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The role of Quaternary ice sheet fluctuations in driving meltwater pulses and ocean circulation perturbations is widely acknowledged. What is less clear is the role of these processes in driving changes in past atmospheric dust activity, and possible wider links between dust and climate. Terrestrial windblown dust (loess) deposits along the northern fringe of the European loess belt potentially record past atmospheric dust emission from regions close to the former Eurasian Ice Sheet (EIS) and provide a means to evaluate the role of ice sheet fluctuations in the past dust cycle. Numerical loess chronologies across this region generally agree on greatly enhanced dust deposition rates during MIS 2, when the EIS reached its maximum extent. Yet, uncertainties over the sources of this material prevent understanding of the precise causes of this greatly enhanced atmospheric dustiness, and any potential link to ice sheet fluctuations and climate. In southeast England, loess accumulation dominantly occurred in two phases centered on 25–23.5 ka and 20–19 ka, matching the timing of coalescence of the Fennoscandian and British-Irish ice sheets and specifically advances and retreats of nearby ice lobes in the western North Sea. As such, these deposits provide an ideal test of the role of ice sheet fluctuations in atmospheric dust dynamics. Here we undertake such a test through a detailed provenance study of loess in southeast England and potential dust source sediments across the North Sea region. We group extensive new and published data sets of detrital zircon U–Pb ages from basement rocks and Cenozoic sediments in the North Sea area, which not only provide new insight into both loess source, but also the nature of sediment transport over NW Europe into the North Sea basin more widely. Multi-proxy evidence allows us to unambiguously identify ice sheet derived sediments in the exposed North Sea basin as the dominant source of loess in southeast England, while fluvial sediments

New zircon U-Pb age measurements, whole rock major and trace element geochemistry, and Sr and Nd isotopic analyses of samples from fourteen deep drill holes that penetrated the hidden Precambrian basement of the southernmost Baltic Sea and the coastal area of northern Poland (Pomerania), make it possible to identify a two episodes of Proterozoic magmatism in that area. The basement consists of late Palaeoproterozoic deformed calc-alkaline, magnesian, I-type to A-type diorites to granites of volcanic arc affinity. U-Pb zircon geochronology documents their magmatic crystallization ages to be between 1791 ± 8 Ma and 1750 ± 5 Ma, with an episode of syn- to late-magmatic deformation recorded in thin overgrowths on zircons at about 1740 Ma. These rocks from Pomerania and its offshore area broadly correlate with the bedrock of Blekinge in southern Sweden, where most of the crust was formed at 1.77–1.75 Ga. They may thus be part of the same geological domain, extending on both sides of the present-day southern Baltic Sea, formed along a late Palaeoproterozoic active continental margin. A subordinate suite of undeformed, significantly younger A-type granites was emplaced at 1477 ± 6 Ma, 1449 ± 7 Ma and 1450 ± 9 Ma. This time interval is concurrent with emplacement of A-type granitoids on the Danish island of Bornholm as well as in Blekinge and other parts of southern Fennoscandia. However, their geochemical and isotopic data highlight a genetic diversity of these granites.

The ability to trace and quantify sediment provenance in northwestern Patagonia is increasingly needed to properly understand modern sediment erosion and transport processes in this rapidly changing environment, and to accurately interpret sediment records from adjacent basins in terms of climate and environmental change. Nonetheless, no study so far has systematically evaluated the effectiveness of different tracers to reconstruct sediment provenance in this region. To fill this gap, we assess the effectiveness of commonly-used provenance indicators, including bulk mineralogy, major and rare earth element (REE) geochemistry, and Sr and Nd isotopes, to reconstruct sediment provenance in northwestern Patagonia. First, the ability of these tracers to discriminate between the main sources of sediment in the region is investigated, mostly using data compiled from the literature. Then, the potential of these tracers for provenance reconstruction is assessed by comparing the composition of sediments from six major Chilean rivers between 44 and 48°S to lithological proportions in their respective watersheds. The results suggest that mineralogy, major element geochemistry, and REE geochemistry can be used as qualitative tracers of sediment provenance. However, the compositional overlap between the sources and the relatively large variability within them prevent quantitative reconstructions. By comparison, 87Sr/86Sr and εNd allow to clearly differentiate between the sources, most likely due to significant age differences between the main lithologies, and to estimate the relative contribution of each source. End-member mixing results based on Sr and Nd isotopes show that the relative source contributions are in general agreement with the lithological proportions in the river watersheds. Differences between estimated contributions and lithological proportions in the watersheds are interpreted as the result of the high regional precipitation gradient and unequal glacier distrib, SCOPUS: ar.j, info:eu-repo/semantics/published

