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Sedimentological, textural, and microscale analyses of the Mount McRae Shale revealed a complex postdepositional history, previously unrecognized in bulk geochemical studies. We found that metal enrichments in the shale do not reside with depositional organic carbon, as previously proposed by Anbar et al ., but with late-stage pyrite, compromising claims for a “whiff” of oxygen ~50 million years before the Great Oxygenation Event.

The early Paleoproterozoic was a time of unprecedented change in Earth's climate and surface environment. The key to resolving some of the controversies surrounding the timing and causes of these changes lies with supracrustal sequences, such as the 2.45–2.22 Ga Turee Creek Group in the southern Pilbara craton, northwestern Australia. The group preserves a predominantly siliciclastic sequence; however, its precise age, tectonic setting, and postdepositional history are disputed. Although it is interpreted to have been deposited in a foreland basin setting shortly after 2.45 Ga, the oldest well-recognized deformational event, marked by northward folding and thrusting, is the 2.20–2.15 Ga Ophthalmia orogeny. Evidence for a pre-Ophthalmia fabric-forming tectonic event north of the Archean Sylvania Inlier, southeast Pilbara craton, which is marked by tight to isoclinal folding, has been largely overlooked. In this area, we report in situ U-Pb geochronology of authigenic monazite and xenotime in shale with a well-developed tectonic cleavage from the ca. 2.63 Ga Jeerinah Formation. Monazite porphyroblasts, which are locally wrapped by strain fringes aligned in a tectonic cleavage, yielded weighted mean 207Pb/206Pb ages at 2370 ± 11 Ma and 2312 ± 8 Ma, whereas xenotime, which overprints a crenulation cleavage, gave a weighted mean 207Pb/206Pb age of 2291 ± 11 Ma, constraining fabric development to between 2.31 Ga and 2.29 Ga. Our results confirm the existence of a pre-Ophthalmia deformational event in the southeastern Pilbara craton, herein referred to as the Sylvania orogeny, which is part of an ~300 m.y. interval (2.45–2.15 Ga) of northward-directed compression (“Hamersley orogenic cycle”). This orogenic cycle is marked by east-west and northwest-southeast folding, cleavage development, veining, hydrothermal gold mineralization, and isotopic resetting across the southern Pilbara craton. Our results indicate that the syn–Great Oxidation Event Turee Creek Group was deposited in one or more foreland basins after 2.45 Ga. Our results provide a new tectonostratigraphic and geodynamic framework for understanding the timing and origin of geochemical records in a key succession deposited during an interval of global environmental change.

The Lancang Group in SW Yunnan constitutes a pivotal component of the continental margin bounding the Proto- and Paleo-Tethys oceans, yet its formation timing, composition and tectonic affinity remain ill-defined. In this contribution, we present new zircon U-Pb age and whole-rock geochemistry data from volcanic and sedimentary rock units, which are compiled with published data, to refine the depositional age, provenance and nature of the group and its host terrane. The Lancang Group consists of five formations, two of which (Manlai and Huimin) contain abundant metavolcanic rocks. The metavolcanic rocks show a secular change in geochemistry, from EMORB-like calc-alkaline series of the ca. 495 Ma Manlai Formation, to arc-like high-K series of the Huimin Formation. Five metavolcanic samples from the Huimin Formation yielded zircon U-Pb ages between 478 ± 5 Ma and 442 ± 5 Ma. The late Cambrian-Ordovician arc magmatism is related to an active continental margin setting associated with subduction of the Proto-Tethys Ocean. The time-integrated geochemical variation shown by the volcanic rocks likely reflects evolving maturity of the arc system. The youngest detrital zircon ages of the five formations, in conjunction with age constraints from the interbedded volcanic rocks, suggest that the Lancang Group was largely accumulated during the early Paleozoic. The Lancang Terrane is reconstructed as a continental block, which formed part of the magmatically-active margin of the Proto-Tethys during the early Paleozoic. Provenance analysis based on detrital zircon age spectra and Hf isotope data indicates Gondwana affinities of the terrane. Furthermore, xenocrystic zircon ages and zircon Hf and whole-rock Nd model ages from igneous rocks support presence of Neoarchean-Mesoproterozoic basement underlying the terrane. The reconstructed Lancang Terrane bears important implications for understanding the configuration of the northern margin of Eastern Gondwana and the relationship between the Proto- and Paleo-Tethys oceans.

Timing of the major Baiyun gold deposit (~ 70 t Au) in the northeastern North China Craton is controversial. A textural and geochronological study of high-grade gold ores identifies three generations of xenotime (Xtm-1, Xtm-2 and Xtm-3), even in single grains. The oldest Xtm-1, in grain cores, is of metamorphic origin, with very high U and U/Th ratios, and hump-shaped, HREE-enriched patterns with maximum normalized values at Yb and large negative Eu anomalies. It is dated at 1856 ± 6 Ma, consistent with its crystallization during regional metamorphism related to cratonization. In contrast, 244 ± 2 Ma Xtm-2 overgrowths are of hydrothermal origin, having low U and U/Th ratios and hump-shaped, MREE-enriched patterns with maximum normalized values at Ho and negligible Eu anomalies. Xtm-2 records a previously unrecognized Middle Triassic hydrothermal episode. Xtm-3, in equilibrium with native gold-hosting pyrite and rutile, is also hydrothermal. The Xtm-3 domains have similar U, U/Th ratios, and MREE-enriched patterns to Xtm-2, but a younger crystallization age of 231 ± 1 Ma. Associated rutile grains that show close textural associations with auriferous pyrite and native gold have an in situ SIMS U–Pb an intercept age of 229 ± 4 Ma, consistent with that of Xtm-3. Collectively, these reliable ages indicate that gold mineralization at Baiyun occurred at ca. 230 Ma, predating the emplacement of granite intrusions by more than 3 million years. Both the Middle Triassic hydrothermal event (~244 Ma) and the Late Triassic gold mineralization event (~230 Ma) lie within the temporal window of collisional tectonics in the host orogen. In combination, the new geochronology and fluid-inclusion and geological data support Bayun’s classification as an orogenic gold deposit.

Precambrian iron oxide copper-gold (IOCG) deposits are generally encountered with multistage hydrothermal overprints and hence have complex isotopic records. Precise dating of ore-forming and overprinting events and assessment of time-resolved metal sources are fundamental for understanding ore genesis. Here, we quantify the evolution history by integrating in situ U-Pb dating of texturally constrained allanite and Sm-Nd isotope data of ores and major rare earth element (REE) minerals in the breccia-hosted Lanniping Fe-Cu deposit in Kangdian region, southwestern China. The economically mineralized breccia in Lanniping Fe-Cu deposit is characterized by pervasive and texturally destructive replacement of polymictic clasts, including host metasedimentary packages, the intruded dolerite, and pre-ore halokinetic breccia. Ore minerals in cements are mainly composed of magnetite, chalcopyrite, bornite, and variable amounts of REE-rich minerals (e.g., apatite and allanite/epidote). Two types of allanite were identified in ores. Type I prismatic allanite texturally intergrown with magnetite has a SHRIMP U-Pb age of 1728 ± 20 Ma (1σ), which matches a zircon U-Pb age of 1713 ± 14 Ma (2σ) for the dolerite clasts and provides the direct age constraint on the Fe-Cu mineralization event. Type II anhedral allanite shows complex zoning and is spatially associated with, but texturally later than, magnetite, apatite, and chalcopyrite. This type of allanite yields significantly younger SHRIMP dates of 1015 ± 33 (1σ) and 800 ± 16 Ma (1σ) for cores and rims, respectively, which correspond to discrete regional magmatic events and hence record hydrothermal overprint/remobilization events of ore minerals in the deposit. Integrated Sm-Nd isotope compositions of type I allanite, apatite, and whole ores generally align along the reference Sm-Nd isochron of 1728 Ma, further confirming the primary ore formation at ~1.7 Ga. Corresponding εNd(1728 Ma) values ranging from –2.8 to 0.3 are significantly higher than those of the host metasedimentary rocks (–9.5 to –6.2) but comparable to those of contemporaneous igneous intrusions (–0.3 to 5.3) in the region, demonstrating that REE components of the primary ores were dominantly sourced from rocks of mantle-derived affinity. Both cores and rims of the younger type II allanite grains have Nd isotope compositions consistent with the unique time-evolved line of the ~1.7 Ga ores, implying that REEs incorporated into type II allanite were ultimately sourced from the primary ores in this deposit. The combined texture, chemical, U-Pb, and Sm-Nd isotope data thus demonstrate that REE remobilization was localized during post-ore hydrothermal overprint with negligible external inputs of REEs to the primary ores in the Lanniping deposit. In this contribution, we not only date primary ore formation but also recognize several younger allanite generations that record internal metal redistributions in response to post-ore tectonothermal events. Our study highlights the potential of ore-associated REE minerals such as allanite for resolving the age of multiple stages of hydrothermal events in complex ore deposits by ion probe, provided that careful examination of textural and paragenetic relationship of ores is conducted. Our finding of these younger allanite generations also exemplifies the significance of evaluation on time-resolved metal input for better characterizing the evolution history of the IOCG deposits.

