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Sedimentary rocks of the Ocoee Supergroup crop out in the Appalachian Blue Ridge of western North Carolina and eastern Tennessee. This ∼12 km thick sequence of strata was mapped as nonconformably overlying Mesoproterozoic crystalline basement (about 1.20–1.02 Ga) and beneath the lower Cambrian Chilhowee Group, leading to the traditional interpretation that the Ocoee Supergroup was deposited between about 1.02 and 0.54 Ga. This interpretation was challenged by Unrug and Unrug (1990, Geology, 18: 1041–1045) and Unrug et al. (2000, Geological Society of America Bulletin. Vol. 112, pp. 982–996), who claimed that Paleozoic fossils were recovered from rocks of the Walden Creek Group (upper Ocoee), and thereby created a new tectonic model for the origin of Laurentia. To resolve the age controversy concerning the time of deposition of the Ocoee Supergroup, diagenetic xenotime overgrowths on detrital zircon and diagenetic monazite on detrital monazite were dated by the U–Pb method. Sensitive High Resolution Ion Microprobe ages of diagenetic xenotime from three samples of sandstone (Thunderhead Sandstone, Cades Sandstone, and Shields Formation) indicate that the Ocoee Supergroup was deposited in the interval of about 580–550 Ma. A sample of Sandsuck Formation (uppermost Ocoee) yielded xenotime overgrowths of about 410 Ma, probably related to post-depositional low-grade metamorphism. Various origins of xenotime overgrowths may be distinguished by trace element distributions. Ages and trace element concentrations of monazite overgrowths support the xenotime age results, although concordia systematics are complicated by high concentrations of common Pb and inheritance of ages (∼1.2 and 0.6 Ga). These age data support the observed field relations for a late Neoproterozoic depositional age of the Ocoee Supergroup.

Upper Cambrian through Middle Ordovician sedimentary strata of the Marathon/Solitario Basin (west Texas), which were folded and thrust-faulted during late Paleozoic Appalachian-Ouachita orogenesis, preserve evidence of the pre-Pangean history of the central southern Laurentian margin. New detrital zircon analyses reported here are from three Marathon Basin/Solitario formations: the upper Cambrian Dagger Flat Sandstone; the Lower Ordovician Marathon Formation, including the Rodrigues Tank Sandstone Member; and the Middle Ordovician Ft. Peña Formation. The far-southwestern outcrops of those Iapetus margin strata are within the Solitario dome (Presidio and Brewster Counties, Texas). Solitario zircon U/Pb geochronological results (laser ablation–inductively coupled plasma–mass spectrometry [LA-ICP-MS], sensitive high-resolution ion microprobe [SHRIMP]) expand the record of Cryogenian rifting as the Cuyania terrane separated from Laurentia. We evaluated these new data along with earlier geochronological and geochemical results from rift-related lava clasts in Lower–Middle Ordovician sedimentary subaqueous debris-flow deposits in the northwestern Marathon Basin. Deepening of the Iapetus seaway near the Laurentian margin (late Cambrian–Middle Ordovician) stimulated headward erosion of drainages, reflected in the systematic north-northwestward shift in zircon provenance from the west Texas Grenvillian and Southern Granite-Rhyolite Provinces to Yavapai-Mazatzal and Cheyenne Belt sources. The Cuyania rifted terrane underwent subduction at the western Gondwanan margin of the Iapetus Ocean in mid-Ordovician time (486 ± 7 Ma to 463 ± 4 Ma), and the resulting volcanism in the Famatina complex (Argentina) was most intense from ca. 472 to 468 Ma. Magmatic zircons from Ft. Peña bentonitic layers have identical U/Pb (488–468 Ma) and biostratigraphic (Darriwilian) ages to those from Famatinian bentonites at Talacasto (470 ± 5 Ma) in the Precordillera of Cuyania. Geologically constrained paleomagnetic reconstructions for 470 Ma depict the proximity of the Famatina arc, the rifted Cuyania terrane, and southern Laurentia at low southern latitudes (equator to ~30°S). These first U/Pb geochronological data from the Marathon/Solitario depocenter of western Iapetus appear to be compatible with such a configuration and can serve as test data for emerging tectonic interpretations.

Accurate reconstruction of the Late Cretaceous paleogeography and tectonic evolution of the western North American Cordilleran margin is required to resolve the long-standing debate over proposed large-scale, orogen-parallel terrane translation. The Nanaimo Basin (British Columbia, Canada) contains a high-fidelity record of orogenic exhumation and basin subsidence in the southwestern Canadian Cordillera that constrains the tectonic evolution of the region. Integration of detrital zircon U-Pb geochronology, conglomerate clast U-Pb geochronology, detrital muscovite 40Ar/39Ar thermochronology, and Lu-Hf isotopic analysis of detrital zircon defines a multidisciplinary provenance signature that provides a definitive linkage with sediment source regions north of the Sierra Nevada arc system (western United States).Analysis of spatial and temporal provenance variations within Nanaimo Group strata documents a bimodal sediment supply with a local source derived from the adjacent magmatic arc in the southern Coast Mountains batholith and an extra-regional source from the Mesoproterozoic Belt Supergroup and the Late Cretaceous Atlanta lobe of the Idaho batholith. Particularly robust linkages include: (1) juvenile (εHf >+10) Late Cretaceous zircon derived from the southern Coast Mountains batholith; (2) a bimodal Proterozoic detrital zircon signature consistent with derivation from Belt Supergroup (1700–1720 Ma) and ca. 1380 Ma plutonic rocks intruding the Lemhi subbasin of central Idaho (northwestern United States); (3) quartzite clasts that are statistical matches for Mesoproterozoic and Cambrian strata in Montana and Idaho (northwestern United States) and southern British Columbia; and (4) syndepositional evolved (εHf >−10) Late Cretaceous zircon and muscovite derived from the Atlanta lobe of the Idaho batholith. These provenance constraints support a tectonic restoration of the Nanaimo Basin, the southern Coast Mountains batholith, and Wrangellia to a position outboard of the Idaho batholith in Late Cretaceous time, consistent with proposed minimal- fault- offset models (

