Folkmar Hauff

Missing history (16–71 Ma) of the Galápagos hotspot: Implications for the tectonic and biological evolution of the Americas

We present the results of volcanological, geochemical, and geochronological studies of volcanic rocks from Malpelo Island on the Nazca plate (15.8–17.3 Ma) belonging to the Gala´pagos hotspot tracks, and igneous complexes (20.8–71.3 Ma) along the Pacific margin of Costa Rica and Panama. The igneous complexes consist of accreted portions of ocean island and seamount volcanoes and aseismic ridges, representing the missing (primarily subducted) history of the Gala´pagos hotspot. The age and geochemical data directly link the Gala´pagos hotspot tracks on the Pacific Ocean floor to the Caribbean large igneous province (ca. 72–95 Ma), confirming a Pacific origin for the Caribbean oceanic plateau from the Gala´pagos hotspot. We propose that emplacement of this oceanic plateau between the Americas and interaction of the Gala´pagos hotspot tracks with the Central American Arc played a fundamental role in the formation of land bridges between the Americas in Late Cretaceous–Paleocene and Pliocene-Holocene time. The land bridges allowed the exchange of terrestrial faunas (e.g., dinosaurs, mastodons, saber-tooth cats, and ground sloths) between the Americas and served as barriers for the exchange of marine organisms between the central Pacific Ocean and the Caribbean Sea and the central Atlantic Ocean.

Age and geochemistry of basaltic complexes in western Costa Rica: Contributions to the geotectonic evolution of Central America

The age and origin of magmatic complexes along the Pacific Coast of Central America have important implications for the origin and tectonic evolution of this convergent plate margin. Here we present new 40Ar/39Ar laser age dates, major and trace element data, and initial Sr-Nd-Pb isotope ratios. The 124– 109 Ma tholeiitic portions of the Santa Elena complex formed in a primitive island arc setting, believed to be part of the Chortis subduction zone. The geochemical similarities between the Santa Elena and Tortugal alkaline volcanic rocks suggest that Chortis block may extend south of the Hess Escarpment. The Nicoya, Herradura, Golfito, and Burica complexes and the tholeiitic Tortugal unit formed between 95 and 75 Ma and appear to be part of the Caribbean Large Igneous Province, thought to mark the initiation of the Gala´pagos hotspot. The Quepos and Osa complexes (65–59 Ma) represent accreted sections of an ocean island and an aseismic ridge, respectively, interpreted to reflect part of the Gala´pagos paleo-hotspot track. An Oligocene unconformity throughout Central America may be related to the mid-Eocene accretion of the Quepos and Osa complexes.

Sr‐Nd‐Pb composition of Mesozoic Pacific oceanic crust (Site 1149 and 801, ODP Leg 185): Implications for alteration of ocean crust and the input into the Izu‐Bonin‐Mariana subduction system

We report Sr, Nd and Pb isotopic compositions of sediments and variably altered igneous rocks from ODP Site 801 (Marianas) and ODP Site 1149 (Izu-Bonin). These Sites provide the most complete drilled ocean crust sections located in front of the Mariana and Izu-Bonin trenches and characterize the unmodified isotopic input into these subduction zones. The subducted ocean crust belongs to the oldest (130–167 Ma) in situ Pacific Ocean crust and thus has end-member character with respect to alteration and sediment load. The lithostratigraphic division of sedimentary units at Site 1149 into clays, cherts, lower clays and carbonates with clay is reflected on isotope correlation diagrams. The Pb isotope data of the sediments show much greater variation than previously reported from this region. Particularly noteworthy are zeolite-bearing clays and clay bearing carbonates from the lower Units that have Pb isotopic compositions identical to the Izu Volcanic Front. The basaltic basement samples display variable 87Sr/86Sr ratios at near constant 143Nd/144Nd ratios, indicating mixing with seawater derived Sr. Most basaltic samples from Site 1149 and 801 exhibit highly variable 206Pb/204Pb (17.88–20.00) at near constant 207Pb/204Pb and 208Pb/204Pb ratios. Three samples from Site 801 display the most extreme 206Pb/204Pb (23.70–26.86) and 207Pb/204Pb (15.73–15.83) ratios ever measured in altered MORB reflecting an increase of 238U/204Pb ratios (μ), most likely through addition of seawater derived U. Initial Pb isotopes of most samples overlap with the age corrected field of the Pacific MORB source, thus the increase in μ took place shortly after formation of the crust in most samples. According to our new isotope data the radiogenic end-member of the Izu arc volcanic rocks could either represent Pb from the lower sediment column released from the slab by delayed dewatering or an integrated slab fluid in which 90–95% of the Pb comes from the basaltic crust and 5–10% of the Pb from the sediments. The Pb isotope systematics of the Mariana arc output suggest two component mixing. Both components appear to be input derived with the radiogenic component represented by average Site 801 sediment and the unradiogenic component generated by mixing of ∼80% unaltered crust with ∼20% highly altered crust.

