Zircon Hf Isotopic Compositions Research Articles

Magma Source and Petrogenesis of the Early Cretaceous Granites in The Liaodong Peninsula: Evidence from In Situ Apatite Sr-Nd and Zircon Hf-O Isotopes

Apatite Sr-Nd and zircon Hf-O isotopes are broadly used to trace magma sources and constrain magma evolution processes, further improving our understanding of the origin of granitoids. We present zircon U-Pb ages, whole-rock major and trace elements, and whole-rock Sr-Nd-Hf, zircon Hf-O, and apatite Sr-Nd isotopic data for the coarse-grained quartz monzonite, biotite monzogranite, and granite porphyry in the Yushulinzi pluton in the Liaodong Peninsula, the eastern North China Craton, to establish their magma sources and petrogenesis. The coarse-grained quartz monzonite, biotite monzogranite, and granite porphyry were formed contemporaneously, with zircon U-Pb ages of 123–119 Ma. They share enriched whole-rock Sr-Nd-Hf and zircon Hf isotopic compositions, and the coarse-grained quartz monzonite has crust-like δ18O values (5.7–6.7‰). The coarse-grained quartz monzonite and biotite monzogranite have variable apatite (87Sr/86Sr)i ratios and negative apatite εNd(t) values. These isotopic characteristics indicate that the different rock types in the Yushulinzi pluton were derived from the partial melting of ancient crustal material in the North China Craton. Their geochemical and petrographic characteristics indicate that the crystal-melt segregation model can be employed to elucidate the genetic links among different rock types, with the coarse-grained quartz monzonite representing crystal accumulation and the biotite monzogranite and granite porphyry representing interstitial melts extracted from a crystal-rich magma chamber. Furthermore, the variable apatite Sr isotopic compositions and subtle differences in the peak zircon εHf(t) values of the studied rock samples confirm the possibility of a contribution from shallow crustal components and materials with high εHf(t) values during magma evolution, which is not readily revealed by their whole-rock Sr-Nd-Hf isotopic compositions. These results demonstrate that in situ apatite Sr-Nd and zircon Hf-O isotopic analyses have the potential to provide distinctive insights into the magma sources and evolution of magmatic systems.

Proterozoic evolution of the Alxa block in western China: A wandering terrane during supercontinent cycles

The tectonic affinity of the Alxa block in the western North China craton remains controversial because of the widespread Cenozoic sediments and limited Proterozoic geochronological data, especially in the western Alxa block. To establish the tectonic affinity of the Alxa block with neighbor units, we systematically investigated U-Pb age and Hf isotope composition of zircon and U-Th-Pb age of monazite from Proterozoic rocks in the southwestern Alxa block. Ages of zircon and monazite from granitic gneiss and mica schist indicate that the Paleoproterozoic Longshoushan Complex recorded a magmatic event at ∼2.0 Ga and two metamorphic events at ∼1.95–1.90 and ∼1.85–1.80 Ga. Detrital zircons from quartz schist of the Longshoushan Complex show an age peak at ∼2.0 Ga with εHf(t) values between −4.048 and 6.432. By contrast, detrital zircons from the Late Paleoproterozoic Dunzigou Group yield different Paleoproterozoic age peaks and εHf(t) values, suggesting a provenance change. Detrital zircons from the Neoproterozoic Hanmushan Group exhibit three age peaks at ∼2.5 Ga, ∼1.85 Ga and ∼0.8 Ga, and two types of εHf(t) values with wide variations. The depositional ages of the Dunzigou Group and Hanmushan Group are constrained as 1.8–1.7 Ga and 845–830 Ma, respectively. The detrital zircon age populations suggest that the Longshoushan area experienced a transition from a convergent setting (less polymodal age spectra) at ∼1.98–1.95 Ga to a divergent setting (polymodal age spectra) at 1.8–1.7 Ga and then intracontinental rifting at ∼830 Ma. Compared with previous zircon studies, we propose that the Alxa block may be connected with the Khondalite belt at ∼1.98–1.90 Ga during assemblage of the Columbia supercontinent, and located between the North China craton and the northern Siberian craton at 1.8–1.7 Ga in a divergent setting. The Alxa block probably separated from the North China craton in the Late Mesoproterozoic and moved next to the northwestern Yangtze craton in the Early Neoproterozoic during the assemblage and breakup of the Rodinia supercontinent.

Revisiting the boundary between the Central Asian Orogenic Belt and North China Craton in Alxa area, China: Insights from zircon U-Pb ages and Hf isotopes of Phanerozoic granitoids

