Triassic volcanism along the eastern margin of the Xing'an Massif,NE China: Constraints on the spatial–temporal extent of the Mongol–Okhotsk tectonic regime

We present new zircon U–Pb–Hf and whole-rock geochemical data for volcanic rocks along the eastern margin of the Xing'an Massif of NE China in order to further our understanding of the history of subduction towards the SE and the spatial extent of the Mongol–Okhotsk tectonic regime. Zircon U–Pb dating indicates that the Triassic volcanism in the Xing'an Massif occurred in two stages during the Middle (ca. 242 Ma) and Late (ca. 223–228 Ma) Triassic. Middle Triassic basaltic andesites in the Heihe area have an affinity to arc-type volcanic rocks. The zircon ε_Hf(t) values (+ 8.5 to + 12.7) suggest that the primary magma was generated by the partial melting of a relatively depleted mantle wedge that had been metasomatized by subduction-related fluids. The Late Triassic andesites in the Handaqi area exhibit geochemical affinities to high-Mg adakitic andesites. Their zircon ε_Hf(t) values (+ 11.5 to + 14.5) and T_DM2 ages (313–484 Ma) indicate that their primary magma was derived from the partial melting of a young subducted oceanic crust, followed by interaction with melts derived from mantle peridotite. The Late Triassic basaltic andesites, andesites, and dacites in the Zhalantun–Moguqi area have features similar to those of igneous rocks formed in subduction zones. Their zircon ε_Hf(t) values (+ 8.4 to + 15.4) and T_DM1 ages (260–542 Ma) indicate that their primary magma was derived from the partial melting of a depleted mantle wedge that had been metasomatized by subduction-related fluids. These data suggest that the Triassic volcanic rocks of the Xing'an Massif formed in an active continental margin setting associated with the southward subduction of the Mongol–Okhotsk oceanic plate towards the SE. We conclude that the Mongol–Okhotsk tectonic regime extended at least as far as the eastern margin of the Xing'an Massif, and that the tectonism spanned the period from the late Permian to early Early-Cretaceous.     

U–Pb and Hf isotope data from zircons in the Macquarie Arc,Lachlan Orogen: Implications for arc evolution and Ordovician palaeogeography along part of the east Gondwana margin

The Ordovician Macquarie Arc in the eastern subprovince of the Lachlan Orogen, southeastern Australia, is an unusual arc that evolved in four vertically stacked volcanic phases over ~ 37 million years, and which is flanked by coeval, craton-derived, passive margin sedimentary terranes dominated by detrital quartz grains. Although these two terranes are marked by a general absence of provenance mixing, LA-ICPMS analysis of U–Pb and Lu–Hf contents in zircon grains in volcaniclastic rocks from 3 phases of the arc demonstrates the same age populations of detrital grains inherited from the Gondwana margin as those that characterise the flanking quartz-rich Ordovician turbidites. Magmatic Phase 1 is older, ~ 480 Ma, and is characterised by detrital zircons grains with ages of ~ 490–540 with negative ε_Hf from 0 to mainly –7.78, 550–625 Ma ages with negative ε_Hf from 0 to ?26.6 and 970–1250 Ma (Grenvillian) with ε_Hf from + 6.47 to ?6.44. We have not as yet identified any magmatic zircons related to Phase 1 volcanism. Small amounts of detrital zircons also occur in Phase 2 (~ 468–455 Ma), hiatus 1 and Phase 4 (~ 449–443 Ma), all of which are dominated by Ordovician magmatic zircons with positive ε_Hf values, indicating derivation from unevolved mantle-derived magmas, consistent with formation in an intraoceanic island arc. Because of the previously obtained positive whole rock ε_Nd values from Phase 1 lavas, we rule out contamination from substrate or subducted sediments. Instead, we suggest that during Phase 1, the Macquarie Arc lay close enough to the Gondwana margin so that volcaniclastic rocks were heavily contaminated by detrital zircon grains shed from granites and Grenvillian mafic rocks mainly from Antarctica (Ross Orogen and East Antarctica) and/or the Delamerian margin of Australia. The reduced nature of a Gondwana population in Phase 2, hiatus 1 and Phase 4 is attributed to opening of a marginal basin between the Gondwana margin and the Macquarie Arc that put it out of reach of all but rare turbiditic currents.     

Geochronological and geochemical constraints on the intermediate-acid volcanic rocks along the Chiang Khong–Lampang–Tak igneous zone in NW Thailand and their tectonic implications

Volcanic rocks preserved in the Lampang–Den Chai area in NW Thailand are important components of the giant Paleotethyan igneous belt. Constraining their age and petrogenesis is critical for better understanding their temporal-spatial relationship with the Lancangjiang igneous zone and the Paleotethyan tectonic evolution in SE Asia. The volcanic suite is constituted by intermediate to acid rocks with zircon U–Pb ages of 240.4 ± 1.7 Ma and 240.6 ± 1.9 Ma for the representative andesitic and rhyolitic samples, respectively. Volcanic sequence is dominated by calc-alkaline andesites, dacites and rhyolites. The andesitic and dacitic samples are characterized by high Mg# (37–57) and TiO₂ (0.91–1.59 wt%), and can be classified as high-Mg series. They are enriched in LILEs and LREEs and depleted in HFSEs. Representative andesitic samples have ⁸⁷Sr/⁸⁶Sr (i) ratios of 0.70398–0.70567, ε_Nd (t) values of +3.6–+3.9, zircon ε_Hf (t) values of +2.8–+8.0 and δ¹⁸O values of 7.01–8.11‰, respectively. The rhyolitic samples are characterized by high Mg# (38–70) and low TiO₂ (0.25–0.61 wt%). They are enriched in LILEs and LREEs, along with ⁸⁷Sr/⁸⁶Sr (i) = 0.70468–0.70645, ε_Nd (t) = +2.0–+4.3 and zircon ε_Hf (t) = +5.7–+13.6. Geochemical signatures suggest that the andesitic and dacitic samples might originate from a newly modified mantle source by slab-derived fluids and recycled sediments, and rhyolitic samples were derived from juvenile mafic crust. It is proposed that the Middle Triassic high-Mg volcanic rocks in the Lampang–Den Chai area formed in response to slab roll-back during transition of tectonic regime from subduction to continental collision between the Sibumasu and Indochina blocks. These rocks constitute part of the Chiang Khong–Lampang–Tak igneous zone, and can northerly link with the Lancangjiang igneous zone and southerly extend to the Chanthaburi, Malaysia and Singapore areas.     

