Zircon Hf Isotopic Data Research Articles

Petrogenesis, tectonic setting, and metallogenic significance of the Middle Permian volcanic rock system of the Miaoling Formation, Yanbian area, NE China: Constraints from geochronology, geochemistry, and Sr–Nd–Hf isotopes

The volcanic rock system of the Miaoling Formation contains the main ore-bearing rocks of two volcanogenic massive sulfide (VMS)-type deposits in the Yanbian area of NE China. Investigation of the VRSMF is needed to better understand the formation of these VMS-type deposits and the tectonic evolution of the Yanbian area. To determine the petrogenesis, material sources, and formation age of the VRSMF, and elucidate its late Paleozoic tectonic evolution and metallogenic significance, this paper presents new petrological, geochronological, geochemical, whole-rock Sr–Nd and in situ zircon Hf isotopic data for the VRSMF. The VRSMF is composed of marine carbonate, intermediate–felsic volcanic rocks (andesite–trachyandesite–dacite) and pyroclastic rocks. Laser-ablation–inductively coupled plasma–mass spectrometry zircon U–Pb dating gives an eruption age of ca. 265 Ma for the pyroclastic rocks in the VRSMF. These rocks are classified as low- to medium-K calc-alkaline series. They are characterized by enrichments in large-ion lithophile elements (e.g., K, Rb, and Ba) and light rare earth elements, and depletions in high field-strength elements (e.g., Nb, Ta, and Ti) and heavy rare earth elements, showing affinity to igneous rocks formed in arc-related tectonic settings. These features, together with homogeneous zircon εHf(t) values of 10.9–15.7 and depleted Sr–Nd isotopic compositions [εNd(t) values of 2.4–5.0], suggest that the parental magma was derived from the partial melting of depleted mantle that had been metasomatized by subduction-related fluids. These results, along with findings of regional geological investigations, suggest that the formation of the VRSMF was related to subduction of the Paleo-Asian oceanic plate during the middle Permian. The VMS-type mineralization in the Hongtaiping and Dongfengnanshan deposits is interpreted to have formed in a bimodal–felsic setting in a back-arc extensional tectonic environment.

The Neoarchean and Paleoproterozoic crustal evolution of the Clearwater block, northwestern Laurentia: Implications for the assembly of supercontinents

We report new coupled zircon U-Pb age and Hf isotope data, along with whole-rock Hf-Nd isotope data for 20 samples from the Priest River and Clearwater complexes—Neoarchean and Paleoproterozoic basement exposures in northern Idaho, northwest Laurentia. The new zircon data reveal two well-defined periods of magmatism at ∼ 2.66 and ∼ 1.86 Ga in each complex, with no evidence of any intervening or older magmatic events. Positive zircon initial εHf values of the Neoarchean rocks (+1 to +3) indicate juvenile magmas derived from a depleted mantle source. The Paleoproterozoic rocks, in both complexes, share a much wider range of initial zircon εHf values (−7 to +6) which suggests magmas derived from a depleted mantle source intruded and assimilated pre-existing Neoarchean continental crust. The shared age and isotope compositions in the Priest River and Clearwater complexes suggest that the two complexes likely belong to a single crustal block—the Clearwater block.Based on these new zircon U-Pb ages and Hf isotopic data of the Neoarchean and Paleoproterozoic rocks, the Clearwater block is shown to be distinct from the nearby Wyoming Province, the Medicine Hat block, and components of the Great Falls tectonic zone. We also report new zircon Hf isotope data for the ∼ 1.58 Ga Laclede orthogneiss in the Clearwater block, which along with published U-Pb and Hf isotope constraints, support a paleogeographic connection between the Gawler craton, East Antarctica, and northwestern Laurentia during ∼ 1.9 Ga to ∼ 1.6 Ga. Comparison with other examples of co-existing Neoarchean and Paleoproterozoic igneous rocks present in other continents suggests that the global record of 2.7–2.5 Ga magmatism often represents new crustal additions from a depleted mantle reservoir. The record of 2.0–1.7 Ga rocks also represent additions of juvenile magma, but with significantly larger contributions from pre-existing continental crust. In many cases the 2.0–1.7 Ga crust preserved on Earth today was added during the assembly of the supercontinent Nuna.

