Neoproterozoic Orogeny Research Articles

Gold mineralization related to rifting of the Rodinia surpercontinent: As gauged from the Dongyuan Au deposit, Jiangnan orogen, China

Abundant orogenic gold (Au) deposits, widely distributed in medium to low-grade metamorphic rocks, formed episodically since the Middle Archean. Orogenic Au mineralization waned during the Neoproterozoic era, although Neoproterozoic orogenies were prevalent. The Jiangnan Orogen, South China, as part of the sutures uniting the Rodinia (Meso- and Neoproterozoic) supercontinent, is situated between the Cathaysia and Yangtze blocks. Many orogenic Au deposits, such as the Wan’gu, Huangjindong, Dongyuan, and Jinshan Au deposits, are located in the northeastern section of the Jiangnan Orogen. The orebodies of the recently discovered Dongyuan deposit display a horizontal zonation, as follows: a peripheral quartz–chlorite–sulfide–calcite (ankerite, manganocalcite, and calcite) veinlets/veins and a central sulfide (mainly arsenopyrite) veinlets/veins. The former veinlets/veins also contain a small amount of albite, scheelite, TiO2 minerals, xenotime, and monazite. Compared with the other orogenic Au deposits, arsenopyrite from the Dongyuan Au deposit is characterized by enrichment of Sb–Co–Cd–Ag element assemblages. Based on the electron microprobe and Raman analyses, TiO2 mineral grains, including anatase, rutile, and anatase–rutile intergrowths, are present in the Au veins. In contrast with previous studies, TiO2 minerals (anatase and rutile) have a nearly consistent concentration range of each element detected, which taken together can be used for constraining fluid sources of ores. TiO2 minerals with enriched V–Fe assemblages, combined with initial 187Os/188Os ratio (0.64 ± 0.11) of arsenopyrite, reflect that the Dongyuan Au veins were probably precipitated from a metamorphic fluid. The Liyangdou biotite granodiorite and Donggang granite, located about one kilometer north and six kilometers south of the deposit, have LA-ICP-MS U–Pb zircon ages of 803 ± 3.4 Ma and 814 ± 3.4 Ma, respectively. The analysis of five arsenopyrite samples selected from the Dongyuan Au veins yields an isochron age of 744 ± 36 Ma (with an initial 187Os/188Os ratio of 0.64 ± 0.11 (2σ) and MSWD = 30). We found that the Dongyuan Au mineralization was later than the peripheral Neoproterozoic magmatic activities and metamorphic events of country rocks. Combined with previous studies, the Dongyuan deposit was formed in the tectonic setting of Rodinia supercontinent rifting, after the Neoproterozoic collision event in the Jiangnan Orogen, which likely triggered orogenic Au mineralization.

Sources, evolution and ages of A-type granites from the post-orogenic Itu batholith, SE Brazil: Inferences from zircon U–Pb dating, Lu–Hf isotope ratios and trace-element geochemistry

A combination of U–Pb dating by SHRIMP and Lu–Hf isotope and trace-element analyses by LA-ICPMS in zircon crystals from representative samples of the Itu Granitic Batholith, allowed to determine timing, sources and intensive parameters of crystallization (T, fO2) of the plutons that generated this large (>300 km2) occurrence of A-type granites that locally marks the end of the Neoproterozoic orogeny in SE Brazil. The main episode of batholith construction is dated at 578 ± 4 Ma, with possible minor manifestations as young as ∼560 Ma. Negative zircon εHf(t) as low as −19 to −17 in the Indaiatuba pluton requires a significant crustal input, but a component from enriched mantle (which has εHf(t) as low as −10, reflecting contamination from previous subduction) is evident in all plutons by the presence of small mafic bodies and frequent mafic microgranular enclaves showing evidence of mixing with the host granites. Distinct sources are implied by large contrasts in redox state, estimated qualitatively from negative Eu anomalies and quantitatively from Ce anomalies in zircon, with samples from the Itupeva and Salto plutons showing fO2 ∼FMQ+2 and a sample from the Cabreúva pluton closer to FMQ. Significant intra-sample variations of εHf(t) and trace-elements (e.g., Th, U) in zircon are also indicative that multiple sources have contributed to individual magma batches and were probably preserved by fast crystallization related to magma mixing processes.

Mid-Neoproterozoic tectonic switch from orogeny to intraplate extension in NW Tarim Craton: New evidence from a composite dike of the Aksu Group

