Early Paleozoic Magmatic Rocks Research Articles

Early Paleozoic granitic magmatism and mineralization in the Debao Sn-Cu deposit, South China: Constraints from zircon and cassiterite U-Pb geochronology and whole-rock geochemistry

Numerous W-Sn deposits are developed in South China. While the majority of these deposits are related to the Yanshanian granites, a few of them are associated with the Early Paleozoic granites, and their geological significance is poorly understood. The Debao deposit is a typical skarn Sn-Cu polymetallic deposit that is spatially related to the Early Paleozoic Qinjia granites. Zircon U-Pb dating of three lithofacies (coarse-grained biotite granite, medium-grained porphyritic biotite granite and fine-grained porphyritic biotite granite) of the Qinjia granites yielded emplacement ages of 437.8 ± 3.0 Ma, 440.2 ± 2.0 Ma and 441.0 ± 3.0 Ma, respectively, consistent with cassiterite U-Pb ages of skarn ore (439.6 ± 2.7 Ma), indicating a close genetic relationship between the granitic magmatism and Sn mineralization. Biotite from the Qinjia granites belong to the ferro-biotite series with relatively high F contents (up to 0.70 wt. %). The Biotite compositions plot near the Ni-NiO (NNO) buffer on a Fe3+-Fe2+-Mg2+ diagram, suggesting formation under relatively low oxygen fugacity. The Qinjia granites are characterized by highly silicious (70.37–72.88 wt. %), high alkali (Na2O + K2O = 6.98–8.88 wt. %) and metaluminous to strongly peraluminous with the A/CNK ratios of 0.92–1.21, belonging to the I-S transform-type granites. They are enriched in U, Th, Zr, Nd and Hf, and depleted in Ba, Sr, Nb, Ta and Ti. They display right-declining chondrite-normalized REE patterns with significant negative Eu anomalies (EuN/Eu* = 0.33–0.66), and have low Nb/Ta and K/Rb ratios, indicating that the Qinjia granites experienced a high degree of fractional crystallization. The zircon εHf(t) values (−2.7 to +1.4), together with TDMC of 1.59 to 1.33 Ga, indicate that the granites formed via partial melting of Mesoproterozoic crustal with minor addition of mantle materials. The reduced (fO2 near NNO and Ce4+/Ce3+ ratios of zircon < 100), fractionated and volatile-rich magma facilitated the enrichment of Sn in the residual melt and hydrothermal fluids. Combined with previous studies on the Early Paleozoic magmatic rocks and tectonic activities in South China, we suggest that the Qinjia granites and associated Sn-Cu mineralization were likely formed in the post-collisional extensional environment during the Wuyi-Yunkai orogeny.

Geodynamic controls on the Paleo-Asian oceanic plate evolution: Constraints from Paleozoic intrusive suites along the northern margin of the North China Block

Identifying the spatio-temporal variations of arc-relation magmatism is critical for determining the polarity, geometry, localization, and onset of subduction zones on Earth. When and how the Paleo-Asian oceanic plate subducted beneath the northern margin of the North China Block (NCB) have been widely debated. Here we conducted systematic petrological, geochronological, and geochemical investigations on the Paleozoic magmatic rocks in the northern NCB. The Early Paleozoic magmatic rocks (ca. 490–420 Ma) are only distributed in the Bainaimiao arc and show typical continental arc geochemical characteristics, indicating a south dipping subduction zone. The Devonian alkaline rocks (ca. 400–370 Ma) constitute a ∼ 900 km-long magmatic belt in the northern margin of the NCB. Combined with a striking ca. 370–355 Ma magmatic quiescence and the absence of high-pressure rocks during that period, a flat-slab subduction model is proposed to better account for the tectonic evolution of the northern NCB. Subsequently, the Carboniferous to Permian calc-alkaline arc magmatism (ca. 355–250 Ma) began to emerge and showed northward younging and migration, suggesting slab retreat with roll-back of the subducting Paleo-Asian slab and again opening of mantle wedge along the northern NCB. Our findings therefore suggest that the Paleozoic magmatism in the northern NCB records an entire spatio-temporal evolution of the Paleo-Asian oceanic plate from early subduction angle deepening to flat-slab subduction, then slab rollback and finally normal subduction. This is tentatively interpreted as a combined effect from the Paleo-Asian oceanic plate subduction angle change and a migrating keel in the mantle wedge region.