Late Carboniferous intrusions along the Kalamaili suture zone, southwestern Central Asian Orogenic Belt (CAOB): implications for a tectonic switch from subduction to collision

ABSTRACT A tectonic switch from subduction to collision and/or arc–arc collision is a key issue for understanding accretionary orogenic processes. We present new U-Pb ages, geochemistry, whole-rock Nd and zircon Hf isotope data for a suite of late Carboniferous intrusive rocks along the Kalamaili suture zone of the southwestern Central Asian Orogenic Belt (CAOB) and demonstrate their petrogenesis and the transition of their tectonic settings. Zircon U-Pb dating for the gabbros, diorites, granodiorites, and monzogranites yields ages of 317–301 Ma. The gabbros (311 Ma) were likely derived from partial melting of a mixed source of depleted MORB-like asthenospheric mantle with minor old crustal material; the diorites (301 Ma) from the mixed depleted lithospheric mantle and crustal components; the granodiorites (303 Ma) from the mixed mantle- and crust-derived magmas; and the monzogranites (317 Ma) from melting of the newly underplated basaltic lower crust. Combined with previous data, we have grouped all the intrusive rocks along the Kalamaili suture zone into three phases: 350–340 Ma, 330–320 Ma, and 320–300 Ma. The first phase consists of tholeiitic and high-K calc-alkaline granites, the second phase is composed of high-K calc-alkaline I-type granites with strong deformation, and the third phase comprises voluminous and various rock types (mainly mafic and felsic, including many A-type granites), revealing a magmatic flare-up. The magmatic associations and evolution from the first to the third phase, together with regional geology, suggest a tectonic transition from subduction/accretion (350–340 Ma) through syn-collision (330–320 Ma) to post-collision (or post-accretionary, 320–300 Ma), respectively. This study provides new magmatic evidence for the switch from subduction to collision (arc-arc collision) along the Kalamaili suture zone in the southwestern CAOB.

Geochronology and Zircon Hf Isotope of the Paleoproterozoic Gaixian Formation in the Southeastern Liaodong Peninsula: Implication for the Tectonic Evolution of the Jiao-Liao-Ji Belt

The Jiao-Liao-Ji belt (JLJB), in the Eastern Block of the North China Craton, is a major Paleoproterozoic orogen and underwent a complicated tectonic evolution during 2.2–1.8 Ga. The Liaohe Group, an important stratigraphic unit in the JLJB, is key to understanding the complex evolution of this belt. In this paper, we present new detrital zircon U–Pb ages and Hf isotope data for meta-sedimentary rocks from the Gaixian Formation in different areas of the JLJB, in addition to compiled data for other formations of the Liaohe Group, to establish the depositional age and source of detrital materials of the group. U–Pb age results show that the age ranges of zircons from the different samples are broadly similar. The youngest zircon group is ca. 2.06 Ga, and the youngest single-grain age is ca. 2.0 Ga, constraining the depositional age of the Gaixian Formation to between 2.0 Ga and the metamorphic age of ca. 1.9 Ga. The zircon age data indicate that the provenance was primarily Archaean basement of the Nangrim Block and Paleoproterozoic volcanic rocks of the Li’eryu Formation. On the basis of the new geochronological data and results from previous studies, it is inferred that the JLJB underwent a successive process of rifting–subduction–collision, with the different formations of the Liaohe Group being deposited in different stages from rift to passive continental margin and then to active continental margin. Zircon Hf isotope data from the JLJB and adjoining Longgang and Nangrim blocks indicate that a major crustal growth event occurred at 2.9–2.5 Ga, followed by crustal growth and intense recycling of ancient crust at ca. 2.2 Ga.

