The Central Basin Fault Rift (CBFR) is a key area for studying deep-sea sedimentation and paleoclimate, yet its sedimentary process and provenance and their links to geological and climatic changes remain poorly understood. This study therefore conducted systematically sedimentological, mineralogical and geochemical analyses of sediments in core ZK06 from the CBFR to address the above question. The results show that the sediments are dominated by silt and clay, with multiple graded rhythms related to gravity flows. Provenance analysis shows that the sediments are composed primarily of proximal andesitic volcaniclastic detritus, with additional Asian aeolian dust and minor authigenic components. It is recognized that the proportion of Asian aeolian dust increases from the lower to medium part of the sediment sequence but decreases in the upper part, which may correspond to the input history of Asian aeolian dust in the West Philippine Basin during the late Pleistocene to Holocene. This study therefore provides not only new insights into sedimentary processes and the provenance of sediments but also the input history of the Asian aeolian dust in central CBFR.

The concentration and transport of metals (e.g., Sn) in granitic melts is key processes for magmatic-hydrothermal tin mineralization. The Sn-bearing Dupangling batholith located in the western Nanling Mountains of South China hosts a number of Sn deposits. The enrichment and transport processes of Sn in granitic melts remain poorly known. This study focuses on geochemical, mineralogical, and isotopic analyses in order to assess the role of magmatim in Sn enrichment of granites in the Dawan area of the northern Dupangling Batholith. Results show that the Dawan granites were emplaced at 224-232 Ma, and are both temporally and spatially correlating with Sn mineralization. Zircon epsilon Hf(t) values (-9.47 - -0.21) and corresponding T-DM2 ages (1.28-1.87 Ga) suggest that their parental magmas originated mainly from partial melting of Proterozoic basement rocks. The magmas were highly fractional, characterized by high temperatures (similar to 819.5 degrees C) and reduced oxygen fugacities (an average Delta FMQ of -0.15). Therefore, it appears that a combination of high-melting temperature, and highly-evolved and reduced granitic melts is the primary condition for Sn enrichment. Furthermore, the compositional zoning of mica and its decreasing of rare metals (e.g., Li, Rb, Cs, Nb, Ta and Sn) and increasing of Fe3+/Fe2+ from core to rim suggests an interaction between magmatically-derived F-bearing hydrothermal fluids and micas after crystallization. Tin mineralization in the Dupangling region is therefore likely associated with the ponding of magmaticallyderived hydrothermal fluids that were capable of concentrating and transporting Sn.

Rapakivi-type granites not only document magmatic processes but also archive subsolidus interactions between granitic rock and fluid, and thereby provide crucial information about fluid infiltration in the Earth's crust. However, the key process to generate rapakivi texture is still debated. Here, we report comprehensive mineralogical, geochemical and Hf isotopic compositions of the Dupangling rapakivi granites (210.4-214.9 Ma) in the South China Block to investigate the effect of fluid-rock interaction on the origin of rapakivi feldspar. Dupangling rapakivi granites have high SiO2 (72.63-78.21 wt%) and alkali contents (Na2O + K2O = 6.14-9.06 wt%) with high K2O/Na2O ratios (1.37-2.64), characteristic of weakly peraluminous (A/CNK = 1.04-1.10) high-K calcalkaline granites. Samples have weakly fractionated REE patterns with negative Eu anomalies (delta Eu = 0.05-0.38). They have negative whole-rock epsilon Nd(t) (-8.45 to -7.91), variable zircon epsilon Hf(t) (-9.7 to -1.0) and two-stage Hf isotope model ages (1.32-1.84 Ga), due to their derivation from a major early Mesoproterozoic crustal source with a subordinate late Paleoproterozoic component. Rapakivi feldspars in Dupangling granites are composed of an alkali-feldspar core and a plagioclase mantle. Fractures, pores and secondary inclusions (biotite, sericite, epidote and hematite) are closely associated with the mantles and oligoclase patches within alkali-feldspar cores. These pervasive microtextural features and variations of Be, Rb, Ba, Sr and LREE within rapakivi feldspars are interpreted to have formed through subsolidus fluid-induced dissolution-reprecipitation replacement processes. This study highlights that fluid-rock interaction plays an important role in generating rapakivi texture.