The P-T evolution (and particularly the prograde path segment) of ultrahigh-temperature (UHT) granulites is commonly ambiguous, hampering our understanding of deep crustal processes. Here, we establish the P-T path by distinguishing garnet origin (peritectic or retrograde) based on the combined Ca, Ti, Zr, and Y+REE chemical signatures, using the residual UHT granulites of the Khondalite Belt, North China Craton, as a test case. In these rocks, peritectic garnet is characterized by rare inclusions, whereas retrograde garnet has overprinted the main foliation and is characterized by abundant biotite and sillimanite inclusions, which are interpreted to have grown together with retrograde garnet during cooling. Zirconium in peritectic garnet increases from 10 to 50 ppm with garnet growth. In contrast, Zr in retrograde garnet generally decreases from 60 to 10 ppm with garnet growth. A similar trend is observed for Ti. Temperatures calculated from the Ti-in-garnet geothermometer increase from 830 to 980 °C based on Ti in peritectic garnet, indicating prograde partial melting, whereas decrease from 900 to 700 °C based on Ti in retrograde garnet, indicating post-peak cooling. Peritectic and retrograde garnets show distinct Eu/Eu* (0.2–0.5 vs. 0.05–0.2, respectively) and Ca contents (6000–12 000 vs. 4000–6000 ppm, respectively), which generally decrease with progressive garnet crystallization. The pressures calculated from the Ca-in-garnet geobarometer in peritectic and retrograde garnet are 9–11 and 7–9 kbar, respectively. Peritectic garnet shows a bell-shaped Y (80–340 ppm) pattern, whereas retrograde garnet shows an increase in Y content (20–100 ppm) toward rims. Taken together, these results establish a P-T path comprised of an earlier high-pressure peritectic garnet formation during prograde partial melting before the UHT peak and a late abundant retrograde formation during post-peak cooling stage. We conclude that change of Zr and other elements (e.g., Ti, Ca, Y, and Eu/Eu*) can well distinguish different garnet formation events in UHT granulites, which is critical for the P-T path establishment, and further sheds light on the cause of UHT metamorphism and the geodynamic evolution.

Uranium-Th-Pb dating of phosphate minerals in very low-grade metasedimentary rocks from the Archean Pilbara Craton, Western Australia, has revealed a long history of deformation and fluid flow during the Paleoproterozoic. However, this technique has not detected evidence for fluid flow along craton margins during Phanerozoic rifting and breakup. We report the use of in situ Th-Pb geochronology of rhabdophane, a hydrous light rare earth element phosphate, to date fluid flow in shale from the 2.76 Ga Mount Roe Basalt from drill hole number 6 of the Archean Biosphere Drilling Program (ABDP6), northwestern Pilbara Craton. Thorium-Pb dating of rhabdophane in carbonaceous shale yields three main populations with weighted mean 208Pb/232Th ages of 152 ± 6 Ma, 132 ± 4 Ma, and 119 ± 4 Ma, which indicates phosphate growth up to 2.64 b.y. after deposition. The rhabdophane ages are coeval with three major breakup events in eastern Gondwana: separation of Southwest Borneo and Argoland from Australia (ca. 156–152 Ma), breakup of Greater India from Australia (ca. 140–135 Ma), and separation of Greater India/India from Antarctica (ca. 123 Ma). The proximity of drill hole ABDP6 to major Mesoarchean faults and shear zones on the craton margin, which are parallel to rift propagation and basin development, points to episodic reactivation of ancient crustal structures >2.8 b.y. after their formation. Our results also highlight the potential of rhabdophane as a U-Th-Pb geochronometer for dating low-temperature (

An enduring problem in the assembly of Laurentia is uncertainty about the nature and timing of magmatism, deformation, and metamorphism in the Paleoproterozoic Wisconsin magmatic terranes, which have been variously interpreted as an intra-oceanic arc, foredeep or continental back-arc. Resolving these competing models is difficult due in part to a lack of a robust time-frame for magmatism in the terranes. The northeast part of the terranes in northern Wisconsin (USA) comprise mafic and felsic volcanic rocks and syn-volcanic granites thought to have been emplaced and metamorphosed during the 1890–1830 Ma Penokean orogeny. New in situ U-Pb geochronology of igneous zircon from the volcanic rocks (Beecher Formation), and from two tonalitic plutons (the Dunbar Gneiss and Newingham Tonalite) intruding the volcanic rocks, yielded crystallization ages ranging from 1847 ± 10 Ma to 1842 ± 7 Ma (95% confidence). Thus, these rocks record a magmatic episode that is synchronous with bimodal volcanism in the Wausau domain and Marshfield terrane farther south. Our results, integrated with published data into a time-space diagram, highlight two bimodal magmatic cycles, the first at 1890–1860 Ma and the second at 1845–1830 Ma, developed on extended crust of the Superior Craton. The magmatic episodes are broadly synchronous with volcanogenic massive sulfide mineralization and deposition of Lake Superior banded iron formations. Our data and interpretation are consistent with the Penokean orogeny marking west Pacific-style accretionary orogenesis involving lithospheric extension of the continental margin, punctuated by transient crustal shortening that was accommodated by folding and thrusting of the arc-back-arc system. The model explains the shared magmatic history of the Pembine-Wausau and Marshfield terranes. Our study also reveals an overprinting metamorphic event recorded by reset zircon and new monazite growth dated at 1775 ± 10 Ma suggesting that the main metamorphic event in the terranes is related to the Yavapai-interval accretion rather than the Penokean orogeny.

Fluid flow in the upper crust not only impacts the redistribution of heat and elements, driving the formation of economic ore deposits, but it also exerts control on metamorphism, metasomatism, and deformation. However, reconstructing the history of fluid flow in ancient basins is exceedingly difficult, particularly in Archean sedimentary rocks because of extensive overprinting and recrystallization. Here, we report U-Pb ages for monazite and xenotime that grew in bedding-parallel veins in 2.63–2.5-b.y.-old shales along the southern Pilbara craton, Australia. The U-Pb ages define six discrete populations, at 2.41 Ga, 2.30 Ga, 2.20 Ga, 2.10 Ga, 2.05 Ga, and 1.66 Ga, which formed ≥200 m.y. after deposition. The abundance of bedding-parallel crack-seal and fibrous veins in banded iron formations (BIFs) and underlying shales suggests a history of episodic buildup of fluid pressure followed by microfracturing, fluid expulsion, and mineral growth. Thermometry of vein minerals indicates temperatures between 230 °C and 320 °C, implicating the migration of hydrothermal fluids. The development of bedding-parallel veins at 2.41 Ga, 2.20 Ga, and 1.66 Ga was coeval with regional orogenic events known to have affected the craton, whereas vein growth at 2.30 Ga, 2.10 Ga, and 2.05 Ga reveals new episodes of deformation and fluid flow. Our results show that well-preserved Archean shales devoid of structural fabrics and >150 km inboard of the craton margin preserve a cryptic history of fluid overpressure, crack-seal vein development, and hydrothermal fluid flow between 2.41 and 1.66 b.y. ago.

