Search

[Display omitted] • The migmatite records the evolution of the Dabie orogen from Triassic to Cretaceous. • The upwelling asthenosphere provided a heat source for the Triassic metamorphism. • The migmatite is the product of multiple anatexis of the subducted continental crust. The Dabie orogen underwent a 'complete' orogenic cycle from Triassic collisional orogeny to Early Cretaceous tectonic collapse. Zircons of the migmatite in the North Dabie terrane recorded the processes from Triassic granulite-facies metamorphism to Early Cretaceous anatexis. Three types of zircon are recognized in the migmatite: the Neoproterozoic inherited magmatic zircon, the Triassic metamorphic zircon, and the Late Jurassic–Early Cretaceous anatectic zircon. The Neoproterozoic inherited magmatic zircons suggest the protolith of the migmatite has a tectonic affinity with the Yangtze Craton (YC). The Triassic metamorphic zircon domains have variable ε Hf (t) values from −4.1 to 3.6 and low δ18O compositions ranging from −4.36‰ to −0.30‰. The anatectic zircon domains have clearly negative ε Hf (t) values of −19.8 to 0.8 (mostly less than −10.0) and relatively high δ18O values from −4.24‰ to 3.49‰. Based on the chronological and isotopic data of migmatite and the results of previous studies, the Triassic granulite-facies metamorphism was closely related to the asthenosphere upwelling after the slab break-off during the orogenic stage, and the Early Cretaceous anatexis respond to widely heat event during the collapse stage of orogen. [ABSTRACT FROM AUTHOR]

Several orogenies have shaped the bedrock of southern Sweden. While mafic intrusions represent significant sources of information for reconstructing geodynamics and crustal evolution, the characterization of the various generations of such intrusions in Sweden remains limited. We report in situ zircon U–Pb ages and Hf isotope data from a Fe-Ti eclogite and a coronitic metagabbro from the Eastern Segment in southern Sweden. Crystallisation ages at 1683 ± 17 Ma of the eclogite suggest affiliation with the surrounding 1730–1660 Ma Transscandinavian Igneous Belt intrusions that dominate the Eastern Segment. Secondary zircon growth and Pb-loss in the eclogite sample at 1459 ± 44 Ma and the crystallisation of the metagabbro at 1431 ± 26 Ma overlap and are related to magmatic activity during the Hallandian orogeny. Zircon Hf isotope signatures with chondritic and sub-chondritic values at ~1683 Ma and ~1431 Ma, respectively, correspond to an enriched (or mildly depleted) source in line with a "Mixed Svecofennian Crustal Reservoir". These isotope signatures are more enriched than those in the surrounding gneisses. Zircon isotope data from the herein analysed zircon grains indicate that the eclogite and metagabbro had an enriched mafic source in the mid to lower crust, or within the subcontinental lithospheric mantle below Fennoscandia. [ABSTRACT FROM AUTHOR]

In situ U–Pb and Hf analyses were used for crustal zircon xenocrysts from Triassic kimberlites exposed in the Rangnim Massif of North Korea to identify components of the basement hidden in the deep crust of the Rangnim Massif and to clarify the crustal evolution of the massif. The U–Pb age spectrum of the zircons has a prominent population at 1.9–1.8 Ga and a lack of Archaean ages. The data indicate that the deep crust and basement beneath the Rangnim Massif are predominantly of Palaeoproterozoic age, consistent with the ages of widely exposed Palaeoproterozoic granitic rocks. In situ zircon Hf isotope data show that most of the Palaeoproterozoic zircon xenocrysts have negative ϵ Hf(t) values (−9.7 to +0.7) with an average Hf model age of 2.86 ± 0.02 Ga (2 σ), which suggests that the Palaeoproterozoic basement was not juvenile but derived from the reworking of Archaean rocks. Considering the existence of Archaean remanent material in the Rangnim Massif and their juvenile features, a strong crustal reworking event is indicated at 1.9–1.8 Ga, during which time the pre-existing Archaean basement was exhausted and replaced by a newly formed Palaeoproterozoic basement. These features suggest that the Rangnim Massif constitutes the eastern extension of the Palaeoproterozoic Liao–Ji Belt of the North China Craton instead of the Archaean Liaonan Block as previously thought. A huge Palaeoproterozoic orogen may exist in the eastern margin of the Sino-Korean Craton. [ABSTRACT FROM AUTHOR]

