Francis Albarede - Academia.edu (original) (raw)
Papers by Francis Albarede
Journal of Archaeological Science, Jan 31, 2024
Was silver coinage minted from fresh metal newly extracted from the mine or was it from recycled ... more Was silver coinage minted from fresh metal newly extracted from the mine or was it from recycled silver deriving from older coins, silverware, or cult objects? The answer helps understand the provenance of the coins and their circulation. Using Pb isotopes, the present work proposes a method to disentangle the sources of 368 silver-alloy coins from Athens,
Journal of Archaeological Science, Jan 31, 2024
Was silver coinage minted from fresh metal newly extracted from the mine or was it from recycled ... more Was silver coinage minted from fresh metal newly extracted from the mine or was it from recycled silver deriving from older coins, silverware, or cult objects? The answer helps understand the provenance of the coins and their circulation. Using Pb isotopes, the present work proposes a method to disentangle the sources of 368 silver-alloy coins from Athens,
SSRN Electronic Journal, 2021
Over the last 60 years, much analytical research has sought to determine the ore sources of ancie... more Over the last 60 years, much analytical research has sought to determine the ore sources of ancient Greek silver artefacts. Lead isotopic analysis has played a key role in this endeavor. While most studies so far have limited their search to places mentioned in historical sources, the present study takes a different approach by first identifying Ag-bearing ore sources in the Aegean world based on their geological characteristics and then using Pb isotopes to determine whether they were exploited in antiquity. To this end, we have geolocated, sampled, and measured high-precision Pb isotopic compositions of 17 Ag-bearing mineralizations in Greece for which we have evidence of ancient mining activity, and a further 10 exhibiting minor Ag occurrences that may also have been exploited in ancient times. We found that Pb model ages provide better discrimination of ore sources than the more conventional plots of raw Pb isotope data. Our study establishes Lavrion, northeast Chalkidiki, Pangaeon, Thasos, Siphnos, Palaea Kavala, Angistron, and south Euboea as the most important ancient silver mining districts in Greece. Two previously undiscovered ancient mining areas in Pelion and in the Kroussia mountain range are also documented. The latter may be identified with ancient Mount Dysoron, from which King Alexander I of Macedon reportedly extracted the fabulous sum of a talent of silver per day. For the first time, we isotopically differentiate some of the mining districts in Thraco-Macedonia, and show that the mines of Thasos include geologically different silver-bearing ore sources. We further identify the hitherto unrealized importance of Euboean silver mines and demonstrate that they isotopically overlap those of Siphnos, with major implications for our understanding of ancient Greek history.
Journal of Archaeological Science, 2021
Hacksilber facilitated trade and transactions from the beginning of the second millennium BCE unt... more Hacksilber facilitated trade and transactions from the beginning of the second millennium BCE until the late fourth century BCE in the southern Levant. Here we demonstrate the use of new, data-driven statistical approaches to interpret high-precision Pb isotope analysis of silver found in archaeological contexts for provenance determination. We sampled 45 pieces of Hacksilber from five hoards (Megiddo Area H, Eshtemoa, Tel Dor, ʿEn Gedi, and Tel Miqne-Ekron) and combined our data with recent literature data for the same hoards plus five more (Beth Shean, Ashkelon, Tell Keisan, Tel ʿAkko, and ʿEn Ḥofez) thus covering silver from the Late Bronze Age III (c.1200 BCE) to the end of the Iron Age IIC (586 BCE). Samples were taken by applying a new minimally destructive sampling technique. Lead was extracted using anion-exchange chromatography, and Pb isotopic compositions were measured by MC-ICP-MS. Data were treated using a new clustering method to identify statistically distinct groups of data, and a convex hull was applied to identify and constrain ore sources consistent with the isotopic signature of each group. Samples were grouped by minimizing variance within isotopic clusters and maximizing variance between isotopic clusters. We found that exchanges between the Levant and the Aegean world continued at least intermittently from the Late Bronze Age through to the Iron Age III, demonstrated by the prevalence of Lavrion (Attica), Macedonia, Thrace (northern Greece), southern Gaul (southern France), and Sardinia as long-lived major silver sources. Occasional exchanges with other west Mediterranean localities found in the isotopic record demonstrate that even though the Aegean world dominated silver supply during the Iron Age, exchanges between the eastern and the western Mediterranean did not altogether cease. The mixture of silver sources within hoards and relatively low purity of silver intentionally mixed with copper and arsenic suggest long-term hoarding and irregular, limited supply during the Iron Age I.
