A-type Granites Research Articles

Petrogenesis and Tectonic Setting of Early Cretaceous A-Type Granite from the Southern Great Xing’an Range, Northeastern China: Geochronological, Geochemical, and Hf Isotopic Evidence

The southern Great Xing’an Range is located in the eastern Central Asian Orogenic Belt, where voluminous igneous rocks developed during the Late Mesozoic period. The east slope of the southern Great Xing’an Range has been the topic of numerous debates on the level of influence of the Mongol-Okhotsk and the Paleo-Pacific regimes in the Late Mesozoic period. Therefore, this area is a suitable region in which to study the temporal changes in magma sources and tectono-magmatic evolution. In this paper, whole-rock geochemical data, zircon U-Pb geochronology, and zircon Hf isotope studies were carried out on the granitoids in the east slope area of the southern Great Xing’an Range. LA-ICP-MS zircon U-Pb dating revealed the ages of four granitoid samples: 135.0 ± 0.6 Ma, 130.7 ± 1.4 Ma, 130.4 ± 1.0 Ma, and 127.6 ± 0.8 Ma, respectively. The Hf isotope values 176Hf/177Hf = 0.282751–0.283015, εHf (t) = +2.0~+11.5, and T2DM = 583~1442 Ma suggest that the magma was generated by partial melting of Meso- and Neoproterozoic accreted and thickened low crust. The whole-rock geochemical data implied that these granitoids are A-type granite and their formation is closely linked to the subduction of the Paleo-Pacific Ocean plate. These geochemical, isotopic, and geochronological data suggest that the Early Cretaceous magmatism in the east slope area of the southern Great Xing’an Range formed in an extensional back-arc tectonic setting associated with the slab roll-back of the Paleo-Pacific plate subduction.

Nature of the Two Episodes of Paleoproterozoic Magmatism (2495 Ma and 2190 Ma) in the Trans-North China Orogen, North China, with Implications for the Tectonic Evolution

Abstract Understanding the temporal and spatial evolution of the North China Craton (NCC) basement, formed by amalgamation, is a crucial issue in global geosciences. The Huozhou complex is situated at the core of the Trans-North China Orogen (TNCO) in the NCC and comprises a considerable number of Palaeoproterozoic granitic gneisses, providing valuable insights into the tectonic evolution of the TNCO. In this study, comprehensive field geological surveys, petrology, chronology, geochemistry, and Hf isotope analysis were conducted to investigate the genesis and tectonic context of the Xingtangsi and Zhengnangou granitic gneisses and elucidate the TNCO’s tectonic evolution. The Xingtangsi granite gneiss yielded a magmatic zircon age of 2495±34 Ma, implying its Palaeo-proterozoic or Archean origin, as previously suggested. Its protolith was I-type peraluminous granite, primarily generated through the partial melting of pre-existing continental crust materials with a small quantity of mantle-derived magma. The Zhengnangou granitic gneiss’s protolith was A-type granite, and its magmatic zircon age was 2,190 ±11 Ma, indicating its Palaeoproterozoic origin rather than Archean. TDM1(Ma) for the Zhengnangou granitic gneiss ranged from 2,424 to 2,498 Ma, TDM2(Ma) varied from 2563 to 2684 Ma, and the εHf(t) value ranged from 1.3 to 3.3. These results suggest that it was primarily derived from newly formed crustal materials without any mantle-derived addition. Integrating our data with the literature, the ∼2.5 Ga magmatic activity in the Huozhou area may have formed in the tectonic setting of the continental arc, and ∼2.2 Ga A-type granite may have formed in a post-collisional extensional environment.

Geochemical characterizations and rare metal exploration of post-orogenic and anorogenic A-type granites from the Gabal El Dob area, Eastern Desert, Egypt.

Geochemical characterizations and rare metal exploration of post-orogenic and anorogenic A-type granites from the Gabal El Dob area, Eastern Desert, Egypt.

Newly Identified A-type Granite in Western Yangtze Block and Its Geochemistry Characteristics: Evidence for Ridge Subduction beneath the South China Craton

Newly Identified A-type Granite in Western Yangtze Block and Its Geochemistry Characteristics: Evidence for Ridge Subduction beneath the South China Craton

Petrogenesis and rare-metal mineralization of the Ririwai alkaline granitoids, north-central Nigeria: mineralogical and geochemical constraints

