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• Drill core samples constrain the age and evolution of the buried Wyoming Province. • Zircon U-Pb geochronology records Mesoarchean magmatism and metamorphism. • Reflector east of the Bighorn Mountains may juxtapose Archean terranes with similar ages and isotopic signature. • Geochemical, geochronologic, and geophysical data are most easily explained by a contiguous eastern Wyoming Province. • Integration of geologic, geochemical, geochemical, and geophysical datasets is critical to evaluate Archean and Proterozoic terrane boundaries. The extent and nature of the Wyoming Province, an Archean craton in southwestern Laurentia, are poorly understood due to limited exposure between spatially isolated basement-cored uplifts. This lack of exposure has led to debate about whether the northeastern Wyoming Province is underlain by contiguous Archean crust or Proterozoic rocks and suture zone associated with the Trans-Hudson orogeny. To assess these models we analyzed samples recovered from drill cores in the buried northeastern Wyoming Province that straddle the proposed Proterozoic suture. Whole-rock geochemical and Nd-Pb-O isotopic data suggest the rocks formed by partial melting of > 3.5 Ga hydrated mafic to tonalitic sources similar to elsewhere in the northern Wyoming Province. Zircon U-Pb dates record Mesoarchean magmatism and metamorphism (3.0–2.8 Ga). Published whole-rock Rb-Sr, hornblende and biotite K-Ar, and apatite fission track dates suggest these rocks have not been heated above 300 °C since 2.5–2.1 Ga. Geophysical potential field data are consistent across northeastern Wyoming contrasting with major discontinuities associated with documented Proterozoic orogens on all other margins of the Wyoming Province. Hence, geochemical, isotopic, and geochronologic data along with geophysical imaging can be most simply interpreted in terms of continuous Archean crust in the northeastern Wyoming Province. A geophysically-imaged reflector east of the Bighorn Mountains may juxtapose Archean terranes with similar ages and sources, similar to the boundary between the Montana metasedimentary terrane and Beartooth-Bighorn magmatic zone in the northwestern Wyoming Province. This work emphasizes the value of integrating geologic and geophysical constraints to constrain Archean provinces and their tectonic evolution. [ABSTRACT FROM AUTHOR]

• A continuum of Paleoproterozoic heritage, seen in Nd model ages, from N to S in the Bushmanland Domain (BD), with the Buffels River shear zone simply a regional discontinuity. • The southern BD (SBD) has a greater juvenile component than the northern BD (NBD), becoming more dominant post-1.10 Ga. • Orthogneisses derived from crustal magmas with subduction-influenced signatures with mixed Meso- to Paleoproterozoic model ages. The SBD Koperberg Suite derived from low degrees of melting of enriched SCLM, but at deeper levels than those of the NBD. • The paragneisses derived from largely reworked, mixed Meso- to Paleoproterozoic felsic to intermediate sources. • Paragneisses derived from largely reworked, mixed Meso- to Paleoproterozoic felsic to intermediate sources. • SBD Koperberg Suite derived from low degrees of melting of enriched SCLM, but at somewhat deeper levels than NBD Koperberg magmas. • D 2 deformation constrained to ~ 1.11-1.09 Ga, with peak M 3 metamorphism at ~ 1.05-1.02 Ga. The timing of tectonomagmatic events and petrogenesis of ortho- and paragneisses within the high-grade southern Bushmanland Domain (SBD) of the Namaqua Metamorphic Province is, largely, poorly constrained. U-Pb age dating and whole rock lithogeochemistry of the rocks of the upper granulite facies Kliprand dome provide constraints with regards to the evolution of the SBD during the 1.2–1.0 Ga Namaquan Orogeny. The SBD has a greater juvenile component, particularly added between ∼1.1 and 1.02 Ga, compared to the northern Bushmanland Domain (NBD). This is reflected in marginally younger T DM model ages (1.60–1.95 Ga) than for the NBD (∼1.9–2.4 Ga), and higher ε Nd(t) values for magmatic rocks, particularly for the late- to post-tectonic Spektakel Suite (SS), concentrated in the SBD. The ∼1.06 Ga Klein Lieslap Charnockite of the SS was derived from reworking of radiogenic Paleoproterozoic arc crust, but has a large juvenile depleted component compared to that of the ∼1.19 Ga Grootberg Gneiss of the syn-tectonic Little Namaqualand Suite. SBD mafic magmas were derived from low degrees of partial melting of subduction-influenced enriched subcontinental lithospheric mantle. The pre-tectonic ∼1.17 Ga Oorkraal Suite shows limited crustal contamination of mantle-derived melts. The post-tectonic ∼1.05 Ga Koperberg Suite was derived from deeper mantle melting than that in the NBD, but shows less crustal contamination. The supracrustal Kamiesberg Group was derived from mixed, reworked Meso- to Paleoproterozoic crust that showed a more dominant depleted component compared to that in the NBD. Incongruent anatexis of the paragneisses gave rise to crosscutting garnetiferous quartzofeldspathic segregations, notably the strongly peraluminous ∼1.07 Ga Ibequas Leucogranite. D 2 deformation, at ∼1.11–1.09 Ga, resulted in penetrative foliation. D 3 deformation, related to the development of a sub-vertical foliation in the limbs of F 2 folds, is constrained to ∼1.07–1.06 Ga, between emplacement of the Ibequas Leucogranite and the Koperberg Suite. Peak granulite facies M 3 metamorphism occurred at ∼1.05–1.02 Ga. These age constraints are similar to those of the NBD reflecting a synchronous tectonomagmatic and kinematic history. The SBD represents a deeper crustal level with a greater mantle influence than the NBD. [ABSTRACT FROM AUTHOR]

[Display omitted] • Ediacaran-Cambrian series of Cap de Creus studied through Nd isotopic sources. • Eastern Pyrenees series (Cap de Creus) show Nd model ages ranging 1.4–1.6 Ga. • Coeval series from different Iberian terranes show contrasted Nd isotopic sources. • These data suggest different original locations along the Gondwana margin. • Isotopic tracers are a useful tool to check the provenance in paleoreconstructions. The North African margin of Gondwana formed by subduction and accretion during Ediacaran to Cambrian times. Sections of this active margin were incorporated during the late Paleozoic to the Variscan and Appalachian orogens. In the Variscan realm, these sections define in some regions a Cadomian basement comprising thick metasedimentary series associated with coeval subduction-related magmatic rock dated in the range 650–500 Ma. In the Cap de Creus Massif (Eastern Pyrenean domain), the Cadomian metasedimentary rocks formed from sediments derived from mixed felsic and intermediate/mafic sources, intruded by granitoid and minor mafic igneous rocks. These series were formed in a peri -Gondwanan volcanic arc setting, like other Cadomian series described in the SW of the Iberian Massif, such as Serie Negra Group of the Ossa Morena Complex. However, the Nd model ages of the Cap de Creus metasedimentary samples range from 1431 to 1620 Ma and are younger than those of their SW Iberia equivalents. This result can be interpreted as an indication of an eastern location in the Ediacaran - Cambrian peri -Gondwanan magmatic arc. Furthermore, the Cadomian series in the Central Iberian Zone have even younger Nd model ages than those of SW and NE Iberia. We present two end-member paleogeographic models consistent with reconstruction of the initial location of the Cap de Creus Massif and its relations with other domains (Ossa Morena Complex and Central Iberian Zone) in this sector of the North African Gondwanan margin. [ABSTRACT FROM AUTHOR]

