Triassic Granitic Rocks Research Articles

Apatite chemistry of Late Triassic granitic rocks from Yidun Terrane: Implications for petrogenesis and mineralization

Apatite chemistry of Late Triassic granitic rocks from Yidun Terrane: Implications for petrogenesis and mineralization

Skarn mineralogy and in-situ LA–ICP–MS U–Pb geochronology of wolframite for the Caojiaba tungsten deposit, southern China: Implications for a reduced tungsten skarn deposit

The Caojiaba tungsten deposit (19.03 Mt@ 0.37 wt% WO3) is hosted in skarn within clastic and carbonate rocks in the Xiangzhong metallogenic province (XZMP), southern China. The deposit is characterized by an early prograde skarn overprinted by a retrograde assemblage, and then by quartz–scheelite–sulfide veins. The Caojiaba skarn is characterized by grossular garnet (Grs65–85Adr7.1–31) and hedenbergitic pyroxene (Hd63–86Di11–33), similar to the well–studied reduced tungsten skarns worldwide. In this paper, we present in-situ laser ablation inductively coupled plasma mass spectrometry (LA–ICP–MS) analysis of U–Pb isotopes and trace elements of wolframite grains coexisting with scheelite in the quartz–scheelite–sulfide veins. Uranium is correlated positively with Nb5+, tetravalent (Ti4+, Sn4+, Zr4+, Hf4+), and trivalent (Sc3+, V3+, Y3+, REE3+) cations in all wolframite samples, suggesting that the incorporation of U into wolframite is controlled by the coupled substitution mechanisms. Two wolframite samples (CJB–43 and CJB–44) yielded 206Pb/238U ages of 212.4 ± 1.0 Ma (2σ, n = 50, MSWD = 0.92) and 211.8 ± 1.1 Ma (2σ, n = 43, MSWD = 1.4), overlapping with the late Triassic granitic rocks (225.6–204.5 Ma) in the XZMP. Mineralogical and geochronological evidence collectively indicate that Caojiaba is a typical example of the late Triassic reduced tungsten skarn deposits in the XZMP. This study demonstrates the potential of U–Pb dating of wolframite and highlights its importance for directly dating hydrothermal ore–forming processes.

Evolution of the Kolyvan-Tomsk granitoid magmatism (Central Siberia): Insights into the tectonic transition from post-collision to intraplate settings in the northwestern part of the Central Asian Orogenic Belt

Late Paleozoic – early Mesozoic geological evolution of the Kolyvan-Tomsk Fold Zone (KTFZ) located in the northwestern part of the Central Asian Orogenic Belt is significant to understanding the tectonic transition from post-collision to intraplate settings. We present new whole-rock geochemical and Sr-Nd isotopic data, and in situ zircon U-Pb ages for granitic rocks from the KTFZ basement to constrain their petrogenesis and to characterize changing of the tectonic setting and geodynamic evolution. Zircon U-Pb ages reveal extended multi-stage emplacement of the KTFZ granitoids for about 20 Ma from ~260 to ~240 Ma, that can be divided into two stages: the Permian-Triassic (~260 to 250 Ma) and the Triassic (~250 to 240 Ma). The Permian –Triassic granitic rocks with SiO2 between 63% and 74% have high LREE, HFSE (except Nb and Ta), Sr, Mg#, Cr, Ni concentrations, Sr/Y and (La/Yb)N ratios and remarkably low Y and Yb contents and 87Sr/86Sr(T) values (0.704682 and 0.703368). They are magnesian and show metaluminous to weakly peraluminous natures, indicating their formation through high degree fractionation of mantle-derived magmas. The Triassic granitoids exhibit extremely high SiO2 (73–77%), HFSE, HREE, Rb contents, Rb/Sr ratios and elevated negative Eu and Sr anomalies, low Mg#. They are ferroan and have a peraluminous nature with the absence of aluminium-rich minerals, all of which indicate the presence of the crustal substance in the magma source. Isotopic Nd compositions show that the both the Permian –Triassic and Triassic granitoids have uniform magma's, which were derived from partial melting of juvenile Neoproterozoic sources.These two stages of granitoid magmatism are interpreted as reflecting the transition from post-collisional magmatism, related to the final closure of the Paleo-Asian Ocean due to collision between the Baltica and Siberian paleocontinents during the Late Permian – Early Triassic and hence, to the intraplate magmatism. The formation of the KTFZ granitic rocks was induced by an upwelling asthenosphere in an extensional geodynamic setting. During the post-collisional process, the large-scale lithospheric delamination plays a key role in the genesis of the Permian-Triassic granitoids and provide the magma generation for them. In the Triassic, we propose additional source of heat from mantle plume beneath the KTFZ, which promote extending of the granitoid magmatism in intraplate setting.