The Alxa Block, located in the southern Alxa area of Inner Mongolia, is generally accepted as the westernmost part of the North China Craton (NCC), but there is still a controversy over the boundary between the southern CAOB and the Alxa Block. Currently, either the Enger Us ophiolite belt or Quagan Qulu ophiolite belt in the mid-eastern Alxa area is a candidate for the NCC-CAOB boundary, and the extension of the two ophiolite belts in the western Alxa area is ambiguous. In this study, we present a compilation of newly obtained and published zircon U-Pb age and Hf isotopic data from the Ordovician-Triassic granitoids in the Alxa area and discuss the implications of two contrasting isotope provinces for the NCC-CAOB boundary. Specifically, the granitoids in the Zongnaishan-Shalazhashan belt between the two ophiolite belts and the North Beidashan belt in the western Alxa area share similar emplacement ages (Carboniferous to Triassic) and juvenile zircon Hf isotopic compositions (two-stage mode ages < 1.30 Ga), and both Carboniferous to Permian granitoids in the Yabulai-Honggueryulin belt to the south of Quagan Qulu ophiolite belt and Ordovician to Devonian granitoids in the South Beidashan belt of the western Alxa area are characterized by similar ancient zircon Hf isotopic features (two-stage mode ages > 1.30 Ga), but most Late Carboniferous to Permian granitoids in the South Beidashan belt are characterized by juvenile zircon Hf isotopes. The two contrasting isotope provinces (juvenile in the north and generally ancient in the south) for the Phanerozoic granitoids could not result from differential denudation, but drastic differences in compositions of deep crusts. The Yabulai-Honggueryulin and South Beidashan belts with ancient crust sources are parts of the Alxa Block, whereas the Zongnaishan-Shalazhashan and North Beidashan belts with juvenile crust sources could be parts of CAOB, and thus the boundary between the CAOB and the Alxa Block is inferred located in between.

Petrogenesis of potassic granite suites along the southern margin of the Zimbabwe Craton

AbstractAn integrated approach embracing field studies, petrographic and geochemical investigations together with zircon U-Pb-Hf data was used to investigate the petrogenesis of potassic granite suites along the southern margin of the Zimbabwe Craton. Zircon U-Pb geochronology identifies age relationships, revealing coeval magmatism of the ca. 2 635 ± 5 to 2 625 ± 3 Ma Chilimanzi Suite, and the ca. 2 627 ± 7 Ma Razi Suite. Both suites represent syn- to late-tectonic, high-K, calc-alkaline, and metaluminous to weakly peraluminous granites and granodiorites with I-type affinity. The granite suites contain xenocrystic zircons, with the Chikwanda Pluton of the Chilimanzi Suite yielding a grain of up to 3 206 Ma old. Both granite suites exhibit eHf values of between -5.6 ± 1.3 and -7.3 ± 1.6 and TDM model ages of ca. 3.4 to 3.5 Ga which suggests a similar crustal source. The unradiogenic zircon Hf isotopic compositions are consistent with formation of the granite suites through partial melting of pre-existing crustal protoliths, including Palaeoarchaean tonalite-trondhjemite-granodiorites (TTGs) of the Zimbabwe proto-craton. Partial melting of lower crust gave rise to granitic melts that became emplaced over a relatively short time interval from 2 635 to 2 625 Ma and heralded the stabilisation of the Zimbabwe Craton.In addition to virtually identical ages, the Razi and Chilimanzi suites have similar geochemistry. Small geochemical differences between the Chilimanzi and the Razi suites are attributed to the crustal level at which they are preserved, the modal mineralogy and the extent to which the melts are evolved. The Razi Suite melts were generated from lower crust partial melting of thickened charnockite-enderbite source rocks rich in heat producing elements. The partial melting occurred under fluid-absent conditions and magmas were emplaced at lower to mid crustal levels. The Chilimanzi Suite magmas were similarly derived by the partial melting of TTG lower crust and were emplaced at upper crustal levels. Accordingly, the Chilimanzi Suite exhibits more evolved magmatic fractionation indices indicated by high Rb/Sr, as well as low K/Rb ratios relative to the Razi Suite. Both suites reveal varying degrees of enrichment in incompatible elements including Rb, Th, and U, as well simultaneous depletions in Ba, Sr, and Hf which underscores the role of fractional crystallisation in the evolution of the granitic magmas.

One size does not fit all: Refining zircon provenance interpretations via integrated grain shape, geochronology, and Hf isotope analysis

Sediment provenance studies commonly utilize isotopic signatures to resolve detrital mineral sources and routing. However, non-unique ages and geochemical characteristics across geographically distinct crystalline source regions can lead to significant ambiguities in mineral provenance interpretations. Such ambiguity is apparent in southern Australia’s Cenozoic Eucla Basin, which hosts world-class heavy mineral sand resources. Here, new Hf isotope data are provided from four heavy mineral prospects (N = 8, n = 844 [N = samples, n = grains]). Zircon grain shape data are also presented for a suite of detrital Eucla Basin samples (N = 22, n = 35,604) and the basin’s underlying basement, the Coompana Province (N = 13, n = 824). The data are integrated with published detrital and non-detrital primary zircon data to investigate the efficacy of grain shape analysis to better resolve the basin’s mineral provenance. Zircon Hf isotope compositions indicate a primary Mesoproterozoic juvenile source for zircon melts (∼1250–1000 Ma, −2.5 <ɛHf > ∼+5) with additional contributions from a range of juvenile to evolved late Archean to Phanerozoic-aged zircon bearing magmas (−28.0 <ɛHf > +11). U–Pb geochronology and Hf isotopes are incapable of differentiating Mesoproterozoic-aged source rocks bounding the region for the majority of heavy mineral deposits analyzed as potential sources express overlapping crystallization ages and similarities in Hf-isotope characteristics. However, distinct zircon grain shapes (i.e., perimeter, major axis and circularity) facilitate improved differentiation across these Mesoproterozoic sources. Filtering of U–Pb age, Hf isotope and shape data implicate the underlying Madura and Coompana provinces as dominant sediment sources for Eucla Basin detritus aged ∼1400–1000 Ma. The lack of direct sediment pathways between the underlying basement provinces and placer sediments analyzed demonstrates the significance of zircon reworking from intermediate sedimentary basins in the formation of the economically significant Eucla Basin beach placers. Zircon grain shape represents a cheaply acquired and readily incorporated grain characteristic that can enhance provenance investigations.