The Jiaodong gold province, the largest gold producer in China, formed in a setting dominated by a 30-m.y. episode of Izanagi plate rollback and widespread extension, concomitant with late Mesozoic craton destruction. This study presents new high precision in situ sensitive high-resolution ion microprobe (SHRIMP) U-Th-Pb and laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) U-Pb ages for hydrothermal monazite from the largest of the Jiaodong gold deposits, which were previously dated as indicating ore formation over a few tens of millions of years when applying sericite Ar-Ar, zircon U-Pb, and less robust analytical techniques. Our U-Pb dating on monazite from the Jiaojia and Linglong deposits in western Jiaodong yielded consistent ages at ca. 120 Ma. The new geochronologic results, coupled with recently reported in situ monazite dates from smaller deposits in western Jiaodong, reveal that the deposits that host most of the ≥4,000-t Au resource formed during a relatively brief period at ca. 120 Ma. In eastern Jiaodong, the much smaller resource may have formed about 5 m.y. later, recorded by 114.2 ± 1.5 Ma gold mineralization at the Rushan deposit. The postsubduction opening of a slab gap at ca. 120 Ma is the most likely cause of the extensive gold mineralization in Jiaodong. The gap induced a local and rapid devolatilization of the hydrated mantle wedge at submelt temperatures. The transient event included release of a major volume of gold-transporting aqueous-carbonic fluid that was stored in the wedge into major NNE-trending structures in the overlying lithosphere.

Recent geological survey has identified the Early Paleoproterozoic meta-mafic intrusions in the southwestern Yangtze Block. We present geochronological, whole-rock geochemical and Nd isotopic data for these meta-mafic rocks to better address the tectonic evolution of the Yangtze Block during the Early Paleoproterozoic Period. Geochronological data show that the meta-mafic rocks have zircon ages of 2 395-2 316 Ma. They have high TiO2 contents of 1.40 wt.%3.66 wt.% and Nb concentrations of 13.7 ppm45.5 ppm, thus aregrouped as Nb-enriched mafic rocks. These mafic rocks are characterized by tholeiitic compositions with enrichment of LREEs and LILEs, and can be divided into two groups. Group 1 samples display E-MORB-like geochemical characteristics. Group 2 samples have positive eNd(t) values of 4.0–5.0. Geochemical data indicate that all meta-mafic rocks were likely derived from a depleted asthenospheric mantle. REE modeling indicates lower degree of partial melting for Group 2 samples (3%–10%) relative to Group 1 samples (15%–20%). Taking into account contemporaneous post-collisional granitoids in southwestern Yangtze Block, we propose that these meta-mafic rocks were formed in a post-collisional extension setting. These meta-mafic rocks can be compared with those in Africa, South America and Europe, and might be linked with the Arrowsmith orogenic belt. KEY WORDS: zircon dating, geochemistry, Early Paleoproterozoic, Nb-enriched rocks, Yangtze Block.

High-grade hematite mineralization is widely developed in banded iron formations (BIFs) worldwide. However, in the North China craton where Neoarchean-Paleoproterozoic BIFs are abundant, economic high-grade hematite ores are scarce. High-grade hematite ores hosted in the Paleoproterozoic Yuanjiacun BIFs represent the largest occurrence of this type of ore in the North China craton. The orebodies are fault controlled and show sharp contacts with lower greenschist facies metamorphic BIFs. In situ U-Pb geochronology of monazite and xenotime intergrown with microplaty hematite and martite in high-grade ore established two episodes of metamorphic-hydrothermal monazite/xenotime growth after deposition of the BIFs. The earlier episode at ca. 1.94 Ga is interpreted as the timing of lower greenschist-facies metamorphism, and the later episode at 1.41 to 1.34 Ga represents the timing of high-grade hematite mineralization. Petrography and microthermometry of primary fluid inclusion assemblages indicate that the high-grade hematite ore formed from hot (313°–370°C), CO2-rich, and highly saline (~20 wt % NaCl equiv) hydrothermal fluids. These fluids channeled along faults, which concentrated iron through interaction with the BIFs—a process similar to typical hematite mineralization elsewhere. The deposition of hematite was probably related to tectonic extension in the North China craton related to the breakup of the Columbia/Nuna supercontinent. Our results challenge a previously proposed model ascribing the scarcity of high-grade hematite ores in the North China craton to the lack of prolonged weathering conditions. Rather, we argue that the high-grade ore formed in lower metamorphic-grade BIFs at shallower depths than magnetite mineralization and was largely eroded during later exhumation and uplift of the craton.

New age data for the Baoban Complex, South China establishes that it lay outboard of western Laurentia in the early Mesoproterozoic but was not part of the Cathaysia Block, with which it is traditional linked, until the mid-Paleozoic. Our geochronology data for detrital zircon and authigenic monazite grains from metasedimentary rocks indicate accumulation between ca. 1.55 Ga and 1.45 Ga for the Gezhencun succession of the Baoban Complex and ca. 1.45 Ga and 1.30 Ga for the Ewenling succession. The former unit is dominated by detrital zircon populations between 1900 Ma and 1500 Ma with two peaks at 1780 Ma and 1580 Ma. The Ewenling succession has detrital zircon peaks at 1720 Ma and 1450 Ma. Newly discovered gneissic granites were emplaced at 1550 Ma and intruded by 1450 Ma leucogranite dykes that are coeval with 1460–1430 Ma bimodal magmatism. The whole Baoban Complex was metamorphosed over the range of 1.3–0.9 Ga based on ages of authigenic zircon and monazite. Depositional ages of metasedimentary rocks are coeval with successions of the Belt-Purcell Basin, western Laurentia. Detrital zircon from the two regions have similar age populations and Lu-Hf compositions, and display a synchronous provenance shift at ca. 1.45 Ga. Basement lithologies on Hainan Island range in age from ca. 1.55–1.43 Ga and underwent metamorphism during 1.3–0.9 Ga. This is younger than basement rocks on the mainland of the Cathaysia Block in South China, suggesting the two regions are spatially unrelated at this time and hence the Mesoproterozoic record of the island cannot constrain the location of the Cathaysia Block in the Nuna and Rodinia supercontinents.

The Great Oxidation Event (GOE) is marked by the loss of readily oxidizable detrital minerals and the onset of oxidative weathering. One of the oldest post-GOE weathering surfaces, which extends for almost 350 km along strike, occurs in Griqualand West, South Africa. It is best preserved east of the Blackridge thrust, where oxidized paleoweathering profiles are developed below the unconformity at the base of Mapedi-Gamagara red beds. In the Maremane Dome, the red beds preserve pisolitic hematite laterites, which indicate a highly oxygenated atmosphere and suggest hot and humid climatic conditions. The Mapedi and Gamagara Formations are undated east of the Blackridge thrust but were thought to be lithological correlatives of the ≥1.91 Ga Mapedi red bed sequence to the west. Here, we report a U-Pb zircon age of 1.25 Ga for a felsic tuff in red beds of the Mapedi Formation in the Kalahari manganese field. The new tuff age shows that the Mapedi red beds east of the thrust were deposited >650 m.y. after the Mapedi Formation to the west, and therefore they are part of a distinct Mesoproterozoic sequence. Based on lithologic and sedimentological similarities, the Mapedi-east and Gamagara formations are likely to be correlatives that were deposited on an ancient weathering surface at ca. 1.25 Ga. Our findings suggest that key evidence for a highly oxygenated atmosphere during the early Paleoproterozoic actually formed at ca. 1.25 Ga during a major episode of Mesoproterozoic oxidative weathering.