Petrogenesis and Tectonic Implications of Early Paleozoic Magmatism in Awen Gold District, South Section of the Truong Son Orogenic Belt, Laos

The Truong Son orogenic belt (TSOB) is one of the most important orogenic belts in the Indochina block. There are numerous mafic to felsic intrusions in the Early Paleozoic caused by the Tethyan orogeny. However, the tectono-magmatic evolution of the TSOB in the Early Paleozoic is still unclear. In this paper, zircon U-Pb dating, whole-rock geochemistry, and the Sr-Nd isotopic data of the Early Paleozoic magmatic rocks have been systematically investigated to explore the petrogenesis and tectonic significance of these rocks in the TSOB. Based on our new results integrated with previous geological data, four major tectono-magmatic episodes are identified. (1) The Middle Cambrian (~507 Ma) is the early stage of northward subduction of the Tamky-Phuoc Son Ocean. (2) The Early Ordovician to Middle Ordovician (483–461 Ma) is the main subduction stage of the Tamky-Phuoc Son Ocean. The intrusive rock associations imply the closure of the Tamky-Phuoc Son Ocean. (3) The Late Ordovician to Early Silurian (461–438 Ma) is the collision stage of the Kontum massif and Truong Son terrane. (4) The Early Silurian to Late Silurian (438–410 Ma) is the late stage of collision accompanied by slab roll-back.

Provenance and tectonic implications of the Carboniferous sediments in the Bainaimiao arc belt, northern margin of the North China Craton: evidence from detrital zircon U–Pb–Hf isotopes and trace elements

Sedimentological and zircon U–Pb–Hf isotopic analyses of the Carboniferous strata in the Bainaimiao arc belt (BAB) provide provenance information for the northern margin of the North China Craton (NCC). The late Carboniferous strata in the eastern BAB were dominantly shallow marine carbonate-clastic deposits. Detrital zircon data show that: (1) sandstone from lower Sidaozhangpeng Formation displays two major age peaks of 369 Ma and 2522 Ma, with eHf (t) values of − 25.9 to − 20.4 and 2.2–6.4, respectively; (2) sandstone from upper Sidaozhangpeng Formation shows a significant age peak at 384 Ma, with eHf (t) values of − 25.3 to − 14.5. Determination of detrital zircon parent rock types based on trace element proxies suggests that the protolith rock types consist of felsic (73%) and mafic rocks (22%), with minor alkaline rocks (5%), implying a continental arc setting. The U–Pb–Hf dating of the Carboniferous strata in the western and eastern BAB shows different provenances: the Carboniferous sediments in the western BAB were derived from early Paleozoic magmatic rocks, micro-block (Hunshandake Block) and the NCC basement; the provenances of the Carboniferous strata from the eastern BAB were mainly local Devonian magmatic rocks, with subordinate input of the Neoarchean NCC basement rocks. The early Paleozoic zircon grains recorded by the early Devonian rhyolitic tuff and late Carboniferous sandstone indicate that the early Paleozoic arc magmatic activities also occurred in the eastern BAB.

Weakly fractionated I-type granitoids and their relationship to tungsten mineralization: A case study from the early Paleozoic Shangmushui deposit, Dayaoshan area, South China

