TDM Model Ages Research Articles

Early Mesozoic magmatism and tectonic evolution of east-central Tibet

The Early Mesozoic granitoids in the east-central Tibet are the key to understand the tectonic evolution of the Tibetan Plateau. In this study, three stages of Early Mesozoic granitic magmatism were indicated by LA-ICP-MS zircon U–Pb dating on 14 samples. The Early Triassic (248–243 Ma) and the Late Triassic (213–208 Ma) were distributed in the North Qiangtang terrane, and the Early Jurassic (ca. 187 Ma) occurred in the Tongka and Jiayuqiao blocks. The Late Triassic and Early Jurassic granitoids show similar negative zircon eHf(t) values (− 5.5 to − 16.6) with TDM2 model ages of 1.60–2.28 Ga, suggesting a Paleoproterozoic crustal source, whereas the Early Triassic granitoids have zircon eHf(t) values from − 3.4 to + 5.3 with TDM2 model ages of 0.94–1.50 Ga, indicating a Mesoproterozoic crustal source. Based on the whole-rock geochemical data, we suggest that the Early Triassic rocks from the North Qiangtang terrane include I- and S-type granites and the Late Triassic rocks are S-type granites, which were related to the northward subduction of the Longmu Tso–Shuanghu–Dingqing Paleo-Tethys Ocean and subsequent collision between the North Qiangtang terrane and Tongka block, respectively. The Early Jurassic granitoids from the Tongka and Jiayuqiao blocks also included both I- and S-type granites and were probably generated in an arc-related setting during the northward subduction of the Bangong–Nujiang Tethys Ocean. Therefore, we suggest a collision–accretion model that attributes the Early Mesozoic tectonic-magmatic event to the sequential multistage subduction and collision in the east of central Tibet.

Middle Permian–early Triassic magmatism in the Western Pontides, NW Turkey: Geodynamic significance for the evolution of the Paleo-Tethys

Permian-Triassic magmatic rocks are widely exposed in different tectonic terranes and continental blocks in the Aegean region. This study is focussed on the İstanbul Zone and the Istranca (Strandja) Massif, which are located in the Western Pontides of NW Turkey. The Kırklareli and the Tepecik plutons intruded into the metamorphic basement rocks of the Istranca Massif, and the Sancaktepe pluton is emplaced into the İstanbul Paleozoic sedimentary sequences. We present new geochemical data for these plutons, in order to interpret their petrogenesis and time of emplacement and use this information for geodynamic interpretation. The zircon U–Pb crystallization ages are 268.3 ± 2.1 Ma for the Kırklareli pluton, 249.4 ± 1.5 Ma for the Tepecik pluton and 257.3 ± 1.5 Ma and 253.7 ± 1.75 Ma for the the Sancaktepe pluton. They are high-K, calc-alkaline to shoshonitic granitoids with aluminum saturation index (ASI) values between 0.9 and 1.3, which define them as peraluminous and slightly metaluminous. 87Sr/86Sr(i) values for the studied plutons range between 0.701123 and 0.707704. 143Nd/144Nd(i) ratios calculated for crystallization ages are between 0.512052 and 0.512431, and εNd(i) values vary from −4.71 to 2.22. TDM model ages range between 0.83 and 1.41 Ga. These plutons are enriched in LILEs and LREE and depleted in HFSEs with negative Eu anomalies, indicating that the melts were derived from mafic crustal sources. Our new data suggest that the Kırklareli pluton was generated in a subduction-related magmatic arc, and the highly fractionated Sancaktepe and Tepecik plutons were formed in a back-arc setting in response to the northward subduction of the Paleo-Tethys Ocean during the Mid Permian–Early Triassic.

Palaeoproterozoic meta-rhyolite and meta-dacite of the Liaohe Group, Jiao-Liao-Ji Belt, North China Craton: Petrogenesis and implications for tectonic setting

Whole-rock major and trace element geochemistry, along with zircon U–Pb ages and Lu–Hf isotope data, are reported for Palaeoproterozoic meta-rhyolites and meta-dacites of the Liaohe Group in the northern segment of the Jiao-Liao-Ji Belt, North China Craton. These data are used to constrain the petrogenesis of the rocks and the Palaeoproterozoic tectonic evolution of the Jiao-Liao-Ji Belt. Zircons from these rocks are euhedral–subhedral, display oscillatory growth zoning, and have high Th/U ratios (0.26–1.21), implying a magmatic origin. LA–ICP–MS zircon U–Pb age data indicate that the silicic metavolcanic rocks formed during the Palaeoproterozoic (2184–2127 Ma). The zircons yield εHf(t) values of −9.7 to +8.9 and TDM2 model ages of 2205–3313 Ma. Geochemically, the silicic metavolcanic rocks are metaluminous to weakly peraluminous and belong to the calc-alkaline I-type series. The rocks are characterized by enrichment in large-ion lithophile elements and depletion in high-field-strength elements (e.g., Nb, Ta, P, and Ti), and have affinities with igneous rocks that form in an active continental margin setting. The geochemical and isotopic data suggest that the rocks were derived mainly from partial melting of Meso-Neoarchaean juvenile lower crust, with a possible contribution from older materials. The present results, combined with the regional geology, further demonstrate that an oceanic plate was subducted northward beneath the Longgang Block during the Palaeoproterozoic.