Large zircon age spans record multi-stage history of batholith assembly: Insights from the Late Triassic Dongcuo batholith in the eastern Tibetan Plateau

Large and homogeneous plutons can assemble incrementally over millions of years, yielding large age spans. Determination of the age span is crucial to constrain the timing and nature of the batholith assembly. This paper reports comprehensive whole-rock geochemical data, LA-ICP-MS zircon U-Pb age, and zircon Hf isotopic data to constrain the timing and assembly process of the Late Triassic Dongcuo batholith, the largest batholith in the Yidun Terrane, eastern Tibetan Plateau. Samples from the batholith consist of metaluminous to weakly peraluminous granitoids (SiO2 = 69.91–79.85 wt%). These granitoids show large variation of zircon Hf isotopic compositions with εHf(t) of -17.15 to +0.13. The multiple zircon populations in single hand specimens revealed by kernel density estimation spread over 20 Myr (ca. 225–204 Ma), which is also confirmed by core-rim ages of single zircon grains, suggesting prolonged magmatism of the Dongcuo batholith. Our data indicate that the assembly of the batholith resulted from emplacement of discrete magma batches which derived from spatially varied sources and underwent variable differentiation. The assembly mainly involved three stages, including an early episode of magmatism (ca. 228 Ma), a high-flux magmatism between ca. 220 Ma and ca. 216 Ma, and a late-stage thermal event (ca. 211–204 Ma) possibly related to high temperature and localized remelting of the batholith. This study highlights the complexity of zircon populations in composite granitic batholith, showing that the search for single crystallization ages for a sample is fraught with difficulties and may mask rather than elucidate the crystallization history of the magmatic body.

Petrogenesis of Neoproterozoic magmatic rocks in the Songnen Massif (northeastern China): Implications for basement composition and crustal growth

This paper reports new zircon U–Pb geochronological, whole-rock geochemical, and zircon Hf isotopic data for Neoproterozoic intrusive rocks in the Songnen Massif in the eastern Central Asian Orogenic Belt (CAOB), with the aim of revealing the petrogenesis of the Neoproterozoic intrusive rocks, and constraining the basement composition and crustal growth process of the Songnen Massif. Dating results identify three episodes of Neoproterozoic magmatism at ca. 950, ca. 856, and ca. 790 Ma in the eastern Songnen Massif. The ca. 950 Ma magmatic rocks consist of syenogranites, the ca. 856 Ma magmatic rocks comprise mainly gneissic monzogranites, and the ca. 790 Ma magmatic rocks consist of gneissic monzonites and monzogranites. The Neoproterozoic granitoids have high contents of SiO2 and K2O, low contents of total Fe2O3 and MgO, and show characteristics of enrichment in large-ion lithophile elements (e.g., K and Rb), and depletion in high-field-strength elements, implying that their primary magmas could have been derived from partial melting of the lower crust. However, compared with the ca. 790 Ma monzogranites [εHf(t) = +7.3 to +9.5] in the south of the Songnen Massif, the ca. 950 and ca. 856 Ma granitoids in the north have much lower zircon εHf(t) values (−2.0 to −0.2 and −10.6 to −8.9, respectively), suggesting that the ca. 950 and ca. 856 Ma magmas were generated by the reworking of ancient mafic lower crust, whereas the ca. 790 Ma granitic magma was generated by the reworking of juvenile mafic lower crust. In contrast, the ca. 790 Ma gneissic monzonites were formed by mixing of the mantle-derived and crust-derived melts. Considering the Precambrian magmatism, detrital and captured zircons, and zircon Hf model ages together, the Precambrian basement of the Songnen Massif includes not only the Neoproterozoic crustal materials, but also the Neoarchean–Mesoproterozoic components. Zircon εHf(t) values of the Neoproterozoic granitoids in the Songnen Massif appear to progressively decrease from south to north, reflecting a lateral heterogeneity of basement composition of the eastern Songnen Massif, and indicating that crustal growth occurred mainly during the late Mesoproterozoic and Neoproterozoic in the south, while during the late Paleoproterozoic in the north.