It is widely acknowledged that the Tarim Craton plays a crucial role in the supercontinent Rodinia. However, the timing and regime of the Neoproterozoic orogeny, as well as the subsequent tectonic evolution along the northern margin of the Tarim Craton, remain contentious. Recent research has revealed a composite dike in the Aksu blueschist terrane located in the NW Tarim, which sheds new light on the pivotal Neoproterozoic tectonic transition. This dike comprises deformed granites and undeformed diabases, resulting from two-episode igneous events shortly after the orogenic metamorphism. The granites exhibit S-type affinities, with high silica, calcic-alkalic, and peraluminous compositions. Enriched isotopic signatures and diagnostic inherited zircons suggest that they derived from the metasedimentary rocks of the accretionary complex. Conversely, the following diabase dike displays tholeiitic affinity, right-sloping REE patterns, enriched LILEs, and a pronounced depletion of high-field-strength elements. Moderately enriched Sr-Nd isotopes and chondrite-akin Hf isotopes of these diabases imply that they were likely derived from partial melting of the metasomatized subcontinental lithospheric mantle. Zircon U-Pb chronological results reveal that the crystallization of these granites occurred at around 780 Ma. When combined with the maximum depositional age of protolith of the Aksu Group metapsammite obtained by detrital zircon dating, the metamorphic age of the Aksu blueschist terrane is limited to a short duration of 800–780 Ma, which is similar to the syn-orogenic metamorphism and crustal melting in the NE Tarim margin constrained to 830–790 Ma. Structural and petrological analysis suggests that the granites underwent deformation and dynamic recrystallization, while the diabases did not. This likely reflects the post-orogenic processes followed by the extrusion of mafic dike swarm associated with lithospheric stretching. The composite dike highlights a rapid tectonic shift from orogeny to intraplate extension during the mid-Neoproterozoic (780–760 Ma). Widespread late Neoproterozoic intraplate mafic and A-type granitic magmatism occurred in the Tarim and its adjacent blocks (Central Tianshan, Yili, and Kazakhstan) along the southwestern Central Asian Orogenic Belt, indicating that these blocks shared a similar geodynamic evolution related to the breakup of Rodinia.

Orogenic gold mineralization in the Huangling region and its intimate tectonic linkage to the Neoproterozoic orogeny of South China

Gold mineralization types were rarely exposed in the Neoproterozoic accretionary-to-collisional orogen, particularly in China, throughout Earth’s history. The Huangling region in South China contains more than 70 gold deposits/occurrences hosted in Archean-Paleoproterozoic metamorphic rocks and Neoproterozoic granitic complexes. However, the absolute age of hydrothermal mineralization, genesis, and their relationship with regional-scale processes, such as tectonism, magmatism, and metamorphism, remains unclear. Therefore, in this study, we investigated three gold deposits (Shuiyuesi, Hongwucun, and Guaizigou) hosted in different lithological units from the northern, central, and southern regions of Huangling, respectively. We conducted detailed fieldwork and analyzed the hydrothermal apatite and monazite geochronology and Sr-Nd isotopic composition of these deposits. The gold mineralization is mainly hosted within sulfide-quartz veinlets, and it is structurally controlled by second-order NW- or NNW-striking faults of the first-order NW trending main fault zone. Gold is present in various forms, such as native gold, electrum, and petzite or in fine-grained pyrite as invisible gold co-precipitated with alteration mineral assemblages that include sericite, quartz, and hydrothermal apatite, and monazite. LA-ICP-MS U-Pb dating of the hydrothermal monazite and apatite for the Shuiyuesi deposit yielded two ages: 831 ± 2 Ma and 830 ± 23 Ma. These ages are consistent with the weighted mean 206Pb/238U age of 834 ± 3 Ma for apatite, obtained from the southern Guaizigou deposit within margin of error. Monazite and apatite dating of the Hongwucun gold deposit yielded younger ages of 810 ± 3 Ma and 800 ± 10 Ma, respectively. The new dates suggest that the gold deposits in the Huangling region underwent two distinct metallogenic episodes of gold mineralization during the Neoproterozoic, coeval with the temporal post-collisional mafic dykes, which postdated the regional metamorphism by ∼100 m.y, as indicated in the Huangling region after the peak period of collisional orogeny and in response to an extensional setting, possibly due to asthenosphere wedging. The Sr-Nd isotope of apatite and monazite (87Sr/86Sr: 0.69555–0.76244, εNd(t): −22.1–−2.9) and collective geochemical data indicate that ore-forming fluids are mainly consistent with magmatic sources with significant contribution from mantle materials. The results of the study suggest that the Huangling gold mineralization province is genetically related to Neoproterozoic post-collisional magmatism. Additionally, the region shares many characteristics of large orogenic gold provinces around the world, including alteration types, element associations, occurrence states of gold, and the evolution of orogenic belts, offering valuable new insights into the gold metallogeny of the early Neoproterozoic period, which is generally not known for its abundance of Au deposits.