Tungsten deposits related to weakly fractionated granitoids are scarce worldwide. The geological significance of early Paleozoic magmatism and associated mineralization in South China remains poorly understood compared with well-documented Mesozoic magmatism and related mineralization. Early Paleozoic magmatic rocks, previously thought to be only rarely associated with mineralization, crop out widely in the Dayaoshan area, South China, and have significant prospecting potential for tungsten polymetallic deposits. Shangmushui is a newly discovered W-bearing skarn (with minor Cu) deposit in the Dayaoshan area. The zircon U–Pb age of the granodiorite that hosts the tungsten deposit is 465.4 ± 1.5 Ma, which is consistent with scheelite Sm–Nd age (466.6 ± 5.5 Ma) within the error. The present data, combined with previous findings, indicate a protracted period of magmatism and related W–Mo polymetallic mineralization during 470–420 Ma in the Dayaoshan area. Elevated zircon δ18OV-SMOW values (5.5‰ to 6.6‰) and mostly negative εHf(t) values (–9.5 to +0.7), together with TDM2 of 1.6 Ga indicate that these plutons formed via partial melting of Mesoproterozoic crust with some contributions from mantle materials. Estimates of the oxygen fugacity of the magmas show that the Shangmushui granodiorite is relatively reduced (FMQ–0.11). Shangmushui granodiorite is a weakly fractionated I-type granitoid with low differentiation index values (DI = 59.6–66.9), B contents (8.6–30.1 ppm), and Rb/Sr ratios (0.34–0.73), which are different from most highly fractionated tungsten-bearing S- and I-type granitoids globally. The low oxygen fugacity and high W contents of the granodiorites, and the close spatio-temporal relationship between the granodiorites and the tungsten ore bodies, indicate that early Paleozoic weakly fractionated I-type granitoids in the Shangmushui region have a close genetic relationship with tungsten mineralization.

Early to mid-Paleozoic magmatic and sedimentary records in the Bainaimiao Arc: An advancing subduction-induced terrane accretion along the northern margin of the North China Craton

The early to mid-Paleozoic subduction-induced terrane accretion along the northern margin of the North China Craton is not well understood. To address this issue, we investigate the magmatic and sedimentary records, including both new and previously published geochemical, Sr–Nd isotopic, and zircon U–Pb–Hf isotopic data from the Bainaimiao Arc. The collected gabbro–diorites and granitoids have been dated to 431–453 Ma. The gabbro–diorites have high Mg/(Mg + Fe) molar ratios (44.41–73.39); depleted Nb, Ta and Ti; and negative εNd(t) values (-9.43–-6.80). They were derived from a mantle wedge metasomatized by subduction-derived fluids with crustal contamination. The granitoids are characterized by high silica, low to high K, low Fe and Mg contents, strong fractionation of rare earth elements, and positive εHf(t) values (+1.42–+8.19). They were derived from crustal melts with juvenile additions. The clastic rocks from the Baoerhantu Group and Xibiehe Formation are dominated by early Paleozoic zircons, whereas those from the Bainaimiao Group are dominated by early Paleozoic and Precambrian zircons. Detrital zircon geochronology and field geology confirm their deposition in early to mid-Paleozoic. The U–Pb ages and petrographic and geochemical analyses indicate that the clastic rocks were deposited in arc-related basins with felsic sources from the Bainaimiao Arc. The xenocrystic and detrital zircons in the magmatic and clastic rocks, respectively, imply a Precambrian basement for the Bainaimiao Arc. The early Paleozoic magmatic rocks of the Bainaimiao Arc show secular changes with decreasing age: increasing K2O contents and Sr/Y ratios and decreasing Fe2O3T + MgO contents and εHf(t) and εNd(t) values. This is likely in response to advancing subduction and related crustal thickening. Accordingly, the following tectono-paleogeographic model was proposed for the Bainaimiao Arc: (a) ∼500–455 Ma initial subduction and juvenile arc development, (b) ∼455–415 Ma continuous subduction with mature arc development, and (c) ∼415–400 Ma accretion to the North China Craton.

The passive margin of northern Gondwana during Early Paleozoic: Evidence from the central Tibet Plateau

