Late Triassic Granitoids Research Articles

Unraveling the genesis of wolframite mineralization in the West Qinling Belt, China: Evidence from geochronology, geochemistry, and fluid inclusion study

The West Qinling Belt is a pivotal part of the Central China Orogenic Belt renowned for producing abundant Au-polymetallic deposits. Nonetheless, reports of wolframite mineralization within this region were absent. The Xuehuashan deposit is the premier documented quartz-vein type wolframite deposit in West Qinling, which has significant implications of W mineralizing potential in the West Qinling Belt. The ore bodies are predominantly composed of wolframite-quartz veins and/or veinlets which are proximal or within the Late Triassic Baijiazhuang granitoid. To elucidate the age and genesis of the Xuehuashan wolframite mineralization, we presented analyses of U-Pb dating and chemical composition on wolframite, fluid inclusion study, and hydrogen–oxygen isotopes on wolframite and quartz. The Xuehuashan wolframite U-Pb dating yielded an age of 213.0 ± 6.7 Ma, which is consistent with the age of the Baijiazhuang granitoid. The correlation among trace elements and the Y/Ho vs. Zr/Hf diagram suggests trace elements in wolframite were influenced by crystalline chemical factors and the geochemistry of parental ore-forming fluid. Homogeneous texture and stable chemical composition of wolframite, as well δD vs. δ18O isotopes, suggest a single magmatic fluid from the Baijiazhuang granitoid. Fluid inclusions in wolframite and quartz have high homogenization temperatures and varying salinities of 0.4 – 16.4 wt%, suggesting that intense decompression and fluid boiling during fracture open caused the wolframite precipitation. Compared with the Late Triassic granitoids in the Qinling Belt, the Baijiazhuang granitoid shows higher ratios of Rb/Sr and lower ratios of Zr/Hf, K/Rb, Nb/Ta, LREE/HREE, as well as negative Eu anomalies, which are consistent with the W-related highly evolved granitoids but distinct to W-barren granitoids. Hence, this study highlights W mineralization potential in the Qinling belt associated with the highly evolved Late Triassic granitoids.

Magma mixing formed mineralized Middle–Late Triassic granitoids in the Qimantagh Metallogenic Belt, NW China: A case study from the Hutouya skarn deposit

Although a number of petrographic observations and isotopic data suggest that magma mixing is common in the genesis of granitoids, it is still controversial whether mantle-derived magmas are involved in their formation. Zircon Hf and O isotopes can place robust constraints on the origin of granitoids, particularly deciphering the contributions of mantle- versus crust-derived magmas. In this study, we carried out a systematic examination of in-situ zircon Hf–O isotopes, as well as whole-rock major and trace elements, for mineralized Middle–Late Triassic syenogranite and diorite in the Hutouya deposit, NW China. Our results show that the parental magmas for syenegranite and diorite both underwent significant crystal fractionation, and belong to I-type and A-type granitoid magmas, respectively. The Hutouya syenogranite and diorite are very homogeneous in terms of zircon Hf–O isotopes, with εHf(t) and δ18O values ranging from − 3.15 to 1.55 and 5.97 ‰ to 7.77 ‰, respectively. These lines of evidence collectively emphasize that both mantle- and crust-derived magmas contribute to the formation of mineralized granitoids from the Hutouya deposit, although the latter seemingly plays a predominant role compared to the former. Combined with published studies, we suggest that magma mixing may be the key to forming fertile magmas related to the Cu polymetallic mineralization in the Hutouya deposit.

Origin and tectonic setting of middle–late Triassic Lalingzaohuo granitoids in the western East Kunlun Orogen, northern Tibetan Plateau

ABSTRACT Triassic granitoids are widespread in the East Kunlun Orogen (EKO), with Middle Triassic granitoids being dominant and Late Triassic granitoids being subordinate. This paper presents new whole-rock geochemical and Sr – Nd isotope, and zircon U – Pb age and Lu – Hf isotope data for eight granitoids in the Lalingzaohuo area, western EKO, northern Tibetan Plateau. These granitoids yield Middle and Late Triassic ages of 245–239 and 223–220 Ma, respectively. The granitoids from the Lalingzaohuo area have features typical of I-type granites and belong to the high-K calc-alkaline series. They exhibit variable rare earth and trace element patterns, and Sr – Nd – Hf isotopic compositions, indicative of different petrogenetic processes. The Middle Triassic samples have higher ISr values of 0.71440–0.71572 and lower εNd(t) values of −6.18 to −4.26 than the Late Triassic samples (ISr = 0.71139–0.71348; εNd(t) = –3.23 to −1.51), which are consistent with I-type granitoids derived from the lower crust. Geochemical and isotopic data indicate that the two stages of I-type granitoids had a significant mantle contribution. The Middle Triassic granitoids in the EKO, particularly the western EKO, have adakitic characteristics and formed by partial melting of lower continental crust. The T2–T3 granites formed by oceanic slab breakoff related to subduction and mantle convection, and the Late Triassic granites formed by lithospheric thinning and asthenospheric upwelling after slab breakoff.