Large volume recycling of oceanic lithosphere over short time scales: geochemical constraints from the Caribbean Large Igneous Province

Oceanic flood basalts are poorly understood, short-term expressions of highly increased heat flux and mass flow within the convecting mantle. The uniqueness of the Caribbean Large Igneous Province (CLIP, 92–74 Ma) with respect to other Cretaceous oceanic plateaus is its extensive sub-aerial exposures, providing an excellent basis to investigate the temporal and compositional relationships within a starting plume head. We present major element, trace element and initial Sr–Nd–Pb isotope composition of 40 extrusive rocks from the Caribbean Plateau, including onland sections in Costa Rica, Colombia and Curacao as well as DSDP Sites in the Central Caribbean. Even though the lavas were erupted over an area of ∼3×106 km2, the majority have strikingly uniform incompatible element patterns (La/Yb=0.96±0.16, n=64 out of 79 samples, 2σ) and initial Nd–Pb isotopic compositions (e.g. 143Nd/144Ndin=0.51291±3, ϵNdi=7.3±0.6, 206Pb/204Pbin=18.86±0.12, n=54 out of 66, 2σ). Lavas with endmember compositions have only been sampled at the DSDP Sites, Gorgona Island (Colombia) and the 65–60 Ma accreted Quepos and Osa igneous complexes (Costa Rica) of the subsequent hotspot track. Despite the relatively uniform composition of most lavas, linear correlations exist between isotope ratios and between isotope and highly incompatible trace element ratios. The Sr–Nd–Pb isotope and trace element signatures of the chemically enriched lavas are compatible with derivation from recycled oceanic crust, while the depleted lavas are derived from a highly residual source. This source could represent either oceanic lithospheric mantle left after ocean crust formation or gabbros with interlayered ultramafic cumulates of the lower oceanic crust. High 3He/4He in olivines of enriched picrites at Quepos are ∼12 times higher than the atmospheric ratio suggesting that the enriched component may have once resided in the lower mantle. Evaluation of the Sm–Nd and U–Pb isotope systematics on isochron diagrams suggests that the age of separation of enriched and depleted components from the depleted MORB source mantle could have been ≤500 Ma before CLIP formation and interpreted to reflect the recycling time of the CLIP source. Mantle plume heads may provide a mechanism for transporting large volumes of possibly young recycled oceanic lithosphere residing in the lower mantle back into the shallow MORB source mantle.

Geodynamic evolution of the Galápagos hot spot system (Central East Pacific) over the past 20 m.y.: Constraints from morphology, geochemistry, and magnetic anomalies

[1] We report results of magnetic data from the Nazca Plate and of geochemical (major element and Sr-Nd-Pb-isotope) analyses of rocks dredged from the Galapagos hot spot tracks (Cocos, Carnegie, Malpelo and Coiba Ridges and adjacent seamounts) in the Central East Pacific. Magnetic anomalies indicate that the Malpelo and Carnegie Ridges were once attached and that seafloor spreading separated the two ridges between 14.5 Ma and 9.5 Ma. The variations in Sr-Nd-Pb isotopic composition show that three of the mantle components currently observed at the Galapagos (Central, Southern, and Eastern) existed in the hot spot for at least 20 m.y., whereas the Northern Galapagos mantle component has been present for at least ∼15 Ma. Our data are consistent with the existence of a compositionally zoned/striped Galapagos plume since ∼20 Ma. Combined constraints from the morphology of the hot spot tracks, the magnetic record, and the isotope geochemistry of the rock samples provide new insights into the hot spot-ridge geometry and interaction of the Galapagos hot spot with the Cocos-Nazca spreading center (CNS) over the past 20 m.y. At 19.5 Ma a ridge jump moved the spreading axis to the northern edge of the hot spot. Between 19.5 and 14.5 Ma, the spreading axis was located above the center of the hot spot. At 14.5 Ma, a new ridge jump moved the spreading axis to the south, splitting the paleo-Carnegie Ridge into the present Carnegie and Malpelo Ridges. The repeated ridge jumps reflect capture of the northwardly drifting spreading center by the Galapagos hot spot. At 11–12 Ma an offset of the spreading axis lay above the plume center. Spreading between the Carnegie and Malpelo Ridges continued until 9.5 Ma.

