TDM Model Ages Research Articles

Geochronology and Geochemistry of the Granite Xenolith within the Lamprophyre at the Zhenyuan Gold Deposit (Yunnan Province, SW China)

AbstractThe xenoliths in host rocks of hydrothermal gold deposits can generally provide much geochemical information of the deep rocks, which may have an implication for the sources of ore‐forming materials. Geochronology and geochemical characteristics are reported for a granite xenolith, which is enclosed by the lamprophyre in the Zhenyuan gold deposit (Yunnan Province, SW China). This granite xenolith mainly consists of K‐feldspar, quartz, and plagioclase with trace amounts of magnetite, titanite, apatite, zircon, and sulfides. Zircons from the granite xenolith yield a weighted average U‐Pb age of 281.1 ± 1.3 Ma (MSWD = 2.1), which could represent the crystallization age of this granite xenolith. The Ti‐in‐zircon geothermometer and the Mn concentration in apatite calculate that this granite xenolith formed at 685 ± 43°C with the logfO2 values ranging from NNO + 3.7 to NNO + 6.4. The zircons in the granite xenolith have a restricted range of positive ∊Hf(t) values ranging from +9.4 to +10.8, and the corresponding Hf TDM2 model ages range from 588 to 678 Ma. The zircon U‐Pb age and the Hf isotopic compositions indicate this granite xenolith within the lamprophyre is mainly derived from partial melting of juvenile crustal rocks before the completed closure of the Ailaoshan Ocean. The pyrites in the granite xenolith have higher Bi concentrations, and lower As, Sb, and Tl concentrations than the gold‐bearing pyrites of the ores in the Zhenyuan gold deposit. The low Au concentrations of the pyrites together with the ore‐forming age of the Zhenyuan gold deposit (Oligocene) indicate the granite xenolith may have limited contribution to the gold mineralization of the Zhenyuan gold deposit.

Zircon U–Pb geochronology and Sr–Nd–Hf–O isotopic constraints on the relationship between Mo and Pb–Zn mineralization in the Haisugou pluton in the southern Great Xing’an Range, northeast China

The Haisugou pluton and its contact zones with Middle Permian strata contain Cu–Mo and Pb–Zn ore deposits, providing an excellent example to study the relationship between Pb–Zn–Ag and Mo mineralization in the southern Great Xing’an Range (SGXR). Here we present U–Pb zircon ages and Sr–Nd–Hf–O isotope data for biotite monzogranite in the Xiaojingzi Pb–Zn deposit and Mo-bearing biotite monzogranite in the Xiaojingzi Cu–Mo deposit. These rocks yield zircon U–Pb ages of 136.2 ± 1.1 and 135.5 ± 1.3 Ma, respectively. The biotite monzogranites are enriched in SiO2 (average = 68.9 wt%) and Na2O + K2O (average = 7.7 wt%), contain 14.3–15.1 wt% Al2O3 (average = 14.7 wt%), and have A/CNK values of 0.97–1.05, indicating the biotite monzogranites are high-K calc-alkaline granites, and peraluminous. The biotite monzogranites are also characterized by negative Eu anomalies (Eu/Eu* = 0.78–0.45), enrichments in Rb, Th, U, Nd, and Hf, and depletions in Ba, Sr, P, Ti, and Nb. The biotite monzogranites have (87Sr/86Sr)i ratios of 0.70519–0.70457, εNd(t) values of + 0.37 to –0.39, and TDM2 ages of 978–915 Ma. They also have zircon εHf(t) values of 3.6–9.1, TDM2 model ages of 959–608 Ma, and δ18O values of 6.68‰–7.42‰. The Mo and Pb–Zn mineralization around the Haisugou pluton were genetically related to the granitic pluton and occurred simultaneously, forming a porphyry system. Geochemical and Sr–Nd–Hf–O isotope data indicate the Haisugou pluton was probably formed by partial melting of juvenile crust and mixing with mantle-derived components. In the Early Cretaceous, the SGXR was in an extensional setting, which was related to asthenospheric upwelling after the closure of the Mongol–Okhotsk Ocean.

New clues for magma-mixing processes using petrological and geochronological evidence from the Castelo Intrusive Complex, Araçuaí Orogen (SE Brazil)

Bimodal magmatism was recorded during the post-collisional stage that occurred during the Brasiliano/Pan-African cycle in the Araçuaí Orogen (southeastern Brazil) at ∼500 Ma. The Castelo Intrusive Complex (CIC) is a zoned post-collisional pluton in the orogen and is composed of monzogranites, granodiorites, quartz monzodiorites and diorites. CIC (∼100 km2) was emplaced along a regional lineament during the post-collisional stage of the orogeny and cut pre-collisional granitoids and metasedimentary sequences. In this work, a detailed petrographic study associated with data on U–Pb ages and Hf isotopic compositions of zircons from monzogranites, quartz monzodiorites and leucocratic dikes is presented to detail the geochronology, composition and context of CIC emplacement. Macroscale and microscale records show that several CIC lithotypes demonstrate the direct interaction of contemporaneous felsic and mafic magmas. U–Pb age dating of zircons (by laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS)) reveal crystallization ages of 486 ± 6 Ma for quartz monzodiorites and 524 ± 5 Ma to 499 ± 4 Ma for monzogranites. The analyzed leucocratic dike at 426 ± 15 Ma represents a late magmatic pulse. Hafnium isotopic data show variable ƐHf(t) values (from −24.05 to +12.7) and depleted mantle model ages (TDM) of 2.71–0.64 Ga, indicating the involvement of distinctly different mantle and crustal sources. At least two crustal sources with different Hf isotope signatures were distinguished (TDM of 2.6–2.4 Ga and ƐHf(t) of −26 to −22; and TDM of 2.2–1.7 Ga and ƐHf(t) of −17 to −8). These results suggest that the rocks in this study were partially derived from Archean and Paleoproterozoic crust. The isotopic data also show TDM model ages ranging from 1.28 to 0.64 Ga, with highly positive ƐHf(t) values (from +1.6 to +12.7). These data suggest the existence of a mantle reservoir source for magma generation and for heat that induced crustal melting during the post-collisional stage of the Araçuaí Orogen.

