Widespread Granitic Magmatism Research Articles

Late Jurassic Intracontinental Extension and Related Mineralisation in Southwestern Fujian Province of SE China: Insights from Deformation and Syn-Tectonic Granites

Late Mesozoic igneous intrusions and extensional structures in Carboniferous to Permian sequences in the SW Fujian region acted as important controls on the localisation of Fe-polymetallic deposits. Here we document the identification of extensional deformation at shallow crustal levels and syn-tectonic granites related to normal faults. Based on spatial distribution and structural features, the extensional deformation can be divided into cover-only and basement-intersecting styles. A series of syn-tectonic plutons were emplaced into the footwall of normal faults. Representative samples of the Tangquan Granite have high SiO2 (66.4 wt.%-73.9 wt.%) assays and Mg# values (37-59). The samples also have relatively homogenous initial 87Sr/86Sr (0.708 3-0.708 9) and eNd (-9.2--10.2) values. Geochemical and isotopic evidences indicate that the Tangquan granite originates from a hybrid source including lower crustal-derived felsic and lithospheric mantle-derived mafic magmas. Zircon U-Pb dating indicates that the granodiorite phase from the pluton crystallised at 161±4 Ma and the monzogranite phase crystallised at 159±1 Ma. Combined with the granitic rocks in a wider region of SE China, the widespread granitic magmatism and polymetallic mineralisation have been synchronous during the Late Mesozoic, probably resulting from extensional tectonics related to the lithospheric thinning.

U–Pb geochronology and Lu–Hf zircon isotopy of the Santinho Granitic Association: A remnant of the early magmatic stages of the Florianópolis Batholith, Santa Catarina, Brazil

One of the main characteristics of the orogenic systems formed during the assembly of southwestern Gondwana in the Late Neoproterozoic is the widespread granitic magmatism. The Florianópolis Batholith in South Brazil is an excellent example of this process, as it is part of a ca. 1400 km long intrusive association that is a key unit in the reconstruction of the paleogeography of Gondwana on both sides of the Atlantic. The Santinho Granitic Association in the Island of Santa Catarina is an exceptionally well-exposed section exhibiting a complex lithological variety that includes orthogneisses intruded by multiple generations of leucogranite injections and associated with mafic magmatic enclaves. We present a detailed geochronological study of this unit based on field and petrographic characterizations, which includes U–Pb LA-ICP-MS geochronology of zircon, titanite and monazite, as well as Lu–Hf isotopy in zircon. Single-spot ages in individual hand samples are widespread and determine a magmatic process that mostly extends between ca. 640 and 600 Ma, with average crystallization ages between 625 and 605 Ma that are in accordance with field relationships. Overlapping ages support the magmatic coexistence of different magma batches with contrasting compositions that reflect heterogeneous source rocks with a predominance of old continental crust, as indicated by negative εHf values (−1.08 to −23.18) and Hf TDM model ages between 2.95 and 1.57 Ga. The strong crustal affinity of the Hf signatures of mafic enclaves suggests a complex petrogenesis associated with the recycling of older magmatic phases, instead of representing a direct mixing of coeval mantellic magmatism. The new geochronological data, together with the complex magmatic and deformational history recorded in the association, suggest that it represents the early stages of granitic magmatism in the Florianópolis Batholith in a pre-to syn-collisional setting, preserved in the surrounding main intrusions as a mega-xenolith.

Neoarchean structural evolution of the Murchison Domain (Yilgarn Craton)

The progressive strengthening of the continental lithosphere triggered a secular transition in tectonic style during Neoarchean times, allowing the progressive establishment of Plate Tectonics on our planet. Structural investigations in Neoarchean cratons offer therefore a critical tool to constrain how such transition took place. The highly-mineralized Yilgarn Craton of Western Australia exposes one of the largest and best preserved portions of Archean continental crust worldwide. The Yilgarn crust was intensely deformed during the c. 2730–2650 Ma Neoarchean Yilgarn Orogeny, which was accompanied by widespread granitic magmatism, and was mostly unaffected by post-Archean pervasive tectonic events, representing therefore an ideal area for the study of Neoarchean tectono-magmatic events. Here, I combine new structural data with a re-examination of the recent regional structural literature, to offer an updated view of the structural evolution of the Murchison Domain, one of the best-exposed and mineralized portions of the Yilgarn Craton. The result is a new fourfold scheme for the structural evolution of the domain, supported by a detailed and structurally-controlled geochronological dataset. The preserved tectono-magmatic evolution of the domain started with a pre-orogenic period of dominant polydiapirism, during times of prevailing tectonic quiescence. This was followed by a sequence of orogenic deformation events that produced north-striking large-scale shear zones, along which syntectonic plutons, up to 100 km in size, were emplaced during three major tectonic pulses characterized by bulk east–west shortening, between 2730 and 2660 Ma. The deformation events identified here at the scale of the Murchison Domain are likely the local expression of Yilgarn-wide tectono-magmatic events, highlighting the importance of syntectonic granitic magmatism in shaping Neoarchean orogens.