The Ok Tedi copper-gold mine in Western Province, Papua New Guinea, is situated in the western part of the Ok Tedi Complex where monzodiorite to quartz monzonite intrusions are associated with porphyry- and skarn-style copper-gold mineralization. The Pleistocene age of the intrusive rocks and mineralization provides an opportunity to study the longevity of the magmatic and hydrothermal evolution at Ok Tedi through U-Pb dating of zircon and high-precision Re-Os dating of molybdenite. Six main phases of intrusive rocks can be recognized within the mine area, with the sequence of intrusion indicated by contact relationships. Each has been dated by the SHRIMP U-Pb technique with correction for Th-U disequilibrium based on the U and Th content of each sample. In order of intrusion from oldest to youngest these include: Sydney Monzodiorite (1.368 ± 0.045 Ma), Warsaw Monzodiorite (1.269 ± 0.039 Ma), Kalgoorlie Monzodiorite (1.261 ± 0.050 Ma), Ningi Quartz Monzonite Porphyry (QMP)(1.229 ± 0.051 Ma), Bonn Quartz Monzonite (1.219 ± 0.040 Ma), and Fubilan QMP (1.213 ± 0.049 Ma). The intrusions are alkaline, high K to shoshonitic rocks with high Sr/Y ratios typical of Cu-fertile arc magmas. Chondrite-normalized REE patterns have minor or no negative Eu anomalies and downward sloping to listric-shaped HREE patterns typical of arc magmas in which high water contents supress plagioclase fractionation in favor of an evolution by hornblende ± garnet ± titanite fractionation. Cu-Au mineralization at Ok Tedi can be divided into four main stages based on crosscutting relationships: (1) skarn-endoskarn and associated vein-style mineralization in the Darai Limestone, Ieru siltstone, and Sydney Monzodiorite; (2) porphyry-style veins and breccias within the Ningi QMP and older intrusions, and at Siltstone Ridge: (3) porphyry-style veins and breccias in the Fubilan QMP and older intrusions: and (4) skarn-style mineralization in the lower part of the Darai Limestone along the Taranaki thrust. High-precision Re-Os dating of molybdenite has enabled a chronology to be established for the first three stages. Molybdenite from a quartz-mushketovite-epidote-carbonate-pyrite-chalcopyrite-molybdenite vein in clinopyroxene- and garnet-altered Sydney Monzodiorite has an age of 1.3206 ± 0.0020 Ma, and this dates the formation of the Gold Coast and Berlin skarns. Molybdenite from a quartz-pyrite-chalcopyrite-molybdenite vein in the sericite-altered Sydney Monzodiorite yields an age of 1.3166 ± 0.0043 Ma, and a quartz-pyrite-chalcopyrite-molybdenite vein with K-feldspar alteration selvages hosted in Ieru siltstone beneath the Gold Coast skarn has an age of 1.3031 ± 0.0015 Ma. Samples of molybdenite from quartz-sulfide veins from Siltstone Ridge have ages of 1.2116 ± 0.0029 and 1.2078 ± 0.0031 Ma. Molybdenite from a quartz-K-feldspar-pyrite-molybdenite vein, which overprints propylitic alteration in the Sydney Monzodiorite, has an age of 1.2120 ± 0.0024 Ma. These samples date porphyry-style mineralization in and around the Ningi QMP and at Siltstone Ridge. A sample of molybdenite from the matrix of hydrothermal intrusive breccia in the Fubilan QMP has an age of 1.2146 ± 0.0020 Ma, similar to the age of the adjacent Siltstone Ridge mineralization, and is interpreted to have been mechanically incorporated into the breccia during its formation. Several samples have been dated from the Fubilan porphyry system, including molybdenite from the matrix of a hydrothermal intrusive breccia (1.1648 ± 0.0020 Ma) and three samples from veins which postdate the breccias: a vuggy quartz-sulfide vein (1.1532 ± 0.0027 Ma), chalcopyrite-pyrite-molybdenite vein (1.1446 ± 0.0028 Ma), and duplicate analyses of a molybdenite-only vein (1.1326 ± 0.0034 and 1.1297 ± 0.0026 Ma) in agreement at 2σ. Molybdenite from a quartz-K-feldspar-biotite-magnetite-pyrite-chalcopyrite-molybdenite vein in endoskarn-altered Sydney Monzodiorite (beneath the Gold Coast skarn) has an age of 1.1459 ± 0.0012 Ma, and a similar vein without magnetite hosted in Warsaw Monzodiorite has an age of 1.1438 ± 0.0042 Ma, both within error of the chalcopyrite-pyrite-molybdenite vein in Fubilan QMP. Intrusive rocks in the Ok Tedi mine were emplaced over a period of approximately 200,000 years, with Cu-Au mineralization formed in discrete episodes of much shorter duration. The Gold Coast skarn and associated porphyry-style veins in Sydney Monzodiorite and Ieru siltstone formed in 14,000 to 21,000 years (n = 3), the Siltstone Ridge porphyry system in 2,000 to 12,000 years (n = 4), and the Fubilan porphyry system in 31,000 to 40,000 years (n = 6). The Taranaki skarn has not been dated in the mine area due to a lack of molybdenite, but geologic relationships indicate it is younger than the Fubilan QMP.

As the southernmost segment of the Central Asian Orogenic Belt (CAOB), the northern Alxa orogenic belt (NAOB) connects the southeastern and southwestern segments of the CAOB. The NAOB amalgamated with the closure of the Paleo-Asian Ocean; however, the closure time of the Paleo-Asian Ocean is still on great debate. In this study, we reported new detrital zircon U–Pb geochronology and Hf–O isotopes for the Permo–Carboniferous sediments in the northern Alxa to constrain the provenance and its tectonic implications. The Permo–Carbonifereous Amushan Formation is composed of volcanic-carbonite-clastic rocks and was deposited in a shallow marine environment. Based on the zircon U–Pb geochronology, the Amushan Formation was deposited in the late Carboniferous to early Permian, but some outcrops of volcanic and clastic rocks in the Quaganqulu area were likely formed in the middle to late Permian. The integrated zircon age spectrum for the clastic rocks shows a wide range from late Archean to Paleoproterozoic, Mesoproterozoic (with a peak age at 1458 ​Ma), early Neoproterozoic (with peak ages of 988 ​Ma and 929 ​Ma), early Paleozoic (with a peak age at 447 ​Ma) and late Paleozoic (with a peak age at 294 ​Ma). Combined with the zircon Hf–O isotopes, the provenance was considered to be the Alxa Block, the Shalazhashan terrane and the Zhusileng–Hangwula block (and the southern Beishan orogenic belt). The multiple source regions to the south and north of the Paleo-Asian Ocean indicate the closure of this ocean before the late Carboniferous. The absence or small proportion of depositional age-approximated zircons in most samples makes their age spectra similar to extensional basins. Combined with the intra-plate volcanism, the deposits were considered to be formed in extensional settings. Accordingly, after the closure of the Paleo-Asian Ocean, the NAOB stepped into an extensional stage.

Comision Nacional de Investigacion Cientifica y Tecnologica (CONICYT) Fondecyt 11140012 1161806 PAI79160139