Multiple sources for Archean granitoids in the Yalgoo area, Yilgarn Craton, Western Australia: Geochemical and isotopic evidence

In the Yalgoo area of the north-central Yilgarn Craton, three small granitoid bodies, named the Lady Lydia (LLG), Yalgoo east (YEG) and Yalgoo north granitoids (YNG) intruded ∼2.8 Ga mafic supracrustal rocks. They form two suites: i) granodiorites (from both the LLG and YEG) with strongly fractionated REE patterns, high LREE contents, low HREE contents, weakly positive Eu anomalies, and of Archean TTG affinity, and ii) biotite monzogranites (from the YNG) with very high LREE contents and prominent negative Eu anomalies. All the granitoids are calc-alkaline, with the granodiorites recording ages of 2763–2752 Ma, and the biotite monzogranites recording ages of 2636–2634 Ma. The REE and HFSE characteristics of the granodiorites favor an Archean subduction environment. Abundant xenocrystic zircons (3.00–2.94 Ga) in the granodiorites and their Lu-Hf isotopic characteristics imply a long history of crustal recycling in the north-central Yilgarn. The Lu-Hf isotopes indicate that the ∼2.76 Ga granodiorites and xenocrysts were formed from a composite source ranging in age from 3.5 to 3.0 Ga. Increased crustal thickening due to convergence (after cessation of subduction) caused melting in the upper/mid-crustal levels, with generation of parental melt at ∼2.64 Ga to source the biotite monzogranites. The latter are characterized by strongly −ve εHf(t) (−10 to −12) and largely Eoarchean TDM2(Hf) model ages (∼3.85–3.6 Ga). Significantly, they provide evidence of Eoarchean crustal material in this part of the Yilgarn Craton.

Eastern Paranapanema and southern São Francisco orogenic margins: Records of enduring Neoproterozoic oceanic convergence and collision in the southern Brasília Orogen

The late Neoproterozoic processes of western Gondwana assembly are well-preserved in most Brazilian orogens. In the southern edge of the São Francisco Craton, a syn-metamorphic pile of nappes is the result of the closure of the Goiás-Pharusian Ocean through the collision between the São Francisco (passive margin) and Paranapanema (active margin) paleoplates. The inner segments of the orogen suggest active margin- to syn-collisional-type sedimentation and magmatism recorded by the Andrelândia and Liberdade Nappes, among others.The Liberdade Nappe metasedimentary rocks, which have a maximum depositional age of 760 Ma, suggest a source area in an evolved Tonian-Cryogenian continental magmatic arc located in the east-northeastern Paranapanema margin. The Santo Antonio Unit (maximum depositional age of 680 Ma) of the lower Andrelândia Nappe for the same age interval instead presents a source primarily in an island arc. The Serra da Boa Vista, the upper unit of the Andrelândia Nappe, seems to record the beginning of continental collision because of its Rhyacian source, recognized as being in the São Francisco Craton, and no important evidence for Neoproterozoic arc magmatism. Grenville- and Rondonian-San Ignacio-type source areas, as well as Statherian ages, are observed in all units.Metabasic rocks interlayered in the Liberdade Nappe metasedimentary rocks have chondritic to suprachondritic εNd(t) (−1.86 to 1.75) and 1.09–1.48 Ga Nd TDM model ages, suggesting juvenile magmatism. Retroeclogitic and metavolcaniclastic rocks of Calymmian age (1.46–1.48 Ga) occur as exotic blocks within the same metasedimentary rocks.The complete ocean closure and the beginning of continental collision must have occurred at approximately 670 Ma, which corresponds to the maximum depositional age of the syn-collisional unit (Serra da Boa Vista) and to the age of the eclogitic rocks. The Andrelândia Nappe System migration was probably restricted to the 635–600 Ma interval, followed by the thinning of the orogenic crust.

Crust periodic evolution: Evidence from the Taihua complex, southern North China Craton

The Taihua complex in the southern North China Craton (NCC), recording muti-episodes continental crust growth events, was divided into the lower and upper units. The lower unit were mainly composed of Neoarchean-Mesoarchean TTG gneisses and amphibolites. Here we report the whole-rock geochemistry, zircon U-Pb dating, trace element and Lu-Hf isotope compositions from the Wugang TTG within the lower unit of the Taihua complex LTC. They are characterized by high-SiO2 (62.2–70.73 wt%), high-Al2O3 (13.23–16.66 wt%), low-Mg# (31–53) and Cr contents (20–60 ppm), HREE and HFSE depletion with low to moderate Sr/Y (12.0–76.3) and (La/Yb)N (5.2–48.3, N denotes normalization by chondrite) in compositions. Magmatic zircons from representative samples, one granodioritic gneiss and one tonalitic gneiss (both are drilled samples), gave a consistent upper intercept ages at 2.85 Ga, reflecting the time of crystallization of the first time TTG pluton within LTC. They have positive zircon εHf(t) values (0.9–7.1) with the TDM1(Hf) model ages ranging from 2.85 Ga to 3.09 Ga with an average of 2.95 Ga, and TDM2(Hf) model ages ranging from 2.85 Ga to 3.23 Ga with an average of 3.01 Ga, their youngest Hf model ages (2.85 Ga) were close to the crystallized ages. In combination with data from Lushan Mesoarchean TTG rocks, they shared similar geochemical features, except for the depleted degree in HREE, indicating that they are generated from similar geologic dynamic setting but in different depths. These TTG rocks were principally derived from a depleted mantle sources, indicating a key juvenile crust accretion in the southern margin of the NCC at 2.85 Ga. They were most likely formed from occasional subduction and partial melting of oceanic plateaus, leaving a garnet-bearing amphibolitic residue at shallow depths (>25 km, Wugang TTG) and deep depths (>50 km, Lushan TTG) with different degree’s fractionation. In associated with previous study, we identified at least four stages of TTG formation, ∼2.85 Ga, ∼2.80 Ga, ∼2.76 Ga and ∼2.72 Ga, from the Southern NCC, which reconfirmed that the Archean continental evolution is episodic and periodic at least in the Taihua complex.