The Chitradurga Greenstone Belt is one of the largest belts in the central part of the Western Dharwar Craton (WDC). We present new SHRIMP U-Pb zircon and titanite ages, whole-rock geochemical and Sm-Nd isotopic data for granitoids that developed at both its eastern and western margins, and for those that are intrusive into the belt. Western margin TTG samples yield emplacement ages ofca. 3.21 Ga and are of the high-Al TTG type characterized by weakly negative epsilon Ndt values. Eastern margin granite samples yield emplacement ages of -3.0 Ga and 2.56 Ga with negative epsilon Ndt values. The granites intrusive into the belt are of Neoarchean age (-2.61 Ga) with more-evolved Nd isotopic signatures consistent with the involvement of older crustal material. Meta-morphic events are documented at ca. 3.0 Ga and ca. 2.5 Ga. The ca. 3.0 Ga event is synchronous with the diapiric emplacement of trondhjemites and high-K granitic plutons in the WDC. The peak metamorphic event at -2.5 Ga is the major tectono-thermal event evident throughout the Dharwar Craton. Geochemical systematics imply the involvement of convergent margin tectonics in the evolution of studied granitoids. The role of hori-zontal tectonics in the crustal growth of WDC is evident from at least 3.2 Ga, whereas signatures for the reworking of the older crust are more prominent from -3.0 Ga.

Bekker et al. (2020) and Philippot et al. (2018) discussed implications of the geological and geochemical records of the Turee Creek Basin in Western Australia with regards to the understanding of the Great Oxidation Episode (GOE). Whereas Bekker et al. (2020) inferred that, due to its deposition in a foreland basin with high sedimentation rates, the succession bears a high-resolution record leading to, and of, the early stage of the GOE, Philippot et al. (2018) maintained that it provides a detailed and continuous (i.e., stratigraphically unbroken) record spanning 2.45 Ga to 2.22 Ga. The disagreement is largely rooted in different readings of the geochronological data presented in Caquineau et al. (2018) and Philippot et al. (2018), but also in different views on the tectonostratigraphic evolution of the Turee Creek Basin, chemostratigraphic records of the succession, and correlation with other early Paleoproterozoic sequences. The disagreement has far-reaching implications for the GOE and its relationship to early Paleoproterozoic climate changes. Philippot et al. (2021) provided a detailed critique of our approach, allowing us to clarify our original interpretations. Based on the analysis provided below, we stand by our original reading, and provide a more nuanced view of the early Paleoproterozoic global correlations and events. By combining global records, we infer that the similar to 2.45-2.22 Ga time interval experienced so-far underappreciated large-scale swings in atmospheric oxygen level across the 10(-5) PAL threshold that were associated with, and likely led to, early Paleoproterozoic glaciations by impacting atmospheric levels of methane, a powerful greenhouse gas in an anoxic atmosphere.

Decoupling between Hf and Nd isotopes in trench sediments is an important way to produce, via subduction‐related recycling, the mantle chemical heterogeneity that is evident in many arc‐related magmas. Sediments collected from >7,000 m water depths on the southern and northern slopes of the Challenger Deep were analyzed to understand the factors controlling the variation in Hf and Nd isotopic compositions. These sediments were transported to both flanks of the Challenger Deep by synchronous density currents. All sediment samples show positive ɛHf values and negative ɛNd values, mostly plotting above the seawater and terrestrial arrays in Hf‐Nd isotope space. Hafnium isotopic compositions in each depositional unit vary (high up to 9.2 ɛHf units) from lower, coarse‐grained laminae to upper, fine‐grained graded intervals, showing a good correspondence between ɛHf values and lamination within depositional units. Such variations are explained by the concentration of Fe‐Mn oxyhydroxide‐bearing clays in the upper graded intervals, whereas diatom fragments and arc‐volcanic detritus are preferentially sorted into lower laminae. These findings demonstrate that the decoupling of Hf‐Nd isotopes in trench sediments is not only linked to the nature of provenance but also to hydrodynamic sorting processes during sediment transport. Our results suggest that geographical and stratigraphic variations in sedimentary components (resedimented density‐current deposits vs. oceanic pelagites), as well as overall grain size, of the subduction wedge can complicate Hf‐Nd isotopic decoupling in resulting arc magmas.