The late Neoproterozoic Sao Rafael pluton, located in the Serido Belt of the Borborema geologic province, northeastern Brazil, is an unfoliated, metaluminous, epidote-bearing, high-K calc-alkalic granitoid. Three facies are present in its northern lobe: (i) a dominant massive granite to quartz monzonite porphyritic facies containing microcline phenocrysts, (ii) subordinate fine-grained facies, similar to the porphyritic facies except lacking amphibole, that crop out as inselbergs (“Serras”), and (iii) rare pillows of microgranular mafic enclaves (MMEs) that are present within the porphyritic facies. Chemical analyses include 19 bulk-rock data, and 33 microprobe data of epidote and amphibole. Beginning with bulk chemistry and postulated mineral compositions, an iterative procedure of solving matrices characterizes a rock sample. Derived information includes: (i) identifying what minerals are present, (ii) their relative abundances, and (iii) their chemical compositions, even for minerals (such as biotite or amphibole) with complexly variable compositions. Calculated mineral compositions are compatible with microprobe data. The matrix solutions further indicate alternative mineral assemblages, and the compositions of “phantom” minerals that could have existed in the magma source, although absent in the pluton. They establish that olivine, but not clinopyroxene, was a possible phantom mineral and that MMEs are of unrelated magmatic origin. According to matrix analysis, amphibole in an outer zone of the porphyritic facies is solely of neoformed origin, whereas amphibole in an inner zone of the porphyritic facies is of mixed origin—partly neoformed and partly residual (i.e., xenocrystic) “patchy” amphibole derived from MMEs. A qualified geothermometer provides Tsolidus = 730 ± 6 °C for the outer subfacies, and a qualified geobarometer provides P = 0.78 ± 0.06 kbar. Amphibole in MMEs crystallized at depth, at P~3.3 kbar. Corroded epidote attests to the pressure-sensitive instability of that mineral during rapid ascent decompression. Cathodoluminescence reveals complexly structured zircons with magmatic overgrowths and inherited cores. 207Pb/206Pb ages of inherited components cluster at ~2.0 Ga and ~2.4 Ga, these ages being prominent in the local basement. Oscillatory-zoned magmatic components yield a concordia upper intercept age of 580 ± 9 Ma, interpreted as the age of igneous crystallization. Values of δ18O in zircon are only slightly higher than δ18O in mantle-like zircon. At 0.58 Ga, eHf in magmatic zircon was notably unradiogenic (−22 to −26), indicating a magma source in old continental crust as adduced by ages of inherited zircon. A U-Pb titanite date is around 0.55 Ga. For the Rb-Sr and Sm-Nd whole-rock systems, isotopic inheritance from the magma protolith is so extreme and variable that isochrons are actually “scatterchrons” that provide no useable age information. Rb-Sr cooling ages of biotite are 498 ± 1 Ma. Most Sm-Nd depleted mantle ages lie in the range of 2.6 ± 0.13 Ga. Sao Rafael magma was “unregenerate,” not isotopically homogenized when emplaced.

The Eastern Andean Metamorphic Complex (EAMC) in southwestern Patagonia (4°-52°S) is a 450 km long belt mainly composed by low-grade metasedimentary rocks of Upper Devonian-lower Carboniferous, and Permian-lower Triassic ages. Previous works have suggested a passive margin environment for the deposition of the protolith. The EAMC comprise scarce interleaved tectonic slices of marbles, metabasites, and exceptional serpentinite bodies. At Lago O´Higgins-San Martin (48°30’S-49°00’S) the metasedimentary sucessions are tectonically juxtaposed with lenses of pillowed metabasalts and greenschists having OIB, N-MORB, BABB and IAT geochemical affinities. The Nd-isotopic composition of metabasalts is characterized by εNd(t=350 Ma) of +6 and +7. The metabasalts show no signal of crustal contamination, instead, the mantle source was probably modified by subduction components. New and already published provenance data based on mineralogy, geochemistry and zircon geochronology indicate that the quartz-rich protolith of metasandstones were deposited during late Devonian-early Carboniferous times (youngest single zircon ages around of latest Devonian-earliest Carboniferous times) sourced from igneous and/or sedimentary rocks located in the interior of Gondwana, as the Deseado Massif, for instance. Noticeable, the detrital age patterns of all samples reveal a prominent population of late Neoproterozoic zircons, probably directly derived from igneous and/or metaigneous rocks of the Brasiliano/Pan-African orogen or from reworked material from variably metamorphosed sedimentary units that crops out at the same latitudes in the extra-Andean region of Patagonia. We propose that the protolith of metabasites formed part of the upper part of an oceanic-like lithosphere generated in a marginal basin above a supra-subduction zone, where plume-related oceanic island volcanoes were generated. The closure of the marginal basin, probably in mid-Carboniferous times, or soon after. The oceanic lithosphere was likely underthrusted within an east-to-northeast-dipping subduction zone, where ophiolitic rocks and metasedimentary sequences were tectonically interleaved at the base of an accretionary wedge.

The Western Domain of the Magallanes Fold-and-Thrust Belt (MFTB) between 52°-54°S is part of a poorly studied hinterland region of the southernmost Andean Cordillera. This domain consists of NNW-SSE trending tectonic slices of pre-Jurassic basement units and Upper Jurassic-Lower Cretaceous ophiolitic complexes and volcano-sedimentary successions of the Rocas Verdes Basin (RVB). New detrital zircon U–Pb ages of metatuffs and metapsammopelites constrain episodes of Late Jurassic rift-related volcanism (ca. 160 Ma) followed by Early Cretaceous sedimentation (ca. 125 Ma) during the opening of the RVB. Shear bands developed in the RVB units further record the initial phases of the Andean Orogeny. The 30-km wide thrust stack located on top of the Eastern Tobífera Thrust consists of mylonitic metatuffs, metapelites and metabasalts with a NE-verging brittle-ductile S1* foliation. Phengite-bearing metatuffs commonly record pressure-temperature (P-T) conditions between ~3–6 kbar and ~210–460 °C, consistent with underthrusting of the RVB beneath the parautochthonous magmatic arc in the west. Peak metamorphic conditions of ~6 kbar and 460 °C are derived from a metapsammopelite with textures of contact metamorphism overprinting early mylonitic structures (at least S1*). A back-arc quartz-diorite, intruded at ca. 83 Na, is in contact with the metapsammopelite and constrain the minimum age of deformation at deep crustal depths. Campanian-Maastrichtian (ca. 70–73 Ma) 40Ar/39Ar phengite dates from a mylonitic metapelite indicate the timing of thrusting and backthrusting during the initial uplift of the underthrusted crustal stack. These findings reveal a ~400 km along-strike connection of mylonite belts in a continent-verging thrust structure that became active at the onset of the Andean orogeny during the closure of the Rocas Verdes back-arc marginal basin. Fil: Muller, Veleda A. P.. Universidade Federal do Paraná; Brasil Fil: Calderón, Mauricio. Universidad Andrés Bello; Chile Fil: Fosdick, Julie C.. University of Connecticut; Estados Unidos Fil: Ghiglione, Matias. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Estudios Andinos "Don Pablo Groeber". Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Estudios Andinos "Don Pablo Groeber"; Argentina Fil: Cury, Leonardo F.. Universidade Federal do Paraná; Brasil Fil: Massonne, Hans Joachim. China University Of Geosciences; China Fil: Fanning, C. Mark. The Australian National University; Australia Fil: Warren, Clare J.. The Open University; Reino Unido Fil: Ramírez de Arellano, Cristobal. Universidad Andrés Bello; Chile Fil: Sternai, Pietro. Università degli Studi di Milano-Bicocca; Italia

Previously undated low-grade metamorphic rocks from the Puerto Cisnes-Queulat area (44°30’ S) contain detrital zircons of mid-Oligocene age (ca. 28 Ma). Their outcrops represent the easternmost occurrence of the late Oligocene to early Miocene marine volcano-sedimentary Traiguén Formation; previous correlation with the Paleozoic metamorphic basement of this sector of the North Patagonian Andes is thus refuted. A similar age and provenance were obtained for a paraconglomerate bed of the La Junta Formation ca. 80 km to the north, which is thought to represent a high-energy lateral facies variation of the Traiguén Formation. Miocene plutonic rocks of the North Patagonian Batholith intruded these metasedimentary rocks, generating a contact metamorphic aureole that reaches biotite grade and overprints a previous metamorphic fabric probably formed during closure of the Traiguén Basin. Similar young ages for metamorphic rocks located immediately west of the Liquiñe-Ofqui Fault Zone 300 km north, near Ayacara, suggest a regional pattern of earliest Neogene metamorphism and rapid exhumation in this segment of the Patagonian Andes.