There is geological evidence for widespread deformation in the Kaapvaal craton, South Africa, between 2.2 and 2.0 Ga. In Griqualand West, post-Ongeluk Formation (ca. 2.42 Ga) and pre-Mapedi Formation (>1.91 Ga) folding, faulting, and uplift have been linked to the development of a regional-scale unconformity, weathering horizons, and extensive Fe-oxide mineralization. However, the lack of deformational fabrics and the low metamorphic temperatures (400 m.y. after deposition. Combined with previous studies, our results show that sedimentary successions across the Kaapvaal craton deposited before ca. 2.26 Ga record evidence for crustal fluid flow at ca. 2.15 Ga, which is locally associated with thrust faulting, folding, and cleavage development. The style of the deformation is similar to that of the Ophthalmian orogeny in the Pilbara craton, Australia, which is interpreted to reflect the northeast-directed movement of a fold-thrust belt between 2.22 and 2.15 Ga. Our results suggest that the Kaapvaal and Pilbara cratons, which some paleogeographic reconstructions place together as the continent Vaalbara, experienced an episode of synchronous folding and thrusting at ca. 2.15 Ga. Deformation was followed by uplift and the development of unconformities that are associated with some of Earth’s oldest oxidative weathering and with the onset of Fe-oxide mineralization.

The Paleoproterozoic (1.7 Ga [billion years ago]) metasedimentary rocks of the Mount Barren Group in southwestern Australia contain burrows indistinguishable from ichnogenera Thalassinoides, Ophiomorpha, Teichichnus, and Taenidium, known from firmgrounds and softgrounds. The metamorphic fabric in the host rock is largely retained, and because the most resilient rocks in the sequence, the metaquartzites, are too hard for animal burrowing, the trace fossils have been interpreted as predating the last metamorphic event in the region. Since this event is dated at 1.2 Ga, this would bestow advanced animals an anomalously early age. We have studied the field relationships, petrographic fabric, and geochronology of the rocks and demonstrate that the burrowing took place during an Eocene transgression over a weathered regolith. At this time, the metaquartzites of the inundated surface had been weathered to friable sandstones or loose sands (arenized), allowing for animal burrowing. Subsequent to this event, there was a resilicification of the quartzites, filling the pore space with syntaxial quartz cement forming silcretes. Where the sand grains had not been dislocated during weathering, the metamorphic fabric was seemingly restored, and the rocks again assumed the appearance of hard metaquartzites impenetrable to animal burrowing.

Sample locations, photomicrographs and backscattered electon images Figures S1-S4, and data Tables S1-S11.

Although less common than hematite ores, high-grade magnetite ores represent a distinct type of iron mineralization hosted by banded iron formations (BIFs). The Gongchangling iron deposit hosted in ~2.55 Ga BIFs in the North China craton represents one of the most economically important iron deposits in China. Located in mining area II, it is a high-grade (>50 wt % Fe) magnetite deposit and one of the largest of its type in the world. However, the lack of reliable age constraints on iron mineralization has hindered the testing of competing genetic models for the formation of the Gongchangling deposit. In situ U-Pb geochronology of monazite and zircon intergrown with garnet from the proximal alteration zone of a high-grade iron orebody yielded an age of 1.86 Ga, which represents the timing of formation of high-grade magnetite mineralization. This age is coeval with a tectonic extension event recorded in the northeastern North China craton. Our results preclude the previously suggested genetic link between high-grade magnetite mineralization and ~2.50 Ga regional metamorphism. Growth of authigenic monazite and zircon is likely related to the breakdown of detrital zircon, which has undergone metamictization. In combination with previously published data, we propose that the development of zoned alteration associated with the deposit, which is characterized by the garnet-amphibole-magnetite assemblage in the proximal zone changing to a chlorite-quartz–dominated assemblage in the distal zone, can be attributed to a gradual decrease in temperature from >550° to ~250°C and to alteration minerals forming from leaching of the BIFs instead of by replacement of the wall rocks. Magnetite mineralization was controlled by the well-developed faults that cut the BIFs and provided conduits for silica-undersaturated alkaline meteoric fluids. Fluid flow likely took place in an extensional tectonic regime, similar to that invoked elsewhere for hematite mineralization but at greater depths.

The Archean Yilgarn Craton in Western Australia is intruded by numerous mafic dykes of varying orientations, which are poorly exposed but discernible in aeromagnetic maps. Previous studies have identified two craton-wide dyke swarms, the 2408 Ma Widgiemooltha and the 1210 Ma Marnda Moorn Large Igneous Provinces (LIP), as well as limited occurrences of the 1075 Ma Warakurna LIP in the northern part of the craton. We report here a newly identified NW-trending mafic dyke swarm in southwestern Yilgarn Craton dated at 1888 ± 9 Ma with ID-TIMS U-Pb method on baddeleyite from a single dyke and at 1858 ± 54 Ma, 1881 ± 37 and 1911 ± 42 Ma with in situ SHRIMP U-Pb on baddeleyite from three dykes. Preliminary interpretation of aeromagnetic data indicates that the dykes form a linear swarm several hundred kilometers long, truncated by the Darling Fault in the west. This newly named Boonadgin dyke swarm is synchronous with post-orogenic extension and deposition of granular iron formations in the Earaheedy basin in the Capricorn Orogen and its emplacement may be associated with far field stresses. Emplacement of the dykes may also be related to initial stages of rifting and formation of the intracratonic Barren Basin in the Albany-Fraser Orogen, where the regional extensional setting prevailed for the following 300 million years. Recent studies and new paleomagnetic evidence raise the possibility that the dykes could be part of the coeval 1890 Ma Bastar-Cuddapah LIP in India. Globally, the Boonadgin dyke swarm is synchronous with a major orogenic episode and records of intracratonic mafic magmatism on many other Precambrian cratons.

The Truong Son and Kon Tum terranes in northeastern Indochina are thought to, respectively, form part of the Indian and Australian margins of Gondwana and separated one another by the Tam Ky–Phuoc Son Ocean during the early Paleozoic. In this paper, we present results of a comprehensive geochronological and geochemical study on a trondhjemite–tonalite suite identified in the Tam Ky–Phuoc Son Suture Zone. LA–ICP–MS zircon U–Pb dating yielded weighted mean 206Pb/238U ages of 518.5 ± 7.1 Ma and 502.1 ± 6.0 Ma for the trondhjemite and tonalite, respectively. These are the oldest magmatic zircons recorded in this area so far. Both rocks consist primarily of plagioclase (oligoclase), quartz, with minor, variable amounts of hornblende and biotite. They have high SiO2, Na2O and Y, but low Al2O3, K2O, Sr and Rb contents, and are characterized by depletion in LREEs with flat HREE patterns. These features are similar to those of typical oceanic plagiogranites. Our new evidences from field geology, geochemistry, and zircon Hf isotopic data, along with previously published data from the Tam Ky–Phuoc Son Suture Zone, suggest that the plagiogranites were originated from extensive fractionation of hydrous basaltic magmas. Furthermore, they were generated in an intra-oceanic arc system above a northward subduction zone within the Tam Ky–Phuoc Son Ocean. The final closure of this ocean took place before the late Silurian, marked by collision of the Truong Son Terrane with the Kon Tum Terrane along the Tam Ky–Phuoc Son Suture Zone to form the Indochina Block. After elimination of the southeastward offset along the Red River shear zone and the clockwise rotation of Indochina relative to South China since the Tertiary, the eastern part of the Tam Ky–Phuoc Son Suture aligns well with the Kuungan Suture on Hainan Island, together they have likely recorded the final assembly of Gondwana in this region.