The Turee Creek Basin of the Pilbara Craton is critical for timing onset of the early Paleoproterozoic Icehouse and the GOE. We establish correlation to the Koegas/Postmasburg Supersequence of the Kaapvaal Craton based on a common compressional basin, with the Pilbara succession deposited near the orogen and the Kaapvaal succession near the flexural arch. Whereas Turee Creek cyclicity was controlled by tectonic subsidence, glacioeustatic influence is discernible in the Koegas/Postmasburg Supersequence. Key features of the Turee Creek Basin are: the mid-Kungarra Formation glaciogenic Meteorite Bore Member; unconformity-bound sequences above the Kungarra Formation; and the basaltic Bubbawalyee Formation conformably above Quartzite 3. On the Kaapvaal Craton, the equivalent glaciogenic unit (Makganyene Formation), overlying the sedimentary Koegas Subgroup and underlying the basaltic Ongeluk Formation, is unconformity-bound. We correlate the sub-Ongeluk unconformity with the sub-Quartzite 3 unconformity, and propose tectonostratigraphic equivalence of the Ongeluk and Bubbawalyee formations. There are no equivalents of the post-Ongeluk, Hotazel and Mooidraai formations above the Bubbawalyee Formation on the Pilbara Craton, which is significant because the Hotazel Formation provides the earliest evidence for the GOE. Consequently, rather than spanning the GOE, the Turee Creek Basin provides a chemostratigraphy during its eve. All carbonate sediments deposited before and after the first global glaciation (Meteorite Bore/Makganyene) yield carbon isotope values close to 0‰, establishing that the first carbon isotope excursion occurred long after closure of the Turee Creek-Koegas/Postmasburg basin and onset of the GOE. It therefore appears that the carbon cycle responded to, rather than triggered, the GOE.

本次研究运用岩相学和碎屑锆石U-Pb年龄物源分析方法获得北海涠洲岛海滩砂的物源特征,从而揭示北部湾大陆边缘"源-汇"系统及其沉积搬运过程.涠洲岛海滩砂以棱角状-次圆状石英为主(70％～75％),生物碎屑次之(20％～25％),含少量玄武岩岩屑和橄榄石碎屑颗粒(约5％),反映碎屑沉积物经历了较短距离的搬运且沉积时间较短.涠洲岛海滩砂碎屑锆石U-Pb年龄集中在288～210 Ma(峰值为236 Ma)和435～380 Ma,表明涠洲岛海滩砂主要来源于桂东南地区印支期花岗岩体以及加里东期和燕山期岩体.花岗岩来源的陆源碎屑经南流江、九洲江等河流快速地搬运至合浦-北海三角洲,在风暴作用下再扩散至北部湾中部海域.这一过程很好地记录了大陆边缘从陆到洋区域性"源-汇"系统.同时,涠洲岛是第四纪火山岛,是北部湾中部海域的隆起剥蚀区之一,其为海滩沉积物提供近源的基性岩碎屑组分,即存在盆地局部"源-汇"系统.因此,涠洲岛海滩砂沉积是大陆边缘区域性"源-汇"系统与盆地局部"源-汇"系统相互叠加的产物.本研究为理解大陆边缘从陆到洋"源-汇"系统与盆地局部"源-汇"系统的相互作用提供范例.

The Dharwar Supergroup comprises the unconformity bound Bababudan and Chitradurga groups. The Bababudan Group, which is best preserved in the Western Dharwar Craton, records a divergent margin comprising a basalt-dominant intracontinental rift sequence, a shale-BIF drift sequence, and a sandstone-shale thermal-subsidence sequence. The rift stage evolved from similar to 2765 Ma to similar to 2720 Ma, whereas the succession was folded, uplifted and eroded during development of a convergent continental margin from similar to 2680 Ma. Ocean opening was to the east or southeast. The Chitradurga Group records a two-stage back-arc basin behind an eastfacing continental arc. Stage I evolved between similar to 2609 Ma and similar to 2582 Ma, and Stage II between similar to 2582 Ma and similar to 2540 Ma. The two stages are separated by a subaerial unconformity. Stage I comprises siliciclastic fluvial, shallow-marine and deep-marine sedimentary rocks and bimodal volcanic rocks. Stage I is best preserved in the Western Dharwar Craton, but there are equivalents in the Eastern Dharwar Craton. Stage II in the Western Dharwar Craton comprises deep-marine turbidites of siliciclastic and volcaniclastic provenance, and basaltic and felsic volcanic rocks. Volcanic Stage II sequences in the Eastern Dharwar Craton define an arc-adjacent position. Tectonically driven cyclic uplift and erosion were responsible for the mismatch between preserved stratigraphic thickness and time, particularly for Stage II sequences. A remnant of a < 2540 Ma late-stage basin in the northeast of the Eastern Dharwar Craton defines a syncollisional tectonic setting. The Dharwar Supergroup was deformed in a SW-verging hinterland magmatic fold/thrust belt from similar to 2540 Ma.

