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Papers by Ian Williams

Geochemistry, Geophysics, Geosystems

In this contribution we report the first systematic study of zircon U‐Pb geochronology and δ18O‐ε... more In this contribution we report the first systematic study of zircon U‐Pb geochronology and δ18O‐εHf(t) isotope geochemistry from 10 islands of the hot‐spot related Galapagos Archipelago. The data extracted from the zircons allow them to be grouped into three types: (a) young zircons (0–∼4 Ma) with εHf(t) (∼5–13) and δ18O (∼4–7) isotopic mantle signature with crystallization ages dating the islands, (b) zircons with εHf(t) (∼5–13) and δ18O (∼5–7) isotopic mantle signature (∼4–164 Ma) which are interpreted to date the time of plume activity below the islands (∼164 Ma is the minimum time of impingement of the plume below the lithosphere), and (c) very old zircons (∼213–3,000 Ma) with mostly continental (but also juvenile) εHf(t) (∼−28–8) and δ18O (∼5–11) isotopic values documenting potential contamination from a number of sources. The first two types with similar isotopic mantle signature define what we call the Galápagos Plume Array (GPA). Given lithospheric plate motion, this result ...

Japan Geoscience Union, 2017

The oxygen isotopic composition of zircon is a powerful tool to characterize parental magma, comp... more The oxygen isotopic composition of zircon is a powerful tool to characterize parental magma, complementing trace element data. Recently technical improvements of a secondary ion mass-spectrometer allow us to obtain highly accurate and precise oxygen isotope data of zircon from thin sections or grain resin mounts. Numerous studies show that non-metamicted zircons can preserve their oxygen isotopic ratios (δO) from the time of crystallization, even though high-grade metamorphism and anatexis. The zircon oxygen isotope record is generally preserved despite other minerals that have been disturbed by high-grade metamorphism or intense hydrothermal alteration due to slower diffusion rate. The Napier Complex in East Antarctica has attracted considerable interest from a viewpoint of long Archaean crustal history from 3800 Ma to 2500 Ma and >1000°C ultrahigh-temperature (UHT) metamorphism in a regional scale. There are many petrological, geochronological, and geochemical reports, but the ...

Ancient crustal rocks provide the only direct evidence for the processes and products of early Ea... more Ancient crustal rocks provide the only direct evidence for the processes and products of early Earth dierentiation. SHRIMP zircon U-Th-Pb dating has identi®ed, amongst the Acasta gneisses of the western Slave Province, Canada, two metatonalites and a metagranodiorite that have igneous ages of 4002 4, 4012 6 and 4031 3 Ga respectively. These are the ®rst identi®ed Priscoan terrestrial rocks. A record of metamorphic events at 3.75, 3.6 and 1.7 Ga also is preserved. These discoveries approximately double, to 40 km, the area over which 4.0 Ga gneisses are known to occur. A single older zircon core in one sample suggests that rocks as old as 4.06 Ga might yet be found in the region. As early as 4.03 Ga, terrestrial dierentiation was already producing tonalitic magmas, probably by partial melting of pre-existing, less dierentiated crust.

page 3, line 21. For Page 4, line 5. For line 17. For page 10, line '3. For Page 13, line 27.... more page 3, line 21. For Page 4, line 5. For line 17. For page 10, line '3. For Page 13, line 27. For Page 21, line 28. For Page 23, line 14. For Page 27, line 19. For line 20. For Page 61, line 3. For Page 68, line 2. For Page 86, line 24. For Page 99, line 7. For Page 113, line 19. For Page 124, line 10. For Page 142, line 27. For line 30. For Page 173, line 21. For Page 175, line 5. For Page 188, line 4. For Page 242, line 14. For line 15. For line 16. For Page 245, line 9. For line 11. For Page 247, line 13. For Page 275, line 2. For 'Garner e_t al., 1976' r ad 'Garner et al., 1975 'with an unique' read 'with a unique'. 'ages in access' read 'ages in excess'. 'into one area' read 'into an area'. 'as stratigraphic' read 'a stratigraohic'. 'axes fellow [ed] ' read 'axes follow [ed] '. 'usually high* read 'unusual_y high'. 'range in, § 'JG' read 'range in § O'...