ABSTRACT The Ririwai anorogenic alkaline complex harbours extensive rare metal (Nb-Zr-Sn-Zn) mineralization. However, uncertainty still surrounds their origin and magmatic-hydrothermal processes responsible for their rare metal mineralization. The complex is composed of peralkaline arfvedsonite ± albite-bearing granites, mildly peralkaline fayalite-bearing granite porphyries, and weakly peraluminous biotite-bearing granites, all of which show diagnostic A1-type characteristics. Zircon U-Pb dating reveals emplacement ages between 181.4 ± 0.81 and 188.6 ± 7 Ma for the three rock units. Sm-Nd and Pb isotopes (εNd (t) = –0.6 to −5.4, 206Pb/204Pb = 17.68–17.93) constrained the Ririwai A-type granites to represent highly fractionated products of enriched mantle-derived magmas. Mass-balance modelling suggests that magma evolution was fuelled by extensive fractional crystallization of 50 ~ 60 vol.% K-feldspar, 30 ~ 35 vol% fayalite, 5 ~ 10 vol.% amphibole, and ~ 5 vol.% apatite under reduced and water-undersaturated (ΔFMQ = –1.55; logfo2 = –18.63; H2O = <2.0 wt.%) conditions and assimilation of ~ 50 vol.% crust. Whole rock and amphibole compositions revealed an increasing degree of fractionation from the fayalite-bearing granite porphyries through biotite-bearing granites to the arfvedsonite ± albite-bearing granites. This extended fractionation at the late stage of magma differentiation, facilitated by fluorine dissolution and concentration of excess HFSE and REE as alkali-fluorocomplexes in the fluorine-rich silicate melt, allowed the accumulation of economic rare metal pyrochlore and columbite mineralizations in the highly fractionated arfvedsonite± albite- and biotite-bearing granites, respectively. Nonetheless, the metasomatic reaction rim textures around the magmatic pyrochlore, coupled with the M-type lanthanide tetrad effect (TE1,3 >1.10) indicate the subsequent effect of hydrothermal processes. Tectonically, reactivated shear fractures and transcurrent faults following lithospheric stresses in a transtensional regime allowed magma uprising and emplacement of A-type granites in the Ririwai complex.

Early Permian Post-Collision Extensional Setting in the Southern Beishan Orogenic Belt: Evidence from the Zhangfangshan Granodiorite and the Baishantang Bimodal Volcanic Rocks

Outcrops of late Paleozoic magmatic rocks are common in the Southern Beishan Orogenic Belt (SBOB), Southern Central Asian Orogenic Belt (CAOB), which is a key object for the understanding of regional tectonism and defining the final closure time of the Paleo-Asian Ocean (PAO). We present zircon U-Pb chronology and whole-rock geochemistry data for late Paleozoic granodiorites and bimodal volcanic rocks from the Shuangyingshan-Huaniushan unit in the north Huitongshan-Zhangfangshan ophiolitic belt in the SBOB. The Zhangfangshan granodiorites (LA-ICP-MS, Ca. 288 Ma) are A2-type granite enriched in Rb, Th, Pb and LREEs and depleted in Nb, Ta, Ti, Sr, Ba and HREEs. They have varying MgO and TFe2O3 contents with high Mg# (38.56~48.97) values; the Lu/Yb ratios (0.14~0.15) of these granodiorites are similar to mantle-derived magma. A clear plagioclase zoning structure and acicular apatite occur in mineral assemblages derived from magma mixing between mafic and felsic magmas. The Baishantang bimodal volcanic rocks (272 Ma) consist of rhyolite and basaltic andesite. Baishantang rhyolites are A2-type felsic rock enriched in Rb, Th, Pb and LREEs and depleted in Nb, Ta, Ti, Sr, Ba and HREEs, with negative εNd(t) and εHf(t) (−5.2~−4.8 and −2.2~−1.9, respectively). Rhyolites originated from the partial melting of the crust, influenced by mantle material. Basaltic andesites belong to calc-alkaline series and have an enrichment of Rb, Ba, Th, U, Pb and LREEs, are weakly enriched in Zr-Hf, and are depleted in Nb, Ta, Ti and HREEs. The Nd-Hf isotopes of these basaltic andesites are not coupled with negative εNd(t) (−2.8~−0.4) and positive εHf(t) (1.8~5.5) values. These characteristics indicate that they originated from the partial melting of the mantle mixed with sediment-derived melts. In combination with previous studies, our findings show that the early Permian Zhangfangshan granodiorites and Baishantang bimodal volcanic rocks formed in a post-collision extensional setting, and the Huitongshan-Zhangfangshan ocean had been closed before early Permian.

Borehole Nuclear Magnetic Resonance Estimation of Specific Yield in a Fractured Granite Aquifer.