The Altyn Tagh Fault (ATF) serves as a key continental‐scale controlling structural element of the Tibetan Plateau. However, its eastward extent remains controversial. Here we use high‐resolution seismic reflection profiles to investigate the subsurface structures of the easternmost ATF and use these to delimit the easternmost extent of the fault. The structural analyses show an eastward geometric change from transpressional positive flower structures to compressional thrusts, with transpression‐induced shortening magnitudes decreasing eastwards from a maximum of ~5.3 km to being absent. Stratigraphic controls indicate that the deformation took place over the last ~<1.2 Ma. Our wider findings lead us to: (a) reject the suggestion that the ATF previously extended beyond the Kuantan Shan‐Hei Shan to link with the Alxa‐East Mongolia Fault; and (b) propose that the rigid block model used to describe the Tibetan Plateau crust is not consistent with the extent and structural details of the easternmost ATF.

海斗深渊是海洋中最深的区域,由水深范围在6000～11000 m范围内的深部海沟组成,以极端的物理化学条件为特征,其沉积物以深海黏土为主.基于目前关于马里亚纳海沟及其沉积物的研究进展,总结了海斗深渊的地貌、物理化学和水动力等方面的特征;归纳了海斗深渊沉积物的粒度特征、矿物组成和古生物特征;探讨了海斗深渊沉积物的物质来源及主要分析方法.海斗深渊沉积物的物质来源具有多源性,综合多种方法示踪是准确揭示其物质物源的关键.

桂东北中生代恭城盆地位于南岭成矿带西段,是研究华南印支期-燕山早期构造事件动力学过程中浅表地质响应的重要窗口.盆地内上二叠统乐平组被上三叠统-下侏罗统天堂组不整合覆盖,天堂组与下侏罗统大岭组、中侏罗统石梯组为整合接触.沉积相分析表明,乐平组为海陆交互相碎屑岩,天堂组底部砾岩、含砾粗砂岩代表盆地早期山前快速堆积的冲积扇相沉积,天堂组上部、大岭组和石梯组砾岩、砂岩和泥质岩则代表河流相沉积.碎屑锆石U-Pb年龄结果显示,乐平组和天堂组底部岩屑石英砂岩均以980 Ma和～2500 Ma锆石为主,暗示晚二叠世以及晚三叠世-早侏罗世早期盆地的碎屑物主要来自南部云开地区.然而天堂组上部、大岭组和石梯组长石岩屑砂岩则以1790～1875 Ma和2370～2490 Ma锆石为主,并伴随有燕山早期(189～174 Ma)锆石,指示早-中侏罗世时盆地的碎屑物主要来源于北东部武夷山-南岭地区,与古水流方向分析的结果一致.恭城盆地早-中侏罗世时沉积物源的变迁规律很好地记录了华南东南部从印支期挤压应力状态向燕山早期伸展拉张作用的转变以及区域构造机制的转换.