Metamorphic and metasomatic evolution of the Western Domain of the Karagwe-Ankole Belt (Central Africa)

The tectonometamorphic evolution of the Western Domain of the Karagwe-Ankole Belt, containing widespread granite-related W–Nb–Ta–Sn mineralization in pegmatites and hydrothermal quartz veins of Early Neoproterozoic age, is largely unknown. This study aims to characterize the Meso- and Neoproterozoic metamorphism and metasomatism in the Karagwe-Ankole Belt, to reconstruct the temperature evolution and to investigate its temporal relation to deformation and the widespread granite magmatism and mineralization. A quantitative geothermometric study was conducted on metasiltstones and amphibolites, and applies thin section petrography, garnet–biotite and chlorite geothermometry on samples collected in the representative Kibuye-Gitarama-Gatumba area in West Rwanda. The presence of garnet, staurolite and kyanite in metasiltstones, and hornblende and andesine-labradorite feldspar in amphibolites indicates prograde Barrovian metamorphism up to syn-to post-deformational (D1 or D2) lower amphibolite facies (up to 630 °C). This peak metamorphism was followed by post-D2 greenschist facies metamorphism (c. 525 °C–440 °C; garnet, biotite, chlorite, muscovite in metasiltstone), probably related to the East African Orogeny as part of the Gondwana assembly. A geothermometric evolution with high temperature conditions (>500 °C) at least from the flare-up of Early Neoproterozoic tin granites and their metasomatic haloes onwards for most of the Neoproterozoic is proposed, in close correspondence with the geodynamic evolution of the neighboring terranes. Additionally, this high temperature regime is an important factor to be taken into account when interpreting thermal diffusion-sensitive geochronological data.

40Ar/39Ar dating of basic–felsic dikes in the Sulu Orogen, Shandong Peninsula, China: Evidence for the destruction of the southeastern North China Craton

During the Early Cretaceous, the North China Craton (NCC) underwent dramatic lithospheric thinning and destruction, resulting in widespread granitic magmatism and lithospheric extension. The geochronology of basic–felsic dikes provides a unique perspective on a crustal‐extension event that was related to the NCC destruction. Previous studies usually used zircon U–Pb dating to constrain the time of dike emplacement. This method is limited in terms of dating basic dikes because the authigenic zircons are rare or absent. Additionally, recording later reheating events during multiple phases of extension that occurred in the NCC after the Mesozoic is impossible. Here, we present40Ar/39Ar geochronological data for basic–felsic dikes in the Sulu Orogen, Shandong Peninsula, East China. Our results indicate that these dikes were emplaced between ca. 127 and 95 Ma, with only two felsic samples recording ages <100 Ma, suggesting that crust‐derived magmatism decreased after this time. Several of these dikes that were adjacent to faults also recorded a later Cretaceous reheating event, which may have been related to fault movement and magmatic activity in the deeper crust. Combined with previous research results, Cretaceous dike emplacement was contemporaneous with crustal extension and widespread magmatic activity, slightly later than the peak time of the NCC destruction, suggesting an intrinsic connection between the dikes' emplacement and NCC destruction. The crustal magma and tectonic activity are direct evidence of the craton destruction, so these age data constrain the timing of destruction in the southeastern portion of the NCC to approximately 95 Ma.