Geochronology,petrogenesis and tectonic implication of Late Paleozoic volcanic rocks from the Dashizhai Formation in Inner Mongolia,NE China

In this paper we present geochemical, zircon U–Pb and Hf isotopic data on the late Paleozoic volcanic rocks of the Dashizhai Formation, which are exposed along the northwestern margin of the Songnen terrane in eastern Inner Mongolia. Our aim is to constrain the petrogenesis and tectonic setting of the volcanic rocks and to unravel the late Paleozoic tectonic evolution of the northwestern part of the Songnen terrane, along the eastern segment of the Central Asian Orogenic Belt. Lithologically, the Dashizhai Formation is composed mainly of rhyolitic tuff, rhyolite, dacite, andesite, basaltic andesite and basalt, with minor basaltic trachyandesite. The zircons separated from these rocks are euhedral–subhedral, have high Th/U ratios (0.2–1.6), and display broad oscillatory growth zoning, indicating a magmatic origin. The results of zircon U–Pb dating indicate the volcanic rocks formed during the early Permian (295–283 Ma). Geochemically, these volcanic rocks belong to the mid-K to high-K calc-alkaline series and are characterized by an enrichment in large ion lithophile elements (LILEs) and a depletion in high field strength elements (HFSEs, such as Nb, Ta, and Ti), similar to igneous rocks that form in active continental margin settings. Most magmatic zircons of the rhyolites show positive ε_Hf(t) values (+ 3.65 to + 13.0) and two-stage model ages (T_DM2) of 1396–551 Ma. These geochemical characteristics indicate that the acidic volcanic rocks of the Dashizhai Formation were most likely derived from the partial melting of dominantly juvenile crustal components with a possible addition of “old” materials. In contrast, the basic to intermediate volcanic rocks were derived from the partial melting of a depleted lithospheric mantle that had been metasomatized by fluids derived from a subducted slab. These data, together with regional geological investigations, suggest that the generation of the early Permian volcanic rocks of the Dashizhai Formation was related to the southward subduction of the Paleo–Asian oceanic plate beneath the Songnen terrane. This also implies that the terminal collision between the Songnen and Xing'an terranes did not occur before the early Permian.     

Triassic volcanism in eastern Heilongjiang and Jilin provinces,NE China: Chronology,geochemistry, and tectonic implications

With the aim of constraining the Early Mesozoic tectonic evolution of the eastern section of the Central Asian Orogenic Belt (CAOB), we undertook zircon U–Pb dating and geochemical analyses (major and trace elements, Sr–Nd isotopes) of volcanic rocks of the Luoquanzhan Formation and Daxinggou Group in eastern Heilongjiang and Jilin provinces, China. The analyzed rocks consist mainly of dacite and rhyolite, with SiO₂ contents of 68.52–76.65 wt%. Three samples from the Luoquanzhan Formation and one from the Daxinggou Group were analyzed using laser ablation inductively coupled plasma-mass spectrometry (LA-ICP-MS) U–Pb zircon techniques. Three zircons with well-defined oscillatory zoning yielded weighted mean ²⁰⁶Pb/²³⁸U ages of 217 ± 1, 214 ± 2, and 208 ± 1 Ma, and one zircon with oscillatory zoning yielded a weighted mean ²⁰⁶Pb/²³⁸U age of 201 ± 1 Ma. These ages are interpreted to represent the timing of eruption of the volcanic rocks. The Triassic volcanic rocks are characterized by high SiO₂ and low MgO concentrations, enrichment in large ion lithophile elements (LILEs) and light rare earth elements (LREEs), depletion in high field strength elements (HFSEs) and heavy rare earth elements (HREEs), (⁸⁷Sr/⁸⁶Sr)_i = 0.7040–0.7050 (Luoquanzhan Formation) and 0.7163–0.7381 (Daxinggou Group), and ε_Nd (t) = 1.89–3.94 (Luoquanzhan Formation) and 3.42–3.68 (Daxinggou Group). These geochemical features indicate an origin involving the partial melting of juvenile lower crust (Nd model ages (T_DM2) of 651–821 Ma) and that compositional variation among the volcanic rocks arose from mineral fractionation and minor assimilation. These volcanic rocks formed within an extensional environment following collision of the NCC and Jiamusi-Khanka Massif during the Late Paleozoic–Early Triassic.     

Mid-Neoproterozoic crustal evolution of the northeastern Yangtze Block: Evidence from the felsic-gneiss xenoliths hosted in the Donghai Cenozoic basalts

