Paleozoic Granitoids Research Articles

A critical review of Early Paleozoic W and Cu mineralized and barren granitoids in Southeast China: Magmatic differentiation, oxygen fugacity, and magmatic sources

In Southeast China, large-scale W and Cu mineralization is traditionally thought to be related to the Late Mesozoic granitoids. However, recent studies have revealed that the Early Paleozoic granitoids have great potentials for exploration of W and Cu deposits. A critical review of magmatic differentiation, oxygen fugacity and sources of major Early Paleozoic W and Cu-mineralized and barren granitoids demonstrates that the magmatic sources were important factors controlling W and Cu mineralization. In contract to Early Paleozoic ore barren granitoids east of the Chenzhou-Linwu fault (CLF), coeval W and Cu-mineralized granitoids to the west of this fault were derived from relatively fertile sources rich in W and Cu. Specifically, the W-mineralized granitoids were originated mainly from the partial melting of W-rich crustal materials of the basement rocks in the Jiangnan Orogen affinity. The sources of the Early Paleozoic Cu-mineralized granitoids may have been added Cu-rich Neoproterozoic arc-derived materials as evidenced by decoupled Nd-Hf isotopic compositions. Considering that the Precambrian basements in the Jiangnan Orogen have much higher W and Cu contents than those in the Cathaysia Block, we propose that the Early Paleozoic granitoids west of the CLF have greater W and Cu metallogenic potential than those to the east of this fault.

Geochronology, geochemistry, and Sr-Nd-Pb-Hf isotopes of the late Paleozoic Dongshuigou composite pluton in the Dunhuang Block, southernmost Central Asian Orogen: Petrogenesis and implications for crustal growth

Late Paleozoic granitoid rocks hold critical information regarding continental crustal growth and evolution of the Dunhuang Block at the southernmost margin of the Central Asian Orogenic Belt (CAOB). Here, we report new zircon U-Pb ages and Hf isotope data, as well as whole-rock geochemistry and Sr-Nd-Pb isotopic compositions for Devonian granitoid rocks and dacite porphyry in the Dongshuigou area of the Dunhuang Block, NW China. Petrographic investigation suggests that the Dongshuigou composite pluton, mainly consisting of quartz diorite, granodiorite, and biotite granite, was emplaced in the middle Devonian (ca. 390–380 Ma), whereas the dacite porphyry intruded into the granodiorite in the late Devonian (ca. 367 ± 4 Ma). The quartz diorite and granodiorite are similarly sodic, middle-K calc-alkaline, high Mg# (48.5–49.8) and Cr-Ni contents, enriched in LREE and LIIE (e.g., Rb, Ba, and P), and depleted in HFSE (e.g., Na and Ta), indicative of typically arc-like geochemical signatures. The quartz diorite has positive εNd(t) (+0.38), variable εHf(t) values (+3.12 to +10.7), juvenile Nd (1.04 Ga), and Hf model ages of 0.83 to 1.15 Ga. In comparison, the granodiorite displays negative εNd(t) values (−0.73) closed to the chondrite line, positive εHf(t) values (+3.75 to +8.36), juvenile Nd (1.12 Ga), and Hf model ages of 0.83 to 1.12 Ga. Both plutonic rocks show low initial Pb isotopes similar to those of typical lower crust-derived rocks. Our data indicate that the diorites and granodiorites were derived from partial melting of the juvenile lower crust with addition of minor mantle materials. The high-K, calc-alkaline dacite porphyry exhibits relatively high SiO2 and K2O contents, moderate Mg# (45.2–46.2) values, enrichment in Rb, U, Pb, and K, depletion in Nb, Ta, and Ti, and low Sr and Y abundance. These geochemical characteristics are similar to those of lower crust-derived arc-related rocks, including the development of abundant inherited zircons, implying that the dacite porphyry was likely generated by a mixed source of the mafic lower crust and minor metasomatized mantle materials. The biotite granites are characterized by high Sr contents (481–542 ppm) and Sr/Y ratios (76.0–98.4), low Y (5.37–6.51 ppm) and Yb (0.50–0.56 ppm) contents, and high Mg# values (55–56) and Cr-Ni contents, showing geochemical affinities of adakitic rocks. They have positive εNd(t) (+2.97 to +3.00), variable εHf(t) values (−6.05 to +12.4; mostly >0) with Nd and average Hf model ages of 0.82 Ga and 0.92 Ga, respectively. The biotite granites exhibit low initial 206Pb/204Pb, 207Pb/204Pb, and 208Pb/204Pb ratios of 18.336–18.339, 15.622–15.622, and 38.478–39.510, respectively, indicating that some subduction-related materials, such as mature arc primitive or ocean island volcanic rocks could have been added to the magma source. The biotite granites were likely derived from partial melting of subducted oceanic crust, which was modified by interactions with mantle wedge, with the addition of minor Mesoproterozoic materials during magma ascent. By synthesizing with the regional geology, we suggest that the middle Devonian granitoids and the late Devonian dacite porphyry in the Dongshuigou are arc/subduction-related rocks that formed in a continental arc setting. Taken together, Devonian arc-related magmatic events in the Dunhuang Block indicate significant crustal growth that was accompanied with minor reworking of ancient lower crust.