In this study, we introduce a novel field-based method to estimate specific yield (Sy) in fractured, low-porosity granite aquifers using borehole nuclear magnetic resonance (bNMR). This method requires collecting a bNMR survey immediately following a pump test, which dewaters the near-borehole fractures. The residual water content measured from bNMR is interpreted as "bound" and represents the specific retention (Sr) while the water drained by the pump is the Sy. The transverse relaxation cutoff time (T2C) is the length of time that partitions the total porosity measured by bNMR into Sr and Sy. When applying a calibrated T2C, Sy equals the bNMR total porosity minus Sr; thus, a calibrated T2C is required to determine Sy directly from NMR results. Based on laboratory experiments on sandstone cores, the default T2C is 33 ms; however, its applicability to fractured granite aquifers is uncertain. The optimal T2C based on our pumping test is 110 ± 25 ms. Applying this calibrated T2C on a saturated, A-type granite at our field site, we estimate the Sy to be 0.012 ± 0.005 m3 m-3 which is significantly different from the Sy (0.021 ± 0.005 m3 m-3) estimate using the default T2C of 33 ms. This Sy estimate falls within a range determined using traditional hydraulic testing at the same site. Using the conventional T2C (33 ms) for fractured granite leads to an inaccurate Sy; therefore, it is essential to calibrate the bNMR T2C for the local site conditions prior to estimating Sy.

Late Jurassic Haobugao granites from the southern Great Xing’an Range, NE China: Implications for postcollision extension of the Mongol–Okhotsk Ocean

Abstract The Mongolia-Okhotsk tectonic regime had a significant impact on the tectonic evolution of Northeastern (NE) China. However, there is no consensus on the role of this regime in the geological evolution of the Xing’an Massif during the late Mesozoic. This article presents the results of zircon U–Pb geochronology, whole-rock major and trace-element geochemistry, and zircon Hf isotopic compositions for granites in the Haobugao area of the southern Great Xing’an Range, NE China, to determine their petrogenesis, source, and tectonic setting. The zircon U–Pb ages indicate that the granites crystallized at 152.7 ± 0.5 Ma. The granites exhibit high SiO2 (70.75–73.19 wt%) and K2O + Na2O (8.00–8.65 wt%) contents and extremely low MgO (0.40–0.59 wt%) and TiO2 (0.24–0.33 wt%) contents. They belong to the metaluminous, high-K calc-alkaline, and ferroan series, with mostly right-inclined REE curves, flat heavy rare earth element patterns, high 10,000 Ga/Al ratios, and intensely negative Eu anomalies. The Zr/Hf ratios are 24.2–27.7, Nb/Ta ratios are 6.4–8.9, and Y/NbN ratios are &gt;1.2. These characteristics suggest an A2-type granite affinity. The zircon εHf values of the rocks range from +5.62 to +9.12, corresponding to T DM2 values of 621–906 Ma, indicating that juvenile materials in the Neoproterozoic may be a source of these granites. Geochemically, these Late Jurassic A2-type granites are similar to those from post-collision extension settings. The primary magma was likely derived from the partial melting of a delaminated region of the lower crust.

Origin of Silurian granite in the Baiganhu field, Eastern Kulun Terrane, NW China: Implications for the tectonic setting of Sn-W mineralization

The Baiganhu area in the Eastern Kunlun Terrane on the northern margin of the Tibetan Plateau contains world-class Sn-W deposits in close association with monzogranite. However, the origin of granite and the tectonic setting for the Sn-W mineralization have not been well constrained. Here we present the petrological and geochemical data of the granite (431 Ma) associated with the Sn-W mineralization to evaluate the geological-tectonic setting for the mineralization. The monzogranite has high SiO2 contents, ranging from 65.8 to 73.5 wt%, and shows a geochemical affinity with A2-type granites. Relatively high zircon saturation temperatures, ranging between 750 °C and 921 °C, suggest that the parental magmas were hot. The whole-rock εNd (t = 431 Ma) values range from –2.7 to –3.1 with TDM ages between 1810 and 1040 Ma, and zircon εHf (t = 431 Ma) values range from + 0.7 to + 4.1 with TDM ages between 1040 and 900 Ma. The data suggest that the magmas had significant contributions of old rocks. The granitic rocks intruded into quartz-muscovite schist of the Proterozoic Xiaomiao Complex, which underlies the vast area. Zircon grains in the schist are magmatic in origin based on sharp oscillatory zoning and high Th/U ratios (>0.2). The 207Pb-206Pb zircon ages (n = 25) of the schist range from 1898 ± 2 to 1700 ± 6 Ma, suggesting that the zircon grains originate from a Paleoproterozoic magmatic belt. Such ancient rocks, either as lower crustal component or subcontinental lithospheric mantle, contributed ∼ 30 % to the parental magmas. We conclude that post-collisional extension within the Eastern Kunlun Terrane was accompanied by upwelling and adiabatic melting of the asthenospheric mantle which induced partial melting of subcontinental lithospheric mantle and lower crustal rocks and formed granitic magmas. Aqueous fluids separated from the granitic magma which preferentially incorporate W and Sn contributed to the mineralization in and around the granites.