Crustal xenoliths can provide new insights into the unexposed crust, and those from the northeastern Yangtze Block have rarely been studied. This paper reports U–Pb–Hf isotopes and trace-element compositions of zircons from six felsic xenoliths hosted by the Neogene alkali basalts in the Donghai region (i.e. Anfengshan and Pingmingshan) of the Sulu orogen in central eastern China. The xenoliths are mainly composed of orthoclase and quartz, or orthoclase and natrolite, with accessory minerals of Fe–Ti oxides and zircon. Most zircon grains show core-rim structures, with the cores and rims being magmatic and metamorphic in origin, respectively. The zircon cores mainly yield ages of ca. 827–794 Ma, while the zircon rims give ages of ca. 232–212 Ma. We interpret the zircon core ages as the time of an early Mid-Neoproterozoic magmatic event in the northeastern Yangtze Block and the zircon rim ages as the time of collision between the Yangtze and North China Blocks. Our data suggest that much more ca. 830–800 Ma magmatic records are possibly preserved in the unexposed deep crust, and the early Mid-Neoproterozoic is an important era for the crust evolution of the northeastern Yangtze Block. The new zircon Hf isotopic analyses show that the Anfengshan sample (south of Donghai) has zircon ε_Hf (820 Ma) values ranging from −15.3 to −9.4, and two-stage Hf model ages of 2.66–2.30 Ga; the Pingmingshan sample (southeast of Donghai) has zircon ε_Hf (820 Ma) values ranging from −1.4 to +3.8, and two-stage Hf model ages of 1.80–1.47 Ga. These data suggest that ancient crust as old as Neoarchean to Mesoproterozoic was involved in the early Mid-Neoproterozoic magmatism. Combined with the previously reported zircon U–Pb–Hf results of the exposed rocks, it is highlighted that crustal recycling was dominant in the early Mid-Neoproterozoic (ca. 830–800 Ma) magmatism, whereas both crustal recycling and addition of mantle-derived melts were significant in the late Mid-Neoproterozoic (ca. 800–720 Ma) magmatism in the northeastern Yangtze Block.     

Constraints on the paleogeographic evolution of the North China Craton during the Late Triassic–Jurassic

This paper reports U–Pb–Hf isotopes of detrital zircons from Late Triassic–Jurassic sediments in the Ordos, Ningwu, and Jiyuan basins in the western-central North China Craton (NCC), with the aim of constraining the paleogeographic evolution of the NCC during the Late Triassic–Jurassic. The early Late Triassic samples have three groups of detrital zircons (238–363 Ma, 1.5–2.1 Ga, and 2.2–2.6 Ga), while the latest Late Triassic and Jurassic samples contain four groups of detrital zircons (154–397 Ma, 414–511 Ma, 1.6–2.0 Ga, and 2.2–2.6 Ga). The Precambrian zircons in the Late Triassic–Jurassic samples were sourced from the basement rocks and pre-Late Triassic sediments in the NCC. But the initial source for the 238–363 Ma zircons in the early Late Triassic samples is the Yinshan–Yanshan Orogenic Belt (YYOB), consistent with their negative zircon ε_Hf(t) values (−24 to −2). For the latest Late Triassic and Jurassic samples, the initial source for the 414–511 Ma zircons with ε_Hf(t) values of −18 to +9 is the Northern Qinling Orogen (NQO), and that for the 154–397 Ma zircons with ε_Hf(t) values of −25 to +12 is the YYOB and the southeastern Central Asian Orogenic Belt (CAOB). In combination with previous data of late Paleozoic–Early Triassic sediments in the western-central NCC and Permian–Jurassic sediments in the eastern NCC, this study reveals two shifts in detrital source from the late Paleozoic to Jurassic. In the Late Permian–Early Triassic, the western-central NCC received detritus from the YYOB, southeastern CAOB and NQO. However, in the early Late Triassic, detritus from the CAOB and NQO were sparse in basins located in the western-central NCC, especially in the Yan’an area of the Ordos Basin. We interpret such a shift of detrital source as result of the uplift of the eastern NCC in the Late Triassic. In the latest Late Triassic–Jurassic, the southeastern CAOB and the NQO restarted to be source regions for basins in the western-central NCC, as well as for basins in the eastern NCC. The second shift in detrital source suggests elevation of the orogens surrounding the NCC and subsidence of the eastern NCC in the Jurassic, arguing against the presence of a paleo-plateau in the eastern NCC at that time. It would be subsidence rather than elevation of the eastern NCC in the Jurassic, due to roll-back of the subducted paleo-Pacific plate and consequent upwelling of asthenospheric mantle.     

Incremental growth and origin of the Cretaceous Renjiayingzi pluton,southern Inner Mongolia,China: Evidence from structure,geochemistry and geochronology

The Renjiayingzi intermediate-acid pluton is located along a pre-existing ENE–WSW-trending dextral shear zone that forms part of the Xar Moron suture zone that marks the final closure of the Paleo-Asian Ocean. The pluton is composed of three small intrusions, which from northwest to southeast, are named the Shuangjianshan (SI), the Qianweiliansu (QI) and the Xingshuwabeishan (XI) intrusions. LA-ICPMS zircon U–Pb dating of a pyroxene diorite from the SI yields an age of 138 ± 1 Ma; the SHRIMP zircon U–Pb age of a tonalite from the QI records an age of 134 ± 2 Ma, whereas LA-ICPMS zircon U–Pb dating of a monzogranite from the XI has an age of 126 ± 1 Ma, suggesting the entire pluton was built up by three separate emplacement events that young to the ESE: this is further supported by the contact relations. Incremental growth of plutons by amalgamation of repeated small magma pulses is the most viable emplacement model. The pluton was probably emplaced by updoming of the roof along previous tensile fractures and by upward stacking of the three intrusions. The SI and QI have similar U–Pb ages and geochemical characteristics, and most likely had the same magma source and underwent similar petrogenetic processes. They have high MgO concentrations at low silica contents, are enriched in large ion lithophile elements, depleted in high field strength elements, have negative ε_Nd(t) values of −1.8 to −3.7, with Nd model ages of 1.07–1.19 Ga. Pyroxene diorites of the SI also have variable zircon ε_Hf(t) values (from −0.8 to +6.1), indicating that they were mainly derived from juvenile crust with minor crustal contamination and clinopyroxene-dominated fractional crystallization. The late monzogranites from the XI show weak negative ε_Nd(t) values of −2.3 to −2.5, young Nd model ages of 0.99–1.00 Ga, positive zircon ε_Hf(t) values (+1.3 to +4.6) and higher SiO₂ and K₂O contents, with strong depletion in Eu, P and Ti, indicating derivation from a distinct petrogenetic process from the two earlier intrusions. The monzogranites were the result of partial melting of juvenile crust in response to mantle-derived magma underplating, together with plagioclase-dominated fractional crystallization.     