Petrogenesis of the Quxu intrusive complex: Implications for Eocene magmatism in the southern Lhasa Terrane, Tibet

The widely distributed Eocene mafic microgranular enclaves in the Lhasa Terrane of southern Tibet carry important information regarding crust–mantle interactions in collisional zones. Here, we report geochronological and geochemical data of granitoids and mafic enclaves from Quxu in the southern Lhasa Terrane. Zircon LA‐ICP‐MS U–Pb dating indicates that the Quxu granitoids and enclaves were synchronously emplaced at ca. 50 Ma. The granitoids are medium‐ to high‐K calc‐alkaline, metaluminous (A/CNK = 0.82–0.90) and have high Al2O3(14.48–16.57 wt%) and low MgO (2.81–2.99 wt%). The mafic enclaves (SiO2 = 50.55–54.57 wt%) have 5.12–5.37 wt% MgO and an Mg#of 49–51, with weakly negative Eu anomalies (Eu/Eu* = 0.85–0.91). The Quxu granitoids and enclaves have similar zircon Hf isotopic compositions, withεHf(t) values ranging from +7.62 to +13.32. A comprehensive study of the data available for coeval rocks from the Gangdese Batholith indicates that the Quxu granitoids were derived from partial melting of the lower crust, while the parental magmas of the mafic enclaves were most likely derived from lithospheric mantle beneath southern Tibet. The Quxu granitoids are interpreted as the result of mixing between the lower crust‐derived melts and lithospheric mantle‐derived mafic melts, which are likely the magmatic response to the breakoff of the Neo‐Tethyan Oceanic slab at about 50 Ma.

Tectonomagmatic evolution of southwestern Laurentia: Insights from zircon U-Pb geochronology and hafnium isotopic composition of the Red Bluff Granite Suite, west Texas, USA

AbstractWe provide laser ablation–multicollector–inductively coupled plasma–mass spectrometry (LA-MC-ICP-MS) and high-precision chemical abrasion–isotope dilution–thermal ionization mass spectrometry (CA-ID-TIMS) U-Pb ages and Hf isotopic compositions of zircons from the Red Bluff Granite Suite and mafic dikes in the Franklin Mountains of El Paso, Texas, USA. Granitoids exposed in the Franklin Mountains were previously divided into five magmatic stages based on cross-cutting relationships. Major and trace element compositions showed that these granitoids are ferroan, alkaline, and A2 type. Homogeneity in the whole-rock geochemistry suggests that the granite stages are genetically related and share similar petrogenetic histories. Weighted mean zircon 206Pb/238U dates from the older magmatic stage 1 alkali-feldspar quartz syenite and stage 2 alkali-feldspar granite are 1112.36 ± 0.35 and 1112.46 ± 0.37 Ma, respectively. The weighted mean εHf(t) values varying from +5.3 to +7.2 are similar to those of other regional ca. 1.1 Ga magmatic rocks throughout southwestern Laurentia. Geochemical characteristics, petrological modeling, and enriched Hf isotopic composition suggest fractional crystallization of a basaltic magma that was produced by melting of an enriched mantle reservoir. However, zircon inheritance ages of ca. 1.3 Ga and 1.26–1.15 Ga are consistent with a minor contribution from felsic crustal basement. Our data and regional geology are consistent with a post-collisional slab break-off that facilitated asthenospheric upwelling and partial melting of the enriched mantle, possibly subcontinental lithospheric mantle, extending from Llano Uplift, Texas, in the southeast to California to the northwest. Magma thus generated upon differentiation produced ferroan and A-type granitoids.

Late Cretaceous tectono‐magmatism of southeast China: Evidence from Qushandao Granite in the eastern Zhejiang province

AbstractThe Qushandao Granite, mainly composed of alkali‐feldspar granite, is situated in the eastern Zhejiang province of coastal southeast China. In this paper, we present whole‐rock geochemistry, zircon U–Pb geochronology, and Hf isotopes to constrain the age, magma sources, and geodynamic setting of the Qushandao Granite. LA‐ICP‐MS zircon U–Pb dating results revealed that the Qushandao Granite was emplaced in the Late Cretaceous (101–98 Ma). Geochemically, the Qushandao Granite exhibits relatively high silica and alkali contents, metaluminous to weakly peraluminous (A/CNK = 0.98–1.02), and low abundances of phosphorus, titanium, magnesium, and calcium. It is also characterized by enrichment in Rb, K, Th, and depletion in Nb, Ta, P, Ti, and Sr with moderately to weakly negative europium anomalies (Eu/Eu* = 0.71–0.87). Furthermore, the Qushandao Granite displays lower FeOT/MgO, 104 × Ga/Al, and Zr + Nb + Ce + Y values relative to typical A‐type granites. Therefore, we classify the Qushandao Granite as calc‐alkaline I‐type granite based on a synthesis of geological and geochemical characteristics. The Qushandao Granite shows variable zircon Hf isotopic compositions (εHf(t) = −7.6 to +2.3) and TDM2 model ages of 1.40–0.83 Ga with a mean value of 1.17 Ga. We argue that the Qushandao Granite was most likely generated by mixing of mantle‐derived mafic magma and crust‐derived felsic magma in the lower crust, and that it was formed during post‐collisional extension in the Late Cretaceous, related to the gradually increasing subduction angle of the Paleo‐Pacific plate.