Genesis of Middle Triassic high-Mg# quartz diorites from the Xiahe area, West Qinling Orogen, Central China, and their geodynamic implications

The West Qinling Orogen (WQO) features widespread Triassic granitic rocks, which are crucial to constrain the tectonic evolution of the WQO. Here, we conducted an integrated petrological, geochronological, geochemical, and Sr-Nd-Hf isotope study on quartz diorites and mafic microgranular enclaves (MMEs) from the Ren’ai and Daerzang plutons, Hezuo area, WQO. The quartz diorites and MMEs have crystallization ages between 244 and 241 Ma. The quartz diorites display intermediate SiO2, high Mg# values (62–66) and evolved S-Nd-Hf isotope compositions, indicating an origin from magma mixing process. The MMEs display mineral compositions similar to those of the host rocks, only with more mafic minerals. The The Ren’ai and Daerzang plutons were part of the early Indosinian magmatic belt mainly distributed in the western and middle parts of the northern WQO. In comparison, late Indosinian magmatic rocks are mainly exposed in the eastern WQO. The asymmetric distribution of Early Mesozoic magmatism in the WQO might have been caused by a specific subduction pattern of the A’nimaque-Mianlue oceanic crust. The western and middle WQO experienced a period of flat or low angle subduction in the early stage, followed by slab rollback of the oceanic crust, which accounted for the flare-up of early Indosinian magmatism in the northern WQO. However, the distribution of late Indosinian magmatism might have been caused by asymmetric crustal delamination in the WQO.

Final-Stage Magmatic Record of Paleo-Asian Oceanic Subduction? Insights from Late Permian to Early Triassic Intrusive Rocks in the Yanbian Area, Easternmost Central Asian Orogenic Belt

This paper reports new zircon LA–ICP–MS U–Pb and Hf isotope data, and whole-rock major and trace element data for Late Permian to Early Triassic intrusive rocks in the Yanbian area, NE China. These data provide new insights into the timing of the final subduction of the Paleo-Asian Ocean beneath the North China Craton. The zircon U–Pb age data indicate that a suite of Late Permian to Early Triassic intrusive rocks related to subduction is present within the Yanbian area. The Late Permian intrusive rocks consist of diorites while the Early Triassic granites and hornblende gabbros constitute a geochemically bimodal igneous rock association. Furthermore, the Early Triassic granites show the geochemical characteristics of shoshonitic rocks. All the rocks are characterized by enrichment in LILEs and LREEs, and depletion in HREEs and HFSEs, suggesting they formed in a subduction setting. Zircons from the Early Triassic gabbros have εHf(t) values and TDM2 ages of +7.6 to +10.7 and 735–1022 Ma, respectively, suggesting that they formed from a primary magma generated by the partial melting of lithospheric mantle material that had been previously modified by subduction-related fluids. The Late Permian diorites have εHf(t) values and TDM2 ages of +0.5 to +9.5 and 853 to 1669 Ma, respectively, while they have high contents of Al2O3, Fe2O3, and low contents of SiO2, Cr, and Ni, indicating Late Permian diorites should derive from the mantle and are influenced by some crustal material. Early Triassic granitic rocks have a wide range of εHf(t) values and TDM2 ages of −4.8 to +9.4 and 852 to 2136 Ma, respectively. Their zircons imply that the Early Triassic granites could be mainly derived from partial melting of the crust, with minor contribution of the crustal material of an ancient crust. The Early Triassic bimodal intrusive rocks in Yanbian area, combined with the regional geologic information; therefore, record a final post-subduction extensional environment due to the break-off of the previously subducted slab.