Petrogenesis and geodynamic setting of Neoproterozoic and Late Paleozoic magmatism in the Manzhouli–Erguna area of Inner Mongolia,China: Geochronological,geochemical and Hf isotopic evidence

U–Pb dating and Hf isotopic analyses of zircons from various granitoids, combined with major and trace element analyses, were undertaken to determine the petrogenesis and geodynamic setting of Neoproterozoic and Late Paleozoic magmatism in the Manzhouli–Erguna area of Inner Mongolia, China. The Neoproterozoic granitoids are mainly biotite monzogranites with zircon U–Pb ages of 894 ± 13 Ma and 880 ± 10 Ma, and they are characterised by enrichment in large ion lithophile elements (LILEs; e.g., Rb, Ba, K) and light rare earth elements (LREEs), depletion in high field strength elements (HFSEs; e.g., Nb, Ta, Ti) and heavy rare earth elements (HREEs). The Late Devonian granitoids are dominantly syenogranites and mylonitised syenogranites with zircon U–Pb ages of 360 ± 4 Ma, and they form a bimodal magmatic association with subordinate gabbroic rocks of the same age. The Late Devonian syenogranites have A-type characteristics including high total alkalis, Zr, Nb, Ce and Y contents, and high FeOt/MgO, Ga/Al and Rb/Sr ratios. The Carboniferous granitoids are mainly tonalites, granodiorites and monzogranites with U–Pb ages varying from 319 to 306 Ma, and they show very strong adakitic characteristics such as high La/Yb and Sr/Y ratios but low Y and Yb contents. The Late Permian granitoids are dominated by monzogranites and syenogranites with zircon U–Pb ages ranging between 257 and 251 Ma. Isotopically, the ε_Hf(t) values of the Neoproterozoic granitoids range from +4.3 to +8.3, and the two-stage model ages (T_DM2) from 1.2 to 1.5 Ga. The Late Devonian granitoids are less radiogenic [ε_Hf(t) from +12.0 to +12.8 and T_DM2 from 545 to 598 Ma] than the Carboniferous [ε_Hf(t) from +6.8 to +9.5 and T_DM2 from 722 to 894 Ma] and Late Permian granitoids [ε_Hf(t) from +6.1 to +9.4 and T_DM2 in the range of 680–895 Ma]. These data indicate (1) the Neoproterozoic granitoids may have been generated by melting of a juvenile crust extracted from the mantle during the Mesoproterozoic, probably during or following the final stages of assembly of Rodinia as a result of the collision and amalgamation of Australia and the Tarim Craton; (2) the Late Devonian granitoids may have formed by partial melting of a new mantle-derived juvenile crust in a post-orogenic extensional setting; (3) the Carboniferous granitoids appear to have been produced by melting of garnet-bearing amphibolites within a thickened continental crust during and following the collision of the Songnen and Erguna–Xing’an terranes; and (4) the Late Permian granitoids may have been generated by melting of garnet-free amphibolites within the Neoproterozoic juvenile continental crust, probably in the post-collisional tectonic setting that followed the collision of the North China and Siberian cratons.     

A possible transition from island arc to continental arc magmatism in the eastern Jiangnan Orogen,South China: Insights from a Neoproterozoic (870–860 Ma) gabbroic–dioritic complex near the Fuchuan ophiolite

The Fuchuan ophiolite belt in the eastern Jiangnan Orogen of South China provides important constraints on the tectonic setting and evolution of the Neoproterozoic suture zone between the Yangtze and Cathaysia blocks. Combined UPbHf isotopic and REE analysis of zircon from gabbroic and dioritic samples of the Shexian complex, located 10 km southwest of the main Fuchuan ophiolite body, indicate that the complex crystallized at ca. 870–860 Ma with a large variation of zircon ε_Hf(t) values from − 4.80 to + 13.30. Whole-rock geochemistry reveals that the magma mainly experienced fractionation of olivine, clinopyroxene and plagioclase and was partly affected by crustal contamination, which resulted in elevated Th/Nb, Th/La and La/Sm ratios, as well as the scattered ε_Hf(t) values. The most mafic and least contaminated sample shows MORB affinity and was probably formed by partial melting of a depleted subduction-metasomatized mantle wedge. Other samples exhibit arc-like signatures and were probably modified by both melt- and fluid-related subduction metasomatism. The emplacement of the Shexian complex corresponds to the time that subduction switched from a ca. 1000–880 Ma intra-oceanic island arc to a 870–830 Ma continental arc along the southeastern Yangtze Block. The sequence of igneous rocks associated with this continental arc resemble those preserved in forearc Tethyan ophiolites, with magma evolving from ca. 870–860 Ma MORB to ca. 860–850 Ma arc tholeiite and ca. 830 Ma boninite. Arc magmatism concluded with the final assembly of the Yangtze and Cathaysia blocks at 830–800 Ma.     