The petrogenesis and geodynamic setting of Late Carboniferous magmatism in Inner Mongolia, China, hold a key to understanding the final closure of the Paleo-Asian Ocean and formation of the Xing' an-Inner Mongolia Orogenic Belt ( XMOB) . This study carried out secondary ion mass spectrometer ( SIMS) zircon U-Pb geochronological, and bulk-rock geochemical and Sr-Nd-Hf isotopic analyses of gabbroic diorites sampled in the Xilinhot region with the aim of investigating its petrogenesis and unravelling the geodynamic setting of its emplacement. Cathodoluminescence ( CL) images show that the analyzed zircon grains are euhedral to subhedral in shape, with paint zoning or oscillatory zoning (Th/U = 0.3 similar to 2.5) . SIMS U-Pb zircon dating shows that Xilinhot gabbroic diorites were intruded at 316. 9 +/- 2. 2Ma, suggesting a Late Carboniferous magmatic event in the XMOB. The effects of crystal accumulation and crustal contamination on the whole-rock composition of the gabbroic rocks are insignificant, whereas fractional crystallization of olivine and clinopyroxene played an important role in magma differentiation. The source of the rocks display depleted signatures as evidenced by presence of low initial Sr-87/Sr-86 ratios (0. 7034 similar to 0. 7041) and MORB-mantle source-like positive epsilon(Nd) ( t) (+ 5.58 similar to 6.88) and epsilon(Hf) (t) values ( +12.07 similar to +13.44) , and they also have enriched features as characterized by enrichment of fluid-mobile elements ( Rb , U, Sr, Pb) , but depletion of fluid-immobile elements ( Nb, Ta). Such co-existence of depleted Sr-Nd-Hf isotopes and enriched trace element signatures suggests the enrichment of mantle source by water-rich fluids may occur during or shortly prior to the melting event, i. e. a recent metasomatic event. The gabbroic rocks are also characterized by relatively high SiO2 (51.7% similar to 53.2%) , Cr (138. 4 x 10(-6) similar to 757. 2 x 10(-6)) , Ni (50.4 x 10(-6 )similar to 141.1 x 10(-6)) and Zn/Fe ratios ( 10.8 similar to 11.5 ) , but relatively low Al2O3 (13.1% similar to 16.8%) contents, indicating that they derived from a mixed source composed of an orthopyroxene-rich pyroxenite vein-plus-peridotite source. A range of geological evidence indicates an intracontinental extensional origin for the Late Carboniferous abbroic intrusions in Xilinhot area, rather than a subduction setting . To g ether with the hi g h water contents ( up to 4. 41% ) of contemporaneous basalts, the geochemical and isotopic characteristics of the studied g abbroic rocks indicate that the Late Carboniferous magmatism in Xilinhot and adjacent areas was g enerated by partial meltin g of mantle sources hydrated by water-rich fluids released from subducted slabs stagnated in mantle transition zone. Therefore, we proposed a deep-Earth water cycling process to account for mantle hydration and subsequent Late Carboniferous magmatism in XMOB, supporting a geodynamic link between deep-Earth water cycling, and post-orogenic magmatism and lithospheric extension.

The Nanling Region in South China hosts numerous W-dominated polymetallic deposits that are related to Mesozoic granites. Although considerable amounts of age data have been obtained, the genetic relationship between granitic magmatism and W mineralization remains unclear. The Nanling Scientific Drilling (SP-NLSD-2) in the Pangushan W deposit has penetrated Upper Devonian sedimentary rocks (4.1-721.9 m), Sinian sedimentary rocks (721.9-1287.9 m) and Mesozoic granite (1287.9-2012.1 m). The drill hole clearly reveals a zonation including exocontact W-bearing quartz veins, alkali autometasomatic zone and primary K-feldspar granite. The K-feldspar granite at the depth of 1880 m, and rocks of potassium autometasomatic zone at 1414 m and greisenized zone at 1288 m have magmatic zircon grains with U-Pb ages of 164.8 +/- 1.4 Ma, 161.7 +/- 1.6 Ma, and 153.8 +/- 1.2 Ma, respectively. Molybdenite Re-Os ages of endocontact mineralization at the depths of 1302 m and 1291 m are 155.9 +/- 3.1 Ma and 155.0 +/- 2.3 Ma, respectively. Muscovite Ar-Ar ages of exocontact mineralization at the depths of 1050 and 885 m are 154.9 +/- 1.5 Ma and 154.0 +/- 3.0 Ma, respectively, and molybdenite Re-Os age of exocontact quartz-vein type mineralization at 860 m is 152.0 +/- 2.6 Ma. These new ages indicate that the granite emplacement, potassium autometasomatism, greisenization, and W mineralization occurred at similar to 164.8 Ma, similar to 161.7 Ma, similar to 153.8 Ma, and 155.9-152 Ma, respectively. The W mineralization was approximately 9-13 Myr younger than the hosting granite. The whole-rock and feldspar chemical compositions of-K-feldspar granite, potassium autometasomatic zone, greisenized zone, and feldspar-quartz veins indicate the sequence of metal transportation and concentration to form the zonation. The granite crystallized from high-K calcalkaline, metaluminous to peraluminous, highly differentiated magmas that were enriched in W and Bi. During crystallization, the magmas underwent potassium autometasomatism caused by post-magmatic fluids which were rich in K, Fe, W, and rare-earth elements (REE) but poor in Na and Ca, and formed the potassium autometasomatic zone. The evolved post-magmatic fluids became rich in K, Si, Ca, REE, and W but poor in Na and Fe and initiated greisenization to generate the greisenized zone, which almost exhausted Ca, REE, Na, and Fe of the fluids. The later crystallization of feldspar quartz veins exhausted K and caused the residual post-magmatic fluids to be rich in Si and W. The fluids formed W-bearing quartz veins with decreasing temperature and pressure. The main reason for W enrichment in the hydrothermal fluids was due to the successive crystallization of minerals rather than autometasomatism.