The results of Sr–Nd–Pb–Hf isotope analysis of Late Paleozoic granitoids of Central Chukotka, which are exemplified by the Kibera and Kuekvun plutons, are presented. The ages of these granitic plutons and of granite pebbles from conglomerates at the base of the overlying Lower Carboniferous strata are 351–363 Ma (U–Pb zircon, TIMS, SIMS, LA–ICP–MS). Thus, granitic magmatism is contemporaneous to tectonic events of the Ellesmerian orogeny in the Arctic region. The Sr–Nd–Pb–Hf isotopic compositions of the granitoids indicate the contribution of mantle and crustal components to the granite melt source. The formation of granitoids probably occurred in the geodynamic settings of an Andean type continental margin with interaction between mantle melts, forming in a mantle wedge under suprasubduction conditions, and the continental crust. [ABSTRACT FROM AUTHOR]

The Baoulé-Mossi Paleoproterozoic domain on the West African Craton is known for its world-class orogenic gold deposits formed during the Eburnean orogeny between ca. 2.15 and 2.07 Ga. New results of U-Pb zircon dating in combination with Hf-isotope geochemical data indicate that a suite of mafic and felsic potassic plutonites were emplaced in Guinea (in vicinity to the Archean Kéména-Man domain, KMD) between ca. 2.10 and 2.08 Ga. All plutonites are characterized by (i) enrichment in LILE and LREE, (ii) strong positive Pb spikes and (iii) depletion in Ta-Nb-Ti, but based on zircon U-Pb-Hf isotope data two groups can be distinguished, each comprising Qtz-monzodiorites and Bt-granites. Bt-granites of group 1, sampled away from the craton are xenocryst-free despite similar or higher Zr-saturation temperatures (∼820 °C) compared to group 2 rocks (∼780 °C), and reveal mostly superchondritic ɛHf (2.1 Ga) up to +3.7, (T DM = 2.8–2.4 Ga). Rocks of group 2, sampled in close vicinity to the KMD, show highly negative ɛHf (2.1 Ga) of −16 to −10 (T DM = 3.5–3.2 Ga) and contains abundant zircon xenocrysts with ages between 3.71 and 2.78 Ga (T DM = 4.2–3.4), overlapping with zircon U-Pb-Hf data obtained from three granodiorites of the KMD, dated at ca. 3.09, 3.08 and 2.87 Ga. This difference indicates that the potassic plutonites resulted from partial melting of different sources within the crust and mantle during the same magmatic event at ca. 2.10–2.08 Ga. The Qtz-monzodiorites derived from metasomatized mantle sources enriched by subducted sediments that in case of group 1 were derived from relatively juvenile Paleoproterozoic island arcs, and in case of group 2 from the Archean KMD. Bt-granites of group 1 might result either from reworking of relatively juvenile Paleoproterozoic crust, or from hybridization between (fractionated) monzodiorites and hot crustal melts, whereas Bt-granites of group 2 can be explained by in situ reworking of Archean TTG crust. Contemporaneous partial melting of the different mantle and crustal domains perhaps happened in response to lithospheric delamination following the collision of the juvenile Paleoproterozoic domain with the KMD. We further propose that this process also caused remelting of residual Au-rich cumulates left in the deep lithosphere by previous arc magmatism or Au-enriched metasomatic veins in lithospheric mantle. [ABSTRACT FROM AUTHOR]