70 m.y. history (139-69 Ma) for the Caribbean large igneous province

It is commonly accepted that large igneous provinces are formed through catastrophic volcanic events occurring over vast areas within a few million years at the initiation of hotspots (mantle plumes). New 40Ar/39Ar ages (111–139 Ma) and geochemical results from the Nicoya Peninsula, Costa Rica, extend the age range of volcanism in the Caribbean large igneous province to 70 m.y. (69–139 Ma). Our results are not consistent with the formation of this vast igneous province through a single plume head at the initiation of a mantle plume such as the Galapagos. Instead we propose that multiple oceanic intraplate igneous structures, such as plateaus and hotspot tracks, were accumulated through the subduction process. The igneous structures could be remnants of the earlier history of the Galapagos hotspot, making it one of the oldest active hotspots on Earth. Alternatively they could have been derived from several spatially distinct mantle-melting events that sampled similar source material, e.g., oceanic lithosphere of similar age.

A Mid Cretaceous origin for the Galápagos hotspot: volcanological, petrological and geochemical evidence from Costa Rican oceanic crustal segments

Abstract The Quepos, Nicoya and Herradura oceanic igneous terranes in Costa Rica are conspicuous features of a Mid to Late Cretaceous regional magmatic event that encompasses similar terranes in Central America, Colombia, Ecuador and the Caribbean. The Quepos terrane (66 Ma), which consists of ol-cpx phyric, tholeiitic pillow lavas overlain by highly vesicular hyaloclastites, breccias and conglomerates, is interpreted as an uplifted seamount/ocean island complex. The Nicoya (∼90 Ma) and Herradura terranes consist of fault-bounded sequences of sediments, tholeiitic volcanics (pillow lavas and massive sheet flows) and plutonic rocks. The volcanic rocks were emplaced at relatively high eruption rates in moderate to deep water, possibly forming part of an oceanic plateau. Major and trace element data from Nicoya/Herradura tholeiites indicate higher melting temperatures than inferred for normal mid-ocean-ridge basalts (MORB) and/or a different source composition. Sr–Nd–Pb isotopic ratios from all three terranes are distinct from MORB but resemble those from the Galápagos hotspot. The volcanological, petrological and geochemical data from Costa Rican volcanic terranes, combined with published age data, paleomagnetic results and plate tectonic reconstructions of this region, provide strong evidence for a Mid Cretaceous (∼90Ma) age for the Galápagos hotspot, making it one of the oldest known, active hotspots on Earth. Our results also support an origin of the Caribbean Plate through melting of the head of the Galápagos starting plume.

Galapagos‐OIB signature in southern Central America: Mantle refertilization by arc–hot spot interaction

[1] Although most Central American magmas have a typical arc geochemical signature, magmas in southern Central America (central Costa Rica and Panama) have isotopic and trace element compositions with an ocean island basalt (OIB) affinity, similar to the Galapagos-OIB lavas (e.g., Ba/La 10, 206Pb/204Pb > 18.8). Our new data for Costa Rica suggest that this signature, unusual for a convergent margin, has a relatively recent origin (Late Miocene ∼6 Ma). We also show that there was a transition from typical arc magmas (analogous to the modern Nicaraguan volcanic front) to OIB-like magmas similar to the Galapagos hot spot. The geographic distribution of the Galapagos signature in recent lavas from southern Central America is present landward from the subduction of the Galapagos hot spot tracks (the Seamount Province and the Cocos/Coiba Ridge) at the Middle American Trench. The higher Pb isotopic ratios, relatively lower Sr and Nd isotopic ratios, and enriched incompatible-element signature of central Costa Rican magmas can be explained by arc–hot spot interaction. The isotopic ratios of central Costa Rican lavas require the subducting Seamount Province (Northern Galapagos Domain) component, whereas the isotopic ratios of the adakites and alkaline basalts from southern Costa Rica and Panama are in the geochemical range of the subducting Cocos/Coiba Ridge (Central Galapagos Domain). Geological and geochemical evidence collectively indicate that the relatively recent Galapagos-OIB signature in southern Central America represents a geochemical signal from subducting Galapagos hot spot tracks, which started to collide with the margin ∼8 Ma ago. The Galapagos hot spot contribution decreases systematically along the volcanic front from central Costa Rica to NW Nicaragua.