Chemical Geology, 2021
In an attempt to clarify the significance of Pb model ages in Pb-Zn sedimentary deposits, we repo... more In an attempt to clarify the significance of Pb model ages in Pb-Zn sedimentary deposits, we report high-precision Pb isotopic compositions for 64 galenas and 52 K-feldspars, the former from ores and the latter separated from granites. All samples are from Spain and the French Pyrenees. Lead from galena ores is of unequivocal continental origin. With few exceptions, Pb model ages systematically exceed emplacement ages by up to 400 Ma, a gap which is well outside the uncertainties of ~30 Ma assigned to the model. The histogram of the new high-precision Pb isotope data shows prominent peaks of galena Pb model ages at 94±38 Ma and 392±39 Ma. When the data are consolidated with literature data and examined in 3-dimensional Pb isotope space, cluster analysis identifies five groups. The model ages of the peaks occur, in order of decreasing peak intensity, at 395±40 (Middle Devonian), 90±34 Ma (Middle Cretaceous), and 613±42 Ma (Neoproterozoic), with two minor peaks at 185+26 Ma (Jurassic) and 313±41 (Upper Carboniferous). To a large extent, the model ages centered around these peaks correspond to distinct localities. The ages of the peaks do not coincide with any of the Betic, Variscan, or Pan-African tectonic events, which are the main tectonic episodes that shaped Iberian geology, but rather match well-known global oceanic anoxic events. It is argued that surges of metals weathered from continental surfaces scorched during anoxic events accumulated and combined in anoxic water masses with unoxidized marine sulfide released by submarine hydrothermal activity to precipitate the primary Pb-Zn stock. Frozen Pb isotope compositions require that galenas from black shales are the source of the final ores. The Revised manuscript with no changes marked Click here to view linked References 2 sulfides were later remobilized by large-scale convective circulation of basinal and hydrothermal fluids. The peaks of K-feldspar Pb model ages are distinct from those of galenas and do not correlate with magmatic emplacement ages. It is suggested that they instead reflect local circulation in Paleozoic sediments surrounding individual plutons. While Pb isotopes can be used as a regional provenance tool, such an approach requires that the data are considered in a fully 3-dimensional space.
Archaeometry, 2020
The reasons why the Western Mediterranean, especially Carthage and Rome, resisted monetization re... more The reasons why the Western Mediterranean, especially Carthage and Rome, resisted monetization relative to the Eastern Mediterranean are still unclear. We address this question by combining lead (Pb) and silver (Ag) isotope abundances in silver coinage from the Aegean, Magna Graecia, Carthage and Roman Republic. The clear relationships observed between 109Ag/107Ag and 208Pb/206Pb reflect the mixing of silver ores or silver objects with Pb metal used for cupellation. The combined analysis of Ag and Pb isotopes reveals important information about the technology of smelting. The Greek world extracted Ag and Pb from associated ores, whereas, on the Iberian Peninsula, Carthaginians and Republican‐era Romans applied Phoenician cupellation techniques and added exotic Pb to Pb‐poor Ag ores. Massive Ag recupellation is observed in Rome during the Second Punic War. After defeating the Carthaginians and the Macedonians in the late second century bce, the Romans brought together the efficient, ...
Geochemical Perspectives Letters, 2016
The defeat of Hannibal's armies at the culmination of the Second Punic War (218 BC-201 BC) was a ... more The defeat of Hannibal's armies at the culmination of the Second Punic War (218 BC-201 BC) was a defining moment in Western world history. One of the underappreciated consequences of the conflict was the Roman monetary reform of 211 BC, which ushered in a monetary system that would sustain Roman power for the next many centuries. This system would encapsulate many of the issues plaguing finances of governments until today, such as inflation, debasement, and the size of monetary mass. Here we approach the issue of financial fluxes using a newly developed powerful tracer, that of silver isotopic compositions, in conjunction with Pb isotopes, both of which we measured in Roman coinage minted before and after the 211 BC monetary reform. The results indicate that pre-reform silver was minted from Spanish metal supplied by Carthage as war penalty after the First Punic War, whereas post-reform silver was isotopically distinct and dominated by plunder, most likely from Syracuse and Capua. The 211 BC monetary reform and the end of debasement, therefore, were aimed at accommodating new sources of silver rather than being the response to financial duress. The drastic weight reduction of silver coins implemented by the Roman mint was not motivated by metal shortage but by the need to block inflation after a major surge of war booty.
Proceedings of the National Academy of Sciences of the United States of America, Sep 28, 2017
Heavy metals from urban runoff preserved in sedimentary deposits record long-term economic and in... more Heavy metals from urban runoff preserved in sedimentary deposits record long-term economic and industrial development via the expansion and contraction of a city's infrastructure. Lead concentrations and isotopic compositions measured in the sediments of the harbor of Ostia-Rome's first harbor-show that lead pipes used in the water supply networks of Rome and Ostia were the only source of radiogenic Pb, which, in geologically young central Italy, is the hallmark of urban pollution. High-resolution geochemical, isotopic, and (14)C analyses of a sedimentary core from Ostia harbor have allowed us to date the commissioning of Rome's lead pipe water distribution system to around the second century BC, considerably later than Rome's first aqueduct built in the late fourth century BC. Even more significantly, the isotopic record of Pb pollution proves to be an unparalleled proxy for tracking the urban development of ancient Rome over more than a millennium, providing a semi...