1.88 Ga São Gabriel AMCG association in the southernmost Uatumã-Anauá Domain: Petrological implications for post-collisional A-type magmatism in the Amazonian Craton

In the southernmost Uatumã-Anauá Domain, central Amazonian craton (Brazil), crop out 1.98Ga basement inliers represented by (meta)leucosyenogranites and amphibolites (Igarapé Canoas Suite), 1.90–1.89Ga high-K calc-alkaline granitoids (Água Branca Suite), a 1.88–1.87Ga alkali-calcic A-type volcano-plutonic system (Iricoumé-Mapuera), Tonian SiO2-satured alkaline granitoids, 1.45–1.25Ga orthoderived metamorphic rocks (Jauaperi Complex) and Orosirian–Upper Triassic mafic intrusions. New data on petrography, multielementar geochemistry, in situ zircon U–Pb ages and Nd and Hf isotopes of alkali-calcic A-type granites (São Gabriel Granite, Mapuera Suite) and related rocks are indicative of a 1.89–1.87Ga volcano-plutonic system integrated to the São Gabriel AMCG association. Its magmatic evolution was controlled by the fractional crystallization combined with magma mixing and cumulation processes. Nd isotope values (εNdt values=−3.71 to +0.51 and Nd TDM model age=2.44 to 2.12Ga) and U–Pb inherited zircon crystals (2115±22Ma; 2206±21Ma; 2377±17Ma, 2385±17Ma) of the São Gabriel system indicate a large participation of Siderian–Rhyacian crust (granite-greenstones and granulites) and small contribution of Rhyacian mantelic magma. εHft values (+5.2 to −5.8) and Hf TDM ages (3.27–2.14Ga) also point to contribution of Paleoarchean–Rhyacian crustal melts and small participation of Siderian–Rhyacian mantle melts. Residual melts from the lower crust have been mixed with basaltic melts generated by partial melting of the subcontinental lithospheric mantle (peridotite) in a post-collisional setting at 1.89–1.87Ga. The mafic melts of such a mixture could have been originated through partial melting of residual ocean plate fragments (eclogites) which ascended onto a residual mantle wedge (hornblende peridotite) and melted it, resulting in modified basaltic magma which, by underplating, led heat to the anatexis of the lower continental crust. This widespread alkali-calcic A-type magmatism was caused by destabilization and magmatic reactivation in the Ventuari-Tapajós and Central Amazonian Provinces, resulting from the Ventuari-Tapajós collision periods. Younger igneous reactivations have been registered at 1.45 to 1.25Ga, ~1.0Ga and ~100Ma, culminating with the production of mafic and felsic alkaline magmas, along of the northern border of the Amazon Basin.

Petrogenesis and tectonic implication of Paleoproterozoic granites and granulites in the Fengzhen area of North China craton

The North China Craton (NCC) is one of the oldest cratons in the world that preserves the records of many important geological events in the early evolution of the Earth. However, the early Precambrian tectonic evolution history of the NCC is still controversial. Here we report Paleoproterozoic leucogranites, garnet granites and granulites in the Fengzhen area that constitutes a junction between the Khondalite Belt and the Trans-North China Orogen (TNCO). The leucogranites have high SiO2 content (75–85wt%), and magmatic zircon U-Pb age of 2199±3 Ma. Their zircons have slightly various εHf(t) values (−0.45 to 1.41) with TDM model ages of 2.5–2.6Ga. The granites show strong LREE enrichment with La/Ybcn ratio of 12–176, and have high initial Nd isotope (εNd(t)=3.5–4.5). Most of them display positive Eu anomaly, excluding fractional crystallization contribution on the high Si feature. The leucogranite was produced by melting of Late Archean felsic TTGs (tonalite–trondhjemite–granodiorite) and addition of juvenile crust. Magmatic zircons yield the garnet granite age of 2002±3Ma. The zircons show various εHf(t) values (−5.8 to 7.1) and TDM model ages (2.1–2.6Ga). Low initial εNd(t) isotope value (−4.2 to −8.3) was determined in the granites. The granulites are high pressure metamorphic rocks with a peak pressure of 12.0±0.8 kbar, and have similar metamorphic age of 1967±10Ma to the garnet granites. This indicates that the Fengzhen area underwent 2-Ga inter-continental orogeny, in which the melting of sedimentary rock formed the garnet granites. Similarly, sodic TTG melting to form K-rich leucogranites also needs high pressure. However, the leucogranite age is obviously older than the peak metamorphic timing of continent–continent collision. This implies that the Fengzhen area may have underwent arc-continental collision at 2.2Ga.