Paleozoic crustal evolution and tectonic switching in the Northeastern Tianshan: insights from zircon Hf isotopes of granitoids

Decoding the crustal and tectonic evolution of ancient accretionary orogens is not always straightforward. Here, four episodes of Paleozoic granitoids have been identified with distinct zircon–Hf isotopic characteristics from the Northeastern Tianshan. The first stage granitoids in the Dananhu–Harlik arc system are characterized by highly positive zircon ε Hf ( t ) values and short crustal incubation times with a rising event signature, suggesting a northward trench advance for the Kangguer Ocean. During the second stage, granitoids in the Dananhu and Kangguer belts have high zircon ε Hf ( t ) values and short crustal incubation times, but with a decreasing event signature for the Dananhu granitoids, implying a reworking of the juvenile arc crust. However, the near-zero ε Hf ( t ) values and the longest crustal incubation times of the Yamansu granitoids in this stage elucidate an origin from a Precambrian basement. These variations suggest that the northern trench of the Kangguer Ocean retreated southward while the southern trench advanced southward. During the third stage, the enlarged ranges of zircon ε Hf ( t ) values and crustal residence ages as well as crustal incubation times for the Dananhu and Kangguer granitoids show an interaction of juvenile material and the pre-existing crust, whereas the highly positive zircon ε Hf ( t ) values with a sharp rising event signature of the Yamansu granitoids suggest an significant crustal growth, indicating that a northward trench advance and a southern trench retreat for the Kangguer Ocean. However, the last stage granitoids in the Northeastern Tianshan entirely exhibit decreasing zircon ε Hf ( t ) values and long crustal incubation times, demonstrating a reworking of the pre-existing juvenile crust with minor input of ancient crustal materials in a post-collisional setting. Supplementary material : Table S1 and S2 and analytical methods are available at https://doi.org/10.6084/m9.figshare.c.5197889

Multiple Early Paleozoic granitoids from the southeastern Qilian orogen, NW China: Magma responses to slab roll-back and break-off

The slab dynamic processes, such as roll-back during oceanic subduction and break-off during collision orogenesis, would affect the movement of mantle material and the interaction between crust and mantle, accompanied by significant amounts of magmatism. Providing accurate depictions for these processes are extremely difficult, especially in the case of ancient orogens. Here, we present an integrated study of petrology, geochronology, geochemistry and Sr–Nd–Hf isotopes for Early Paleozoic granitoids from the Duojielaka, Ledu and Binglingsi plutons of the southeastern Qilian orogen. Our LA-ICP-MS UPb zircon data show that these granitoids were emplaced at 476–432 Ma. The petrological and geochemical data suggest that the ~476 Ma Duojielaka porphyritic syenogranites formed by feldspar-dominated fractionation from relatively K-rich basaltic rock-derived adakitic parental magma. The ~454 Ma Duojielaka biotite monzogranites are highly fractionated I-type granites and were derived from basement orthogneisses mixed with minor mafic rocks. The Ledu fine- and medium-grained quartz diorites (~446 and ~452 Ma) are high-K calc-alkaline to shoshonitic and were produced by partial melting of relatively old K-rich mafic crust followed by minor mixing with mantle-derived magmas. The ~432 Ma Binglingsi biotite monzogranites with adakitic characteristics most likely originated by partial melting of thickened mafic lower crust. Based on the new data, in combination with previously published data, we suggest that the roll-back of the South Qilian oceanic slab occurred during the Middle Cambrian to early Middle Ordovician. The Duojielaka porphyritic syenogranites represented crustal anatexis in an arc front associated with slab roll-back. The Late Ordovician–early Middle Silurian intrusive rocks probably resulted from diachronous slab break-off in the post-collisional stage. The rocks record the opening of the break-off window from east to west and the gradual heat propagation from the central part to the southern and northern margins of the eastern Central Qilian due to the widening of break-off window and asthenospheric upwelling. We propose that complex geodynamic processes and their thermal effects can be traced by a comprehensive consideration of the petrogenetic, temporal and spatial evolution of related magmatism.