Zircon Hf-Isotopic Mapping Applied to the Metal Exploration of the Sanjiang Tethyan Orogenic Belt, Southwestern China

Zircon Hf-isotopic mapping can be regarded as a useful tool for evaluating the coupling relationship between lithospheric structure and metallic mineralization. Hence, this method shows important significance for mineral prediction. To explore this potential, the published granite zircon Hf isotope data from the Sanjiang Tethyan Orogen were systematically compiled. This study uses the Kriging weighted interpolation in the Mapgis software system to contour Hf isotopes, revealing a relation between the crustal structure and metallogenesis. The mapping results suggest that the Changning–Menglian suture zone is the boundary between ancient and juvenile crust, viz., the western terranes have ancient crust attributes, whereas the eastern terranes exhibit the properties of new juvenile crust. In addition, this study also found that the mineralization and element types in the Sanjiang Tethyan Orogen have a coupling relationship with the crustal structure. The distribution of porphyry Cu-Mo-Au deposits is mainly controlled by the new juvenile crust, whereas the magmatic-hydrothermal Sn-W and porphyry Mo-W(-Cu) deposits are closely related to the reworked ancient crust. The results of zircon Hf isotope mapping prove that the formation and spatial distribution of deposits are related to the composition and properties of the crust. Hf isotope mapping can reveal the regional metallogenic rules and explore metallogenic prediction and metallogenic potential evaluation.

Final‐stage Southward Subduction of the Eastern Paleo‐Asian Ocean: Evidence from the Middle Permian Mafic Intrusions in the Northern Margin of the North China Craton

AbstractThe northern margin of the North China Craton (NCC) contains widespread Permian magmatic rocks, but the origin of these rocks remains controversial. This uncertainty hampers us from better understanding of tectonic framework and evolution of the eastern Paleo‐Asian Ocean, particularly with respect to its final‐stage subduction and closure time. To address these questions, this study presents petrological, zircon U‐Pb geochronological, whole‐rock geochemical and in situ zircon Hf isotopic data for these Permian mafic intrusions in the northern margin of the NCC. Precise zircon U‐Pb dating results indicate that these mafic intrusions were emplaced in the Middle Permian (ca. 260 Ma). Geochemically, the studied mafic intrusions have high MgO and transition metals element contents, with high Mg# values, indicating a mantle origin. These mafic intrusions are characterized by enrichments in large ion lithophile elements (LILEs; e.g., Rb, Ba, and K) and light rare earth elements (LREEs), and depletions in high field strength elements (HFSEs; e.g., Nb, Ta, and Ti) and heavy rare earth elements (HREEs), indicating that they were formed in a subduction‐related setting. These geochemical features, together with zircon ∊Hf(t) values (–1.1 to +11.2), indicate that their parental magmas were derived from partial melting of heterogeneous mantle wedge metasomatized by subduction‐related fluids, with the contributions of slab sediments. The studied mafic intrusions also show wide range of major and trace elements contents, and variable Mg# values, Eu and Sr anomalies, suggesting that their parental magmas had undergone variable degrees of fractional crystallization. Together with the E–W trending Permian continental arc along the northern margin of the NCC, we confirm that the generation of the Middle Permian mafic intrusions was related to southward subduction of the Paleo‐Asian oceanic lithosphere beneath the NCC and the Paleo‐Asian Ocean had not closed prior to the Middle Permian.

Detrital zircon provenance of the Archean Moodies Group, Barberton Greenstone Belt, South Africa and Eswatini