• The Linte massif reveals a protracted magmatism which lasted at least 60 Ma. • Rocks show geochemical affinities of I-type, shoshonitic and metaluminous granitoids. • The 660 and 630 Ma rocks originate from source involving mantle material which could have been mingled or mixed with crustal component while the 600 Ma rocks come from crustal material. • They were formed during the syn- collisional phase of the Pan-African orogeny. The Central African Fold Belt (CAFB) holds a key position in understanding the process and implications of the Pan-African orogeny in central Africa. However, it has not been fully understood as geological information on some vital domains is not yet available. The Linte massif in the Adamawa-Yade, one of the unrepresented terranes, was investigated and its whole rock geochemical, zircon U-Pb geochronology and Hf-O isotope characteristics and whole rock Sr-Nd data are presented and discussed here. The Linte massif is largely constituted of syenite and subordinate monzonite. The zircon U - Pb dating reveals three major ages at 660, 630 and 600 Ma, indicating a protracted magmatism which lasted at least 60 Ma, during the Neoproterozoic. The rocks are shoshonites, I-type and metaluminous. They have high LILEs (Cs, Rb, Ba and Sr), HFSEs (Th and U) and LREE contents. Their Nb/U, Ta/U, Ce/Pb, Th/La and Th/U ratios, δ18O zrn (5.3–7.6‰) and zircon εHf(t) (−14.7 to +3.2), point toward predominantly crustal with or without a mantle component in the sources. The negative εNd(t) values (−8.1 to −10.0), Paleoproterozoic Nd-T DM model ages (ca. 1700–1900 Ma), Hf-T DM2 ages of ca. 1300–2400 Ma of zircon grains in Neoproterozoic rocks underline their derivation from Mesoproterozoic to Paleoproterozoic basement rocks. The lithospheric mantle-generated heat facilitated partial melting in the sources region, as inferred from the shoshonitic affinity and the subduction-related geochemical features (Nb, Ta and Ti depletion). A mainly crustal source with a minor mantle component is inferred for the 660 Ma magmatism and for the 630 Ma rocks emplaced during crustal thickening. On the other hand, the 600 Ma (youngest) magmatic rocks were derived from a crustal source. We infer a subduction-collision setting for the Linte massif during the 660–600 Ma interval. The 630–600 Ma interval of the culmination of collision is consistent with the timing of the main convergence of the Brasiliano Orogeny recorded in South America (∼630–600 Ma), suggesting continuation of tectonic features into the western Gondwana. [ABSTRACT FROM AUTHOR]

Abstract: TIMS and SHRIMP U–Pb zircon geochronology of selected parts of the Puncoviscana Formation suggest its deposition took place mainly during the Early Cambrian, coeval with 540–535Ma calc-alkaline Pampean arc volcanism mainly preserved as tuff beds in the oldest identified parts of this unit. Syn- to post-tectonic plutons constrains the Tilcarian–Pampean orogeny to have occurred between ca. 530Ma and deposition of the unconformably overlying Middle-Upper Cambrian Meson Group. Deposition of the Puncoviscana Formation continued after the onset of the Tilcarian–Pampean orogeny. We propose that the Puncoviscana Formation rocks older than 530Ma were deposited in the arc-trench gap of the west-facing Pampean arc and/or the associated trench, whereas the rocks younger than 530Ma were deposited in a syn-collision foreland basin. The Puncoviscana Formation rocks were progressively assembled into a west-younging accretionary complex, consistent with the style of deformation and low-grade metamorphism. The age of the syn-collision plutons (≤530Ma) suggest the foredeep deposits record the transition from trench to foreland basin, due to arrival of the Arequipa-Antofalla block at the west-facing trench at ca. 530Ma. Our geochronological and Pb-isotope investigations suggest that the Arequipa-Antofalla terrane was a coherent, ribbon-shaped crustal block that also included the western part of the Pampia terrane. A compilation of existing U–Pb zircon studies suggests that the Pampean arc extended along the length of the proto-Andean margin of West Gondwana, represented by the previously amalgamated Amazonia and Rio de La Plata cratons, and probably was initiated during the late Ediacaran after 600Ma. Following earlier workers, we reaffirm that the Arequipa-Antofalla block was originally separating Laurentia and Amazonia in Rodinia. It probably rifted from Laurentia during the Ediacaran between 600 and 570Ma, following an earlier departure of Amazonia (∼650Ma?). The separation of Arequipa-Antofalla from Amazonia and Laurentia opened the Puncoviscana and Iapetus oceans respectively. [Copyright &y& Elsevier]