Journal of Petrology, 2021

Early Palaeozoic ultrahigh-temperature (UHT) metamorphism in eastern Gondwana was an event that s... more Early Palaeozoic ultrahigh-temperature (UHT) metamorphism in eastern Gondwana was an event that started with Gondwana amalgamation at c. 580 Ma and lasted at least 50 Myr. Sapphirine + quartz, Mg–Al granulites preserve a record of the timing and duration of the event along the metamorphic belt. U–Th–Pb dating of zircon and monazite shows that metamorphism peaked almost simultaneously in Antarctica (554.0 ± 4.7 Ma), Sri Lanka (555.5 ± 4.6 Ma), southern India (548.1 ± 8.1 Ma) and Madagascar (550.6 ± 6.0 Ma), and ended in all locations at the same time, 530–520 Ma. Rare earth element (REE) compositions of the metamorphic zircon zones can be matched to the REE zoning in the associated garnet. Phase-diagram modelling indicates that the peak UHT P–T conditions in Antarctica, Sri Lanka, and India were very similar, 1020–1040 °C at 0.8 GPa. Peak conditions in Madagascar were at higher T and similar P: 1090 °C and 0.8 GPa. The East African Orogeny before 600 Ma preconditioned the crust of th...

The Journal of the Geological Society of Japan, 2021

Syn-plutonic dikes show the intermingling process of partially molten silicic and mafic magmas. W... more Syn-plutonic dikes show the intermingling process of partially molten silicic and mafic magmas. We found some syn-plutonic dikes with different ages between their silicic and mafic rocks from the Chubu and Kinki districts. The zircon U-Pb ages of the silicic rocks are-Ma while those of the mafic rocks are-Ma. It is unlikely that the granitic magma of-Ma survived in partially molten state until the injection of the mafic magma at-Ma because the time discrepancy of-Ma seems too long for a lifetime of a single magma chamber. In a silicic rock of the syn-plutonic dike we found a zircon grain which show Cathodoluminescence image of an irregular zoning with partly dissolved and re-grown texture. The U-Pb age of the re-grown part of it is ca. Ma and the that of the undissolved core is ca. Ma. Considering that the mafic rocks nearby is of Ma and the host rock of the syn-plutonic dike is Older Ryoke granitoid of-Ma, it could be reasonably interpreted that the syn-plutonic dike was formed by injection of mafic magma at ca. Ma into the already solidified-Ma granitoids and partially melted them, leading to the physical interaction of the local silicic crystal mush and the mafic magma, unlike the case where mafic magma was injected into preexisting mushy granitic magma chamber.

Geoscience Frontiers, 2019

The dominant geodynamic processes that underpin the formation and evolution of Earth's early crus... more The dominant geodynamic processes that underpin the formation and evolution of Earth's early crust remain enigmatic calling for new information from less studied ancient cratonic nuclei. Here, we present UePb ages and Hf isotopic compositions of detrital zircon grains from w2.9 Ga old quartzites and magmatic zircon from a 3.505 Ga old dacite from the Iron Ore Group of the Singhbhum craton, eastern India. The detrital zircon grains range in age between 3.95 Ga and 2.91 Ga. Together with the recently reported Hadean, Eoarchean xenocrystic (up to 4.24 Ga) and modern detritus zircon grains from the Singhbhum craton, our results suggest that the Eoarchean detrital zircons represent crust generated by recycling of Hadean felsic crust formed at w4.3e4.2 Ga and w3.95 Ga. We observe a prominent shift in Hf isotope compositions at w3.6e3.5 Ga towards super-chondritic values, which signify an increased role for depleted mantle and the relevance of plate tectonics. The Paleo-, Mesoarchean zircon Hf isotopic record in the craton indicates crust generation involving the role of both depleted and enriched mantle sources. We infer a short-lived suprasubduction setting around w3.6e3.5 Ga followed by mantle plume activity during the Paleo-, Mesoarchean crust formation in the Singhbhum craton. The Singhbhum craton provides an additional repository for Earth's oldest materials.

