Geochemical diversity of Mesozoic island arc tectonic blocks in eastern Puerto Rico

Abstract

Eastern Puerto Rico is composed of two distinctive volcanic terranes, the northeastern and central volcanic provinces, that represent independent tectonic blocks assembled in mid-Santonian time by left-lateral strike-slip faulting with displacement of at least 50 km. Volcanic strata in the juxtaposed tectonic blocks occur in five successive volcanic phases: (I) Upper Aptian to Lower Albian island arc tholeiites (IAT); (II) Upper Albian cal-calkaline (CA) volcanic rocks; (III) Cenomanian to Lower Santonian shoshonites (SHO, central block) and cal-calkaline (northeastern block) volcanic rocks; (IV) Upper Santonian to Maastrichtian cal-calkaline to shoshonitic volcanic rocks; and (V) Lower Tertiary, predominantly felsic, cal-calkaline volcanic rocks. The geochemical evolution is marked by progressive increases in ratios of large-ion lithophile (LILE) and light rare earth (LREE) elements relative to high field strength (HFSE) and heavy rare earth (HREE) elements. Compositional changes with time are also evident in the Nd isotope ratios of the volcanics of the central tectonic block, which are MORB-like and display a gradual decrease in ε Nd from +8 to about +6 between phases I and IV. In contrast, Sr and Pb isotope ratios show no evidence of compositional evolution. Initial (i) Sr isotope compositions overlap the field of Mesozoic MORB with i 87 Sr/ 86 Sr ratios exhibiting a broad range from about 0.7034 to 0.7044 (ε Sr from -12 to +1.0) and an average of 0.7037 (-10.0). Pb isotope compositions form a trend emanating from the MORB field and oriented along or subparallel to the Northern Hemisphere Reference Line (NHRL).HFSE ratios in Puerto Rican basalts overlap the MORB trend at all concentrations, consistent with incompatible behavior. As in modern island arcs, low absolute HFSE abundances compared with MORB indicate the wedge was more depleted in incompatible elements than a MORB-type source. Uniformly flat normalized HREE patterns, together with wide ranges in Nb/Hf ratios reflecting variation in degree of melting, indicate magma generation at relatively low P t . Cooling of the shallow wedge during the 35-Ma eruption period is inferred to have produced the observed geochemical shifts. Superimposed on the magmas are effects of low-P t gabbroic and, in

Discovery of Lower Cretaceous synmetamorphic thrust tectonics in French Lesser Antilles (La Désirade Island, Guadeloupe): Implications for Caribbean geodynamics

“…[41] Most Caribbean evolutionary models seemingly require a change in subduction polarity [Mattson, 1979;Pindell and Barrett, 1990;Jolly et al, 1998;Kerr et al, 1999Kerr et al, , 2003Pindell and Kennan, 2009], and two possible timings of polarity reversal have been proposed: Aptian-Albian times [Lebron and Perfit, 1994;Pindell et al, 2006;Pindell and Kennan, 2009] and Turonian-Santonian times [Burke, 1988;Sinton et al, 1998;White et al, 1999;Kerr et al, 1999Kerr et al, , 2003. Because, as recently suggested by Neill et al [2010], in the framework of Caribbean geodynamics the initiation of southwest-dipping subduction occurred to the east of La Désirade, the tectonic evolution of the latter island is a key aspect of the polarity reversal event.…”

Geochemical constraints on the origin of the late Jurassic proto-Caribbean oceanic crust in Hispaniola

“…The olivine basalt is slightly enriched in LREE (La/Sm = 1.6) and other incompatible Kerr et al (1997Kerr et al ( , 2002, Lapierre et al (1997Lapierre et al ( , 1999, Sen et al (1988), and Escuder Viruete et al (2007a). PACPR = MORB samples from pre-arc complex of Puerto Rico (Jolly et al 1998). BABB = Mesozoic back-arc basalts in Hispaniola (J. Escuder Viruete et al unpublished data).…”

Geochemical evidence for island-arc origin of the Villa de Cura blueschist belt, Venezuela

“…Typically, felsic rocks are volumetrically minor (Beets et al, 1984;Jolly et al, 1998). REE patterns are fl at to only slightly LREE enriched relative to HREE (Beets et al, 1984;Frost and Snoke, 1989;Lebrón and Perfi t, 1994;Jolly et al, 1998). LILE are enriched relative to HFSE as typical of island-arc Figure 12.…”

“…Most volcanic suites span a compositional range from basaltic to andesitic (Beets et al, 1984;Lebrón and Perfi t, 1994). Typically, felsic rocks are volumetrically minor (Beets et al, 1984;Jolly et al, 1998). REE patterns are fl at to only slightly LREE enriched relative to HREE (Beets et al, 1984;Frost and Snoke, 1989;Lebrón and Perfi t, 1994;Jolly et al, 1998).…”

“…86 Ma calc-alkaline El Salado granite of Margarita Island (Venezuela) intrudes >105 Ma high-pressure rocks of the Juan Griego and La Rinconada Groups (Stöckhert et al, 1995). In Puerto Rico, calc-alkaline assemblages include the upper Albian to Campanian Robles-Río Orocovis Formations, as well as Cenomanian to Lower Santonian and upper Santonian to Maastrichtian calcalkaline and shoshonitic volcanic phases (Donnelly et al, 1990;Jolly et al, 1998;Schellekens, 1998;Jolly et al, 2001). Calcalkaline rocks in Hispaniola include the Tiero Formation, the Loma la Vega Formation, and the Las Guajabas tuffs (Lebrón and Perfi t, 1994;Lewis et al, 2002).…”