The Mozambique Channel plays a key role in the exchange of water masses between the Indian and Atlantic Oceans, which include the North Atlantic Deep Water (NADW) inflow from the south and the North Indian Deep Water (NIDW), an aged form of the NADW spreading poleward from the northern and equatorial Indian Ocean basin. Several authors assume that the Davie Ridge acts as a topographic barrier to the northward advection of NADW, which would therefore be absent in the Comoros Basin. Other studies suggest that the NADW flows from the south of the Mozambique Channel to the Comoros Basin, indicating that the Davie Ridge may not currently constitute a blocking topographic barrier to deep water mass circulation. To address this question, we studied ferromanganese (Fe, Mn) crusts collected over 2000 km in the Mozambique Channel, from the Agulhas Plateau to the Glorieuses Islands. Neodymium (Nd) isotope compositions (εNd) of surface scrapings range between εNd = −10.1 above the Agulhas Plateau, which might reflect the NADW inflow, and more radiogenic values between εNd = −8.0 and − 8.2 in the Glorieuses area, highlighting the NIDW influence. However, value of εNd = −9.4 measured north of the Davie Ridge cannot be explained by the sole influence of the NIDW and therefore highlights the advection of the NADW northeast of the Comoros Basin. We estimate that the contribution of the NADW through the channel is up to 68% in the Agulhas Plateau and 60% north of the Davie Ridge. These findings are consistent with previous hydrographic studies and suggest that the Davie Ridge does not currently act as topographic barrier to deep currents.

Eoarchean mantle and mantle-derived rocks can provide primary information on geodynamic processes operating on the early Earth. This study combines new petrological observations, comprehensive major and trace element data as well as Lu-Hf and Sm-Nd isotope compositions of >3.81 Ga ultramafic rocks from the Itsaq Gneiss Complex (IGC) in southern West Greenland. The sample set includes mantle peridotites and associated amphibolites from the Narssaq ultramafic body (Færingehavn terrane) and from the region south of the Isua supracrustal belt (Isukasia terrane). Lutetium-Hf whole rock age regression lines mainly yield Eoarchean ages of ca. 3.9–3.8 Ga, in good agreement with minimum ages inferred from field relationships (>3.8 Ga). Major and trace element signatures, the Lu-Hf isotope inventory as well as most major elements, MREE, HREE, and HFSE were only slightly disturbed during metamorphic overprint. Nearly flat primitive mantle-normalized REE patterns obtained for the mantle peridotites resemble those of refertilized modern abyssal peridotites and may reflect re-enrichment of initially depleted peridotite by melt-like subduction components, as also indicated by Th-HFSE-REE characteristics. Based on a simple evolution-model for the investigated mantle rocks, we suggest that the compositions are best explained by partial hydrous melt depletion in the spinel stability field, followed by refertilization by low quantities of adakite-like melt. Altogether, the geochemical data can be put in the framework of a geodynamic model, where Eoarchean mantle underwent significant melt extraction and subsequent re-fertilization by subduction-like components. Based on this finding, we propose that the Eoarchean mantle peridotites from SW Greenland represent remnants of a mantle wedge, confirming that subduction-like processes were in operation since at least the Eoarchean.

Resolving the possible mantle and crustal sources for shergottite meteorites is crucial for understanding the formation and early differentiation of Mars. Orbiter and rover characterization of the martian surface reveal that the major element composition of most of its surface does not match the shergottites (McSween et al. 2009) leaving the relationship between them poorly understood. The identification of the meteorite NWA 7034 and its pairs as a Mars surface rock (Cartwright et al. 2014) provides access to a representative sample of Mars' crust (Agee et al. 2013; Humayun et al. 2013). Utilizing the short-lived 146Sm–142Nd, and long-lived 147Sm–143Nd and 176Lu–176Hf chronometers, which are sensitive to silicate differentiation, we analyzed three fragments of NWA 7034. The very negative mean isotopic compositions for this breccia, μ142NdJNdi-1=−45±5 (2SD), ε143NdCHUR=−16.7±0.4 (2SD) and ε176HfCHUR=−61±9 (2SD) point to an ancient origin for this martian crust. However, modeling of the data shows that the crust sampled by NWA 7034 possesses a Hf/Nd ratio and coupled ε143Nd–μ142Nd model age that are incompatible with this crustal reservoir being an end-member that generated the shergottite source mixing array. In addition, this crust is not juvenile, despite its rare earth element profile, but has had a multistage formation history. Therefore, early crustal extraction alone was not responsible for the creation of the reservoirs that produced the shergottites. Instead mantle reservoirs formed via other early differentiation processes such as in a Mars magma ocean must be responsible for the trace element and isotopic signatures present in shergottites., SCOPUS: ar.j, info:eu-repo/semantics/published