Chemical Geology, 2018

Early to mid Carboniferous I-type granites distributed in a broad meridional belt west of Sydney,... more Early to mid Carboniferous I-type granites distributed in a broad meridional belt west of Sydney, southeastern Australia, represent the last phase of granite magmatism in the southern Lachlan Fold Belt. Rare inherited zircon in the granites, in combination with zircon precipitated from the melt phase of the magmas, provides direct evidence of the nature and age of the source rocks from which the granites were derived, and the isotopic compositions of those rocks. Most granites from the north and central parts of the belt, represented by the Wuuluman, Home Rule, Oberon and Lett plutons (334 ± 3, 328 ± 4, 339 ± 2 and 328 ± 2 Ma, respectively), are characterized by scarce inherited zircon dominantly of Siluro-Devonian age, consistent with all being derived from a common zircon-poor source rock of mid to late Devonian age. Based on the isotopic compositions of the igneous zircon rims, that source was relatively homogeneous and immature ( 18 Ozrn 6-7‰, Hf(t) 0-+4). Two samples of the Tarana pluton (331 ± 2 Ma), near the centre of the belt, show evidence for heterogeneity in that source and the presence of a more evolved component that is also more zircon rich. Together with the Lett pluton from the same geochemical suite, their zircon rim compositions define a mixing array between more and less evolved end members ( 18 Ozrn 5.5-9.5‰, Hf(t)-4-+4). Only in the southern Chapmans Creek pluton (327 ± 3 Ma) is there clear evidence that the source of the granite also contained a minor component with a similar older protolith to the LFB early Palaeozoic sediments that host most of the LFB pre-Carboniferous granites. Presence of that component, which overwhelmingly dominates the inheritance in the pre-Carboniferous granites, is also reflected in a slightly elevated whole rock initial 87 Sr/ 86 Sr (> 0.7050) and igneous  18 Ozrn (ca. 7.5‰), but not in the igneous zircon Hf(t) (ca. +2). The amount of restitic zircon in granite is determined by not only the proportion of restite present but also the zircon contents of the various source rock components. The process of restite unmixing does not necessarily mean that more mafic, restite-rich granites will contain more inherited zircon.

Page 43. Photomicrograph, detail of opacity variations in zircon crystals 165 44. Photomicrograph... more Page 43. Photomicrograph, detail of opacity variations in zircon crystals 165 44. Photomicrograph, grain mount of higher radioactivity zircons .. 165 45. Photomicrograph, opacity variations in zircon crystals ........

Encyclopedia of Astrobiology, 2015

In astrophysics, Z is used to denote the mass fraction of all elements except hydrogen and helium... more In astrophysics, Z is used to denote the mass fraction of all elements except hydrogen and helium in a star or other astronomical object. Those elements, considered as "heavy elements" and often called "metals" by astronomers, differ with respect to hydrogen and helium because their production implies processing by a star, either through nuclear reactions during the Main Sequence or giant phase or as a consequence of a ▶ supernova explosive event at the end of the star's life. The abundance of these heavy elements is thus a very important indicator of the processing by stars in a galaxy. In contrast, lower case z is used by astronomers to denote the ▶ redshift of a (typically) distant object moving away from the observer.