Petrogenesis of the Mesozoic granitoids from the Yuanlinzi Sn-Cu deposit, Northeast China: Implications for Cu-rich Sn mineralization

Granite-related hydrothermal Sn deposits are commonly expected to contain little or no Cu because Cu and Sn have markedly different geochemical properties. However, examples of Sn deposits rich in Cu are well-known in many Sn belts worldwide. So far, the magmatic processes of ore-related rocks and genesis of Cu-rich Sn deposits remain controversial. The newly discovered Yuanlinzi Sn-Cu deposit is located in the southern Great Xing’an Range (SGXR), Northeast China. It is a typical Cu-rich Sn deposit in the SGXR. This contribution reports new cassiterite and zircon U-Pb ages, geochemical compositions, and Sr-Nd isotopic data for the granitoids in the Yuanlinzi deposit to decipher the genesis of Cu-rich Sn deposit. Cassiterite U-Pb dating reveals that the Sn mineralization at Yuanlinzi was formed at ∼ 138 Ma. Zircon U-Pb dating of the granitoids yielded two age clusters: Early Triassic (247.6–246.3 Ma) for the granodiorite, and Early Cretaceous (145.3–141.9 Ma) for the granites, including K-feldspar granite (145.3 ± 0.5 Ma), granite porphyry (143.6 ± 0.9 Ma), fine-grained granite (142.8 ± 1.1 Ma) and albite granite (141.9 ± 1.3 Ma). The Early Cretaceous granites have geochemical affinities for A-type granites, for example, A/CNK = 0.98–1.07, high TFeO/(TFeO + MgO) ratios, total alkali (Na2O + K2O), and Ga/Al ratios. The Early Triassic granodiorite have relatively low (87Sr/86Sr)i values of 0.7034–0.7041, whereas the Early Cretaceous granite has slightly variable and higher (87Sr/86Sr)i values, varying from 0.7020 to 0.7065. The Early Triassic granodiorite and Early Cretaceous granites have similar bulk-rock εNd (t) values and TDM2 ages, ranging from + 1.89 to + 3.53 and 732 to 845 Ma, respectively. The geochemical data and Sr-Nd isotopes indicate that the Early Cretaceous granites were derived from partial melting of the juvenile middle-upper crust. This study further suggests that the 145.3–141.9 Ma granites are associated with back-arc extension environment during the low-angle subduction of Paleo-Pacific plate. In addition, the whole-rock and zircon compositions show that the Cu-Sn magma is characterized by relatively oxidized and less evolved features compared to the Cu-poor Sn deposits in the region. The rapid increase of oxygen fugacity of the latest episode of the Early Cretaceous magma is supposed to have initiated by the injection of mafic magma, which supported the Cu source for the deposit. Our studies suggest that the Cu-bearing mafic magma/fluid injection plays a key role on the formation of Cu-rich Sn deposit.

Ocean–Continent Conversion in Beishan Orogenic Belt: Evidence from Geochemical and Zircon U-Pb-Hf Isotopic Data of Luotuoquan A-Type Granite

Devonian magmatism is one of the most important tectonothermal events in the Central Asian Orogenic Belt (CAOB). However, little is known regarding the petrogenesis and geodynamic setting of the widely distributed Devonian granitoids in the eastern Southern Beishan Orogenic Belt (SBOB). Early-Devonian granitic magmatism has been recognized from the Luotuoquan area, and the granites were emplaced between 404.9 Ma and 399.4 Ma according to LA-ICPMS zircon U–Pb dating. Geochemically, the granites exhibit high SiO2 and Al2O3 contents and are enriched in light rare earth elements as well as Rb, Th, Nd, Zr, and Hf, while being depleted in heavy rare earth elements and Ba, U, Sr, and Ti, with distinct rare earth element fractionation and pronounced negative Eu anomalies. According to the comprehensive analysis, they closely resemble the features typically associated with A-type granites. The zircons εHf(t) values are within the range of +0.90–+5.19 (averaged 3.23) for the monzogranite and syenogranite, whereas their TDM2 values fall between 1.05 and 1.34 Ga, suggesting that the magma source of the monzogranite–syenogranite originated from the partial melting of the Mesoproterozoic crust dominated by metagreywackes. Furthermore, the monzogranite and syenogranite exhibit high temperatures (average 782 °C), thin crustal thickness (average 30 km), and A-type characteristics, suggesting their formation in post-collision extensional settings. We propose the closure of the Beishan Ocean occurred before the early Devonian, followed by a transition in the Southern Beishan Orogenic Belt from a compressional to an extensional setting.