• Analysing depth to basement using aeromagnetic data. • Precambrian terranes followed by gravity and magnetic surveys. • A remote sensing method for finding the depth of strata. • Using several methods to achieve the same results. • Making a 3D model for an area that has never been modelled. New faults and shear zones discussed and their connection to previous structures. Continuation of Greenstone belts showed using potential field data. The bedrock geology of Finnmark, northern Norway, consists primarily of rock complexes dating back to the Precambrian and early Mid Palaeozoic eras and comprises (1) a mid-crustal lithospheric basement which is characterised by granitoid and greenstone complexes dating from Neoarchean to late Paleoproterozoic in age; (2) the Caledonide Orogen, characterised by a series of nappes and thrust sheets. Finnmark forms part of the northern margin of the Fennoscandian Shield, which extends across northern Finland into northwestern Russia. Precambrian rock complexes are also found as thrust slices in Caledonian nappes at several places in Finnmark and Troms, as well as in tectonic windows. Recently acquired high-resolution aeromagnetic data have provided spectacular and confirmatory evidence for the continuation of the diverse Precambrian greenstone belts and granulite terranes beneath the magnetically transparent Caledonian nappes. This study aims at analysing this subsurface continuation of the terranes using potential field data and estimating the depths of the main magnetic sources beneath the nappes. In this study, several geophysical methods are used, including 3D Euler deconvolution and 2D Werner deconvolution. We have focused specifically on the depth-to-basement beneath nappes and purposefully excluded anomalies associated with shallow structures, such as dykes and faults. Different methods have produced similar results and indicate an appreciable increase in the depth of the Precambrian basement rocks from south to north. In the south, Precambrian basement rocks are either exposed on the surface southeast of the Caledonian front or reappear within tectonic windows. A prominent positive magnetic anomaly on the Porsanger Peninsula is thought to represent an extension of the anomaly ascribed to the greenstone belt of the Repparfjord Tectonic Window. A 3D model of this has also been provided. According to estimates, the depths-to-basement below nappes close to the Caledonian front range from less than 500 to 2000 m, whilst in the northern part of the study area the depths generally reach 3000 to 4000 m, and are locally estimated to range between 5000 m and 6000 m. [ABSTRACT FROM AUTHOR]

• The metavolcanic rocks of the Erdaowa Group were formed at 2.46–2.35 Ga, and metamorphosed at 1.95–1.85 Ga. • The metavolcanic rocks were originated from the partial melting of the depleted lithospheric mantle and experienced a small amount of crustal contamination. • The metavolcanic rocks of the Erdaowa Group were likely formed in an arc environment of active continental margin at the southern margin of the Yinshan Block. • Initial subduction between the Yinshan and Ordos Blocks had started since ∼ 2.46 Ga, and then collided at 1.95–1.85 Ga to form the Khondalite Belt. As a typical continent–continent collision belt, the Khondalite Belt (KB) of the North China Craton (NCC) represents a Paleoproterozoic orogenic belt that underwent subduction and collision. Although many high-grade metamorphic rocks have been well studied, the low to medium grade metamorphic rocks well preserved in KB are less studied, which hinders a better understanding of the initiation of Paleoproterozoic subduction and collision processes. The Erdaowa Group is a representative of such a metamorphic rock series. Zircon U-Pb dating of the metavolcanic rocks in the Erdaowa Group yields the eruption ages of 2465 ± 24 Ma and 2350 ± 34 Ma, and the metamorphic ages of 1933 ± 32 Ma and 1844 ± 30 Ma. The geochemical results show that the metavolcanic rocks of the Erdaowa Group belong to tholeiitic basalts series. The enrichment of large ion lithophile elements (LILEs) such as Rb and Ba, and the depletion of high field strength elements (HFSEs) such as Ta, Nb and Ti indicate that the metavolcanic rocks have arc geochemical affinities and may have been formed at an active continental margin associated with subduction. Zircon Lu-Hf isotopic analysis shows that ε Hf (t) values are −0.15 – + 8.72, and the single-stage depleted mantle model age is 2448 – 2707 Ma, indicating that the primary magma originated from partial melting of the depleted lithospheric mantle and experienced slight crustal contamination. The results further prove that the low and medium grade rocks were directly involved in the subduction and collision between the Yinshan Block and the Ordos Block. [ABSTRACT FROM AUTHOR]

Abstract: U–Pb zircon geochronology of two Permo-Triassic granites (samples OT-52 and OT-272 with ages of 229±8Ma and 256±2Ma, respectively) in the Unazuki area, Hida Metamorphic Belt, southwest Japan, revealed the presence of Eoarchean to Paleoproterozoic inheritance. Inheritance is consistent with both samples showing low zircon saturation temperatures for their bulk compositions. In OT-52, dark in CL, low Th/U zircon domains have a mean 207Pb/206Pb age of 1940±17Ma, which is consistent with an age of 1937±6Ma for anatexis in the Precambrian Busan gneiss complex in Korea. Eoarchaean inherited zircons with 207Pb/206Pb ages from ca. 3750 to 3550Ma are common in OT-272 but are few in OT-52, suggesting a source from rocks with affinities to those in the Anshan area in the northeast China part of the North China Craton. On the other hand, a Hida Metamorphic Belt metasedimentary gneiss into which the granites were intruded contains ca. 1840, 1130, 580, 360, 285 and 250Ma zircons (). These ages suggest that the Unazuki Mesozoic granites did not originate from proximal Hida Metamorphic Complex rocks, but instead from unrelated rocks obscured at depth. The predominance of Eoarchean to Paleoproterozoic age components, and the marked lack of 900–700Ma components suggest that the source was the (extended?) fringe of the North China Craton, rather than from Yangtze Craton crust. The Mesozoic evolution of Japan and its linkages to northeast Asia are discussed in the context of these results. [ABSTRACT FROM AUTHOR]

Abstract: Detrital zircon dating from Neoproterozoic successions in the Sirwa inlier of the Anti-Atlas belt in Morocco confirms that the maximum depositional age of the main stratigraphic groups is significantly younger than has been previously proposed in lithostratigraphic correlations. This can probably be extended to the whole Anti-Atlas according to other recent data from the Saghro inlier. Although the relative stratigraphic position of the different units remains valid as published previously, a crucial implication of the new ages is that the sequences believed to be contemporaneous with oceanic crust and island arc formation during the rifting and break-up of the northern margin of the West African Craton (WAC), and believed to be involved in the first phases of the Pan-African orogeny, are actually late to post-orogenic. The age of the main deformation associated with the collision of the oceanic- and arc-derived terranes to the WAC, allegedly affecting the sediments of the Saghro Group, has been estimated at around 663–640Ma. However, the youngest zircon populations of sediments of the Saghro and Bou Salda Groups, obtained in this study, cluster around 620–610Ma, constraining the maximum age of deposition. This age of sedimentation is indistinguishable from the age of intrusive high-K calc-alkaline plutons of the Assarag Suite, suggesting a very rapid cycle of magmatism, relief formation, erosion and sedimentation in an active geodynamic scenario. Moreover, the proportion of the 610Ma detrital zircons becomes less with respect to the Paleoproterozoic zircons at higher stratigraphic levels, suggesting that the source of young zircons was progressively eroded and more extensive cratonic areas, that probably underlie the Neoproterozoic rocks, were exposed. We interpret these data in terms of the development of a ca. 610Ma magmatic arc, built upon WAC basement, and its progressive dismantling. This arc can be correlated with the voluminous late Neoproterozoic (ca. 640–570Ma) arc magmatism characteristic of the north Gondwana margin and the peri-Gondwanan terranes. The diamictite beds that appear in the Imghi Formation of the Saghro Group have been correlated with the Sturtian glacial period ca. 700Ma. However, zircons from one sample of these diamictites indicate that this correlation cannot be longer maintained, and instead they should be correlated with the Marinoan glacial period ca. 630–610Ma, with a widespread distribution of glaciogenic deposits in West Africa. In addition, around 375 U–Pb concordant analyses obtained from Paleoproterozoic zircons from six samples represent a statistically significant population of this area of the WAC basement, which can be a useful database for comparison with the detrital zircon populations of the peri-Gondwanan terranes of Europe and North America, as the WAC margins were one of the major sediment suppliers for these terranes. [Copyright &y& Elsevier]

Abstract: New U–Pb SHRIMP zircon ages and Sm–Nd isotopic results identify early Mesoarchean (∼3150Ma) granitic crust cropping out in the eastern Gawler Craton, southern Australia. These rocks are more than 500 million years older than the oldest previously dated rocks from the Gawler Craton, and challenge the view that pre-3.0Ga crust in Australia is restricted to the Yilgarn and Pilbara Cratons of Western Australia. We interpret these new data to indicate the presence of ∼3150Ma crust at or near the surface throughout a wedge-shaped region covering an area of at least ∼1500km2. The region is characterised by high surface heat flow, and contains Paleo- and Mesoproterozoic intrusive rocks with evolved Nd isotopic compositions and high radiogenic heat production values. The newly identified Mesoarchean rocks provide an obvious source for the evolved Nd signatures, and are themselves relatively enriched in heat producing elements, particularly considering their age. We speculate that the presence of relatively radiogenic Mesoarchean crust underlies much of the area covered by the South Australian Heat Flow Anomaly. Identification of Mesoarchean crust near the eastern margin of the Gawler Craton prompts consideration of links with other Australian Cratonic elements. As far as we are aware, no direct age equivalents of these rocks have been identified elsewhere in Australia, although we note that some recent models for Australian Proterozoic geodynamic evolution may be used to predict the presence of equivalent aged crust in the North Australian Craton. [Copyright &y& Elsevier]

