline lavas was gradual and not abrupt. These new data, although limited, provide geochemical constraints on the tectonic development of the northern part of the Caribbean plate. In consequence, we present a new plate tectonic model for this area of the Caribbean. This content is PDF only. Please click on the PDF icon to access. 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