Implications of the distribution, age and origins of the granites of the Mesoproterozoic Spektakel Suite for the timing of the Namaqua Orogeny in the Bushmanland Subprovince of the Namaqua-Natal Metamorphic Province, South Africa

The Spektakel Suite comprises voluminous late- to post-tectonic granitoids that intruded the pre-tectonic gneisses of the Bushmanland Subprovince (BSP) of the Mesoproterozoic Namaqua-Natal Metamorphic Province (NNMP). Based on new U-Pb zircon geochronology and geochemical data, we redefine the suite as consisting of 22 plutons of porphyritic monzogranite, granodiorite and charnockite that intruded the granulitic core of the BSP between 1097 and 1033 Ma. The new data show that some granites previously incorporated into the Spektakel Suite should be excluded: a) garnetiferous leucogranites (Concordia, Hangsfontein and Ibequas Granites) are excluded on petrological grounds and genetic considerations and b) the porphyritic Nuwefontein Granite (∼783 Ma) is younger and is now placed within the Richtersveld Suite. The Spektakel Suite has geochemical and isotopic compositions suggesting that it was derived from recycled Palaeoproterozoic crust with Mesoproterozoic mantle input. The main Namaqua Orogeny (D2) in the BSP comprises at least two phases of compressional tectonics at ∼1200 Ma and ∼1110 Ma separated by a period of extension. The new ages for the Spektakel Suite tightly constrain the end of D2 to between 1109 Ma, the age of the youngest pre-tectonic gneiss and 1097 Ma, the age of the oldest Spektakel Suite granite. Peak low-P, high-T metamorphism (∼1050–1020 Ma) occurred well after D2 and its close spatial and temporal relationship to the Spektakel Suite suggests this prolonged period of granite magmatism was responsible for the transfer of the heat into the BSP. Several other late- to post-tectonic megacrystic granitic suites intruded into other tectonic domains across the NNMP coevally with the Spektakel Suite, indicating widespread granite magmatism at this time, probably due to mafic under- and intra-plating in a back-arc setting as previously suggested.

Neoproterozoic metamorphic events along the eastern margin of the East Sahara Ghost Craton at Sabaloka and Bayuda, Sudan: Petrology and texturally controlled in-situ monazite dating

Recent geodynamic models for the evolution of the East Sahara Ghost Craton (ESGC) propose delamination of the subcontinental lithospheric mantle due to the formation of Pan-African orogenic belts along its margins. To identify the behavior of the craton's basement during the Neoproterozoic we studied metapelitic rocks from the eastern margin of the craton at Sabaloka and Bayuda, both of which lie about 230km apart along the boundary with the Arabian-Nubian Shield and are considered to be parts of the ESGC. The results are compared to those published for the central part of the craton at Uweinat for a better understanding of the Neoproterozoic tectonic evolution of the craton as a whole.Petrology and texturally controlled in-situ monazite dating reveals that the Sabaloka granulites and the Bayuda metasediments experienced two different metamorphic events. The events at Sabaloka and Bayuda are neither synchronous nor similar in intensity and/or nature, with the events in Bayuda being older than those in Sabaloka and also of lower intensity. At Sabaloka, monazite inclusions in garnet record the timing of an early Neoproterozoic high temperature crustal thickening event at 780–720Ma, while monazite grains in coarse-grained cordierite–spinel symplectites indicate the timing of a Neoproterozoic high to ultra-high temperature overprint at ∼602Ma. Applying the same approach of monazite dating to the pelitic schists from the Dam El Tor fold-and-thrust-belt in the Kurmut Terrane at Bayuda, a crustal thickening event leading to amphibolite-facies metamorphism is dated at ∼890Ma. It was followed by low-grade metamorphism at ∼670Ma leading to recrystallization of matrix minerals. This study thus indicates that the nature and timing of Neoproterozoic tectonometamorphic events along the eastern margin of the ESGC were heterogeneous, both temporally and in their intensity. The ∼890Ma age obtained from the Kurmut Terrane metasediment provides, for the first time, a direct age of the amphibolite-facies metamorphism, slightly later than the magmatism during the Bayudian event dated at 920–900Ma in the Rahaba-Absol Terrane. We infer that tectonism in the juvenile oceanic arc and ophiolitic terranes of the Arabian Nubian Shield (ANS) in the east triggered the end of the passive margin stage of the ESGC and led to the subduction related magmatic–metamorphic Bayudian event. The passive margin stage of the craton further south at Sabaloka seems to have ended later at around 780–720Ma, which may have caused the first high temperature crustal thickening event there. Published magmatic formation ages of 810–806Ma from basalts and ophiolites indicate a rifting stage that formed oceanic re-entrants in the Bayuda and Nubian desert areas along the margin of the craton, subsequent to the Bayudian event. After collision with some of the eastern juvenile ANS terranes the oceanic re-entrants were closed, causing magmatism and a low-grade metamorphic overprint on the amphibolite-facies rocks dated here at ∼670Ma. At Sabaloka, the high-T to UHT granulite-facies decompression event at ∼602Ma and the widespread granitic magmatism all along the eastern margin between 650 and 570Ma was most likely due to the final collision of the ESGC and the ANS. The heterogeneity of Neoproterozoic tectonometamorphic events along the eastern margin of the ESGC thus indicates a local tectonic control on these metamorphic events.In contrast to the eastern margin, no evidence for a metamorphic event during the Neoproterozoic has been found in the center of the craton at Uweinat. The granulites at Uweinat record a Neorchean UHT metamorphism and a Paleoproterozoic UHT reworking. Therefore, it is more likely that the proposed delamination of the subcontinental lithospheric mantle of the entire ESGC was not synchronous and was caused by different orogenic events in different parts of the craton.