Zir con U-Pb dat ing of ig ne ous rocks in the Radzi mowice and Wielis³aw Z³oto ry jski aurif er ... more Zir con U-Pb dat ing of ig ne ous rocks in the Radzi mowice and Wielis³aw Z³oto ry jski aurif er ous po ly metal lic de pos its, Sude tes, SW Po land. An nales So cie ta tis Ge olo go rum Po lo niae, 84: 213-233. Ab stract: A rhyo lite por phyry in the Radzi mowice de posit at Bu kow inka Hill has a SHRIMP zir con U-Pb age of 314.9 ± 3.1 Ma. This is con sis tent with pre vi ous zir con dat ing of a mon zo gran ite and a rhyo dac ite (ca. 315 Ma) in the ¯eleŸniak sub-volcanic in tru sion (ZI), con sid ered to be the ig ne ous rocks, rep re sent ing the old est mag matic pulses in the re gion. First-stage meso ther mal aurif er ous sul phide min er ali za tion in the de posit was con nected to hy dro ther mal pro cesses, as so ci ated with the rhyo dac ite in tru sions. This was fol lowed by tec tonic ac tiv ity and younger al ka line mag ma tism in a post-collisional geo tec tonic set ting. The first-stage Au-bearing sul phide min er ali za tion was cata clased and over printed by younger epi ther mal base-metal sul phides with mi cro scopic Au, as soci ated with BiTe -Ag min er als. The younger mag matic pulses are rep re sented by por phy ritic an des ites and lampro phy ric dykes, which cut the ZI. Zir con from these dykes yielded ages of 312.8 ± 2.8 Ma for an an des ite por phyry and 312.4 ± 4 Ma for a lam pro phyre. All these mag matic pulses, evi denced in the Radzi mowice de posit, are con sid ered to be the old est post-orogenic sub-volcanic mag ma tism cut ting the base ment of the in tra mon tane ba sins in the Sude tes, on the NE mar gin of the Bo he mian Mas sif. A rhyo lite por phyry in the fa mous "O rgany" ex po sure at Wielis³aw Z³oto ry jski (WZ) on the SE mar gin of the North-Sudetic Ba sin is younger, 297.5 ± 2.8 Ma. Vein-type aurif er ous ore min er ali za tion, hosted by Early Pa laeo zoic graphitic schists in in ti mate con tact with rhyo lite por phyry in WZ, is also cor re lated with this mag ma tism. The aurif er ous ore min er ali za tion at Radzi mowice and Wielis³aw Z³oto ry jski formed at dif fer ent times, dur ing dif fer ent mag matic pulses and suc ces sive hy drother mal stages, de spite sev eral simi lari ties in geo logic set ting and coun try-and host-rock com po si tions. There was a tran si tion from a post-collisional to a within-plate set ting over about 20 Ma in Late Carboniferous-Early Permian times, with the older ¯eleŸniak and Bu kow inka sub-volcanic in tru sions in the up lifted part of the Kac zawa Meta mor phic Com plex (ZI) and the younger Wielis³aw Z³oto ry jski sub-volcanic in tru sion in the meta mor phic base ment of an in tra mon tane ba sin.

Revision of the "oldest" rocks age in the crystalline basement of NE Poland. Prz. Geol., 54: 967-... more Revision of the "oldest" rocks age in the crystalline basement of NE Poland. Prz. Geol., 54: 967-973. S u m m a r y. The oldest geochronological results between 2.69-2.57 Ga was previously obtained by using K-Ar method on biotite from pegmatite from Jastrzêbna IG-1 borehole. In consequence, in many published reports up to 1998, the Mazowsze (or Masovian) granitoid massif has been regarded as Archean age structure. Therewithal, other rocks in the area, e.g. Barg³ów gneiss sequence traditionally were described as Archean in age. In the paper we present new U-Pb SHRIMP zircon and monazite results for above mentioned rocks which have been considered as Archean. Cathodoluminescence images and SHRIMP analysis were carried out for zircons and monazites from Jastrzebna IG-1 pegmatite of 514 m depth (a historical sample previously dated by K-Ar method) and for zircon magmatic cores from Barg³ów IG-2 orthogneiss of the 708 m depth. The obtained U-Pb ages of 1826 ±12 Ma (zircon) and 1789±34 Ma (monazite), and 1835±28 Ma (zircon) for two rock samples respectively have shown Paleoproterozoic origin. Only 4 of the 24 analysed zircons have clearly discordant results, which are all from the Jastrzebna pegmatite, where Pb-loss was possible (in partially metamict U-rich zircon grains). The new U-Pb SHRIMP dating indicates that Jastrzêbna pegmatite and Barg³ów magmatic protolith of the orthogneiss is only Late Paleoproterozoic in age and in general about 700 Ma younger than previously reported by K-Ar method. Therefore, there is no unequivocal evidence of the presence of Archean rocks in crystalline basement of NE Poland. This study has been undertaken as a part of a collaborative research agreement between the