Geochemistry and Zircon U–Pb Geochronology of the Zhuxi Granites in the Jingdezhen Area, Jiangxi Province, China: Implications for the Mesozoic Tectonic Development of South China

Mesozoic granitic magmatism in Northeastern Jiangxi, China is of tectonic significance for the evolution of the South China Block. Whole-rock geochemical and zircon U–Pb geochronological and Lu–Hf isotopic data for Mesozoic Zhuxi granites in the Jingdezhen area of Northeastern Jiangxi were presented. The Zhuxi granites are composed of granodiorite, biotite granite, and two-mica granite. Zircon LA–ICP–MS U–Pb isotopic analyses indicated emplacement at 159–147 Ma. The granites are characterized by a strongly peraluminous nature with high A/CNK values (>1.1), high SiO2 (66.09–74.46 wt.%) and K2O (3.50–5.52 wt.%) contents, depletion in Ba, Nb, Ce, Sr, and Ti, moderately negative Eu anomalies (Eu/Eu* = 0.40–0.63), enrichment in LREE, and depletion in HREE ((La/Yb)N > 7.43). The A/CNK > 1.1, widespread aluminum-rich minerals (e.g., muscovite and tourmaline), indicating they are S–type granites and belong to muscovite–bearing peraluminous granites (MPG). The Zhuxi granites exhibited negative εHf(t) values (−9.9 to −3.7) and the TDM2 model ages of 1840–1442 Ma indicated derivation from ancient crustal sources. The magma is possibly caused by the subsequent process of intracontinental subduction. It is inferred that the Mesozoic magmatism in Northeastern Jiangxi was associated with oceanic–continental convergence of the Paleo–Pacific and Eurasian plates as well as the intracontinental subduction of the Yangtze and Cathaysia blocks. The Zhuxi granites highlight the primary role of oceanic–continental convergence and intracontinental subduction in early Yanshanian granitoid magmatism in South China.

Detrital zircon provenance of metasedimentary rocks in the Proterozoic Caiziyuan‐Tongan accretionary complex: Constraints on crustal and tectonic evolution of the Yangtze Block, South China

Detrital zircon U–Pb ages and Lu–Hf isotopes of three metasandstone samples from the recently identified Caiziyuan‐Tongan accretionary complex (CTAC) in the southwestern Yangtze Block are presented. The detrital zircons are characterized by high Th/U ratios, oscillatory zoning, and nonabrasive crystal shapes, implying that these metasandstones in the CTAC were dominantly derived from proximal magmatic sources. The detrital zircon age spectrum shows three prominent intervals of 2.8–2.6 Ga, 2.5–2.2 Ga, and 2.1–1.7 Ga with minor dispersions between 3.8 and 2.9 Ga, matching well with those of the exposed magmatic rocks in the Yangtze Block. Two samples show consistent youngest age peaks at ~1.72 Ga, but the remaining sample has the youngest age peak at ~1.56 Ga, indicative of their differences in depositional ages. The Eoarchean zircons have negative εHf(t) values with Hadean depleted mantle two‐stage (TDM2) model ages, indicating the earliest crustal growth of the Yangtze Block in the Hadean. The Mesoarchean to Neoarchean zircons show both negative and positive εHf(t) values, suggesting a prolonged and complicated crustal reworking and growth process. By contrast, the Paleoproterozoic zircons have dominantly negative εHf(t) values, suggestive of extensive crustal reworking in response to the Nuna supercontinent assembly. Available detrital zircon TDM2 model ages from the southwestern Yangtze Block produce three prominent peaks at ~3.06 Ga, ~2.95 Ga, and ~2.84 Ga, suggesting significant crustal growth pulses in the Mesoarchean. Given that the ~1.38 Ga Caiziyuan SSZ‐type ophiolitic mélange and the complex tectonothermal evolution process, we deduce that the CTAC belt may represent a relict suture zone between micro‐blocks in the Yangtze Block and may have witnessed the Nuna breakup and subsequent Rodinia assembly.

Geochemical and zircon U-Pb-Hf isotopic study of volcanic rocks from the Yaolinghe Group, South Qinling orogenic belt, China: Constraints on the assembly and breakup of Rodinia