U-Pb isotope geochronology and geochemistry of granites from Hainan Island (northern South China Sea margin): Constraints on late Paleozoic-Mesozoic tectonic evolution

Hainan Island is a key component of the South China Sea region and provides insights on regional geological evolution since the Paleozoic. Ten new LA-ICPMS zircon U-Pb ages from granites of Hainan Island include Late Permian (254±3Ma; 252±3Ma), Middle-Late Triassic (243±2Ma; 242±3Ma; 240±2Ma; 228±2Ma) and late Early to early Late Cretaceous (105±1Ma; 101±1Ma; 96±2Ma; 95±3Ma) ages. All samples in the present study, including late Permian, Middle-Late Triassic, and late Early to early Late Cretaceous granitic rocks show geochemical characteristics similar to those of calc-alkaline to high-K calc-alkaline I-type granites. Major and trace element geochemical variations show that during petrogenesis, these granites experienced fractional crystallization of minerals (e.g., Ti oxides and apatite). Compared to the late Permian and Middle-Late Triassic granitic rocks, middle to late Cretaceous granites generally have lower initial 87Sr/86Sr ratios of 0.70594 to 0.70886, lower TDM2 ages of 1314 to 1382Ma, and higher εNd(t) of −4.94 to −5.96, implying that the magmatic source for Cretaceous granites received more significant contribution from juvenile material relative to that for Permo-Triassic granites. These new data, combined with data from literature for Hainan Island and the South China Sea (SCS) region underpin a conceptual model for late Paleozoic to Mesozoic tectonic evolution for Hainan Island and the general SCS region as follows, (a) Late Permian (272–252Ma), the initiation and development of continental arc related to the subduction of Palaeo-Tethys ocean; (b) Triassic (249–228Ma), continued arc magmatism, the gradual cessation of Palaeo-Tethys subduction and subsequent development of an extensional setting; (c) Early Jurassic to early Cretaceous (190–130Ma), the development of an Andean-type continental arc, and regional tectonic regime switch to the westward subduction of the Palaeo-Pacific plate; (d) Middle to late Cretaceous (128–70Ma), the continuation of the Andean-type arc, the development of an extensional setting due to slab rollback, and the cessation (~70Ma) of Palaeo-Pacific plate subduction.

Geochronology and Petrogenesis of Mesozoic Granitoids in the Geological Corridor of Western Liaoning Province, China

Geochronology and Petrogenesis of Mesozoic Granitoids in the Geological Corridor of Western Liaoning Province, China

Early Mesozoic Southward Subduction of the Eastern Mongol–Okhotsk Oceanic Plate: Evidence from Zircon U–Pb–Hf Isotopes and Whole‐rock Geochemistry of Triassic Granitic Rocks in the Mohe Area, NE China