Geochemistry, Geophysics, Geosystems, 2016
Lead isotopic systematics of U‐poor minerals, such as sulfides and feldspars, can provide unique ... more Lead isotopic systematics of U‐poor minerals, such as sulfides and feldspars, can provide unique insights into the origin and evolution of continents because these minerals “freeze in” the Pb isotopic composition of the crust during major tectonothermal events, allowing the history of a continent to be told through Pb isotopes. Lead model ages constrain the timing of crust formation while time‐integrated U/Pb, Th/Pb, and Th/U ratios shed light onto key geochemical processes associated with continent formation. Using ∼6800 Pb isotope measurements of primarily lead ores and minor K‐feldspar, we mapped out the Pb isotope systematics across Europe and the Mediterranean. Lead model ages define spatially distinct age provinces, consistent with major tectonic events ranging from the Paleozoic to the Proterozoic and latest Archean. However, the regions defined by time‐integrated U/Pb and Th/Pb ratios cut across the boundaries of age provinces, with high U/Pb systematics characterizing most ...
Nature, Jan 7, 2000
Up to 10 per cent of the ocean floor consists of plateaux--regions of unusually thick oceanic cru... more Up to 10 per cent of the ocean floor consists of plateaux--regions of unusually thick oceanic crust thought to be formed by the heads of mantle plumes. Given the ubiquitous presence of recycled oceanic crust in the mantle source of hotspot basalts, it follows that plateau material should also be an important mantle constituent. Here we show that the geochemistry of the Pleistocene basalts from Logudoro, Sardinia, is compatible with the remelting of ancient ocean plateau material that has been recycled into the mantle. The Sr, Nd and Hf isotope compositions of these basalts do not show the signature of pelagic sediments. The basalts' low CaO/Al2O3 and Ce/Pb ratios, their unradiogenic 206Pb and 208Pb, and their Sr, Ba, Eu and Pb excesses indicate that their mantle source contains ancient gabbros formed initially by plagioclase accumulation, typical of plateau material. Also, the high Th/U ratios of the mantle source resemble those of plume magmas. Geochemically, the Logudoro basal...
Science, 2005
The long-favored paradigm for the development of continental crust is one of progressive growth b... more The long-favored paradigm for the development of continental crust is one of progressive growth beginning at ∼4 billion years ago (Ga). To test this hypothesis, we measured initial 176 Hf/ 177 Hf values of 4.01- to 4.37-Ga detrital zircons from Jack Hills, Western Australia. ϵ Hf (deviations of 176 Hf/ 177 Hf from bulk Earth in parts per 10 4 ) values show large positive and negative deviations from those of the bulk Earth. Negative values indicate the development of a Lu/Hf reservoir that is consistent with the formation of continental crust (Lu/Hf ≈ 0.01), perhaps as early as 4.5 Ga. Positive ϵ Hf deviations require early and likely widespread depletion of the upper mantle. These results support the view that continental crust had formed by 4.4 to 4.5 Ga and was rapidly recycled into the mantle.
Proceedings of the National Academy of Sciences, 2014
Significance Thirty years ago, Jerome Nriagu argued in a milestone paper that Roman civilization ... more Significance Thirty years ago, Jerome Nriagu argued in a milestone paper that Roman civilization collapsed as a result of lead poisoning. Clair Patterson, the scientist who convinced governments to ban lead from gasoline, enthusiastically endorsed this idea, which nevertheless triggered a volley of publications aimed at refuting it. Although today lead is no longer seen as the prime culprit of Rome’s demise, its status in the system of water distribution by lead pipes ( fistulæ ) still stands as a major public health issue. By measuring Pb isotope compositions of sediments from the Tiber River and the Trajanic Harbor, the present work shows that “tap water” from ancient Rome had 100 times more lead than local spring waters.
Journal of Geophysical Research: Solid Earth, 2002
The isotopic compositions of basaltic lavas from the Quaternary and Plio‐Pleistocene Italian volc... more The isotopic compositions of basaltic lavas from the Quaternary and Plio‐Pleistocene Italian volcanics (Tuscan Magmatic Province, Roman Magmatic Province, Vesuvius, Aeolian Islands, Etna, and Iblean Basin) define binary hyperbolic relationships in the 87Sr/86Sr–206Pb/204Pb–εNd–εHf space. The isotopic compositions of the two end‐members of these mixing arrays are assessed by least‐squares regression. The mantle‐derived component (206Pb/204Pb = 19.8, 87Sr/86Sr = 0.7025, εNd = +8, εHf = +9) is a rather homogeneous mixture of the standard high‐μ (HIMU) and depleted mantle (DM) components. The crust‐derived component (206Pb/204Pb = 18.5, 87Sr/86Sr > 0.715, εNd = −12, εHf = −11) accounts for the enrichment of K and other large‐ion‐lithophile elements in the Italian volcanics. As shown by the relationship in εHf–εNd space and the lower‐than‐chondritic Hf/Sm ratio, this crustal component is dominated by pelagic sediments rather than terrigenous material. The overall scarcity of calc‐alka...
