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2018
Castillo, PR, Macisaac C, Perry S, Veizer J.  2018.  Marine carbonates in the mantle source of oceanic basalts: Pb isotopic constraints. Scientific Reports. 8   10.1038/s41598-018-33178-4   AbstractWebsite

For almost fifty years, geochemists have been interpreting the clues from Pb isotopic ratios concerning mantle composition and evolution separately. The Pb isotopes of ocean island basalts (OIB) indicate that their mantle source is heterogeneous, most likely due to the presence of end-components derived from recycled crust and sediment. Some OIB have unusually high Pb-206/Pb-204 coming from one of the end-components with a long time-integrated high U-238/Pb-204 or mu (HIMU). Most OIB and many mid-ocean ridge basalts (MORB) also have high Pb-206/Pb-204, indicating a HIMU-like source. Moreover, measured Th-232/U-238 (kappa) for most MORB are lower than those deduced from their Pb-208/Pb-204 and Pb-206/Pb-204. Such high mu and low kappa features of oceanic basalts are inconsistent with the known geochemical behavior of U, Pb and Th and temporal evolution of the mantle; these have been respectively termed the 1st and 2nd Pb paradox. Here we show that subducted marine carbonates can be a source for HIMU and a solution to the Pb paradoxes. The results are consistent with the predictions of the marine carbonate recycling hypothesis that posits the Pb isotopes of oceanic basalts indicate a common origin and/or magma generation process.

2016
Castillo, PR.  2016.  A proposed new approach and unified solution to old Pb paradoxes. Lithos. 252:32-40.   10.1016/j.lithos.2016.02.015   AbstractWebsite

One of the most remarkable features of many and, perhaps, all oceanic basalts is that their Pb isotopic ratios ((206)pb/(204)pb, Pb-207/Pb-204 and (208)pb/Pb-204) are too radiogenic to be coming from the undifferentiated mantle or bulk silicate Earth. This has created three major concerns in the behavior of U, Th and Pb in the Earth's mantle that have been termed the Pb paradoxes. These are the unexpectedly long time-integrated high U/Pb (1st paradox), long time-integrated low Th/U (2nd paradox) and constant Ce/Pb and Nb/U (3rd paradox) in the mantle sources of oceanic basalts. The origins of such unexpected ratios have been the object of intense studies that produced several highly significant, but generally individualized results during the last four decades. Detailed analysis of available data shows that the paradoxes are closely interrelated as they all pertain to the mantle and have many common characteristic features. Thus, the Pb paradoxes constitute a system of equations that must be solved all together as each solution must satisfy every equation in the system. For example, compositional data for the voluminous mid-ocean ridge basalts (MORE) show that the 1st and 2nd paradoxes exhibit a long time-integrated enrichment of U and the Th/U and Nb/Th ratios are also constant. A single solution to simultaneously explain the paradoxes in MORE is possible if recycled materials with variable enrichments in incompatible trace elements, particularly U and its daughter Pb* plus Nb, Ce, and Th are added to or mixed with the depleted upper mantle. Significantly, a similar binary mixing solution has been proposed for the Pb paradoxes in ocean island basalts. (c) 2016 Elsevier B.V. All rights reserved.

2015
Castillo, PR.  2015.  The recycling of marine carbonates and sources of HIMU and FOZO ocean island basalts. Lithos. 216:254-263.   10.1016/j.lithos.2014.12.005   AbstractWebsite