Abstract: Results of more than 400 in situ U–Th–Pb and Lu–Hf zircon isotope analyses combined with cathodoluminescence images and field relationships reveal that the oldest magmatic rocks of the Limpopo Belt (Musina area) formed during the Palaeoarchaean between 3.40 and 3.27Ga, experienced a first anatexis at 3.24–3.07Ga (M1) and were overlain by sediments mainly between 3.24 and 3.0Ga. Subsequently, the infra- and supracrustal rocks together underwent two high-grade metamorphic overprints, a first during the Neoarchaean at 2.65Ga (M2), and a second at 2.025Ga (M3). Hafnium isotope data additionally reveal that the Palaeoarchaean magmatic rocks result from substantial recycling of much older crust. This is well reflected by nearly chondritic ɛHfint obtained from primary magmatic zircon domains of four Sand River TTG-gneiss samples (ɛHf3.27–3.28Ga =−1.3 to −1.8), from leucosomes within the Sand River Gneisses (ɛHf3.40Ga =−2.0; ɛHf3.28Ga =−1.5), and from two meta-anorthosite samples of the Messina layered intrusion (ɛHf3.35Ga =0.1–1.4). Crustal recycling is also supported by hafnium isotope data of detrital zircon grains from two quartzite samples. These data reflect a general increase of the ɛHfint between 3.65 and 3.2Ga from ca. −4.0 to 0.0, indicating that an Eo- to Palaeoarchaean crust was mixed with juvenile mantel material in the hinterland of the Limpopo Belt. The present study also demonstrates that Hf isotope data provide a powerful tool, which makes it possible to distinguish zircon domains formed during distinct magmatic or metamorphic events, from such affected by a pseudomorphic alteration, even if the investigated zircon grain underwent multiple alteration processes. [Copyright &y& Elsevier]

Abstract: Numerous U–Pb zircon geochronological data show that rocks of the Precambrian basement from the North China craton (NCC) have two age peaks at 1.8–1.9 and ∼2.5Ga, respectively. Whether the most prominent peak at ∼2.5Ga really registered a period of major crustal growth in the NCC thus making it different from the global major crustal growth period of ∼2.7Ga is uncertain. In this paper, we carried out in situ U–Pb and Hf isotopes of zircons and whole rock chemical and Sr–Nd isotopic analyses for six Precambrian samples from the NCC in order to understand crustal growth and reworking. The samples have U–Pb zircon ages of 1.8–1.9, ∼2.5 and ∼2.7Ga, respectively. The two samples with U–Pb zircon ages of ∼2.7Ga have zircon Hf model ages (THf DM) and/or whole rock Nd model ages (TNd DM) close to their U–Pb zircon ages. It is clear that they represent juvenile crust generation, thus providing direct evidence that ∼2.7Ga was a period of new crustal addition. The samples with U–Pb zircon ages of ∼1.8 and ∼2.5Ga also have THf DM and/or TNd DM similar to those of the ∼2.7Ga samples, indicating that these samples also have a mantle extraction time of 2.7±0.1Ga and their ∼1.8 and ∼2.5Ga ages may represent periods of reworking of the 2.7±0.1-Ga crust rather than juvenile crust generation. The reworking is manifested either as metamorphism or as lower crustal-derived magmatism. Specifically, the ∼2.5-Ga tonalitic gneiss sample is thought to be derived by melting of the ∼2.7Ga lower crust. Since many ∼2.5-Ga tonalite–trondhjemite–granodiorites (TTGs) and calc–alkaline granitoids in the NCC contain ∼2.7-Ga xenocrystic and inherited zircons, we postulate that they are probably also derived mainly from the 2.7±0.1-Ga crust. Our data imply that the quantity of ∼2.7Ga continental crust in the NCC is probably greater in extent than that exposed today. [Copyright &y& Elsevier]

Abstract: We present a new, reliably dated Mesoproterozoic paleopole for Siberia, based on a combined geochronological and paleomagnetic study of mafic rocks within the Mesoproterozoic Sololi Group of the Olenek Uplift in northern Siberia. Ion microprobe (SHRIMP) U–Pb analysis yields crystallisation ages of 2036±11Ma for zircon from a basement granite and 1473±24Ma for baddeleyite from a large dolerite sill within the Kyutingde Formation. The baddeleyite result indicates that the lower Sololi Group is significantly older than was suggested by previous K–Ar results. Paleomagnetic analysis of the dolerite sill and related mafic intrusive rocks yields a paleopole at 33.6°N, 253.1°E, A 95 =10.4°. A positive baked-contact test between the Kyutingde sill and sedimentary country rocks shows that the magnetisation is primary. Comparison of this paleopole with coeval results for Laurentia provides a revised reconstruction between Siberia and Laurentia, and implies that these two continents were parts of a single Mesoproterozoic supercontinent since at least 1473Ma. We argue that Siberia, Laurentia, and Baltica belonged to the same supercontinent between 1473Ma and mid-Neoproterozoic time. [Copyright &y& Elsevier]

Abstract: U–Pb single zircon crystallization ages were determined using TIMS and sensitive high resolution ion microprobe (SHRIMP) on samples of granitoid rocks exposed in the Serrinha nucleus granite–greenstone terrane, in NE Brazil. Our data show that the granitoid plutons can be divided into three distinct groups. Group 1 consists of Mesoarchaean (3.2–2.9Ga) gneisses and N-S elongated TTG (Tonalite-Trondhjemite-Granodiorite) plutons with gneissic borders. Group 2 is represented by ca. 2.15Ga pretectonic calc-alkaline plutons that are less deformed than group 1. Group 3 is ca. 2.11–2.07Ga, late to post-tectonic plutons (shoshonite, syenite, K-rich granite and lamprophyre). Groups 2 and 3 are associated with the Transamazonian orogeny. Xenocryst ages of 3.6Ga, the oldest zircon yet recorded within the São Francisco craton, are found in the group 3 Euclides shoshonite within the Uauá complex and in the group 2 Quijingue trondhjemite, indicating the presence of Paleoarchaean sialic basement. Group 1 gneiss-migmatitic rocks (ca. 3200Ma) of the Uauá complex constitute the oldest known unit. Shortly afterwards, partial melting of mafic material produced a medium-K calc-alkaline melt, the younger Santa Luz complex (ca. 3100Ma) to the south. Subsequent TTG melts intruded in different phases now exposed as N-S elongated plutons such as Ambrósio (3162±26Ma), Araci (3072±2Ma), Requeijão (2989±11Ma) and others, which together form a major part of the Archaean nucleus. Some of these plutons have what appear to be intrusive, but are probably remobilized, contacts with the Transamazonian Itapicuru greenstone belt. The older gneissic rocks occur as enclaves within younger Archaean plutons. Thus, serial additions of juvenile material over a period of several hundred m.y. led to the formation of a stable micro-continent by 2.9Ga. Evidence for Neoarchaean activity is found in the inheritance pattern of only one sample, the group 2 Euclides pluton. Group 2 granitoid plutons were emplaced at 2.16–2.13Ga in a continental arc environment floored by Mesoarchaean crust. These plutons were subsequently deformed and intruded by late to post-tectonic group 3 alkaline plutons. This period of Transamazonian orogeny can be explained as a consequence of ocean closure followed by collision and slab break-off. The only subsequent magmatism was kimberlitic, probably emplaced during the Neoproterozoic Braziliano event, which sampled older zircon from the basement. [Copyright &y& Elsevier]