The closing of the southern branch of the Paleo-Asian Ocean: Constraints from sedimentary records in the southern Beishan Region of the Central Asian Orogenic Belt, NW China

The Carboniferous–Permian strata in the southern Beishan Orogenic Collage (BOC) have been regarded as deposits formed either in a branch of the Paleo-Asian Ocean (PAO) or in continental rift basins. This paper presents stratigraphic, sedimentological, and provenance data of a continuous Carboniferous–Permian sequence on the southern margin of the Shuangyingshan Block within the southern BOC in NW China. Carboniferous Baishan and Shibanshan formations record a shallowing-upward change from marine tidal flat to continental braided stream environments. Integrated sandstone modes and U-Pb-Hf data indicate that these formations were fed from an orogenic uplift composed of Precambrian and early Paleozoic rocks of the Shuangyingshan and Dunhuang blocks (ca. 2492, 953, and 439–400 Ma). Latest Carboniferous–Early Permian depositional environments shifted from alluvial fans (Ganquan Formation) to delta-front and prodelta environments in an open marine setting (Shuangbutang and Jushitan formations) and source areas were composed of early Paleozoic granitoids (ca. 433 Ma) and penecontemporaneous volcanoes (ca. 278 Ma). These results indicate that the closure of the branch of the PAO between the Shuangyingshan and Dunhuang blocks occurred before the Visean (ca. 347 Ma), and was followed by the development of the latest Carboniferous–Early Permian marine rift basin on the amalgamated continental block.

Mesozoic reworking of the Paleozoic subducted continental crust beneath the south-central margin of the North China Block: Geochemical evidence from granites in the Xiaoqinling-Xiong’ershan region

Mesozoic granites are common in the south-central margin of the North China Block, beneath which the North Qinling microcontinent was subducted northwards in the early Paleozoic to subarc depths for ultrahigh-pressure (UHP) metamorphism. Although the continental deep subduction would have produced UHP eclogite facies metamorphic rocks in the North Qinling orogen, it is intriguing whether the Mesozoic granites record reworking of the crustal rocks from the subducted North Qinling microcontinent. This issue is addressed by an integrated study of zircon in-situ U-Pb ages and Hf-O isotopes as well as whole-rock geochemistry for four typical granitic plutons from the Xiaoqinling-Xiong’ershan region in the south-central margin of the North China Block. These plutons are metaluminous to weakly peraluminous, and belong to high-K calc-alkaline to shoshonitic series. They are enriched in LREE and LILE but depleted in HREE and HFSE. In terms of trace element and Sr-Nd-Hf isotope compositions, these granites can be categorized into two groups. Group I granites from the Huashan, Wenyu and Heyu plutons are high in Sr concentrations and Sr/Y and (La/Yb)N ratios without any significant Eu anomalies and thus similar to adakitic rocks, and have more enriched Sr-Nd-Hf isotope compositions. In contrast, Group II granites from the Funiushan pluton have low Sr concentrations and Sr/Y and (La/Yb)N ratios with negative Eu anomalies, and show less enriched Sr-Nd-Hf isotope compositions. Although zircon U-Pb dating for syn-magmatic zircons from the two groups of granite gives consistent emplacement ages of 120 to 137 Ma, relict zircons in them show different U-Pb ages. In detail, relict zircons from Group I granites exhibit Neoarchean to Paleoproterozoic U-Pb ages, with Hf-O isotope compositions similar to those of the ancient basement such as the Taihua Group and the Xionger Group in the south-central margin of the North China Block. In comparison, relict zircons from Group II granites display not only Paleoproterozoic U-Pb ages but also Neoproterozoic and early Paleozoic U-Pb ages. The Paleoproterozoic relict zircons exhibit Hf-O isotope compositions similar to those of the ancient basement in the south-central margin of the North China Block, whereas the younger ones have Hf-O isotope compositions consistent with those of the Neoproterozoic protoliths of metamorphic rocks and early Paleozoic granitoids in the North Qinling orogen. Therefore, Group I granites were derived from partial melting of the ancient basement in the south-central margin of the North China Block, whereas Group II granites were produced by partial melting of a mixing source that was composed of not only the ancient crust from the North China Block but also the juvenile crust from the North Qinling microcontinent. This provides the geochemical evidence for late Mesozoic reworking of the crustal rocks from the North Qinling microcontinent through its northward subduction in the early Paleozoic beneath the south-central margin of the North China Block.

Lu–Hf Isotope Composition of Zircon and Magma Sources of the Vendian–Early Paleozoic Granitoids in Tuva (by the Example of the Kaa-Khem and East Tannu-Ola Batholiths)

Abstract —We present results of geochemical and Sr–Nd isotope studies of rocks and of local dating and determination of the Lu–Hf isotope composition of zircons from late Vendian–early Cambrian and Cambrian–Ordovician intrusive associations (granitoids and gabbroids) of the Kaa-Khem and East Tannu-Ola batholiths in Eastern Tuva. The wide ranges of the eNd values (6.9 to 0.5) of rocks and the εHf values of magmatic and inherited zircons reflect the diversity of the magma sources of late Vendian–early Paleozoic intrusive associations formed at the island arc and accretion–collision stages. Late Vendian (572–562 Ma, Kopto and Buren massifs) and early Cambrian (522–518 Ma, East Tannu-Ola batholith) island arc tholeiitic and calc-alkalic plagiogranitoids resulted from the melting of the Vendian–early Cambrian island arc crust without the contribution of a more ancient crustal material. The subalkalic gabbro–monzodiorite–granosyenite association of the Zubovka massif (510 Ma) formed from a mantle source depleted isotopically but enriched in incompatible elements, with the participation of an island arc crust material; this process took place in the early phase of plume activity at the accretion–collision stage. Island arc complexes were the main source of Cambrian–Ordovician accretion–collision calc-alkalic plagiogranitoids (500–450 Ma, Terektyg-Cheder, Karaos, Tapsa, Baisyut, and other massifs). Variations in their composition were due to the melting of thick crust, whose isotopic heterogeneity was caused by the different contributions of a more ancient crustal source. The crust of the Tuva–Mongolian terrane made the main contribution to the formation of the potassic granitoids of the Bren’ massif (450 Ma), marking the completion of accretion–collision processes in this region. The isotope parameters of the Vendian–early Paleozoic granitoids are indicators of the crust formation and evolution in the course of subduction and accretion–collision processes.