Icarus, 2013
While metal rapidly segregates out of the melt and sinks into the core, the vaporized material or... more While metal rapidly segregates out of the melt and sinks into the core, the vaporized material orbits the Earth and eventually rains back onto its surface. The content of the mantle in siderophile elements and their chondritic relative abundances hence is accounted for, not by the impactors themselves, as in the original late-veneer model (Chou, C.L. [1978]. Proc. Lunar Sci. Conf. 9, 219-230; Morgan, J.W. et al. [1981]. Tectonophysics 75, 47-67), but by the vapor resulting from impacts. The impactor's non-siderophile volatiles, notably hydrogen, are added to the mantle and hydrosphere. The addition of late veneer may have lasted for 130 Ma after isolation of the Solar System and probably longer, i.e., well beyond the giant lunar impact. Constraints from the stable isotopes of oxygen and other elements suggest that, contrary to evidence from highly siderophile elements, $4% of CI chondrites accreted to the Earth. The amount of water added in this way during the waning stages of accretion, and now dissolved in the deep mantle or used to oxidize Fe in the mantle and the core, may correspond to 10-25 times the mass of the present-day ocean. The Moon is at least 100 times more depleted than the Earth in volatile elements with the exception of some isolated domains, such as the mantle source of 74220 pyroclastic glasses, which appear to contain significantly higher concentrations of water and other volatiles.
Geophysical Research Letters, 1998
The 176 Hf/ 177 Hf ratio was measured on 34 ferromanganese nodules, mostly from the Atlantic ocea... more The 176 Hf/ 177 Hf ratio was measured on 34 ferromanganese nodules, mostly from the Atlantic ocean. The different ocean basins are isotopically distinct with the extreme compositions being less radiogenic in the Atlantic (Hf ∼ +1) than in the Pacific (Hf ∼ +9). A good correlation of Hf and Nd is observed amongst most samples which supports that Hf isotopic compositions in nodules reflect those of ambient seawater. For a given Nd , Hf is more radiogenic in ferromanganese nodules than in rocks from either the mantle or the crust. This correlation makes the coupled Hf-Nd systems a potential paleoceanographic tool. It is argued that a zircon-free clayish component of probable eolian origin may account for the radiogenic Hf in nodules.
Geochimica et Cosmochimica Acta, 2007
Kimberlites from West Greenland have Hf-Nd isotope as well as major and trace element composition... more Kimberlites from West Greenland have Hf-Nd isotope as well as major and trace element compositions that are similar to other Group I kimberlites, but that are distinctive in the spectrum of magmas sampled at Earth's surface. The West Greenland kimberlites have e Ndi that ranges from +1.6 to +3.1 and e Hfi that ranges from À4.3 to +4.9. The samples exhibit ubiquitous negative De Hfi (deviation from the ocean island basalt e Hf-e Nd reference line), ranging from À1.8 to À11.2. The kimberlites are characterized by steep heavy rare earth element patterns, positive Ta-Nb anomalies and negative Hf-Zr anomalies. These chemical signals are consistent with the presence of ancient, subducted oceanic crust in the kimberlite source region. In the model we present, dewatering and possibly partial melting of rutilebearing oceanic crust during subduction results in characteristic trace element patterns in the residual crust. During aging, the Hf-Nd isotopic composition of this dewatered/partially melted EMORB-type crust evolves to negative De Hfi values. Metasomatic fluids derived from this ancient subducted oceanic crust infiltrate and impart their trace element and isotopic signal on proximal peridotitic mantle. Melting of this metasomatized mantle peridotite results in kimberlite magmas.
Geochemistry, Geophysics, Geosystems, 2014
We report 3He/4He for 150 mid‐ocean ridge basalt (MORB) glasses from the Southeast Indian Ridge (... more We report 3He/4He for 150 mid‐ocean ridge basalt (MORB) glasses from the Southeast Indian Ridge (SEIR). Between 81°E and 101°E 3He/4He varies from 7.5 to 10.2 RA, encompassing more than half the MORB range away from ocean island hot spots. Abrupt transitions are present and in one case the full range occurs over ∼10 km. Melting of lithologically heterogeneous mantle containing a few percent garnet pyroxenite or eclogite leads to lower 3He/4He, while 3He/4He above ∼9 RA likely indicates melting of pyroxenite‐free or eclogite‐free mantle. Patterns in the length scales of variability represent a description of helium isotopic texture. We utilize four complementary methods of spectral analysis to evaluate this texture, including periodogram, redfit, multitaper method, and continuous wavelet transform. Long‐wavelength lobes with prominent power at 1000 and 500 km are present in all treatments, similar to hot spot‐type spectra in Atlantic periodograms. The densely sampled region of the SE...
Geochemistry, Geophysics, Geosystems, 2002
Volcan Ecuador, a young, active shield volcano at the northwest tip of Isabela Island, Galápagos,... more Volcan Ecuador, a young, active shield volcano at the northwest tip of Isabela Island, Galápagos, experienced at least one sector collapse event that removed its western half. The compositions of lavas exposed in the old caldera wall and fault scarps dissecting the outer shield together with young post‐collapse lavas provide insights into the history of this volcano. 40Ar/39Ar and cosmogenic 3He dating reveal that sector collapse occurred at <100 Ka. Prior to sector collapse most magma erupted from circumferential dikes that fed the summit carapace and other dikes that fed vents on the caldera floor. Almost all of the erupted magmas cooled and underwent fractional crystallization in the lower crust or upper mantle, where clinopyroxene crystallization dominated. Magmas then rose to a small (∼0.1 km3), steady state, subcaldera magma chamber where plagioclase, along with lesser amounts of olivine and clinopyroxene, crystallized. Sector collapse perturbed the plumbing system in a way...