Mid-Mesoproterozoic (ca. 1.37 Ga) anorogenic magmatism in the Dabie orogen, northern Yangtze Craton: Response to the breakup of Columbia

It is evident that the Yangtze Craton was involved in the formation and breakup of the Columbia supercontinent. However, due to the scarcity of Mesoproterozoic geological records and reliable paleomagnetic data, little is known about the timing, paleogeographic position, and geological processes of the Yangtze Craton. We conducted detailed geological mapping, petrographic, geochemical, and in situ zircon U-Pb and Lu-Hf isotopic investigations on newly recognized Mesoproterozoic quartz syenite and monzogranite in the Dabie orogen, northern Yangtze Craton. The results show that the quartz syenite and the monzogranite were emplaced at 1369 ± 12 Ma and 1372 ± 5 Ma, respectively. Both rocks are high in total alkali (K2O + Na2O) content and FeOt/(FeOt + MgO), with elevated diagnostic 10,000*Ga/Al ratios and Zr + Nb + Ce + Y concentrations, and enrichment in light rare earth elements. They are also depleted in heavy rare earth elements with significant negative Eu anomalies but remarkably low Sr, Cr, and Ni contents. These compositions define affinity to A1-type granite. In addition, the quartz syenite displays variable zircon Hf and homogeneous whole-rock Nd isotopic compositions with positive εHf(t) values of +0.7 to +5.7 (average +2.4) and εNd(t) values of −0.1 to +2.5 (average +1.0). In contrast, the monzogranite has homogeneous zircon Hf and whole-rock Nd isotopic compositions with negative εHf(t) values of −5.7 to −2.6 (average −4.8) and εNd(t) values of −3.5 to −1.5 (average −2.2). We propose that the quartz syenite was likely generated by the partial melting of juvenile, crust-derived melt with involvement of minor mantle-derived material, while the monzogranite was likely derived from the partial melting of ancient crust in an extensional tectonic regime (e.g., continental rift). Based on the newly recognized ca. 1.37 Ga granitic magmatism and previously reported magmatic events, we argue that the mid-Mesoproterozoic (ca. 1.37 Ga) magmatism in the Yangtze Craton occurred in response to the breakup of Columbia, and represents the separation of the Yangtze Craton from Columbia. Furthermore, according to comparable magmatic and sedimentary events, we propose that the Yangtze Craton, along with central Hainan Island, may have been linked to northwestern Laurentia, southwestern Siberia, and northeastern Australia during 1.6−1.4 Ga.

Petrogenesis of the Eocene Highly Fractionated Granite Porphyry with REE Tetrad Effect: An Example from Western Yunnan, Southeastern Tibetan Plateau

Highly fractionated granites are widely distributed in the crust and provide unique windows into magmatic evolution. This study reports petrography, zircon U–Pb ages, trace elemental, and Hf isotopic, as well as whole-rock elemental and Nd isotopic data of highly fractionated granite porphyries from the Shiguanshan area in western Yunnan, southeastern Tibet. The granite porphyries were formed at 34.0 ± 0.3 Ma in a post-collisional setting. They are strongly peraluminous (A/CNK = 1.95–2.80), have high SiO2 content (SiO2 = 78.16–79.13 wt.%) and zircon saturation temperatures (803–829 °C, average 819 °C), and low MgO, with pronounced enrichment in Pb, U, Th, and Rb, and depletion in Ti, Eu, P, Sr, and Ba, and belong to highly fractionated A-type granites. These rocks define linear trends on Harker diagrams and display similar enriched whole-rock Nd isotopic (εNd(t) = −12.8 to −12.3) and zircon Hf isotopic (εHf(t) = −10.4 to −8.8) compositions compared to the published data of coeval mantle-derived syenite porphyries, which can be attributed to fractional crystallization processes. A quantitative model suggests that the Shiguanshan granite porphyries likely formed through the fractionation process of a mineral assemblage consisting of plagioclase, K-feldspar, biotite, and amphibole (in a ratio of 40:30:25:5), with fractionation degrees of 50%–55%. The magmatic textures and zircons, decoupling between the REE tetrad effect and fractionation of twin-elements, along with the modeling result of Rayleigh fractionation, suggest that the REE tetrad effect in the Shiguanshan granite porphyries may be caused by fractionation of accessory minerals. Our data, along with regional observations, propose that the generation of these granite porphyries is possibly related to lithospheric removal following the Indo–Asia collision.