Partial melting of subducted continental crust during the exhumation: Insights from Palaeozoic granitic rocks in South Altyn, western China

The early Palaeozoic continental subduction–collisional belt in South Altyn (SA) western China distributes a large amount of (ultra)-high-pressure ((U)HP) metamorphic and granitic rocks associated with subduction, collision, and exhumation. In this study, four granitic rocks were collected from Bashenwake located in eastern SA. The ages of the garnet-bearing alkali-feldspar granite (GAFG), garnet-bearing granitic gneiss (GGG), alkali-feldspar granite (AFG), and syenogranite (SG) are 458.0 ± 4.1, 483.0 ± 4.1, 450.0 ± 2.4, and 482.0 ± 4.9 Ma, respectively. Whole-rock major and trace elements and Sr–Nd–Pb isotope, and zircon Hf isotope compositions for all samples exhibit characteristics of a continental crustal source. Based on partial melting modeling, the source temperature of the GGG, GAFG, AFG and SG was concluded as 750–780 °C, 730–760 °C, 730–770 °C and ca. 800 °C, respectively. The source pressure was estimated as ca. 0.8 GPa for the GGG, GAFG and AFG, and ca.1.2 GPa for SG. Combined with studies on (U)HP metamorphic rocks in SA, this study reveals that GGG is formed by metamorphism while SG is formed from partial melting of upper crustal rocks heated by upwelling mantle during the initial stage of exhumation (ca. 480 Ma) of subducted continental crust in SA. During further stage of exhumation of the subducted continental crust at ca. 450 Ma, the GAFG and AFG were formed from partial melting of GGG as a result of decreased pressure and further mantle upwelling. Consequently, the exhumation age of subducted continental crust in eastern SA is ca. 30 Myr earlier than that in western SA. Thus, the geochronology and petrogenesis of four granitic samples in this study exhibit one of very few evidence for partial melting of subducted continental crust during the exhumation and also provide magmatism exhibits evidence for the differential exhumation model of eastern SA in Palaeozoic.

Neoproterozoic lithospheric extension related to break-up of the Rodinia supercontinent: Constraints from a newly-identified granite porphyry in southeastern Yunnan, China

Although the southeastern Yunnan region preserves an important record of the evolution of the South China block (SCB), its Precambrian geology is not well understood due to poor exposure. The newly-discovered Laojunshan granite porphyry (LNGP) is the only Precambrian unmetamorphosed granitoid unit exposed in the southwestern SCB. Here, we present integrated studies of the LNGP including whole-rock major and trace-element geochemistry and Nd isotopes, together with zircon U-Pb chronology and Lu-Hf isotopes by LA-ICP-MS. Zircon U-Pb dating results for two granite porphyry dykes yielded ages of 811.2 ± 7.0 Ma and 830.3 ± 5.2 Ma. The studied samples have high total alkalis (6.46–9.68 wt%), SiO2 (69.44–75.6 wt%), P2O5 (0.11–0.33 wt%) and Al2O3 (10.44–14.39 wt%) but low CaO (0.09–1.29 wt%) contents; these characteristics together with high Al saturation indices (1.1–1.7), indicate the LNGP is of strongly peraluminous S-type granite affinity. The LNGP is characterized by Rb-Th-U-K enrichments and Ba-Sr-Nb-Ti-Ta depletions, and right-sloping REE patterns with obvious negative Eu anomalies (Eu/Eu* = 0.2–0.4). Major and trace elements show good correlations with SiO2. Diagrams of Th vs Th/Nd, La vs La/Sm and Zr vs Zr/Sm indicate that fractional crystallization was an important process in the genesis of the LNGP. The Ba vs Eu, Sr vs Eu and Ba vs Sr correlations and high Rb/Sr (8.2–74) and Ca/Sr (12–614) ratios demonstrate that magmatic evolution involved extensive fractionation of plagioclase and K-feldspar. The initial zircon Hf isotopic composition of the porphyry varies widely (εHf(t) = −10.1 to +6.7), with corresponding two-stage Hf model ages of 1291–2331 Ma; whereas whole-rock Nd isotopes are relatively uniform (εNd(t) = −5.8 to −4.6), with two-stage Nd model ages of 1886–2130 Ma. The variable zircon Hf isotopic compositions suggest a heterogenous source for the LNGP, containing juvenile components (with higher εHf(t) values) and ancient reworked crustal materials (with lower εHf(t) values). Geochemical data, including Rb/Sr, Rb/Ba, Al2O3/(MgO + Fe2O3T), CaO/(MgO + Fe2O3T) and (Na2O + K2O)/(Fe2O3T + MgO + TiO2) ratios and (Na2O + K2O + Fe2O3T + MgO + TiO2) content suggests a meta-pelite/greywacke source. Early arc-continent or continent–continent collision may produce mixtures of juvenile sediments formed by erosion of with ancient crustal materials that were strongly folded and deeply buried in the studied area. The LNGP has medium to high magmatic temperatures (761–875 °C) and low oxygen fugacity (ΔFMQ −5.4 to ΔFMQ −2.8). The LNGP was emplaced at middle-upper crustal levels (pressure < 5kbar) in an extensional setting analogous to granitoid associated with the Neoproterozoic age rift-related Nanhua and Kangdian magmatic belts that bound the periphery of the Yangtze block. These belts are interpreted to be the result of the break-up of the Rodinia supercontinent during the period 850 to 700 Ma. We similarly interpret the emplacement of the LNGP, which occurred within an extensional setting, to be a response to the break-up of the Rodinia supercontinent.