We present new geochemical and Nd isotopic data on two Mesoproterozoic Listvyanka (1350 ± 6 Ma) and Goloustnaya (1338 ± 3 Ma) mafic dyke swarms located in the Irkutsk Promontory of the southern part of the Siberian craton. Listvyanka dykes are sub-vertical with NNE trend, while Goloustnaya dykes are characterized by prevailing W trend. Listvyanka and Goloustnaya dykes are composed of medium to coarse grained dolerites. All dolerites correspond to sub-alkaline tholeiitic basalts according to their major-element compositions with lower to moderate mg#, varying from 36 to 54. The trace and rare earth element abundances in Listvyanka and Goloustnaya dolerites are generally close to basalts of the oceanic island basalts (OIB) type. The Listvyanka dolerites demonstrate slight

The Arabian–Nubian Shield (ANS) represents a major site of juvenile Neoproterozoic crustal addition on Earth and documents Neoproterozoic tectonics bracketed by two supercontinent cycles, namely the fragmentation of Rodinia and the amalgamation of Gondwana. There is general consensus that the ANS formed by juvenile magmatic arc accretion and subsequent shield–wide post–tectonic magmatism. However, detailed understanding about the timing of events and the nature of magma sources in parts of the shield are lacking. To date, there are no isotopic data from the Paleozoic sedimentary sequences of the ANS, except those from the northern part. New zircon U–Pb, δ18O and whole–rock Nd isotopes are presented for plutonic rocks from the eastern Ethiopia, Yemen and southernmost Arabian Shield in Saudi Arabia. This thesis also presents the first combined in situ zircon U–Pb–O–Hf isotope data on the Cambrian–Ordovician sandstones of the Arabian Shield. The results are used to elucidate the crustal evolution of these parts of the ANS and to evaluate terrane correlations. Specifically, the nature of crustal growth, i.e., relative proportions of juvenile magmatic additions vs. crustal reworking, nature of the magma source and mechanism of crust formation (plume material vs. subduction zone enrichment) and understanding the provenance of the Cambrian–Ordovician sandstone sequences were important research questions addressed. The results from Paper I suggest that the eastern Ethiopian Precambrian basement is dominated by reworking of pre-Neoproterozoic supracrustal material unlike contemporaneous rocks in the remaining parts of Ethiopia— indicating the presence of two distinct lithospheric blocks of contrasting isotopic compositions in Ethiopia. Metamorphic age distributions suggest that the eastern Ethiopian block was amalgamated with the juvenile Western Ethiopian Shield during ca. 580–550 Ma. Importantly, the suture between them may represent the northern continuation of a major su, At the time of the doctoral defense, the following papers were unpublished and had a status as follows: Paper 3: Manuscript. Paper 4: Manuscript.

Results from new geologic mapping, SHRIMP U-Pb geochronology, and petrologic studies indicate that Mesoproterozoic basement in the northern French Broad massif near Mount Rogers consists of multiple, mostly granitic plutons, mapand outcrop-scale xenoliths of pre-existing crustal rocks, and remnants of formerly overlying meta-sedimentary lithologies. Zircon and titanite ages demonstrate that these rocks collectively record nearly 350 m.y. of tectonic evolution including periods of igneous intrusion at ca. 1190 to 1130 Ma (Early Magmatic Suite) and ca. 1075 to 1030 Ma (Late Magmatic Suite) and three episodes of regional metamorphism at ca. 1170 to 1140, 1070 to 1020, and 1000 to 970 Ma. The existence of ca. 1.3 Ga age crust is indicated by (1) orthogranofels of ca. 1.32 Ga age in a map-scale xenolith, (2) inherited zircons of ca. 1.33 to 1.29 Ga age in Early Magmatic Suite plutons, and (3) ca. 1.36 to 1.30 Ga age detrital zircons in meta-sedimentary lithologies. Mineral assemblages developed in amphibolites and granofelses indicate that metamorphism during both Mesoproterozoic episodes occurred at upper amphibolite-to lower granulite-facies conditions. Syn-orogenic Early Magmatic Suite plutons emplaced at ca. 1190 to 1145 Ma are characterized by high-K, variably magnesian, dominantly calc-alkalic compositions, and have trace-element characteristics indicative of continental-arc magmatic origin involving melting of thick continental crust. In contrast, ca. 1140 Ma age quartz syenite displays A-type features indicating derivation from depleted crustal sources with increased mantle input during waning stages of regional contraction. Plutons of the compositionally bimodal Late Magmatic Suite include (1) ca. 1060 Ma meta-granite with geochemical characteristics transitional between silicic rocks of arc systems and post-collisional granites of A-type lineage, and (2) ca. 1055 Ma monzodioritic rocks with A-type compositional characteristics that likely reflect derivation fro