Abstract: Zircon and monazite U–Pb data document the geochronology of the felsic crust in the Mozambique Belt in NE Mozambique. Immediately E of Lake Niassa and NW of the Karoo-aged Maniamba Graben, the Ponta Messuli Complex preserves Paleoproterozoic gneisses with granulite-facies metamorphism dated at 1950±15Ma, and intruded by granite at 1056±11Ma. This complex has only weak evidence for a Pan-African metamorphism. Between the Maniamba Graben and the WSW–ENE-trending Lurio (shear) Belt, the Unango and Marrupa Complexes consist mainly of felsic orthogneisses dated between 1062±13 and 946±11Ma, and interlayered with minor paragneisses. In these complexes, an amphibolite- to granulite-facies metamorphism is dated at 953±8Ma and a nepheline syenite pluton is dated at 799±8Ma. Pan-African deformation and high-grade metamorphism are more intense and penetrative southwards, towards the Lurio Belt. Amphibolite-facies metamorphism is dated at 555±11Ma in the Marrupa Complex and amphibolite- to granulite-facies metamorphism between 569±9 and 527±8Ma in the Unango Complex. Post-collisional felsic plutonism, dated between 549±13 and 486±27Ma, is uncommon in the Marrupa Complex but common in the Unango Complex. To the south of the Lurio Belt, the Nampula Complex consists of felsic orthogneisses which gave ages ranging from 1123±9 to 1042±9Ma, interlayered with paragneisses. The Nampula Complex underwent amphibolite-facies metamorphism in the period between 543±23 to 493±8Ma, and was intruded by voluminous post-collisional granitoid plutons between 511±12 and 508±3Ma. In a larger context, the Ponta Messuli Complex is regarded as part of the Palaeoproterozoic, Usagaran, Congo-Tanzania Craton foreland of the Pan-African orogen. The Unango, Marrupa and Nampula Complexes were probably formed in an active margin setting during the Mesoproterozoic. The Unango and Marrupa Complexes were assembled on the margin of the Congo-Tanzania Craton during the Irumidian orogeny (ca. 1020–950Ma), together with terranes in the Southern Irumide Belt. The distinctly older Nampula Complex was more probably linked to the Maud Belt of Antarctica, and peripheral to the Kalahari Craton during the Neoproterozoic. During the Pan-African orogeny, the Marrupa Complex was overlain by NW-directed nappes of the Cabo Delgado Nappe Complex before peak metamorphism at ca. 555Ma. The nappes include evidence for early Pan-African orogenic events older than 610Ma, typical for the Eastern Granulites in Tanzania. Crustal thickening at 555±11Ma is coeval with high-pressure granulite-facies metamorphism along the Lurio Belt at 557±16Ma. Crustal thickening in NE Mozambique is part of the main Pan-African, Kuunga, orogeny peaking between 570 and 530Ma, during which the Congo-Tanzania, Kalahari, East Antarctica and India Cratons welded to form Gondwana. Voluminous post-collisional magmatism and metamorphism younger than 530Ma in the Lurio Belt and the Nampula Complex are taken as evidence of gravitational collapse of the extensive orogenic domain south of the Lurio Belt after ca. 530Ma. The Lurio Belt may represent a Pan-African suture zone between the Kalahari and Congo-Tanzania Craton. [Copyright &y& Elsevier]

• Two Paleoproterozoic episodes of unrelated magmatism compose the NW SFC crust. • Subalkaline (>2.18–2.11 Ga) and alkaline (2.05 Ga) rocks constitute the NW SFC crust. • The subalkaline crust was intensely reworked during ongoing subduction and the alkaline represent the post-collisional magmatism. • The Paleoproterozoic Guanambi and Correntina Erosive Window crust represents the accretionary to post-collisional magmatism. The interaction of multiple sources during convergent setting generates a wide compositional diversity of magmas, sometimes with initial mafic components. Subduction zones produce extensive magmatism, derived from several reservoirs at different depths. New and published geologic data were used here to constrain the tectonomagmatic evolution in the northwestern São Francisco craton. The study area comprises the Correntina Window and Guanambi batholith, where a suite of calc-alkaline rocks was dated at 2.18–2.11 Ga. This suite has metaluminous to peraluminous compositions and chemical characteristics typical of a calc-alkaline series produced through slab melting. The age-corrected Sr-Nd isotope compositions are similar to those of MORB (ƐNd(T): −4 to +4; Sr/Sri: 0.701–0.706), consistent with an origin in a moderately juvenile subduction setting and variable crustal input. This convergent process progressively enriched the subcontinental mantle. The available geologic data indicate that peak metamorphism interpreted to reflect crustal thickening in a convergent regime occurred between 2.11 and 2.05 Ga, and was associated with regional-scale granulitization and migmatization. At the end of this period, a second suite of alkaline rocks was emplaced at ~2.05 Ga in the northwestern São Francisco craton. The petrochemical features indicate a shoshonitic affinity with high compatible element contents, metaluminous to peralkaline compositions, and enriched isotopic compositions (ƐNd(T): −7 to −6 and Sr/Sri: 0.706–0.707), indicating derivation from enriched ultramafic sources. This suite is derived from enriched lithospheric mantle components, with contributions from slab-derived fluids, and possibly asthenospheric mantle. This voluminous magmatism was likely triggered by slab breakoff, which can cause asthenospheric upwelling and accelerated the tectonic transition from convergence to decompression. These processes induced melting of mantle components that were emplaced along transtensional zones and generated the present-day tectonic architecture in the NW São Francisco craton. [ABSTRACT FROM AUTHOR]

• Tectonometamorphic evolution of the Southern Ethiopian Shield. • The U-Pb zircon dating of high-grade rocks and intrusives (Hammar Domain) • Geodynamic evolution of the East-African Orogen. Based on new U–Pb zircon data, field structural analysis and a detailed petrological study of the plutonic and high-grade metamorphic rocks of the Hammar Domain (Southern Ethiopian Shield) overall geodynamic scenario was inferred, bringing broad implications for the East-African Orogeny. The structural evolution of the Hammar Domain can be summarized into four phases, D 1 to D 4 , resulting in (a) relict compositional banding (S 1), (b) flat-lying migmatite foliation (S 2) defining the primary contacts of granulites and migmatites, (c) superimposed steeply dipping N–S trending compressional foliation (S 3) due to regional ~E–W oriented compression and (d) later ~NW–SE trending left-lateral transpressive fabric (S 4). New geochronological data point to long-lasting orogenic convergence forming the East-African Orogeny which resulted in two main geodynamic events: (a) Late Tonian to late Cryogenian episode (ca. 770 to 650 Ma) where large volcanic arc construction as the source of rock photoliths (dated at ca. 770 Ma) was followed by crustal accretion and flat-lying fabrics origin (D 2 stage), intense migmatization and HT-MP metamorphism (T: 700–850 °C and P: 0.7–0.9 GPa) at depths of ~25–35 km (dated at ca. 720 and 715 Ma). (b) Late Cryogenian to early Ediacaran episode (ca. 650 to 620 Ma) as the key era of continental collision leading to the Greater Gondwana assembly. An early ~E–W oriented compression (D 3 stage) resulted in ~N–S trending fabrics that have been continuously changed to the left-lateral transpression (D 4 stage) forming ~NW–SE oriented foliations. The time-scale of D 3 and D 4 events is inferred by syn -tectonic granitoid intrusions yielded at ca. 648 Ma and ca. 630 Ma respectively. Furthermore, the syn- to post-tectonic leucogranite dike, dated at ca. 630 Ma, marks the upper limit for the ductile or brittle-ductile deformation and regional metamorphic events. [ABSTRACT FROM AUTHOR]

The Keraf Shear Zone (KSZ) of NE Sudan formed in Neoproterozoic time when juvenile crust of the Arabian–Nubian Shield collided with reworked older crust of the Saharan Metacraton. Orthogneisses and deformed granitoids which intrude carbonate sediments are calc-alkaline, medium-K, metaluminous and I-type diorites and granodiorites, with subduction-related trace element signatures. 207Pb/206Pb zircon single grain ages are ∼730 Ma for the high-grade gneiss and ∼710 Ma for granitoids. K/Ar ages are 660 Ma for hornblende from the granitoids and 560 Ma for biotite from the high-grade gneiss and the plutons. The geochronologic data indicate that the crust formed ∼730–710 Ma and that orogenic activity ended by ∼565 Ma. Cooling occurred over much of NE Africa at about the same time, possibly caused by orogenic collapse or unroofing caused by extensive glaciation. Pb isotopic ratios indicate an oceanic source for both the magmatic and metamorphic rocks in the KSZ. Sm/Nd model ages are 620–770 Ma for the post-tectonic plutons and 830–900 Ma for the gneiss, indicating negligible involvement of a pre-Neoproterozoic material in the evolution of Keraf igneous rocks. The (87Sr/86Sr)i values range from 0.7026 to 0.7046, which are indistinguishable from initial ratios for juvenile crust of the Arabian Nubian Shield and are lower than initial Sr isotopic compositions for the Saharan Metacraton. The isotopic data indicate that Keraf igneous rocks are juvenile additions to the crust and that the boundary between the Saharan Metacraton and the Arabian–Nubian Shield lies to the west. [Copyright &y& Elsevier]