AbstractIn this paper, we present new U–Pb zircon ages, Hf isotope data and major and trace elements for Early Mesozoic granitic rocks in Mohe area in the Erguna Massif of northeast China to elucidate the southward subduction of the eastern Mongol–Okhotsk Oceanic plate in Early Mesozoic. Zircons from two representative intrusions, syenogranites and monzogranites, in the Mohe area are euhedral–subhedral in shape, display oscillatory growth zoning in cathodoluminescence (CL) images, and have Th/U ratios of 0.10–0.72, and in combination these features indicating that the zircons are of igneous origin. U–Pb zircon dating results demonstrate that the syenogranites formed at 245.1 ± 1.4 Ma and monzogranites formed at 212.2 ± 1.7 Ma. These granitic rocks are characterized by high SiO2, Al2O3 and (Na2O + K2O), low TFeO, MgO, TiO2 and P2O5 concentrations, belonging to the high‐K calc‐alkaline series. They are enriched in LREE and large ion lithophile elements (e.g., Rb, K, and Sr), depleted in HREE and high field strength elements (e.g., Nb, Ta, Th, and Ti), as well as very weak negative Eu anomalies (Eu/Eu* = 0.48 ~ 1.01). Their zircon εHf(t) values range from −7.9 to −2.0 and range from 0.20 to 0.49, in response to their two‐stage Hf model ages (TDM2) range from 1.40 Ga to 1.77 Ga range from 0.94 Ga to 1.24 Ga, respectively, indicating that primary magmas of syenogranites were derived from partial melting of newly accreted juvenile crustal material that formed from the enriched mantle during the Mesoproterozoic, monzogranites are generated by partial melting of newly accreted juvenile crustal material that formed from the depleted mantle during the Meso‐ to Neoproterozoic. We conclude, therefore, that the early Mesozoic granitic rocks of the Mohe area are associated with the continuous southward subduction of the Mongol–Okhotsk oceanic plate rather than the Paleo‐Asian and circum‐Pacific tectonic regimes.

Implications of U–Pb and Lu–Hf isotopic analysis of detrital zircons for the depositional age, provenance and tectonic setting of the Permian–Triassic Palaeotethyan Karakaya Complex, NW Turkey

New zircon U–Pb age data, combined with Lu–Hf isotopic data, are presented here for sandstones of mainly arkosic composition from the Permian–Triassic Karakaya Complex. Predominantly, Carboniferous, Triassic and Devonian zircon age groups are recognised, most of which have a Late Triassic (Carnian–Norian) maximum depositional age. Carboniferous- and Devonian-aged zircon populations exhibit intermediate e Hf(t) values (−11 to +2), consistent with formation in a continental margin arc setting where juvenile mantle-derived magma mixed with (recycled) old crust of Palaeoproterozoic Hf model age. In contrast, the Triassic-aged zircon population exhibits higher e Hf(t) values (−5 to +4), consistent with mixing of juvenile mantle-derived melts with (recycled) old crust of Neoproterozoic Hf model age. Potential igneous source rocks for the sandstones of the Karakaya Complex exist in the Devonian and Carboniferous granitic rocks of the Sakarya continental basement to the north. Their e Hf(t) and corresponding model ages are nearly identical to the age-equivalent zircon populations within the Karakaya Complex sandstones. However, the Triassic granitic rocks of the Sakarya continental crust differ significantly in e Hf(t) and corresponding model age from the sandstones of the Karakaya Complex. Late Triassic sandstones from the Tauride continental unit to the south lack the dominant Late Palaeozoic and Triassic zircon populations of the Karakaya Complex sandstones. Triassic granitic bodies and intermediate-composition extrusive rocks in the Tauride continental unit also differ in e Hf(t) and corresponding Hf model ages from the Karakaya Complex sandstones. In addition, Late Triassic sandstones of the Kocaeli Triassic unit (Istanbul Terrane) in the north differ strongly from the Karakaya Complex sandstones in zircon population ages and e Hf(t). In the regional context, the new zircon age and lutetium–hafnium isotopic data are consistent with derivation of the Late Triassic Karakaya Complex sandstones from a Late Palaeozoic–Triassic continental margin arc located somewhere along the southern margin of Eurasia, although its exact position cannot be pinpointed at present owing to lack of suitable outcrop and comparable isotopic data.