Origins and evolution of two types of Late Triassic granitic magmas in the Caolong-Xiangkariwa area of central-eastern Songpan-Ganze terrane, northern Tibet: Implications for pegmatite lithium mineralization

Pegmatite-type lithium (Li) deposits are an important source of the low-carbon energy metal, which is generally considered to be formed by the high degrees of differentiation of strongly peraluminous granitic magma. However, the question of whether the parental rocks of these peraluminous magmas are igneous or sedimentary has been widely debated. Recent studies have identified a world-class pegmatite-type Li deposit belt (up to 2800 km long) closely associated with the Late Triassic granitoids and (meta)sedimentary rocks along the West Kunlun and Hoh Xil-Songpan-Ganze terranes in northern Tibet. This study presents a comprehensive petrological, geochronological, and geochemical study on the two types of Late Triassic granitoids in the Caolong-Xiangkariwa area of the Yushu region of central-eastern Hoh Xil-Songpan-Ganze terrane in northern Tibet: type A includes the Tongtianhe-Zhenqin-Zhaduo-Zhaya-Xiangkariwa (TZX) diorites and granodiorites (218−212 Ma), and type B includes the Caolong two-mica and muscovite granites (213−205 Ma), as well as ore-barren, beryl-bearing, and spodumene-bearing pegmatite dikes (209−196 Ma). The TZX diorites and granodiorites contain variable amounts of amphibolite and biotite. They are metaluminous to slightly peraluminous with variable SiO2 (54.4−71.3 wt%), MgO (0.72−7.26 wt%) contents, and Mg# values (40−70). Some samples with low SiO2 (54.4−58.5 wt%) contents have geochemical features similar to high-Mg andesites: e.g., high MgO contents (5.24−7.26 wt%) and Mg# values (61−70). The TZX diorites and granodiorites exhibit less enriched (86Sr/87Sr)i (0.7080−0.7118) and εNd(t) (−4.8 to −8.0). By contrast, the Caolong two-mica and muscovite granites are characterized by the occurrence of abundant muscovite (plus tourmaline and garnet) and are strongly peraluminous. The Caolong granites and pegmatites are geochemically characterized by high SiO2 contents (68.8−79.8 wt%) and low MgO contents (0.01−0.10 wt%) and Mg# values (4−23). They have εNd(t) values (−8.8 to −11.4; granites: −8.8 to −10.8; pegmatites: −9.2 to −11.4) that are more enriched than the TZX diorites and granodiorites but similar to those of Songpan-Ganze (meta)sedimentary rocks (−7.4 to −12.9), and the Caolong two-mica granites have high zircon δ18O values (11.6−12.1). In addition, decreasing K/Rb ratios correspond to increasing Cs contents in K-feldspar and muscovite from the Caolong granites and pegmatites. Taking into account the Late Triassic granitoids and (meta)sedimentary rocks in the Hoh Xil-Songpan-Ganze terrane, we suggest that the TZX diorites and granodiorites were most probably formed by the partial melting of metasomatized lithospheric mantle that subsequently underwent extensive fractional crystallization. Conversely, the Caolong two-mica and muscovite granites were likely generated purely by the partial melting of (meta)sedimentary rocks rather than via the evolution of dioritic-granodioritic magmas. In summary, there were two kinds of granitic magmas with different sources in the Caolong-Xiangkariwa area. Finally, the Caolong pegmatites were most likely formed by the extreme differentiation of two-mica granitic magmas rather than the dioritic-granodioritic magmas. Therefore, the evolution of magmas derived from (meta)sedimentary rocks were most likely to have formed the Li-rich pegmatites. Moreover, these (meta)sedimentary rocks representing the ultimate Li source must have undergone strong chemical weathering, resulting in significant Li enrichment.