The Qinling Complex lies in the Qinling orogenic belt of Central China and holds the key to understanding the evolution of this feature. The Qinling Complex comprises a basement complex composed of amphibolite and ecologite, overlain by a supra-crustal succession that has been metamorphosed to the upper greenschist facies at approximately 516-509 Ma. The protoliths of the meta-sedimentary rocks are graywackes, which are divided into lower, middle and upper units. Detrital zircons from nine samples of the supra-crustal succession have ages ranging from 1182 to 1158 Ma for the lower unit, 957 to 955 Ma for the middle unit and 917 to 840 Ma for the upper unit. The lower unit is intruded by a ca. 960 Ma pluton. The bulk compositions of these mew-sedimentary rocks and their detrital zircon ages clearly indicate derivation from Meso- and Neo-proterozoic granites. Thus, we suggest that the sedimentary succession was derived from an arc-related tectonic setting and that none of the detritus was sourced from the southern margin of the North China Block or from the northern and western margins of the South China Block. We conclude that the North Qinling Belt was an independent micro-continental block during the Meso- to Neo-proterozoic.

The Cuddapah Basin is one of many Proterozoic, intracontinental sedimentary basins across Peninsular India. The basin comprises several unconformity-bounded successions, the lowermost of which (the Papaghni Group and overlying Chitravati Group) are intruded by dolerite sills that contact metamorphosed their host rocks. A mafic-ultramafic sill from the base of the Tadpatri Formation in the Chitravati Group was previously dated at c. 1885 Ma, and interpreted to be part of a large igneous province (LIP). We have dated two samples of a felsic tuff from the upper part of the Tadpatri Formation at 1864 ± 13 Ma and 1858 ± 16 Ma; combining data from the two samples yields a weighted mean date of 1862 ± 9 Ma. Mafic sills intrude rocks stratigraphically above the tuffaceous beds, indicating that mafic magmatism continued until after c. 1860 Ma. Given that the sills intruded lithified rocks, some of the sills may be considerably younger than 1860 Ma. Mafic volcanic rocks are also known from below the unconformity at the base of the Chitravati Group, within the basal Papaghni Group (> c. 1890 Ma). Collectively, these data indicate that mafic sill emplacement spanned more than 30 myr so that it is likely to have been a protracted event or a series of events, and, therefore unlikely to represent a LIP. The time span for mafic magmatism is more compatible with episodic, lithospheric extension (passive rifting) during basin evolution than it is with a mantle plume (active rifting).

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 strati graphic 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. (C) 2017 Elsevier B.V. All rights reserved.

Banded iron formation (BIF) of the c. 3020 Ma Cleaverville Formation is correlated across the Pilbara Craton and is considered to be the first stratigraphic unit common to the West Pilbara Superterrane and the East Pilbara Terrane. New field mapping and geochronology from the Shay Gap and Goldsworthy belts on the northeastern margin of the East Pilbara Terrane test that correlation. Along that margin, the Farrel Quartzite at the base of the Gorge Creek Group nonconformably overlies granite and unconformably overlies metavolcanic rocks. The Farrel Quartzite is conformably overlain by what is interpreted to be Cleaverville Formation, which is divided into a lower BIF member, a middle mudstone member and an upper BIF member. We have dated a tuff from the middle mudstone member by the Sensitive High-Resolution Ion Microprobe (SHRIMP) U-Pb zircon method at 3104 16 Ma. The underlying Farrel Quartzite has a maximum depositional age of 3295 5 Ma and no zircon population at c. 3105 Ma. Therefore, the SHRIMP date for the tuff does not represent reworking of underlying sedimentary rocks and is interpreted to be a depositional age. This new date refutes correlation of the Cleaverville Formation across the craton, and it implies that BIFs should not be used as chronostratigraphic markers across Archean greenstone terrains. We suggest reinstating the name Nimingarra Iron Formation for BIFs that crop out along the northeastern margin of the Pilbara Craton, to distinguish them from the Cleaverville Formation. If the Cleaverville Formation, as defined in the West Pilbara Superterrane, is not the oldest stratigraphic unit common to the craton, then our understanding of the Mesoarchean evolution of the Pilbara Craton needs to be revised. (C) 2017 Elsevier B.V. All rights reserved.