Syn-exhumation melting of the subducted continental crust: Geochemical evidence from early Paleozoic granitoids in North Qaidam, northern Tibet

Syn-exhumation partial melting of the deeply subducted continental crust commonly occurs in collisional orogenic settings. The resulting felsic melts not only form granitoids, but can also modify the composition of the mantle wedge above continental subduction zones. This study investigates crustal anatexis and its role in granitoid formation and crust–mantle interaction during continental collision using new whole-rock geochemical, Sr–Nd–Hf isotope, and zircon U–Pb geochronological and Lu–Hf isotope data for early Paleozoic granitoids of the North Qaidam area of northern Tibet, a collisional orogen that contains ultrahigh-pressure (UHP) metamorphic rocks. Zircon U–Pb dating of the granitoids in this area yielded ages between 416 ± 6 Ma and 393 ± 2 Ma, coeval with the exhumation of the deeply subducted continental crust. This indicates that these granitoids formed as a result of syn-exhumation magmatism during the continental collision. Relict zircons in the granitoids yield concordant Neoproterozoic and early Paleozoic U–Pb ages that are consistent with the protolith and metamorphic ages of UHP metaigneous rocks in the orogen, respectively. The granitoids have calc-alkaline to high-K calc-alkaline compositions, with total alkali contents of 4.07–8.09 wt%. They are also metaluminous to weakly peraluminous with A/CNK ratios of 0.86–1.14. They are enriched in large ion lithophile elements (LILE) and depleted in high field strength elements (HFSE), yielding arc-like trace element patterns. They also have high (87Sr/86Sr)i ratios (0.7058–0.7195) and negative εNd(t) values (−7.1 to −1.4) and have whole-rock and zircon εHf(t) values of −2.8 to +2.7 and − 8.6 to +4.7, respectively. These data indicate that the granitoids are compositionally similar to the UHP metaigneous rocks in the collisional orogen, suggesting a genetic link. This in turn indicates that the granitoids in the study area formed from magmas generated by the partial melting during the exhumation of deeply subducted continental crust. The resulting granitic melts not only generated the syn-exhumation granitoids in this area, but also caused metasomatism associated with crust–mantle interaction in continental subduction channels.

Early Paleozoic geodynamic evolution of the Eastern Central Asian Orogenic Belt: Insights from granitoids in the Xing’an and Songnen blocks

The early Paleozoic tectonic framework and evolutionary history of the eastern Central Asian Orogenic Belt (CAOB) is poorly understood. Here we present zircon U–Pb geochronology, whole rock geochemistry, and Sr-Nd-Hf isotope data of the early Paleozoic granitoids in eastern CAOB to investigate the petrogenesis and geodynamic implications.The early Paleozoic granitoids from the Songnen Block yield zircon U–Pb ages of 523–490 ​Ma, negative εNd(t) values of –6.7 to –0.8, and εHf(t) values of –8.6 to 7.1, indicating they were generated by partial melting of ancient crustal materials with various degrees of mantle contribution. They generally show affinities to A-type granites, implying their generation from an extensional environment after the collision between the Songnen and Jiamusi blocks. In comparison, the early Paleozoic granitoids from the Xing’an Block have zircon U–Pb ages of 480–465 ​Ma, εNd(t) values of –5.4 to 5.4, and εHf(t) values of –2.2 to 12.9, indicating a dominated juvenile crustal source with some input of ancient crustal components. They belong to I-type granites and were likely related to subduction of the Paleo-Asian Ocean. The statistics of TDM2 Hf model ages of the granitoids indicate that the Erguna and Jiamusi blocks contain a significant proportion of Mesoproterozoic crystalline basement, while the Xing’an Block is dominated by a Neoproterozoic basement.Based on these observations, the early Paleozoic evolutionary history of eastern CAOB can be divided into four stages: (1) before 540 ​Ma, the Erguna, Xing’an, Songnen, and Jiamusi blocks were discrete microcontinents separated by different branches of the Paleo-Asian Ocean; (2) 540–523 ​Ma, the Jiamusi Block collided with the Songnen Block along the Mudanjiang suture; (3) ca. 500 Ma, the Erguna Block accreted onto the Xing’an Block along the Xinlin–Xiguitu suture; (4) ca. 480 Ma, the Paleo-Asian Ocean started a double-side subduction beneath the united Erguna–Xing’an and Songnen–Jiamusi blocks.