Geochemistry of onshore deposits from Rio del Rey sub-basin of the western Atlantic margin of Cameroon (Coastal basin, Southwest Cameroon): provenance and environments of sedimentation

The Rio del Rey sub-basin belonging to the Cretaceous–Cenozoic coastal basins of Cameroon is studied with geochemistry (major and trace elements) associated to mineralogy, palynology and petrography. One dominant facies (calcareous shales/siltstones/claystones) occurs in the Cretaceous series and two others (calcareous fine- to coarse-grained sandstones and calcareous claystones/shales in the Paleocene series. Ratios of LREE/HREE (9.27–24.23), Cr/Th (2.24–12.60), Th/Sc (0.54–6.10), Eu/Eu* (> 1 on PAAS normalized and ˂ 1 on Chondrite normalized), Al2O3/TiO2 (10.42–112.93) plotted in the Ce vs. La/Yb, Zr vs.TiO2 and La/Sc vs.Th/Co diagrams indicate that the sediments derivate from felsic rocks associated with subordinate intermediate composition to mafic igneous rocks. CIA (Chemical Index of Alteration, 61.69–92.76), PIA (Plagioclase to Index of Alteration; 62.16–99.47) and K2O/Na2O ratios (0.08–22.13) suggest that the source rocks have experienced low to high weathering (during the Paleocene), high chemical weathering (at the Campanian–Maastrichtian transition) and moderate to high chemical weathering (during the Cenomanian). The Zr/Sc vs. Th/Sc diagram of sample groups reveals that the Paleocene coarse-grained sediments have higher zircon content. Al/Si ratios, low in the coarse-grained (0.04–0.06) and high in the fine-grained (0.2–0.58) sediments, behavior of Al/Si vs. CIA and some elemental concentrations, such as Zr, Hf, Ca, K, and Na, suggest that the geochemical composition is controlled by grain sizes. The petrographic and X-ray diffraction results point early to mesodiagenesis effects and an important role of sea level change on the environments of sedimentation. These latter vary from marginal to shallow marine during the Cretaceous and fluctuated between shallow marine/lagoonal and brackish/littoral settings during the Paleocene according to facies analysis and palynology, with marine species such as Dinopterygium cladoides and continental species such as Classopollis sp. The SiO2 vs. Al2O3 + K2O + Na2O plot suggests that a predominant semi-arid to arid climate with periodically semi-humid periods was the rule during the Paleocene, The Arc-Rift-Collision, with two sets of high and low-silica rocks and SiO2 vs. K2O/Na2O diagrams, indicates a Collisional or Active Continental Margin tectonic as also recorded in the Cretaceous and Paleocene deposits in the Douala coastal sub-basin and in the Cretaceous Campo coastal sub-basin in Cameroon. These tectonic events could reflect the Precambrian basement history linked to the Neoproterozoic orogeny. The geological history of the Rio del Rey sub-basin is similar to those of Nigerian and Brazilian East costal basins, with local variations of the sea level changes on both sides of the Atlantic Ocean and the sediments distribution which is related to the source rock lithology.

Insights into sedimentary provenance and the evolution of the Potiguar Basin, NE Brazil, using U–Pb ages and Lu–Hf isotopes in detrital zircons

U–Pb and Lu–Hf data obtained from detrital zircon of 21 samples from four wells were used to determine the source terrains of the Cretaceous sedimentary rocks of the Pendência, Pescada and Alagamar Formations (rift and post-rift sections) of Potiguar Basin, northeast Brazil. More than 1500 U–Pb concordant ages allowed the determination of the main age peaks in Paleoproterozoic (ca. 2.2–2.0 Ga and 1.9–1.7 Ga) and Neoproterozoic (ca. 0.62–0.55 Ga), matching the ages of rocks from the basement adjacent to the basin (northern portion of Borborema Province). εHf values obtained from 61 zircon grains range from −0.53 to −8.86 for Paleoproterozoic and from 7.67 to −25.43 for Neoproterozoic zircons, consistent with published data from rocks of the adjacent basement. Neoproterozoic zircons shows εHf values more negative from bottom to top, and presents a trend in U–Pb age vs εHf where the older grains show juvenile signature and the younger, continental crustal signature. This trend mimics the evolution of granitoid generation in the basement adjacent to the Potiguar Basin during the Neoproterozoic orogeny. The age pattern varies vertically in most wells, reflecting the contribution of distinct source areas following the rift evolution. Furthermore, the age pattern in the wells located at southeast of the grabens and horsts system of the onshore Potiguar Basin show Paleoproterozoic zircons concentrated in a single peak age, few or no zircon grains of 1.8–1.6 Ga and lesser amount of 0.6–0.7 Ga zircons, in contrast with the wells located at northwest, with Paleoproterozoic ages distributed in more than one peak, significant presence of 1.8–1.6 Ga zircons and proportionally more 0.6–0.7 Ga zircon grains. It suggests that this system acted as a barrier to sediment transport, delimiting the basin in two sectors fed by two different sources, one being the northeast portion of Borborema Province and the other, the northwest portion, both in the rift and post-rift sections. Such differences can result in distinct quality for the potential reservoirs in these sectors and would be an important guide for hydrocarbon exploration in Potiguar basin.