Zircon U-Pb ages and Hf isotopes for the Diablillos Intrusive Complex, Southern Puna, Argentina: Crustal evolution of the Lower Paleozoic Orogen, Southwestern Gondwana margin

The evolution of the rocks of the Lower Paleozoic Orogen in Puna, at the Southwestern Gondwana margin, has been widely debated. In particular, the scarce amount of geological and geochemical data available for the Diablillos Intrusive Complex, Eastern Magmatic Belt, Southern Puna, require a further study for new evidence towards the understanding of sources, magmatic processes and emplacement of magmas, in order to better comprehend the crustal evolution in this setting. We present new combined U–Pb and Hf isotope analyses on zircon by LA-MC-ICP-MS from monzogranite, granodiorite and diorite rocks of the Diablillos Intrusive Complex. We obtained 206Pb/238U concordant weighted average ages of 517 ± 3 Ma and 515 ± 6 Ma for the monzogranite and diorite, respectively, and a concordant age of 521 ± 4 Ma for the granodiorite. These ages permit to constrain the climax of magmatic activity in the Diablillos Complex around ∼515–520 Ma, while the emplacement of the complex took place between ∼540 Ma and 490 Ma (representing a ca. 50 Ma magmatic event). Major and trace element data, initial 87Sr/86Sr values varying from 0.70446 to 0.71278, positive and negative ɛNd(t) values between +2.5 and −4, as well as ɛHf(t) for zircon data between + 3 and −3 indicate that the analyzed samples represent contaminated magmas. The ɛHf(t) and the ɛNd(t) values for this complex specify that these rocks are derived from interaction of a dominant Mesoproterozoic crystalline and/or a metasedimentary source and juvenile mantle-derived magmas, with a TDM model age range of ∼1.2–1.5 Ga, with later reworking during lower Paleozoic times. The combined data obtained in this contribution together with previous data, allow us to suggest that the formation of the Eastern Magmatic Belt of the Puna was part of a long-lived magmatic event during Early Paleozoic times. Whereby the granitoids of the Eastern Magmatic Belt formed through intra-crustal recycling at an active continental margin, with minor contributions from juvenile material in the back-arc setting.

Petrografia e geoquímica de gnaisses da região de Indiara, porção central do arco magmático de Goiás

Na região de Indiara, Goiás, ocorre uma extensa faixa de gnaisses relacionados ao Arco Magmático de Goiás, próximo ao contato com as rochas supracrustais da Sequência Metavulcanossedimentar Anicuns-Itaberaí. Dados geoquímicos e isotópicos (Sm/Nd) mostram que os gnaisses da região de Indiara não são semelhantes às rochas de regiões tipo do Arco Magmático de Goiás (regiões de Arenópolis, Firminópolis, Iporá e Mara Rosa). São rochas cálcio-alcalinas e peraluminosas, com composição predominantemente granítica, em contraste com o caráter prevalentemente cálcico e metaluminoso das regiões tipo, que também apresentam composição dominantemente tonalítica a granodiorítica. Os altos teores de SiO2, o caráter fortemente peraluminoso e os altos teores de coríndon normativo sugerem que os gnaisses da região de Indiara são derivados de granitos tipo-Sin-colisionais e/ou correspondem à mistura de protólitos ígneos e sedimentares. As idades modelo TDM (1,88 e 1,90 Ga) sugerem que os gnaisses da região evoluíram de crosta siálica mais antiga do que as rochas que compõem o Arco Magmático de Goiás.

Provenance and tectonic setting of siliciclastic rocks associated with the Neoproterozoic Dahongliutan BIF: Implications for the Precambrian crustal evolution of the Western Kunlun orogenic belt, NW China

The Late Neoproterozoic Dahongliutan BIF is associated with siliciclastic rocks in the Tianshuihai terrane of the Western Kunlun orogenic belt (WKO), NW China. The sedimentary rocks have various weathering indices (e.g., CIA=57–87, PIA=61–96 and Th/U=4.85–12.45), indicative of varying degrees of weathering in the source area. The rocks have trace element ratios, such as Th/Sc=0.60–1.21 and Co/Th=0.29–1.67, and light rare earth element (LREE) enriched chondrite–normalized REE patterns, suggesting that they were mainly sourced from intermediate and felsic rocks. Available U–Pb ages of detrital zircon from these rocks reveal that the detrital sources may have been igneous and metamorphic rocks from the WKO and the Tarim Block. Our study suggests that the Dahongliutan BIF and hosting siliciclastic rocks may have deposited in a setting transitional from a passive to active continental margin, probably related to the Late Neoproterozoic–Early Cambrian seafloor spreading and subduction of the Proto–Tethys Ocean. U–Pb dating of 163 detrital zircons defines five major age populations at 2561–2329Ma, 2076–1644Ma, 1164–899Ma, 869–722Ma and 696–593Ma. These age groups broadly correspond to the major stages of supercontinent assembly and breakup events widely accepted for Columbia, Rodinia and Gondwana. Some zircons have TDM2 model ages of 3.9–1.8Ga and negative εHf(t) values, suggesting that the Archean to Paleoproterozoic (as old as Eoarchean) crustal materials were episodically reworked and incorporated into the late magmatic process in the WKO. Some Neoproterozoic zircons have TDM2 model ages of 1.47–1.07Ga and 1.81–1.53Ga and positive εHf(t) values, indicating juvenile crustal growth during the Mesoproterozoic. Our new results, combined with published data, imply that both the Tianshuihai terrane in the WKO and the Tarim Block share the same Precambrian tectonic evolution history.