Journal of Archaeological Science, Jan 31, 2024
Was silver coinage minted from fresh metal newly extracted from the mine or was it from recycled ... more Was silver coinage minted from fresh metal newly extracted from the mine or was it from recycled silver deriving from older coins, silverware, or cult objects? The answer helps understand the provenance of the coins and their circulation. Using Pb isotopes, the present work proposes a method to disentangle the sources of 368 silver-alloy coins from Athens,
Journal of Archaeological Science, Jan 31, 2024
Was silver coinage minted from fresh metal newly extracted from the mine or was it from recycled ... more Was silver coinage minted from fresh metal newly extracted from the mine or was it from recycled silver deriving from older coins, silverware, or cult objects? The answer helps understand the provenance of the coins and their circulation. Using Pb isotopes, the present work proposes a method to disentangle the sources of 368 silver-alloy coins from Athens,
SSRN Electronic Journal, 2021
Over the last 60 years, much analytical research has sought to determine the ore sources of ancie... more Over the last 60 years, much analytical research has sought to determine the ore sources of ancient Greek silver artefacts. Lead isotopic analysis has played a key role in this endeavor. While most studies so far have limited their search to places mentioned in historical sources, the present study takes a different approach by first identifying Ag-bearing ore sources in the Aegean world based on their geological characteristics and then using Pb isotopes to determine whether they were exploited in antiquity. To this end, we have geolocated, sampled, and measured high-precision Pb isotopic compositions of 17 Ag-bearing mineralizations in Greece for which we have evidence of ancient mining activity, and a further 10 exhibiting minor Ag occurrences that may also have been exploited in ancient times. We found that Pb model ages provide better discrimination of ore sources than the more conventional plots of raw Pb isotope data. Our study establishes Lavrion, northeast Chalkidiki, Pangaeon, Thasos, Siphnos, Palaea Kavala, Angistron, and south Euboea as the most important ancient silver mining districts in Greece. Two previously undiscovered ancient mining areas in Pelion and in the Kroussia mountain range are also documented. The latter may be identified with ancient Mount Dysoron, from which King Alexander I of Macedon reportedly extracted the fabulous sum of a talent of silver per day. For the first time, we isotopically differentiate some of the mining districts in Thraco-Macedonia, and show that the mines of Thasos include geologically different silver-bearing ore sources. We further identify the hitherto unrealized importance of Euboean silver mines and demonstrate that they isotopically overlap those of Siphnos, with major implications for our understanding of ancient Greek history.
Journal of Archaeological Science, 2021
Hacksilber facilitated trade and transactions from the beginning of the second millennium BCE unt... more Hacksilber facilitated trade and transactions from the beginning of the second millennium BCE until the late fourth century BCE in the southern Levant. Here we demonstrate the use of new, data-driven statistical approaches to interpret high-precision Pb isotope analysis of silver found in archaeological contexts for provenance determination. We sampled 45 pieces of Hacksilber from five hoards (Megiddo Area H, Eshtemoa, Tel Dor, ʿEn Gedi, and Tel Miqne-Ekron) and combined our data with recent literature data for the same hoards plus five more (Beth Shean, Ashkelon, Tell Keisan, Tel ʿAkko, and ʿEn Ḥofez) thus covering silver from the Late Bronze Age III (c.1200 BCE) to the end of the Iron Age IIC (586 BCE). Samples were taken by applying a new minimally destructive sampling technique. Lead was extracted using anion-exchange chromatography, and Pb isotopic compositions were measured by MC-ICP-MS. Data were treated using a new clustering method to identify statistically distinct groups of data, and a convex hull was applied to identify and constrain ore sources consistent with the isotopic signature of each group. Samples were grouped by minimizing variance within isotopic clusters and maximizing variance between isotopic clusters. We found that exchanges between the Levant and the Aegean world continued at least intermittently from the Late Bronze Age through to the Iron Age III, demonstrated by the prevalence of Lavrion (Attica), Macedonia, Thrace (northern Greece), southern Gaul (southern France), and Sardinia as long-lived major silver sources. Occasional exchanges with other west Mediterranean localities found in the isotopic record demonstrate that even though the Aegean world dominated silver supply during the Iron Age, exchanges between the eastern and the western Mediterranean did not altogether cease. The mixture of silver sources within hoards and relatively low purity of silver intentionally mixed with copper and arsenic suggest long-term hoarding and irregular, limited supply during the Iron Age I.