Destruction of the lower crust beneath the North China Craton recorded by granulite and pyroxenite xenoliths

The lower crust beneath the North China Craton (NCC) was transformed during the craton destruction in the Mesozoic, however, the transformation processes are yet to be fully understood. Compositional and geochronological variations of granulite and pyroxenite xenoliths provided insights into the nature of the lower crust before and after the craton destruction. In this study, we summarized the latest results of geochemistry and zircon geochronology coupled with Hf-O isotopes from granulite and pyroxenite xenoliths hosted by Phanerozoic igneous rocks in NCC. Comparing previous studies on the granulite terranes and adakitic rocks of NCC, we aim to discuss the destruction processes of lower crust beneath the NCC. The granulite and pyroxenite xenoliths of NCC were divided into two and three groups, respectively, based on the differences of geochemical features. Group I granulite xenoliths from the NCC have silicic-basic compositions, with metamorphic ferrosilite. The Group I granulite xenoliths show relatively lower Mg# values of pyroxenes and whole-rock than that of the Group II granulite xenoliths, and enrichments of light rare earth elements and Sr-Nd isotopic compositions. Their zircons display Archean-Phanerozoic ages with three peaks of Neoarchean, Paleoproterozoic, and Mesozoic. Generally, Group I granulite xenoliths show close affinities to the granulite terranes of the NCC in terms of the major and trace elements and Sr-Nd isotopic compositions, with a consistent Archean-Proterozoic evolutionary history. However, Group I granulite xenoliths have abundant Phanerozoic zircons with variable Hf isotopic compositions from depleted to enriched, which could be formed by modifications of magma underplating. Therefore, Group I granulite xenoliths represent the modified ancient lower crust beneath the NCC. The Group II granulite and Group III pyroxenite xenoliths from the NCC have similar geochemical features and are basic in compositions, with metamorphic to magmatic orthopyroxenes. The Group II granulite and Group III pyroxenite xenoliths usually show higher MgO and lower incompatible elements compositions in minerals and bulk rocks than that in the granulite terranes and Group I granulite xenoliths, but their Sr-Nd isotopic compositions fall into the fields of granulite terranes and group I granulite xenoliths. Zircons from the Group II granulite and Group III pyroxenite xenoliths are predominantly Phanerozoic with subordinate Archean-Proterozoic ages, and the Hf-O isotopic compositions of zircons are similar to those in the Group I granulite xenoliths. Additionally, the trace element compositions of Group II granulite and Group III pyroxenite xenoliths are complementary to those of the adakitic rocks from the NCC. Furthermore, the similar Sr-Nd and zircon Hf isotopic compositions among Group II granulite and Group III pyroxenite xenoliths and adakitic rocks indicate that they are cognate. Therefore, we suggest that the Group II granulite and Group III pyroxenite xenoliths could be restites left after partial melting of the ancient basic lower crust that produced voluminous adakitic rocks. In contrast, Group I and II pyroxenite xenoliths from the NCC have cumulate and reaction origins, respectively. The Group I and II pyroxenite xenoliths commonly have magmatic enstatite and show higher Mg# values and depleted Sr-Nd isotopic compositions of minerals and bulk rocks relative to that in the granulite and Group III pyroxenite xenoliths. Formation of voluminous Group I pyroxenite cumulates in the crust-mantle transition zones implies extensive magma underplating beneath the NCC during the Mesozoic-Cenozoic, which also provided exotic materials and heat for the reworking of the ancient lower crust. Therefore, the destruction of the lower crust beneath the NCC could result from continuous modifications and remelting of the ancient lower crust triggered by magma underplating. These processes led to not only the transformations of some ancient basic lower crust into granulite and pyroxenite restites but also the compositional modifications of the ancient lower crust. Consequently, the lower crust beneath the NCC showed downward rejuvenation, similar to the lithospheric mantle.

A refined Archean-Paleoproterozoic magmatic framework of the Cuoke Complex, SW China, and its implications for early Precambrian evolution of the Yangtze Block

New age data from the Cuoke Complex in southwestern Yangtze Block, integrated with published data from this region, indicate an Archean to early Paleoproterozoic magmatic history distinct from the northern Yangtze Block. Zircon cores and rims from eleven granitoids of the Cuoke Complex were analyzed by LA-ICP-MS and SHRIMP and show magmatic U-Pb ages ranging from 2850 to 2194 Ma. Combined U-Pb zircon igneous age data from the Kunming-Hainan Domain in the southwestern Yangtze Block display major magmatism ranging 3.10–3.06 Ga with a peak at ca. 3.08 Ga, 2.92–2.77 Ga with a peak at ca. 2.85 Ga and 2.4–2.1 Ga with peaks at 2.36–2.32 Ga and 2.22 Ga. This age distribution contrasts with the zircon U-Pb magmatic age data from the igneous rocks of the Kongling Domain in the northern Yangtze Block. A gap in magmatic activity in the northern domain between 2.4 and 2.2 Ga overlaps with the major peak in magmatism in the southwestern domain. Furthermore, potassic granitoids, which mark the cratonization of the two domains are more than 200 Ma years earlier in the Kongling Domain than that in the Kunming-Hainan Domain. Hf isotopic compositions of zircons from igneous rocks of the southwestern domain indicates significant juvenile crustal generation during the Mesoarchean era peaked at ca. 3.08 Ga, whereas the early Paleoproterozoic was characterized by crustal reworking and remelting. Zircon Hf isotopic compositions also reveal differences in crustal growth between the two domains. The northern domain shows a wider two-stage Hf model age range, with a peak at ca. 3.17 Ga and a subsidiary peak at ca. 3.78 Ga. Therefore, the northern domain also shows significant crustal growth in the Mesoarchean, though the age peak is about 100 Ma older compared to the southwestern domain. The Eoarchean crustal growth event recorded in the northern domain is absent in the southwestern domain. Therefore, the southwestern and northern Yangtze blocks display independent magmatic histories during the Archean and early Paleoproterozoic. The common records of late Paleo- and Mesoproterozoic tectonothermal events indicate the two domains were juxtaposed at this time, probably in association with assembly of the Nuna supercontinent.