The tectonic mechanism responsible for the Neoproterozoic magma generation at the northern margin of the Yangtze craton is crucial to understanding the assembly and breakup of the Rodinia supercontinent. Here, we present a systematic study of the petrology, whole-rock geochemistry and geochronology of mafic and felsic volcanic rocks from the Yaolinghe Group, which outcrops mainly in the Shangnan area (north) and the Wudang area (south) of the South Qinling orogenic belt along the northern margin of Yangtze craton. Basalts from the Shangnan area are tholeiitic and calc-alkaline and indicated an arc environment. They have a LA-ICP-MS zircon U-Pb age of 847 ± 5 Ma with positive εHf(t) values of + 6.93 to + 8.79 and TDM1 model ages of 1130–1053 Ma. The rhyolites from this area exhibit geochemical characteristics similar to S-type granites and have a zircon U-Pb age of 841 ± 7 Ma, with a wide range of εHf(t) values of + 1.02 to −11.40 and TDM2 model ages of 2453–1674 Ma. This is different from the rhyolites from the Wudang area, which reveal geochemical affinities similar to A2-type granites, with a zircon U-Pb age of 788 ± 28 Ma, uniform negative εHf(t) values of −8.75 to −0.15 and TDM2 model ages of 2214–1663 Ma. Both rhyolites were sourced from partial melting of Paleoproterozoic crust with minor input of mantle material, but were formed in an arc setting and a post-collision extension setting, respectively. The 663–644 Ma mafic volcanic rocks from the Wudang area are enriched in Th, U, Nb and Ta, similar to oceanic island basalts and have positive zircon εHf(t) values ranging from + 9.24 to + 4.89 with TDM1 model ages peaking at 1018 Ma. They were derived from partial melting of an asthenospheric mantle source that had been modified by slab-derived melts and erupted during late Neoproterozoic continental rifting. Combining our results with existing data, we suggest that the South Qinling orogenic belt resulted from bidirectional subduction of the South Qinling Ocean between the Douling block and the Yangtze craton at ca. 950–750 Ma, accompanied by the formation of a trench-arc-basin system along the Douling block and an Andean-type continental arc belt at the northern margin of the Yangtze craton. After accretion, the amalgamated Douling block and Yangtze craton were affected by oceanic subduction of the Mirovoi Ocean at ca. 750–680 Ma, and subsequent continental rifting at ca. 680–620 Ma. The model further poses that the Yangtze craton was assembled to the periphery of the Rodinia supercontinent.

Petrogenesis and tectonic implications of Maoniushan monzogranites in the western margin of the Yangtze Block, Southwest China: Constraints from geochemistry, zircon U–Pb geochronology, and Hf–Nd–Sr isotopes

The Neoproterozoic granites along the western margin of the Yangtze Block are crucial for understanding the evolution of the Rodinia supercontinent and crust–mantle interaction. Based on a regional geological survey, this study analyses the zircon U–Pb geochronology, Lu–Hf isotope, whole‐rock Sr–Nd isotopes, and geochemistry of the Maoniushan granites along the western margin of the Yangtze Block and discusses the Neoproterozoic tectonic evolution history of the Mianning–Maoniushan belt. The results show that the Maoniushan granites belong to calc‐alkaline weak peraluminous monzogranite. The granites are enriched in large‐ion lithophile elements (i.e., Rb, Sr, Cs, and Ba) but relatively depleted in high‐field‐ strength elements (i.e., Nb, Ta, U, and Th). The zircon saturation temperature (TZr) ranges from 628 to 766°C, and the weighted average 206Pb/238U ages of zircon range from 771 ± 30 to 759 ± 26 Ma. The εHf(t) values range from −2.0 to +7.2, with TDM2 model ages ranging from 1,797 to 1,208 Ma. The whole‐rock Sr–Nd isotopic data show (87Sr/86Sr)i ratios of 0.7039–0.7093, and the εNd(t) values range from +1.25 to +1.76 with TDM2 model ages ranging from 1,303 to 1,344 Ma. These findings indicate the presence of deep Mesoproterozoic crustal materials in the source area. The Maoniushan monzogranites belong to I‐type granite, which is formed by the partial melting of the basic rocks and pelites in the ancient lower crust due to the metasomatism of fluids from the subducted oceanic crust. The Maoniushan monzogranites may be formed in the process of transformation from regional thickening to thinning under the oceanic crust subduction setting.

Sr-Nd isotope geochemistry and petrogenesis of ca. 2.26–2.25 Ga and ca. 2.08 Ga mafic dyke swarms from the Dharwar craton, India: Insights into their mantle sources and geodynamic implications

Whole-rock and Sr-Nd isotopic data on the N-S to NNE-SSW trending ca. 2.26–2.25 Ga Ippaguda-Dhiburahalli and the N-S, NW-SE to NE-SW trending ca. 2.08 Ga Devarabanda mafic dyke swarms of the Dharwar craton have been studied. The ca. 2.26–2.25 Ga dykes are linear in nature and contain markedly high SiO2 (53.27–55.85 wt%) and Mg# (60–67) with low TiO2 (0.56–0.61 wt%) contents. While the ca. 2.08 Ga dykes are emplaced in a radiating fashion and contain relatively low SiO2 (47.34–52.67 wt%) and Mg# (34–53) with high TiO2 (0.67–2.11 wt%) contents. The multi-element patterns for both the dyke swarms reflect enrichment in the large-ion lithophile elements (LILEs) and depletion in the high-field-strength elements (HFSEs) with prominent negative Nb-Ta and Ti anomalies. Furthermore, samples of the ca. 2.26–2.25 Ga swarm are relatively more enriched than the ca. 2.08 Ga samples, which is supported by the Nd-isotopic signature. εNd(t) values in the ca. 2.26–2.25 Ga samples vary between −4.5 and 2.4, whereas in the ca. 2.08 Ga dykes it varies between −0.6 and 0.2. The parental magmas are derived from a MORB-like depleted mantle source for both the dyke swarms. Moreover, the interaction between primary melt and the metasomatized sub-continental lithospheric mantle (SCLM) is suggested for the ca. 2.26–2.25 Ga swarm, whereas, the ca. 2.08 Ga swarm show imprints of crustal contamination. The trace element modelling suggests that the ca. 2.26–2.25 Ga swarm were derived from a relatively low (≤5%) degree of partial mantle melting as compared to the ca. 2.08 Ga swarm with a high (~10–15%) degree of partial mantle melting. A deeper mantle source is suggested for the ca. 2.26–2.25 Ga swarm (Garnet/Spinel >80/20), whereas the ca. 2.08 Ga swarm were derived from a relatively shallower mantle source (Garnet/Spinel ~40/60–80/20). The TDM model age for the ca. 2.26–2.25 Ga swarm is supportive of the Neoarchean convergence-related growth of the Dharwar craton, possibly created an enriched lithospheric mantle reservoir. Absence of OIB like plume component in the ca. 2.08 Ga swarm defines the plume centre not precisely below the cratonic lithosphere of the Dharwar craton but several hundred kilometers away from the cratonic margin.