Hydroclimate variability has exerted a fundamental control on the alternating deposition of organic-lean marl and organic-rich sapropel sediments in the eastern Mediterranean Sea (EMS). However, the exact mechanisms regarding the freshwater sources and related changes are still debated. Here, Sr and Nd isotopes and high-resolution elemental data are used to constrain different riverine and eolian supplies to the central Mediterranean over the past 9.8 ka. The detrital sediments in core CP10BC, taken at the margin of the Libyan shelf in the southwestern Ionian Sea, can be described by a three-endmember mixing system based on Sr and Nd isotopic compositions. The same systematics can also be deduced from Ti and K compositional variability. The endmembers comprise: Saharan Dust, Aegean/Nile, and Libyan Soil, representing the eolian supply from North Africa, the riverine inputs from the Aegean/Nile areas, as well as the riverine and shelf-derived fluxes from the Libyan-Tunisian margin, respectively. For the sapropel S1 period in particular, we find important detrital supplies from fossil river/wadi systems along the Libyan-Tunisian margin, activated by intensified African monsoon precipitation. Combining the temporal profiles with the consistent variability observed in the 87Sr/86Sr–1000/Sr diagram, such Libyan contribution has been most prominent during the uppermost period of sapropel S1 in core CP10BC. This observation is in agreement with hydroclimate reconstructions of northwestern Libya. Comparison of the Sr-Nd isotope data between core CP10BC and four cores taken along a west–east transect throughout the EMS shows that this detrital supply originated mainly from western Libya/Tunisia, and was transported as far eastward as ∼25°E while being diluted by an increasing Nile contribution.

Summer iron (Fe) fertilization in the Ross Sea has previously been observed in association with diatom productivity, lithogenic particles and excess Fe in the water column. This productivity event occurred during an early breakout of sea ice via katabatic winds, suggesting that aeolian dust could be an important source of lithogenic Fe required for diatom growth in the Ross Sea. Here we investigate the provenance of size-selected dust deposited on sea ice in McMurdo Sound, south-western (SW) Ross Sea. The isotopic signature of McMurdo Sound dust (0.70533< 87Sr/86Sr< 0.70915 and -1.1 < εNd(0) <3.45)confirms that dust is locally sourced from the McMurdo Sound debris bands and comprises a two-component mixture of McMurdo Volcanic Group and southern Victoria Land lithologies. In addition, the provenance of lithogenic sediment trapped in the water column was investigated, and the isotopic signature (εNd(0) =3.9, 87Sr/86Sr = 0.70434) is differentiated from long-range transported dust originating from South America and Australia. Elevated lithogenic accumulation rates in deeper sediment traps in the Ross Sea suggest that sinking articles in the water column cannot simply result from dust input at the surface. This discrepancy can be best explained by significant upwelling and remobilization of lithogenic Fe from the sea floor.

Altogether 1130 U-Pb analyses on zircons from 25 samples across the Pajala shear zone in northern Fennoscandia were performed by LA-ICPMS methodology to study the origin of the zone. The samples were also analyzed for their Sm-Nd isotope systematics and geochemically. The new data is tested with existing geological information to elaborate the provenance and maximum depositional ages, the stratigraphic position of studied samples, and finally to assess the tectonic evolution in the Pajala shear zone area. Chromium-enriched metasedimentary rocks are found within and to the east and west of the N-S trending Pajala shear zone. No material originating from Proterozoic felsic igneous (zircons) or mafic (Sm-Nd) rocks was found in these rocks and thus, only Neoarchean or very early Paleoproterozoic ages of deposition are possible. Our new results indicate that the bimodal 1.99-1.97 Ga supracrustal rocks of the Rovaniemi Supersuite cover a large area east of the Pajala shear zone. Based on the absence of Archean zircons typical of the metasedimentary rocks covering the Archean basement, it seems that the basement and its sedimentary cover were not exposed at the time of deposition of the Rovaniemi Supersuite. The metasedimentary rocks of the Uusivirka Supersuite, located within the Pajala shear zone, vary from hornblende-bearing metasedimentary rocks, metapelite, and meta-arkose to orthoquartzite. Their characteristic features include a dominant Proterozoic zircon population (65-87%), with a high proportion of analyzed grains yielding ages between 1.96 Ga and 1.91 Ga, and maximum depositional ages of 1.92-1.91 Ga. We record at least three metamorphic events; at ca. 1.92-1.90 Ga, ca. 1.85 Ga and at 1.82-1.78 Ga, of which the youngest can possibly be separated into two events at 1.83-1.82 Ga and 1.79-1.77 Ga, respectively. We propose a tectonic model in which continental breakup occurred at 2.1-2.05 Ga, followed by the development of a magmatic arc (Kittila arc) at ca. 2.0 Ga