Late Paleoproterozoic collision-related granitic magmatism in the Cuoke Complex, SW China: New evidence for the early evolution of the Yangtze Block

The Paleoproterozoic tectonic evolution of the southwestern Yangtze Block has been ambiguous due to the scarce preservation of geological records, confusing the history of the entire Yangtze Block in the Nuna supercontinent. We here report an integrated study involving petrology, whole-rock geochemistry, zircon U-Pb geochronology and Hf-Nd isotopes of the recently identified late Paleoproterozoic granitoids from the Cuoke Complex in the southwestern Yangtze Block. LA-ICP-MS zircon U-Pb dating reveals three episodes of granitic magmatism at ca. 1.94 Ga, 1.89 Ga, and 1.85 Ga. Geochemically, the ca. 1.94 Ga albite granites (AGs) and ca. 1.89 Ga and 1.85 Ga monzogranites (MGs) exhibit features of I-type granite, while the ca. 1.85 Ga AGs display characteristics of A-type granite. The zircon εHf(t) values range from −13.0 to −8.1 for the 1.94–1.89 Ga granitoids and from −8.9 to −7.2 for the ca. 1.85 Ga granitoids, with two-stage model ages of 3.3–3.1 Ga and ca. 3.0 Ga, respectively, indicative of their derivation from remelting of Mesoarchean crustal materials. The relatively low heavy rare earth elements (HREEs) (e.g., Yb < 1.9 ppm) and Y (<18 ppm) contents, and moderately negative Eu anomalies of the ca. 1.94–1.89 Ga granitiods suggest they may have been produced in a late collisional or earliest post-collisional setting. The ca. 1.85 Ga AGs and MGs were probably formed in a post-collisional setting indicated by their high HREE (e.g., Yb > 1.9 ppm) and Y (>18 ppm) contents and strongly negative Eu anomalies. Combined with available data, we provisionally divided the tectonic evolution of the southwestern Yangtze Block into four stages: 1) ca. 2.01 Ga subduction, 2) ca. 1.97–1.95 Ga metamorphism associated with collision events, 3) ca. 1.94–1.89 Ga late collisional or earliest post-collisional stage, and 4) ca. 1.85 Ga post-collisional extensional stage. The subduction and collision of the southwestern Yangtze Block initiated slightly later than the northern part, but their near-synchronous tectonic process since ca. 1.97 Ga suggest they may have collaged together at that time. The ca. 1.94–1.89 Ga and ca. 1.85 Ga late collisional to post-collisional granitic magmatism likely recorded the convergence of discrete Archean rock provinces of the Yangtze Block during the Nuna supercontinent assembly.

Early Jurassic A-type granitoids in the Xing'an block constrain on the spatial extent of the Paleo-Pacific tectonic regime

Northeast (NE) China underwent complex tectonic processes during the early Mesozoic era, influenced by both the Paleo-Pacific and Mongol-Okhotsk tectonic regimes. However, the dominant factor responsible for the early Jurassic magmatism in the Xing'an block, whether it was the Mongol-Okhotsk or the Paleo-Pacific tectonic regime, remains uncertain. This study aims to investigate the geochemical characteristics, petrogenesis, and geodynamic implications of the early Jurassic A-type granitoids in Heihe, Xing'an block, in order to shed light on the evolution and spatial extent of the Paleo-Pacific tectonic regime. The Heihe A-type granitoids were formed by partial melting of calc-alkaline meta-andesite/basalt under high-temperature and low-pressure conditions. During the later stages of magma evolution, fractional crystallization of K-feldspar played a significant role. The geochemical characteristics of the Heihe A-type granitoids resemble both A1-type and intraplate granite, similar to the early Jurassic A-type granites in the Songnen block. The Xing'an block, at least its southeastern margin, was mainly overprinted by the subduction of the Paleo-Pacific oceanic plate during the early Jurassic. This is evidenced by the north-south distribution pattern and the decreasing zirconium saturation temperature from east to west of the early Jurassic igneous rocks in the Xing'an block. The occurrence of early Jurassic various types of A-type granitoids and coeval OIB mafic rocks in NE China could be attributed to the back-arc extension and asthenosphere upwelling triggered by the Paleo-Pacific slab rollback.