Chemical Geology, 2021
In an attempt to clarify the significance of Pb model ages in Pb-Zn sedimentary deposits, we repo... more In an attempt to clarify the significance of Pb model ages in Pb-Zn sedimentary deposits, we report high-precision Pb isotopic compositions for 64 galenas and 52 K-feldspars, the former from ores and the latter separated from granites. All samples are from Spain and the French Pyrenees. Lead from galena ores is of unequivocal continental origin. With few exceptions, Pb model ages systematically exceed emplacement ages by up to 400 Ma, a gap which is well outside the uncertainties of ~30 Ma assigned to the model. The histogram of the new high-precision Pb isotope data shows prominent peaks of galena Pb model ages at 94±38 Ma and 392±39 Ma. When the data are consolidated with literature data and examined in 3-dimensional Pb isotope space, cluster analysis identifies five groups. The model ages of the peaks occur, in order of decreasing peak intensity, at 395±40 (Middle Devonian), 90±34 Ma (Middle Cretaceous), and 613±42 Ma (Neoproterozoic), with two minor peaks at 185+26 Ma (Jurassic) and 313±41 (Upper Carboniferous). To a large extent, the model ages centered around these peaks correspond to distinct localities. The ages of the peaks do not coincide with any of the Betic, Variscan, or Pan-African tectonic events, which are the main tectonic episodes that shaped Iberian geology, but rather match well-known global oceanic anoxic events. It is argued that surges of metals weathered from continental surfaces scorched during anoxic events accumulated and combined in anoxic water masses with unoxidized marine sulfide released by submarine hydrothermal activity to precipitate the primary Pb-Zn stock. Frozen Pb isotope compositions require that galenas from black shales are the source of the final ores. The Revised manuscript with no changes marked Click here to view linked References 2 sulfides were later remobilized by large-scale convective circulation of basinal and hydrothermal fluids. The peaks of K-feldspar Pb model ages are distinct from those of galenas and do not correlate with magmatic emplacement ages. It is suggested that they instead reflect local circulation in Paleozoic sediments surrounding individual plutons. While Pb isotopes can be used as a regional provenance tool, such an approach requires that the data are considered in a fully 3-dimensional space.
Archaeometry, 2020
The reasons why the Western Mediterranean, especially Carthage and Rome, resisted monetization re... more The reasons why the Western Mediterranean, especially Carthage and Rome, resisted monetization relative to the Eastern Mediterranean are still unclear. We address this question by combining lead (Pb) and silver (Ag) isotope abundances in silver coinage from the Aegean, Magna Graecia, Carthage and Roman Republic. The clear relationships observed between 109Ag/107Ag and 208Pb/206Pb reflect the mixing of silver ores or silver objects with Pb metal used for cupellation. The combined analysis of Ag and Pb isotopes reveals important information about the technology of smelting. The Greek world extracted Ag and Pb from associated ores, whereas, on the Iberian Peninsula, Carthaginians and Republican‐era Romans applied Phoenician cupellation techniques and added exotic Pb to Pb‐poor Ag ores. Massive Ag recupellation is observed in Rome during the Second Punic War. After defeating the Carthaginians and the Macedonians in the late second century bce, the Romans brought together the efficient, ...
Geochemical Perspectives Letters, 2016
The defeat of Hannibal's armies at the culmination of the Second Punic War (218 BC-201 BC) was a ... more The defeat of Hannibal's armies at the culmination of the Second Punic War (218 BC-201 BC) was a defining moment in Western world history. One of the underappreciated consequences of the conflict was the Roman monetary reform of 211 BC, which ushered in a monetary system that would sustain Roman power for the next many centuries. This system would encapsulate many of the issues plaguing finances of governments until today, such as inflation, debasement, and the size of monetary mass. Here we approach the issue of financial fluxes using a newly developed powerful tracer, that of silver isotopic compositions, in conjunction with Pb isotopes, both of which we measured in Roman coinage minted before and after the 211 BC monetary reform. The results indicate that pre-reform silver was minted from Spanish metal supplied by Carthage as war penalty after the First Punic War, whereas post-reform silver was isotopically distinct and dominated by plunder, most likely from Syracuse and Capua. The 211 BC monetary reform and the end of debasement, therefore, were aimed at accommodating new sources of silver rather than being the response to financial duress. The drastic weight reduction of silver coins implemented by the Roman mint was not motivated by metal shortage but by the need to block inflation after a major surge of war booty.
Proceedings of the National Academy of Sciences of the United States of America, Sep 28, 2017
Heavy metals from urban runoff preserved in sedimentary deposits record long-term economic and in... more Heavy metals from urban runoff preserved in sedimentary deposits record long-term economic and industrial development via the expansion and contraction of a city's infrastructure. Lead concentrations and isotopic compositions measured in the sediments of the harbor of Ostia-Rome's first harbor-show that lead pipes used in the water supply networks of Rome and Ostia were the only source of radiogenic Pb, which, in geologically young central Italy, is the hallmark of urban pollution. High-resolution geochemical, isotopic, and (14)C analyses of a sedimentary core from Ostia harbor have allowed us to date the commissioning of Rome's lead pipe water distribution system to around the second century BC, considerably later than Rome's first aqueduct built in the late fourth century BC. Even more significantly, the isotopic record of Pb pollution proves to be an unparalleled proxy for tracking the urban development of ancient Rome over more than a millennium, providing a semi...