Sources and petrogenesis of Late Triassic granitoids in the Yajiang gneiss dome group (eastern Songpan-Ganze orogenic belt) with tectonic implications

Numerous Mesozoic granitoid plutons with a substantial variety of petrologic and geochemical signatures intrude the Triassic metasedimentary rocks of the Songpan-Ganze accretionary-orogenic wedge in the eastern Tibetan Plateau. These granitoid rocks generally exhibit sharp contact with the Triassic sedimentary rocks. To better understand the genesis and emplacement of magmas associated with tectonic accretion along convergent plate boundaries, we present new LA-ICP-MS zircon U-Pb geochronology, major and trace elements, and Sr–Nd–Pb–Hf isotopic compositions for intermediate-to-felsic plutons in the Yajiang gneiss dome group (YGDG), including the Changzheng pluton, the Jiajika (Majingzi) pluton, the Rongxuka pluton, the Xiya pluton, the Xinduqiao pluton, and the Waduo diorite dikes in the eastern margin of the Songpan-Ganze orogenic belt (SGOB). By their typical petrological and geochemical characteristics, these plutons are classified as I-type granodiorite-diorite (Rongxuka, Xiya, Xinduqiao plutons, Waduo dikes) or S-type granite (Changzheng and Jiajika plutons). I-type granodiorite-diorites exhibit a high Mg# (average 49), medium-K cala-alkiline signature and are enriched in large-ion lithophile elements (e.g., Rb, Th, and U) but depleted in high field strength elements (e.g., Nb, Ta, and Ti), and with lower initial 87Sr/86Sr values (0.70622 to 0.70863) but a relatively high and concentrated εHf(t) (−27 to −1.9) and εNd(t) (−4.02 to −7.51); while S-type granites exhibit a high silica, high-K cala-alkiline signature with strong negative Eu anomalies (Eu/Eu* = 0.17–0.64), and possess high initial 87Sr/86Sr values but low εHf(t) (−40.1 to −0.9) and εNd(t) (−8.72 to −12.14) signatures, forming through partial melting of metasedimentary rocks from an ancient crust source. LA–ICP–MS zircon U-Pb dating indicates that they were emplacement between 207.2 ± 1.4 and 223.6 ± 2.2 Ma. Both types of granitoid rock were formed by the crustal partial melting followed by extensive fractional crystallization under high-temperature (700–850 °C), low-pressure (<15 kb) conditions. In combination with previous studies, our data provide evidence for an affinity between the eastern Songpan-Ganze andthe Yangtze craton basements, and suggest that the granitoid plutons formed in a syn-collisional to post-collisional setting at ca. 207–223 Ma.

Petrogenesis and tectonic setting of Early Permian–Late Triassic granitoids in the Qinling Orogenic Belt: Constraints from petrology, geochemistry and zircon U–Pb–Hf isotopes

The widely distributed Late Hercynian–Indosinian granites in the West Qinling Orogenic Belt are keys to better understand the tectonic–magmatic evolution of the West Qinling Orogenic Belt. In this paper, granitoids from the Zhacanggou area of Guide Basin in the western section of the West Qinling Orogenic Belt were studied on petrography, geochemistry, zircon U–Pb dating, and Lu–Hf isotopes. Zircon U–Pb dating yield granitoids in the Zhacanggou area were emplaced at 228.3 ± 4.4 Ma, 265.2 ± 2.2 Ma and 277.8 ± 2.5 Ma, respectively. The whole-rock geochemical compositions of these granitoids belong to the weakly peraluminous calc-alkaline to metaluminous high-K calc-alkaline series, and exhibit different degrees of negative Eu anomalies, loss of high-field strength elements (Nb, P and Ti), and enrichment of large ion lithophile elements (Rb, Th, U and Sr). The εHf (t) values of Early–Middle Permian and Late Triassic granitoids range from −12.0 to 5.3 and –10.6 to −5.0, and corresponding two-stage model ages (TDM2) of 956 to 2051 Ma and 1581 to 1936 Ma, respectively. A summary of geochronology for granitoids formed in the West Qinling Orogenic Belt during the Late Hercynian–Indosinian indicating magmatic activities concentrated in the Late Triassic (210–230 Ma) and Permian–Middle Triassic (235–277 Ma). These granitoids were both formed by partial melting of ancient crust, which then mixed with enriched lithospheric mantle, and the former has a higher mantle contribution than the latter. The early granitoids were associated to northward subduction of the Mianlue oceanic slab, while the late granitoids were formed in the transition from collision to extension.