Petrogenesis of the Newly Discovered Early Cretaceous Peralkaline Granitic Dikes in Baerzhe Area of Jarud Banner, Inner Mongolia: Implications for Deciphering Magma Evolution

The super-large Baerzhe Be–Nb–Zr–REE deposit in NE China is hosted in the Early Cretaceous peralkaline granites. In this work, the newly discovered granitic dikes developed around the Baerzhe deposit were studied for the first time, focusing on their genesis and genetic relationships with the Baerzhe peralkaline granites. Zircon U-Pb dating of these granitic rocks (including the granite porphyry, rhyolite and miarolitic granite) yielded Early Cretaceous ages of 125–121 Ma. Their mineral assemblages and geochemical features suggest that they share similar features with the peralkaline A-type granites. Their geochemical data and zircon Hf isotopic compositions (εHf(t) = +3.4 to +10.5) indicate that the peralkaline granitic rocks were formed by the partial melting of dehydrated charnockite with extensive plagioclase crystal fractionation, which resulted in a peralkaline affinity. There are two types of distinct zircons in the studied samples: the type I zircon with a bright rim and dark core, which may represent a cumulate mineral phase captured together with aggregates during eruption, and the type II zircon with a higher evolution degree crystallized in the residual melts. Combined with the simulation results using whole-rock trace elements, we proposed that the peralkaline granitic dikes represent more evolved interstitial melts than the Baerzhe granitic magma. In the Early Cretaceous extensional tectonic settings, mantle-derived magma upwelled, which induced the melting of the lower crust and prolonged the evolutionary process of the magma crystal mush.

Early Jurassic high-temperature granites along eastern Bangong-Nujiang suture in Tibet and its geodynamic implications

The varying geochemical compositions of granites are generally considered as the proxy record of different geodynamic processes. The granites collected in the Kaqiong microblock along the eastern Bangong-Nujiang suture in Tibet show A-type granite affinity, but do not strictly follow the definition of A-type granite in some aspects. Zircon U Pb dating shows that the Kaqiong granite pluton was emplaced in the Early Jurassic (186–176 Ma), bracketing in the timing of the lithospheric and asthenospheric mantle-derived magmatism (197–175 Ma) in the Kaqiong microblock. These granites are metaluminous to peraluminous and high-K calc-alkaline to shoshonitic rocks. They have high contents of alkalis (K 2 O + Na 2 O), high field strength elements (e.g., Zr, Nb), and rare earth elements (except Eu), with high magmatic temperatures; these features are typical of A-type granite. However, these granites show slightly lower 10,000 × Ga/Al ratios of 2.3–3.0 and lower FeO tot /(FeO tot + MgO) values of 0.58–0.68 than the typical A-type granite. Their whole-rock Sr Nd isotopic compositions ( I Sr = 0.72996–0.73481, ε Nd (t) = −12.4 to −10.8, T DM C = ~1.9 Ga) and zircon Hf isotopic compositions (ε Hf (t) = −18.9 to −6.1, T DM2 = ~2.0 Ga) indicate that they mainly originated from pre-existing crustal materials. We suggest that the Kaqiong granites were produced by protracted partial melting of the basement rocks at relatively high temperature and high oxygen fugacity conditions. The Early Jurassic high-temperature granites were formed due to a significant mantle heat addition into the crust in an extensional continental arc, caused by the rollback of the subducted Bangong-Nujiang Tethyan oceanic slab. The study is an example of how high-temperature granites could shed light on the geodynamic processes. • Geochronology, geochemistry, and Sr-Nd-Hf isotope compositions of the Kaqiong granites • The Kaqiong granites are the high-temperature granites. • The Kaqiong granites formed in an extensional continental arc • The type of granites provides insight into the geodynamic processes of a subducting slab.

Late Permian A-type granites in Ma'andi in the Jinping area, southwestern China: Petrogenesis and implications for plume–slab interaction