The First Evidence of Cambrian Granitoid Magmatism during the Formation History of the Bureya Continental Massif of the Central Asian Fold Belt

The results of U–Pb geochronological studies of Early Paleozoic granitoids from the northern part of the Bureya continental massif are presented. It has been established that porphyroblastic hornblende–biotite granites of the Kivili massif referring to the complex of the same name are of 502+6 Ma in age, while weakly gneissic biotite granites of the Kivity massif, Sularin complex, are of 492+6 Ma in age. Thus, granitoids of both complexes are of Cambrian rather than Ordovician age, as was previously assumed. In combination with materials already obtained, these data indicate that intensive granitoid magmatism manifested itself in the Middle Cambrian–Early Ordovician within the Bureya continental massif. It is noteworthy that, in the structure of the Jiamusi–Khanka continental massif, which is adjacent to the Bureya one, Early Paleozoic magmatism manifested itself in a broader range, which is from the Early Cambrian to the Silurian. This may indicate both differences in the formation history of these continental massifs and insufficient knowledge of the Bureya massif.

Ordo-Silurian assemblage in the Indochina interior: Geochronological, elemental, and Sr-Nd-Pb-Hf-O isotopic constraints of early Paleozoic granitoids in South Laos

AbstractIn order to verify the early Paleozoic accretionary assemblage in the Indochina interior and constrain the Prototethyan tectonic evolution in Southeast Asia, this study presents a set of new U-Pb geochronological, elemental, and Sr-Nd-Pb-Hf-O isotopic data for the fifty-two representative granitoids in South Laos. The granitoids from the Kontum terrane, Tam Ky-Phuoc Son tectonic zone, and southern Truong Son igneous zone in South Laos yield the crystallization ages of 464–485 Ma, 455–471 Ma, and 427–446 Ma, respectively, with a northerly younging trend within the Indochina interior. They are mainly monzogranite with A/CNK = 0.96–1.99 and K2O > Na2O, which are marked by enrichment in large-ion lithophile elements and depletion in high field strength elements with remarkable Nb-Ta, Sr-P, and Ti negative anomalies. Their initial 87Sr/86Sr ratios range from 0.70510 to 0.71559, εNd(t) from −9.5 to −3.0, (206Pb/204Pb)i from 18.65 to 19.72, (207Pb/204Pb)i from 15.66 to 15.80, and (208Pb/ 204Pb)i from 38.84 to 39.79. The corresponding zircon ɛHf(t) and δ18O values are in the range of −10.6 to +1.0 and 6.88‰ to 8.94‰, respectively. In addition, their Sr-Nd-Pb and Hf-O isotopic compositions are generally similar with those of time-equivalent granitoids in South Tibet and SW Yunnan, China, and synchronous mafic-intermediate igneous rocks in South Laos, but distinctive from those of the supracrustal sedimentary-derived South China Paleozoic granite and Lincang-Sukhothai S-type granite. The early Paleozoic granitoids in South Laos might have originated from a mixed source of the wedge-derived juvenile crust coupled with supracrustal materials. All these data synthetically suggest the southward subduction of the Tam Ky-Phuoc Son Ocean and the northerly on-growing Ordo-Silurian accretionary orogenesis within the previously defined “single-ancient” Indochina block. The assemblage of the Indochina block might initiate at ca. 430 Ma in the Silurian and terminate in the Early-Middle Devonian.

A mid-Cretaceous change from fast to slow exhumation of the western Chinese Altai mountains: A climate driven exhumation signal?

The Chinese Altai Mountains in western China are bound by Cenozoic transpressional strike-slip faults, many of which show Quaternary activity. To better understand how Mesozoic–Cenozoic deformation has affected the history of exhumation and uplift of the Chinese Altai Mountains, we collected Paleozoic granitoid samples for apatite fission track and apatite U-Th-Sm/He thermochronology. Central apatite fission track ages for N = 6 samples range from 68 to 104 Ma, whereas apatite U-Th-Sm/He ages range from 56 to 272 Ma for N = 23 samples (n = 80 individual analyses) across four transects in the western Chinese Altai. Our results indicate fast cooling during the late Early Cretaceous followed by slow cooling since. Thermal modeling results suggests < 2 km exhumation has occurred over most of the Chinese Altai since the Paleocene. If significant late Cenozoic surface uplift occurred in the Altai Mountains, as has been proposed, it must have been associated with minimal erosional exhumation. We suggest that the relief of the Chinese Altai largely developed during the late Mesozoic and denudation since has been minimal because of semi-arid climate conditions.