Contribution of carbonaceous strata to intrusion–related Au mineralization: Evidence from trace elements and S–Pb isotopes in pyrite from the Qukulekedong Au–Sb deposit, East Kunlun, NW China

The large intrusion–related Qukulekedong Au–Sb deposit was recently discovered in the East Kunlun Orogenic Belt (EKOB). Mineralization occurs in the Late Triassic granitoid intrusion and its surrounding carbonaceous siltstone. Pyrite is an important Au-rich mineral in the deposit, and can be classified into three types: Py1, Py2 and Py3. The lattermost Py3 represents the main metallogenic episode. In–situ trace elements and S–Pb isotopes of pyrites indicate that the Py3 has a relatively high Au content (mean 7.84 ppm), high Co/Ni ratios (mean 4.93), with δ34S values around 0‰ (-2.03 to 1.69‰) and matched Pb isotopic ratios to the intrusions, suggesting that Au and other ore-forming material were most likely derived from a magmatic source. Carbonaceous siltstone contains organic carbon up to 3.39 wt%. According to the evidence of paragenetic minerals, texture, and S isotopes, the carbonaceous material may have played a key role in the precipitation of Au and pyrite in the carbonaceous strata. The Au–As decoupling of pyrite in intrusions may be attributed to the Au precipitation and crystallization of arsenopyrite, which was caused by the decreasing of oxygen fugacity. Overall, the new understanding highlights the importance of carbonaceous strata in intrusion–related Au ore-forming processes, the combination of carbonaceous strata and Late Triassic intrusions provides a new exploration direction for Au prospecting in the EKOB and similar settings.

Origin of Late Triassic Granitoids of the Coastal Cordillera of Southern Central Chile (34°–37°S): Multi‐Isotopic Evidence of Slab Tearing Effects on Pre‐Andean Magmagenesis

AbstractThe Coastal Cordillera of Central Chile (34°–37°S) holds a series of Late Triassic granitoids classically interpreted as early Andean subduction‐related magmatism based on their arc‐like geochemical signature. Here, we present geochemical, isotopic, and geochronological data and a tomotectonic analysis that challenge this idea indicating a local interruption of the normal subduction process likely associated with a slab‐tearing event. Our results suggest that the source of the magmas is related to melting of asthenospheric mantle and crustal rocks of a metasedimentary Paleozoic complex. We suggest that partial melting of these sources was triggered by a slab tear‐related asthenosphere upwelling producing high‐silica S/I‐ and S‐Type granites of the Constitución and Hualpén areas, and anorogenic A‐Type granitoids in Cobquecura area. Also, partial melting of a metasomatized asthenospheric mantle plus continental crust that experienced previous high‐temperature hydrothermal alteration would have generated high‐silica magmas with low δ18O, high Pb, CHUR‐like 87Sr/86Sr, and 143Nd/144Nd ratios that originated La Estrella Granite. Our results offer an alternative explanation for the existence of subtle magmatic arc‐like geochemical signatures in the study area and support a segmentation of the active margin during the Late Triassic. The widespread upper‐plate magmatic record of slab‐tearing, spanning the Coastal Cordillera of Central Chile to the intraplate Neuquén basin in Argentina, and the lower mantle record of a slab gap, detected in ours and previous tomotectonic analyses, make the Late Triassic slab‐tearing event in southwestern Pangea the most robustly constrained pre‐Cenozoic slab tear process so far.

Petrogenesis and tectonic implications of Late Triassic granitoids in the Alananshan, East Kunlun belt: evidence from geochemistry, geochronology, and zircon Hf isotopic compositions

Petrogenesis and tectonic implications of Late Triassic granitoids in the Alananshan, East Kunlun belt: evidence from geochemistry, geochronology, and zircon Hf isotopic compositions

Geochronology and geochemistry of Late Triassic granitoids in Harizha Cu polymetallic deposit (East Kunlun Orogen) and their metallogenic constraints

The large Harizha copper (Cu) polymetallic deposit is located in the eastern section of East Kunlun Orogen. The ore-related lithologies include mainly the granodiorite, monzogranite, and their porphyries. Zircon U-Pb dating of the ore-bearing granodiorite porphyry and granite porphyry yielded Late Triassic age of 217 Ma. The rocks are characterized by being rich in SiO2 (68.44–78.13 wt%) and high alkali (4.03–8.33 wt%) and peraluminous (A/CNK = 1.02–1.68). In general, the granite samples are peraluminous and high-K calc-alkaline. The rocks are significantly enriched in light rare earth elements (LREE), large ion lithophile elements (e.g., K, Rb, Ba) and other incompatible elements (e.g., U, Th), but are depleted in heavy rare earth elements (HREEs), with weakly negative Eu and Ce anomalies, resembling I-S transitional granite. The zircons have εHf (t) = -8 to -4, and the corresponding zircon two-stage Hf model age (TDM2) from 1.5 to 1.8 Ga. We speculated that the ore-forming materials in the mining area were mainly from partial remelting of crustal materials, and that the tectonic regime was post-collisional extension.