This study was financially supported by projects from the China Natural Science Foundation (41672222) and State Key Laboratory of Geological Process and Mineral Resources, China University of Geosciences, Wuhan (MSFGPMR201802). PAC acknowledges support from Australian Research Council grant FL160100168. This study was also supported by the Ministry of Natural Resources and Environment of Viet Nam, Project BĐKH.29/16-20 to Dung My Tran. Our understanding of the early evolution of the Yangtze Block is limited by the sparsely dispersed nature of pre-Neoproterozoic exposures. New, integrated petrographic, zircon U-Pb age and Hf-Nd isotope analyses, and whole-rock geochemical data for early Paleoproterozoic granites in the Phan Si Pan Complex provides new insights into the evolution of the Yangtze Block as well as its role in the Pre-Nuna supercontinent. LA-ICP-MS zircon U-Pb dating of magmatic zircons from quartz monzonite and gneissic granite yielded 207Pb/206Pb ages of 2306 ± 12 Ma and 2096 ± 15 Ma, respectively. Zircons from the quartz monzonite have εHf(t) values ranging from -4.1 to -2.1, corresponding to TDM2 model ages of 3002–2890 Ma, whereas zircons in the gneissic granite have εHf(t) values between -0.95 and +1.72 and corresponding TDM2 model ages of 2660–2516 Ma, which are consistent with their whole-rock Nd isotope values. Geochemically, the quartz monzonites are I-type granites. Combined with their relatively high Sr/Y ratios and low Y concentrations, as well as fractionated REE patterns with relatively high LREE but low HREE concentrations, they were probably generated by partial melting of the thickened middle-lower crust under elevated temperature. Geochemical and isotopic signatures suggest that the ca. 2.1 Ga gneissic granites are high-K calc-alkaline, ferroan A-type granites formed by partial melting of juvenile crustal source at high temperature and low pressure with little involvement of ancient crustal material. The Phan Si Pan complex has a distinct early Paleoproterozoic crustal evolution history compared with the other crustal provinces of the Yangtze Block, suggesting independent histories that were not unified until the late Paleoproterozoic during the assembly of Nuna. Moreover, the magmatism and tectonic evolution of the north Vietnam region is broadly similar to that of the Arrowsmith Orogen of the Rae craton in Laurentia suggesting a potential spatial linkage. The geologic record of the Yangtze Block does not support an early Paleoproterozoic shutdown of plate tectonics. Postprint

Mafic-ultramafic rocks of the Kabanga-Musongati alignment in the East African nickel belt occur as Bushveld-type layered intrusions emplaced in metasedimentary sequences. The age of the mafic-ultramafic intrusions remains poorly constrained, though they are regarded to be part of ca. 1375 Ma bimodal magmatism dominated by voluminous S-type granites. In this study, we investigated igneous monazite and zircon from a differentiated layered intrusion and metamorphic monazite from the contact aureole. The monazite shows contrasting crystal morphology, chemical composition, and U-Pb ages. Monazite that formed by contact metamorphism in response to emplacement of mafic-ultramafic melts is characterized by extremely high Th and U and yielded a weighted mean 207Pb/206Pb age of 1402 ± 9 Ma, which is in agreement with dates from the igneous monazite and zircon. The ages indicate that the intrusion of ultramafic melts was substantially earlier (by ∼25 m.y., 95% confidence) than the prevailing S-type granites, calling for a reappraisal of the previously suggested model of coeval, bimodal magmatism. Monazite in the metapelitic rocks also records two younger growth events at ca. 1375 Ma and ca. 990 Ma, coeval with metamorphism during emplacement of S-type granites and tin-bearing granites, respectively. In conjunction with available geologic evidence, we propose that the Kabanga-Musongati mafic-ultramafic intrusions likely heralded a structurally controlled thermal anomaly related to Nuna breakup, which culminated during the ca. 1375 Ma Kibaran event, manifested as extensive intracrustal melting in the adjoining Karagwe-Ankole belt, producing voluminous S-type granites. The Grenvillian-aged (ca. 990 Ma) tin-bearing granite and related Sn mineralization appear to be the far-field record of tectonothermal events associated with collision along the Irumide belt during Rodinia assembly. Since monazite is a ubiquitous trace phase in pelitic sedimentary rocks, in contact aureoles of mafic-ultramafic intrusions, and in regional metamorphic belts, our study highlights the potential of using metamorphic monazite to determine ages of mafic-ultramafic intrusions, and to reconstruct postemplacement metamorphic history of the host terranes.\ud GeoRef Subject\ud absolute age Africa East Africa gabbros igneous rocks intrusions Mesoproterozoic metamorphic rocks metamorphism metasedimentary rocks monazite Neoproterozoic nesosilicates norite orthosilicates phosphates plutonic rocks Precambrian Proterozoic silicates Tanzania U/Pb ultramafics upper Precambrian zircon zircon group

Unlike many Phanerozoic orogens, where the primary effects of orogenic events can be easily determined, Precambrian orogens are commonly characterised by repeated tectonothermal events maki...

The Permian-Triassic boundary (PTB) mass extinction, the most severe biocrisis in Earth's history, is thought to have been triggered by catastrophic volcanic activity. PTB sections in South China contain numerous volcanic ash beds, the source of which is inferred to have been either the Siberian Traps Large Igneous Province (STLIP) or intraregional subduction-zone arc volcanism. In this study, the provenance of these ash beds is determined through a comprehensive analysis based on the geochronological and geochemical signatures of zircons from four PTB sections (Dongpan, Xinmin, Ganxi and Shangsi). Inherited zircons yielded U–Pb ages of 250–3521 Ma with major age clusters in the Permian, Carboniferous to Silurian, early Cambrian to Neoproterozoic, early Neoproterozoic to late Mesoproterozoic, and early Paleoproterozoic. The age spectrum of these zircons is similar to those of detrital zircons from sedimentary and magmatic rocks of the South China and Indochina cratons but different from those of the Siberian Craton, providing evidence for an intraregional source of the volcanic material. The trace-element, eHf(t), and δ18O signatures of syn-depositional magmatic zircons are consistent with an arc-related/orogenic setting. PTB sections in South China can be assigned to sectors based on the number and cumulative thickness of ash beds and the length of zircon crystals. Sector I (South) includes the Dongpan and Xinmin sections, which have cumulative ash-bed thicknesses of 0.86–1.14 m and average zircon lengths of 151–217 μm. Sector II (North) includes the Ganxi, Shangsi and Daxiakou sections, which have cumulative ash-bed thicknesses of 0.17–0.33 m and average zircon lengths of 82–104 μm. Sector III (Northeast) includes the Niushan and Meishan sections, which have cumulative ash-bed thicknesses of 0.1–0.14 m and average zircon lengths of 71–73 μm. Systematic trends toward fewer and thinner ash beds and as well as smaller zircon sizes from Sector I to Sector III indicate a paleo-northward or -northeastward direction of ash transport. Collectively, our findings provide evidence that the source of volcanic ash in South China PTB sections was intraregional subduction-zone arc volcanism along the convergent margin between the South China and Indochina cratons.

Proterozoic orogens commonly host a range of hydrothermal ores that form in diverse tectonic settings at different times. However, the link between mineralization and the regional-scale tectonothermal evolution of orogens is usually not well understood, especially in areas subject to multiple hydrothermal events. Regional-scale drivers for mineral systems vary between the different classes of hydrothermal ore, but all involve an energy source and a fluid pathway to focus mineralizing fluids into the upper crust. The Mount Olympus gold deposit in the Proterozoic Capricorn Orogen of Western Australia, was regarded as an orogenic gold deposit that formed at ca. 1738 Ma during the assembly of Proterozoic Australia. However, the trace element chemistry of the pyrite crystals closely resembles those of the Carlin deposits of Nevada, with rims that display solid solution gold accompanied by elevated As, Cu, Sb, Hg, and Tl, surrounding gold-poor cores. New SHRIMP U–Pb dating of xenotime intergrown with auriferous pyrite and ore-stage alteration minerals provided a weighted mean 207Pb*/206Pb* date of 1769 ± 5 Ma, interpreted as the age of gold mineralization. This was followed by two discrete episodes of hydrothermal alteration at 1727 ± 7 Ma and 1673 ± 8 Ma. The three ages are linked to multiple reactivation of the crustal-scale Nanjilgardy Fault during repeated episodes of intracratonic reworking. The regional-scale drivers for Carlin-like gold mineralization at Mount Olympus are related to a change in tectonic regime during the final stages of the intracratonic 1820–1770 Ma Capricorn Orogeny. Our results suggest that substantial sized Carlin-like gold deposits can form in an intracratonic setting during regional-scale crustal reworking. Keywords: Geochronology, Xenotime, SHRIMP, LA-ICP-MS, Gold mineralization, Capricorn orogen

Several techniques have been proposed to predict undiscovered mineral resources at the regional scale by integrating multiple spatial datasets and mineral deposit models using Geographical Information Systems (GIS). An unresolved issue, however, is that predictive proxies are two-dimensional GIS layers at a regional scale, whereas mineralising processes occur in four dimensions (i.e., space and time). In the past 10 years, mineral system modelling approaches have been proposed and developed for the critical doubt that are described in terms of two characteristics: spatial scales and relevant geochemical processes. This paper demonstrates the modelling and combination of multiple scales based on mineral system prospectivity analysis and then present a resource estimation method that involves the calculation of three variables. In applying a GIS-based approach to a mineral system, we compared the resource estimation in a trap on the district scale to the extrapolation of reserve estimations of representative deposits in the same mineral system. The procedure used for the implementation of this method includes: (i) the incorporation of a descriptive model based on the mineral deposit type; (ii) the digitalization of the favourable characteristics of the type of investigated deposit; (iii) the implementation of the mineral system theory (approach) to pinpoint the locations of potential structural or stratigraphic traps at the district scale using GIS-based two-dimensional prospectivity mapping; (iv) the calculation of similarities and ore-bearing ratios; (v) the restructuring of models of favourable features at multiple scales (i.e., district and ore deposit scales); and (vi) the assessment of undiscovered mineral resources in traps. This method was used to estimate MVT-type Pb-Zn mineralisation in a promising potential region in northwestern Hunan Province, China. In addition, this study is divided into two parts, and this paper mainly describes the methodology.