The Gara, Yalea, and Gounkoto Au deposits of the >17 Moz Loulo mining district, largely hosted by the Kofi series metasediments, are located several kilometers to the east of the 650-Mt Fe skarn deposits in the adjacent Falémé batholith. The Au deposits are interpreted to have formed through phase separation of an aqueous-carbonic fluid, which locally mixed with a hypersaline brine of metaevaporite origin. Recognition of an intrusive relationship between the Falémé batholith and Kofi series opens the possibility that the Fe skarns and Au deposits are part of the same mineral system. In this paper, we combine new δ13C, δ18O, and δ34S data from the Karakaene Ndi skarn, Au occurrences along the western margin of the Kofi series, and zircons within plutonic rocks of the Falémé batholith. We combine these with existing data from the Loulo Au deposits to model the contribution of magmatic volatiles to Au mineralization. C and O isotope compositions of auriferous carbonate-quartz-sulfide veins from the Loulo Au deposits have wide ranges (δ13C: –21.7 to –4.5‰ and δ18O: 11.8 to 23.2‰), whereas values from carbonate veins in Kofi series Au prospects close to the Falémé batholith and the Karakaene Ndi Fe skarn deposit have more restricted ranges (δ13C: –16.8 to –3.7‰, δ18O: 11.4 to 17.2‰, and δ13C: –3.0 ± 1‰, δ18O: 12.6 ± 1‰, respectively). Kofi series dolostones have generally higher isotopic values (δ13C: –3.1 to 1.3‰ and δ18O: 19.1 to 23.3‰). Pyrite from Kofi series Au prospects adjacent to the Falémé batholith have a wide range of δ34S values (–4.6 to 14.2‰), similar to pyrite from the Karakaene Ndi skarn (2.8 to 11.9‰), whereas δ34S values of pyrite and arsenopyrite from the Loulo deposits are consistently >6‰. Comparison of the C and O isotope data with water-rock reaction models indicates the Loulo Au deposits formed primarily through unmixing of an aqueous carbonic fluid derived from the devolatilization of sedimentary rocks with an organic carbon component. Isotopic data are permissive of the hypersaline brine that enhanced this phase separation including components derived from both Kofi series evaporite horizons interlayered with the dolostones and a magmatic-hydrothermal brine. This magmatic-hydrothermal component is particularly apparent in O, C, and S isotope data from the Gara deposit and Au prospects immediately adjacent to the Falémé batholith.

Palynomorphs and detrital zircon U-Pb dating have provided important new age constraints for the Pirispiki Formation that crops out in the Northern Thrust Zone, Kurdistan, northern Iraq. Fauna and flora have not been previously been reported from the Pirispiki Formation at outcrop in Iraq. Spores and acritarchs recovered from the Chia Zinnar section during this study indicate a Late Devonian age for the Pirispiki Formation and a continental environment of deposition. This is supported by U-Pb dating of detrital zircon, which indicates that deposition was no earlier than Fammenian/Frasnian in the Chia-Zinnar and Nazdur sections and Givetian in the Ora section.

The Early Paleozoic evolution of the northern margin of Gondwana is characterized by several episodes of bimodal magmatism intruded or outpoured within thick sedimentary basins. These processes are well recorded in the Variscan blocks incorporated in the Ligurian Alps because they experienced low temperature Alpine metamorphism. During the Paleozoic, these blocks, together with the other Alpine basements, were placed between the Corsica-Sardinia and the Bohemian Massif along the northern margin of Gondwana. In this framework, they host several a variegated lithostratigraphy forming two main complexes (Complexs I and II) that can be distinguished by both the protoliths and their cross-cutting relationships, which indicate that the acidic and mafic intrusives of Complex II cut an already folded sequence made of sediments, basalts and granitoids of Complex I. Both complexes were involved in the Variscan orogenic phases as highlighted by the pervasive eclogite-amphibolite facies schistosity (foliation II). However, rare relicts of a metamorphic foliation at amphibolite facies conditions (foliation I) is locally preserved only in the rocks of Complex I. It is debatable if this schistosity was produced during the early folding event – occurred between the emplacement of Complex I and II – rather than during an early stage of the Variscan metamorphic cycle.New SHRIMP and LA ICP-MS U–Pb zircon dating integrated with literature data, provide emplacement ages of the several volcanic or intrusive bodies of both complexes. The igneous activity of Complex I is dated between 507 ± 15 Ma and 494 ± 5 Ma, while Complex II between 467 ± 12 Ma and 445.5 ± 12 Ma. The folding event recorded only by the Complex I should therefore have occurred between 494 ± 5 Ma and 467 ± 12 Ma. The Variscan eclogite-amphibolite facies metamorphism is instead constrained between ∼420 Ma and ∼300 Ma. These ages and the geochemical signature of these rocks allow constraining the Early Paleozoic tectono-magmatic evolution of the Ligurian blocks, from a middle–upper Cambrian rifting stage, through the formation of an Early Ordovician volcanic arc during the Rheic Ocean subduction, until a Late Ordovician extension related to the arc collapse and subsequent rifting of the PaleoThetys. Furthermore, the ∼420–350 Ma ages from zircon rims testify to thermal perturbations that may be associated with the Silurian rifting-related magmatism, followed by the subduction-collisional phases of the Variscan orogeny. Keywords: U–Pb zircon dating, Early Paleozoic magmatism, Pre-Alpine basements, Gondwana margin, Ligurian Alps

The geological significance of Early Paleozoic (Caledonian) magmatism and associated mineralization in South China is, as yet, poorly understood compared to the well-documented Mid-Late Mesozoic (Yanshanian) magmatism and associated mineralization. The Early Paleozoic granitoids were previously thought to be rarely mineralized. Both Caledonian granitoids and Yanshanian granitoids occur in the Dayaoshan area from the Qin–Hang metallogenic belt, South China. Zircon U–Pb ages of granodiorite at the Yupo skarn W deposit and the monzonite and granodiorite at the Dali porphyry Mo deposit, all I-type granites, analyzed by Sensitive High Resolution Ion Micro-Probe (SHRIMP) and/or laser ablation inductively coupled mass spectrometry (LA–ICP–MS) are 441.9 ± 1.9 Ma (2σ), 104.6 ± 1.6 Ma (2σ) and 105.3 ± 1.4 Ma (2σ), respectively. Both elevated zircon δ18OV-SMOW values (5.8–7.7‰) and negative eHf(t) values (−3.2 to −0.2) indicate that these plutons formed via partial melting of a Mesoproterozoic continental crust with minor mantle materials. The Caledonian W-bearing Yupo granodiorite is relatively reduced (FMQ−0.57), whereas the Yanshanian Mo-bearing granodiorite at Dali (FMQ+1.11) is more oxidized than the associated ore-barren monzonite (FMQ+0.52). Thus, it is likely that the contrasting mineralization between the two plutons was controlled by redox states of granitic magmas.