High-spatial-resolution secondary-ion mass spectrometry (SIMS) U-Pb zircon ages, whole-rock Nd isotopic and geochemical data are reported for granites and granitic gneisses from a traverse across the Abas terrane, Yemen, a part of the Precambrian basement of southern Arabian Peninsula. SIMS U-Pb dating identifies two magmatic episodes, the first at c. 790-725 Ma represented by granitic gneisses, the second clearly post-tectonic at c. 625-590 Ma. The oldest sample in the post-tectonic group is slightly deformed while younger samples are undeformed indicating that penetrative deformation ceased at c. 625 Ma in the Abas region. Whole-rock(Nd)(t) values between -11 and +0.8, Nd model ages of 1.70-1.13 Ga indicate a significant contribution of evolved continental material in the genesis of the Abas granitoids, unlike most of the juvenile Arabian-Nubian Shield (ANS), although there are few inherited zircons. Secular variation in epsilon(Nd)(t)reflects a change in magma source with increasing juvenile magma and diminishing crustal input during post-tectonic (625-590 Ma) magmatism. The combination of subduction zone chemistry, absence of older rocks, paucity of inherited zircons, evolved Nd isotopic signatures and the I-type characteristics of the samples suggest that assimilation occurred at depth.

High-precision high field strength element (HFSE: Zr, Hf, Nb, Ta, Th, U, W, Mo), Y/Ho, and Nd isotope chemostratigraphy of two contrasting Deccan Traps weathering profiles - an ancient, deeply weathered laterite, and a younger (Quaternary), more moderately weathered saprolite - are used to reconstruct different aspects of basalt weathering. Precision of the HFSE analyses is demonstrated through a report of the long-term concentrations and ratios determined in United States Geological Survey (USGS) and Geological Survey of Japan (GSJ) basalt rock standards (BHVO-1, BHVO-2, BIR-1, BCR-2, JB-2). The oxyanion-forming members (U, Mo, W) are the most mobile of the considered HFSE group. Extreme loss of W, far exceeding those of U and Mo during certain stages of basalt alteration, is first reported here. The ability to strongly fractionate Mo and W during weathering may contribute to solving the unresolved mass imbalance between the crustal and marine inventories of W. By contrast, Zr, Hf, Nb, and Ta preserve the ratios of the parent basalt in the profiles due to their limited mobility; these are therefore of great potential value in reconstructing basalt flow stratigraphy and correlating lava flows in weathered flood basalt provinces. Of the HFSE, Th is not a good choice as a conservative element because it is strongly susceptible to addition of aeolian dust; this is evidenced by strong excursions in Th/Nb that are correlatable with alkali element enrichment and less radiogenic Nd-143/Nd-144 ratios. The chemical fingerprints of dust were identified in a paleo-flow top of the saprolite profile, suggesting that dust accumulation occurred during periods of quiescence between basaltic eruptions. During protracted exposure and laterite development, the magnitude to which dust overprints the basalt chemistry increases substantially as evident from much less radiogenic Nd isotope ratios and higher Th/Nb ratios in the Bidar profile relative to the protolith basalt. Attempts at qu

The Arabian-Nubian Shield is an excellent natural laboratory to study crust formation processes during the Neoproterozoic. It is one of the largest juvenile tracts of continental crust formed during this time. It diachronously evolved between the breakup of Rodinia (c.780 Ma) and amalgamation of Gondwana (c.550 Ma). New SIMS zircon U-Pb, whole-rock Sm-Nd isotopic and geochemical data are presented. The results are used to establish the geochronology of the Abas terrane and constrain its crustal evolution. The U-Pb data show bimodal age distribution: an older age group c. 790-760 Ma, which corresponds to the arc-forming stage of the ANS and a younger group c. 625-590 Ma, belonging to post-collisional episode in the region. The oldest sample in the post-collisional tectonomagmatic group is slightly deformed indicating that pervasive deformation in the area was decaying by c. 625 Ma. The inherited zircons documented range in age from Meso-to-Paleoproterozoic. Although few, these inherited zircons indicate that crust material of that age was assimilated during the Neoproterozoic magmatic events. The U-Pb geochronologic also resolved the temporal transition from high-K calc-alkaline to alkaline magmatism in the post-collisional suits. This transition commonly marks the end of orogeny. Almost all samples studied exhibit a strongly enriched initial εNd compositions and Nd model ages that predate the crystallization ages of the rocks by several hundred million years. These features highlight the sharp contrast in the magmatic sources between the Abas granitoids and the rest of the ANS, which is dominantly juvenile except that of the Afif terrane of Saudi Arabia. This suggests that the Abas terrane of Yemen had a distinctive crustal evolution history compared to the rest of the shield and these features provide evidence for the presence of pre-Neoproterozoic crust at depth in this region.