The central–south domain of the Tibet Plateau represents an important part of the northern segment of Gondwana during the early Paleozoic. Here we present zircon U–Pb, Lu–Hf isotope, and whole–rock geochemical data from a suite of early Paleozoic magmatic rocks from the central Tibet Plateau, with a view to gain insights into the nature and geotectonic evolution of the northern margin of Gondwana. Zircon grains in four granitic rocks yielded ages of 532−496 Ma with negative εHf(t) values (−13.7 to −0.6). Zircon grains in meta–basalt and mafic gneiss yielded ages of 512 ± 5 Ma and 496 ± 6 Ma, respectively. Geochemically, the granitic rocks belong to high–K calc–alkaline and shoshonitic S–type granite suite, with the protolith derived from the partial melting of ancient crustal components. The mafic gneiss and meta–basalt geochemically resemble OIB (Oceanic Island Basalt) and E–MORB (Enriched Mid–Ocean Ridge Basalt), respectively. They were derived from low degree (∼5–10%) partial melting of an enriched mantle (garnet and spinel lherzolite) that was contaminated by upper crustal components. The parental magmas experienced orthopyroxene–dominated fractional crystallization. Sedimentological features of the Cambrian–Ordovician formations indicate that the depositional cycle transformed from marine regression to transgression leading to the formation of parallel/angular unconformities between the Cambrian and Ordovician strata. The hiatus associated with these unconformities are coupled with the peak of the early Paleozoic magmatism in Tibet Plateau, indicating a tectonic control. We conclude that the Cambrian–Ordovician magmatic suite and sedimentary rocks formed in an extensional setting, and we correlate this with the post–peak stage of the Pan–African orogeny. The post–collision setting associated with delamination, orogenic collapse or lithospheric extension along the northern margin of Gondwana, can account for the Cambrian–Ordovician magmatism and sedimentation, rather than oceanic subduction along the external margin. We thus infer a passive margin setting for the northern Gondwana during the Early Paleozoic.

Geochemistry and chronology of the early Paleozoic diorites and granites in the Huangtupo volcanogenic massive sulfide (VMS) deposit, Eastern Tianshan, NW China: Implications for petrogenesis and geodynamic setting

The Eastern Tianshan orogen contains many late Paleozoic porphyry Cu and magmatic Cu-Ni deposits. Recent studies demonstrate that several early Paleozoic volcanogenic massive sulfide (VMS) Cu-polymetallic and porphyry Cu deposits were discovered in the northern part of Eastern Tianshan. This study presents zircon U-Pb, whole-rock geochemical, and Sr-Nd isotopic data for granites and diorites from the Huangtupo VMS Cu-Zn deposit, northern part of the Eastern Tianshan. Our results can provide constraints on the genesis of intermediate and felsic intrusions as well as early Paleozoic geodynamic setting of the northern part of Eastern Tianshan. LA-ICP-MS zircon U-Pb analyses suggest that the granites and diorites were formed at 435 ± 2 Ma and 440 ± 2 Ma, respectively. Geochemical characteristics suggest that the Huangtupo granites and diorites are metaluminous rocks, exhibiting typical subduction-related features such as enrichment in LILE and LREE and depletion in HFSE. The diorites have moderate Mg#, positive εNd(t) values (+6.4 to +7.3), and young Nd model ages, indicative of a depleted mantle origin. The granites exhibit mineral assemblages and geochemical characteristics of I-type granites, and they have positive εNd(t) values (+6.7 to +10.2) and young Nd model ages, suggesting a juvenile crust origin. The early Paleozoic VMS Cu-polymetallic and porphyry Cu deposits in the northern part of Eastern Tianshan were genetically related. The formation of the early Paleozoic magmatic rocks as well as VMS and porphyry Cu deposits in the northern part of Eastern Tianshan was due to a southward subduction of the Junggar oceanic plate.

The distribution, geochronology and geochemistry of early Paleozoic granitoid plutons in the North Altun orogenic belt, NW China: Implications for the petrogenesis and tectonic evolution