30 million years of Permian volcanism recorded in the Choiyoi igneous province (W Argentina) and their source for younger ash fall deposits in the Paraná Basin: SHRIMP U–Pb zircon geochronology evidence

We present four SHRIMP U–Pb zircon ages for the Choiyoi igneous province from the San Rafael Block, central–western Argentina. Dated samples come from the Yacimiento Los Reyunos Formation (281.4 ± 2.5 Ma) of the Cochicó Group (Lower Choiyoi section: andesitic breccias, dacitic to rhyolitic ignimbrites and continental conglomerates), Agua de los Burros Formation (264.8 ± 2.3 Ma and 264.5 ± 3.0 Ma) and Cerro Carrizalito Formation (251.9 ± 2.7 Ma Upper Choiyoi section: rhyolitic ignimbrites and pyroclastic flows) spanning the entire Permian succession of the Choiyoi igneous province. A single zircon from the El Imperial Formation, that is overlain unconformably by the Choiyoi succession, yielded an early Permian age (297.2 ± 5.3 Ma), while the main detrital zircon population indicated an Ordovician age (453.7 ± 8.1 Ma). The new data establishes a more precise Permian age (Artinskian–Lopingian) for the section studied spanning 30 Ma of volcanic activity. Volcanological observations for the Choiyoi succession support the occurrence of explosive eruptions of plinian to ultraplinian magnitudes, capable of injecting enormous volumes of tephra in the troposphere–stratosphere. The new SHRIMP ages indicate contemporaneity between the Choyoi succession and the upper part of the Paraná Basin late Paleozoic section, from the Irati up to the Rio do Rasto formations, encompassing about 24 Ma. Geochemical data show a general congruence in compositional and tectonic settings between the volcanics and Paraná Basin Permian ash fall derived layers of bentonites. Thickness and granulometry of ash fall layers broadly fit into the depletion curve versus distance from the remote source vent of ultraplinian eruptions. Thus, we consider that the Choiyoi igneous province was the source of ash fall deposits in the upper Permian section of the Paraná Basin. Data presented here allow a more consistent correlation between tectono-volcanic Permian events along the paleo-Pacific margin of southwestern Gondwana and the geological evolution of neighboring Paleozoic foreland basins in South America and Africa.     

Zircon U–Pb and Hf isotopic study of Mesozoic felsic rocks from eastern Zhejiang,South China: Geochemical contrast between the Yangtze and Cathaysia blocks

The Jiangshan–Shaoxing Fault Zone (JSFZ) in Zhejiang Province has been proposed to represent a suture between the Yangtze and Cathaysia blocks in South China. In this study, in-situ zircon U–Pb and Hf isotopic analysis and whole-rock major- and trace-element measurement of early to middle Cretaceous felsic rocks across the fault zone were conducted to constrain the nature of the fault zone. Twelve Cretaceous granitoid bodies were sampled from the NW and SE sides of the fault zone, respectively, with composition ranging from diorite to granite (SiO₂ = 56.2–76.6 wt.%). These granitoids yielded U–Pb ages ranging from 135–100 Ma, with a systematic variation in zircon Hf isotopic compositions (ε_Hf(t) = + 6.9 to –7.0 in the NW side vs. + 1.9 to ? 12.9 in the SE side). The T_DM2 values for the granitoids from the NW side are 0.34 to 1.33 Ga, with two peaks at ca. 876 and 1170 Ma respectively, whereas those from the SE side are 0.70 to 1.62 Ga, with a single peak at ca. 1126 Ma. The Hf isotopic disparity for the two sides may indicate a fundamental difference in the lower crustal compositions of the Yangtze and Cathaysia blocks, supporting that the JSFZ is possibly a suture zone between the two blocks. Our results together with the available geological data suggest that the Mesoproterozoic materials are important for both the Yangtze and Cathaysia basement and the Neoproterozoic magmatic activities were important in the Yangtze Block, possibly related to the break-up of the Rodinia supercontinent, but less significant in the Cathaysia Block. This may imply that the two blocks have not completely juxtaposed in the Neoproterozoic.     

Reconstructing Late Paleozoic exhumation history of the Inner Mongolia Highland along the northern edge of the North China Craton

The Inner Mongolia Highland (IMH), along the northern edge of the North China Craton, was considered to be a long-standing topographic highland, whose exhumation history remains elusive. The aim of this study is to reveal Late Paleozoic exhumation processes of the IMH based on an integrated analysis of stratigraphy, petrography of clastic rocks, and U–Pb ages and Hf isotopes of detrital zircons from Permian–Triassic succession in the middle Yanshan belt. The results of the study show that the Benxi Formation, which was originally regarded as a Late Carboniferous unit, proves to be Early Permian in age because it contains detrital zircons as young as ∼298 Ma. The Lower Shihezi Formation is demonstrated to be a unit whose age spans the boundary of the Middle and Upper Permian, constrained by a U–Pb age of 260 ± 2 Ma from a dacite layer. Clastic compositions of conglomerate and sandstone change markedly, characterised by the predominance of sedimentary components in the Benxi–Shanxi Formations, by large amounts of volcanic clastics in the Lower and Upper Shihezi Formations, and by the presence of both metamorphic and igneous clastics in the Sunjiagou–Ermaying Formations. Sedimentary clastics include chert, carbonate, sandstone and quartzite, which may have been derived from Proterozoic to Lower Paleozoic sedimentary covers. Volcanic clasts were directly related to volcanic eruptions, while granite and gneiss grains were sourced from exhumed Late Paleozoic intrusive rocks and basement rocks. Detrital zircon U–Pb ages can be divided into five populations: 2.6–2.4 Ga, 1.9–1.7 Ga, 400–360 Ma, 325–290 Ma and 270–250 Ma. Precambrian detrital zircons are typically subrounded to rounded in shape, implying a recycling origin. Late Paleozoic zircons show oscillatory zones and their Th/U ratios >0.4, suggesting a magmatic origin. Most Phanerozoic zircons have negative ε_Hf(T) values of −3.2 to −25.5, which are compatible with those of Late Paleozoic plutons in the IMH. The results indicate that the IMH may have been covered with Proterozoic to Lower Paleozoic sedimentary strata, which then underwent subsequent erosion and served as provenances for adjacent Late Paleozoic basins. Vertical changes in both clastic compositions and detrital zircon ages in Permian–Triassic strata imply an unroofing process of the IMH. Three phases of the IMH uplift are distinguished. The first-phase uplift commenced 325–312 Ma and resulted from magmatic intrusion related to southward subduction of the Paleo-Asian Ocean. The second-phase uplift took place in the Middle Permian and may be attributed to crustal contraction related to the collision of the North China Craton and the Southern Mongolia terrane. The third-phase uplift happened at the end of the Permian, and may have been induced by upwelling of calc-alkali magma under an extensional setting.     