Zircon U–Pb ages, major and trace elements, and Hf isotope characteristics of the Tiantangzhai granites in the North Dabie orogen, Central China: tectonic implications

AbstractCretaceous granites are widespread in the North Dabie orogen, Central China, but their emplacement sequence and mechanism are poorly known. The Tiantangzhai Complex in the North Dabie Complex is the largest Cretaceous granitic suite consisting of six individual intrusions. In this study, zircon U–Pb ages are used to constrain the crystallization and protolith ages of these intrusions. The Shigujian granite is a syn-tectonic intrusion with an age of 141 Ma. This granite was emplaced under a compressional regime. Oscillatory rims of zircons have yielded two peaks at 137±1 Ma and 125±1 Ma. The 137±1 Ma peak represents the beginning of orogenic extension and tectonic collapse, whereas the 125±1 Ma peak represents widespread granitic magmatism. Zircon cores have yielded concordant ages between 812 and 804 Ma, which indicate a crystallization age for the protolith. The Tiantangzhai granites show relatively high Sr contents and high La/Yb and Sr/Y ratios. The Shigujian granite has positive Eu anomalies resulting from partial melting of a plagioclase-rich source in an over-thickened crust. Correspondingly, in situ Lu–Hf analyses from zircons yield high negative εHf(t) values from −24.8 to −26.6, with two-stage Hf model ages from 2748±34 to 2864±40 Ma, suggesting that the magmas were dominantly derived from partial melting of middle to lower crustal rocks. The Dabie orogen underwent pervasive NW–SE extension at the beginning of the early Cretaceous associated with subduction of the Palaeo-Pacific plate beneath eastern China.

Reconciling the geological history of western Turkey with plate circuits and mantle tomography

We place the geological history since Cretaceous times in western Turkey in a context of convergence, subduction, collision and slab break-off. To this end, we compare the west Anatolian geological history with amounts of Africa–Europe convergence calculated from the Atlantic plate circuit, and the seismic tomography images of the west Anatolian mantle structure. Western Turkish geology reflects the convergence between the Sakarya continent (here treated as Eurasia) in the north and Africa in the south, with the Anatolide–Tauride Block (ATB) between two strands of the Neotethyan ocean. Convergence between the Sakarya and the ATB started at least ~ 95–90 Myr ago, marked by ages of metamorphic soles of ophiolites that form the highest structural unit below Sakarya. These are underlain by high-pressure, low-temperature metamorphic rocks of the Tavşanlı and Afyon zones, and the Ören Unit, which in turn are underlain by the Menderes Massif derived from the ATB. Underthrusting of the ATB below Sakarya was since ~ 50 Ma, associated with high-temperature metamorphism and widespread granitic magmatism. Thrusting in the Menderes Massif continued until 35 Ma, after which there is no record of accretion in western Turkey. Plate circuits show that since 90 Ma, ~ 1400 km of Africa–Europe convergence occurred, of which ~ 700 km since 50 Ma and ~ 450 km since 35 Ma. Seismic tomography shows that the African slab under western Turkey is decoupled from the African Plate. This detached slab is a single, coherent body, representing the lithosphere consumed since 90 Ma. There was no subduction re-initiation after slab break-off. ATB collision with Europe therefore did not immediately lead to slab break-off but instead to delamination of subducting lithospheric mantle from accreting ATB crust, while staying attached to the African Plate. This led to asthenospheric inflow below the ATB crust, high-temperature metamorphism and felsic magmatism. Slab break-off in western Turkey probably occurred ~ 15 Myr ago, after which overriding plate compression and rotation accommodated ongoing Africa–Europe convergence. Slab break-off was accommodated along a vertical NE trending subduction transform edge propagator (STEP) fault zone, accelerating southwestward slab retreat of the Aegean slab. The SE Aegean slab edge may have existed already since early Miocene times or before, but started to rapidly roll back along the southeastern Aegean STEP in middle Miocene times, penetrating the Aegean region in the Pliocene.