Decades of study on Phanerozoic sedimentary deposits indicates that changes in Earth's orbital parameters are one of the main drivers of climate change on the 104-105 yr time scales, however understanding the relationships between climate change on coeval marine and continental deposits is difficult due to post-depositional erosion and tectonic processes. Nd isotopes measured in marine carbonates are a proxy for regional-scale continental weathering flux (CWF) and can help resolve these difficulties because its short residence time (less than ocean mixing times). This study focuses on cyclic Middle Pennsylvanian (Desmoinesian) marine successions from the Pedregosa (Arizona) and Bird Spring (southern Nevada) basin to address the interbasin and intrabasin response of Nd. Two types of orbital-scale subtidal cycles (1-7 m thick) are observed. Transgressive-regressive (TR) cycles (44%) are characterized by basal transgressive shallow subtidal deposits, deep subtidal deposits and capped by shallow subtidal deposits. Regressive (R) cycles (56%) are composed of basal deep subtidal deposits capped by shallow subtidal deposits; approximately 55% of T-R and R cycle caps show evidence of subaerial exposure. Due to the interpreted large magnitude sea-level changes and the position of study areas along the inner/middle platform, the cycles are dominated by highstand (or interglacial) deposition. Seventeen cycles were sampled (<0.5 m sample resolution) for Nd-isotope analysis of whole rock limestones. єNd values for all three locations range between -12.3 to -5.95 and two contrasting orbital-scale єNd trends are recognized. Trend 1 (30%) is characterized by low єNd (high CWF) during sea-level highstands (interglacial stages) and trend 2 (45%) is defined by high єNd (low CWF) during sea-level highstands (interglacial stages). The absence of fluvial deposits within either studied basin combined with previous reports of thick Pennsylvanian loess deposits throughout the U.S. Southwest

This thesis focuses on the effects of volcanism, river incision, epeirogenic uplift, and faulting on the landscape evolution of the Grand Canyon region. In the first chapter the migration of increasingly asthenospheric basaltic volcanism is used to constrain lithospheric modification of the Colorado Plateau margins. Buoyancy modification of the upper mantle, driven by the upwelling, is a likely driver for recent uplift of the area. In the second chapter, correlation between oversteepened rivers and areas of high-velocity upper mantle is used to show that recent and ongoing mantle-driven uplift is modulating the surface along the western margin of the Colorado Plateau. Differential oversteepening of rivers in the Zion National Park area can't be explained by climatic or bedrock-hardness differences and are best explained by localized uplift of the area, which explains the area's high relief and dramatic slot canyons. In the third chapter, new geochronology and geochemistry are used to reconstruct the timing, sequence, and structure of Grand Canyon's lava dams. Associated gravel deposits, internal cooling structures, and a general lack of lacustrine deposits suggests that the dams were removed in multiple stages and probably did not last for more than a few hundred to thousand years. Perched gravels under lava dams show steady incision rates indicating that the blockages were ephemeral and did not significantly affect long-term bedrock incision. In the final chapter, new Grand Canyon incision rates are used to quantify the spatial and temporal variations in incision. Results show temporally steady incision at any one location and a spatial pattern of increasing incision towards the east. This spatial pattern is most consistent with differential uplift of the area. Temporally steady incision suggests a lack of transient incision most consistent with sustained uplift. These studies suggest at the landscape of the region is young and actively being modified by deep fo

Late Paleoproterozoic sedimentary basins across eastern Australia record a significant change in their neodymium isotopic composition at ca. 1655 Ma. Prior to ca. 1655 Ma, detritus was derived from comparatively evolved sources generating bulk εNd(1650 Ma) values of generally -8 to -6. Subsequent sedimentary successions, which accumulated between ca. 1655 Ma and 1600 Ma, have bulk εNd(1650 Ma) values of -2 to -1. This change is interpreted to reflect the input of sediments from a new, probable felsic volcanic source, corresponding to a fundamental change in tectonism and/or tectonic drivers for basin evolution in northern Australia. One possible driver for the change in sedimentary source is the initiation of renewed rifting from 1655 Ma along the eastern margin of Paleoproterozoic Australia. As the 1655–1600 Ma sedimentary successions that record the isotopic change are voluminous, a large, juvenile source of volcanic detritus must have been present, either within Paleoproterozoic Australia or in the cratonic block immediately to the east of Australia in the NUNA supercontinent. Although voluminous juvenile felsic magmatic sources are known in eastern and central Australia (e.g. 1639–1631 Ma volcanics in the Warumpi Province; 1620–1610 Ma granites of the St. Peter Suite in the Gawler Province), these sources are too young to have acted as a source for the juvenile detritus. Felsic intrusions of ~1650 Ma age are present in the Mount Isa Province, but the known exposed volume is very small. Of these possible sources, we favour either a buried or eroded eastern Proterozoic Australian source or an outboard Laurentian source.