Abstract: The southern Brasília Orogen is organized in a pile of nappes that records the Neoproterozoic history of the subduction and collision between passive and active margins, respectively belonging to the São Francisco and Paranapanema Plates. The whole pile of allochthons comprises the rootless Andrelândia Nappe System (the upper kyanite-bearing granulite of Três Pontas-Varginha Nappe, the intermediate high-pressure amphibolite-to eclogite facies of Liberdade Nappe and the lower Andrelândia Nappe) that is located below an Andean-type magmatic arc (Socorro-Guaxupé Nappe) and overrides the Lima Duarte Nappe and the Carrancas Nappe System. The tectonic units of the Andrelândia Nappe System seem to be exotic to the São Francisco Plate. The retroeclogite of the Liberdade Nappe yielded a 670 Ma SHRIMP U–Pb age in zircon, that is interpreted as the age of N-MORB-type basic magmatism. Detrital zircon grains of proximal flysh deposits of wackes in the Andrelândia Nappe present similar ages that reflect the crystallization in its source area. Both, rocks present Nd isotopic juvenile signatures with TDM in the range of 1.4 to 1.1 Ga. Rhyacian orthogneisses occur as slices in the Liberdade Nappe and have Nd isotope signature of juvenile source. The building of the collision pile of the whole system of nappes was diachronic and records a continuous outward migration of the orogen. The main structure is a middle crust-level duplex. The propagation of the structure and the metamorphism advanced progressively from the upper to the lower nappes, as is shown by U–Pb monazite ages in the range of 618–595 Ma for the Andrelândia Nappe System and 590–575 Ma for the Carrancas and Lima Duarte nappes. [Copyright &y& Elsevier]

The article discusses the correlation between episodic uranium/lead (U/Pb) age clusters and hafnium (Hf) isotopic ratios in detrital zircons with supercontinent formation, which preserves juvenile and reworked continental crust in collisions. It states that the crust preservation rate increases by capture and a paucity of zircon ages may relate with supercontinent breakup times. This may reportedly imply that a planet with plate tectonics should exhibit episodic ages in continental crust.

The article presents a study to examine the geochronological and isotope geochemical characteristics of layered gabbros of the Khan-Ula Pluton. The study gathered Khan-Ula Pluton, a massif intruded by Late Paleozoic granites composed of layered gabbro, which is located from the southeastern part of Bayan-Khongor ophiolite zone (BKZ), which reconstructs the first stages of Caledonian tectogenesis. The data gathered allows to distinguish the Vendian stage in the development of the structural-material complexes of the BKZ. Decomposition and extraction of Zircon was measured on a mass spectrometer. It concludes that age estimation in the BKZ history contributes to the establishment of the convergence boundary origin and the end of its development within the ophiolite system.

The "Taihua Group" is a collective term for a series of old terranes scattered along the southern margin of the North China Craton. The timing of formation and thermal overprinting of the Taihua Group have long been contentious, and its relationship with the Qinling orogenic belt has been unclear. In this study, new data from integrated in-situ U–Pb dating and Hf isotope analysis of zircons from an amphibolite (from the Xiong’ershan terrane) and a biotite gneiss (from the Lantian-Xiaoqinling terrane) indicate that the Upper Taihua Group formed during the Paleoproterozoic (2.3–2.5 Ga) and thus was originally part of the southern edge of North China Craton, detached during the Mesozoic Qinling orogeny and displaced about 100 km north from its original location. This suggests that the Taihua Group became part of the tectonic terrane associated with the Qinling orogeny and now forms part of the overthrust basement section of the Qinling belt. Before the Qinling orogeny, the Taihua Group was metamorphosed at 2.1 Ga. The initial Hf-isotope compositions of zircons, together with positive εNd(t) values for the whole-rocks, imply that the original magmas were derived from a juvenile source with some assimilation of an Archean crustal component. [ABSTRACT FROM AUTHOR]