Contrasting provenance and timing of metamorphism from paragneisses of the Araçuaí-Ribeira orogenic system, Brazil: Hints for Western Gondwana assembly

The Araçuaí orogen and the Ribeira belt make up a complex Neoproterozoic-Cambrian orogenic system, the Araçuaí-Ribeira orogenic system (AROS) located from the eastern to southeastern Brazil. Along the AROS, the Ediacaran Rio Doce magmatic arc represents a geotectonic connection between the Araçuaí and the Ribeira orogenic domains. Although the nature and evolution of the Rio Doce plutonic rocks is regionally well established, it lacks detailed studies on the paragneisses found along the western and central regions of this magmatic arc. Besides information on the nature and provenance of their sedimentary protoliths, the paragneisses provide data to unravel the palaeogeographic scenario from the precursor to arc-related basins. Six samples of Al-rich gneisses covering a large AROS region were selected for electron microprobe (EMP) mineral analyses in order to obtain geothermobarometric data and monazite ages, as well as for Laser Ablation-Inductively Coupled Plasma-Mass Spectrometry (LA-ICP-MS) isotopic analyses on zircon (U-Pb, Lu-Hf) and monazite (U-Pb). The different age spectra from detrital zircon grains and contrasting Hf isotopic signatures suggest a complex sedimentary history. Located in the western sector of the study region, the samples RC-02 and RC-34, with an 80% age peak of detrital zircon grains from 2158Ma to 1830Ma, εHf(t) from −2.2 to −22.7, and Hf TDM model ages from 3530Ma to 2440Ma, suggest sediment sources located in the São Francisco craton basement. The samples RC-03, also from the western sector, and RC-46 from the southern sector, have a more complex assemblage of detrital zircon grains with an 87% age peak from 987Ma to 592Ma, εHf(t) from +14.9 to −2.9, and Hf TDM model ages from 2220Ma to 720Ma, indicating provenance from mainly juvenile sources of distinct ages. Candidates to be juvenile sources for RC-03 and RC-46 sedimentary protoliths are the Rhyacian Juiz de Fora and Pocrane complexes in the basement of the Rio Doce arc, the Neoproterozoic Rio Negro arc system of the Ribeira belt, and AROS ophiolite complexes. Samples RC-30 and RC-38 from the eastern sector of the study region, with most detrital zircon ages between 650Ma and 552Ma and very negative εHf(t) (−25.3 to −16.5), suggest main sediment sources in the Rio Doce arc. By extending U-Pb analyses on metamorphic zircon and monazite, we have identified a complex timing of metamorphism, represented by metamorphic ages ranging from 621Ma to 480Ma, with the main collisional activity between 580Ma and 540Ma. Geothermobarometric studies on garnet porphyroblasts, syn-kinematic to the D2 regional foliation, show a retrograde metamorphic path typical of continental collision belts, starting with P-T conditions of Tmax=733°C and Pmax=6.43kbar. Our data also suggest: i) the studied paragneisses represent distinct Neoproterozoic basin stages, shifting from passive to active margin settings; ii) if the Rio Negro arc system really provided sediments for the basin stage represented by the RC-03 and RC-46 paragneisses, it would have amalgamated with the AROS before 614Ma; iii) the final amalgamation of Western Gondwana took place around 540Ma in the focused region; iv) an important re-heating period (520–480Ma) can be related to the AROS gravitational collapse, after Western Gondwana assembly.

U–Pb zircon, geochemical and Sr–Nd–Hf isotopic constraints on age and origin of the intrusions from Wunugetushan porphyry deposit, Northeast China: implication for Triassic–Jurassic Cu–Mo mineralization in Mongolia–Erguna metallogenic belt