The Humr Akarim and Humrat Mukbid plutons, in the central Eastern Desert of Egypt, are late Neoproterozoic post-collisional alkaline A-type granites. Humr Akarim and Humrat Mukbid plutonic rocks consist of subsolvus alkali granites and a subordinate roof facies of albite granite, which hosts greisen and Sn–Mo-mineralized quartz veins; textural and field evidence strongly suggest the presence of late magmatic F-rich fluids. The granites are Si-alkali rich, Mg–Ca–Ti poor with high Rb/Sr (20–123), and low K/Rb (27–65). They are enriched in high field strength elements (e.g., Nb, Ta, Zr, Y, U, Th) and heavy rare earth elements (Lan/Ybn = 0.27–0.95) and exhibit significant tetrad effects in REE patterns. These geochemical attributes indicate that granite trace element distribution was controlled by crystal fractionation as well as interaction with fluorine-rich magmatic fluids. U–Pb SHRIMP zircon dating indicates an age of ~630–620 Ma but with abundant evidence that zircons were affected by late corrosive fluids (e.g., discordance, high common Pb). eNd at 620 Ma ranges from +3.4 to +6.8 (mean = +5.0) for Humr Akarim granitic rocks and from +4.8 to +7.5(mean = +5.8) for Humrat Mukbid granitic rocks. Some slightly older zircons (~740 Ma, 703 Ma) may have been inherited from older granites in the region. Our U–Pb zircon data and Nd isotope results indicate a juvenile magma source of Neoproterozoic age like that responsible for forming most other ANS crust and refute previous conclusions that pre-Neoproterozoic continental crust was involved in the generation of the studied granites.

This paper reports detailed stratigraphic analysis, whole rock geochemistry and Nd isotopic ratios of basalts from the northern Maine inliers. These data place constraints on first-order controversies about the tectonic conditions leading up to and during the early stages of the Acadian Orogeny in northern Maine. Late Silurian and early Devonian stratigraphic sequences indicate a progressive change from shallow water and subaerial exposure (Ripogenus and The Forks formations, East Branch Group) to a rapidly subsiding basin prior to the onset of Acadian deformation. Subsidence was accompanied by mafic to intermediate volcanism of the West Branch, Spider Lake, and Fish Pond volcanics, and that continued with intrusion of the syn-deformational Greenville Plutonic Belt, including the Flagstaff Lake Igneous Complex, whose properties we report in this paper. Trace element geochemistry indicates that magmatism is transdiscriminant, showing aspects of within-plate, volcanic arc, and back-arc affinities and Nd isotopic ratios are moderately positive (+2.3 to +3.8) indicating either an uncontaminated and moderately enriched mantle source, or a depleted mantle source contaminated by continental crust. Four possible tectonic models of the Acadian Orogeny and the Siluro-Devonian sedimentary-volcanic sequences of northern Maine are evaluated in the context of a subsiding basin associated with this magmatism developed on the amalgamated Laurentian plate. These include 1) slab detachment during southeast-directed subduction of the Laurentian continental margin; 2) “Laramide-style” thrust basins above a shallow, northwest-dipping subduction zone; 3) back-arc extension followed by thin-skinned shortening above a northwest-dipping subduction zone; and 4) “Moluccan-style” dual-dipping subduction zones.

Author Posting. © Cambridge University Press, 2004. This article is posted here by permission of Cambridge University Press for personal use, not for redistribution. The definitive version was published in Geological Magazine 141 (2004): 195-207, doi:10.1017/S001675680400891X., Because magmatism associated with subduction is thought to be the principal source for continental crust generation, assessing the relative contribution of pre-existing (subducted and assimilated) continental material to arc magmatism in accreted arcs is important to understanding the origin of continental crust. We present a detailed Nd isotopic stratigraphy for volcanic and volcaniclastic formations from the South Mayo Trough, an accreted oceanic arc exposed in the western Irish Caledonides. These units span an arc–continent collision event, the Grampian (Taconic) Orogeny, in which an intra-oceanic island arc was accreted onto the passive continental margin of Laurentia starting at [similar] 475 Ma (Arenig). The stratigraphy corresponding to pre-, syn- and post-collisional volcanism reveals a progression of [varepsilon]Nd(t) from strongly positive values, consistent with melt derivation almost exclusively from oceanic mantle beneath the arc, to strongly negative values, indicating incorporation of continental material into the melt. Using [varepsilon]Nd(t) values of meta-sediments that represent the Laurentian passive margin and accretionary prism, we are able to quantify the relative proportions of continent-derived melt at various stages of arc formation and accretion. Mass balance calculations show that mantle-derived magmatism contributes substantially to melt production during all stages of arc–continent collision, never accounting for less than 21% of the total. This implies that a significant addition of new, rather than recycled, continental crust can accompany arc–continent collision and continental arc magmatism.