Late-stage hydrothermal alteration and heteromorphism of calc–alkaline lamprophyre dykes in Late Jurassic Granite, Southeast China

Three generations of calc–alkaline lamprophyre, occurring as patches or segregations in granite and as dyke swarms with a NNW–SSE trend, are associated with the Late Jurassic Shanqi–Xiaqi granite, SE China. They comprise coarse-grained, hornblende-dominated spessartite and two types of panidiomorphic kersantite: type-1 contains clinopyroxene and biotite phenocrysts, whereas type-2 is fine-grained and plagioclase-rich. The granite is characterised by large feldspar crystals and Al-rich annite. This rare occurrence of outcrops with no influence from atmospheric weathering allows the investigation of extensive alteration from hydrothermal interaction between lamprophyres and granite. At a depth of ca. 18 km, the breakdown of annite in the granite to magnetite+K-feldspar was the result of reheating above 670 °C at oxygen activities >10−17 bar. In the lamprophyres, a variety of reactions due to autometasomatism include: breakdown of Ti-rich pargasites to chlorite, epidote, titanite; olivine to talc, tremolite, saponite, beidellite and Fe–Cr spinels; biotite to chlorite and titanite; calcic plagioclase to orthoclase, albite, epidote, chlorite and beidellite. Late-stage magmatic hydrothermal fluids from granite and lamprophyres resulted in redistribution of F, Ba, Sr, and CO2 with the formation of calcite–fluorite veins. Amphibole-rich spessartite and biotite–diopside dominated kersantite exhibit heteromorphism in that they have similar geochemical characteristics but different mineralogies. The alkali-rich lamprophyric magmas are inferred to have been derived from melting in the mantle wedge during the subduction of the Kula Plate, and show typical backarc rift chemistry. Prior to intrusion of lamprophyre, underplating of large volumes of basaltic magma is thought to have enhanced partial melting in the overlying continental crust resulting in widespread granite magmatism in SE China.

Metallogenetic Mechanism and Timing of Late Superimposing Fluid Mineralization in the Dongguashan Diplogenetic Stratified Copper Deposit, Anhui Province

Abstract An important diplogenetic mineralization event superimposed on pre-existing exhalation sediments in the Tongling area, Anhui province, was triggered by widespread granitic magmatism along the northeastern margin of the Yangtze Block during 140–135 Ma under extensional tectonic circumstances following the collision between the North China and Yangtze blocks. The main orebodies of the Dongguashan copper deposit, a typical diplogenetic stratified deposit among many polymetallic ore deposits in China, are hosted by strata between Upper Devonian sandstone and Carboniferous limestone, and its mineralization was genetically related to the Qingshanjiao intrusive. The Rb-Sr isotopic isochron of the Qingshanjiao intrusive yields an age of about 136.5±1.4 Ma. The ore-forming fluid reflected by the inclusion fluid in quartz veins is characterized by high temperature and high salinity, and its age was also determined by Rb-Sr isotope dating as 134±11 Ma. Oxygen and hydrogen isotope composition data suggest that the ore-forming fluid was derived mainly from magmatism. By integrating these isotopic dating data, characteristics of fluid inclusions and the geology of the deposit, the mineralization of the Dongguashan copper deposit is divided into two stages. First, a stratiform sedimentary deposit or protore layer formed in the Late Devonian to the Early Carboniferous, while in the second stage the pre-existing protore was superimposed by hydrothermal fluid that was derived from the Yanshanian magmatic activities occurring around 135 Ma ago. This two-stage mineralization formed the Dongguashan statiform copper deposit. Associated “porphyry” mineralization found in the bottom of and in surrounding intrusive rocks of the orebodies might have occurred in the same period as a second-stage mineralization of this deposit.