The Changning–Menglian suture represents a remnant of the main Paleo-Tethys in the Sanjiang Orogen (SW China), and preserves abundant magmatic rocks formed during orogenic processes related to the closure of the Paleo-Tethys. Our geochronology study on granitoids of the Lincang Batholith, a prominent magmatic feature along the Changning-Menglian suture, yields crystallization age of 261 ± 1 Ma, 252 ± 1 Ma, to 203 ± 1 Ma, confirming a multi-stage emplacement of the batholith. The Late Permian granodiorites are medium- to high-K calc-alkaline, metaluminous (A/CNK = 0.99–1.10), with high Al2O3 content (14.03 wt%), high Mg# (46), high (87Sr/86Sr)i (0.7192–0.7278), negative whole-rock eNd(t) (− 14.7 to − 8.5), (206Pb/204Pb)t of 18.199 to 18.791, (207Pb/204Pb)t of 15.714 to 15.765, (208Pb/204Pb)t of 38.500 to 38.851, zircon δ18OSMOW = 7.13‰–8.57‰, and zircon eHf(t) of − 14.8 to + 0.4. The Late Triassic granites are characterized by high SiO2 value (68.52 wt%), high Mg# values of 50, with negative Eu anomalies (δEu = 0.32–0.78), high (87Sr/86Sr)i (0.7202–0.7424), negative whole-rock eNd(t) (− 15.6 to − 10.7), (206Pb/204Pb)t of 18.659 to 18.793, (207Pb/204Pb)t of 15.752 to 15.791, (208Pb/204Pb)t of 38.865 to 38.959, zircon δ18OSMOW = 8.07‰–9.76‰. These geochemical and isotopic features suggest that the primary magma of both Late Permian and Late Triassic granitoids most likely originated from partial melting of the underlying Proterozoic crustal rocks, with limited addition of mantle components. Our new geochronological and geochemical results together with previously published data, suggest that the composite Lincang Batholith records three magmatic episodes related to the Paleo-Tethys evolution, corresponding to subduction (prior to ~ 252 Ma), syn-collisional (250–237 Ma), and post-collisional (235–203 Ma) stages.

The Archean Yilgarn Craton in Western Australia hosts at least five generations of mafic dykes ranging from Archean to Neoproterozoic in age, including the craton-wide ca. 2408 Ma Widgiemooltha and the 1210 Ma Marnda Moorn Large Igneous Provinces (LIP), the 1888 Ma Boonadgin dykes in the southwest and the 1075 Ma Warakurna LIP in the northern part of the craton. We report here a newly identified NNW-trending mafic dyke swarm, here named the Biberkine dyke swarm, in the southwestern Yilgarn Craton dated at 1390 ± 3 Ma by ID-TIMS U-Pb geochronology of baddeleyite. The regional extent of the dyke swarm is uncertain but aeromagnetic data suggest that the dykes are part of a linear swarm several hundred kilometers long, truncated by the Mesoproterozoic Albany-Fraser Orogen to the south. Geochemical data indicate that the dykes have tholeiitic compositions with a significant contribution from metasomatically enriched subcontinental lithospheric mantle and/or lower continental crust. Paleogeographic reconstructions suggest that a prolonged tectonic quiescence in the Yilgarn Craton from ca. 1600 Ma was interrupted by renewed subduction along the southern and southeastern margin at ca. 1400 Ma, reflecting a transition from Nuna to Rodinia configuration. The 1390 Ma Biberkine dykes may be a direct consequence of this transition and mark the change from a passive to active tectonic setting, which culminated in the Albany-Fraser Orogeny at ca. 1330 Ma. The Biberkine dykes are coeval with a number of other mafic dyke swarms worldwide and provide an important target for paleomagnetic studies.

Early Paleozoic trondhjemites, gneissic granites and alkali granites in southern Yunnan preserve important records of the tectonic evolution of the Prototethyan Ocean and regional correlations. Zircon ages suggest that these granitoids were emplaced from 476 to 436 Ma. The trondhjemites are characterized by high Na2O and low K2O contents, with eNd(t) values of −1.9 to −3.5 and eHf(t) values of −2.8 to +3.9. The trondhjemites were derived from an amphibolite source with a juvenile mafic component. The gneissic granites belong to the metaluminous low-K calc-alkaline series with an eNd(t) value of −6.2 and eHf(t) values of −5.0 to −0.4. The alkali granites belong to the high-K calc-alkaline series and yield eNd(t) values of −10.1 to −10.7 and eHf(t) values of −7.9 to −2.3. The gneissic granites were derived from an ‘ancient9 lower mafic crust, whereas the alkali granites were derived from a meta-sedimentary source. These granitoids were formed during the subduction of the Prototethyan Ocean beneath the Simao Block and can be compared with similar igneous rocks from the Truong Son and Tam Ky-Phuoc Son zones in southern Laos. Our study, along with Early Paleozoic igneous suites from southern Laos, central Vietnam and the Malay Peninsula, suggests an arc–back-arc system along the northern margin of Gondwana. Supplementary material: Tables of zircon U–Pb and in-situ Hf and geochemical data are available at https://doi.org/10.6084/m9.figshare.c.5322386

The Teutonic Bore Camp, comprised of the Teutonic Bore, Jaguar and Bentley deposits, is one of the most significant volcanic-hosted massive sulphide (VHMS) camps in Western Australia. Despite being extensively studied, only recently there have been advances in the understanding of the mechanism that drove the formation of mineralisation. It has been recognized by recent studies that the volcanic-hosted deposits from the Teutonic Bore Camp represent replacement-type VHMS systems, with significant input of fluids and metals from a magmatic source. This paper tests the existing hypothesis that the nearby Penzance granite acted as the metals source and/or thermal engine driving the development of these ore deposits. New age constraints on the formation of the host volcanic sequence at the Bentley deposit and the crystallization of the Penzance granite allows for the construction of a 4D evolutionary model for the ore system. A new U-Pb SHRIMP monazite age of 2681.9 ± 4.5 Ma indicates that the Penzance granite post-dates the host stratigraphy at Bentley (ca. 2693 Ma) and is probably coeval with mineralisation. All zircons (Penzance, Bentley units I and III) have very similar ƐHf(i), with most values between −1 and + 6, slightly higher than the ƐHf(i) of zircons from other granites and volcanics within the Kurnalpi Terrain, and indicative of juvenile sources. The mean Th/U ratios are ~0.7 and ~0.6 for the Penzance and Bentley zircons, respectively. All zircons have similar Ce/Nd(CN) ratios. The chemical similarities between the zircons from the granite and the volcanic rocks at Bentley support a shared magmatic source between the Penzance and the Teutonic Bore Camp sequence. The Penzance granite is the likely source of heat, and potentially metals, which drove the VHMS mineralisation at the Teutonic Bore Camp.