Petrogenesis and tectonic significance of early Indosinian A-type granites in the Xinxing pluton, southern South China

The Xinxing granitic pluton is a large batholith cropping out in southern South China with its long axis parallel to the regional NE–trending faults. We conduct the first comprehensive study of zircon laser ablation–inductively coupled plasma–mass spectrometry (LA-ICP-MS) U–Pb chronology and trace element chemistry, rock-forming mineral chemistry and whole-rock element and Sr–Nd isotope geochemistry for this pluton. Our new data indicate that the pluton was emplaced during the interval 234–232 Ma, i.e. early Indosinian rather than late Mesozoic as previously considered. The southern pluton consists of syenogranite and monzogranite, which are composed of K-feldspar, oligoclase, quartz and ferri-biotite. The northern pluton consists of monzogranite and granodiorite, which are composed of andesine, K-feldspar, quartz and magnesio-biotite. The southern granites have high SiO2 contents (72.5–79.2 wt%) and high FeOT/(FeOT + MgO) (T refers to total) ratios with low Mg# [atomic Mg/(Mg + FeT)]. They are enriched in rare earth elements and depleted in Sr and Ba with Zr + Y + Ce + Nb >350 ppm and 10,000 × Ga/Al >2.6. Their initial magma temperatures are unusually high (>886 °C). All those features strongly suggest an affinity with A-type granites. The northern granites have lower SiO2 contents (63.4–72.5 wt%) and lower FeOT/(FeOT + MgO) ratios as well as higher Mg# than the southern granites. They are also enriched in rare earth elements and depleted in Sr and Ba, with high Ga/Al ratios and high Zr + Y + Ce + Nb contents. Geochemical data and major element modeling confirm that the southern A-type granites were generated by the moderate degree (~49%) shallow (ca. 15–20 km depth) dehydration melting of the early Paleozoic granitoids triggered by intraplating of basaltic magmas. Subsequent moderate degree (~57%) fractionation of such crustal melts produced the more felsic granites in the southern pluton, whereas subsequent mixing of such crustal melts with about 8 to 48% intraplated mafic magmas generated the less felsic granites in the northern pluton. Interaction of mafic magmas with A-type crustal melts causes the northern granites to lose some diagnostic geochemical features of A-type granites such as high FeOT/(FeOT + MgO) ratios and to be transitional towards I-type granites. We further suggest their origin to have been related to the transtension of the regional NE–trending strike-slip faults coupled with the early Indosinian continental collisions.

Origin of Paleozoic granitoids in the Yuhai Cu–Mo deposit, Eastern Tianshan, NW China and implications for regional metallogeny

The Yuhai porphyry Cu–Mo deposit is located at the eastern section of the Dananhu–Tousuquan Arc in Eastern Tianshan, NW China. Cu–Mo mineralization generally occurs as disseminations and veins in potassic and phyllic alteration zones, and is predominantly hosted in the Yuhai quartz diorite, granodiorite and minor syenogranite intrusions. New LA–ICP–MS zircon U–Pb dating indicates that the acidic syenogranite was emplaced at 318–320 Ma, younger than the intermediate rocks (i.e., quartz diorite and granodiorite) with Silurian ages. The acidic to intermediate intrusions exhibit geochemical affinities with normal arc rocks (e.g. high Y and Yb contents, and low Sr/Y ratios), in contrast with the subducted slab-derived adakites hosting large porphyry Cu deposits (e.g. Tuwu–Yandong) in the middle section of the Dananhu–Tousuquan Arc. The Yuhai acidic syenogranite rocks have high SiO2 (≥74.90 wt%), and K2O (≥3.48 wt%), relatively low Mg# and compatible element contents (e.g. Cr = 0.65–3.37 ppm; Ni = 0.63–1.02 ppm), and strong depletions in HFSE (e.g. Nb, Ta, and Ti). These geochemical features, coupled with isotopic data such as low initial 87Sr/86Sr (≤0.7033), positive εNd(t) (4.0 to 5.9) and εHf(t) (≥11) values, young Hf model ages, and variable 206Pb/204Pb ratios (18.549 to 19.465) reported in this study, suggest that their parental magmas originated from the partial melting of a juvenile lower crust and mixed with some old crustal components beneath the Dananhu–Tousuquan Arc. In contrast, the Yuhai intermediate intrusions exhibit relatively low SiO2 and K2O contents, high Mg# values (40–56), and a wide range of εHf(t) values, suggesting a source of sub-continental lithospheric mantle metasomatized by slab-derived fluids and melts. Zircon trace element and plagioclase compositions of the Yuhai granitoids further imply that the Silurian intermediate intrusion-related magma was moderately oxidized (mostly EuN/EuN* > 0.6) and water-rich (~9 wt%), favorable for the copper mineralization, whereas the Carboniferous syenogranite-related magma was weakly oxidized (mostly EuN/EuN* = 0.3–0.6) but also hydrous (~6 wt%). Combined with the regional tectono-magmatic activities and metallogenic processes, we suggest that the Yuhai Cu–Mo deposit and associated granitoids were formed in an arc setting, and that the magma nature and its source components are the key factors constraining the distribution, scale and style of the porphyry copper mineralization in Eastern Tianshan.