Many, and perhaps all, oceanic island basalts (OIB) clearly contain a component of crustal materials that have been returned to the mantle through subduction or other processes. One of the first recycled materials to be identified as a potential source of OIB was mid-ocean ridge basalt (MORE), and this was later fine-tuned as having a long time-integrated (b.y.) high U/Pb ratio or high mu (HIMU) and producing OIB with the most radiogenic Pb isotopic ratios (Pb-206/Pb-204 > 20). However, it is becoming more evident that the compositional connection between subducted MORE and HIMU basalts is problematic. As an alternative hypothesis, a small amount (a few %) of recycled Archaean marine carbonates (primarily CaCO3) is proposed to be the main source of the distinct Pb-206/Pb-204, Pb-207/Pb-204 and Sr-87/Sr-86 isotopic and major-trace element compositions of classic HIMU and post-Archaean marine carbonates for younger HIMU or the so-called FOZO mantle source. As an extension of the hypothesis, a conceptual model that combines the separate evolutionary histories of ancient oceanic lithosphere, which is the source of OIB, and upper mantle, which is the source of MORE, is also proposed. The model claims that FOZO mainly consists of the lithospheric mantle portion of the ancient metamorphosed oceanic slabs that have accumulated in the deep mantle. Such an ultramafic source is geochemically depleted due to prior extraction of basaltic melt plus removal of the enriched subduction component from the slab through dehydration and metamorphic processes. Combined with other proposed models in the literature, the conceptual model can provide reasonable solutions for the Pb-208/Pb-204, Nd-143/Nd-144, Hf-176/Hf-177 and He-3/He-4 isotopic paradoxes or complexities of oceanic lavas. Although these simultaneous solutions for individual paradoxes are qualitative and non-unique, these are unified under a single, marine carbonate recycling hypothesis. 10 2014 Elsevier B.V. All rights reserved.

2001
Janney, PE, Castillo PR.  2001.  Geochemistry of the oldest Atlantic oceanic crust suggests mantle plume involvement in the early history of the central Atlantic Ocean. Earth and Planetary Science Letters. 192:291-302.   10.1016/s0012-821x(01)00452-6   AbstractWebsite

Controversy has surrounded the issue of whether mantle plume activity was responsible for Pangaean continental rifting and massive flood volcanism (resulting in the Central Atlantic Magmatic Province or CAMP, emplaced around 200 Ma) preceding the opening of the central Atlantic Ocean in the Early Mesozoic. Our new Sr-Nd-Pb isotopic and trace element data for the oldest basalts sampled from central Atlantic oceanic crust by deep-sea drilling show that oceanic crust generated from about 160 to 120 Ma displays clear isotopic and chemical signals of plume contamination (e.g., (87)Sr/(86)Sr(i) = 0.7032-0.7036, epsilon (Nd)(t) = +6.2 to +8.2, incompatible element patterns with positive Nb anomalies), but these signals are muted or absent in crust generated between 120 and 80 Ma, which resembles young Atlantic normal mid-ocean ridge basalt. The plume-affected pre- 120 Ma Atlantic crustal basalts are isotopically similar to lavas from the Ontong Java Plateau, and may represent one isotopic end-member for CAMP basalts. The strongest plume signature is displayed near the center of CAMP magmatism but the hotspots presently located nearest this location in the mantle reference frame do not appear to be older than latest Cretaceous and are isotopically distinct from the oldest Atlantic crust. The evidence for widespread plume contamination of the nascent Atlantic upper mantle, combined with a lack of evidence for a long-lived volcanic chain associated with this plume, leads us to propose that the enriched signature of early Atlantic crust and possibly the eruption of the CAMP were caused by a relatively short-lived, but large volume plume feature that was not rooted at a mantle boundary layer. Such a phenomenon has been predicted by recent numerical models of mantle circulation. (C) 2001 Elsevier Science B.V. All rights reserved.

1999
Hilton, DR, Gronvold K, Macpherson CG, Castillo PR.  1999.  Extreme He-3/He-4 ratios in northwest Iceland: constraining the common component in mantle plumes. Earth and Planetary Science Letters. 173:53-60.   10.1016/s0012-821x(99)00215-0   AbstractWebsite