Petrogenesis and geodynamic significance of Late Triassic mafic microgranular enclaves and its host granodiorite in the Shuanghu area, central Qiangtang

The genesis of Late Triassic granitoids in the central Qiangtang is significant for deducing the evolution of the Palaeo‐Tethys Ocean in Qiangtang Block. Herein, we present a comprehensive study of zircon U–Pb ages, whole‐rock geochemistry and zircon Lu–Hf isotopes for the mafic microgranular enclaves (MMEs) and host granodiorites from the Shuanghu area, in order to evaluate their petrogenesis and geodynamic implications. New zircon U–Pb dating show identical formation ages for host granodiorites (207.1 ± 2.2 Ma and 206.6 ± 3.8 Ma) and MMEs (205.4 ± 2.9 Ma and 209.2 ± 2.2 Ma). The Shuanghu granodiorites contain amphibole and biotite and are characterized by moderate SiO2 (64.74–66.40 wt%) and K2O contents (2.48–3.62 wt%) as well as low A/CNK (0.69–1.00), indicating I‐type granite affinity. Its enriched zircon Hf isotopes (εHf(t) = −12.04 to −5.09) indicate that they were derived from the ancient mafic lower crust. The MMEs have a similar mineral assemblage, emplacement ages, trace elemental and zircon Hf isotopic compositions with the host granodiorites, indicating the cognate origin. These MMEs represent autoliths captured by latter ascending host magmas in the middle‐upper magma chamber. The highly variable Mg# (37–53), Cr (16.9–190 ppm) and Ni (5.71–67.2 ppm) in the Shuanghu MMEs and host granodiorites indicate that the mantle‐derived magma provided not only the heat but also the mafic components. In combining with previous studies, we suggest that the Shuanghu granodiorites and MMEs were formed in the post‐collision stage, which were caused by the asthenosphere upwelling related to the slab breakoff.

Petrogenesis and tectonic implications of late Permian and Triassic granitoids on Hainan Island, South China

Hainan Island is a key part of the eastern Tethyan region and contains detailed geological information that can enhance our understanding of the tectonic evolution of this region since the late Palaeozoic. In this paper, we report geochronological, geochemical, and Sr–Nd isotopic data for granitoids from Baomei and Chahe in the northern part of Hainan Island. Three new zircon U–Pb ages of 243.3 ± 1.7 Ma, 237.1 ± 5.1 Ma, and 257.0 ± 4.0 Ma were obtained for these granitoids. The late Permian Chahe granite (257 Ma) is weakly peraluminous to peraluminous, and has rare earth element patterns and Ga/Al and FeOT/MgO ratios typical of A‐type granites formed in an extensional tectonic setting. The Middle Triassic Baomei granitoids (243–237 Ma) are weakly peraluminous, and exhibit a negative correlation between P2O5 and SiO2, which is typical of I‐type granites. All the granitoids have EM II‐type‐enriched mantle Sr–Nd isotopic compositions, which indicate that they were derived from a mantle source that had experienced enrichment and metasomatism. Hainan Island was in an extensional tectonic setting from the late Permian to Middle Triassic when widespread A‐ and I‐type granites were generated. We speculate that Hainan Island was mainly affected by the Tethyan tectonic domain during the Permian–Triassic, which involved closure of the Palaeo‐Tethys Ocean, collision of the Indochina and South China blocks, and subsequent post‐collisional extension.

Latest Permian–Triassic magmatism of the Taimyr Peninsula: New evidence for a connection to the Siberian Traps large igneous province

Abstract This study presents new whole rock major and trace element, Sr-Nd isotopic, petrographic, and geochronologic data for seven latest Permian (Changhsingian)–Late Triassic (Carnian) granitoid intrusions of the northwestern and northeastern Taimyr Peninsula in the Russian High Arctic. U-Pb zircon ages, obtained using secondary ion mass spectrometry (SIMS), sensitive high-resolution ion microprobe (SHRIMP), and laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS), define the crystallization age of the Taimyr intrusions studied as ranging from ca. 253 Ma to 228 Ma, which suggests two magmatic pulses of latest Permian–Early Triassic and Middle–Late Triassic age. Ar-Ar dating of biotite and amphibole indicate rapid cooling of the intrusions studied, but Ar-Ar ages of several samples were reset by secondary heating and hydrothermal activity induced by the Middle–Late Triassic magmatic pulse. Petrographic data distinguish two groups of granites: syenite–monzonites and granites–granodiorites. Sr-Nd isotopic data, obtained from the same intrusions, show a variation of initial (87Sr/86Sr)i ratios between 0.70377 and 0.70607, and εNd(t) values range between –6.9 and 1.2. We propose that the geochemical and isotopic compositions of the Late Permian–Triassic Taimyr granites record the existence of a magma mush zone that was generated by the two pulses of Siberian Traps large igneous province (LIP) magmatism.