Geochemistry, Geophysics, Geosystems, 2016
Lead isotopic systematics of U‐poor minerals, such as sulfides and feldspars, can provide unique ... more Lead isotopic systematics of U‐poor minerals, such as sulfides and feldspars, can provide unique insights into the origin and evolution of continents because these minerals “freeze in” the Pb isotopic composition of the crust during major tectonothermal events, allowing the history of a continent to be told through Pb isotopes. Lead model ages constrain the timing of crust formation while time‐integrated U/Pb, Th/Pb, and Th/U ratios shed light onto key geochemical processes associated with continent formation. Using ∼6800 Pb isotope measurements of primarily lead ores and minor K‐feldspar, we mapped out the Pb isotope systematics across Europe and the Mediterranean. Lead model ages define spatially distinct age provinces, consistent with major tectonic events ranging from the Paleozoic to the Proterozoic and latest Archean. However, the regions defined by time‐integrated U/Pb and Th/Pb ratios cut across the boundaries of age provinces, with high U/Pb systematics characterizing most ...
Nature, Jan 7, 2000
Up to 10 per cent of the ocean floor consists of plateaux--regions of unusually thick oceanic cru... more Up to 10 per cent of the ocean floor consists of plateaux--regions of unusually thick oceanic crust thought to be formed by the heads of mantle plumes. Given the ubiquitous presence of recycled oceanic crust in the mantle source of hotspot basalts, it follows that plateau material should also be an important mantle constituent. Here we show that the geochemistry of the Pleistocene basalts from Logudoro, Sardinia, is compatible with the remelting of ancient ocean plateau material that has been recycled into the mantle. The Sr, Nd and Hf isotope compositions of these basalts do not show the signature of pelagic sediments. The basalts' low CaO/Al2O3 and Ce/Pb ratios, their unradiogenic 206Pb and 208Pb, and their Sr, Ba, Eu and Pb excesses indicate that their mantle source contains ancient gabbros formed initially by plagioclase accumulation, typical of plateau material. Also, the high Th/U ratios of the mantle source resemble those of plume magmas. Geochemically, the Logudoro basal...
Science, 2005
The long-favored paradigm for the development of continental crust is one of progressive growth b... more The long-favored paradigm for the development of continental crust is one of progressive growth beginning at ∼4 billion years ago (Ga). To test this hypothesis, we measured initial 176 Hf/ 177 Hf values of 4.01- to 4.37-Ga detrital zircons from Jack Hills, Western Australia. ϵ Hf (deviations of 176 Hf/ 177 Hf from bulk Earth in parts per 10 4 ) values show large positive and negative deviations from those of the bulk Earth. Negative values indicate the development of a Lu/Hf reservoir that is consistent with the formation of continental crust (Lu/Hf ≈ 0.01), perhaps as early as 4.5 Ga. Positive ϵ Hf deviations require early and likely widespread depletion of the upper mantle. These results support the view that continental crust had formed by 4.4 to 4.5 Ga and was rapidly recycled into the mantle.
Proceedings of the National Academy of Sciences, 2014
Significance Thirty years ago, Jerome Nriagu argued in a milestone paper that Roman civilization ... more Significance Thirty years ago, Jerome Nriagu argued in a milestone paper that Roman civilization collapsed as a result of lead poisoning. Clair Patterson, the scientist who convinced governments to ban lead from gasoline, enthusiastically endorsed this idea, which nevertheless triggered a volley of publications aimed at refuting it. Although today lead is no longer seen as the prime culprit of Rome’s demise, its status in the system of water distribution by lead pipes ( fistulæ ) still stands as a major public health issue. By measuring Pb isotope compositions of sediments from the Tiber River and the Trajanic Harbor, the present work shows that “tap water” from ancient Rome had 100 times more lead than local spring waters.
Journal of Geophysical Research: Solid Earth, 2002
The isotopic compositions of basaltic lavas from the Quaternary and Plio‐Pleistocene Italian volc... more The isotopic compositions of basaltic lavas from the Quaternary and Plio‐Pleistocene Italian volcanics (Tuscan Magmatic Province, Roman Magmatic Province, Vesuvius, Aeolian Islands, Etna, and Iblean Basin) define binary hyperbolic relationships in the 87Sr/86Sr–206Pb/204Pb–εNd–εHf space. The isotopic compositions of the two end‐members of these mixing arrays are assessed by least‐squares regression. The mantle‐derived component (206Pb/204Pb = 19.8, 87Sr/86Sr = 0.7025, εNd = +8, εHf = +9) is a rather homogeneous mixture of the standard high‐μ (HIMU) and depleted mantle (DM) components. The crust‐derived component (206Pb/204Pb = 18.5, 87Sr/86Sr > 0.715, εNd = −12, εHf = −11) accounts for the enrichment of K and other large‐ion‐lithophile elements in the Italian volcanics. As shown by the relationship in εHf–εNd space and the lower‐than‐chondritic Hf/Sm ratio, this crustal component is dominated by pelagic sediments rather than terrigenous material. The overall scarcity of calc‐alka...