Tectono-magmatic evolution of the Gaoligong belt,southeastern margin of the Tibetan plateau: Constraints from granitic gneisses and granitoid intrusions

The Gaoligong belt is located in the southeastern margin of the Tibetan plateau, and is bound by the Tengchong and Baoshan blocks. This paper presents new data from zircon geochronology, geochemistry, and whole-rock Sr–Nd–Pb–Hf isotopes to evaluate the tectonic evolution of the Gaoligong belt. The major rock types analysed in the present study are granitic gneiss, granodiorite, and granite. They are metaluminous to peraluminous and belong to high-K, calc-alkaline series. Laser ablation inductively coupled plasma mass spectrometry (LA–ICP–MS) analyses of zircons from nine granitic rocks yielded crystallization ages of 495–487 Ma, 121 Ma, 89 Ma, and 70–63 Ma. The granitoids can be subdivided into the following four groups. (1) Early Paleozoic granitic gneisses with high ε_Nd(t) and ε_Hf(t) values of − 1.06 to − 3.45 and − 1.16 to 2.09, and model ages of 1.16 Ga to 1.33 Ga and 1.47 Ga to 1.63 Ga, respectively. Their variable ⁸⁷Sr/⁸⁶Sr and Pb values resemble the characteristics of the Early Paleozoic Pinghe granite in the Baoshan block. Our data suggest that the rocks were derived from the break-off of the Proto-Tethyan oceanic slab between the outboard continent and the Baoshan block, which induced the partial melting of Mesoproterozoic pelitic sources mixed with depleted mantle materials. (2) Early Cretaceous granodiorites with low ε_Nd(t) and ε_Hf(t) values of − 8.92 and − 4.91 with Nd and Hf model ages of 1.41 Ga and 1.49 Ga, respectively. These rocks have high initial ⁸⁷Sr/⁸⁶Sr (0.711992) and lower crustal Pb values, suggesting that they were derived from Mesoproterozoic amphibolites with tholeiitic signature, leaving behind granulite residue at the lower crust. (3) Early Late Cretaceous granites with low ε_Nd(t) and ε_Hf(t) values of − 9.58 and − 4.61 with Nd and Hf model ages of 1.43 Ga and 1.57 Ga, respectively. These rocks have high initial ⁸⁷Sr/⁸⁶Sr (0.713045) and lower crustal Pb isotopic values. These rocks were generated from the partial melting of Mesoproterozoic metapelitic sources resulting from the delamination of thickened lithosphere, following the closure of the Bangong–Nujiang Ocean and collision of the Lhasa–Qiangtang blocks. (4) Late Cretaceous to Paleogene granitic gneisses with low ε_Nd(t) and ε_Hf(t) values of − 4.41 to − 10 and − 5.95 to − 8.71, Nd model ages ranging from 1.08 Ga to 1.43 Ga, and Hf model ages from 1.53 Ga to 1.67 Ga, respectively. These rocks show high initial ⁸⁷Sr/⁸⁶Sr (0.713201 and 714662) and lower crustal Pb values. The data suggest that these rocks are likely related to the eastward subduction of the Neo-Tethyan Oceanic slab, which induced partial melting of Mesoproterozoic lower crustal metagreywacke. The results presented in this study from the Gaoligong belt offer important insights on the evolution of the Proto-Tethyan, Bangong–Nujiang, and Neo-Tethyan oceans in the southeastern margin of the Tibetan Plateau.     

In situ zircon U–Pb and Hf–O isotopic results for ca. 73 Ma granite in Hainan Island: Implications for the termination of an Andean-type active continental margin in southeast China

We report in the paper integrated analyses of in situ zircon U–Pb ages, Hf–O isotopes, whole-rock geochemistry and Sr–Nd isotopes for the Longlou granite in northern Hainan Island, southeast China. SIMS zircon U–Pb dating results yield a crystallization age of ∼73 Ma for the Longlou granite, which is the youngest granite recognized in southeast China. The granite rocks are characterized by high SiO₂ and K₂O, weakly peraluminous (A/CNK = 1.04–1.10), depletion in Sr, Ba and high field strength elements (HFSE) and enrichment in LREE and large ion lithophile elements (LILE). Chemical variations of the granite are dominated by fractional crystallization of feldspar, biotite, Ti–Fe oxides and apatite. Their whole-rock initial ⁸⁷Sr/⁸⁶Sr ratios (0.7073–0.7107) and ε_Nd(t) (−4.6 to −6.6) and zircon ε_Hf(t) (−5.0 to 0.8) values are broadly consistent with those of the Late Mesozoic granites in southeast China coast. Zircon δ¹⁸O values of 6.9–8.3‰ suggest insignificant involvement of supracrustal materials in the granites. These granites are likely generated by partial melting of medium- to high-K basaltic rocks in an active continental margin related to subduction of the Pacific plate. The ca. 73 Ma Longlou granite is broadly coeval with the Campanian (ca. 80–70 Ma) granitoid rocks in southwest Japan and South Korea, indicating that they might be formed along a common Andean-type active continental margin of east–southeast Asia. Tectonic transition from the Andean-type to the West Pacific-type continental margin of southeast China likely took place at ca.70 Ma, rather than ca. 90–85 Ma as previously thought.     