An ancient continental crustal source for Mo mineralisation in the eastern Central Asian Orogen: A case study of the Bilugangan Mo deposit

The Bilugangan porphyry Mo deposit is located in the southern Great Xing'an Range, and the Bilugangan area near the Hegenshan-Heihe Fault in the eastern part of the Central Asian Orogen (CAO). The deposit is hosted by a NE-trending, partly concealed, composite granite consisting of highly altered porphyritic granite (G1), porphyritic monzogranite (G2), fine- to medium-grained monzogranite (G3), medium -grained monzogranite (G4), and monzogranitic porphyry dykes (G5). The Mo mineralisation forms hydrothermal stockworks or disseminated sulphides in the G2 and G3 phases and the adjoining hornfels. Magmatic zircons from the intrusions yield 206Pb/238U weighted mean ages of 295 ± 2 Ma for G1, 240 ± 1 Ma for G2, 235 ± 2 Ma for G3, 230 ± 1 Ma for G4, and 100 ± 2 Ma for G5,indicating that multiple magmatic events have been active during the Early Permian to Early Cretaceous emplacement of the Bilugangan Granite. The age of the Mo is constrained between the Middle and Late Triassic and the magma-related hydrothermal activity proceeded in at least two pulses over a period of around 5 Ma. The first pulse has a molybdenite Re-Os weighted mean age of 238 ± 2 Ma, and the second dates at 236 ± 1 Ma. These dates are coeval with those of G2 and G3, indicating a genetic association between them and the mineralisation.The Sr-Nd-Hf isotopic systematics shows that the Bilugangan Granite was probably formed by partial melting of at least two sources. The first source is a dominant Late Mesoproterozoic to Early Carboniferous juvenile lower crust indicated by the whole rock εNd(t) values of −1.9 to 5.1 and zircon εHf(t) values of 3.5 to 14.3 with two-stage depleted mantle Nd (TDM2) and Hf (tDM2) model ages of ca. 1086 to 350 Ma, which is possibly related to the evolution of the Palaeo-Asian Ocean. The second source includes Neoarchaean to Palaeoproterozoic crustal components and a subordinate Mesoproterozoic crustal component. The Neoarchaean to Palaeoproterozoic component is indicated by the presence of ca. 2700 to 2600 Ma xenocrystic zircons, negative εHf(t) values of −16.4 to −10.1 with tDM2 ages of ca. 2300 to 1900 Ma. The Mesoproterozoic component yields εHf(t) values of −4.5 to 1.1 and tDM2 ages of ca. 1600 to 1200 Ma. These data show that pre- Mesoproterozoic substrate is present beneath the southern Great Xing'an Range. Although the post-mineralisation G4 and G5 phases have comparable positive εHf(t) values with the earlier granitic phases, the G2 and G3 phases have a more complex source with distinctly negative εHf(t) values of −16.4 to –1.3, indicating that the older crustal components in the magma’s source are also probable sources for the Mo mineralisation.

Granitic rocks from Rwanda: Vital clues to the tectonic evolution of the Karagwe–Ankole Belt

Petrological, geochemical and geochronological studies of granitic rocks from the Karagwe–Ankole Belt (KAB) have helped to establish the tectonic setting of the orogenic belt. Four categories of granitic rocks have been recognized, providing constraints on the geodynamics and evolution of the KAB. Anorogenic (A-type) garnet-biotite granite was emplaced at 1372 ± 5 Ma along deep, weak crustal structures. Its major, trace and rare earth element composition, TDM model age of 2.33–1.96 Ga, high initial 87Sr/86Sr (0.71193–0.72159) and negative ƐNd (−1.9 to −4.0), indicates derivation from a much older mafic source, probably originated from lower-crustal granulitic residue or lower continental lithospheric mantle contaminated by crustal material. Ascent of the small-batch A-type magma was aided by a localized crustal-scale zone of weakness within Archaean crust underlying both the Eastern and Western Domains of the KAB. The rest of the granites have S-type orogenic characteristics. Large batholiths of two-mica granite emplaced at 1369 ± 5 Ma have major, trace and rare earth element compositions, high initial 87Sr/86Sr (0.70808–0.71795), strongly negative ƐNd (−9.4 to −10.1) and a TDM model age of 2.82–2.40 Ga, indicative of derivation by partial melting of a pelitic source containing Palaeoproterozoic and Archaean components, possibly with a minor contribution from magma of lower crustal derivation. This magmatism occurred during the amalgamation of the Congo and Tanzania cratons at an early stage of Rodinia formation. Muscovite granite and leucogranite, derived from fluid-fluxed partial melting of metapelites, were emplaced at 1011 ± 18 to 976 ± 11 Ma in a late to post-collisional setting during final Rodinia formation. Their high initial 87Sr/86Sr (0.72893–0.74456) and strongly negative ƐNd (−6.8 to −12.4) indicate a supracrustal source. One younger S-type leucogranite (614 ± 9 Ma) was emplaced in a volcanic-arc setting during the assembly of West Gondwana. The combined available evidence points to tectonic evolution of the Mesoproterozoic KAB during accretion-collisional tectonism.