Tectonophysics, 2008

The Central Iberian-Ossa-Morena transition zone (SW Iberian Massif) represents a segment of the n... more The Central Iberian-Ossa-Morena transition zone (SW Iberian Massif) represents a segment of the northern Gondwana margin with a long geodynamic evolution, characterized by the superposition of Cadomian and Variscan events. The Early Ordovician is mainly represented by porphyritic felsic volcaniclastic rocks (the Urra Formation) that pass up into a siliciclastic sediments typical of the Central Iberian Zone (Lower Ordovician Armorican Quartzite Formation). The Urra Formation unconformably overlies the previously deformed and metamorphosed Ediacaran sediments of the Série Negra (with Ossa-Morena Zone paleogeographic affinity). New SHRIMP zircon data obtained from the Urra Formation volcaniclastic rocks indicate an Early Ordovician age (206 Pb/ 238 U ages ranging from 494.6 ± 6.8 Ma to 488.3 ± 5.2 Ma) for this magmatic event. The inherited zircon cores indicate the presence of multicycle protoliths with different Precambrian ages: Neoproterozoic (698-577 Ma), Paleoproterozoic (2.33 Ga) and Paleoarchean (3.2-3.3 Ga). There is a noticeable lack of Meso-to Neoarchean and Mesoproterozoic ages. The data support the hypothesis that the volcaniclastic rocks were derived by partial melting of Cadomian basement (linked to a West African Craton provenance). The Urra Formation volcaniclastic rocks have rhyolitic to dacitic compositions, are peraluminous and similar to calc-alkaline high-K series suites elsewhere. Isotopic signatures present a wide range of values (87 Sr/ 86 Sr) t = 0.7085-0.7190, more restricted εNd t (−2.65 to − 0.35) and δ 18 O = 9.63-10.34‰, compatible with magmas derived from crustal rocks, including portions of the lower crust. Some samples show disturbance of the Rb-Sr system as shown by unrealistic values for (87 Sr/ 86 Sr) t b 0.703, probably due to Variscan deformation and metamorphism. The volcaniclastic rocks with a significant sedimentary contribution (upper unit) are distinguished from the others by the lowest values of εNd t (−5.53 to −4.85). The geochemical data are compatible with an orogenic geodynamic environment. However, the "orogenic" signature can be considered to represent, in part, an inherited feature caused by melting of the Cadomian basement which also has calc-alkaline affinities. The Early Ordovician crustal growth and associated magmatism, represented by the Urra felsic volcaniclastic rocks and associated calc-alkaline granitoids, diorites and gabbros, can be interpreted in terms of the underplating and temporal storage of mantle-derived magmas as the potential source for the "orogenic melts" that were intruded during Early Paleozoic extension. This record of Early Ordovician magmatism has striking similarities with other correlatives from the Iberian, Bohemian and Armorican massifs that are discussed in this paper. This comparison reinforces the probable existence of a large-scale crustal melting process linked to a significant episode of extension on the northern Gondwana margin that probably resulted in the birth of the Rheic Ocean.

The Journal of Geology, 2013

The Journal of Geology, 2006

High-grade gneisses from Mt. Riiser-Larsen, East Antarctica, have been dated by whole-rock-minera... more High-grade gneisses from Mt. Riiser-Larsen, East Antarctica, have been dated by whole-rock-mineral Sm-Nd and SHRIMP zircon and monazite U-Pb to help define the thermal history of ultrahigh temperature (UHT) metamorphism in the Napier Complex. Both the monazite and youngest zircon yield a range of apparent ages (∼2.51-2.47 Ga), consistent with crystallization during an extended period of metamorphism. Some zircon also preserves an isotopic record of earlier events, placing an upper limit of a few million years on the duration of peak metamorphic conditions. The similarity of the monazite and zircon U-Pb ages implies rapid initial postpeak cooling to below the blocking temperature of these minerals (∼900ЊC). Consistently lower Sm-Nd whole-rock-mineral isochron ages (∼2.38 Ga) indicate that cooling slowed before the temperature reached ∼650ЊC. The history of the UHT metamorphism is interpreted to be (1) protracted high-temperature (≥800ЊC) conditions ∼2.51-2.47 Ga, (2) peak conditions (up to 1100ЊC) for at most a few million years, (3) rapid cooling (10Њ-60ЊC /m.yr.) immediately after peak metamorphism, and (4) very slow cooling (≤4ЊC/m.yr.) at midcrustal levels (∼30-km depth) to a steady state geotherm by 2.38 Ga.