Olivine and clinopyroxene phenocrysts contained in late Tertiary basalts from Selardalur, northwest Iceland, carry volatiles with the highest helium isotope ratio yet reported for any mantle plume. He-3/He-4 ratios measured on three different samples and extracted by stepped crushing in vacuo fall consistently similar to 37 R-A (R-A = air He-3/He-4) - significantly higher than previously reported values for Iceland or Loihi Seamount (see K.A. Farley, E. Neroda [Annu. Rev. Earth Planet. Sci. 26 (1998) 189-218]). The Sr, Nd and Ph isotopic composition of the same sample places it towards the center of the mantle tetrahedron of Hart et al. (S.R. Hart, E.H. Hauri, L.A. Oschmann, J.A. Whitehead [Science 256 (1992) 517-520]) - in exactly the region predicted for the common mantle endmember based on the convergence of a number of pseudo-linear arrays of ocean island basalts worldwide (E.H. Hauri, J.A. Whitehead, S.R. Hart [J. Geophys. Res. 99 (1994) 24275-24300]). This observation implies that Selardalur may represent the best estimate available to date of the He-Sr-Nd-Pb isotopic composition of the 5th mantle component common to many mantle plumes. (C) 1999 Elsevier Science B.V. All rights reserved.

1998
Hawkins, JW, Castillo PR.  1998.  Early history of the Izu-Bonin-Mariana arc system: Evidence from Belau and the Palau Trench. Island Arc. 7:559-578.   10.1046/j.1440-1738.1998.00210.x   AbstractWebsite

Volcanic rocks of the Kyushu-Palau Ridge (KPR) from Deep Sea Drilling Project (DSDP) site 448 and from Belau comprise a low-to-medium-K are tholeiitic series. Belau rocks include (probable) Mid-Eocene low-Ca type-3 boninite and pre-Early Oligocene-Early Miocene low-K are tholeiitic basalt, basaltic andesite, andesite and dacite. Palau Trench samples include sparsely phyric high-Prig, -Cr and -Ni Pocks which resemble the Belau boninite and Izu-Bonin - Mariana (IBM) system boninites. The high-Mg Palau Trench samples also resemble other primitive are lavas (e.g. ape picrites). Their chemistry suggests an origin involving steep thermal gradients in multiply depleted mantle. Subduction of hot, young lithosphere under a young hot upper plate is postulated to explain this occurrence. The KPR is inferred to be the source of Eocene boninite and are tholeiitic terranes presently in forearc regions of the IBM system. A model is presented here showing how many IBM boninites may have originated in a small area near Belau. These have migrated eastward by episodic back-are opening accompanying eastward migration of arcs and trenches. Oldest known KPR rocks (ca 47.5 Ma at DSDP site 296), and presumed KPR-derived exotic terranes of Guam (ca 43.8 Ma), presage the postulated Eocene (en 42-43 Ma) change in Pacific plate motion invoked as the cause of subduction initiation at the KPR. The KPR has been rotated more than 40 degrees clockwise since the Eocene, thus the age mismatch may indicate a different tectonic style, for example transtension or transpression, in earliest KPR history.

Tarduno, JA, Brinkman DB, Renne PR, Cottrell RD, Scher H, Castillo P.  1998.  Evidence for extreme climatic warmth from Late Cretaceous Arctic vertebrates. Science. 282:2241-2244.   10.1126/science.282.5397.2241   AbstractWebsite

A Late Cretaceous (92 to 86 million years ago) vertebrate assemblage from the high Canadian Arctic (Axel Heiberg Island) implies that polar climates were warm (mean annual temperature exceeding 14 degrees C) rather than near freezing. The assemblage includes Large (2.4 meters Long) champsosaurs, which are extinct crocodilelike reptiles. Magmatism at six Large igneous provinces at this time suggests that volcanic carbon dioxide emissions helped cause the global warmth.