Sandstones of the 3.22 Ga Archean Moodies Group represent one of the world9s oldest quartz-rich sedimentary sequences. The provenance of this unit is unresolved because its quartz and common microcline can be sourced both from either now eroded or covered granitoid plutons outside the Barberton Greenstone Belt (BGB) or, alternatively and perhaps more controversially, (rhyo-)dacitic (sub-)volcanic rocks within the BGB. We compiled 31 detrital zircon data sets (n = 2588) from sandstones, reworked tuffs and conglomerate of the Moodies Group in order to constrain its age and provenance. After selection using quality criteria, the remaining zircons (n = 1621) in nearly all samples show a distribution corresponding to the four known major pulses of felsic magmatism in the BGB: 1) the <i>ca.</i> 3550 to 3530 Ma Theespruit and Sandspruit Formations at the base of the Onverwacht Group; 2) the <i>ca.</i> 3440 to 3410 Ma rhyo-dacites of the upper Hooggenoeg Formation, Onverwacht Group; 3) the <i>ca.</i> 3300 to 3280 Ma thin felsic tuffs in the Mendon Formation; and 4) the <i>ca.</i> 3260 to 3215 Ma felsic volcanic and shallow intrusive rocks of the Auber Villiers, Bien Venue and Schoongezicht Formations of the upper Fig Tree Group and the Moodies Group as well as their co-magmatic plutonic counterparts. Almost all data sets also contain near-concordant younger zircons as young as 2820 Ma, which can be attributed to one of six tectonic or magmatic events affecting the young Kaapvaal Craton in post-BGB time, causing the partial or complete resetting of the U-Pb system in some grains. The youngest (near-)concordant zircon clusters yield ages of <i>ca.</i> 3220 Ma in most locations, and the youngest discordant group of zircons from a reworked tuff near the top of the Moodies Group at 3212 ± 13 Ma agrees well with previous estimates of the maximum depositional age. With very few exceptions, the oldest zircons (<i>ca.</i> 3564 Ma) are only slightly older than the oldest rocks in the BGB stratigraphy (<i>ca.</i> 3550 Ma). Subtle regional and stratigraphic differences in age spectra may indicate localized or nearby sediment sources within a synorogenic setting. Preliminary age spectra along vertical stratigraphic profiles show little systematic variation, possibly indicating that intrabasinal recycling was dominant over considerable time periods of the basin9s evolution. Extra-basinal plutonic sources of similar age and composition as the intra-BGB sources appear to be required to provide quartz and some feldspar to Moodies Group sandstones, although zircon age spectra, limited zircon Hf isotope data, sandstone petrography, facies analysis, and the high variability in Moodies conglomerate clast composition are consistent with uplift, deformation and erosion of several intra-BGB sources, but in particular from the region of the Onverwacht Anticline. Zircon populations, conglomerate clasts, and sandstone composition show no evidence that high-grade metamorphic rocks from the adjacent Ancient Gneiss Complex (AGC) contributed significantly to the Moodies Group.

Geochronology and geochemistry of the PiaOac granites: Implication for Late Cretaceous magmatism and metallogeny in NE Vietnam

Sn-W deposits have recently been found in NE Vietnam, which has been considered as southwestern extension of the South China Block. The timing and relationships between the Sn-W mineralization and associated granitic magmatism in this area have not been well understood. This study presents new zircon and cassiterite U-Pb geochronology, whole-rock geochemistry, and zircon Hf-isotope data for the PiaOac granites, greisens, and cassiterite veins in NE Vietnam. The PiaOac granites are characterized by high Na2O + K2O, and K2O/Na2O, and low Fe2O3T and Mg#. The presence of primary muscovite, and high A/CNK (1.23–1.26), Rb/Sr (20–25), and P2O5 (0.33–0.35%) suggest that they are strongly peraluminous S-type granites. Low K/Rb, Zr/Hf, Nb/Ta, and Eu/Eu* indicate that the granitic magma experienced strong fractional crystallization. The PiaOac granites have homogeneous zircon Hf-isotope compositions with average εHf(t) values of −9.6 to −8.7 and two-stage Hf model ages of 1.76–1.71 Ga. They probably were sourced from Neoproterozoic metasedimentary rocks with late Paleoproterozoic model ages in NE Vietnam. Low CaO/Na2O (<0.3) and high Rb/Sr and Rb/Ba ratios further suggest a clay-rich pelitic source. Zircons from greisen have significantly unradiogenic Hf-isotope compositions (εHf (t) = -12.2) and large variations, implying strong interaction with wall rocks in late fluid-rich stage during magmatic evolution. Extended magmatic differentiation was followed by interaction with wall rocks, which has altered the redox environment, facilitating the Sn-W mineralization.Zircon U-Pb dating results reveal that the PiaOac granites formed in the Late Cretaceous (89–88 Ma), coincident with the ∼ 89 Ma mineralization constrained by cassiterite U-Pb dating, suggesting that the Sn-W mineralization is closely related to the granitic magmatism and greisenization. Late Cretaceous magmatism and mineralization in NE Vietnam are similar to those in SW South China in terms of formation age, rock association, deposit type, source composition, and tectonic setting, all together constituting an E-W trending Late Cretaceous metallogenic belt. The Late Cretaceous granites and associated deposits in the belt were probably formed in an intracontinental orogenic setting in response to the combined action of the subduction of Pacific and Neo-Tethys Plates.