The Journal of Geology, 1995

The northeastern portion of the Idaho batholith (NIB) intruded Proterozoic rocks of the Belt-Purc... more The northeastern portion of the Idaho batholith (NIB) intruded Proterozoic rocks of the Belt-Purcell supergroup between SO and 90 Ma. Whole-rock Sm-Nd isotopic analyses of batholithic rocks yield depleted mantle model ages (T oM) between 1. 72 and 1.93 Ga and values of eNd between-17. 7 and-21.2, similar to associated metamorphic rocks and within the range for Belt-Purcell sedimentary rocks. Premagmatic zircons from one sample of the NIB were analyzed individually using the SHRIMP ion microprobe and yielded a single age population at 1.74 Ga. This apparently single-aged source contrasts with the range of ages reported for zircons from sedimentary rocks of the Belt-Purcell supergroup and suggests that the batholith was not the product of melting Belt-Purcell sediments, nor was it significantly contaminated with these sediments. The source of the batholith, however, appears to be of appropriate age and composition to be a major contributor of sediment to the Belt basin. In addition, the near coincidence of TOM and the age derived from premagmatic zircons in one sample suggests the source of at least part of the batholith was extracted largely from 1.74 Ga depleted mantle, with little or no input from older rocks. If so, this crust may represent a possible continuation of crust of similar age and character exposed to the north in the Canadian cordillera and to the south in Nevada, Arizona, and southeastern California.

Science, 2008

The positions of Laurentia and other landmasses in the Precambrian supercontinent of Rodinia are ... more The positions of Laurentia and other landmasses in the Precambrian supercontinent of Rodinia are controversial. Although geological and isotopic data support an East Antarctic fit with western Laurentia, alternative reconstructions favor the juxtaposition of Australia, Siberia, or South China. New geologic, age, and isotopic data provide a positive test of the juxtaposition with East Antarctica: Neodymium isotopes of Neoproterozoic rift-margin strata are similar; hafnium isotopes of ∼1.4-billion-year-old Antarctic-margin detrital zircons match those in Laurentian granites of similar age; and a glacial clast of A-type granite has a uraniun-lead zircon age of ∼1440 million years, an epsilon-hafnium initial value of +7, and an epsilon-neodymium initial value of +4. These tracers indicate the presence of granites in East Antarctica having the same age, geochemical properties, and isotopic signatures as the distinctive granites in Laurentia.

Journal of Petrology, 2001

Journal of Petrology, 2008

Sensitive high-resolution ion microprobe (SHRIMP) analyses of zircon from granites of the medium-... more Sensitive high-resolution ion microprobe (SHRIMP) analyses of zircon from granites of the medium-high grade AspromonteP eloritani Unit, Calabria^Peloritani Orogen (CPO), southern Italy, show that one of the minor trondhjemites (313Á7 AE 3Á5 Ma) represents the earliest identified occurrence of Late Hercynian peraluminous igneous rocks in the CPO, predating the emplacement of the more common peraluminous leucogranodiorites by about 14 Myr. Some of the trondhjemite zircon grains contain small cores with ages of about 2Á45 Ga, 625 Ma and 490 Ma, consistent with the presence of a sediment component in the magma. A newly dated leucogranodiorite (300Á2 AE 3Á8 Ma) is rich in inherited zircon. Cores with ages of about 2Á36 Ga, 870 Ma, 630 Ma, 545 Ma and 460 Ma are overgrown by two generations of Hercynian igneous zircon, the first with moderate to high Th/U (up to 1Á 67), and the second with low Th/U (50Á1). The overgrowths probably crystallized from magmas of two compositions, the first metaluminous and the second peraluminous. This could indicate either magma mixing or, more probably, crystallization in a single, evolving magma. In either case, the leucogranodiorite magma is considered to have been the product of anatexis of a metasedimentary source. Differences in the inherited zircon age spectra, and the relatively small amount of inheritance in the trondhjemite, indicate that the trondhjemite and leucogranodiorite are unlikely to be genetically related.The ages of the inherited zircons are consistent with the sedimentary component in both magmas being derived from North Africa, with a possible contribution from Pan-African granitoids similar to those exposed in southern Calabria.