1996
Graham, DW, Castillo PR, Lupton JE, Batiza R.  1996.  Correlated He and Sr isotope ratios in South Atlantic near-ridge seamounts and implications for mantle dynamics. Earth and Planetary Science Letters. 144:491-503.   10.1016/s0012-821x(96)00172-0   AbstractWebsite

He-4/He-3 and Sr-87/Sr-86 ratios are highly anti-correlated for a suite of seamount glasses from both sides of the Mid-Atlantic Ridge at 26 degrees S; the linear correlation coefficient (r(2)) is 0.99 for 5 localities at 3 different seamounts. The seamounts are located on crust up to 2.5 myr old, and have He-4/He-3 as low as 65,400 (He-3/He-4 = 11 R(A)) and Sr-87/Sr-86 as high as 0.70350. These isotopic values are significantly lower and higher, respectively, than those for basaltic glasses recovered from 13 localities along the adjacent ridge axis, where the lowest He-4/He-3 ratio is 92,000 (He-3/He-4 = 7.8 R(A)) and the highest (87)/(86) Sr is 0.70258. Geophysical studies and the small (1-2%) degree of helium isotope disequilibrium between vesicles and glass for three seamount lavas suggest that the seamounts formed on or near the ridge axis. Because no off-ridge hotspots are present in this area, formation of the seamounts probably involved capture by the ridge of a passive mantle heterogeneity of 'blob' during rift propagation and tectonic evolution of the Moore fracture zone. The He-Sr-Nd-Pb isotopic results for the seamounts show a general trend toward compositions observed for the Reunion hotspot in the Indian Ocean. Collectively, the seamount and ridge axis results are somewhat enigmatic. In addition to the highly correlated He and Sr isotopes at the seamounts, a fair correlation exists between He and Nd isotopes (r(2) = 0.70). in contrast, a correlation between He and Pb isotopes is absent for the seamount glasses, while an independent, positive correlation exists between He-4/He-3 and Pb-206/Pb-204 for axial lavas. Apparently, different processes are responsible for the seamount He-Sr-Nd isotope relationships and for the nearby ridge He-Pb isotope relationship. If these relations are only of local significance and result from complications inherent in multi-stage mixing of more than two mantle components, then they imply that the upper mantle may contain domains with variable 4He/ 3He ratios, in some cases significantly lower than 80,000 (He-3/He-4 > 9 R(A)), On the other hand, binary mixing adequately explains the linear He-Sr isotope trend in the seamount lavas. This linear trend suggests similar He-3/Sr-86 ratios in the local MORE mantle source and in the source region of the low He-4/He-3 blob, which is most likely the lower mantle or the transition zone region. This similarity in He-3/Sr-86 is inconsistent with a lower mantle 3 He/Sr-86 ratio that exceeds the upper mantle ratio by at least a factor of 501 deduced from geochemical models of mantle evolution. Consequently, rare gas models involving a steady-state upper mantle and quasi-closed lower mantle may be inappropriate if applied at length scales on the order of similar to 100 km, characteristic of mid-ocean ridge segments.

Janney, PE, Castillo PR.  1996.  Basalts from the Central Pacific Basin: Evidence for the origin of Cretaceous igneous complexes in the Jurassic western Pacific. Journal of Geophysical Research-Solid Earth. 101:2875-2893.   10.1029/95jb03119   AbstractWebsite