Sapphirine-bearing UHT granulites from the Dongpo locality in the Khondalite Belt of the North China Craton have been comprehensively characterized in terms of petrology, mineral chemistry, metamorphic evolution and zircon geochronology. However, the precise timing of the peak-UHT metamorphism and other key stages in the P–T–t evolution remain controversial due to the complexity of multiple metamorphic overprints and the lack of petrographic context for zircon age data. In this study, monazite from four samples of the Dongpo granulite are divided into six groups based on chemical composition and textural context, and dated (in-situ SHRIMP and LA–ICP–MS U–Pb). An age population of 1·91–1·88 Ga was obtained from high-Y cores of monazite inclusions in garnet (Group 1) and on grains in the rock matrix (Group 2). The maximum age of c.1·91 Ga is interpreted as the minimum timing for prograde metamorphism before UHT metamorphism (M1). An age population of 1·90–1·85 Ga was obtained from low-Y domains of monazite inclusions (Group 3) and of matrix grains (Group 4). Combined with previous zircon dating results, the age population from low-Y Mnz constrains the timing and duration of the UHT metamorphism to 1·90–1·85 Ga and 50 (±15) million years, respectively. The large (50 m.y.) age spread is interpreted to reflect continuous monazite formation, and it is consistent with the slow post-peak near-isobaric cooling stage (M2). An age of c.1·86 Ga was obtained from monazite in textural contact with sapphirine/spinel + plagioclase intergrowths (Group 5), which is interpreted as the timing of the subsequent decompression–heating stage (M3). The younger age clusters at c.1·80 and 1·77 Ga, obtained from Th-rich monazite rims (Group 6) and one single Th-depleted monazite in textural contact with matrix biotite, respectively, indicate dissolution–reprecipitation and new monazite growth from fluid released by crystallizing anatectic melt during retrogression. These results, along with the previous 1·93–1·91 Ga data for UHT metamorphism, suggest that there was a very long-lived Paleoproterozoic UHT metamorphism (1·93–1·85 Ga) in the Khondalite Belt of the North China Craton. This supports the large hot orogeny model for the generation of Paleoproterozoic UHT metamorphism in the Khondalite Belt during the amalgamation of the Nuna supercontinent.

The Helanshan complex in the Khondalite Belt, North China Craton (NCC) is characterized by the occurrence of both medium-pressure (MP) and high-pressure (HP) pelitic granulites. This paper presents new results from phase equilibrium modelling and SHRIMP zircon U–Pb dating on the MP garnet-sillimanite granulites, in order to better understand the relationship between the MP and HP pelitic granulites, the tectonic implications of the MP pelitic granulites for the formation of the Khondalite Belt, and their geodynamic implications for the Paleoproterozoic orogenesis. Based on petrographic observations, the metamorphic evolution can be divided into four stages (M1–M4). The M1–M3 stages are suprasolidus as reflected by the migmatitic structure on the outcrop. The peak metamorphic stage (M1) is represented by the rim of garnet porphyroblasts along with inclusions of sillimanite + quartz ± biotite, and rutile relicts + plagioclase + K-feldspar in the matrix; the M2 is defined by the ilmenite that have partially replaced rutile; and the M3 is characterized by the replacement of garnet by cordierite. The subsolidus mineral assemblage is garnet + biotite + plagioclase + K-feldspar + sillimanite + cordierite + ilmenite + quartz (M4). Combined with the phase equilibrium modelling in the Na2O–CaO–K2O–FeO–MgO–Al2O3–SiO2–H2O–TiO2–O2 chemical system, the MP pelitic granulites record a clockwise P–T path, which is characterized by near-isothermal decompression (ITD) from ∼10.1 kbar at ∼830 °C to ∼5.8 kbar at ∼800 °C and subsequent close-to-isobaric cooling (IBC). SHRIMP zircon U–Pb dating yielded a metamorphic age of 1931 ± 21 Ma, interpreted as the time of the retrograde cooling. Integrated with previously reported results, we propose that slab break-off subsequent to Yinshan-Ordos collision at ca. 1.95 Ga led to uplift of the MP and HP granulites in the Khondalite to the middle crustal level in an extensional regime as indicated by their ITD evolution, which was followed by slow cooling at ca. 1.93 Ga as evidenced by their nearly IBC evolution.

Uranium-lead geochronology of zircon in felsic tuffs plays a key role in the development of chronostratigraphic frameworks for sedimentary successions. This is particularly true for Precambrian basins, where biostratigraphy is of limited use for age determination or stratigraphic correlation. Although zircon is widely used to date tuffs, it can yield null results due to the presence of xenocrystic populations or isotopic resetting. Other potential U-Pb chronometers, such as monazite, which also crystallize from felsic magmas, are largely unreported from felsic tuff layers. Consequently, there has been a lack of studies to evaluate the potential of monazite for U-Pb isotope geochronology of tuffs. We present results of in situ U-Pb ion microprobe dating of monazite that co-exists with zircon in felsic tuffs from two Precambrian basins: the Earaheedy Basin (Frere Formation) in Western Australia and the Bushveld Basin (Lephala Formation) in southern Africa. We show that 207Pb/206Pb ages from monazite in felsic tuffs from the Frere Formation (1891 ± 9 Ma) and the Lephala Formation (2307 ± 9 Ma) are identical to zircon ages from the respective tuffs. Also, monazite in the Bushveld tuff preserves additional information, including a chronological fingerprint of the volcanic source (2.4–2.5 Ga xenocrysts) and the timing of low-grade metamorphism (2.16 Ga overgrowths). The ca. 2.16 Ga low-grade metamorphism identified in the Bushveld Basin is reminiscent of that widely recorded in the Pilbara Craton, Western Australian, lending support to arguments for a connection between the Kaapvaal and Pilbara cratons. Igneous and low-grade metamorphic monazites are readily distinguished based on texture and chemistry. Our study demonstrates that monazite can be used to accurately date felsic tuffs, offering a powerful tool for constraining depositional and metamorphic histories of Precambrian sedimentary basins.

Antarctica contains continental fragments of Australian, Indian and African affinities, and is one of the key elements in the reconstruction of Nuna, Rodinia and Gondwana. The Bunger Hills region in East Antarctica is widely interpreted as a remnant of the Mesoproterozoic Albany–Fraser Orogen, which formed during collision between the West Australian and Mawson cratons and is linked with the assembly of Rodinia. Previous studies have suggested that several generations of mafic dyke suites are present at Bunger Hills but an understanding of their origin and tectonic context is limited by the lack of precise age constraints. New in situ SHRIMP U-Pb zircon and baddeleyite dates of, respectively, 1134 ± 9 Ma and 1131 ± 16 Ma confirm an earlier Rb-Sr whole-rock age estimate of ca. 1140 Ma for emplacement of a major mafic dyke suite in the area. Existing and new geochemical data suggest that the source of the dyke involved an EMORB-like source reservoir that was contaminated by a lower crust-like component. The new age constraint indicates that the dykes post-date the last known phase of plutonism at Bunger Hills by ca. 20 million years and were emplaced at the end of Stage 2 of the Albany-Fraser Orogeny. In current models, post-orogenic uplift and progressive tectonic thinning of the lithosphere were associated with melting and reworking of lower and middle crust that produced abundant plutonic rocks at Bunger Hills. A major episode of mafic dyke emplacement following uplift, cooling, and plutonic activity with increasing mantle input, suggests that the dykes mark the end of a prolonged interval of thermal weakening of the lithosphere that may have been associated with continued mafic underplating during orogenic collapse. If the undated olivine gabbro dykes with similar trend, geochemistry and petrology at Windmill Islands are coeval with the ca. 1134 Ma dyke at Bunger Hills, this would suggest the presence of a major dyke swarm at least 400 km in extent. In such case, the dykes could have been emplaced laterally from a much more distant mantle source, possibly a plume, and interacted with the locally heterogeneous and variably metasomatised lithosphere.