LA‐ICP‐MS zircon U–Pb age, whole‐rock geochemistry, Sr–Nd–Pb isotope, and zircon Hf isotope constraints on the origin and dynamic setting of Mesozoic mafic dykes, Henan Province, southeastern North China Craton

Mafic dykes from the Henan Province within the southeastern North China Craton (NCC) were sampled. Herein, we present new zircon laser ablation‐inductively coupled plasma‐mass spectrometry U–Pb age, whole‐rock geochemical, Sr–Nd–Pb isotopic, and zircon Hf isotopic data for the five areas where these mafic dykes outcrop. The mafic dykes are all dolerite and were emplaced between 121.6 ± 1.1 Ma and 131.7 ± 1.2 Ma. These are characterized by enrichment in some of the large‐ion lithophile elements (e.g., Rb, Ba, Th, U, K, and Sr), light rare earth elements, and depletion in high‐field‐strength elements (Nb, Ta, Hf, and Ti) and Eu (Eu/Eu* is between 0.62 and 0.96) relative to chondrite‐ and primitive mantle‐values. The dykes have high initial Sr isotopic ratios ([87Sr/86Sr]i = 0.7056–0.7058), negative εNd (t) ratios (−12.3 to −12.1), relatively constant Pb isotopic ratios ([206Pb/204Pb]i = 16.771–16.778; [207Pb/204Pb]i = 15.461–15.467; [208Pb/204Pb]i = 36.850–36.857), negative εHf (t) (−14.9 to −3.5), as well as old Nd (TDM2; 2.22–2.54 Ga) and Hf (TDM2; 2.99–4.34 Ga) model ages. These geochronological, geochemical, and isotopic data indicate that the investigated Henan Province dykes were likely derived from magmas generated by low to moderate degree partial melting (1.0–10%) of an EM1‐like garnet lherzolite mantle source. Moreover, the mafic melts fractionated olivine, clinopyroxene, plagioclase, Ti‐bearing oxides (e.g., ilmenite, titanite, apatite, etc.) prior to emplacement, and assimilated only minimal amounts of crustal material. Several possible models have previously been proposed to explain the origin of Mesozoic magma activities in Henan Province. However, here we propose a foundering model for the mafic dykes studied, involving the foundering of eclogite from thickened lower crust due to the collision between the Yangtze Block, Qinling ocean crust, and southeastern NCC.

Evidence of Eoarchean crust beneath the Yakutian kimberlite province in the Siberian craton

The Siberian craton is one of the largest Precambrian cratons in the world. However, unlike other cratons, the Siberian craton can only provide a relatively limited amount of geochronological data since a large part of it is covered by younger sedimentary deposits. Xenoliths from numerous kimberlite and lamprophyre pipes and alkali basalts allow us to investigate the composition and evolution of the Siberian Craton crust. The available isotopic and geochemical data show that the crust of the Anabar tectonic province of the Siberian craton is not age stratified, and consists of variably reworked Paleoarchean rocks and juvenile Proterozoic rocks at all crustal levels. Hence, a detailed geochronological study of crustal xenoliths (mainly zircon U-Pb age and Hf isotopic composition) in the kimberlite pipes of the Yakutian kimberlite province is required. In this study, we present U-Pb ages and Hf isotope data of zircons derived from crustal xenoliths in the Zarnitsa (Daldyn kimberlite field) and the Nyurbinskaya (Nakyn kimberlite field) kimberlite pipes. The obtained data provided grounds for identifying four main tectono-thermal events during the evolution of the Archean crust in the Anabar tectonic province of the Siberian craton. The first event at 3.2 Ga denotes the beginning of zircon crystallisation. These zircons are eventually recrystallised during the second event at 2.9 Ga, and radiogenic Hf (formed from 176Lu decay in the host rock) was introduced into the system. The third event at 2.8–2.7 Ga featured further recrystallisation of zircons and the incorporation of additional radiogenic 176Hf. The minor addition of radiogenic Hf during the final event at 1.9 Ga indicates a relatively large range for the initial 176Hf/177Hf ratio. Our data indicate that Eoarchean or even Hadean crust, which were reworked in the Paleoproterozoic, may be present beneath the Daldyn and Nakyn kimberlite fields. Zircon grains with low 176Hf/177Hf (0.28047–0.280661) were found in the xenoliths of the mafic garnet granulite (Zar-1–02) and garnet biotite gneisses (Nrb-13 and Nrb-65).