Decratonization by rifting enables orogenic reworking and transcurrent dispersal of old terranes in NE Brazil

Dispersion and deformation of cratonic fragments within orogens require weakening of the craton margins in a process of decratonization. The orogenic Borborema Province, in NE Brazil, is one of several Brasiliano/Pan-African late Neoproterozoic orogens that led to the amalgamation of Gondwana. A common feature of these orogens is that a period of extension and opening of narrow oceans preceded inversion and collision. For the case of the Borborema Province, the São Francisco Craton was pulled away from its other half, the Benino-Nigerian Shield, during an intermittent extension event between 1.0–0.92 and 0.9–0.82 Ga. This was followed by inversion of an embryonic and confined oceanic basin at ca. 0.60 Ga and transpressional orogeny from ca. 0.59 Ga onwards. Here we investigate the boundary region between the north São Francisco Craton and the Borborema Province and demonstrate how cratonic blocks became physically involved in the orogeny. We combine these results with a wide compilation of U–Pb and Nd-isotopic model ages to show that the Borborema Province consists of up to 65% of strongly sheared ancient rocks affiliated with the São Francisco/Benino-Nigerian Craton, separated by major transcurrent shear zones, with only ≈ 15% addition of juvenile material during the Neoproterozoic orogeny. This evolution is repeated across a number of Brasiliano/Pan-African orogens, with significant local variations, and indicate that extension weakened cratonic regions in a process of decratonization that prepared them for involvement in the orogenies, that led to the amalgamation of Gondwana.

Unravelling depositional setting, age and provenance of the Simlipal volcano-sedimentary complex, Singhbhum craton: Evidence for Hadean crust and Mesoarchean marginal marine sedimentation

The Singhbhum craton of eastern India preserves an extensive record of basin formation spanning the Paleoarchean to Neoarchean. Although spatially extensive and well exposed, the absolute age, depositional environment, and regional correlations of many of the purportedly Archean basins of this craton remain poorly resolved. We present a detailed lithostratigraphic analysis of siliciclastic strata in the (lower) Simlipal volcano-sedimentary succession and report the first detrital zircon U-Pb ages from this succession. The studied section is dominated by fine- to medium-grained, quartz-rich sandstones, which preserve herringbone stratification, tidal bundles, soft sediment deformation structures along with ubiquitous trough cross-stratification. Petrographic study confirms these sandstones as quartz arenites and reveal their high textural and mineralogical maturity. These features are consistent with deposition of the lower siliciclastic succession of the Simlipal volcano-sedimentary complex within a tidally-influenced marginal marine setting. The new detrital zircon data support a ~3.08 Ga maximum depositional age for the succession and reveal a provenance with age peaks at ca. 3.55–3.45 Ga, 3.38–3.24 Ga, and 3.10–3.08 Ga. These ages likely correspond to local basement sources including the Older Metamorphic Tonalite Gneisses, the Singhbhum Granitoid Complex, and the Mayurbhanj Granite Suite. Two detrital zircons from our dataset have concordant ages of ~4.02 Ga and ~4.03 Ga. They represent the first Hadean detrital zircons recovered from any Archean strata in the Singhbhum craton, documenting the involvement of Hadean crust in the early development of the craton. The detrital zircons show prominent Pb-loss at ~1.2–1.0 Ga that exemplifies the tectonothermal imprint of a late Mesoproterozoic to early Neoproterozoic orogeny (likely related to the assembly of Rodinia) on the Singhbhum craton. Our findings further support the interpretation that the lower siliciclastic strata in the Simlipal succession are the lateral facies equivalents of alluvial fan deposits at the base of the Dhanjori Formation, exposed to the north.

Shortening history of the Neoproterozoic oroclinal bending in Paraguay belt, Central Brazil, based on structural interpretation of field work and high resolution aerogeophysical data

Different phases of the orogen's evolutionary history can be geometrically restored by identifying associated tectonic features in the thrust-and-fold belts in the foreland basin. The geometry and fold styles allow understanding the rate of crustal shortening of the Paraguay Belt Neoproterozoic oroclinal. We suggest that high resolution airborne geophysical data provides critical information to understand the tectonic history of Brasiliano fold belts. Geophysical studies integrated to structural analysis in field mapping may unveil the crustal architecture as well as the sequence of events of rocks exposed in two structural windows of the basement in the region of Planalto da Serra and Nova Xavantina, in the state of Mato Grosso, northern segment of the Paraguay Belt, Central Brazil.The evolutive history of rocks exposed southwards of the Amazonian craton margin represents extensional tectonics followed by the development of a passive margin. It is estimated that the original width of the depositional space was ~350 km during the formation of the hyperextended platform and, after the intense shortening during the Brasiliano orogenesis, the oroclinal was restricted to ~130 km wide, in the post-deformation phase. Planalto da Serra region is characterized by asymmetrical, harmonic folds with thickened hinge zones. They show variable styles between tight and isoclinal and form pairs of EW and NE anticlines and synclines. In Nova Xavantina structural window, the magnetic lineaments mark important lithospheric discontinuities represented by the Campinápolis (CAL) and General Carneiro (GCL) lineaments, which seem to be the deep basement faults that controlled the extension and where the rift axial zone developed. The Transbrasiliano Lineament (TBL) is a major shear zone that controls the secondary lineaments propagation, forming a network of folds and drag faults, with lateral escapes and vertical movement. Between the two main lineaments occurred the deposition of sediments and volcanic successions related to Nova Xavantina Metavolcanosedimentary Sequence representing a marginal ocean basin. The transition from EW trending features of the Paraguay Belt to NE trend Araguaia Belt lies within Nova Xavantina region and is marked by the direct influence of TBL. TBL is evident in the magnetic images, forming a mosaic of different crustal blocks and corresponding to various curvilinear shear zones with unidirectional trend N30-45E. It is composed of mega-sigmoids interlaced with mainly dextral kinematics, within shallow and deep levels.During the Neoproterozoic orogeny, a foreland basin system was formed in response to the flexural subsidence due to the tectonic inversion of the basin. Several depocenters were formed and served as accumulation sites for the deposition of sediments of the Alto Paraguay Group (Raizama, Sepotuba and Diamantino formations). Gravimetric data allowed individualization of the foreland basin system, which is characterized by four discrete depozones (back-bulge, forebulge, foredeep and wedge-top), between the Amazonian Craton and the inner structural zone.