Structural characteristics and LA–ICP-MS U–Pb zircon geochronology of the deformed granitic rocks from the Mesozoic Xingcheng-Taili ductile shear zone in the North China Craton

We describe the recently detected ENE-trending Xingcheng-Taili ductile strike-slip shear zone, which is an important Mesozoic low- to middle-grade tectonic element formed during the reactivation of the North China Craton (NCC) at the eastern termination of the Yanshanian orogenic belt. Within the Xingcheng-Taili ductile shear zone, the degree of deformation weakens gradually from NW to SE. Three main types of banded granitic gneisses represent low- to middle-grade metamorphic tectonites. New U–Pb zircon dating gives a wide range of protolith ages. Neoarchean granitic rocks with an emplacement age of 2498.4±6.3Ma have obvious E–W trending banded structures. Upper Triassic granitic rocks with U–Pb zircon ages of 219.7±1.1Ma, 218.74±0.61Ma, 212.1±1.6Ma and 212.3±1.9Ma are considered to relate to the collision of the NCC and Yangtze craton in early Mesozoic times. The emplacement of biotite adamellite bodies with ages of 159.0±0.8Ma and 152.4±1.9Ma is related to the thinning of the NCC's continental crust. An ENE-trending sinistral ductile shear zone developed within these granites. The strongly deformed biotite adamellite bodies bear a gneissosity with S–C fabrics, ENE-trending sinistral shear zones and show the deformation characteristics of a shallow crustal level, reflecting decratonization of the NCC. Crystal lattice preferred orientations (LPO) of quartz, determined by electron back-scatter diffraction, suggest sinistral strike-slip shear and a deformation temperature at about 400 to 500°C. Quartz mainly shows low-temperature fabrics with a dominant {0001}-slip system similar to the temperature estimated by the micro-structural characteristics of quartz and feldspar. This deformation event might have occurred in Early Cretaceous times and is related to the lithospheric thinning and extension of the North China Craton triggered by an ongoing roll-back of the Pacific Plate beneath the eastern North China Craton.

SHRIMP zircon and EPMA monazite dating of granitic rocks from the Maizuru terrane, southwest Japan: Correlation with East Asian Paleozoic terranes and geological implications

Abstract The Maizuru terrane, distributed in the Inner Zone of southwest Japan, is divided into three subzones (Northern, Central and Southern), each with distinct lithological associations. In clear contrast with the Southern zone consisting of the Yakuno ophiolite, the Northern zone is subdivided into the western and eastern bodies by a high‐angle fault, recognized mainly by the presence of deformed granitic rocks and pelitic gneiss. This association suggests an affinity with a mature continental block; this is supported by the mode of occurrence, and petrological and isotopic data. Newly obtained sensitive high mass‐resolution ion microprobe (SHRIMP) zircon U–Pb ages reveal the intrusion ages of 424 ± 16 and 405 ± 18 Ma (Siluro–Devonian) for the granites from the western body, and 249 ± 10 and 243 ± 19 Ma (Permo–Triassic) for the granodiorites from the eastern body. The granites in the western body also show inherited zircon ages of around 580 and 765 Ma. In addition, electron probe microanalysis (EPMA) monazite U–Th–total Pb dating gives around 475–460 Ma. The age of intrusion, inherited ages, mode of occurrence, and geological setting of the Siluro–Devonian granites of the Northern zone all show similarities with those of the Khanka Massif, southern Primoye, Russia, and the Hikami granitic rocks of the South Kitakami terrane, Northeast Japan. We propose that both the Siluro–Devonian and Permo–Triassic granitic rocks of the Northern zone are likely to have been juxtaposed through the Triassic–Late Jurassic dextral strike‐slip movement, and to have originated from the Khanka Massif and the Hida terrane, respectively. This study strongly supports the importance of the strike‐slip movement as a mechanism causing the structural rearrangement of the Paleozoic–Mesozoic terranes in the Japanese Islands, as well as in East Asia.