ABSTRACTThe Wunugetushan porphyry Cu–Mo deposit is located in northeastern China. The deposit lies within the Mongolia–Erguna metallogenic belt, which is associated with the evolution of the Mongol–Okhotsk Ocean. The multiple episodes of magmatism in the ore district, occurred from 206 to 173 Ma, can be divided into pre-mineralization stage (biotite granite), mineralization stage (monzogranitic porphyry and rhyolitic porphyry), and post-mineralization stage (andesitic porphyry). The biotite granite has (87Sr/86Sr)i values of 0.704105–0.704706, εNd(t) values of −0.67 to −0.07, and εHf(t) values of −0.4 to 2.8, yielding Hf two-stage model ages (TDM2) 1250–1067 Ma, and Nd model ages of 1.04–0.96 Ga, indicating that the pre-mineralization magmas were generated by the remelting of Neoproterozoic juvenile crustal material. The monzogranitic porphyry has (87Sr/86Sr)i values of 0.704707–0.706134, εNd(t) values of 0.29–1.33, and εHf(t) values of 1.0–2.9, yielding TDM2 model ages of 1173–1047 Ma. The rhyolitic porphyry has (87Sr/86Sr)i ratio of 0.702129, εNd(t) value of −0.21, and εHf(t) values of −0.5 to 7.1, TDM2 model ages from 1269 to 782 Ma. These results show that the magmas of mineralization stage were generated by the partial melting of juvenile crust mixed with mantle-derived components. The andesitic porphyry has (87Sr/86Sr)i ratio of 0.705284, εNd(t) value of 0.82, and εHf(t) values from 4.1 to 7.4, indicating that the post-mineralization magma source contained more mantle-derived material. The Mesozoic Cu–Mo deposits which genetically related to Mongol–Okhotsk Ocean were temporally distributed in Middle to Late Triassic (240–230 Ma), Early Jurassic (200–180 Ma), and Later Jurassic (160–150 Ma) period. The Middle Triassic to Early Jurassic Cu–Mo mineralization was dominated by Mongol–Okhotsk oceanic plate southeast-directed subducted beneath the Erguna massif. The Later Jurassic Cu–Mo mineralization was controlled by the continent–continent collision between Siberia plate and Erguna massif.

Whole rock geochemistry, Zircon U–Pb and Hf isotope systematics of the Çangaldağ Pluton: Evidences for Middle Jurassic Continental Arc Magmatism in the Central Pontides, Turkey

The Central Pontides (Turkey) includes several igneous complexes, which are predominantly Permo-Carboniferous and Middle Jurassic in age. The Çangaldağ Pluton is one of the largest igneous bodies located in the northern Central Pontides, whose age and tectono-magmatic evaluation is important to constrain the geological evolution of the Northern Neotethys. The pluton tectonically overlies the Çangaldağ Metamorphic Complex, which represents an arc–back-arc complex of Middle Jurassic age. The Çangaldağ Pluton consists mainly of non-metamorphic gabbroic diorite, dacite porphyry, and lesser amount of granitic rocks. Geochemically, the various rock types are akin to volcanic arc magmas displaying Th/Nb and light rare earth element/heavy rare earth element enrichments. In-situ U–Pb age results of zircons from dacite porphyry and granite samples yield ages of 161±5Ma and 170±2Ma, respectively. Corresponding in-situ average 176Hf/177Hf initial ratios are 0.28287±0.00004 and 0.28213±0.00002 for the dacite porphyry and granite samples, respectively. These results are consistent with derivation from a subduction-modified mantle source. Based on Hf isotope compositions, TDM model ages vary between 624 and 1512Ma and suggest that the arc magmatism associated with the Çangaldağ Pluton may have involved partial melting of Neoproterozoic/Mesoproterozoic crustal rocks, a common feature in Gondwana-derived terranes. The geochemical, Hf isotope, and geochronological data reported here confirm the presence of a continental arc system during the Middle Jurassic in the Central Pontides, and suggests that the Çangaldağ Pluton formed during northward subduction of the Intra-Pontide branch of the Northern Neotethys.

Current Literature Survey

The Imiter inlier (eastern part of the Moroccan Anti-Atlas) is located on the northwestern border of the West African Craton (WAC) and exhibits a range of Pan-African granitoids. Three massifs that crosscut the Imiter Saghro Group were targeted in this work: the Igoudrane granodiorite, Bou Teglimt granodiorite and Bou Fliou granite. We present here additional geochemical analyses (major and trace elements) and Sm-Nd isotopic data, which define two distinct groups: (i) the Igoudrane massif (677 Ma) and (ii) the Bou Teglimt granodiorite (576 Ma) and the Bou Fliou granite (550 Ma).Geochemical data confirm the calc-alkaline signature of the studied granitoids. Both groups of granitoids are slightly peraluminous and show strong negative anomalies in Nb, Ta and Ti in multi-element plots normalized to the primitive mantle. The granitoids have low 143Nd/144Nd initial ratios (0.5116–0.5117), with TDM model ages ranging from 1.73 to 1.52Ga. The εNd(t) values are negative, decreasing from the Igoudrane samples (−1.1 to −3.1) to the Bou Teglimt granodiorite (−3.0 to −3.3) and Bou Fliou (−4.2 to −4.8). All these data suggest a mixed magmatic origin involving a juvenile mantle source and an old, at least Paleoproterozoic crust. Given Mesoproterozoic rocks are lacking or very scarce in the Anti-Atlas, these results confirm the existence of an old cratonic basement beneath the eastern Anti-Atlas, and therefore suggest that the northern border of the West African Craton must be placed further to the north, as suggested by previous work in this region.