Geophysical evidences for large-scale mullion-type structures at the mantle–crust interface in southern Madagascar: implications for Neoproterozoic orogeny

This study uses gravimetric data integrated with recent seismic data published on south Madagascar to investigate geometry of crust–mantle interface. The regional tectonic framework of Madagascar is characterised by anastomosing network of up to 15-km-wide, 600-km-long and north-oriented high-strain zones, which originated during Neoproterozoic convergence. The studied Bouguer anomalies obtained from the International Gravimetric Bureau were high-pass filtered to emphasise short-wavelength gravimetric variations (shorter than 200 km). The Pan-African high-strain zones coincide with the positive gravimetric anomalies suggesting a link with deep seated high-density material. Considering the present-day thickness of the crust (35 km) and its seismic velocity record, the gravimetric anomalies can be visualised as narrow vertical tabular bodies located at the base of the Moho. Modelling further confirmed that such narrow vertical bodies could be stable over geologic time scale since these structures are relatively small (10 to 30 km wide). The vertical tabular bodies possibly reflect material transfer such as vertical motion of sub-crustal weak and possibly partially molten mantle along vertical deformation zones. It is proposed that these structures were initiated by folding of weak mantle–crust interface characterised by low-viscosity contrast between weak mantle and stronger granulitized lower crust during bulk pure shear-dominated horizontal shortening. It is proposed that the cuspate-lobate “mullion-type” geometry mimics rheological inversions of mafic and felsic rocks and shape of folds of variable scale observed in southern Madagascar. The formation of such mega-mullion structures is possibly an expression of “creme brulee” rheological model, where the deformation of the lithosphere is governed by stronger granulitic lower crust and weaker partially molten and/or hydrated mantle.

Multi-chronometer thermochronological modelling of the Late Neoproterozoic to recent t-T-evolution of the SE coastal region of Brazil

South-eastern Brazil is as an important geological archive for understanding and reconstructing various plate tectonic stages of the Wilson Cycle. In the Neoproterozoic, the area of the today's South Atlantic passive continental margin (SAPCM: e.g. between São Paulo and Laguna) of south-eastern Brazil underwent subduction, followed by the collision of the contemporary plates of South America and Africa creating a Neoproterozoic orogeny within the supercontinent Gondwana. During the Palaeozoic and Lower Mesozoic (stage 1), the future SAPCM, as an intracratonic area, experienced erosion, denudation of the Neoproterozoic mobile belts (Pan African/Brasiliano orogeny), and large basin formation (Paraná Basin) (stage 2). Possibly plume-driven pre-to syn-rift (embryonic), ocean spreading (juvenile), and post-break up (mature) processes led to the recent evolution of the SAPCM since the Upper Mesozoic (stage 3).For the first time, this research aims to reconstruct the syn-to post-orogenic t-T-evolution of Neoproterozoic basement rocks of the SE coastal region of Brazil covering the entire geological evolution since the Late Neoproterozoic. Therefore, this study uses geochronological and thermochronological data combined with numerical modelling. This includes published geochronological data of Neoproterozoic basement samples such as U-Pb, Sm-Nd and Rb-Sr analyses, and low temperature thermochronology (LTT) data revealed by K/Ar, 40Ar/39Ar analyses. To this existing LTT data set, we report new apatite (AFT) and zircon (ZFT) fission-track, and (U-Th-Sm)/He (AHe, ZHe) data. Numerical modelling of that LTT data attached to the existing geochronological data indicates the following evolution:- Stage 1: In the central part of the future SAPCM, the Pan African/Brasiliano post-orogenic cooling and exhumation (uplift and erosion of Neoproterozoic rocks to the surface) history occurs in three phases: (i) rapid Late Neoproterozoic exhumation, (ii) a period of relative thermal stability (temperatures of about 200–300 °C) in which rocks reside at upper crust levels during the Early Cambrian to Devonian, and (iii) a second rapid exhumation phase moving the Neoproterozoic basement rocks to the surface during the Devonian. The northern and southern parts indicate a distinct post-orogenic exhumation suggesting faster cooling and exhumation from the Late Neoproterozoic to Devonian/Carboniferous than in the central section.- Stage 2: A phase of subsidence leading to the formation of the Paraná Basin followed by pre-to syn-rift processes and the emplacement of the Paraná-Etendeka flood basalts.- Stage 3: Post-South Atlantic break up processes, such as erosion and exhumation.