We report here SHRIMP U-Pb geochronological, geochemical, and Nd isotopic data for the Jinchuan ultramafic intrusion (Gansu Province, China), which hosts the world’s third largest magmatic Ni-Cu sulfide deposits. U-Pb baddeleyite analyses yield an age of 812 ± 26 Ma for the ultramafic intrusion. This age is indistinguishable within analytical uncertainties from the U-Pb zircon ages of 827 ± 8 Ma and 828 ± 3 Ma for the sulfide-bearing ultramafic rocks and the dolerite dykes that cut the ultramafic intrusion, respectively. These U-Pb dating results show beyond doubt that the Jinchuan ultramafic intrusion and associated Ni-Cu sulfide deposit were formed at _825 Ma, rather than _1500 Ma as has been widely believed. The ultramafic rocks exhibit large negative eNd(T) values (_8.9 to _12.0) that decrease with increasing La/Sm, suggesting that their parental magmas were derived from a long-term enriched lithospheric mantle and experienced crustal contamination. Mineralogical, petrological, and geochemical data all indicate that the Jinchuan intrusion was generated by melting of the enriched lithospheric mantle heated by an anomalously hot plume. The U-Pb ages of _825 Ma for igneous baddeleyites and zircons and _900–880 Ma for inherited zircons in the Jinchuan mafic-ultramafic rocks are comparable with those in the Qaidam block and Qilian belt, the western extension of the Qinling belt that was likely derived from northern Yangtze craton. The Jinchuan N -Cu sulfide-bearing intrusion, along with coeval regional plumerelated mafic dykes and tholeiites, and mafic-ultramafic complexes with associated V-Ti and Ni-Cu-PGE mineralization, is interpreted to be genetically related to the _825 Ma south China mantle plume.

Because magmatism associated with subduction is thought to be the principal source for continental crust generation, assessing the relative contribution of pre-existing (subducted and assimilated) continental material to arc magmatism in accreted arcs is important to understanding the origin of continental crust. We present a detailed Nd isotopic stratigraphy for volcanic and volcaniclastic formations from the South Mayo Trough, an accreted oceanic arc exposed in the western Irish Caledonides. These units span an arc–continent collision event, the Grampian (Taconic) Orogeny, in which an intra-oceanic island arc was accreted onto the passive continental margin of Laurentia starting at [similar] 475 Ma (Arenig). The stratigraphy corresponding to pre-, syn- and post-collisional volcanism reveals a progression of [varepsilon]Nd(t) from strongly positive values, consistent with melt derivation almost exclusively from oceanic mantle beneath the arc, to strongly negative values, indicating incorporation of continental material into the melt. Using [varepsilon]Nd(t) values of meta-sediments that represent the Laurentian passive margin and accretionary prism, we are able to quantify the relative proportions of continent-derived melt at various stages of arc formation and accretion. Mass balance calculations show that mantle-derived magmatism contributes substantially to melt production during all stages of arc–continent collision, never accounting for less than 21% of the total. This implies that a significant addition of new, rather than recycled, continental crust can accompany arc–continent collision and continental arc magmatism.

Sm-Nd data on rock suites from early Archaean provinces in northern Canada and West Greenland clearly demonstrate that tectonothermal (i.e. igneous, metamorphic, tectonic) processes which affected the rocks long after their formation produced open-system behaviour leading to effective resetting of the Sm-Nd system accompanied by complete, or near-complete, Nd-isotope homogenisation. This means that extreme caution is required in interpreting highly variable initial epsilon(Nd) values of ancient rocks in terms of long-standing regional mantle heterogeneity or of complex mantle-crust interaction processes. In particular, calculated initial epsilon(Nd), values based on high-precision zircon U-Pb dates may be of little or no significance in terms of geochemical evolution of early mantle and crust source regions. A striking example is provided by the Acasta gneisses of northern Canada, with published SHRIMP U-Pb zircon dates in the range 3.6-4.0 Ga and apparent, initial epsilon(Nd) values in the range -4.8 to +3.6 (Bowring and Housh, 1995). A combination of 34 published and new Sm-Nd whole-rock analyses for a wide range of rock types yields a regression (errorchron) age of 3371 +/- 59 Ma (MSWD = 9.2), with initial epsilon(Nd) = -5.6 +/- 0.7. Whilst the very negative initial epsilon(Nd) provides strong, independent support for the extreme age of the Acasta gneiss protolith, resetting of the Sm-Nd system at similar to 3.4 Ga renders calculation of initial epsilon(Nd) based on the zircon U-Pb dates geologically meaningless. Analogous considerations for early Archaean Akilia enclaves and host Amitsoq gneisses of West Greenland suggest that their published range of initial epsilon(Nd) values of similar to -4.5 to +4.5 at similar to 3.73-3.87 Ca (Bennett et al., 1993) may be unrealistically wide and, therefore, inappropriate for modelling upper-mantle heterogeneity. In an attempt to determine a realistic initial epsilon(Nd) value, we have regressed 58 published and new Sm-Nd d

Wei R., Abouchami W., Zahn R., Masque P. (2016). Deep circulation changes in the South Atlantic since the Last Glacial Maximum from Nd isotope and multi-proxy records. In Earth and Planetary Science Letters, (413), 18-29. Available here.