The Jinshajiang–Ailaoshan suture zone in southwestern China preserves the magmatic record of the late Permian Paleo-Tethyan oceanic subduction system and the Emeishan mantle plume. However, little is known about whether direct plume–subduction interaction occurred in southwestern China during the late Permian. Here we report a study of late Permian (ca. 254 Ma) quartz monzonites and granites in the locality of Ma'andi in the Jinping area in the southern part of the Ailaoshan suture zone. The quartz monzonites and granites have medium–high SiO 2 (62.1–74.9 wt%), high Na 2 O + K 2 O (7.8–9.7 wt%), and low TiO 2 (0.24–0.84 wt%) and CaO (0.18–4.1 wt%) contents. The studied rocks are enriched in Rb, Th, U, and light rare earth elements and depleted in Ba, Sr, Eu, and Ti. They exhibit A-type granite mineral assemblages and geochemical characteristics, including the occurrence of anhedral amphibole and biotite interstitial to quartz and feldspar, high 10,000 × Ga/Al (1.8–5.1, mean = 2.9) and FeO T /MgO (3.8–23.7) ratios, and high Zr + Nb + Ce + Y contents (345–1024 ppm, mean = 613 ppm). The quartz monzonites and granites have slightly enriched to depleted whole-rock Nd compositions (ε Nd (t) = −0.9 to +1.3; T DM = 1.2 to 0.8 Ga) and depleted zircon Hf isotopic compositions (ε Hf (t) = +3.6 to +9.2; T DM = 0.8 to 0.5 Ga) that are similar to those of Emeishan OIB-type high-Ti basalts. The studied rocks also show ( 206 Pb/ 204 Pb) i ratios of 17.206–18.304, ( 207 Pb/ 204 Pb) i ratios of 15.515–15.571, and ( 208 Pb/ 204 Pb) i ratios of 36.404–38.294, respectively, which can best be explained by a mixture of dominant enriched-mantle and subordinate depleted-mantle materials. Combining regional geological data with geochemical characteristics, we suggest that the primary mafic magmas of the quartz monzonites and granites were formed mainly by partial melting of a hybridized source consisting of dominant Emeishan-fossil-plume material (85%–90%) and subordinate (10%–15%) recycled Paleo-Tethyan oceanic crust. Subsequently, these mafic magmas underwent sequential fractional crystallization, forming the A-type quartz monzonites and granites. Plume–slab interaction has been only rarely identified in pre-Cenozoic systems, which casts doubt on the importance of plume–slab interaction through the geological record. However, our study provides direct magmatic evidence for pre-Cenozoic plume–slab interaction. • The Ma'andi A-type granites were formed at late Permian (ca. 254 Ma). • The Ma'andi A-type granites were fractionated products of mafic magmas. • Paleo-Tethys slab was interacted with Emeishan mantle plume during late Permain.

Ediacaran mafic magmatism recorded in Cambrian eclogites of the Ross orogen, Antarctica: Implications for the Neoproterozoic rifting episodes along the Pacific‐Gondwana margin

AbstractWe report the first finding of Ediacaran mafic magmatism in northern Victoria Land of the Ross orogen, Antarctica, based on ca. 600–590 Ma magmatic zircon cores in Cambrian eclogites. The mafic magmatism could be either linked to ca. 615–590 Ma incipient convergent margin magmatism in central segment of the Ross orogen, or ca. 600–580 Ma continental rift‐related volcanism widespread in eastern Australia. The latter is preferred based on the trace‐element compositions distinctive from those of arc‐related basalts and the depleted mantle‐like Hf isotopic compositions of zircon. Our results suggest dual rifting episodes during both the Ediacaran and Cryogenian (ca. 670–650 Ma) in the East Antarctic margin, correlative with those in eastern Australia. A spatial distribution of coeval rifting and subduction along the Ediacaran margin of East Antarctica is readily accounted for by rift inheritance; the upper‐ and lower‐plate geometry resulting from detachment and transform faulting.

Rejuvenation of silicic magmatic systems: Insights from the formation of garnet-bearing, crystal-rich tuff in Southeast China

Crystal-rich volcanic rocks are important for understanding the evolution of large silicic magma systems. However, the magmatic evolution and rejuvenation processes that form the eruptible crystal-rich magma remain controversial. In this study, we conducted petrological, whole-rock major and trace element geochemical and zircon U–Pb and Hf–O isotopic analyses on the Banshan crystal-rich tuff from the large Cretaceous volcanic belt of southeast China. Systematic SIMS and LA-ICP-MS zircon U–Pb geochronology indicate that the Banshan tuff was formed at ∼114–112 Ma. Their zircon Hf isotopic compositions [εHf(t) = −10.9 − 4.2; TDMC = 2.18–1.68 Ga] indicate that the magma of Banshan tuff was derived from a combination of mantle-derived melts and partial melting of the Paleoproterozoic crust of southeast China. In addition, they have low zircon O isotopic compositions (δ18OVSMOW = 4.39–5.36‰) reflecting that the assimilation of wall-rocks which underwent high-temperature hydrothermally exchange with meteoric waters. Extremely Mn-rich garnets in the Banshan tuff (MnO = 30.48–35.82 wt%) suggest that the magma once reached a high degree of crystallization which was nearing consolidation. The subsequent mush rejuvenation caused by magma recharge is evidenced by partly resorbed alkali feldspar, quartz and garnet, as well as the CL-bright rims of zircon. Crystal-rich volcanic rocks are widely distributed in the lower sequences of Cretaceous volcanic strata from southeast China, but rarely developed in the upper sequences. We suggest this reflects that the magmas of lower sequences have higher volatile contents and were formed in a subduction tectonic setting.