Geochemistry and geochronology of the volcanic rocks associated with the Dong'an adularia–sericite epithermal gold deposit,Lesser Hinggan Range,Heilongjiang province,NE China: Constraints on the metallogenesis

Late Mesozoic volcanism is widespread throughout NE China. On the basis of lithological associations and spatial relationships, the volcanic rocks in the Lesser Hinggan Range can be divided into two formations, i.e., felsic-dominant Fuminghe Formation and overlying mafic-dominant Ganhe Formation. The Dong'an gold deposit, a typical adularia–sericite epithermal system, is spatially closely associated with rhyolitic porphyry, which is a subvolcanic intrusion of the Fuminghe Formation. Total measured, indicated, and inferred resources for the Dong'an deposit are 70 tonnes (2.25 Moz) of gold with the grade of 5.04 g/t Au, making it one of the largest epithermal gold deposits in China.SHRIMP U–Pb zircon and ⁴⁰Ar/³⁹Ar geochronology applied to one rhyolitic porphyry sample and sericite separated from auriferous quartz veins of the main mineralization stage were carried out to constrain magmatic and hydrothermal events. The results suggest that the mineralization age of 107.2 ± 0.6 Ma overlaps with the age of the rhyolitic porphyry 108.1 ± 2.4 Ma. Our new age data indicate that there was a previously unrecognized mineralization event in NE China at 107–108 Ma.Systematic geochemical investigations on the volcanic rocks in the Lesser Hinggan Range show that both Fuminghe and Ganhe Formations are characterized by significant large ion lithophile elements (LILE) and light rare earth elements (LREE) enrichment coupled with high field strength elements (HFSE) depletion, but they have distinct Sr and Nd isotopic compositions. The Fuminghe Formation has relative high ⁸⁷Sr/⁸⁶Sr ratios of 0.707253 to 0.707373, and negative ε_Nd(t) values of ?2.78 to ?3.05 (t = 108 Ma), whereas the Ganhe Formation displays slightly lower ⁸⁷Sr/⁸⁶Sr range of 0.705434–0.705763 and positive ε_Nd(t) values of + 0.76 to +1.83. These geochemical data suggest that the rhyolitic magmas of the Fuminghe Formation probably represent the final differentiates of parental andesitic magmas, resulted from the partial melting of mafic lower crust, whereas the volcanic rocks of the Ganhe Formation were produced by fractionation of basaltic magmas generated from partial melting of a mixture of an incompatible element depleted anhydrous lherzolite asthenospheric mantle source and a hydrous enriched lithospheric mantle source in an extensional tectonic setting, in response to upwelling of asthenospheric mantle. The rhyolite porphyries of the Fuminghe Formation are inferred to have supplied heat that drove the convective hydrothermal system at Dong'an deposit, but also provided some of the fluid sources responsible for the development of the Dong'an epithermal system.     

Gold-hosting high Ba-Sr granitoids in the Xincheng gold deposit,Jiaodong Peninsula,East China: Petrogenesis and tectonic setting

The Xincheng deposit is the only large gold deposit with a proven reserve of >200 t gold hosted by the Early Cretaceous granitoids in northwest Jiaodong Peninsula, East China. The granitoids hosting this ore deposit comprise an inner medium- to fine-grained quartz monzonite and an outer medium- to coarse-grained monzogranite with distinctive K-feldspar megacrysts. LA–ICP–MS zircon dating yields U–Pb ages of 128 ± 1 to 132 ± 1 Ma and 127 ± 2 to 129 ± 1 Ma, for the quartz monzonite and the monzogranite, respectively. The Early Cretaceous ages obtained in our study are comparable with the 126–130 Ma age range reported for the Guojialing granitic suite. The monzogranites, typical high Ba–Sr granites, possess high SiO₂ (70.89–73.35%), K₂O (3.85–4.32%), total alkalis (K₂O + Na₂O = 8.08–8.68%), Sr (634–888 ppm), Ba (1395–2111 ppm) and LREE (59.43–145.88), with low HREE and HFSE contents and insignificant Eu anomalies. The rocks display markedly high Sr/Y (114–297) and (La/Yb)_N (20–79) ratios. They have low MgO (0.23–0.62%), Cr (0.4–8.33 ppm) and Ni (0.47–2.92 ppm) contents. The typical high Ba–Sr signatures of the outer acidic monzogranites are also shared by the inner intermediate-acidic quartz monzonites, with a relatively higher abundance of these elements. The plagioclases in the quartz monzonites and monzogranites are oligoclase–andesine with An contents of 11.7–44.5%, and oligoclase with An contents of 12.9–29.3%, respectively, which both show the reverse zoning texture. The quartz monzonites have zircon ε_Hf(t) values of −21.3 to −13.9 (average −18.7), which are less negative and show larger variations than those of the monzogranites (ε_Hf(t) = −24.7 to −18.1, average −19.5). Detailed elemental, mineralogical and isotopic data suggest that the high Ba–Sr quartz monzonites and monzogranites were most likely generated by partial melting of the basement rocks of the Jiaobei terrane accompanied by crustal assimilation, with minor addition of the intermediate magma derived from the partial melting of juvenile mafic lower crust formed by the earlier underplating of mantle magma, and the quartz monzonites may represent the path of intermediate magma inputting into felsic magma. In combination with previous investigations, we suggest subduction of the paleo-Pacific slab beneath the North China Craton (NCC) and associated asthenosphere upwelling were most likely the mechanism associated with the generation of the high Ba–Sr granites.     

Zircon U-Pb geochronology,Lu-Hf isotope systematics,and geochemistry of bimodal volcanic rocks and associated granitoids from Kotri Belt,Central India: Implications for Neoarchean–Paleoproterozoic crustal growth