Integration of a new monazite U–Pb age for the Atalla monzogranite (615 ± 9 Ma) and a 40Ar/39Ar plateau age of hydrothermal white mica (601 ± 5.5 Ma, 2σ) disseminated in gold-bearing quartz veins at the Atalla mine indicates post-intrusion Au-mineralization, overlapping with cooling and regional exhumation ages of the Central Eastern Desert. The mica age is in agreement with published Re–Os age of gold mineralization in the Fawakhir area, ~ 20 km to the south along the Atalla shear zone. The new geochronological data demonstrate lode gold formation during the ~ 600 Ma period, controlled by wrench tectonics along Najd-related structures in the region (620–585 Ma). Fluid focusing and gold deposition during the Ediacaran were promoted by contrasting lithological and rheological properties at the granite-ophiolites contacts. This seems to be a typical setting for gold ores in this part of the Nubian Shield, and can aid exploration for undiscovered resources in the region.

Models for exploration targeting are often developed by assessing known gold deposits in a region, and targeting similar geological features such as geochemical anomalies, favourable host rocks or structural settings with the assumption that they represented the footprint of the mineralizing event. Belvedere and Paulsens are gold deposits with similar characteristics located in the Wyloo Inlier in the north Capricorn Orogen, Western Australia. Gold at both deposits is hosted in quartz–carbonate–sulfide veins within mafic intrusive rock. Prior to this study they were thought to have formed during the same hydrothermal mineralizing event. At Belvedere, in situ baddeleyite geochronology yields a weighted mean 207Pb∗/206Pb∗ crystallization age of 2082 ± 30 Ma for the Belvedere dolerite which hosts the ore body. Xenotime intergrown with ore-stage alteration minerals, and encased in arsenopyrite, yielded a 207Pb∗/206Pb∗ date of 1681 ± 9 Ma, interpreted to represent the timing of hydrothermal activity related to gold mineralization at the Belvedere deposit. Despite the similarities between the two deposits, our results indicate that they underwent different geological histories with primary gold mineralization at Paulsens occurring at c. 2400 Ma, pre-dating both the Belvedere dolerite and mineralization within the dolerite. Furthermore, field relationships show that the suite of dolerite dykes to which the Belvedere dolerite belongs, crosscut gold mineralization at Paulsens. The in situ U–Pb geochronology techniques employed here, combined with field relationships, have led to a better understanding on age constraints of gold deposition in the Wyloo Inlier and challenges the assumption that orogenic deposits in a given region probably formed during a single mineralizing event.

Extensional episodes in Precambrian orogens are often difficult to decipher because of subsequent orogenesis and intracontinental reworking. Here, we use geochemical and geochronological constraints of a suite of preserved mafic–ultramafic rocks in the Paleoproterozoic Capricorn Orogen of Western Australia to reveal ophiolites, continental ribbons and aborted rifts. The Capricorn Orogen separates the Archean Yilgarn and Pilbara cratons and includes mafic–ultramafic rocks of the fault-bounded Trillbar Complex and Bryah Sub-basin. The Trillbar Complex is situated within a fault wedge between the Yilgarn Craton and a reworked portion of the craton to the north (Yarlarweelor Gneiss Complex), and has been variously interpreted as an obducted ophiolite, oceanic plateau or continental rift-related magmatic suite. In this study, a new U–Pb zircon age of 2069 ± 9 Ma from the Trillbar Complex indicates that it is at least 40 Myr older than the mafic and ultramafic rocks of the Bryah Sub-basin, with which it has previously been linked. The Trillbar Complex is characterised by E-MORB-like signatures, hydrous crystallization and a lack of crustal contamination, and probably formed in a mid-ocean ridge or, alternatively, an oceanic intraplate setting. Conversely, the 2030–1990 Ma mafic and ultramafic rocks in the Bryah Sub-basin show evidence of crustal contamination and are interpreted to have formed in a continental rift setting. Moreover, there is no evidence for boninites in the Bryah Sub-basin and, therefore, no justification for invoking a fore-arc setting. Thus, these pieces of evidence reveal a different tectonic and geodynamic origin for the Trillbar Complex compared to the Bryah Sub-basin rocks. The tectonic setting for the Trillbar Complex requires oceanic crust to have existed between the Yilgarn Craton and the Yarlarweelor Gneiss Complex. However, almost identical Archean histories of these crustal blocks support a proximal origin for the Yarlarweelor Gneiss Complex and a likely origin as a microcontinental ribbon. Farther east (in present-day coordinates), the Bryah Sub-basin and other sedimentary basins record punctuated rifting that never led to the formation of oceanic crust. Therefore, rigorous evaluation of high quality geochemical data coupled to geochronology from mafic–ultramafic rocks is able to provide valuable constraints on extensional episodes, where other evidence has since been erased from the rock record.

The origin of bedded iron-ore deposits developed in greenstone belt-hosted (Algoma-type) banded iron formations of the Archean Pilbara Craton has largely been overlooked during the last three decades. Two of the key problems in studying these deposits are a lack of information about the structural and stratigraphic setting of the ore bodies and an absence of geochronological data from the ores. In this paper, we present geological maps for nearly a dozen former mines in the Shay Gap and Goldsworthy belts on the northeastern margin of the craton, and the first U-Pb geochronology for xenotime intergrown with hematite ore. Iron-ore mineralisation in the studied deposits is controlled by a combination of steeply dipping NE- and SE-trending faults and associated dolerite dykes. Simultaneous dextral oblique-slip movement on SE-trending faults and sinistral normal oblique-slip movement on NE-trending faults during initial ore formation are probably related to E–W extension. Uranium–lead dating of xenotime from the ores using the sensitive high-resolution ion microprobe (SHRIMP) suggests that iron mineralisation was the cumulative result of several Proterozoic hydrothermal events: the first at c. 2250 Ma, followed by others at c. 2180 Ma, c. 1670 Ma and c. 1000 Ma. The cause of the first growth event is not clear but the other age peaks coincide with well-documented episodes of orogenic activity at 2210–2145 Ma, 1680–1620 Ma and 1030–950 Ma along the southern margin of the Pilbara Craton and the Capricorn Orogen farther south. These results suggest that high-grade hematite deposits are a product of protracted episodic reactivation of a structural architecture that developed during the Mesoarchean. The development of hematite mineralisation along major structures in Mesoarchean BIFs after 2250 Ma implies that fluid infiltration and oxidative alteration commenced within 100 myr of the start of the Great Oxidation Event at c. 2350 Ma.

An early Paleozoic Proto-Tethys ocean in western Yunnan has long been postulated although no robust geological evidence has been identified. Here we investigated the recently-identified Mayidui and Wanhe ophiolitic melanges in SW Yunnan, which occurs in a N–S trending belt east of the late Paleozoic Changning–Menglian suture zone. The ophiolites consist mainly of meta-basalts (amphibole schists), meta- (cumulate) gabbros and gabbroic diorites, and meta- chert-shale, representing ancient oceanic crust and pelagic and hemipelagic sediments, respectively. Six samples of gabbros and gabbroic diorites from 3 profiles (Mayidui, Kongjiao and Yinchanghe) yielded zircon U-Pb ages between 462 ± 6 Ma and 447 ± 9 Ma, constraining the formation of the Mayidui and Wanhe ophiolites to Middle Ordovician. Gabbros from the Mayidui and Kongjiao profiles share similar geochemical characteristics with affinities to tholeiitic series, and are characterized by depleted to slightly enriched LREEs relative to HREEs with (La/Sm)N = 0.69–1.87, (La/Yb)N = 0.66–4.72). These, along with their predominantly positive whole-rock eNd(t) and zircon eHf(t) values, indicate a MORB-like magma source. By contrast, the meta-mafic rocks from the Yinchanghe profile show significantly enriched LREEs ((La/Sm)N = 0.97–3.33, (La/Yb)N = 1.19–14.93), as well as positive whole-rock eNd(t) and positive to negative zircon eHf(t) values, indicating an E-MORB-type mantle source. These geochemical features are consistent with an intra-oceanic setting for the formation of the Mayidui–Wanhe ophiolites. Our data, integrated with available geological evidence, provide robust constraints on the timing and nature of the Mayidui–Wanhe ophiolitic melange, and suggest that the ophiolites represent remnants of the Proto-Tethys Ocean, which opened through separation of the Indochina and Simao blocks from the northern margin of Gondwana before the Early Cambrian, and evolved through to the Silurian.