Late Paleozoic tectonic transition in East Junggar, NW China: Insights from I- and A-type granitic magmatism in the Karamaili region

The closure time of the Karamaili Ocean is the key to understand the accretionary history of the East Junggar at the southern Central Asian Orogenic Belt in the Paleozoic. In this study, we report geochronology, whole-rock elemental and Sr-Nd isotopic data and zircon Lu-Hf isotopic data of four Late Carboniferous to Early Permian I- and A-type granitic plutons in the Karamaili region in East Junggar, NW China. The Carboniferous Hongliuxia gneissic granite and the Hongliugou granodiorite yield zircon 206Pb/238U ages of 324 ± 1 Ma and 306 ± 1 Ma, respectively, and both of them are high-K calc-alkaline and belong to I-type granitoids. These granites show (87Sr/86Sr)i values from 0.7034 to 0.7046, ɛNd(t) values from 4.4 to 6.3, with Nd TDM2 model ages of 559–727 Ma; and ɛHf(t) values from 9.4 to 12.8, with Hf TDM2 model ages of 481–710 Ma. The variable positive Nd-Hf isotopic signature and young TDM2 model ages suggest that the I-type granitoids were derived from partial melting of juvenile crustal source, probably earlier arc intrusion. The Early Permian Daliugou and Mawangmiao plutons have 206Pb/238U ages of 297 ± 1 Ma and 284 ± 2 Ma, respectively, show high-K calc-alkaline to shoshonitic characteristics and belong to A2-type granite. They exhibit (87Sr/86Sr)i values from 0.7040 to 0.7065, ɛNd(t) values from 2.1 to 5.4, with Nd TDM2 model ages of 612–887 Ma; and ɛHf(t) values from 5.2 to 11.5, with Hf TDM2 model ages ranging from 548 Ma to 955 Ma, and the Nd-Hf isotope data also suggest that they were derived from juvenile crustal source. Mafic microgranular enclaves in the Daliugou pluton yield zircon 206Pb/238U age of 299 ± 2 Ma, and show similar geochemistry affinity with the granite host. The presence of enclaves and reverse zoning K-feldspars indicate that the magma mixing may have played an important role in the evolution of the Daliugou pluton. In this study, only the Hongliuxia gneissic granite was deformed, and a Nd-Hf isotopic transition occurred at ~300 Ma. Furthermore, the Late Carboniferous I-type granitoids from the Hongliuxia and the Hongliugou plutons show an arc affinity, and the Early Permian A-type granitoids from the Mawangmiao and the Daliugou plutons show post-collisional affinity. These lines of evidence enable us to argue that the Karamaili Ocean probably closed at a period between 324 Ma and 306 Ma. The post-collisional Early Permian magmatism in East Junggar was independent from the Tarim mantle plume.

Permian-triassic magmatic and thermal events in the Dunhuang orogenic belt: implications for subduction records of the Paleo-Asian Ocean

ABSTRACT The final subduction and suture of the Paleo-Asia Ocean (PAO) are controversial, and the key to this question is to locate the latest subduction/final suture of the accretionary type orogenic belt. Previous studies mainly focused on the Tianshan, Beishan, Alxa, and Solonker Orogens for this issue. As a Phanerozoic orogenic belt located further south of the Beishan-Alxa Tectonic Belts, the Dunhuang Orogenic Belt (DOB) is becoming a research hotspot for revealing the evolutionary history of the southernmost Central Asia Orogenic Belt (CAOB). The youngest subduction-related arc magmatism is pivotal for constraining the lower limit of subduction of a lost ocean. This study presents integrated investigations of field observation, whole-rock geochemistry, and geochronology, targeting diabase dykes, intermediate-acid magmatic rocks, and garnet-bearing metabasite samples in the middle part of the DOB. LA-ICP-MS U-Pb dating of zircon yielded episodic magmatism of ca. 274–273 Ma for Xiaohongshan granite and Dongbatu syenogranite, ca. 250 Ma for Keziletage syenite, ca. 243–239 Ma for diabase and granitic dykes in the Kalatashitage area and Mogutai syenogranite, and maximum deposition age of ca. 262 Ma for pyroclastic rock in the Kalatashitage area. Most of those Permian-Triassic magmatic rocks show continental arc-related geochemical features during the subduction stage. The negative εHf(t) values and ancient TDM2 model ages of zircon indicate they were mainly derived from the partial melting of ancient crustal materials. The hornblende 40Ar/39Ar ages of ca. 258–250 Ma of the garnet-bearing metabasite samples also reflect a high heat flow setting during this period possibly triggered by arc activities. These Permian-Triassic magmatic and thermal records in the DOB are similar to contemporaneous records in surrounding South Tianshan-Alxa-Beishan orogens. We suggest that the final subduction of the PAO in the DOB possibly at least lasted to the Middle Triassic.

Multiple sources and multi-stage emplacement of the Esperança Granitic Complex and its relationship with the Patos – Campina Grande shear zone system, Borborema Province - NE Brazil