Transformation from Neoproterozoic Sinistral to Early Paleozoic Dextral Shearing for the Jingdezhen Ductile Shear Zone in the Jiangnan Orogen, South China

The Jingdezhen ductile shear zone is evolved from the Neoproterozoic Zhangyuan ophiolite melange belt in the eastern Jiangnan Orogen, South China. Comprehensive study of geometry, kinematics, quartz c-axis fabric, temperature-pressure conditions and geochronology were conducted in this study. The Jingdezhen shear zone extends ∼180 km along the NE orientation with two groups of subvertical foliation and subhorizontal lineation. One group of foliation strikes NEN orientation whereas another one NEE orientation. Field investigation, microscopic observation and quartz c-axis fabric show that sinistral shearing along NEN-striking foliation occurred earlier than dextral shearing along NEE-striking foliation. Syn-tectonic staurolite porphyroblasts and deformation manner of feldspar imply that sinistral shearing occurred at 530–420 oC and 6–2 kbar. Deformation manner and c-axis fabric of quartz and pre-tectonic staurolite porphyroblasts indicate that dextral shearing took place at 420–300 oC. LA-ICP-MS zircon U-Pb and mica 40Ar/39Ar dating indicate that the sinistral shearing occurred during Neoproterozoic orogeny (830–800 Ma) whereas the dextral shearing at 447±12 Ma. The sinistral shearing resulted from the Neoproterozoic final assembly between the Yangtze and Cathaysia blocks. The dextral shearing was caused by Early Paleozoic orogen parallel extension and clockwise rotation.

The White Nile as a source for Nile sediments: Assessment using U-Pb geochronology of detrital rutile and monazite

Basement terranes exposed at the headwaters of the White Nile include Archean-Paleoproterozoic rocks of the Congo Craton, whose northern sectors were severely reworked during Neoproterozoic orogeny. New U-Pb analyses of detrital rutile and monazite from early Quaternary to Recent coastal quartz sands of Israel, at the northeast extension of the Nile sedimentary system, yield mostly late Neoproterozoic ages, with a dominant peak at ca. 600 Ma. While derivation from the reworked sectors of the Craton cannot be negated, the absence of pre-Neoproterozoic rutile and monazite indicates that the detrital contribution from the Congo cratonic nuclei into the main Nile was insignificant.The near absence of White Nile basement-derived heavy minerals from the Nile sands arriving at the Eastern Mediterranean may be explained by a number of factors such as relatively minor erosion of the Cratonic basement nuclei during the Quaternary, late connection of the White Nile to the main Nile system with a possibility that northern segments connected prior to more southerly ones, and a long-term effective sediment blockage mechanism at the mouth of White Nile. Likewise, our previous study demonstrated that Nile sands display a detrital zircon U-Pb-Hf pattern consistent with significant recycling of NE African Paleozoic sediments. It is thus plausible that any detrital contribution from White Nile basement rocks was thoroughly diluted by eroded Paleozoic sediments, or their recycled products, which were likely the greatest sand reservoir in the region.This study adds to previous studies showing the advantage of a multi mineral U-Pb geochronology strategy in constraining sediment provenance patterns.

The Proterozoic Choma-Kalomo Block, SE Zambia: Exotic terrane or a reworked segment of the Zimbabwe Craton?

The Choma-Kalomo Block in south-eastern Zambia was hitherto considered as solely Mesoproterozoic in age based on granitoids which were previously dated at 1.37 and 1.18Ga respectively. The Choma-Kalomo Block was therefore thought to constitute an exotic terrane with respect to the neighbouring Palaeoproterozoic Magondi Belt and Archaean Zimbabwe Craton. This study of the Choma-Kalomo Block presents new U-Pb SIMS age data for zircons collected from previously undated metasedimentary rocks, revealing an abundant Palaeoproterozoic component (2040–1861Ma). Palaeoproterozoic (2040±5Ma) xenocrystic zircons in a Mesoproterozoic (1370±3Ma) leuconorite point to reworking of older crustal material, and suggest that the Choma-Kalomo Block is not a juvenile Mesoproterozoic terrane. Our U-Pb age data on columbite-tantalite fragments from tin-bearing pegmatites in both the Choma-Kalomo Block and the Dete-Kamativi Inlier (which is part of the Magondi Belt) indicates that Sn-(Ta-Nb-W-Li-Be) mineralisation within the two terranes occurred c. 1030 to 920Ma. New 40Ar-39Ar dating, confirms previous data, and indicates that a thermal event affected the region between 1020 and 980Ma. The similarities between the Choma-Kalomo Block and the Dete-Kamativi Inlier imply that these two terranes have a common history, at least as far back as the Palaeoproterozoic, but were certainly juxtaposed by the late Mesoproterozoic era. A large difference in lithospheric thickness between the Choma-Kalomo Block and the adjacent Zimbabwe Craton could explain the different rheological behaviour of the Choma-Kalomo and Dete-Kamativi areas, with the former being strongly deformed during the Neoproterozoic (Pan-African) orogeny. Our data indicate that the Choma-Kalomo Block is not an exotic terrane, rather it may represent a reworked portion of the Zimbabwe Craton, however what is unclear is whether the subcontinental lithosphere has been thinned, or the Choma-Kalomo Block represents a terrane with an originally thinner lithosphere.