Petrogenesis of two episodes of Neoarchean TTG gneisses (∼2.72 Ga and 2.56–2.54 Ga) from the Zhongtiao Mountains, North China Craton: Implications for crustal evolution

The petrogenesis of tonalite-trondhjemite-granodiorite (TTG) suites can provide key clues for the formation and evolution of continental crust. Neoarchean TTG gneisses are widely distributed in the Zhongtiao Mountains (ZTM), North China Craton (NCC). In this contribution, to better understand Neoarchean crustal evolution of the NCC, two discrete episodes of TTG gneisses (∼2.72 Ga and ∼2.56–2.54 Ga) from the ZTM are investigated. New results approve that the two episodes of TTG gneisses are all characterized by high SiO2, Na2O contents, (La/Yb)N and Sr/Y values, but low K2O/Na2O ratios. These geochemical features are similar to the Archean TTG suites and Phanerozoic high-SiO2 adakites, suggesting that they were both derived from partial melting of mafic rocks. The characteristics of trace elements (e.g., La/Yb, Sr/Y, Y/Yb, (Ho/Yb)N and Nb/Ta ratios) imply that both of them correspond to MP-TTGs, and garnet-amphibole exist in the residue phase. The ∼2.72 Ga TTGs show high Mg# values (ave. = 51), Cr (4.87–104 ppm) and Ni (6.37–55.7 ppm) contents, and negative Nb, Ta anomalies. Some high Nb/Ta ratios (up to 17.6) imply that rutile might be involved in the residual phase, which should require a higher pressure. Zircons from these rocks yield positive εHf(t) values of +4.0 ∼ +6.8 (ave. = +5.6), with two-stage Hf model ages (TDM2) of ∼2.85–2.70 Ga, indicating a juvenile basaltic crustal source. Hence, we interpret that ∼2.72 Ga TTGs in the ZTM were derived from partial melting of mafic rocks, and more likely related to subduction process. In contrast, the ∼2.56–2.54 Ga TTGs have lower Mg# values (39–54, mostly <45), Cr (6.02–22.8 ppm) and Ni (4.93–15.7 ppm) contents. They exhibit more evolved zircon Hf (average εHf(t) = +3.21) and whole-rock Nd (εNd(t) = +1.87) isotopic compositions, and their TDM2 ages are concentrated at ∼2.85–2.68 Ga. These ∼2.5 Ga TTGs in the ZTM show similar geochemical features with contemporary TTGs in the XQL, DF and EZT of the southern NCC, identical to melts from partial melting of mafic rocks under a thickened lower crust. The ∼2.5 Ga TTGs, A-type granites and mafic rocks in the ZTM jointly indicate a complicated crust-mantle process at different depths related to mantle plume activity during the late Neoarchean. Based on comparison of the spatial-temporal distribution and geochemical features of ∼2.7 Ga and ∼2.5 Ga TTGs in the NCC, we propose that Neoarchean crustal evolution of the ZTM is similar to the whole NCC, which recorded a significant crustal growth event at ∼2.7 Ga, and an important crustal reworking event associated with some juvenile crustal growth at ∼2.5 Ga.

Integration of Whole-Rock Geochemistry and Mineral Chemistry Data for the Petrogenesis of A-Type Ring Complex from Gebel El Bakriyah Area, Egypt

El Bakriyah Ring Complex (BRC) is a prominent Neoproterozoic post-collisional granite suite in the southern part of the Central Eastern Desert of Egypt. The BRC bears critical materials (F, B, Nb, and Ta) in appreciable amounts either in the form of rare-metals dissemination or in the form of fluorite and barite vein mineralization. The complex consists of inner syenogranite and outer alkali feldspar granite that have been emplaced in a Pan-African assemblage made up of granitic country rocks (granodiorite and monzogranite), in addition to post-collisional fresh gabbro as a part of the Arabian-Nubian Shield (ANS) in northeast Africa. Granites of the BRC are characterized by enrichment in silica, alkalis, Rb, Y, Ga, Nb, Ta, Th, and U and depletion in Sr, Ba, and Ti. Geochemical characterization of the BRC indicates that the magma is a crustal melt, which originated from the partial melting of metasedimentary sources. Concentrations of rare-earth elements (REEs) differ in magnitude from the ring complex and its granitic country rocks but they have similar patterns, which are sub-parallel and show LREEs enrichment compared to HREEs. The presence of a negative Eu anomaly in these rocks is related to plagioclase fractionation. The abundance of fluorine (F) in the different granite varieties plays an important role in the existence of a tetrad influence on the behavior of REEs (TE1, 3 = up to 1.15). Geochemical parameters suggest the crystallization of the BRC granite varieties by fractional crystallization and limited assimilation. Mn-columbite and Mn-tantalite are the most abundant rare-metals dissemination in the BRC granite varieties. We present combined field, mineralogical and geochemical data that are in favor of magma originating from a metasedimentary source for the BRC with typical characteristics of A-type granites. Our geodynamic model suggests that the Gebel El Bakriyah area witnessed the Neoproterozoic post-collisional stage of the ANS during its late phase of formation. This stage was characterized by the emplacement of fresh gabbros followed by the syenogranite and alkali-feldspar granite of the BRC into an arc-related assemblage (granodiorite and monzogranite). It is believed that the mantle-derived magma was interplated and then moved upward in the extensional environment to a shallower level in the crust owing to events of lithospheric delamination. This presumably accelerated the processes of partial melting and differentiation of the metasedimentary dominated source (Tonian-Cryogenian) to produce the A-type granites building up the BRC (Ediacaran).