Expressive granitic magmatism and a complex system of transcurrent shear zones are the main features associated with the Ediacaran evolution of the Borborema Province (northeastern Brazil). Their petrogenesis and relationships with tectonic structures can provide important insights into lithospheric processes during the collisional to post-collisional stages of the Brasiliano Orogeny. The Esperança Complex is a NE-trending elongated granitic batholith with ca. 650 km2 comprising five plutons emplaced between the Patos and Campina Grande dextral shear zones in the central–eastern part of the Borborema Province. An integrated study of the complex was carried out using UPb zircon SHRIMP and LA-ICPMS geochronology, mineral and whole-rock geochemistry, and NdHf isotope geochemistry (whole-rock and zircon). The plutons are metaluminous to slightly peraluminous with geochemical and isotopic signature reflecting different sources. The Remigio and Areial plutons have Paleoproterozoic to Neoarchean Nd and Hf TDM model ages and strong negative εNd(t) (−15.29 to −16.71) and εHf (−12.20 to −21.03) values. Their geochemistry is compatible with derivation through partial melting of mafic to intermediate metaigneous sources like the Paleoproterozoic basement (Areial pluton) and metasedimentary sources (Remígio pluton). The Puxinanã, Serrote da Cobra and Pocinhos plutons show higher ɛNd (−5.90 to −7.35) and ɛHf (−2.83 to −6.91) values, and Statherian to Calymmian Nd and Hf TDM model ages, ranging from 1.4 to 1.7 Ga and from 1.6 to 1.8 Ga, respectively. They have geochemical affinity with A-type ferroan granites. The geochemical and isotopic signature are similar to those of Tonian orthogneiss that constitute part of the plutons' host rocks, suggesting derivation from Tonian crustal sources. Evidence of magma mixing and the presence of inherited zircon grains with ages like those of metasedimentary host rocks suggest contribution of the lithospheric mantle and sedimentary sources in different proportions in their petrogenesis. The reported data are compatible with building of the Esperança Complex by multiple intrusive events. The Pocinhos and Serrote da Cobra plutons are the oldest (~600 Ma) and their genesis is probably associated with heat input resulting from crustal thickening at the end of a long contractional period (ca. 630–600 Ma). The genesis of the Puxinanã and Areial plutons (~585 to 565 Ma) involved interactions of crustal and mantle mafic melts, with magma transport and emplacement controlled by the Campina Grande shear zone at the beginning of the transcurrent regime. The Remígio pluton is the youngest intrusion (~565 Ma) and its genesis can be related to a high geothermal gradient resulting from emplacement of the older plutons, possibly enhanced by strain heating related to displacement along the Patos shear zone.

Paleoproterozoic tectonic evolution of the Yangtze Craton: Evidence from magmatism and sedimentation in the Susong area, South China

Paleoproterozoic and Archean rocks in the poorly exposed Yangtze Craton provide a unique proxy for understanding early cratonic evolution. In this study, we report the newly discovered Paleoproterozoic granitoids, mafic dikes, and metasedimentary rocks in the Susong area near the northern margin of the Yangtze Craton. The zircon U–Pb analysis results of the Luohanjian granite (hereinafter referred to as LHJ-granite) and mafic dikes yielded 207Pb/206Pb ages of 2020–2002 Ma and 1837 ± 21 Ma, respectively. Metasedimentary strata that were intruded by the mafic dikes yielded detrital zircon 207Pb/206Pb ages of 2.55–2.32 Ga and 2.15–1.93 Ga, suggesting a depositional age of ∼ 1.90–1.85 Ga for the metasedimentary rock. The whole-rock εNd(t) and zircon εHf(t) values of the LHJ-granite were negative and ranged from − 10.4 to − 9.4 and − 11.4 to − 9.0, with corresponding TDM2 model ages of 3.3–3.2 Ga and ∼ 3.1 Ga, respectively. This implies that the granitic magma originated from the reworking of ancient pre-existing crustal components. The granitoids were weakly peraluminous (A/CNK = 1.00–1.18) with high SiO2 concentrations of 71.98–76.00 wt%, LREE enrichment, high (La/Yb)N values of 26.55–100.49, and moderately negative Eu anomalies, characterized by the enrichment of Rb, Ba, Th, U, and Nd, and the relative depletion of Nb, Ta, Sr, P, and Ti. These granite samples exhibited a negative correlation between SiO2 and P2O5 and low Rb/Ba (0.15–0.33) and Rb/Sr (0.30–1.55) ratios. All these features indicate that the LHJ-granite is most likely belongs to I-type granite, which may have formed via the reworking of the TTG gneiss during subduction–collisional events. In combination with the mafic dikes and metasedimentary strata, our study proposes a mid–late Paleoproterozoic geological transition from a compressional to an extensional setting, indicating a tectonic shift from a collision orogeny (2.0 Ga) to a post-collision extensional environment (1.84 Ga) in the Susong region.

Post-collisional, high-Ba-Sr Teixeira Batholith granites: Evidence for recycling of Paleoproterozoic crust in the Alto Pajeú domain, Borborema Province – NE-Brazil

Late-Neoproterozoic granitoids of diversified nature and ages (640–525 Ma) are widely distributed in the Borborema Province and their petrogenesis can provide important insights about the Brasiliano/Pan-African Orogeny (ca. 650–550 Ma). The Neoproterozoic Teixeira Batholith comprises an ENE – elongated intrusion of c. 800 km2 emplaced in metasedimentary rocks and orthogneisses in central Borborema Province immediately south of the Patos Shear Zone. Textures and modal mineral percentage allow to divide the batholith into six petrographic facies, ranging in composition from monzogranite to quartz syenite, containing less than 10% of modal mafic mineral phases (amphibole ± clinopyroxene and biotite). Titanite, epidote, apatite, zircon and Fe-Ti oxide are the main accessory phases. LA-ICP-MS U-Pb zircon data from four facies yield ages ranging from 585 to 600 Ma, like other Neoproterozoic pre- to early-transcurrent intrusions related to the Brasiliano orogeny. The granitoids belong to the magnetite series, are metaluminous and have high-K calk-alkaline to shoshonitic affinities. Major and trace elements data are typical of granites originating from high barium‑strontium (HiBaSr) magmas, i.e., high Ba (1825–7370 ppm), Sr (1110–2530 ppm), low Rb (56–137 ppm), Th (1.6–15.8 ppm), Nb (6.2–34.7 ppm), Y (3.7–33.2 ppm) and HREE contents (Gd-Lu: 3.64–24.36 ppm). The granitoids have negative ƐNd(590Ma) (−13.68 to −16.04) and ƐHf(t) (−16.27 to −20.80) values, and Paleoproterozoic Nd and Hf TDM model ages ranging from 2.08 to 2.23 and 2.3 to 2.6, respectively, similar to the ages of basement rocks of the Central subprovince. The isotopic data and trace elements signature suggest magma generation by partial melting of Paleoproterozoic mafic/intermediate lower crust, leaving a plagioclase-free and garnet and/or amphibole-bearing residue. Partial melting occurred after a long period of contractional tectonics, and predated development of the Patos shear zone by ca. 20 Ma.