Gold-bearing volcanogenic massive sulfides and orogenic-gold deposits in the Nubian Shield

The Nubian Shield is a large region of juvenile Neoproterozoic rocks that, together with its counterpart in the Arabian Shield, is part of a major accretionary orogen. It originated as late Tonian-Cryogenian island arcs on the site of the Mozambique Ocean formed by breakup of Rodinia. Arc collisions, subsequent magmatism, volcanism, sedimentation, and orogeny, associated with Cryogenian-Ediacaran convergence of cratonic blocks during the assembly of Gondwana, converted the region into the East African Orogen. The Nubian Shield region also has important Paleozoic-Neogene strata, including significant flood basalt, that conceal large areas of the basement. The Shield contains hundreds of gold occurrences and evidence of a 5,500-year history of gold mining. The main deposit types are orogenic gold and gold associated with volcanogenic massive sulfides (VMS). The juvenile subduction-related origin of the Shield rocks and the pervasiveness of shearing and greenschist-to-amphibolite facies metamorphism associated with late Neoproterozoic orogeny are geologic features highly favorable for the development of these types of deposits, and make the combined Arabian-Nubian Shield the Earth’s largest Neoproterozoic gold resource. Gold-bearing VMS deposits are currently mined at Bisha (Eritrea) and are soon to be mined at Hassai (Sudan). Orogenic gold is mined at Sukari and Hamash (Egypt), Qbgbih and Kamoeb (Sudan), Koka (Eritrea), and Lega Dembi and Sakaro (Ethiopia), and mining is due to start at Gupo (Eritrea) and Tulu Kapi (Ethiopia) in the near future. More than twenty companies are actively exploring for gold in the region and potentially important deposits are known in Egypt (Hamama-VMS), in northern Sudan (orogenic gold and VMS), along strike from Bisha and in the Asmara area, Eritrea (VMS and orogenic gold), in northern Ethiopia (VMS), and in western and southern Ethiopia (orogenic gold and sparse VMS).

Inferring a Neoproterozoic orogeny preceding the Rodinia break-up in the Sirohi Group, NW India

Abstract Recent studies indicate the Delhi Orogeny to be a Grenvillian-age collision event in the NW Indian Shield. West of the southern part of the South Delhi Fold Belt, aeromagnetic anomalies show a high-angle relationship with the Delhi Fold Belt trend. We examined an argillaceous–calcareous metamorphosed sequence exposed within and adjacent to this aeromagnetic anomaly. This sequence, deposited over a granitic basement, is reported as the Sirohi Group. The basement granite is dated to be 892±10 Ma (Erinpura age) and this was partially reset at 815±43 Ma. The metapelites preserve a low- to medium-grade metamorphic assemblage (peak temperature of c. 460°C) and the metamorphism took place at 822±29 Ma, which was partially reset at 723±65 Ma. The partial resetting can be ascribed to the Malani eruption. Control of accessory minerals on the garnet trace element chemistry is evident in the Y distribution of the two analysed garnets. It is contended that the Rodinia break-up, marked by Malani Igneous Suite, was preceded by an orogenic event (the Sirohi Orogeny) which marked the culminating mountain-building event in the cratonization of the NW Indian Shield.

Detrital zircon provenance of upper Cambrian-Permian strata and tectonic evolution of the Ellsworth Mountains, West Antarctica

Detrital zircons from the upper Cambrian-Devonian sandstones (Crashsite Group; n=485) and Carboniferous tillite (Whiteout Conglomerate; n=81) of the Ellsworth Mountains, Antarctica record a steady supply of Neoproterozoic (“Pan-African”) orogeny (~550–600Ma), Grenville (~1000Ma) and Neoarchean (~3000–3500Ma) zircons into the northern marginal basin of Gondwana. The overlying Permian Glossopteris-bearing Polarstar Formation shales (n=85) have the same zircon provenance as underlying units but also include a dominance of depositional-age (263Ma) euhedral zircons which are interpreted to be of local, volcanic arc origin. Modeling of detrital zircon provenance suggests that source areas were present in Pan-African and Laurentian crust throughout the Paleozoic. We also report calcite twinning strain results (12 strain analyses; n=398 twins) for the Cambrian Minaret Fm. in the Heritage range which is predominantly a layer-parallel shortening strain in the direction (WSW-ENE) of Permian Gondwanide orogen thrust transport. There is a secondary, sub-vertical twinning strain overprint. The initiation of localized lower-middle Cambrian rifting (Heritage Group deposition) in Grenville-aged crust as Gondwana amalgamated and the subsequent Jurassic counterclockwise rotation of the Ellsworth-Whitmore terrane out of the Permian Gondwanide belt into central Antarctica each remain tectonic curiosities.