The Oribi Gorge Suite is a voluminous suite of rapakivi granite-charnockite plutons which occur in the Mzumbe and Margate terranes of the eastern (Natal) sector of the Mesoproterozoic Namaqua–Natal Belt of Southern Africa. Previous geochronological studies have provided contradictory results for the age of emplacement of the suite.New single zircon evaporation dates and detailed SHRIMP zircon analyses for three of the plutons confirm the previously observed complexity with two episodes of intrusion at ∼1070 and 1030 Ma. Metamorphic growth of zircon at ∼1030 Ma is also recorded from the Oribi Gorge pluton. The two intrusive episodes are further apart timewise (∼45 Ma) than expected for plutons belonging to a single suite. The range of ages probably reflects long-lived, post-collisional trans-current shearing in the eastern (Natal) sector of the Namaqua–Natal Belt when conditions suitable for formation of similar, megacrystic, A-type granitoids were repeated. Similar granitoids from the western (Namaqua) sector of the Belt indicate that these tectonic conditions were regional in extent. [Copyright &y& Elsevier]

The southern part of the early Archaean Itsaq Gneiss Complex (southern West Greenland) on Akilia and adjacent islands consists of polyphase dioritic–tonalitic–granitic injection components with inclusions of metavolcanic amphibolites, chemical sediments such as banded iron formation (BIF), gabbros and ultramafic rocks. Incipient in situ partial melting and strong deformation during several Archaean tectonothermal events strongly modified these injection components, so that they are now mostly banded, schlieric migmatites with neosome produced during several events. The margins of many inclusions have been loci for either segregation of neosome and/or higher strain—obliterating the relationship between the inclusions and the older components of the migmatites. An added complication is that none of the inclusion lithologies in the southern part of the complex contain protolith zircon, which would provide precise, direct dates. Instead, minimum ages of inclusions are obtained by dating invasive components of the granitic (sensu lato) migmatites. Previous age determinations of the inclusions were centred on a ∼200 m long body of amphibolites, BIF and ultramafic rocks on the southwestern corner of Akilia. Geochronology of this locality has been controversial, with our proposed age of &ges;3850 Ma making the inclusion the world''s oldest-dated sedimentary and mafic rocks. We continue the debate on the age of the inclusion on southwest of Akilia, and we broaden it by presenting mapping and zircon dating studies of inclusions on islands with 20 km of Akilia. This (1) addresses the contentious ages of these rocks, (2) examines the broader issue of how the complex field relationships in migmatites can lead to geochronological controversies, and (3) addresses the problem of precise dating of rocks in gneiss complexes which do not carry zircon from their protoliths. On Qilanngaarsuit (island), a gneiss sheet cutting a metaperidotite inclusion has an age of ∼3850 Ma. On an islet ∼2 km west of Akilia, tonalite and quartz-diorite which intrude and envelop two mafic amphibolite and hornblendite inclusions have dates of ∼3850 Ma also. With our proposed ages of &ges;3850 Ma, these inclusions are older than similar rocks in the 3700–3800 Ma Isua supracrustal belt. At other investigated localities ∼3850 Ma zircon dates have not been obtained from the orthogneisses enveloping or intruding inclusions. At two localities invasive leucogranite neosome and a discordant diorite sheet cutting inclusions have ages of 3600–3660 Ma—a period of known tectonothermal events including crustal melting and intrusion of gabbros and diorites. At three localities, banded-schlieric orthogneisses adjacent to supracrustal, gabbroic and ultramafic rocks contain 3800–3700 Ma igneous components. In these cases, the inclusions could still be &ges;3850 Ma and be equivalent in age to similar rocks on Akilia, but this has been masked by the local tectonothermal history and greater amount of neosome development. An alternative explanation is that some younger (<3850 Ma, but still &ges;3600 Ma) supracrustal and mafic/ultramafic inclusions (as pre-migmatisation tectonic slivers between older rocks?) might also be present within the migmatites. Thus different minimum zircon dates can be obtained for the inclusions by dating the varied components of orthogneisses. This study shows the difficulty of dating rock types in migmatite complexes that do not carry zircon from their protolith, and the importance of full integration of field observations and geochronology in these studies. [Copyright &y& Elsevier]

Enveloped by orogenic belts during the assembly of Laurentia (∼2.0–1.7 Ga), the Rae and Hearne domains of the western Churchill Province experienced a complex sequence of tectonic events historically referred to as the “Hudsonian orogeny”. In Hearne domain, diverse thick-skinned intraplate structures developed in response to accretionary processes in Trans-Hudson orogen. These structures include infolds of Archean basement and Paleoproterozoic cover, and broken foreland thrusts. In central Hearne domain, an intracratonic basin succession of continental to shallow-marine strata (Hurwitz Group; <2.45–<1.91 Ga) is exposed in outliers that constitute the keels of doubly plunging basement-cover synclinoria, defining a fold train with wavelengths of 35–45 km. With the exception of local out-of-syncline shear zones, basement and Hurwitz Group are welded. Formed under greenschist facies conditions, the basement-cover infolds are open, concentric, and commonly display complex structures in their interiors. In the Poorfish–Windy outlier, southwestern Hearne domain, continental rift deposits of the Kiyuk Group unconformably overlie the Hurwitz Group. In contrast to basement-cover infolding to the north and east, Archean basement, the Hurwitz Group and the Kiyuk Group are imbricated by thick-skinned northwest-vergent thrusts and folds. Thrusting in the Poorfish–Windy belt was completed by 1815±10 Ma, as indicated by new U–Pb data from hydrothermal–metamorphic titanite recovered from recrystallized cements at the top of the Kiyuk Group. We interpret that shortening from shallow-level basement-cover infolding is balanced at depth by intrabasement faulting and distributed ductile strain, and that the geometric link between central Hearne basement-cover infolding and Poorfish–Windy thrusting is via intrabasement faults that cut to the surface. The main controls on thick-skinned deformation were: the high competency of the lower Hurwitz Group; previous thermal weakening; basement heterogeneities; and possibly, shallow subduction preceding terminal collision in Trans-Hudson orogen. [Copyright &y& Elsevier]

U–Pb sensitive high resolution ion microprobe (SHRIMP) zircon analyses have been used to place time constraints on the Proterozoic reworking of Archaean rocks during the Rayner Structural Episode in the Oygarden Group of islands, Kemp Land, East Antarctica. Felsic orthogneiss that preserves evidence for foliations that pre-date the Rayner Structural Episode, was deformed by two events during the Rayner Structural Episode: the first characterised by east-directed sub-horizontal thrusting, and the second by a regional scale south-dipping extensional shear zone. Metamorphic overgrowths on zircon grains from felsic orthogneiss, which have 929±12 and 924±17 Ma ages, are interpreted to have formed during granulite facies metamorphism that accompanied the thrusting event. Crystallisation of zircon in migmatite that also formed during this event, occurred in two stages: 904±16 and 884±24 Ma. Overgrowths on zircon in a pegmatite that intruded during the second event formed at 931±14 Ma. Charnockite that was emplaced in the Stillwell Hills prior to a regional thrusting event, was metamorphosed at 913±8 Ma. However, the distribution of isotopic data suggest the charnockite may have intruded at ca. 960 Ma. The ages for regional thrusting in the Oygarden Group and the Stillwell Hills correlate, suggesting that the Rayner Structural Episode did not affect Kemp Land until ca. 930 Ma. This age for peak metamorphism in Kemp Land is therefore 50 Myr younger than the age inferred for the Rayner Structural Episode further to the east on the Mawson Coast and south in the northern Prince Charles Mountains. The ages from the Oygarden rocks correlate with the second half of the orogenic episode seen on the Mawson Coast and northern Prince Charles Mountains, consistent with the possibility of two phases of collision in a transition from an Andean-style margin to continent–continent collision between 1000 and 900 Ma. Previously unreported ca. 1600–1650 Ma ages were also discovered in orthogneiss and pegmatite samples, indicating a thermal event in Kemp Land at this time. The 1600–1650 and 930–900 Ma ages from the Oygarden Group correlate with metamorphic and magmatic ages from the Eastern Ghats, placing further constraints on the correlation between these metamorphic belts. [Copyright &y& Elsevier]