The Bastar Craton of Central India has a thick sequence of volcano–sedimentary rocks preserved in Kotri–Dongargarh belt that developed on a tonalite-trondhjemite-granodiorite (TTG) basement followed upwards by the Amgaon, Bengpal, Bailadila, and Nandgaon Groups of rocks. Here, we report the U-Pb geochronology and Lu-Hf isotope systematics and whole rock geochemistry of volcanic rocks and associated granitoids belonging to the Pitepani basalts, Bijli rhyolites, and Dongargarh granite in the Nandgaon Group of the Kotri belt. The volcanic rocks of the Nandgaon Group are bimodal in nature in which the basalts exhibit intergranular, porphyritic to spherulitic texture composed of pyroxenes, plagioclase, tremolite, actinolite, and chlorite ± Fe oxides. The rhyolites display porphyritic texture consisting of K-feldspar, quartz, and plagioclase as phenocrysts. The associated porphyritic granitoids have K-feldspar, microcline, plagioclase, and biotite phenocrysts within a groundmass of similar composition. The bimodal suite displays LILE, LREE enrichment, and HFSE depletion with significant negative Nb-Ta anomalies combined with slightly fractionated REE patterns in the basalts and highly fractionated patterns and prominent negative Eu anomalies in the rhyolites endorsing their generation in an island-arc/back-arc tectonic setting. The geochemical features of the associated granitoids indicate that these are potassic and classify as within-plate A-type granites. Zircons from the basalts show clear oscillatory zoning in their CL images. They cluster as a coherent group with ²⁰⁷Pb/²⁰⁶Pb spot ages ranging from 2446 to 2522 Ma and weighted mean age of 2471 ± 7 Ma. Zircons from the rhyolite samples are subhedral to euhedral and show simple oscillatory zoning with some heterogeneous fractured domains. The data from two samples define upper intercept ages of 2479 ± 13 Ma and 2463 ± 14 Ma. Zircon grains in the granite show clear oscillatory zoning and their U-Pb data define an upper intercept age of 2506 ± 50 Ma. The Lu-Hf isotopic data on the zircons from the basalts show initial ¹⁷⁶Hf/¹⁷⁷Hf ratios from 0.280925 to 0.281018. Their ε_Hf(t) values are in the range of − 10.0 to − 6.7. The Hf-depleted model ages (T_DM) are between 3038 Ma and 3171 Ma, and Hf crustal model ages (T_DM^C) vary from 3387–3589 Ma. The zircons from the rhyolites show initial ¹⁷⁶Hf/¹⁷⁷Hf ratios from 0.280919 to 0.281020 and from 0.281000 to 0.281103, respectively, with ε_Hf(t) values varying from − 10 to − 6.4 and from − 7.5 to − 3.9. Among these, one sample shows T_DM between 3038 Ma and 3182 Ma, and T_DM^C varies from 3377 to 3596 Ma, whereas the other sample shows ages of 2925 Ma and 3072 Ma with T_DM^C varying from 3208 to 3432 Ma. The initial ¹⁷⁶Hf/¹⁷⁷Hf ratios of the granites range from 0.280937 to 0.281062 with ε_Hf(t) values of − 8.8 to − 4.3. The T_DM shows a range of 2979 Ma and 3170 Ma, and T_DM^C varies from 3269 to 3541 Ma. The predominant negative ε_Hf(t) values of zircons from these rocks suggest that the source material was evolved from the Paleoarchean crust. The geological, geochemical, and geochronological evidence suggests coeval tectonic and magmatic episodes of volcanic and plutonic activity in an island-arc setting where the arc migrated toward the continental margin and played a significant role in the Neoarchean–Paleoproterozoic crustal growth of the Kotri belt of Central India.     

Geochronology of the Xingshan molybdenum deposit,Jilin Province,NE China,and its Hf isotope significance

The Xingshan porphyry Mo deposit is located in the Lesser Xing’an Range–Zhangguangcai Range metallogenic belt, NE China. Mineralization occurred in granodioritic porphyry and monzogranite, which have zircon U–Pb ages of 171.7 ± 2.2 Ma and 170.9 ± 4.6 Ma, respectively. Molybdenite Re–Os dating indicates that Mo mineralization occurred at 167.3 ± 2.5 Ma. These geochronological data suggest that the magmatic and hydrothermal activities of the Xingshan Mo deposit happened during the Middle Jurassic in Mesozoic. Positive ε_Hf values (6.2–11.6) and young T_DM2 (473–826 Ma) of the monzogranite (XS-3) and granodioritic porphyry (XS-5) indicate that the source materials of Xingshan ore-bearing rocks are the juvenile crust, which mainly accreted on the Songnen block during the Meso-Neoproterozoic. Xingshan porphyry Mo deposits resulted from the magmatism and tectonism induced by the subduction of Paleo-Pacific Ocean.     

Mineralogy and geochemistry of claystones from the Guadalupian–Lopingian boundary at Penglaitan,South China: Insights into the pre-Lopingian geological events

The Guadalupian–Lopingian (G/L) boundary, at a stratigraphically well-documented outcrop in Penglaitan, Guangxi Autonomous Region, South China, has been approved as the Global Stratotype Section and Point (GSSP). Several volcanic ashes or tuffs occur at this boundary, but their mineralogy and geochemistry are not available yet and no reliable age for this boundary has been obtained. A combined study of mineralogy, geochemistry and geochronology has been carried out in this study on six layers of claystones collected below (Group 1) and above (Group 2) the G/L boundary at the Penglaitan section. Both Group 1 and Group 2 claystones are likely clastic in origin, rather than volcanic ashes as previously thought. Thus the Penglaitan claystones are not suitable for age determination of the G/L boundary. They are significantly different in terms of mineralogy and geochemistry. Specifically, Group 1 claystones are likely derived from a mafic source which is genetically related to the Emeishan large igneous province, therefore providing additional evidence for the synchroneity between the G/L boundary mass extinction and the Emeishan volcanism. Group 2 samples were derived from a felsic source, of which zircons yield an age spectrum peaked at 262 ± 3 Ma, undistinguishable within the uncertainty from the currently accepted G/L boundary age (260.4 ± 0.4 Ma). Nevertheless, Group 2 samples are not related to Emeishan volcanism, because their negative zircon ε_Hf(t) values differ significantly from those of Emeishan magmas and trace element compositions of zircons are indicative of an arc source, rather than a within-plate source. In consideration of paleogeographic reconstruction, we propose that the Group 2 claystones may have been derived from continental arcs during the palaeo-Tethys evolution. This is the first sedimentary evidence for Permian continental arc in the northern margin of palaeo-Tethys.