From the plutonic root to the volcanic roof of a continental magmatic arc: a review of the Neoproterozoic Araçuaí orogen, southeastern Brazil

The Aracuai-West Congo orogen (AWCO) is one of the various components of the Brasiliano/Pan-African orogenic network generated during the amalgamation of West Gondwana. In the reconstructions of Gondwana, the AWCO, encompassing the Aracuai orogen of South America and the West Congo belt of Southwestern Africa, appears as a tongue-shaped orogenic zone embraced by the Sao Francisco-Congo craton. Differing from the vast majority of the known orogens owing to its singular confined setting, the AWCO contains a large amount of orogenic igneous rocks emplaced in all stages of its tectonic evolution. We present new and revised information about the oldest Ediacaran granitic assemblage, the G1 Supersuite, which together with the Rio Doce Group defines the Rio Doce magmatic arc, and then we propose a new tectonic setting for the arc. Field relationships and mineralogical compositions of the G1 Supersuite allow us to characterize three lithofacies associations, Opx-bearing rocks, enclave-rich Tonalite–Granodiorite and enclave-poor Granite–Tonalite, suggesting different crustal levels are exposed in the central part of the Aracuai orogen. The region is interpreted to represent a tilted crustal section, with deep arc roots now exposed along its western border. Chemically, these plutonic associations consist mostly of magnesian, metaluminous to slightly peraluminous, calc-alkaline to alkali-calcic and medium- to high-K acidic rocks. The dacitic and rhyolitic rocks of the Rio Doce Group are mainly magnesian, peraluminous, calcic to calc-alkaline, and medium- to high-K acidic rocks. Zircon U–Pb data constrain the crystallization of the granitoids between ca. 625 and 574 Ma, while the age of the metamorphosed volcanic rocks is around ca. 585 Ma. Thus, within errors, these rock associations likely belong to the same magmatic event and might represent the subduction-related, pre-collisional, evolution of the Aracuai orogen. In addition, whole-rock Sm–Nd isotopic compositions show variable negative eNd(t) values between −6.7 and −13.8, and TDM model ages varying from 1.39 to 2.26 Ga, while eHf(t) vary between −5.2 and −11.7, with TDM ages from 1.5 to 2.0 Ga. Thus, predominantly constructed upon Paleoproterozoic (Rhyacian) basement, the Rio Doce arc shows crustal sources largely prevailing over mantle sources, providing a well-studied example to be compared with similar orogenic settings around the world.

Mesozoic dykes and sills from Uruguay: Sr – Nd isotope and trace element geochemistry

The Mesozoic mafic intrusions in Uruguay comprise dykes and sills grouped as the Cuaró Formation. They are mainly distributed along the southern portion of the Paraná basin, and they are considered part of the Paraná Magmatic Province. They crop out as typically grey moderately altered dykes and sills, characterized by glomero-porphyritic textures, with clusters of plagioclase and occasional clinopyroxene, set in a fine-grained groundmass composed by labradorite, augite and titaniferous magnetite. We present new lithogeochemical results particularly regarding Sr – Nd isotopes to discuss petrogenetic processes. All samples have high 87Sr/86Sr (0.71160–0.70781) and low 143Nd/144Nd ratios (0.512274–0.512585), with epsilon Nd(0) between −4.37 and −7.1. TDM model ages, calculated for 130 Ma, are composed of approximately 1.41–1.61 Ga, except for one dyke with 1.29 Ga. The isotopic data allow their classification as derived from the Gramado magma-type. Trace element geochemistry and isotopic data indicate that the primary magma would be a product of an enriched mantle source with a strong crustal signature, probably due to inherited subduction components and/or assimilation processes.

Origin and age of coeval gabbros and leucogranites in the northern subprovince of the borborema province, NE Brazil

The Paleoproterozoic Serrinha – Pedro Velho Complex comprises orthogneisses and migmatites, exposed in the south part of the Archean São José do Campestre Massif, Rio Grande do Norte domain of the Borborema Province, NE, Brazil. During the Ediacaran, the Serrinha - Pedro Velho Complex underwent metamorphism at HT/LP conditions in a tectonic setting dominated by dextral transpressive deformation, dated at ∼575Ma. Crustal melting generated various plutons and dykes of leucogranites with composition ranging from syeno-to monzogranites. Mafic rocks, including gabbros, norites and diorites also occur as dykes and small plutons intruded into the Serrinha - Pedro Velho Complex. Features of mixing and mingling between mafic and leucogranitic magmas were recorded locally. The granites and mafic rocks show field features and geochemical signatures of extension related magmatism. U-Pb SHRIMP zircon data yielded similar Concordia ages for felsic (582 ± 5 Ma) and mafic (588 ± 6 Ma) rocks. The leucogranites have strongly negative εNd (580 Ma) values (−19.8 to −24.3) and Paleoproterozoic to Archean Nd TDM model ages (2.2–2.6 Ga), similar to those recorded in the orthogneisses of the Serrinha - Pedro Velho Complex. The mafic rocks show slightly higher εNd (580 Ma) values (−13.09 to −19.63). The leucogranites were probably generated by partial melting of a source similar to the Serrinha Pedro Velho orthogneisses. The mafic rocks are MgO- rich, and the less evolved ones show picritic basaltic composition, similar to mafic rocks from continental flood basalt provinces. We suggest that melting of Paleoproterozoic ponds of picrite (plume related?) generated the mafic magmas studied that, subsequently, evolved by olivine and pyroxene fractionation at great depth and underwent contamination with crustal melts.In the studied area other Ediacaran extension related mafic rocks do occur. They have geochemical and isotopic signatures distinct from those recorded in Riachão mafic rocks. A Paleoproterozoic enriched mantle has been proposed as the source of these mafic rocks. The data suggest that extension and mafic magmatism favoured extensive melting of the Serrinha – Pedro Velho Complex at 582–588 Ma ago. A similar aged event is also recorded in southeastern Ghana, and interpreted as syn-orogenic extension related to the collisional orogeny at the margin of the West African craton.