Petrogenesis and Tectonic Setting of Early Cretaceous Intrusive Rocks in the Northern Ulanhot Area, Central and Southern Great Xing’an Range, NE China

Abundant Early Cretaceous magmatism is conserved in the central and southern Great Xing’an Range (GXR) and has significant geodynamic implications for the study of the Late Mesozoic tectonic framework of northeast China. In this study, we provide new high-precision U–Pb zircon geochronology, whole-rock geochemistry, and zircon Hf isotopic data for representative intrusive rocks from the northern part of the Ulanhot area to illustrate the petrogenesis types and magma source of these rocks and evaluate the tectonic setting of the central-southern GXR. Laser ablation inductively coupled plasma–mass spectrometry (LA-ICP-MS) zircon U–Pb dating showed that magmatism in the Ulanhot area (monzonite porphyry: 128.07 ± 0.62 Ma, quartz monzonite porphyry: 127.47 ± 0.36, quartz porphyry: 124.85 ± 0.34, and granite porphyry: 124.15 ± 0.31 Ma) occurred during the Early Cretaceous. Geochemically, monzonite porphyry belongs to the metaluminous and alkaline series rocks and is characterized by high Al2O3 (average 17.74 wt.%) and TiO2 (average 0.88 wt.%) and low Ni (average 4.63 ppm), Cr (average 6.69 ppm), Mg# (average 31.11), Y (average 15.16 ppm), and Yb (average 1.62 ppm) content with enrichment in Ba, K, Pb, Sr, Zr, and Hf and depletion in Ti, Nb, and Ta. The granitic rocks (e.g., quartz monzonite porphyry, quartz porphyry, and granite porphyry) pertain to the category of high-K calc-alkaline rocks and are characterized by high SiO2 content (&gt;66 wt.%) and low MgO (average 0.69 wt.%), Mg# (average 31.49 ppm), Ni (average 2.78 ppm), and Cr (average 8.10 ppm) content, showing an affinity to I-type granite accompanied by Nb, Ta, P, and Ti depletion and negative Eu anomalies (δEu = 0.57–0.96; average 0.82). The Hf isotopic data suggest that these rocks were the product of the partial melting of juvenile crustal rocks. Notably, fractionation crystallization plays a crucial role in the process of magma emplacement. Combining our study with published ones, we proposed that the Early Cretaceous intrusive rocks in the Ulanhot area were formed in an extensional tectonic background and compactly related to the subduction of the Paleo-Pacific Ocean plate.

Precambrian metamorphic basement of the southern Lhasa terrane, Tibet

The Precambrian basement of the Lhasa terrane provides important information for understanding the formation and evolution of the Tibetan Plateau. However, due to the paucity of exposure, the properties of the Precambrian basement of the Lhasa terrane remain poorly known. Here we report zircon U–Pb ages, bulk-rock geochemical and zircon Hf isotopic data on the orthogneisses in the Milin area of the southeastern Lhasa terrane, southern Tibet. Inherited magmatic zircon cores of these gneisses yield protolith crystalline ages of 1556–1517 Ma, whereas the zircon rims give metamorphic ages of 1197–1192 Ma, both could be local provenance for the Mesoproterozoic detrital zircons in the Neoproterozoic–Paleozoic strata in the Lhasa terrane. Geochemical data indicate that the protoliths of the Mesoproterozoic rocks are continental arc-like granitoids with bulk-rock εNd(t) values of −3.7 to +0.7 (TDM2 = 1.99–2.34 Ga) and zircon core εHf(t) values of +1.8 to +8.6 (TDM2 = 1.71–2.17 Ga), suggesting their most likely derivation from partial melting of Paleoproterozoic crustal materials. We propose that the Mesoproterozoic gneisses in the Milin area represent the Precambrian metamorphic basement of the Lhasa terrane, likely related to the growth of Columbia supercontinent. Local exposure of the Precambrian metamorphic basement may be caused by crustal rapid uplift and erosion in the late Cenozoic and their inhomogeneous distribution.