Neoproterozoic collisional S-type granitoids of the Yenisei Ridge: petrogeochemical composition and U-Pb, Ar-Ar, and Sm-Nd isotope data

Collisional granitoid magmatism caused by the Early Neoproterozoic orogeny in the west of the Siberian craton is considered. New data on the petrogeochemical composition, U-Pb (SHRIMP II), Ar-Ar, and Sm-Nd isotopic ages of the Middle Tyrada granitoid massif in the northwestern Yenisei Ridge are presented. Plagiogranites, granodiorites, and quartz diorites of the massif are of calcareous and calc-alkalic composition. The elevated alumina contents and presence of accessory garnet permit them to be assigned to S-type granitoids. Their spidergrams show Rb, Ba, and Th enrichment, minimum Nb, P, and Ti contents, and no Sr depletion. The granitoids formed through the melting of plagioclase-enriched graywacke source, obviously Paleoproterozoic metaterrigenous rocks of the Garevka Formation and Teya Group (TNd(DM) = 2.0-2.5 Ga), judging from the isotope composition of the granitoids (TNd(DM-2st) = 2200 Ma and 8Nd(T) = −6.0) and the presence of ancient zircon cores (1.80-1.85 Ga). Formation of granitoids took place in the final epoch of the Grenville collision events in the late Early Neoproterozoic (U-Pb zircon age is 857.0 ± 9.5 Ma). In the Late Neoproterozoic, the granitoids underwent tectonothermal reworking caused by Vendian accretion and collision events on the southwestern margin of the Siberian craton, which explain the younger K-Ar biotite age, 615.5 ± 6.3 Ma.

Thermal conditions during deformation of partially molten crust from TitaniQ geothermometry: rheological implications for the anatectic domain of the Araçuaí belt, eastern Brazil

Abstract. During the Neoproterozoic orogeny, the middle crust of the Araçuaí belt underwent widespread partial melting. At the regional scale, this anatectic domain is characterized by a progressive rotation of the flow direction from south to north, suggesting a 3-D deformation of the anatectic middle crust. To better determine whether melt volumes present in the anatectic middle crust of the Araçuaí orogen were large enough to allow a combination of gravity-driven and convergence-driven deformation, we used the titanium-in-quartz (TitaniQ) geothermometer to estimate the crystallization temperatures of quartz grains in the anatectic rocks. When possible, we compared these estimates with thermobarometric estimates from traditional exchange geothermobarometers applied to neighboring migmatitic kinzigites. TitaniQ temperatures range from 750 to 900 °C, suggesting that quartz starts crystallizing at minimum temperatures of ≥ 800 °C. These results, combined with the bulk-rock chemical composition of diatexites, allows the estimation of a minimum of ~ 30% melt and a corresponding viscosity of ~ 109–1010 Pa s. Such a minimum melt content and low viscosity are in agreement with interconnected melt networks observed in the field. Considering that these characteristics are homogeneous over a wide area, this supports the finding that the strength of the middle crust was severely weakened by extensive partial melting, making it prone to gravity-driven flow and lateral extrusion.

Neoproterozoic to Early Paleozoic polyorogenic deformation in the southeastern margin of the Yangtze Block: Constraints from structural analysis and 40Ar/39Ar geochronology

The southeastern margin of the Yangtze Block is a suitable region to decipher Neoproterozoic to Early Paleozoic polyorogenic deformation of the South China Block. Based on 1:50,000-scale geological mapping, four deformational phases were identified through structural analysis and 40Ar/39Ar dating. The earliest event (D1) corresponds to nearly E–W-striking folding and top-to-the south thrusting, developed during Neoproterozoic orogeny caused by the collision between the Yangtze Block and the Cathaysia Block. The D2 event is characterized by the nearly E–W-striking top-to-the north thrusting. The D3 deformation is marked by the NNE-striking folding, thrusting and dextral shearing. The D3 structures constitute a positive flower pattern, with opposing kinematics, rooted in the Jiangwan dextral shear zone. The D4 event is the nearly E–W-striking ductile dextral shearing. 40Ar/39Ar geochronology shows that the NNE-trending dextral shearing and the nearly E–W-striking dextral shearing occurred at 449±4Ma and 429±3Ma, respectively. Combining with previous geochronology, all the D2, D3, D4 events are related to the Early Paleozoic orogeny. Both the D2 top-to-the north thrusts and D3 NNE-striking positive flower structures are syn-orogenic products. These incompatible syn-orogenic structures indicate that the orientation of the principal stress changed from the N–S-striking to E–W-striking at ∼450Ma. The nearly E–W-striking ductile dextral shearing (D4) is the outcome of post-orogeny.