Paired U-Pb and Lu-Hf isotopic compositions of individual detrital zircons reveal that Mesoproterozoic lithosphere in the southernmost Appalachian orogen evolved almost continuously from ∼1200 to ∼900 Ma, with a noticeable concentration only at ∼1050 Ma. The evolution of the Lu-Hf system in this crust is characterized by a systematic, linear evolution pattern of 176Hf/177Hf versus age over this interval, which suggests a limited range of mixing ratios between juvenile and older crustal components to create a new Mesoproterozoic lithospheric reservoir. Extrapolation of the Lu-Hf systematics of this reservoir from the Mesoproterozoic to the Paleozoic using typical crustal values shows general coincidence with the lower part of the Hf isotopic array defined by Paleozoic detrital zircons. Because the Paleozoic array extends to both much higher and much lower ϵHf values than are likely to develop from extrapolations of the Mesoproterozoic array, the Paleozoic array is most compatible with an orogen formed largely from the accretion of numerous discrete crustal blocks that may or may not have derived partly from the southern Appalachian Mesoproterozoic lithosphere. These data are most compatible with existing models for Appalachian orogenesis that invoke accretion of exotic terranes, few, if any, of which were true juvenile terranes. [ABSTRACT FROM AUTHOR]

207Pb--206Pb isotope systematic of zircons from quartzofeldspathic gneisses and metasediments belonging to the basement gneiss and Shillong group of the Meghalaya massif has been investigated using an ion microprobe. The zircon age of the gneissic samples revealed the existence of multiple protolith components ranging in antiquity between ~1.5 and 2.6 Ga. The age distribution of the detrital metasedimentary zircons is similar to the range of the gneissic protoliths. Zircons from a charnockite sample yielded ages of 1.0--1.3 Ga, presumably recording the global Grenvillian orogeny. Our data suggest that crust formation in the Meghalaya massif started during the Archaean and experienced a protracted and episodic evolution that has some similarity with the Eastern Ghats Province. [ABSTRACT FROM AUTHOR]

• Structural deformation can be divided into three stages in the gold orefield. • Main tectonic–magmatic–mineralization event occurred during the Jurassic. • Mineralization is coeval with intracontinental orogenesis in the South Qinling. • Ore formation occurred in three stages. The northern Shiquan–Hanyin gold orefield in southern Shaanxi, China, is located within the South Qinling belt–North Dabashan thrust-nappe system. The ore-bearing rocks in the orefield comprise low-grade metamorphic rocks and intensely deformed schist of the lower Silurian Meiziya Formation (S 1 m), and the structural framework includes five ~E–W-trending brittle–ductile shear zones. However, important aspects of the orefield are still uncertain, such as the genetic type of the deposits, the characteristics and development of brittle–ductile shear zones, the division of structural stages, and the ages of structural deformation and mineralization. The present study uses large-scale structure–alteration mapping, zircon U–Pb chronology, and biotite 40Ar–39Ar isotope dating to characterize the structural development and mineralization of the orefield. Three stages of structural deformation are identified; the second stage (S 2) is dominant and included the formation of thrust-nappe ore-controlling brittle–ductile dextral shear zones. A zircon U–Pb age (180.2 ± 3.6 Ma) of a granite dike in a brittle–ductile shear zone and biotite 40Ar–39Ar plateau ages (191.0 ± 1.1, 178.4 ± 0.8, 170.4 ± 0.9, and 168.4 ± 0.9 Ma) of lamprophyre and altered mineralized rocks indicate that the main structural–magmatic–mineralization event occurred during the Early–Middle Jurassic, coeval with intracontinental orogenesis in the South Qinling belt. Ore formation occurred in three stages. In stage 1 (~190 Ma), the upper crust underwent a transition from a compressive to an extensional tectonic environment, and the initial deposition of gold likely occurred. In stage 2 (~180 Ma), under an intracontinental orogenic collapse regime, several brittle–ductile shear zones and a series of extensional strike-slip normal faults developed, making stage 2 the main stage of mineralization. In stage 3 (~170 Ma), the late stage of intracontinental orogeny, the main tectonic style gradually transformed from extensional collapse to tectonic-extrusion-related nappe-fold deformation, inducing late alteration–mineralization that superimposed and enriched the existing mineralization. [ABSTRACT FROM AUTHOR]