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

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

Diachronous slab-driven Early Cretaceous crustal extension and pulsed magmatic response in southeastern China: Insight from A-type granite and related rocks

The Late Mesozoic magmatic belt in southeastern (SE) China, stretching over 1300 km, resulted from southwestward subduction of the paleo-Pacific plate. Our study focuses on the origin of Early Cretaceous syenite and A-type granite in SE China, utilizing zircon U-Pb and Hf isotopic analyses, bulk-rock compositions, and Nd-Hf isotopic compositions. Findings indicate that ∼ 142 Ma silica-unsaturated syenites in the southwest form through small degrees of partial melting of the metasomatized lithospheric mantle, while ∼ 142 Ma A-type granites originate from partial melting of juvenile felsic rocks. The ∼ 130 Ma A-type granites in the northeast result from mixing of ancient crustal-derived magma and mantle-derived magma. The southwest and northeast regions display distinct magmatic histories, with flare-ups and lulls occurring at different times. These variations suggest diverse extensional and compressional histories. A spatially migrating extensional regime is observed from the southwest (∼147 Ma) to the northeast (∼120 Ma) of SE China. Magmatic flare-ups in the southwest involve reworking juvenile crust, while in the northeast, they modify ancient crust, likely related to paleo-Pacific plate subduction and northeastward slab rollback. Slab subduction rate correlates strongly with observed geological events, indicating diachronous crustal extension, magmatic flare-ups, and lulls during ca. 147–110 Ma due to northeastward slab rollback and changing subduction rate.

Mercury abundance and isotopic composition in granitic rocks: Implications for Hg cycling in the upper continental crust

Mercury (Hg) is a highly volatile metal exhibiting both isotope mass-dependent (MDF, defined as δ202Hg) and mass-independent (MIF, expressed as Δ199Hg) fractionation. Assessing the Hg isotopic composition of the upper continental crust is crucial for the use of this new geochemical tool for petrogenetic tracing, particularly for understanding crust-mantle interaction. Here, we report Hg isotopic compositions of granitic rocks with distinct source affinity (I-, A-, and S-type) and of metasedimentary enclaves from the South China Craton. The results of more than 100 rock samples show large δ202Hg variations of −2.03 to 0.47 ‰ and small Δ199Hg variations of −0.16 to 0.09 ‰. The S-type granites studied here exhibit higher δ202Hg values (−0.58 to 0.00 ‰; n = 57) than their sedimentary protoliths (metasedimentary enclaves; −2.03 to −0.91 ‰; n = 7), suggesting significant Hg-MDF during magmatic processes. The Δ199Hg values of S-type granites (−0.08 to 0.09 ‰) are indistinguishable from their sedimentary protoliths (−0.16 to 0.02 ‰), suggestive of the absence of Hg-MIF during crustal anatexis and subsequent magmatic differentiation. The I- and A-type granites studied have smaller Δ199Hg variations of −0.11 to 0.04 ‰ (n = 28) and −0.07 to 0.04 ‰ (n = 15), respectively, but are within the range of the S-type granites. The compositional range of all granite variants may be explained by the variable intensity of large-scale MASH (melting-assimilation-storage-homogenization) processes. Our new data combined with previously published data of igneous, sedimentary, and metamorphic rocks allow us to estimate that the upper continental crust (UCC) has a Hg abundance of 13.5 ppb and a weighted average δ202Hg of −1.15 ± 1.01 ‰ (2SD), both of which are higher than the corresponding values of the primitive mantle. However, the weighted average Δ199Hg value of the UCC (0.03 ± 0.15 ‰; 2SD) is nondistinguished from the primitive mantle, suggesting no obvious Hg-MIF during the formation and differentiation of the continental crust.