Based on chemical composition and timing of late Paleogene and Neogene igneous rocks in southern Patagonia, six igneous suites are identified and correlated with subduction processes during the approaching and subduction of active oceanic ridges. Neogene magmatism took place after a period of decreased sub-alkaline magmatism during late Paleogene (LPg Suite). Early Miocene calc-alkaline rocks mark the reactivation of magmatism after subduction acceleration (Suite 1). These rocks are located at ca. 200 km from the trench and are typical products of continental magmatic arcs, where focused metasomatism of the mantle wedge results on high-degree of partial melting (>15%) in a restricted area expressed as a narrow volcanic arc. Contrarily, transitional sub-alkaline to alkaline rocks (Suite 2) were formed during the approaching of the Chile spreading ridge and the subduction of hot oceanic lithosphere (prior to the development of a slab window), where metasomatism encompassed a broader region of the mantle wedge, resulting in lower degrees of partial melting (

The Permo-Carboniferous tectonic setting of the SE Central Asian Orogenic Belt is poorly understood, especially with regard to the development of the Solonker (Suture) Zone. New stratigraphic, geochemical and detrital zircon analyses for Permo-Carboniferous sediments have been undertaken to resolve this problem. In the Mandula area, the Baotege Formation and former Amushan Formation were deposited in the early Permian. An unstable alluvial–proluvial fan to a stable shallow marine environment has been proposed. In the NE Sonid Youqi area, late Carboniferous to middle Permian carbonate–clastic rocks were deposited in a relatively stable shallow sea with a series of transgressions. Upper continental crust-like geochemical features, magmatic zircons and petrography show that the clastic rocks have a felsic source ranging from granites to tonalite–trondhjemite–granodiorite. Detrital zircons with prominent age groupings at c. 280–330 Ma, c. 350–370 Ma and/or c. 400–500 Ma with some Precambrian ages, together with zircon Hf isotopic data, indicate that the sediments were dominantly sourced from the orogenic belt itself and microcontinents. Basin analysis shows a transition from restricted basins in the late Carboniferous–early Permian to wider and deeper basins in the middle Permian. Accordingly, an extensional stage has been proposed, at least before the final closure of the Solonker Zone. Supplementary material: Detailed geochemical data, zircon Th/U ratios, U–Pb ages, Hf isotopic data and figures showing samples are available at https://doi.org/10.6084/m9.figshare.c.3948325

Rock clasts entrained in glacial deposits sourced from the continental interior of Antarctica provide an innovative means to determine the age and composition of ice-covered crust. Zircon U-Pb ages from a suite of granitoid clasts collected in glacial catchments draining central East Antarctica through the Transantarctic Mountains show that crust in this region was formed by a series of magmatic events at ∼2.01, 1.88–1.85, ∼1.79, ∼1.57, 1.50–1.41, and 1.20–1.06 Ga. The dominant granitoid populations are ca. 1.85, 1.45 and 1.20–1.06 Ga. None of these igneous ages are known from limited outcrop in the region. In addition to defining a previously unrecognized geologic history, zircon O and Hf isotopic compositions from this suite have: (1) mantle-like δ18O signatures (4.0–4.5‰) and near-chondritic Hf-isotope compositions (eHf ∼ +1.5) for granitoids of ∼2.0 Ga age; (2) mostly crustal δ18O (6.0–8.5‰) and variable Hf-isotope compositions (eHf = −6 to +5) in rocks with ages of ∼1.88–1.85, ∼1.79 and ∼1.57 Ga, in which the ∼1.88–1.79 Ga granitoids require involvement of older crust; (3) mostly juvenile isotopic signatures with low, mantle-like δ18O (∼4–5‰) and radiogenic Hf-isotope signatures (eHf = +6 to +10) in rocks of 1.50–1.41 Ga age, with some showing crustal sources or evidence of alteration; and (4) mixed crustal and mantle δ18O signatures (6.0–7.5‰) and radiogenic Hf isotopes (eHf = +3 to +4) in rocks of ∼1.2 Ga age. Together, these age and isotopic data indicate the presence in cratonic East Antarctica of a large, composite igneous province that formed through a punctuated sequence of relatively juvenile Proterozoic magmatic events. Further, they provide direct support for geological correlation of crust in East Antarctica with both the Gawler Craton of present-day Australia and Proterozoic provinces in western Laurentia. Prominent clast ages of ∼2.0, 1.85, 1.57 and 1.45 Ga, together with sediment source linkages, provide evidence for the temporal and spatial association of these cratonic elements in the Columbia supercontinent. Abundant ∼1.2–1.1 Ga igneous and metamorphic clasts may sample crust underlying the Gamburtsev Subglacial Mountains, indicating the presence of a Mesoproterozoic orogenic belt in the interior of East Antarctica that formed during final assembly of Rodinia.

Two main lines of evidence disagree whether or not the Patagonian blocks collided with Gondwana. All models invoke the voluminous magmatism of the La Esperanza Complex as evidence for active subduction magmatic arc or to a postcollisional setting. The evolution of this bimodal igneous suite is reassessed with field, geochronological (SHRIMP U-Pb zircon and K-Ar mica) and petrophysical data. Emplacement of high-K calk-alkaline granitic magmas occurred at shallow crustal levels (2–8 ± 2 km depth) related to the development and collapse of a caldera associated with a regional NW-SE structural trend. Magmatism involved intermediate hybrid pulses at 273 ± 2 Ma and 255 ± 2 Ma (Prieto Granodiorite) that shifted like a yo-yo to acidic magmas at 260 ± 2 Ma and 250 ± 2 Ma (Donosa and Calvo granites). Absence of solid-state deformation features and the low anisotropy degrees in the granites indicate that its fabric is magmatic in origin. Magnetic fabric in granodiorites displays a concentrical pattern with subhorizontal foliations and lineations. Parallel to the volcanic axis, magnetic foliations and moderately plunging lineations indicate a common feeder system for plutonics and volcanics. Donosa Granite shows a discordant pattern with WNW-ESE ENE-WSW trending low plunging lineations and foliations. The plutono-volcanic system construction (273–255 Ma) followed NW-SE and NE-SW diamond shape faults trends and supracrustal discontinuities. Magmatic Climax is bracketed at 260 Ma. The collapse of the edifice is evidenced by the intrusion of acid magma plugs and dike swarms between 250 and 246 Ma. A similar age range was identified in other areas of Patagonia related to syn and postcollisional tectonic events. No evidence of tectonic activity such as major uplift, metamorphism or thrusting was found excepting regional strike-slip faulting and extension. Therefore, La Esperanza Complex is a high crustal level episode, and as such may not have structurally recorded an active collision during its crystallization and cooling. Fil: Martínez Dopico, Carmen Irene. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Geocronología y Geología Isotopica. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Geocronología y Geología Isotópica; Argentina Fil: Lopez, Monica Graciela. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Geocronología y Geología Isotopica. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Geocronología y Geología Isotópica; Argentina Fil: Rapalini, Augusto Ernesto. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Geociencias Basicas, Aplicadas y Ambientales de Buenos Aires. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Geociencias Basicas, Aplicadas y Ambientales de Buenos Aires; Argentina Fil: Wemmer, Klaus. Universität Göttingen; Alemania Fil: Fanning, Mark. Australian National University; Australia Fil: Basei, Miguel A. S.. Universidade de Sao Paulo; Brasil