Palaeoproterozoic crustal accretion and collision in the southern Capricorn Orogen: the Glenburgh Orogeny

The Capricorn Orogen in central Western Australia records the Palaeoproterozoic collision of the Archaean Pilbara and Yilgarn Cratons. Until recently only one orogenic event was thought to be the cause of this collision, the 1830–1780 Ma Capricorn Orogeny. However, recent work has uncovered an older event, the Glenburgh Orogeny that occurred between 2000 and 1960 Ma. The Glenburgh Orogeny reflects the collision of a late Archaean to Palaeoproterozoic microcontinent (the Glenburgh Terrane) with the Archaean Yilgarn Craton and is therefore tectonically distinct as well as significantly older than the widespread 1900–1800 Ma tectonothermal events recorded in northern Australia. The Glenburgh Terrane preserves a different history from either the Yilgarn or Pilbara Cratons. Granitic gneiss protoliths dated at ca. 2550 Ma were intruded by widespread granite magmatism dated at 2005–1970 Ma, accompanied by high-grade metamorphism and deformation throughout the terrane. At ca. 1960 Ma silicic granite of the Bertibubba Supersuite intruded the northern margin of the Yilgarn Craton along the Errabiddy Shear Zone, a crustal-scale shear zone that today marks the contact of the Glenburgh Terrane and Yilgarn Craton. At ca. 1950 Ma silicic dykes intruded the southernmost part of the Glenburgh Terrane, marking the end of the Glenburgh Orogeny. East of the Glenburgh Terrane the Glenburgh Orogeny resulted in the cessation of mafic volcanism in the Bryah Basin, and the basin’s eventual closure. Siliciclastic, carbonate and chemical sedimentary rocks were deposited in the Padbury Basin that formed a retro-arc foreland basin on top of the Bryah Basin, and probably records the later stages of the Glenburgh Orogeny collision.

Fluid Inclusion and Noble Gas Studies of the Dongping Gold Deposit, HebeiProvince, China: A Mantle Connection for Mineralization?

The Dongping gold deposit (>100 t Au) occurs about 200 km inboard of the northern margin of the North China craton. The deposit is mainly hosted by syenite of a middle Paleozoic alkalic intrusive complex that was emplaced into Late Archean basement rocks. Both groups of rocks are intruded by Late Jurassic to Early Cretaceous crustal-melt granite dikes and stocks, some within a few kilometers of the deposit. The gold ores were deposited during this latter magmatic period at about 150 Ma, a time that was characterized by widespread regional north-south compression that formed the east-west–trending Yanshan deformational belt. The ores include both the telluride mineral-bearing, low sulfide quartz veins and the highly K-feldspar–altered syenite, with most of the resource concentrated in two orebodies (1 and 70). Fluid inclusion microthermometry indicates heterogeneous trapping of low-salinity (e.g., 5–7 wt % NaCl equiv) fluids that varied from a few to 60 mole percent nonaqueous volatile species. Laser Raman spectroscopy confirms that the vapor phase in these inclusions is dominated by CO2 but may be comprised of as much as 9 mole percent H2S and 20 mole percent N2; methane concentrations in the vapor phase are consistently <1 mole percent. The variable phase ratios are consistent with fluid immiscibility during ore formation. Fluid inclusion trapping conditions are estimated to be 250° to 375°C and 0.6 to 1.0 kbar. Helium isotope studies of fluid inclusions in ore-stage pyrites indicate 3He/4He ratios of 2.1 to 5.2 Ra (Ra = 1.4 × 10–6 for air) for orebody 1 and 0.3 to 0.8 Ra for orebody 70. The former data suggest that at least 26 to 65 percent mantle helium occurs in the fluids that deposited the veins in orebody 1. The lower values for orebody 70, which is characterized by a more disseminated style of gold mineralization, are interpreted to reflect an increased interaction of ore fluids with surrounding crustal rocks, which may have contributed additional 4He to the fluids. A mantle source for at least some of the components of the gold-forming fluid is consistent with upwelling of hot asthenosphere and erosion of as much as 100 to 150 km of cool Archean lithosphere beneath the craton during this time. The Dongping deposit is located along the 100-km-wide north-south gravity lineament, which marks the western border of the thinned crust. As both regional metamorphism of Mesoproterozoic and younger cover rocks, and widespread granite magmatism, also occurred at ca. 150 Ma, it is unclear as to whether one or both of these also contributed fluid and/or metals to the hydrothermal system. Importantly, these new data suggest that economically significant gold deposits of similar mineral style and fluid composition, which are scattered along the margins of the craton, may all be products of a fluid originally partly sourced within the mantle.