Recent mapping in the eastern Central Lapland Granitoid Complex and dating of zircons at the NORDSIM facility was performed in order to highlight the existence of an 892-km2 area of Archaean gneisses not previously identified in southeast Lapland, Finland. This Archaean enclave is composed of northeast-trending, km-scale bands of orthogneisses with varying mafic content and is named the Suomuja¨rvi Complex. Along its southeastern boundary lies the Aholanvaara volcano-sedimentary package. The evolution of the Suomuja¨rvi Complex began at ca. 2810 Ma with intrusion of the homogeneous Jumisko biotite tonalite–granodiorite in the west. This lithology becomes increasingly heterogeneous to the east where muscovite and an inherited ca. 2870 Ma old rock component represented by zircon cores are present. These orthogneisses were later intruded by the 2755±18 Ma (1σ) protolith of the Miehinka¨vaara amphibole and biotite bearing diorite–tonalite gneisses producing diffuse contacts characterized by gradual increases in mafic minerals. All of the orthogneisses were then migmatized/metamorphosed. After ca. 2730 Ma the Aholanvaara volcano-sedimentary package was deposited. Its main quartzite unit was dominantly derived from an unknown 2731±17 Ma (1σ) source but it also contains a ca. 3.4 Ga detrital component. The absence of 2800–2820 Ma detrital material in these sediments indicates they were not derived locally from the Suomuja¨rvi Complex. Instead, they share affinities with supracrustal packages further south in Posio, east in the Belomorian Province and north in the Central Lapland Greenstone belt. Widespread, voluminous intrusion of granites occurred in the area surrounding the Suomuja¨rvi gneisses and left a marked metamorphic overprint on the gneisses during the ca. 1.8 extensional collapse of the Svecofennian and Lapland-Kola orogens. Multi-scale folding produced subhorizontal, southwest-plunging, tight to isoclinal, upright folds and the dominant axial planer, northeast-trending fabric in the area. This fabric is cut by a northwest-trending fabric in the southwestern part of the area. Geological characteristics of the Suomuja¨rvi Complex and ages of the orthogneisses within it indicate that it most likely represents the southwestern margin of the Archaean Belomorian block. [Copyright &y& Elsevier]

U–Pb dating of Proterozoic rocks of the tectonic basement windows in the Caledonides of north-central Norway has provided new information of the westernmost margin of the Fennoscandian Shield. Four granitic gneisses dated along a 70-km profile in central Nordland have yielded ages in the interval 1800–1795 Ma. These ages are similar to U–Pb ages from the Lofoten–Vestera˚len area and the Rombak Window in northern Norway. The granitoid rocks are also coeval with the oldest group of granitoids in the Trans-Scandinavian-Igneous Belt (TIB) in southern Sweden (1.81–1.76 Ga) and the late Svecofennian granitoids in central Sweden (1.80–1.77 Ga), confirming the importance of the 1.80 Ga magmatic period at the western parts of the Fennoscandian Shield. The geochemistry of the dated granitoids is consistent with formation in a subduction-related regime. The granitoid rocks are interpreted to have been generated by mixing of mafic melt and a large proportion of melts derived from early Svecofennian granitoids (1.91–1.87 Ga), probably with minor contribution from Archaean crustal material. The new data support a model where the rocks of the basement windows in central Nordland represent the western continuation of the Fennoscandian Shield under the Caledonian nappes. The Sm–Nd isotope data of the granitoid rocks implies that they were generated to the south and west of the Archaean–Proterozoic boundary. [Copyright &y& Elsevier]

Ion microprobe U–Pb zircon geochronology of an orthopyroxene-bearing felsic orthogneiss from central Tonagh Island, Enderby Land, East Antarctica provides insight into the chronological-metamorphic evolution of the Archaean Napier Complex, the details of which have been the source of debate for over two decades. The orthogneiss crystallised at 2626±28 Ma, predating peak, ultra-high temperature (UHT) metamorphism and development of an intense regional S1 gneissosity. Two subsequent episodes of zircon growth/resetting can be identified. A minor period of zircon growth occurred at 2546±13 Ma, the regional significance and geological nature of which is unclear. This was followed by an episode of abundant zircon growth, as mantles on ∼2626 Ma cores and as anhedral grains, partly characterised by high Th/U (>1.2), at ∼2450–2480 Ma. This age coincides with both lower and upper concordia intercept ages from other U–Pb zircon studies, and several Rb–Sr and Sm–Nd whole-rock isochron ages from the Napier Complex. We conclude that UHT metamorphism occurred at ∼2450–2480 Ma, and find no compelling evidence that UHT occurred much earlier as has been postulated. The zircon U–Pb data from this study also indicates a lower intercept age of ∼500 Ma, which coincides with the emplacement of Early Palaeozoic pegmatite swarms and synchronous infiltration of aqueous fluids into the southwestern regions of the Napier Complex. [Copyright &y& Elsevier]

The paper documents a late Palaeoproterozoic episode of metamorphism and anatexis in the Suomuja¨rvi Complex, an Archaean enclave in the Palaeoproterozoic Central Lapland Granitoid Complex of northern Finland. U–Pb ages were obtained from monazite and titanite in four Archaean granitoid rocks, one quartzite and a massive granite. The results show that growth of monazite and titanite in these rocks spanned a period of about 15 million years between 1780 and 1765 Ma, presumably reflecting complex processes of metamorphic (re-) crystallisation, invasion by granitic dykes, veins and fluids and post-peak-metamorphic retrogression. The timing of this activity corresponds to post-orogenic granitoid magmatism throughout the Baltic Shield. In this region, between the Lapland-Kola and that of Svecofennian orogens, it may represent a retarded response to their coeval, ca. 1.9 Ga convergent collision. The results support a proposed affinity of the Suomuja¨rvi Complex with the Belomorian rather than the Archaean Karelian Province. [Copyright &y& Elsevier]

Zircons from six samples collected from igneous and metamorphic rocks were dated using the NORDSIM ion microprobe, in order to investigate the tectonic evolution of the Palaeoproterozoic Svecofennian Orogen in southwestern Finland. These rocks represent pre-collisional, collisional and post-collisional stages of the orogeny. The ion microprobe results reveal two age groups of granodioritic–tonalitic rocks. The intrusions have different tectonic settings: the Orijärvi granodiorite represents pre-collisional 1.91–1.88 Ga island-arc-related magmatism and yielded an age of 1898±9 Ma, whereas the collision-related Masku tonalite was dated at 1854±18 Ma. The latter age accords with more accurate previous conventional zircon age data and constrains the emplacement age of collisional granitoids to ≈1.87 Ga. This is interpreted to reflect the collision between the Southern Svecofennian Arc Complex with the Central Svecofennian Arc complex and the formation of a suture zone between them during D2 deformation. Granulite facies metamorphism in the Turku area was dated at 1824±5 Ma using zircons from leucosome in the Lemu metapelite. This age constrains D3 folding related to post-collisional crustal shortening in this area. Crustal melting continued until ≈1.81 Ga, as indicated by the youngest leucosome zircons and metamorphic rims of enderbite zircons. New metamorphic zircon growth took place in older granitoids at granulite facies, but not at amphibolite facies. Detrital zircons with ages between 2.91 and 1.97 Ga were found in the mesosome of the Lemu metapelite and 2.64–1.93 Ga inherited cores were found in the 1.87 Ga Masku tonalite. [Copyright &y& Elsevier]