Late Paleozoic basaltic volcanism widely occurred in central Inner Mongolia, the southeastern part of the Central Asia Orogenic Blet (CAOB). Three volcanic pulses are identified by ion microprobe (SHRIMP II) zircon U-Pb analysis, which are Late Carboniferous (ca. 315 Ma), the latest Carboniferous (ca. 303 Ma) and early Permian (ca. 284 Ma). Basalts in the earliest stage are characterized by flat HREE, depletion in Nb and Ta, MORB-like Th/Yb ratios and depleted mantle (DM)-like Hf isotopic ratios. These are similar to forearc basalts, that have been generated by melting of a fluxed depleted mantle in an extensional environment. The latest Carboniferous basalts (sample D1363) have no Zr-Hf anomalies, relatively radiogenic Hf isotopic ratios (eHf(t) = +12.1 to +19.7) and high δ18O values up to 8.5‰, VSMOW. These are likely to be magmas originated from decompressional melting of a depleted mantle that interacted with ocean floor pillow basalts during their ascending through the crust. The early Permian sample D1380 have variable 206Pb/238U zircon ages with an interpreted magma crystallization age of 284.4 ± 2.5 Ma. These zircons have scattered Hf isotope (eHf(t) = +5 to +14) and δ18O (1.8–11.0‰, VSMOW), which suggest the involvement of a relatively enriched mantle source. Overall the temporal evolution of the Late Paleozoic basaltic volcanism from central Inner Mongolia suggests a rift-related tectonic setting.

The gneiss complex of Wildhorse Creek (Wildhorse gneiss) forms the central component of the lowest structural plate in the Pioneer metamorphic core complex of south-central Idaho. The oldest rock in the complex is a felsic ortho­gneiss, with Neoarchean U-Pb magmatic zircon ages of 2.60–2.67 Ga. The ortho­gneiss overlaps in age and is interpreted to be part of the Grouse Creek block of the Albion Mountains to the south. This Archean metagranitoid is structurally interleaved with paragneiss containing quartzite and calc-silicate rock. Structurally below the orthogneiss, some quartzites have multiple concordant populations of detrital-zircon grains as young as ca. 1700 Ma, while others have no zircon grains younger than ca. 2500 Ma. Structurally above the Archean gneiss is a heterogeneous paragneiss that contains calc-silicate and quartzitic rocks with detrital zircons as young as ca. 1460 Ma. Amphibolite in this unit contains zircons dated at ca. 1850 Ma, indicating that this rock can be no older than that and implying considerable structural complexity. The upper part of the Wildhorse gneiss contains metaquartzites bearing zircons as young as ca. 1400 Ma. The protolith of this paragneiss is interpreted as the southernmost exposures of the Lemhi subbasin of the Mesoproterozoic Belt Supergroup. The upper Wildhorse gneiss includes ca. 695 Ma intrusive orthogneiss that is coeval with Neoproterozoic rift-related volcanic or intrusive rocks near Poca­tello, House Mountain, and Edwardsburg, Idaho. This Cryogenian meta-intrusive rock is the likely source of the 650–710 Ma detrital-zircon population in the Big Lost River that drains the core complex. Initial eHf values from 675 Ma zircons are between 3.4 and –2.4, suggesting the granitoids had a mixed source in both continental crust and juvenile mantle.

The genesis of Permian magmatism in southern South America is actively debated, particularly in relation to the origin of Patagonia. U-Pb zircon ages of c. 255 Ma for igneous rocks from the basement of Tierra del Fuego are the first evidence for southerly prolongation of this magmatism. Zircon in these rocks has εHft values 7.4‰, indicating recycling of Cambrian rocks. Permian granites in the north of the North Patagonian Massif record mantle-like δ18O magmatic input at c. 280 and 255 Ma, but reworking of upper crust between these two events, paralleling the recognized deformational history. In northwestern Patagonia, Early Permian granitic rocks have zircon with eHft values ranging from +0.1 to -7.2, and δ18O > 6.2‰, suggesting continuity of the Permian magmatic belt along the western margin of South America farther north. Comparison with a sample from the Sierra de la Ventana suggests melting of similar crust on both sides of the Patagonia-South American hypothetical suture. These features, together with other geological considerations, are consistent with an autochthonous or parautochthonous origin of northern Patagonia and connection between southern Patagonia and the Antarctic Peninsula in late Palaeozoic time. Fil: Castillo, Paula. The Australian National University; Australia Fil: Mark Fanning, C.. The Australian National University; Australia Fil: Pankhurst, Robert J.. British Geological Survey; Qatar Fil: Hervé, Francisco. Universidad Andrés Bello; Chile Fil: Rapela, Carlos Washington. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Centro de Investigaciones Geológicas. Universidad Nacional de La Plata. Facultad de Ciencias Naturales y Museo. Centro de Investigaciones Geológicas; Argentina

The New England Orogen, eastern Australia, was established as an outboard extension of the Lachlan Orogen through the migration of magmatism into forearc basin and accretionary prism sediments. Widespread S-type granitic rocks of the Hillgrove and Bundarra supersuites represent the first pulse of magmatism, followed by I- and A-types typical of circum-Pacific extensional accretionary orogens. Associated with the former are a number of small tholeiite–gabbroic to intermediate bodies of the Bakers Creek Suite, which sample the heat source for production of granitic magmas and are potential tectonic markers indicating why magmatism moved into the forearc and accretionary complexes rather than rifting the old Lachlan Orogen arc. The Bakers Creek Suite gabbros capture an early ( ∼ 305 Ma) forearc basalt-like component with low Th ∕ Nb and with high Y ∕ Zr and Ba ∕ La, recording melting in the mantle wedge with little involvement of a slab flux and indicating forearc rifting. Subsequently, arc–back-arc like gabbroic magmas (305–304 Ma) were emplaced, followed by compositionally diverse magmatism leading up to the main S-type granitic intrusion ( ∼ 290 Ma). This trend in magmatic evolution implicates forearc and other mantle wedge melts in the heating and melting of fertile accretion complex sediments and relatively long ( ∼ 10 Myr) timescales for such melting.

This study was supported by awards from the Educational Geologic Mapping Program administered by the U.S. Geological Survey (USGS) to George Washington University (GWU). The research also benefited from additional support provided by the USGS Appalachian Landscape Project.