A major neoproterozoic crustal boundary in the Borborema province of ne Brazil

ABSTRACT The Borborema Province represents a collage of tectonic blocks amalgamated to Gondwana during the Neoproterozoic. The Pernambuco -Alagoas Domain constitutes the southern part of the Borborema Province, which comprises three subdomains (Garanhuns, Água Branca, and Palmares) separated by shear zones. Investigation of an area across the boundary between the Palmares and Garanhuns subdomains revealed contrasting aerogeophysical fabrics and geological setting with igneous and metasedimentary rocks of Paleoproterozoic and Neoproterozoic ages. The Palmares shear zone divides the studied area into 2 subdomains: 1) Palmares to the south and 2) Garanhuns to the north. Nd isotopic studies show contrasting crustal signatures between the Garanhuns and Palmares subdomains, with Nd TDM model ages ranging from 1.8 to 2.70 Ga for the Garanhuns subdomain and from 0.90 to 1.60 for the Palmares subdomain. The Palmares shear zone constitutes a major crustal boundary, and in pre drift reconstructions may have continuity in Africa as the Tcholliré-Banyo shear zone. The data suggest that the area evolved during two distinct orogenies: 1) Rhyacian-Orosirian (2095 Ma to 1987 Ma), which involved mainly the reworking of Archaean crust, and 2) Cryogenian-Ediacaran (630 Ma to 585 Ma), the so-called Brasiliano-Pan African Orogeny. Our findings, i.e. contrasting isotopic subdomains separated by an important shear zone, suggest that Brasiliano Orogeny, at least in the Pernambuco Alagoas domain, had an accretionary nature.

Rhyacian-Orosirian tectonic history of the Juiz de Fora Complex: Evidence for an Archean crustal reservoir within an island-arc system

The southern São Francisco Paleocontinent (SFP) comprises Archean nuclei and Paleoproterozoic complexes encompassing magmatic arcs juxtaposed during a Rhyacian to Orosirian orogenic event. The Juiz de Fora Complex (JFC) represents an imbricated thrust system that comprises orthogranulites with a wide compositional range formed in an intra-oceanic setting during the Siderian to the Orosirian and later accreted to the southeastern margin of the SFP. Here we report new petrological, geochemical, whole-rock Nd and Sr data, as well as zircon U–Pb ages from felsic and mafic orthogranulites from the JFC. The new data is combined with a regional compilation that enables an evaluation of the interaction between magmatism and orogenetic episodes in the context of the consolidation of São Francisco Paleocontinent during the Rhyacian–Orosirian. Pre collisional Island Arc tholeiites (IAT), Tonalites-Trondhjemites-Granodiorites (TTGs) and sanukitoid magmatism occurred from 2200 Ma to 2085 Ma. This was followed by post-collisional magmatism, which is represented by hybrid granitoids coeval with the emplacement of E-MORB basic rocks. Crustal signatures for the Rhyacian to Orosirian evolution are highlighted by the dominance of negative εNd(t) associated with Meso- to Neoarchean Nd TDM model ages as well as inherited zircon grains from the hybrid granitoids. The JFC is extensively highlighted in the literature as a primitive intra-oceanic arc, but here we propose the reworking or recycling of ancient crustal segments within the mature arc stage of the JFC, suggesting a Mesoarchean crustal source involved in the JFC evolution.

Evidence for Neoproterozoic terrane accretion in the central Borborema Province, West Gondwana deduced by isotopic and geophysical data compilation

ABSTRACT The Borborema Province in NE Brazil is part of a large Neoproterozoic orogenic system related to the assembly of West Gondwana. Its evolution is contentious, due to the superposition of events that overprinted former records. We present a compilation of geological, isotopic (U-Pb detrital zircon and whole-rock Sm-Nd), and geophysical data that support a terrane accretion model for the Transversal subprovince (central Borborema Province). Bounded by thrust- and strike-slip shear zones of regional extent, the terranes vary in nature and age, and magmatic-arc related rocks, retro-eclogites, and dismembered ophiolites provide evidence of accretion. In addition, detrital zircon compilation suggests variable sources, including Palaeoproterozoic detritus related to the Rio Capibaribe and Alto Moxotó terranes and Neoproterozoic sources attributed to the Alto Pajeú and Piancó-Alto Brígida blocks. Accordingly, Archaean and Palaeoproterozoic Nd TDM model ages are concentrated within the Alto Moxotó and Rio Capibaribe terranes, whereas early- to late Mesoproterozoic isotopic sources dominate in the Alto Pajeú and Piancó-Alto Brígida. A compilation of robust geophysical data shows contrasts in magnetic, gamma-spectrometric, and gravity signatures between the terranes, whereas modelled depths and density values are variable, coinciding with the proposed terrane boundaries. Our analysis suggests that now eroded oceanic lithospheric branches existed within the Transversal subprovince, later converted into dry suture zones. Terrane accretion is a plausible mechanism to rearrange the crustal pieces of West Gondwana, including those of the Borborema Province, and should be considered in other orogenic belts of South America.