During the Neoproterozoic Cadomian orogeny in northern France, supracrustal rocks of the Brioverian Supergroup were deposited in marginal and back arc basins, and were subsequently variably deformed and metamorphosed. New U–Pb analyses of single, and small multigrain fractions of zircon from selected plutons from the Baie de St. Brieuc region provide robust geochronological constraints on the timing of these events. The Jospinet granodiorite forms part of the local basement directly overlain by Brioverian metasediments and basic volcanics, and yields a U–Pb zircon date of 625.9+3.6/−1.9 (2σ) Ma. The pre-tectonic Port Moguer tonalite, which has been strongly sheared along with its amphibolite facies country rocks, has a crystallization age of 600.4±0.9 Ma. Emplacement ages of 576.3+1.5/−1.2 Ma for the syn-tectonic Fort La Latte quartz diorite and 574.6+1.8/−1.5 Ma for the late-tectonic St. Quay quartz diorite place limits on termination of deposition and timing of subsequent regional deformation of the Brioverian sequence in the Baie de St. Brieuc region. The new dates constrain the age of Brioverian sedimentation to the interval 626–575 Ma, a range consistent with a previously published Pb–Pb zircon evaporation age of ca. 588±22 Ma for Brioverian volcanic rocks (Lanvollen Formation). Deformation within this sector of the Cadomian belt is believed to have occurred shortly before 575 Ma, revising previously published estimates for the age of this major tectonothermal Cadomian event by 10–20 My. [Copyright &y& Elsevier]

The chemical Th–U–total Pb isochron method (CHIME) of dating was carried out on monazite, xenotime, zircon, and polycrase in six samples of ultra-high-temperature (UHT) granulites and one of pegmatite from five localities in the Napier Complex, Enderby Land, East Antarctica. Despite the chronological heterogeneity in many grains, the CHIME ages overall show strong evidence for a major event near 2420 Ma. Analyzed monazite and xenotime grains, except monazite from Mt. Riiser-Larsen, have a narrow range of CHIME ages: 2412±42 Ma from Beaver Island and 2429±36, 2421±18 and 2431±22 Ma from Reference Peak. These ages are indistinguishable from CHIME ages on zircon (2436±17 and 2420±20 Ma) and on central older domains of monazite (2404±54 Ma) from Mt. Riiser-Larsen, and on a zircon rim (2430±15 Ma) from Mt. Cronus. We conclude that the ca. 2420 Ma ages relate to the UHT metamorphism, but we do not exclude the possibility that lead loss has lowered the ages by some 50 Ma. This interpretation is consistent with a preponderance of ages obtained by other methods on the Napier Complex particularly the ca. 2475±25 Ma age for a generation of pegmatites coeval with the UHT event and containing the UHT mineral assemblage beryllian sapphirine–khmaralite+quartz. Events prior to 2500 Ma and after 2420 Ma have also left their imprint on the CHIME ages, for example, a 3646 Ma CHIME age suggests that a zircon core is inherited, whereas ca. 2200 and 2000 Ma CHIME ages in zoned monazite could be due to further lead loss during post-UHT activity. The much younger CHIME age of 1094±67 Ma for monazite from a pegmatite at ‘Zircon Point’, Casey Bay, confirms 1000–1100 Ma lead loss ages reported for this region, and could result from fluid activity in an outlier of Rayner activity near the boundary between the Rayner and Napier Complexes. Approximately 2500 Ma ages have been reported from granulite-facies (but not UHT) rocks in the Madras and Nilgiri blocks in South India; these blocks and the Napier Complex could have constituted a single structural unit by late Archean time. [Copyright &y& Elsevier]

The amphibolite facies Moyar, Bhavani and Palghat shear zones separate the South Indian Dharwar Craton (DC) from the Nilgiri and Madurai high-grade crustal provinces. We present Sm–Nd and Rb–Sr isotopic whole rock, mineral and small slab data for remnant granulites, mylonitic gneisses and granitoids that reveal a Neoproterozoic tectonothermal imprint in these shear zones. Sm–Nd garnet crystallisation ages and Rb–Sr mica cooling ages from reworked rocks suggest that Pan-African structurally-controlled retrogression and successive cooling in the Moyar shear zone (MSZ) (garnet 624–591 Ma; muscovite 594 Ma; biotite 604–540 Ma) predates tectonometamorphism in the Bhavani shear zone (BSZ) (garnet 552 Ma; biotite 521–491 Ma) and Palghat shear zone (PSZ) (garnet 521 Ma; biotite 488–485 Ma). A Rb–Sr small slab isochron age of ∼624 Ma indicates that Pan-African retrogression in the MSZ also led to isotopic reequilibration of the Rb–Sr system on a cm-scale. A Sm–Nd garnet crystallisation age of 513±5 Ma reflects emplacement of a postdeformative pegmatite in the BSZ during the late Cambrian. A Sm–Nd garnet age of 2355±18 Ma obtained from a granulite remnant in the MSZ records early Palaeoproterozoic high-grade metamorphism, which may be related to the amalgamation of the Nilgiri Block and DC along the palaeo-Moyar Zone. A relict charnockite from the southern BSZ yielded a reproducible Sm–Nd garnet age of 1705±11 Ma, presumably recording late Palaeoproterozoic metamorphism. Neoarchaean and Palaeoproterozoic Nd model ages (3.0–2.2 Ga) suggest that the shear zone rocks are mainly reworked material from the adjacent Nilgiri and Madurai crustal domains. Nd model ages of granites and tonalites, which intruded the MSZ syntectonically, provide evidence for ≤1.7 Ga crust generation. Unsheared metasediments, exposed between the Bhavani and Palghat high-strain zones, were subjected to Pan-African high-grade metamorphism, as constrained by Sm–Nd age data of garnets grown during coaxial deformation at ∼610–560 Ma. Sm–Nd whole rock data from these supracrustal rocks indicate average crustal residence ages of ∼1.9 Ga, which implies contributions from an unknown Proterozoic crustal source and disproves their previously suggested correlation to the Archaean Sargur Group. These model ages provide an upper limit for the juxtaposition of DC and Madurai Block along the BSZ and PSZ. [Copyright &y& Elsevier]

Rocks from the Sulphur Springs Group, a newly identified stratigraphic succession hosting volcanogenic massive sulphide (VMS) base-metal deposits in the Soanesville Belt, Pilbara Craton, northwestern Australia, have been analyzed by sensitive high-resolution ion microprobe (SHRIMP) U–Pb zircon mass-spectrometry to determine their age and tectonostratigraphic relationships. Most volcanism occurred between 3238 and 3235 Ma, distinctly different from the time interval spanned by the Wyman Formation (type section is 3315 Ma, other dates ∼3325 Ma) with which it was previously correlated. Outlying volcanic rocks with similar geochemistry at the Bernts and Obelix prospects also produce dates from 3240 to 3235 Ma and are, therefore, best interpreted as structurally-detached fragments of the Sulphur Springs Group. The Strelley Granite, an intrusion which shares geochemical characteristics with the overlying volcanic rocks, also yields similar ages, thus extending the period of temporally-linked extrusive–intrusive silicic magmatism in the evolution of the Pilbara Craton. Model Pb–Pb dating of galena from the Zn–Cu mineralization at the various VMS prospects has yielded ages consistent with the zircon U–Pb ages of the host rocks, indicating that the hydrothermal mineralizing systems were contemporaneous with and apparently initiated by igneous activity. An epicontinental tectonic setting for the Sulphur Springs Group during VMS mineralization is implied by the broad range of old zircon ages obtained from a tuff at the base of the volcanic pile. As the igneous episode coincides with the peak regional metamorphic event recorded in other east Pilbara supracrustal rocks and with voluminous intrusive activity in nearby granitoid complexes, it marks a major event in the crustal evolution of the eastern Pilbara Craton. [Copyright &y& Elsevier]