The Kibali district in the Democratic Republic of Congo hosts the large Karagba-Chaffeur-Durba (KCD) deposit and smaller satellite deposits that together contained 20 million ounces (Moz) of gold when mining recommenced in 2013. An additional 3 Moz of gold was probably mined from the district before 2013. Gold deposits in the Kibali district are located along the KZ trend, a series of folds, contractional shear zones, and altered lithostratigraphic units that coincide with the margin of an earlier 2630 to 2625 Ma intraorogenic basin within the Neoarchean Moto belt. Fluids first responsible for barren carbonate-quartz-sericite alteration, and later for siderite and/or ankerite (±quartz, magnetite, pyrite, and/or chlorite) alteration with associated auriferous pyrite ± rare arsenopyrite veinlets, infiltrated and replaced the siliciclastic, banded iron formation (BIF), and chert host rocks via fold axes, shear zones, and reactive BIF horizons. The complex shape and gentle northeast plunge of the lodes across the Kibali district reflect the shape and plunge of coincident folds that formed during early barren alteration. Many other folded BIF horizons across the wider Moto belt remain barren or only weakly mineralized, suggesting deep extensional structures that may have developed in the vicinity of the KZ trend during basin opening and prior to gold mineralization, were important fluid pathways during later contractional deformation and mineralization.

The composite terrane of Brunovistulia includes basement of the Upper Silesia Block, southern Poland. In its NE part, the basement is elevated by the Rzeszotary Horst. In the Rzeszotary 2 borehole (Rz2) drilled in the horst, partly migmatized amphibolites, felsic gneisses and granites occur. An Na-plagioclase-phengite-K-feldspar neosome contained zircons that yielded U-Pb SHRIMP ages ~2.75–2.6 Ga (cores and single grains) and ~2.0 Ga (rims and single grains). The older ages are interpreted as the time of origin of the igneous protolith of the migmatized amphibolites. The younger ages recorded metamorphism and migmatization that affected both the magmatic precursor of the amphibolites and accompanying felsic rocks during a contractional tectonic/orogenic event. Migmatization was greatly enhanced by an influx of alkali-bearing fluids which heralded intrusion of late-orogenic unfoliated K-granite in an extensional regime, terminating the 2.0 Ga event. It is proposed that the entire orogenic edifice, of which the Brunovistulian rocks drilled in Rz 2 are a small part, represents fragments of the Columbia Supercontinent that was assembled in the Paleoproterozoic and broken up in the Mesoproterozoic. In Ediacaran times, these fragments became eventually incorporated into the Cadomian orogen in the form of its foreland and contributed to the formation of the composite terrane of Brunovistulia. Such a scenario explains why the U-Pb zircon age spectra in the Rzeszotary terrain differ dramatically from those in the remainder of Brunovistulia, which is thought to be the Cadomian hinterland.

Paleoproterozoic (Rhyacian) gold deposits of the Loulo district in western Mali contain >17 million ounces (Moz) Au and form part of the second most highly endowed region within West Africa. The deposits are located within siliciclastic, marble, and evaporitic rocks of the ca. 2110 Ma greenschist facies Kofi series, which were folded and inverted between ca. 2100 and 2070 Ma, prior to gold mineralization. Deposits at Yalea and Gounkoto are located along discontinuous, low-displacement, albite- and carbonate-altered shear zones, whereas Gara is confined to a tourmaline-altered quartz sandstone unit. Lodes typically plunge gently to moderately, reflecting the attitude of folds in the adjacent rocks and bends in the host shear zones, both of which influenced their location. Gold mineralization in the Loulo district was broadly synchronous with emplacement of the Falémé batholith and associated Fe skarn mineralization, which intrude and overprint the western margin of the Kofi series, respectively. However, hydrothermal fluids generated during metamorphic devolatilization of the Kofi series rocks appear responsible for gold mineralization, albeit within a district-wide thermal gradient associated with emplacement of the Falémé batholith. The regional-scale Senegal-Mali shear zone, commonly cited as an important control on the location of gold deposits in western Mali, is absent in the Loulo district.

The La Esperanza plutonic-volcanic complex is the largest Late Paleozoic-Early Triassic composite magmatic system of northern Patagonia. This paper reports new SHRIMP U-Pb zircon ages and K-Ar muscovite dating as well as whole-rock geochemical data for selected units. In addition, we present some new and reprocessed whole-rock Sr isotopic compositions. On the basis of the new and published data, three compositionally and isotopically distinct high-K magnesian calc-alkaline series were distinguished. Two of these are characterized by high Ba-Sr: (i) biotite and muscovite bearing rhyolites and granites (265 ± 2 Ma; 260 ± 2 Ma) and (ii) metaluminous amphibole-biotite bearing granodiorites (273 ± 2 Ma), monzogranites (255 ± 2 Ma), dacites (253 ± 2 Ma), and slightly peraluminous granites (dated herein as 251 ± 2 Ma). There is also a low Ba-Sr series of high-silica metaluminous rocks (granites and acid dike swarms; 250 ± 2 Ma and ≈244 ± 2 Ma). Geochemistry coupled with geochronology revealed a pulsatory multi-sourced open magmatic system with mafic magma replenishment and reactivation of crystal mushes that occurred before upward migration to upper crustal levels. Mafic magmas alternated with crust-derived magmas incrementally assembled in subvolcanic levels over 30 Ma. Zircon crystallization and mica cooling ages in the granite units allowed detection of two magmatic lulls, between 270 and 265 Ma and between 260 and 255 Ma. Both episodes coincide with a period of exhumation in upper crustal levels. The new temporal and geochemical constraints allow correlation of the La Esperanza plutonic-volcanic complex with the Los Menucos Group (258-248 Ma), encompassing a volume of magmatism comparable to a moderately sized large igneous silicic province. These mid-to-late Permian to Middle Triassic rocks record the transition between subduction-related magmatism (>273 Ma) and post-orogenic extensional magmatism (

This paper addresses the Jurassic–Cretaceous stratigraphic evolution of fore-arc deposits exposed along the west coast of the northern Antarctic Peninsula. In the South Shetland Islands, Upper Jurassic deep-marine sediments are uncomformably overlain by a Lower Cretaceous volcaniclastic sequence that crops out on Livingston, Snow and Low islands. U-Pb zircon ages are presented for the upper Anchorage Formation (153.1 ± 1.7 Ma) and the Cape Wallace granodiorite of Low Island (137.1 ± 1.7 Ma) as well as 40Ar/39Ar ages of 136–139 Ma for Low Island andesites. Data are also presented for a U-Pb age of 109.0 ± 1.4 Ma for the upper volcanic succession of Snow Island. In combination with published stratigraphy, these data provide a refined chrono- and litho-stratigraphic framework for the deposits herein referred to as the Byers Basin. Tentative correlation is explored with previously described deposits on Adelaide and Alexander islands, which could suggest further continuation of the Byers Basin towards the south. We also discuss possible correlation of the Byers Basin with the Larsen Basin, a sequence that shows the evolution of foreland to back-arc deposits more or less contemporaneously with the fore-arc to intra-arc evolution of the Byers Basin.