A plume - mantle interaction model for the petrogenesis of komatiite - komatiitic basalt - basalt - basaltic andesite volcanism from the Paleoarchean (3.57–3.31 Ga) Iron Ore Group greenstone belts, Singhbhum craton, India: Constraints from trace element geochemistry and Sm[sbnd]Nd geochronology

The Paleoarchean Singhbhum craton greenstone belts comprise basalt, interbedded minor komatiite (both alumina depleted and undepleted, ADK and AUK, respectively), komatiitc basalt, dacite and chert grouped as (~3.57 Ga) southern Iron Ore Group (S-IOG, Daitari samples) and ~ 3.31 Ga eastern Iron Ore Group (E-IOG, Dabanki samples). Considering the importance of metabasalt in formation of TTG batholiths, modeling their petrogenesis from mantle sources and SmNd geochronology was conducted. The rocks resemble Archean non-arc greenstone basalt (Nb/Th = 3.61–10.3) with tholeiitic affinity. The ADK of S-IOG was modeled by 37% partial melting of garnet lherzolite, komatiitic basalt was derived from ADK magma by ~25% assimilation fractional crystallization (AFC) and ~ 16% AFC of this magma formed tholeiitic basalt. Derived from depleted parental magmas they yield an isochron age of 3573 ± 63 Ma (2SD), Ndi = 0.50810 ± 0.00008, MSWD = 0.59 (n = 10) and εNd (3573 Ma) = +2.03 ± 0.03. Dacite formation, modeled by mixing of melts between Eoarchean felsic crust and metabasalt, yielded an isochron age of 3507 ± 180 Ma (2SD), Ndi = 0.50800 ± 0.00015, MSWD = 0.15 (n = 11), εNd (3507 Ma) = −1.46 ± 1.71; ca. 3.8–3.9 Ga Nd TDM model ages indicate vestiges of Eoarchean crust. The AUK of E-IOG was modeled by ~45% partial melting and ADK by ~33% melting of garnet lherzolite mantle. About 32% AFC of primary ADK magma formed the komatiitic basalt that evolved to tholeiitc basalt magma (~24%) which on ~15% AFC evolved to basaltic andesite - andesite magma. Derived from depleted parental magmas, the E-IOG rocks yielded an isochron age of 3313 ± 110 Ma (2SD), Ndi = 0.50847 ± 0.00013, MSWD = 0.06 (n = 10), εNd (3313 Ma) = +2.62 ± 0.28. Petrogenesis of Paleoarchean greenstone non-arc basaltic volcanism and associated komatiite can be best explained by plume-mantle interaction and partial melting of ambient mantle followed by assimilation fractional crystallization of parental magmas, and does not preclude recycling of pre-existing crust.

Combined use of Sm–Nd isotopes and lithogeochemistry in the sedimentary provenance of the southern Ediacaran-Cambrian Bambuí foreland basin system, Brazil

Sedimentary provenance analysis based on lithogeochemistry and isotope data has been extensively applied in the investigation of ancient sedimentary successions. This approach contributes to understand the tectonic setting in which these strata were deposited and to recognize major provenance patterns in time and space. The Ediacaran to Cambrian Bambuí Group is exposed in the São Francisco craton (SE Brazil) and represents the sedimentary record of a foreland basin system developed during the assembly of the West Gondwana. Different lines of evidence indicate that this basin system evolved into a confined setting, due to the overloads imposed on the western and eastern margins of the São Francisco paleoplate by the diachronic Brasília and Araçuaí orogenic systems, respectively. New whole-rock lithogeochemistry and Sm–Nd isotopic data were applied to evaluate the overall sedimentary provenance patterns of the Bambuí strata exposed in the southern portion of the São Francisco craton (i.e., within the Sete Lagoas basement high) and to identify its possible sources. Coupled (La/Yb)n and Th/Sc ratios with 147Sm/144Nd and εNd isotopes allowed the recognition of three contrasting source patterns associated with different 2nd order sequences. The lower sequence comprises carbonate ramp deposits and shows highly heterogeneous and more negative εNd ranging from −10.5 to −4.5, as well as Th/Sc and (La/Yb)n ratios between 0.6 and 0.7 and 0.54 and 0.76, respectively. The provenance patterns point toward intermediate-dominated and isotopically evolved crustal sources, with mean TDM model ages between 1.5 and 2.0 Ga. The overlying 2nd-order sequence is composed of fine-to medium-grained siliciclastics grading upward into platformal oolitic calcarenites and calcilutites. This succession exhibits homogeneous and less negative εNd(t) values between −6.8 and −5.2, with low Th/Sc (0.6–0.8) and (La/Yb)n (0.60–0.84) ratios. The uppermost Bambuí 2nd-order sequence, marked by greenish siltstones and arkoses grading upward into storm-bedded arkoses and lithic sandstones, shows homogeneous εNd(t) ranging from −8.5 to −6.1, slightly more negative than the underlying successions, and relatively higher Th/Sc and (La/Yb)n ratios ranging from 0.7 to 1.3 and 0.85 to 1.28, respectively. The Sm–Nd isotopic signature of the upper deposits indicates felsic-dominated and more isotopically juvenile crustal sources with TDM model ages of 1.5–1.7 Ga, characteristics compatible with Ediacaran arc-related rocks and post-tectonic granites exposed in the Araçuaí orogen. Our data indicate that the Proterozoic cratonic covers, their correlatives in the surrounding orogens, and magmatic rocks from the Araçuaí orogen acted as major sedimentary sources during the first evolutionary stages of the Bambuí basin-cycle in the Sete Lagoas basement high, which behaved as a forebulge depocenter. During the deposition of the overlying sequences, the Araçuaí orogen rocks became increasingly important in sourcing the Ediacaran- Cambrian foreland system in this depocenter. Besides revealing the major provenance patterns through the evolution of an ancient and partially confined foreland basin system, our data also demonstrates that even minor changes in the Sm–Nd system might be useful as reliable elements on the provenance analysis of sedimentary systems elsewhere.