New constraints on the age and evolution of the Wishbone Ridge, southwest Pacific Cretaceous microplates, and Zealandia-West Antarctica breakup

We present analytical results from four dredge locations across the eastern Zealandia continental margin and adjacent ocean crust. The 115 Ma dacites dredged from the West Wishbone Ridge (WWR) are isotopically primitive, weakly adakitic, slab-derived lavas. The 97 Ma A-type granites and a basalt from the easternmost Chatham Rise enlarge the known area of postsubduction Gondwana magmatism. Amphibolite-grade schists from a fault block south of the Chatham Rise provide a critical bridge between the Zealandia and West Antarctica belts of Jurassic–Cretaceous accretionary prism rocks. The new recognition of the WWR as a remnant of a 115 Ma intraoceanic subduction system means that previous hypotheses of the WWR as a fracture zone or spreading ridge require modification. The dacite ages constrain the start of Osbourn Trough spreading, which caused breakup of the Hikurangi-Manihiki igneous plateau, to before 115 Ma. We speculate that, after 115 Ma, the WWR was rifted by an intraoceanic spreading center that developed along its southeast side. Impingement of this spreading center against the Gondwana margin led to widespread 95–100 Ma postsubduction magmatism, variable lithospheric stretching, and ultimately continental splitting of Zealandia and West Antarctica across basement trends.

Upwelling and melting of the Iceland plume from radial variation of 238U–230Th disequilibria in postglacial volcanic rocks

New 238U–230Th disequilibria data by thermal ionisation mass spectrometry are presented for a comprehensive set of postglacial basaltic lavas from the neovolcanic zones in Iceland. The new data show a striking systematic decrease in 230Th excess towards central Iceland and the presumed centre of the Iceland plume. This finding would appear paradoxical if source composition was the main factor responsible for generating the 238U–230Th disequilibria, because generally main rift lavas erupted proximal to the plume should be generated from a melting column that initiates deeper in the garnet stability field, compared to the marginal rift zones. Preferential crustal interaction in central Iceland, where the crust is thickest, involving either old (>350 kyr) Icelandic crust or lower crustal melts, may provide a viable explanation for only part of the data variation, namely the moderately low 238U–230Th disequilibria found in the more evolved SE rift lavas. Moreover, there is no variation of 230Th excesses with degree of differentiation (Mg# or ppm Th) overall, or within individual rift systems, to indicate that crustal contamination causes the radial variation in 230Th excess. The 238U–230Th disequilibria variation is therefore ascribed to variable dynamic parameters in the melting regime induced by interaction of the Iceland plume with the rift systems. The higher 230Th excesses in alkalic off-rift lavas (Snaefellsnes Peninsula) (24±3%) compared to the main rift lavas (15±3%) is consistent with more garnet-rich lithologies dominating the bulk melt compositions away from the main rifts and indicates small-scale source heterogeneity beneath Iceland. The data are reconciled within a model in which mantle upwelling rates in the centre of the plume are significantly faster than at the margins, consistent with fluid dynamic predictions for a plume head. The radial variation observed in (230Th/238U) provides independent support that the centre of the Iceland plume is located beneath SE Iceland, as has been proposed from seismic tomographic studies. For a reasonable range of mantle porosities (Φ=0.05–0.2%) we can explain the Iceland data with a dynamic melting model, by relatively fast mantle upwelling rates in the centre (∼5–20 cm/yr), compared to those at the margins (∼1–4 cm/yr). The radial variation is also shown to be consistent with, though not requiring, a model of deep dehydration melting [Ito et al., Earth Planet. Sci. Lett. 165 (1999) 81–96]. In such a scenario, the generation of (moderately) low 238U–230Th disequilibria will be confined to the lowermost part of the melting column, which is characterised by fast upwelling and low porosity. For Φ values down to 0.05% in the lower part of the hydrous melting zone, moderately low 230Th excesses (5–10%) are likely to result, whereas higher 230Th excesses may arise for lower values of Φ.