The most complete Permian–Triassic Gondwana succession in Antarctica crops out in the central Transantarctic Mountains. The lower Permian strata were deposited in an intracratonic basin that evolved into a foreland basin in late Permian time. Sedimentary petrology and paleocurrent data have been interpreted as indicating a granitic (craton) provenance and a West Antarctic volcanic provenance. To address the West Antarctic provenance and evolution of the detrital input, detrital-zircon grains from nine sandstones (plus three sandstones reported previously) representing the full extent of the Permo-Triassic succession exposed on that flank of the basin, have been analyzed by sensitive high-resolution ion microprobe. Results define three provenances: an early (early to middle Permian) provenance that is dominated by zircons having Ross orogen ages (600–480 Ma); a middle (late Permian) provenance dominated by Permian zircons with subordinate older magmatic arc grains plus lesser Ross orogen–age grains; and a late (Triassic) provenance, which is quite variable and in which the predominant Triassic arc component ranges from very minor to significant and again with a component of Ross orogen–age grains. Detrital zircons imply a more extensive Permo-Triassic arc, in time and space, on the Gondwana margin than is evident from outcrop data. The zircon data are integrated into a model for basin evolution and infilling, providing broad constraints on the timing of tectonic events and the provenance.

Early Jurassic silicic volcanic rocks of the Chon Aike Province (V1: 187 – 182 Ma) are recognized from many localities in the southern Antarctic Peninsula and NE Patagonia and are essentially coeval with the extensive Karoo (182 Ma) and Ferrar (183 Ma) large igneous provinces of pre-breakup Gondwana. Until recently, plutonic rocks of this age were considered either rare in or absent from the Antarctic Peninsula batholith, which was thought to have been mainly constructed during the Middle Jurassic and the mid-Cretaceous. New U–Pb zircon geochronology from the Antarctic Peninsula and recently published U–Pb ages from elsewhere in the Peninsula and Patagonia are used to demonstrate the more widespread nature of Early Jurassic plutonism. Eight samples are dated here from the central and southern Antarctic Peninsula. They are all moderately to strongly foliated granitoids (tonalite, granite, granodiorite) and locally represent the crystalline basement. They yield ages in the range 188 – 181 Ma, which overlap with published ages of 185 – 180 Ma from granitoids from elsewhere on the Antarctic Peninsula and from the Subcordilleran plutonic belt of Patagonia (185 – 181 Ma). Whereas Early Jurassic plutons of the Subcordilleran plutonic belt of Patagonia are directly related to subduction processes along the proto-Pacific margin of Gondwana, coeval volcanic rocks of the Chon Aike Province are interpreted to be directly associated with extension and plume activity during the initial stages of Gondwana breakup. This indicates that subduction was continuing when Chon Aike Province volcanism started. The Early Jurassic plutonism on the Antarctic Peninsula is transitional between subduction-related and breakup-related magmatism. Supplementary material : Cathodoluminescence images of analysed zircon grains from sites on the Antarctic Peninsula are available at https://doi.org/10.6084/m9.figshare.c.3521973

High-grade metamorphic and igneous rocks originally mapped as the Nimrod Group represent the only known crystalline basement of the East Antarctic shield exposed in the Transantarctic Mountains. SHRIMP U–Pb age data from zircon show that this assemblage preserves multiple geologic events spanning 2.5 b.y. of Archean to early Paleozoic history, culminating in thermomechanical reworking and active-margin magmatism during the Ross Orogeny. New age data from igneous and metamorphic rocks, as well as from detrital zircons in metasedimentary quartzites, refine the Mesoarchean to Paleoproterozoic history and indicate the need to abandon the stratigraphic term Nimrod Group and its five formations. In its place, we redefine only the igneous and high-grade gneissic parts of the assemblage as the Nimrod Complex, and all other metasedimentary rocks exposed in the Miller and Geologists ranges are included in a newly defined Argosy Schist. Within the Nimrod Complex, the oldest layered gneisses represent magmatic Mesoarchean crust formed between about 3150 and 3050 Ma. Correspondence of U–Pb zircon crystallization ages with whole-rock Sm–Nd model ages indicates formation from juvenile mantle melts. Magmatism at ca. 3100 Ma was followed closely by high-temperature metamorphism, recorded by zircon crystallization at 2955–2900 Ma, likely due to high advective heat transfer and/or thermal insulation of newly stabilized crust. Metaigneous units with ages of ca. 2500 Ma indicate a late Neoarchean period of anatexis and/or magmatism, although the geologic context for these events is uncertain. Gneissic, eclogitic and metaigneous rocks record an important period of deep-crustal metamorphism, thickening and magmatism between 1730 and 1700 Ma, referred to as the Nimrod Orogeny, that may have played an early role in assembly of East Gondwana cratons. A new lithodemic unit, Argosy Schist, consists of interlayered mica schist, quartzite, amphibolite, and calc-silicate schist. Quartzites from the schist unit have two distinctive detrital-zircon provenance characteristics; one type has populations that correlate with dated gneissic and metaigneous units of the Nimrod Complex, indicating a proximal provenance, whereas a second type has detrital zircon ages resembling those from Neoproterozoic Beardmore Group sandstones, indicating a common broader East Antarctic shield provenance. Their maximum depositional ages range widely from about 2000 to 900 Ma, leaving unresolved their age and geologic relationship to either the Nimrod Complex or Beardmore Group, yet they comprise a metasedimentary assemblage that is distinctive from the Nimrod Complex. Recent findings of Mesoarchean gneisses in the Gawler Craton, geochronology from Terre Adelie, and our new age data from the Nimrod Complex thus highlight the importance of ca. 3.1, 2.5 and 1.7 Ga events in formation of the composite East Antarctic shield adjacent to the modern Transantarctic Mountains. Correlative crustal units may extend to the southern Prince Charles Mountains and Shackleton Range. Collectively, this extensive crustal province, referred to as the Mawson Continent, represents an elongate belt of primary Mesoarchean crust that experienced major reworking at ca. 2.5 and 1.7 Ga. The latter period includes both high- and low-P/T petrologic signatures, providing evidence of crustal thickening and magmatism that may signify collisional processes related to Paleoproterozoic cratonal amalgamation during formation of the Nuna supercontinent.

The passive to convergent margin transition along western Laurentia drove early development of the North American Cordillera and culminated with the Late Devonian–Mississippian Antler orogeny and emplacement of the Roberts Mountain allochthon in the western United States. New detrital zircon studies in the Pioneer Mountains, east-central Idaho, were conducted to investigate the stratigraphic evidence of this transition and test models for mid-Paleozoic tectonics and paleogeography. Ordovician to Lower Devonian passive margin strata of the Roberts Mountain allochthon and adjacent North American parautochthon contain ca. 1850, 1920, 2080, and 2700 Ma detrital zircons that indicate provenance from the Peace River Arch region of northwestern Laurentia. These detrital zircons are much older than the depositional ages of their host rocks and probably record long-term sediment recycling processes along the Cordilleran margin. Upper Devonian strata, including Frasnian turbidites of the Roberts Mountain allochthon, document the incursion of 450–430 Ma and 1650–930 Ma detrital zircons from an unknown source to the west. Detrital zircon Hf isotope results suggest that the western source was an early Paleozoic arc built on Proterozoic crust, with the Eastern Klamath, Northern Sierra, and Quesnellia terranes as likely candidates. Lower Mississippian syntectonic strata filled a rapidly subsiding, releasing bend basin that was associated with sinistral-oblique plate convergence and reworking of lower Paleozoic rocks in east-central Idaho. The available detrital zircon and stratigraphic data are most consistent with noncollisional models for the Antler orogeny, including scenarios that feature the north to south, time-transgressive juxtaposition of Baltican- and Caledonian-affinity terranes along the Cordilleran margin.