Middle to Late Triassic granitic magmatism in the East Kunlun Orogenic Belt, NW China: Petrogenesis and implications for a transition from subduction to post‐collision setting of the Palaeo‐Tethys Ocean

In this study, we present new geochronological and petrogenetic data for the Triassic granitoids of the East Kunlun Orogenic Belt (EKOB), in order to constrain their precise ages, petrogenesis, and tectonic settings. LA‐ICP‐MS zircon U–Pb data indicate that the Triassic granitoids were emplaced in two stages: (a) Middle Triassic (247–240 Ma), represented by a suite of porphyritic granites and granodiorites; and (b) Late Triassic (234–227 Ma), forming an intrusive rock association of K‐feldspar granites, granodiorites, and porphyritic granites. Geochemical analyses and mineral associations suggest that all the Triassic granitoids belong to I‐type granites but have different origins. The Middle Triassic granitoids have high SiO2, low to moderate Mg# values (25–37 for XSG porphyritic granite; 45–47 for DB granodiorite), low Sr/Y ratios (2.2–4.6 for XSG porphyritic granite; 17.8–20.8 for DB granodiorite), and relatively restricted zircon εHf(t) values (+2.4 − +4.6 for the ca. 247 Ma porphyritic granite, and − 8.0 to −1.5 for the ca. 240 Ma granodiorite), indicating that they were dominantly generated from partial melting of different crust sources (either juvenile or ancient) in a normal lower crust level. In contrast, the Late Triassic granitoids have high SiO2, K2O, and Y contents, low MgO and HREE contents, and variable zircon εHf(t) values (from negative to positive, −4.9 to +3.3), implying a strong crustal–mantle interaction that occurred during the Late Triassic, and this stage of granitoids were derived from a complex magma source possibly a mixture of mantle‐derived and ancient crustal‐derived materials. By combining these new data with the previous data, we conclude that the two stages of Triassic granitoids were emplaced in an active continental margin setting and a post‐collisional extension setting, respectively. Moreover, this study suggests a tectonic shift of the Palaeo‐Tethys Ocean in the EKOB from subduction during the Middle Triassic to a post‐collision during the Late Triassic.

ГРАНИТОИДЫ АЛТАХТИНСКОГО КОМПЛЕКСА ВОСТОЧНОЙ ЧАСТИ БУРЕИНСКОГО КОНТИНЕНТАЛЬНОГО МАССИВА ЦЕНТРАЛЬНО-АЗИАТСКОГО СКЛАДЧАТОГО ПОЯСА: ВОЗРАСТ, ГЕОХИМИЧЕСКИЕ ОСОБЕННОСТИ, ГЕОДИНАМИЧЕСКАЯ ИНТЕРПРЕТАЦИЯ

New data are reported on the age, composition and formation conditions of the Late Triassic granitoids of minor intrusions from the eastern part of the Bureya continental massif of the Central Asian fold belt, and their geodynamic interpretation is given. U-Pb geochronological studies on zircons indicate that the age of rocks of the Altakhta syenite-leucogranite complex is in the 235–224 Ma range, which intrusion proceeding in two phases. The formation of magmatites is associated with the first phase (235.3 ± 2.9–230 Ma), which by their geochemical features are similar to А1-type intraplate granitoids and by REE concentrations to subduction- and collision-related granitoids. Geochemical characteristics of А2-type and А2 + I &amp; S-type granites (226–224 Ma) suggest their formation in a syncollisional setting. The evolution of the chemical composition of the Altakhta granitoids indicates a change in the geodynamic setting type, when the opposing (orthogonal) movement of the plates at the convergent boundary (subduction) changed to their sliding past each other (transform continental margin).

The Permian to early Triassic granitoids of the Nahuel Niyeu - Yaminué area, northern Patagonia: Igneous stratigraphy, geochemistry and emplacement conditions