Icarus, 2013
While metal rapidly segregates out of the melt and sinks into the core, the vaporized material or... more While metal rapidly segregates out of the melt and sinks into the core, the vaporized material orbits the Earth and eventually rains back onto its surface. The content of the mantle in siderophile elements and their chondritic relative abundances hence is accounted for, not by the impactors themselves, as in the original late-veneer model (Chou, C.L. [1978]. Proc. Lunar Sci. Conf. 9, 219-230; Morgan, J.W. et al. [1981]. Tectonophysics 75, 47-67), but by the vapor resulting from impacts. The impactor's non-siderophile volatiles, notably hydrogen, are added to the mantle and hydrosphere. The addition of late veneer may have lasted for 130 Ma after isolation of the Solar System and probably longer, i.e., well beyond the giant lunar impact. Constraints from the stable isotopes of oxygen and other elements suggest that, contrary to evidence from highly siderophile elements, $4% of CI chondrites accreted to the Earth. The amount of water added in this way during the waning stages of accretion, and now dissolved in the deep mantle or used to oxidize Fe in the mantle and the core, may correspond to 10-25 times the mass of the present-day ocean. The Moon is at least 100 times more depleted than the Earth in volatile elements with the exception of some isolated domains, such as the mantle source of 74220 pyroclastic glasses, which appear to contain significantly higher concentrations of water and other volatiles.
Geophysical Research Letters, 1998
The 176 Hf/ 177 Hf ratio was measured on 34 ferromanganese nodules, mostly from the Atlantic ocea... more The 176 Hf/ 177 Hf ratio was measured on 34 ferromanganese nodules, mostly from the Atlantic ocean. The different ocean basins are isotopically distinct with the extreme compositions being less radiogenic in the Atlantic (Hf ∼ +1) than in the Pacific (Hf ∼ +9). A good correlation of Hf and Nd is observed amongst most samples which supports that Hf isotopic compositions in nodules reflect those of ambient seawater. For a given Nd , Hf is more radiogenic in ferromanganese nodules than in rocks from either the mantle or the crust. This correlation makes the coupled Hf-Nd systems a potential paleoceanographic tool. It is argued that a zircon-free clayish component of probable eolian origin may account for the radiogenic Hf in nodules.
Geochimica et Cosmochimica Acta, 2007
Kimberlites from West Greenland have Hf-Nd isotope as well as major and trace element composition... more Kimberlites from West Greenland have Hf-Nd isotope as well as major and trace element compositions that are similar to other Group I kimberlites, but that are distinctive in the spectrum of magmas sampled at Earth's surface. The West Greenland kimberlites have e Ndi that ranges from +1.6 to +3.1 and e Hfi that ranges from À4.3 to +4.9. The samples exhibit ubiquitous negative De Hfi (deviation from the ocean island basalt e Hf-e Nd reference line), ranging from À1.8 to À11.2. The kimberlites are characterized by steep heavy rare earth element patterns, positive Ta-Nb anomalies and negative Hf-Zr anomalies. These chemical signals are consistent with the presence of ancient, subducted oceanic crust in the kimberlite source region. In the model we present, dewatering and possibly partial melting of rutilebearing oceanic crust during subduction results in characteristic trace element patterns in the residual crust. During aging, the Hf-Nd isotopic composition of this dewatered/partially melted EMORB-type crust evolves to negative De Hfi values. Metasomatic fluids derived from this ancient subducted oceanic crust infiltrate and impart their trace element and isotopic signal on proximal peridotitic mantle. Melting of this metasomatized mantle peridotite results in kimberlite magmas.
Geochemistry, Geophysics, Geosystems, 2014
We report 3He/4He for 150 mid‐ocean ridge basalt (MORB) glasses from the Southeast Indian Ridge (... more We report 3He/4He for 150 mid‐ocean ridge basalt (MORB) glasses from the Southeast Indian Ridge (SEIR). Between 81°E and 101°E 3He/4He varies from 7.5 to 10.2 RA, encompassing more than half the MORB range away from ocean island hot spots. Abrupt transitions are present and in one case the full range occurs over ∼10 km. Melting of lithologically heterogeneous mantle containing a few percent garnet pyroxenite or eclogite leads to lower 3He/4He, while 3He/4He above ∼9 RA likely indicates melting of pyroxenite‐free or eclogite‐free mantle. Patterns in the length scales of variability represent a description of helium isotopic texture. We utilize four complementary methods of spectral analysis to evaluate this texture, including periodogram, redfit, multitaper method, and continuous wavelet transform. Long‐wavelength lobes with prominent power at 1000 and 500 km are present in all treatments, similar to hot spot‐type spectra in Atlantic periodograms. The densely sampled region of the SE...
Geochemistry, Geophysics, Geosystems, 2002
Volcan Ecuador, a young, active shield volcano at the northwest tip of Isabela Island, Galápagos,... more Volcan Ecuador, a young, active shield volcano at the northwest tip of Isabela Island, Galápagos, experienced at least one sector collapse event that removed its western half. The compositions of lavas exposed in the old caldera wall and fault scarps dissecting the outer shield together with young post‐collapse lavas provide insights into the history of this volcano. 40Ar/39Ar and cosmogenic 3He dating reveal that sector collapse occurred at <100 Ka. Prior to sector collapse most magma erupted from circumferential dikes that fed the summit carapace and other dikes that fed vents on the caldera floor. Almost all of the erupted magmas cooled and underwent fractional crystallization in the lower crust or upper mantle, where clinopyroxene crystallization dominated. Magmas then rose to a small (∼0.1 km3), steady state, subcaldera magma chamber where plagioclase, along with lesser amounts of olivine and clinopyroxene, crystallized. Sector collapse perturbed the plumbing system in a way...