Abundant early Paleozoic granitoid plutons are widely distributed in the North Altun orogenic belt. These rocks provide clues to the tectonic evolution of the North Altun orogenic belt and adjacent areas. In this paper, we report an integrated study of petrological features, U–Pb zircon dating, in situ zircon Hf isotope and whole-rock geochemical compositions for the Abei, 4337 Highland and Kaladawan Plutons from north to south in the North Altun orogenic belt. The dating yielded magma crystallization ages of 514Ma for the Abei Pluton, 494Ma for the 4337 Highland Pluton and 480–460Ma for the Kaladawan Pluton, suggesting that they are all products of oceanic slab subduction because of the age constraint. The Abei monzogranites derived from the recycle of Paleoproterozoic continental crust under low-pressure and high-temperature conditions are products of subduction initiation. The 4337 Highland granodiorites have some adakitic geochemical signatures and are sourced from partial melting of thickened mafic lower continental crust. The Kaladawan quartz diorites are produced by partial melting of mantle wedge according to the positive εHf(t) values, and the Kaladawan monzogranite-syenogranite are derived from partial melting of Neoproterozoic continental crust mixing the juvenile underplated mafic material from the depleted mantle. These results, together with existing data, provide significant information about the evolution history of oceanic crust subduction during the 520–460Ma. The initiation of subduction occurred during 520–500Ma with formation of Abei Pluton; subsequent transition from steep-angle to flat-slab subduction at ca.500Ma due to the arrival of buoyant oceanic plateaus, which induces the formation of 4337 Highland Pluton. With ongoing subduction, the steep-angle subduction system is reestablished to cause the formation of 480–460Ma Kaladawan Pluton. Meanwhile, it is this model that account for the temporal–spatial distribution of these early Paleozoic magmatic rocks in the North Altun orogenic belt.

Early Triassic Gneissoid Granites in the Gaozhou Area (Yunkai Massif), South China: Implications for the Amalgamation of the Indochina and South China Blocks

The Indosinian granites are widespread in the South China block (SCB) and can give significant information regarding the early Mesozoic tectonic evolution of the SCB. A comprehensive geochronological and geochemical study is carried out on the Gaozhou gneissic granites from the Yunkai massif, in the southern part of the SCB. Laser ablation inductively coupled plasma mass spectrometry U-Pb dating of zircons indicates that the gneissic granites were formed at 246 ± 3 Ma. These rocks are monzogranite in lithology and show features of medium-K calcalkaline series and weak peraluminous rocks. They have high SiO2 composition ranging from 75.85 to 76.84 wt%, high alkalis contents with Na2O + K2O of 7.20–7.51 wt%, and low MgO contents (0.11–0.20 wt%). Rare earth element (REE) compositions of the granitic rocks are fractionated with enriched light REE and moderate Eu anomalies. The samples also show enrichment of large ion lithophile elements (Rb and K) and Pb and depletion of Sr, Ba, and high field strength elements (Nb, Ti, and P). They possess negative εεNd(t) values of −7.1 to −4.8. Petrography and geochemical compositions of the gneissic granites indicate that they belong to I-type granite and are the result of partial melting of the early Paleozoic magmatic rocks in the region combined with minor assimilation of younger crustal components. We propose that the Indosinian gneissic granites in the Gaozhou complex might be the products of an early Indosinian collisional event at the southern part of the SCB. Integrating our new data with documented collision-related magmatic events during the Late Permian to Middle Triassic in the southern part of the SCB, we support the hypothesis of a collision between the Indochina block and the SCB during the Late Permian to Triassic period.

Cambrian ultrapotassic rhyolites from the Lhasa terrane, south Tibet: Evidence for Andean-type magmatism along the northern active margin of Gondwana

The petrogenesis and tectonic significance of early Paleozoic magmatic rocks in south Tibet is debated. In this paper, we report Cambrian ultrapotassic felsic volcanics from the Lhasa terrane. Petrographic and whole-rock geochemical studies indicate that these rocks are rhyolite and rhyolitic ignimbrite, and have varying SiO2 (69.56–82.09wt.%), Al2O3 (9.52–16.61wt.%) and Fe2O3t (1.0–7.9wt.%). The rocks are ultrapotassic (high K2O 4.19–6.90wt.%, and very low Na2O 0.01–0.06wt.%) and peraluminous (A/CNK=1.41–2.22). They are enriched in Rb, Th, U, Pb, Zr and Y, and showed negative Ba, Sr, P, Nb, Ta and Ti anomalies, and slightly fractionated REE patterns with moderately negative Eu anomalies, typical of A-type granitoids. Zircons from six samples yielded crystallization ages of ca. 512Ma. These zircons show εHf(t) values in the range of −4.7 to +1.3, and two-stage Hf model ages of 1734–1392Ma. Combining with previous results, we propose that these ultrapotassic rhyolites were derived from the partial melting of middle Proterozoic crustal rocks in the lower crust under high-temperature and water-absent conditions in an extensional environment of active magmatic arc. Thus, this study provides new insights into early Paleozoic Andean-type orogeny along the northern margin of Gondwana supercontinent.