Untying the Kibaran knot: A reassessment of Mesoproterozoic correlations in southern Africa based on SHRIMP U-Pb data from the Irumide belt

Research Article| June 01, 2003 Untying the Kibaran knot: A reassessment of Mesoproterozoic correlations in southern Africa based on SHRIMP U-Pb data from the Irumide belt Bert De Waele; Bert De Waele 1Tectonics Special Research Centre, Department of Applied Geology, Curtin University of Technology, GPO Box U1987, Perth, Western Australia 6845, Australia Search for other works by this author on: GSW Google Scholar Michael T.D. Wingate; Michael T.D. Wingate 2Tectonics Special Research Centre, School of Earth and Geographical Sciences, University of Western Australia, Crawley, Western Australia 6009, Australia Search for other works by this author on: GSW Google Scholar Ian C.W. Fitzsimons; Ian C.W. Fitzsimons 3Tectonics Special Research Centre, Department of Applied Geology, Curtin University of Technology, GPO Box U1987, Perth, Western Australia 6845, Australia Search for other works by this author on: GSW Google Scholar Benjamin S.E. Mapani Benjamin S.E. Mapani 4Geology Department, University of Zimbabwe, Harare, Zimbabwe Search for other works by this author on: GSW Google Scholar Geology (2003) 31 (6): 509–512. https://doi.org/10.1130/0091-7613(2003)031<0509:UTKKAR>2.0.CO;2 Article history received: 12 Jan 2003 rev-recd: 27 Feb 2003 accepted: 04 Mar 2003 first online: 02 Jun 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation Bert De Waele, Michael T.D. Wingate, Ian C.W. Fitzsimons, Benjamin S.E. Mapani; Untying the Kibaran knot: A reassessment of Mesoproterozoic correlations in southern Africa based on SHRIMP U-Pb data from the Irumide belt. Geology 2003;; 31 (6): 509–512. doi: https://doi.org/10.1130/0091-7613(2003)031<0509:UTKKAR>2.0.CO;2 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGeology Search Advanced Search Abstract The Irumide belt is part of a network of late Mesoproterozoic Kibaran-age orogens in south-central Africa. Sensitive high-resolution ion microprobe (SHRIMP) U-Pb zircon ages for gneisses, migmatites, and granitoids indicate that peak Irumide metamorphism was ca. 1020 Ma and that this was associated with widespread granitic magmatism at 1050–950 Ma. Pre-Irumide protoliths are dominated by 1650–1519 Ma granitic gneisses. These data provide the first robust constraint on the timing of Irumide tectonism and show that previous estimates of ca. 1350 and 1100 Ma are incorrect, thereby negating previously proposed correlations of the Irumide belt with nearby Kibaran-aged tectonism. The correlation between the Irumide belt and Choma-Kalomo block of southern Zambia has had a major influence on models for the tectonic assembly of southern Africa because it required that the intervening Neoproterozoic Zambezi belt was intracratonic and associated with minimal horizontal displacements. Our data indicate that both terranes have distinct histories, consistent with lithologic and metamorphic evidence of Neoproterozoic ocean closure along the Zambezi belt. This implies that the Kalahari and Congo cratons assembled during the Neoproterozoic and not during Kibaran-age tectonism, as previously believed. This new outlook on regional African tectonics supports a configuration of the Rodinia supercontinent that places the Congo craton well away from the Kalahari craton ca. 1000 Ma. You do not have access to this content, please speak to your institutional administrator if you feel you should have access.