Studies of marine magnetic anomalies suggest that oceanic crust of Jurassic age underlies the Nauru, East Mariana and northwestern Central Pacific basins of the west central Pacific Ocean. However, the Deep Sea Drilling Project (DSDP) and Ocean Drilling Program have only recovered basalts of Cretaceous age from these basins, indicating either that large areas of the Jurassic western Pacific are covered by Cretaceous intraplate igneous complexes or that Cretaceous ocean crust is present in these areas. We present chemical and isotopic data on basalts and dolerites recovered by DSDP Leg 17 from the Central Pacific Basin(CPB). Drilling in the predicted Jurassic-age portion of the CPB recovered Late Albian (100-105 Ma) tholeiitic pillow basalts at Site 169 and Late Cretaceous alkalic dolerite sills at Sites 170 and 169 above the extrusives. Early Cretaceous crust was recovered from Site 166. The Site 169 tholeiites are LREE depleted but slightly enriched in highly incompatible elements relative to normal mid-ocean ridge basalt (MORE), giving them trace element ratios similar to MORE erupted near hot spots. The Sr, Nd, and Pb isotopic compositions of the tholeiites (Sr-87/Sr-86(i)=0.70341-0.70348; epsilon(Nd)(t) = +6.2-6.4; Pb-206/(204)pb(meas)=18.63-18.68) overlap with MORB from the Indian Ocean, but fall outside of the Sr and Nd isotopic ranges for Pacific MORE. The Site 169 tholeiites are compositionally almost identical to basalts from the Nauru and East Mariana basins and are isotopically similar to some Ontong Java Plateau basalts. Site 166 crustal lavas are similar to normal-MORE from the East Pacific Rise. Chemical and isotopic data for the Site 169 tholeiites are consistent with an origin at a spreading center contaminated with EM I-type plume materials, probably from the Ontong Java plume head. Based on geochemical and geophysical data from the region, we propose that the Site 169 tholeiites, as well as basalts from the Nauru and East Mariana basins, were created at a system of short-lived mid-Cretaceous spreading centers extending from the East Mariana Basin into the northwestern Central Pacific Basin, and that rifting of Jurassic crust was initiated as a result of the rapid formation of Ontong Java Plateau. The Sites 169 and 170 sills appear to have been intruded as a result of near-ridge, non-hot spot volcanism similar to that producing young seamounts in the eastern Pacific today. However, the intrusion of these sills, as well as their HIMU (high mu) isotopic affinity, may have been influenced by nearby mantle plumes.

1994
Castillo, PR, Pringle MS, Carlson RW.  1994.  East Mariana Basin Tholeiites - Cretaceous Intraplate Basalts of Rift Basalts Related to the Ontong Java Plume. Earth and Planetary Science Letters. 123:139-154.   10.1016/0012-821x(94)90263-1   AbstractWebsite

Studies of seafloor magnetic anomaly patterns suggest the presence of Jurassic oceanic crust in a large area in the western Pacific that includes the East Mariana, Nauru and Pigafetta Basins. Sampling of the igneous crust in this area by the Deep Sea Drilling Program (DSDP) and the Ocean Drilling Program (ODP) allows direct evaluation of the age and petrogenesis of this crust. ODP Leg 129 drilled a 51 m sequence of basalt pillows and massive flows in the central East Mariana Basin. Ar-40/Ar-39 ages determined in this study for two Leg 129 basalts average 114.6 +/- 3.2 Ma. This age is in agreement with the Albian-late Aptian paleontologic age of the overlying sediments, but is distinctively younger than the Jurassic age predicted by magnetic anomaly patterns in the basin. Compositionally, the East Mariana Basin basalts are uniformly low-K tholeiites that are depleted in highly incompatible elements compared to moderately incompatible ones, which is typical of mid-ocean ridge basalts (MORB) erupted near hotspots. The Sr, Nd and Pb isotopic compositions of the tholeiites (Sr-87/Sr-86(init) = 0.70360-0.70374; Nd-143/Nd-144(init) = 0.512769-0.512790; Pb-206/Pb-204(meas) = 18.355-18.386) also overlap with some Indian Ocean Ridge MORB, although they are distinct from the isotopic compositions of Jurassic basalts drilled in the Pigafetta Basin, the oldest Pacific MORB. The isotopic compositions of the East Mariana Basin tholeiites are also similar to those of intraplate basalts, and in particular, to the isotopic signature of basalts from the nearby Ontong Java and Manihiki Plateaus. The East Mariana Basin tholeiites also share many petrologic and isotopic characteristics with the oceanic basement drilled in the Nauru Basin at DSDP Site 462. In addition, the new 110.8 +/- 1.0 Ma Ar-40/Ar-39 age for two flows from the bottom of Site 462 in the Nauru Basin is indistinguishable from the age of the East Mariana Basin flows. Thus, while magnetic anomaly patterns predict that the igneous basement in the Nauru and East Mariana Basins is Jurassic in age, the geochemical and chronological results discussed here suggest that the basement formed during a Cretaceous rifting event within the Jurassic crust. This magmatic and tectonic event was created by the widespread volcanism responsible for the genesis of the large oceanic plateaus of the western Pacific.