Early Paleozoic mafic magmatic events on the eastern margin of the Siberian Craton

Neoproterozoic and Devonian mafic flows, sills and dykes associated with synchronous rifting events are widely distributed along the long-lived Mesoproterozoic to Mesozoic passive eastern margin of the Siberian Craton. Early Paleozoic magmatic events are also present, but are poorly studied, including Early Cambrian volcanic rocks in the Kharaulakh Range and ca. 450Ma age mafic intrusions of the Suordakh event in the Sette–Daban Range. Both suites of early Paleozoic magmatic rocks are characterized by high Ti concentrations (>3wt.% TiO2), ocean island basalt (OIB)-type trace element and rare earth element (REE) patterns, and high εNd(t) values that generally vary between 6 and 9. The Kharaulakh magmas were formed during low degree partial melting of an enriched region of mantle at depths >90km, generating a suite of alkaline basalts. In comparison, the Suordakh magmas were formed during higher degree partial melting of less enriched mantle at depths <90km, forming alkaline to subalkaline basalts. Both suites are characterized by εNd(t) values suggestive of interaction between enriched and depleted magmas and both were emplaced in within-plate tectonic settings. Although Kharaulakh and Suordakh magmatic rocks have relatively small areal extents, significant parts of them are likely hidden below clastic rocks of the Lower Carboniferous–Jurassic Verkhoyansk Complex. The Kharaulakh magmatic rocks may have counterparts in the Canadian Cordillera, that together could be of sufficient scale to define a Large Igneous Province (LIP). Early Cambrian mafic volcanic rocks in the study area are associated with locally distributed terrigenous units in both the Kharaulakh and Sette–Daban ranges, suggesting that this magmatism was related to a rifting event. Modeling of sedimentary basin subsidence in the Sette–Daban area is also supportive of an Early Cambrian rifting event. However, the intrusive rocks associated with the ca. 450Ma Suordakh mafic magmatic event are not related to any rift-related sediments or structures. Contemporaneous granites may be interpreted as silicic magmatism associated with a LIP event.

Middle-Late Ordovician arc-type plutonism in the NW Chinese Tianshan: Implication for the accretion of the Kazakhstan continent in Central Asia

Kazakhstan is one of the largest continental assemblages within the Central Asian Orogenic Belt. It was formed by accretion and amalgamation of several continental fragments and island arcs during early Paleozoic. The Aktau – Wenquan domain is one important continental constituent within the Kazakhstan and is located in the northeast of the Kazakhstan. Late Ordovician arc-type magmatic rocks were recently recognized from the Wenquan Group, which is long known to be Paleoproterozoic. Our investigation in the southern Wenquan area (NW China) suggests that within the Wenquan Group, foliated magmatic rocks are largely different from the amphibolite in terms of petrographic texture, protolith age, geochemical composition and Sm-Nd model age. New SHRIMP zircon U–Pb ages were determined for two deformed diorites, one gabbro enclave and a monzodiorite dyke at 466±4–447±6Ma, 462±5Ma and 450±9Ma, respectively. Zircons of the monzodiorite dyke contain inherited cores of ∼1000 to ∼1400Ma. The new geochemical analyses and literature data show that the magmatic rocks are of subduction-related calc-alkaline affinity. The εNd(t) values range from −2.0 to 0.8 and Nd model ages from 1.0 to 1.2Ga, indicating variable involvement of Proterozoic crust in the generation of the Early Paleozoic magmatic rocks. Consequently, these rocks were mostly likely emplaced in a continental arc environment, probably in the northern margin of the Aktau – Wenquan continental domain. Regional comparison suggests that this arc magmatism could probably be linked with the Karamai and/or North Balkhash accretionary wedges, and resulted from subduction of the Junggar–Balkhash oceanic lithosphere during Middle to Late Ordovician. Subsequent continental – arc collision and continuing accretion during Middle – Late Paleozoic in north of the Kazakhstan overprinted the structure of Early Paleozoic active continental margin in the Aktau – Wenquan domain.