• Archean and Paleoproterozoic rocks emerge within the Neoproterozoic Araguaia Belt-AB. • Northern AB exhibits Mesoarchean (2.93–2.87 Ga) and 1.86 Ga granitic gneisses. • Southern AB shows Rhyacian orthogneisses (2.06 Ga) and 1.87 Ga deformed granite. • Northern and southern basement already formed a single crustal segment by the Orosirian. • This Archean/Paleoproterozoic basement integrated the Amazonian Craton. Archean and Paleoproterozoic basement rocks are exposed in the Araguaia Belt, a Neoproterozoic orogen bordering the eastern portion of the Amazonian Craton. Zircon LA-MC-ICPMS U-Pb and Lu-Hf isotopic systematics allowed a more accurate dating of the basement rocks and investigating the evolution of this large Archean/Paleoproterozoic crustal segment and discuss the relationship with the southeastern Amazonian Craton. Archean TTG orthogneisses (2.93 to 2.87 Ga) prevail in the northern belt while distinct magmatic events generated their protoliths in approximately 60 Ma. Zircon Hf model ages (~3.0 to 3.4 Ga) and Ɛ Hf(2.87-2.93) from −4.3 to +5.3 suggest crustal reworking of Mesoarchean juvenile sources, with the subordinated contribution of older crust. A Mesoarchean source is also indicated by the Hf model ages (2.93–3.25 Ga) and Ɛ Hf(−1.86 Ga) from −4.8 to −1.6 of a 1.86 Ga granitic gneiss intrusive in the Archean TTG. An orthogneiss and an intrusive granitoid from southern segment of the belt were dated 2.06 Ga and 1.87 Ga, respectively. The Hf model ages (2.65–2.86 Ga) determined for these rocks, the Ɛ Hf(-2.06 Ga) (−4.8 to −1.6) for the orthogneiss and the Ɛ Hf(1.87 Ga) (−15.8 to −9.7) found for the granitoid reveal a dominant crustal source for the southern basement rocks. The Archean and Paleoproterozoic basement constituted a single crustal segment by the Orosirian, since both segments present intrusive granites of this geological period. The Archean orthogneisses of the Araguaia Belt and the granitoids of the Carajás Province Mesoarchean domains in southeastern Amazonian Craton share some similarities, such as the TTG affinity magmatism formed in a relatively similar time interval, the Orosirian intrusive granites, and the Mesoarchean juvenile source. Therefore, the basement rocks cropping out in the northern segment of the Araguaia Belt may represent portions of the adjacent Amazonian Craton. [ABSTRACT FROM AUTHOR]

• Rifting along the SW margin of Baltica, constrained by dating of effusive rocks. • Main phase of effusive activity dated at 567.1 ± 4.7 Ma to 551.0 ± 4 Ma. • Early phase of igneous activity dated at 580 ± 8.1 Ma to 588.0 ± 8 Ma. • Emergence of Baltica as an individual palaeocontinent at ca. 550 Ma. • Incipient triple junction, related to Rodinia break-up, developed in the study area. Thick Neoproterozoic rift sequences along the western margin of the East European Craton (EEC) are classically attributed to rifting leading to break-up of super-continent Rodinia/Pannotia. Rifting was associated with intense, mainly mafic, volcanism, known as the Volyn Series, in the Lublin-Podlasie Basin (LPB) and in the Orsha-Volyn Aulacogen. Legacy deep boreholes in Poland provide continuous section through the volcanic series. Zircon from nine samples of tuff layers interbedded with basalt, from four boreholes, were dated with the U–Pb method with SHRIMP. The samples contain syn -eruptive zircons, together with zircon recycled from previous ash falls and zircon from the surrounding Proterozoic basement. The youngest volcanic zircon cluster from each sample of the studied tuff samples yielded concordia ages stratigraphically consistent, which document eruption events that took place between 567.1 ± 4.7 Ma and 551.0 ± 4 Ma. The most intense development of lavas and pyroclastics took place at ca. 557–555 Ma and ca. 567–560 Ma. Older volcanogenic zircon grains, inherited from previous phases of volcanic activity, preceding actual eruptions, were are dated at 588.0 ± 8 Ma to 580 ± 8.1 Ma. Age spectrum of xenocrysts zircon grains, inherited from the crystalline basement rocks of the LPB, ranges from ca. 1830 Ma to ca. 1480 Ma, coherent with the known late Paleoproterozoic and Mesoproterozoic age of crust-forming events in the western part of the EEC. The late Ediacaran syn -rift igneous activity in the LPB continued over a time span of approx. 37 My. It developed along both the SW margin of emerging Baltica and in the western the Orsha-Volyn Aulacogen. The study area was located at the intersection of these regional structures, being thus a site of development of an incipient triple junction, related to Rodinia/Pannotia break-up. Further extension along the SW margin of Baltica led to its separation from the plate adjacent to the west, and to the subsequent development of continental passive margin. Final emergence of Baltica, as an individual palaeocontinent, took place at ca. 550 Ma. [ABSTRACT FROM AUTHOR]

• The Malmberget IOA deposit is hosted by volcanic rocks intruded by various dikes. • The volcanic rocks are dated at 1885 ± 6 Ma and 1881 ± 6 Ma respectively. • Granitic and aplitic dikes are dated at c. 1790 Ma. • A metamorphic overprint event in the Gällivare area is dated at 1775 ± 6 Ma. • Geochemical signatures indicate generation in a volcanic arc environment. The northern Norrbotten region in Sweden hosts abundant iron-oxide apatite (IOA) deposits including Kiirunavaara, the type locality for Kiruna-type deposits, and Malmberget. Felsic and intermediate metavolcanic rocks hosting the Malmberget IOA deposit contain oscillatory zoned zircon which yield magmatic U-Pb SIMS ages of 1885 ± 6 Ma and 1881 ± 6 Ma, respectively. Metamorphic rims on zircon from these rocks yield 1797 ± 7 Ma and 1775 ± 6 Ma, respectively, and record the age of the latest Svecofennian regional metamorphic event in the Gällivare area, tentatively interpreted as regional contact metamorphism. Two granite dikes that cut the ore yield U-Pb zircon emplacement ages of 1790 ± 6 Ma and 1791 ± 7 Ma, respectively, overlapping with the metamorphic overgrowths, and set a lower age limit for ore formation in the Malmberget IOA deposit. Rocks hosting the Malmberget IOA deposit have an alkalic to alkali-calcic affinity with a geochemical signature that favors a continental-arc, transitional to extensional setting. These rocks are suggested to have been generated in a back-arc region, in response to subduction beneath the craton margin retreating to the SW or W. The obtained ages and geochemical signatures of these rocks coincide well with the regionally defined Kiirunavaara group rocks, hosting several other IOA deposits in northern Sweden. [ABSTRACT FROM AUTHOR]

• Integrated study of ophiolite and oceanic arc evolution. • Cambaizinho ophiolite in southern Brasiliano Orogen, Gondwana amalgamation. • U-Pb zircon and rutile dating 787–675 Ma. Integrated study of Tonian ophiolite mélanges and intra-oceanic arc of the São Gabriel juvenile terrane exposes a key geotectonic unit in the evolutionary history of Gondwana during Brasiliano Orogeny. LA-ICP-MS U-Pb geochronology in rutile and zircon were combined with Lu-Hf and rare earth elements in zircon. We report the first rutile dating of ultramafic rock in the Brazilian Shield of 787.6 ± 2.6 Ma for the Cambaizinho ophiolite magnesian schist. Dating of rutile corresponds to the metamorphic age of the mantle section of the ophiolite. São Gabriel arc infrastructure is represented by the Cambaí Complex, including the Vila Nova Suite metatonalite with zircon U-Pb age of 724.6 ± 3.2 Ma and late Sanga do Jobim Suite monzogranite intrusions with two main pulses at 698.9 ± 4.2 Ma and 673.9 ± 6.8 Ma. Zircon εHf (t) values are positive for both rocks and range between +10.1 and +7.4 in metatonalite and +9.2 to +2.5 in monzogranite. Detrital zircon from metasedimentary rocks support superstructure arc investigation. Ages range from 817 to 650 Ma, with strong concentration between 750 and 730 Ma. Positive εHf (t) values and Rare Earth Elements (REE) signature point to main source of metasedimentary rocks in the arc, with ophiolitic contribution. Therefore, geotectonic processes in the Brasiliano Orogeny include the construction of São Gabriel terrane with Tonian oceanic crust evolving to intra-oceanic subduction until 650 Ma to final development along the margin of continental crust. Overthrusting of the São Gabriel terrane onto the Rio de La Plata Craton occurred at 650–620 Ma. Our data correlate with Tonian intra-oceanic arcs from Brasilia belt (Goiás arc ca. 862–630 Ma) and Ribeira belt (Serra da Prata arc – 856–838 Ma; Rio Negro arc – 790–620 Ma). Oceanic crust generation combined with subduction to form Tonian arcs along the Brasiliano Orogen were most significant for construction of West Gondwana. [ABSTRACT FROM AUTHOR]