Banded iron formations (BIFs) were deposited as deep-water fades distal to the late Archean Campbellrand carbonate platform, Transvaal Supergroup, South Africa. They are traditionally interpreted to have formed from iron oxides/hydroxides and silica that precipitated when upwelling hydrothermal water enriched in Fe2+ and silica mixed with cooler, shallow seawater enriched in dissolved oxygen. The ferric oxides/hydroxides were then converted to hematite or, in the presence of organic matter, reduced and incorporated into siderite. New high-resolution microscopy of BIFs from distal fades of the Campbellrand platform questions that interpretation, revealing the presence of abundant greenalite nanoparticles, interpreted to represent primary precipitates from ferruginous seawater, consistent with recent results from equivalent-aged BIFs of the Hamersley Group, Western Australia. The particles locally define primary sedimentary lamination, and are engulfed in diagenetic chert that preserves shrinkage structures, considered to have formed during dehydration and recrystallization of amorphous silica cement. The replacement of greenalite nanoparticles by coarser grained oxide, silicate and carbonate minerals, with destruction of primary textures and structures, indicates that iron-silicate muds were originally much more widespread. Based on our findings we propose a new model for the deposition of the BIFs, involving iron silicate precipitation from seawater followed by diagenetic silica cementation on the seafloor. We suggest that ferrous iron and silica were transported in hydrothermal plumes sourced from acidic vent fluids. Upon mixing with cooler, more alkaline seawater, the solubility of ferrous iron and silica fell to levels that favored rapid nucleation and the precipitation of iron-silicate nanoparticles over vast areas of the seafloor. The close association between iron and silica during the deposition of BIFs may be explained by the precipitation of iron-silicate nanoparticles and possible sorption of silica onto the surfaces of sinking nanoparticles. Furthermore, on the seafloor, iron-silicate nanoparticles presumably acted as nucleation sites for dissolved silica, promoting early diagenetic silica precipitation and cementation of the iron-rich muds. Our results indicate that iron silicates were important primary precipitates and suggest that changes in alkalinity rather than redox state played a key role in the precipitation of the precursor sediments of BIFs. (C) 2016 Elsevier B.V. All rights reserved.

The 2445–2010 Ma tectonic evolution of the southwestern Pilbara Craton is recorded by two depositional basins, but considering the time span involved it is pertinent to question whether only two are preserved and others have vanished. The first, the Turee Creek Basin, developed conformably on an ∼2450 Ma back-arc volcanic province, and was closed long before ∼2208 Ma. It was a retroarc basin sited in front of a magmatic fold-thrust belt on the southwestern margin of the craton. Its folded strata were intruded by ∼2208 Ma dolerite sills that are the preserved rock record of a large igneous province. The basin and dolerites were deformed by the N-verging ∼2195–2145 Ma Ophthalmia Fold-Thrust Belt. The second, the Horseshoe Basin, formed at ≤2050 Ma, unconformably truncating folded strata of the Turee Creek Basin and the ∼2208 Ma dolerites, and was closed prior to intrusion of ∼2008 Ma dolerite dykes. It was an intracontinental rift basin sited on the inverted fold-thrust belt. Detrital zircon age-spectra for the basins have poor fit to the zircon age-spectrum of the Pilbara, and differ significantly in their youngest modes. The youngest mode for the Turee Creek Basin is ∼2442 Ma, whereas the youngest mode for the Horseshoe Basin decreases upwards from ∼2276 Ma to ∼2206 Ma. Although differing in youngest detrital zircon age-modes, zircon age-spectra of the basins are otherwise similar, and broadly match the Glenburgh Terrane on the southwestern margin of the craton. While Turee Creek sediments were derived from the southwest, Horseshoe sediments were derived from the north and northeast. This conundrum is resolved by the Ophthalmia Fold-Thrust Belt, which tectonically loaded the craton to the north and northeast to form a now-vanished Ophthalmia foreland basin that derived sediment from the south and southwest, thereby emplacing zircon with an exotic age-spectrum on the North Pilbara. Inversion of tectonic elements occurred during formation of the Horseshoe Basin, with the fold-thrust belt subsiding beneath the rift while the foreland basin was uplifted. Recycling of the foreland basin inverted its detrital zircon age-spectrum, explaining why the youngest detrital zircon age-mode of the Horseshoe Basin decreases in age upwards.