The Unique Granite Gorge in Mountainous Adygeya, Russia: Evidence of Big and Complex Geosite Disproportions

Geological heritage sites (geosites) are subject to conservation and exploitation for science, education, and tourism. Some geosites are big and comprise diverse phenomena. Concentration of the latter in some parts of these geosites makes them disproportionate. A typical example is the Granite Gorge in SW Russia that is of recognizable tourism importance. It stretches for ~5 km and represents a deep valley of the Belaya River and Late Paleozoic granitoids of the Dakh Crystalline Massif. However, the full spectrum of unique features is much wider. Their inventory permits the establishment of geomorphological, igneous, metamorphic, sedimentary, mineralogical, paleogeographical, tectonic, economic, engineering, and hydrological and hydrogeological types of geological heritage. Spatial distribution of these types and the relevant features indicates their significant concentration near the northern entrance to the gorge and a less important concentration near the southern entrance. This is evidence of geosite disproportion. Apparently, the latter implies the need to focus geoconservation and geotourism activities on the noted loci of concentration. However, this would ’disrupt’ the geosite integrity, and, thus, management of the Granite Gorge geosite requires attention to all its parts, including those with lower heritage value.

PHYSICAL AND CHEMICAL CONDITIONS OF ROCKS METAMORPHISM OF YEREMKINSKY STRATUM (KOCHKAR ANTICLINORIUM)

The article describes the geological structure of the Yeremkinsky stratum, developed in the frame of the Varlamovsky, Borisovsky, Yeremkinsky and Sanarsky granite-migmatite domes (Kochkarsky anticlinorium). The stratum includes biotite-garnet-stavrolite plagiogneisses, crystalline schists, amphibolites, graphite-mica quartzites. Staurolite, kyanite, sillimanite, andalusite, muscovite are noted in association with garnet and biotite in plagiogneisses and schists. The contacts with the underlying formations are unknown, and with the overlapping marbles of the Kuchinsky stratum and quartzites, the quartzitic sandstones of the Alexandrovsky stratum are tectonic. Pb-Pb datings obtained from zircons selected from the rocks of the Yeremkin stratum range from 523 - 1350 Ma. Its Lower Middle Riphean age is accepted in accordance with the South Ural serial legend and is currently not reliably characterized by radiological data. Based on a study of garnet-biotite, garnet-staurolite parageneses, comprehensively studied experimentally and widely represented in the rocks of the Yeremkin stratum, the temperature and pressure of regional metamorphism (T = 640 - 690 °C, P = 3.5 - 4.6 kbar) and diaphtoresis (T = 550 - 580 °C, P = 5.9 - 6.2 kbar) were obtained, which correspond to the conditions of the cummingtonite-amphibolite and epidote(almandine)- amphibolite facies. Consideration of the petrochemical features of amphibolites and graphitic quartzites made it possible to reconstruct the paleogeodynamic and paleogeographic conditions of their formation. Taking into account the obtained physicochemical parameters of metamorphism, it can be assumed that the rocks of the Yeremkin stratum were formed in the lower-middle Riphea in relatively deep-water conditions in the rift-continental geodynamic setting and later they experienced a diaftoresis in the epidote-amphibolite and almandine-amphibolite facies boundary conditions. This is due to the formation of the Late Riphean-Vendian granite-gneiss domes (Borisovsky, Varlamovsky, Yeremkin and Sanarsky), as well as the thermal effects of the Late Paleozoic granitoids of the Sanarsky massif.

Sr-Nd-Pb-Hf isotopic composition of late paleozoic granitoids of Central Chukotka

Results of the study of Sr–Nd–Pb–Hf isotopic composition of Late Paleozoic granitoids of Central Chukotka are represented on the example of Kibera and Kuekvun plutons. The age of granitoids of these plutons and granites from pebbles in conglomerates in the base of overlying Lower Carboniferous deposits is 351–363 Ma (U–Pb zircon, TIMS, SIMS, LA–ICP–MS). Thus, granitoid magmatism corresponds in time to tectonic events of Elsmerian orogeny in Arctic region. Sr–Nd–Pb–Hf isotopic composition of granitoids indicate participation of mantle and crustal components in the source of granite melts. Granitoids formation probably occurred in geodynamic setting of Andean type continental margin during the interaction between mantle melts, forming at the mantle wedge melting in suprasubduction conditions, and continental crust.