We present the first geochronologically constrained igneous stratigraphy of the Permian to Early Triassic magmatism of the Nahuel Niyeu and Yaminué areas, northern Patagonia. This magmatism was separated into the Early Permian Granitoids (>270 Ma, EPG; Navarrete Plutonic Complex) and the Late Permian-Early Triassic Granitoids (260-245 Ma, LPETG) that are made up of the Madsen Tonalite (̴252 Ma, MT), the Yaminué Metaigneous Complex (̴261-249 Ma, YMIC), and the Ramos Mexía Igneous Complex (̴245 Ma, RMIC). Structural observations indicate that EPG are undeformed and intrude a low-grade Ordovician metamorphic basement. LPETG are either mostly undeformed granitoids intruding Cambrian mylonites, i.e. MT or a low-grade Ordovician metamorphic basement i.e. RMIC or they are synkinematic sheeted intrusion (YMIC) concordantly emplaced in Devonian medium grade metaclastic rocks. The EPG are high Ba–Sr granitoids with 66–73% SiO2, K2O/Na2O< 1, and Sr/Y> 34. Major element chemistry indicates mafic sources and volcanic-arc affinities. Average pressure constrains their emplacement at 2.9±0.5 kbar. The LPETG have a wide range of compositions. From sheeted ̴62–75% SiO2 tonalites, to leucogranites (YMIC) to undeformed ̴60–72% tonalites to monzogranites (MT and RMIC). They show low to moderate Ba–Sr, 0.5< K2O/Na2O< 2.8 and Sr/Y< 50. Mafic to intermediate crustal sources are inferred for the LPETG. In contrast with the EPG, the YMIC was emplaced at 5.2±0.3 Kbar. The calculated average pressure of RMIC is 2.8±0.25 kbar. Since RMIC intrudes YMIC, we conclude that there was an uplift of ca. 9 km between ̴249 and 245 Ma. The major compressional event (Dn+1) that controlled the synkinematic emplacement of the YMIC is bracketed between 261 and 249 Ma. Tectonic processes associated with the uplift of YMIC from 20 to 11 km in depth and the coeval emplacement of RMIC at 245±1 Ma could correspond to the collapse of a thickened crust.

Mesozoic juvenile crustal formation in the easternmost Tethys: Zircon Hf isotopic evidence from Sumatran granitoids, Indonesia

Abstract Prior to the collision of India with Asia, the evolution of island arcs and resultant crustal formation in the now-disrupted easternmost Tethys are poorly constrained. Here, we report for the first time zircon U-Pb and Hf isotopic data from Mesozoic granitoids in Sumatra, Indonesia. Our analyses identified three magmatic episodes at 214–201 Ma, 148–143 Ma, and 102–84 Ma, respectively, with a drastic change in magmatic zircon εHf(t) values from −13.1 to +17.7 in the Late Triassic granitoids, which reveals a fundamental restructuring of the arc system in Sumatra. Subsequently, all Jurassic to Late Cretaceous granitoids have exclusively positive zircon εHf(t) values (+17.7 to +10.2), consistent with juvenile arc development owing to subduction of the easternmost Tethyan lithosphere beneath Sumatra. Such highly positive zircon εHf(t) values of the Sumatran granitoids, in general accordance with those of the Gangdese arc system in South Asia, are markedly higher than those (+13.7 to −14.7) of broadly contemporaneous Cordilleran arcs in Americas and Zealandia. Our findings from the easternmost Tethys provide new insights into not only the tectono-magmatic evolution of eastern Tethys, but also its crucial role in global juvenile crustal growth.

Late Triassic post-collisional granites related to Paleotethyan evolution in northwestern Lao PDR: Geochronological and geochemical evidence

The late Paleozoic to early Mesozoic granites exposed in northwestern Lao PDR provide important constraints on the tectonic evolution of the Eastern Paleotethyan Ocean and regional correlation with the giant granitic belt in Southeast Asia. New geochronological data show that the granites have Late Triassic zircon U–Pb ages of 231–220 Ma. They are dominated by monzogranite and biotite granite with an I-type geochemical affinity. These granites are enriched in LREEs and LILEs and depleted in HFSEs. The geochemical variations for these granites indicate the fractional crystallization of plagioclase, K-feldspar, biotite, apatite, and Fe–Ti oxides. Their initial 87Sr/86Sr ratios range from 0.7021 to 0.7105 and εNd (t) values from −1.6 to −7.3. Zircon in-situ εHf (t) values are in range of −6.0–+5.3 (peaks at −2.8 and +2.5, respectively), Hf model ages of 0.67–1.64 Ga (peaks at 0.83 Ga and 1.45 Ga, respectively), and δ18O values of 6.6‰–8.0‰, similar to the Late Triassic granitoids from the Eastern Province in Southeast Asia. These granites originated from a mixed source of ancient metamorphic rocks with juvenile mafic crust. The Late Triassic granites in northwestern Lao PDR formed in a post-collisional setting in response to the thickened crustal collapse during the assembly of the Sibumasu with Indochina blocks. These granites can southerly link with the Eastern granite province of the Eastern Paleotethyan Domain in Southeast Asia.