Paleogeographic affinity of the Alxa Block across the Archean–Proterozoic: Insights from metamorphosed Archean basement

The Alxa, Quanji, and Dunhuang blocks are microblocks that link the North China craton (NCC) and the Tarim craton (TC). Their paleogeographic affinities during the late Archean–early Paleoproterozoic remain poorly constrained due to a paucity of reliable paleomagnetic data and less exposed Archean basement, especially in the Alxa Block. This study presents new geochronological and Hf isotopic data from Archean granitic gneisses in the northern Alxa Block. LA-ICP-MS zircon U-Pb dating results indicate that the protoliths of these granitic gneisses were emplaced at 2.67–2.65 Ga and subsequently metamorphosed at ca. 2.5 Ga and 1.84–1.83 Ga. In addition, in-situ zircon Hf isotopic compositions suggest that the protoliths were likely derived from reworking of Mesoarchean crust. These newly obtained data, together with previous data across the Alxa Block, indicate that Mesoarchean crustal materials were principally reworked to generate the 2.7–2.3 Ga crystalline basements of the Alxa Block. Given the recently reported ca. 2.6–2.5 Ga orthogneisses elsewhere in the Alxa Block, there should have existed a Neoarchean basement in the block, which experienced two episodes of magmatism at 2.7–2.5 Ga and 2.3–2.0 Ga, along with a metamorphic event at ca. 2.5 Ga. A further review of field geology and data across the Alxa Block and its adjacent blocks constrain a late Archean–early Paleoproterozoic crustal evolutionary history of the Alxa Block that was analogous to those of the Kuruktag Block of TC, the Khondalite Belt of NCC and the Quanji Block, indicating a close paleogeographic affinity of these blocks at this time.

Sources and oxidation state of the Permian arc magmatic rocks of SW Jilin Province in the eastern Central Asian Orogenic Belt: evidence from Li, Hf isotopes and oxygen fugacity

AbstractThe late Palaeozoic continental-arc magmatic rocks in the Gongzhuling area are located in the Liaoyuan Accretionary Belt. Here we present new zircon U–Pb ages, whole-rock major- and trace-element compositions, Li and zircon Hf isotopic compositions and oxygen fugacity of these rocks with an aim to constrain the lithium isotopic composition of the source region and origin of the magmas. These rocks were formed during 269–258 Ma in middle–late Permian time. The dioritic rocks were formed through mixing processes, with the mafic melts originating from a metasomatized mantle wedge and the felsic melts from the lower crust of a Neoproterozoic arc. The mantle wedge has been metasomatized by Li-rich fluids derived from subducted oceanic crust, as indicated by the δ7Li values of +0.4 ‰ to +3.5 ‰ and positive ϵHf(t) values (+0.7 to +13.1). Redox-sensitive Ce in the zircons indicates the fO2 of the magmas to be low to intermediate (FMQ−2.2 to FMQ+2.6; FMQ is the fayalite–magnetite–quartz redox buffer), precluding large-scale porphyry Cu–Mo mineralization. The middle–late Permian magmatic rocks represent the terminal magmatic record of the subduction of the Palaeo-Asian oceanic crust, meaning that the final closure of the Palaeo-Asian Ocean in the eastern Central Asian Orogenic Belt occurred at the end of the Permian Period. Recent identification of Mesoproterozoic (c. 1400 Ma) granites suggests some Palaeoproterozoic crustal fragments still exist in the Liaoyuan Accretionary Belt, but only in a small amount; therefore, it is concluded that the crustal growth of the Liaoyuan Accretionary Belt occurred mainly during the Neoproterozoic period.

Sr-Nd-Pb and zircon Hf isotopic constraints on the petrogenesis of two types of early Cretaceous intrusive rocks in the Tongling ore-cluster region: Implications for Cu-Au polymetallic mineralization

Early Cretaceous magmatic activities in the Tongling ore-cluster region of eastern China produced a series of igneous rocks, which can be divided into early-stage ore-bearing intrusions associated with large-scale Cu polymetallic mineralization, and late-stage intrusions that are generally ore-barren. Petrogeneses of these intrusive rocks and their relationship to mineralization are still controversial. To clarify these scientific issues, early-stage ore-bearing intrusive rocks (granodiorite from the Jinziwei deposit and granodiorite porphyry from the Yaojialing deposit) and late-stage ore-barren granodiorite dykes from the Jinziwei deposit are studied. Zircons from early-stage ore-bearing intrusions and late-stage ore-barren rocks yield U–Pb ages of 141–139 Ma, and 129 Ma, respectively, indicating that the gap between the two-stage magmatic events was approximately 10 Ma. The SiO2 contents of the two types of rocks are similar (62.15–68.11 wt% and 64.02–65.91 wt%, respectively), whereas their Sr/Y values (49.26–140.54 and 17.90–21.24, respectively) and Y contents (7.4–16.2 ppm and 20.2–24.0 ppm, respectively) are significantly different, suggesting that the former is adakite and the latter is non-adakite. Whole-rock Sr-Nd-Pb and zircon Hf isotopic compositions indicate that the early-stage ore-bearing intrusions were derived from partial melting of the subducted slab (oceanic crust with marine sediments), followed by the interaction of lithospheric mantle peridotite and the later incorporation of Middle-Upper Yangtze continental crust materials during magma ascent/emplacement. The late-stage ore-barren dykes evolved from the early-stage intermediate-basic magma in the Tongling region, which was originated from the enriched lithospheric mantle metasomatized by slab fluids/melts followed by the addition of a small amount of crustal materials. The zircon and apatite geochemical results show that high oxygen fugacity of the early-stage intrusion is a key factor in regional Cu-Au mineralization. Our study reveals the fact that magma with F-rich or Cl-rich characteristics directly controls the type of mineralization. Furthermore, the F-rich magma is favorable for Cu-Mo deposits, and on the other hand, the Cl-rich magma is favorable for Cu-Au-Zn deposits.