A Paleozoic fore-arc complex in the eastern Central Asian Orogenic Belt: Petrology, geochemistry and zircon U-Pb-Hf isotopic composition of paragneisses from the Xilingol Complex in Inner Mongolia, China

The Central Asian Orogenic Belt (CAOB) is one of the largest and most complex accretionary collages and responsible for considerable Phanerozoic juvenile crustal growth. The Xilingol Complex is a key tectonic unit within the eastern CAOB and consists of strongly deformed quartz-feldspathic gneisses with lenticular or quasi-lamellar amphibolites. Whether the complex in the belt represents Precambrian basement is controversial and here a combined analysis of petrology, geochemistry and geochronology of quartz-feldspathic gneisses from the complex is reported. The rocks belong to upper amphibolite facies and three stages of metamorphism are recognized based on mineral assemblages: prograde metamorphism (Bt-I+Ms-I+Pl+Qz+Mag), peak metamorphism (Alm+Sil+Kfs), and retrograde metamorphism (appearance of Bt-II+Ms-II). Both Precambrian and Paleozoic age populations are identified from each sample. The Precambrian zircons are sourced from magmatic rocks and the crystals display a wide range of 207Pb/206Pb ages from 3141±17Ma to 837±24Ma, and significant variation in εHf(t) values from −17.84 to +10.57 with TDM2 model ages from 3209 to 1389Ma. The Paleozoic zircons have 206Pb/238U ages from 494±14Ma to 402±10Ma, variation in εHf(t) values from −12.82 to +7.72 and TDM2 model ages from 2252 to 960Ma. The biotite 40Ar-39Ar dating yields a plateau age of 301.2±1.9Ma with a low temperature step age 288.1±1.7Ma. The samples have a wide range of whole-rock SiO2 (63.7–89.3%) and Al2O3 contents (5.66–16.3%), with Fe2O3T varying from 0.60% to 6.06%. All of them have trace element compositions consistent with those of the upper continental crust. The protoliths of paragneisses in the Xilingol Complex are wackes and litharenites, representing a part of fore-arc sedimentary sequence (>319Ma) with a major phase of diagenesis age between ca. 387 and 382 Ma in an active continental margin of the South Mongolian microcontinent. The Precambrian zircons from the complex are proposed to have been originally derived from the South Mongolian or those similar microcontinents in the CAOB. These microcontinents have been originally derived from the Tarim craton, instead of the Siberia or North China cratons or Gondwanaland. The prograde biotites from the paragneisses with ages of ca. 312–301Ma recorded the beginning of the accretionary wedge-continent collage during the northward subduction of the Paleo-Asian Ocean, which may last to ca. 282Ma recorded by the retrograde biotites. Detrital materials from the South Mongolian microcontinent and the Baolidao arc instead of the North China craton were deposited in the fore-arc basin indicating the presence of the Solonker zone separating the northern subduction zone from the southern subduction zone in the CAOB. The CAOB is formed as the model of multiple subduction zones with different subduction polarities.

Reconstructing the Cryogenian–Ediacaran evolution of the Porongos fold and thrust belt, Southern Brasiliano Orogen, based on Zircon U–Pb–Hf–O isotopes

ABSTRACTThe Neoproterozoic geotectonic triad of the Brasiliano Orogen is reconstructed in southern Brazil from studies focused on the Porongos fold and thrust belt. We integrate field geology with isotopic studies of zircon U–Pb SHRIMP and Lu–Hf–O laser determinations in seven metasedimentary and three metavolcanic rock samples. The results indicate that the Porongos palaeo-basin was derived from mixed sources (3200–550 Ma), with major contributions from Rhyacian (2170 Ma) and Ediacaran (608 Ma) sources. Minor contributions from Archaean to Tonian sources are also registered. The maximum depositional age of the Porongos palaeo-basin is established by the age range of 650–550 Ma with TDM model ages between 2.5 and 1.3 Ga. The reworked signature (εHf values = −34 to −4) and the characteristic crustal magma reservoirs (δ18O ≥5.3 ‰) indicate that these sediments are equivalent to Neoproterozoic granites of the Dom Feliciano Belt. The episodic depositional history started in the Cryogenian (650 Ma) and lasted until the Ediacaran (most likely 570 Ma). A magmatic event of Tonian age is recorded in rhyodacite samples interleaved with the metasedimentary rocks and dated at 773, 801, and 809 Ma. The crustal evolution of the Sul-Riograndense Shield included mountain building, folding and thrusting and flexural subsidence in the foreland. An orogenic triad is revealed as the Pelotas Batholith, the Porongos fold and thrust belt and the Camaquã Basin, all part of the Dom Feliciano Belt.