Geology and correlation of the central Irumide belt

The Irumide Fold belt of Zambia consists of a Palaeo to Mesoproterozoic complex of gneisses and granite gneisses and a supracrustal sequence of quartzites and pelites. Although no direct correlation is possible, the metasedimentary sequence is tentatively equated with the Manshya River Group described in the NE. The basement to the Irumide belt consists of the Bangweulu Granites to the North, and the Mkushi gneiss basement (MGB) to the Southwest. Age constraints on the Bangweulu Block are limited, but the Mkushi Gneiss has been dated at ∼2050 Ma. A detrital provenance study on a quartzite of the Manshya River Group near Mkushi indicates derivation from terranes of up to 3180 Ma, with a maximum age for the Manshya River Group set by the youngest detrital grain at 1941 Ma. Detrital cores from paragneisses and migmatites in the Serenje area indicate a more uniform detrital source for the sedimentary protolith of 2050–2000 Ma. A more direct age constraint on the Manshya River Group has been provided through an age of 1880 Ma on a concordant rhyolite in the metasedimentary sequence near Chinsali. The Manshya River Group consists of a succession of four pelite and four quartzite Formations. The granitoids, which make up a large portion of the Irumide belt, can be subdivided into an older suite of leucocratic gneisses and biotite-granites, and a younger suite of alkaline, often porphyritic K-feldspar granites. Oversimplified lithostratigraphic division of the “crystalline basement” in the southwest of the Irumide belt has lead to an overestimation of the Palaeoproterozoic basement (MGB). The extent of the Palaeoproterozoic basement awaits re-evaluation through fieldwork. The main structural trend of the Irumide belt is northeast and is related to extensive crustal shortening during the main stage of the Irumide orogeny. Tectonic transport is directed towards the northwest, with southwest directed backthrusting locally developed to define a double verging overall structure. The compressional stage is characterised by amphibolite grade metamorphism and accompanied by widespread granite magmatism and anatexis.

Neoproterozoic ensialic back-arc spreading in the eastern Arabian shield: geochemical evidence from the Halaban Ophiolite

Two continental terranes (Afif and Ar Rayn) of the eastern Arabian Shield are separated by the Al-Amar Suture Zone, the western boundary of which is marked by the Halaban Belt, the largest ophiolite sheet in the eastern shield. REE and other immobile trace element concentrations suggest the Halaban Ophiolite formed in an ensialic back-arc basin in a supra-subduction zone setting. Based on this, a new tectonic model for the eastern Arabian Shield was constructed. This model assumes the existence of a westerly-dipping subduction zone at about 700 Ma above which back-arc spreading resulted in the break up of the continental margin of the Afif Terrane and the formation of a short-lived marginal basin. Basin closure took place at around 680 Ma, but a westerly-dipping subduction zone continued to exist further east beneath the Ar Rayn Terrane for at least 60 Ma. In the period 620—600 Ma, collision with a continental mass (now concealed by Phanerozoic sedimentary rocks) gave rise to widespread granitic magmatism in the eastern shield, as well as crustal-scale strike-slip faulting.

The alkaline silica-saturated ultrapotassic magmatism of the Riacho do Pontal Fold Belt, NE Brazil: an example of syenite–granite Neoproterozoic association

The Neoproterozoic of northeastern Brazil was marked by the development of collisional fold belts, mainly surrounding the São Francisco Craton, and an associated widespread granitic magmatism. The Casa Nova (555±10Ma, Sri=0.7068 and Engraçadinha syenites and granites, intrusive in the Riacho do Pontal Fold Belt, are related to the late stages of this collisional event. Melanocratic syenites, probably generated by magmatic-flow cumulate processes, and mesocratic and leucocratic syenites, representing magmatic liquids, are associated with granites, pegmatites, and syenite–granite dykes. Homogeneous or perthitic alkali feldspar, quartz, aegirine–augite, diopside, titanite, apatite, magnesian biotite, winchite–richterite, and magnetite are the dominant mineral phases. It is suggested that these magmas belong to an ultrapotassic silica-saturated alkaline series, defined on the basis of its alkaline, silica-saturated character and by a K2O/Na2O ratio of >3.0 — that is, intermediate. Major- and trace-element evolution is consistent with mineral fractionation processes, controlled by magmatic flow, and dominated by apatite–titanite–pyroxene in the less differentiated terms and by alkali feldspar in the more evolved. The source of primary magmas is a previously subduction-metasomatised mantle, probably with anomalous enrichment in LREE and LILE elements. Barite–ilmenite mineralisations are related to the more differentiated Engraçadinha granites.