Petrogenesis of Late Triassic mafic enclaves and host granodiorite in the Eastern Kunlun Orogenic Belt, China: Implications for the reworking of juvenile crust by delamination-induced asthenosphere upwelling

Late Triassic granitoids containing abundant mafic microgranular enclaves (MMEs) occur widely in the Eastern Kunlun Orogenic Belt (EKOB). In this work, we present mineral chemistry, zircon U-Pb ages and L-Hf isotopes, whole-rock chemistry and S-Nd isotope compositions of the MMEs and host granodiorite from the Huda pluton in the Elashan area within the easternmost domain of the EKOB. These rocks contain inherited (Meso- to Neoproterozoic) and xenocrystic (ca. 240 Ma) zircon grains that yield apparent older ages, whereas the magmatic zircons from MMEs and granodiorite yield similar weighted mean ages around 224 Ma, which are interpreted as their crystallization ages. The MMEs have low SiO2 but high TiO2, TFe2O3, CaO, MgO and MnO concentrations with relatively high Mg# values (48–54) and 100MnO/(MnO + MgO + TFe2O3) ratios (1.2–1.6). They display identical Sr-Nd-Hf isotope compositions to the host granite. Combined with petrological evidence, we suggest that the MMEs are cognate cumulates that formed by pressure quenching during the late stage of magma evolution from the same parental magma of the host granodiorite, rather than a magma mixing origin. The granodiorite is calc-alkaline to high-K calc-alkaline, metaluminous I-type granite. They show relatively low SiO2 and MnO, but high MgO, Al2O3, CaO and TFe2O3 contents with Mg# values of 45–50. They are enriched in light rare earth elements (LREEs) and large ion lithophile elements (LILEs), such as Rb, Th, K and Pb, and are depleted in P and high field strength elements (HFSE) including Nb, Ta and Ti. These rocks display slightly negative Eu anomalies and low Sr/Y and La/Yb ratios. Together with the rim-ward chemically evolved nature of some phenocrysts, the comparatively high initial Sr isotope (0.70888–0.70912), low whole-rock εNd(t) (−5.6 to −6.0) and zircon εHf(t) (−3.3 to −0.1) values, and low Nb/Th (0.11–0.26) and Ta/U (0.53–0.68) ratios, we suggest that the granodiorite magma was sourced from the lower crust. Considering their comparatively young two-stage Nd and Hf model ages (1.42–1.49 Ga and 1.13–1.42 Ga, respectively) and same trace element character with the juvenile crust beneath the EKOB, we interpret the juvenile lower crust as the dominant source rocks for the granodiorite. Based on our data and regional geological evidence, we suggest that the partial melting of juvenile crust resulted from delamination-related asthenosphere mantle upwelling. The latter process resulted in extensive melting of the lower crust, producing a major Late Triassic magmatic flare-up event in the EKOB.

Geology and geochronology of the super-large Bailongshan Li–Rb–(Be) rare-metal pegmatite deposit, West Kunlun orogenic belt, NW China

The Bailongshan pegmatite deposit is a newly discovered super-large Li–Rb–(Be–Ta–Nb) rare-metal deposit in the West Kunlun orogenic belt, northwest China. Fifty-two rare-metal orebodies (50–1230 m long by 1.5–157 m wide) have been discovered by detailed field surveying, making up a metallogenic field that is larger than 8250 × 400 m. The deposit is estimated to have ore reserves of more than 5.06 million tonnes (t) Li2O, 160,020 t BeO, 316,200 t Rb2O, 40,060 t Nb2O5, and 10,750 t Ta2O5. Pegmatite dikes are zoned around a granodiorite batholith, ranging from barren through orebodies rich in Be, Nb, Ta, Rb, and Li with increasing distance from the batholith, similar to the classical model of a zoned Li–Ce–Ta (LCT)-type pegmatite. LA–ICP–MS analyses of coltan and zircon yield 206Pb/238U ages of 208.1 Ma and 212.3 Ma, respectively, representing the emplacement ages of the pegmatites and granodiorite. These data indicate a temporal link between the emplacement of the granodiorite batholith and rare-metal mineralization in the pegmatites, and that the Bailongshan rare-metal pegmatites are temporospatially related to the granodiorite batholith. The Bailongshan pegmatites and other rare-metal pegmatite deposits in the West Kunlun orogenic belt likely make up a >600-km-long Li metallogenic belt, and further exploration for rare-metal pegmatites should be focused on the area adjacent to Late Triassic granitoid plutons in the belt. This belt likely extends to the East Kunlun and West Sichuan rare-metal belts, forming the >2000-km-long, Late Triassic West Kunlun–Songpan–Garzê rare-metal metallogenic belt.