Petrogenesis and tectonic implications of granitoids from western North Altun, Northwest China

The Altun orogenic belt in northwest China is part of the northern margin of the Tibetan Plateau. The North Altun ophiolitic mélange belt is an important tectonic unit within the Altun orogenic belt that contains voluminous early Paleozoic granitoids. In this study, we report the petrological features, geochemical compositions, and zircon UPb and Hf isotope data of three granitic plutons from the western segment of the North Altun ophiolitic mélange belt. Zircon UPb dating yields magmatic crystallization ages of 499, 493 and 496 Ma for samples of granodiorite, quartz diorite and syenogranite, respectively. The granitoids have metaluminous to weakly peraluminous and medium-K to high-K calc–alkaline characteristics and display relative enrichments in large ion lithophile elements (Rb, Th, U, K) and light rare earth elements (LREE) and relative depletions in Nb, Ta, Sr, P and Ti, suggesting an arc-related origin. The granodiorites (499 Ma) have positive zircon εHf(t) values ranging from +1.87 to +6.59 with two-stage Hf model ages (TDMC) of 1.05 to 1.35 Ga, implying that the granodiorites were derived from juvenile crust. The quartz diorites (493 Ma) have similar Hf isotopic characteristics to the granodiorites (εHf(t) = +2.59 to +6.04, TDMC = 1.08 to 1.30 Ga), indicating derivation from juvenile crust. The syenogranites (496 Ma) have high total REE and K2O contents, and low zircon εHf(t) values (−1.69 to +1.54), suggesting that they were derived mainly from juvenile crust mixed with ancient crustal materials. Combined with data from previous studies, we conclude that magmatism in the North Altun ophiolitic mélange belt can be subdivided into three episodes: Episode 1 (520–470 Ma) granitoids are related to subduction; Episode 2 (460–425 Ma) granitoids formed in a continent–continent collisional setting; and Episode 3 (<420 Ma) granitoids are post-collisional granites. Our results are consistent with south-directed subduction of the North Altun oceanic lithosphere beneath the Central Altun Block during the early Paleozoic (520–460 Ma), which was followed by collision with the Dunhuang Block.

Ordovician to Silurian igneous rocks in southern Mexico and Central America: geochronologic and isotopic constraints on paleogeographic models

Exposures of Ordovician to Silurian magmatic rock in southern Mexico and Central America constitute dismembered parts of an early Paleozoic belt related to the interaction of terranes of northwestern Gondwana with southern Laurentia. Convergent and extensional tectonic scenarios have been proposed to explain the origin of the magmatic activity along this belt. New U–Pb geochronological data, as well as Hf and Nd isotopic analyses were performed on five representative granitoids from southern Mexico and Central America to evaluate the timing and environment of emplacement. Samples from the Acatlán Complex in southern Mexico, as well as from the Altos Cuchumatanes, Rabinal and Chuacús areas along the southern Maya block yield Ordovician (470.9 Ma) to Silurian (427.1 Ma) crystallization ages. These samples have ɛHf values ranging from −6.4 to +1.0 and extraction ages (TDM) between 1.15 and 1.53 Ga, which match with ɛNd whole rock values ranging from −2.4 to −5.3 and TDM between 1.20 and 1.53 Ga. The Hf and Nd isotope compositions suggest incorporation of an evolved crustal reservoir, probably an Oaxaquia-type basement. Our data would better support a convergent tectonic scenario for the origin of the lower Paleozoic granitoids, possibly comprising an extension of the Famatinian arc of northwestern south America.

Early Paleozoic granitoids from South China: implications for understanding the Wuyi-Yunkai orogen

ABSTRACTThe early Paleozoic Wuyi-Yunkai orogeny involves voluminous magmatism and represents the first major tectonothermal event in the South China block since the Neoproterozoic break-up of the Rodinia supercontinent. Here we investigate three representative granitic plutons in Guangxi province of southwest China with a view to understand the magmatic response of the Wuyi-Yunkai orogeny. We present the results of major and trace elements, Sr-Nd isotopes, zircon U-Pb ages and Hf isotope. LA-ICPMS zircon U-Pb geochronology reveals that these plutons emplaced during the early Silurian (441–432 Ma), overlapping with the reported ages of the early Paleozoic magmatism in this orogen. Among the three plutons investigated in this study, the Qinjia pluton is characterized by weakly to strongly peraluminous (A/CNK = 1.0–1.2) nature with SiO2 content varing from 70.6 to 72.3 wt.%. Combined with the relatively high εNd(t) values (−4.9 to −4.2) and εHf(t) values (−2.9 to +6.1), the Qinjia pluton is thought to derive from partial melting of metasedimentary and metabasic rocks and there may exsit juvenile components in magma source. The Damingshan porphyritic granites (SiO2 = 74.8–76.5 wt.%) and Yingqiao granites (SiO2 = 76.5–76.6 wt.%) are strongly peraluminous (A/CNK = 1.1–1.6) and they have negative zircon εHf(t) values (−6.8 to −4.2, −12.8 to −6.1, respectively) and whole-rock εNd(t) values (−6.3 to −6.2, −8.4, respectively). These signatures indicate that the Damingshan and Yingqiao plutons were derived from partial melting of ancient metasedimentary rocks. Combining our data with those from previous studies on the magmatic, sedimentary and metamorphic records of this area, we suggest that the early Paleozoic magmatism is likely associated with lithospheric delamination and the Wuyi-Yunkai orogen is an intracontinental orogen linked to the far-field response to the assembly of the South China block with the Gondwana in the early Paleozoic.