Age and Sources of Metasedimentary Rocks of the Galam Terrane in the Mongol\u2013Okhotsk Fold Belt: Results of U\u2013Pb Age and Lu\u2013Hf Isotope Data from Detrital Zircons

The Mongol–Okhotsk fold belt is one of the major structural elements of East Asia. In this article, we present U–Pb age and Hf isotope data for detrital zircons from metasedimentary rocks of the Galam Terrane. Our new data confirm that these rocks contain a significant amount of Archean and Paleoproterozoic zircons: most grains, regardless of age, have negative εHf(t) values from –30.0 to –10.0 and model age tHf(C) > 2.2 Ga. The main sources of detrital material for the metasedimentary rocks of the Galam Terrane were igneous and metamorphic complexes of the southeastern margin of the Siberian Craton. Some of the Devonian and Carboniferous zircons have slightly negative and positive εHf(t) values of ‒7.4 to +6.9 and younger tHf(C) ages of 1.46–0.90 Ga. These zircons were derived from eroded island arcs in the Mongol–Okhotsk Paleocean. Our results suggest that the Galam Terrane is a Paleozoic accretionary complex of the Siberian Craton.

Protoliths and metamorphism of the central Himalayan eclogites: Zircon/titanite U–Pb geochronology, Hf isotope and geochemistry

The high-pressure (HP) eclogites in the central Himalaya provide insights into the metamorphism and exhumation history of crustal material beneath the Tibetan plateau. Due to the paucity of exposure, the nature and timing of the protolith and metamorphism of the eclogites remain poorly known. Here we report zircon and titanite U–Pb ages, bulk-rock and mineral compositions and zircon Hf isotope data on the eclogites from the Thongmön and Kharta areas in the central Himalaya. The eclogites record peak HP eclogite-facies metamorphism at >1.6 GPa, high-temperature to ultrahigh-temperature (HT-UHT) granulite-facies overprinting (ca. 0.88–0.99 GPa and 875–920 °C), and subsequent decompression-cooling retrograde metamorphism (ca. 0.42–0.62 GPa and 800–820 °C). Geochemical data suggest that the eclogite protoliths are most consistent with being seafloor tholeiitic basalts with an E-MORB signature. Inherited magmatic zircon cores from the eclogites give a protolith age of ∼450 Ma and εHf(t) values of + 3.2 to + 7.0. Metamorphic overgrown mantles or some rims of zircon record an early decompression granulite-facies metamorphic stage (∼17.9–15.3 Ma); other metamorphic overgrown rims and metamorphic growth zircons reflect later decompression-cooling retrograde metamorphic stage (∼14.8–13.3 Ma). The titanite U–Pb age (∼15.4 Ma) further indicates the beginning of the later retrograde metamorphism. All these data and observations allow the proposal that in contrast to the ultrahigh-pressure (UHP) eclogites in the western Himalaya, the HP eclogites in the central Himalaya record the long-lived burial and relatively slow exhumation of the Indian continental crust since initial Indo-Asia collision at ∼55 Ma.

Geochronology and Petrogenesis of Early Pleistocene Dikes in the Changbai Mountain Volcanic Field (NE China) Based on Geochemistry and Sr-Nd-Pb-Hf Isotopic Compositions

Changbai Mountains intraplate volcanism (NE China) developed above the 500 km deep stagnant portion of the Pacific slab in the last 20 Ma. The more recent activity includes a shield-forming stage (2.8–0.3 Ma), the Tianchi cone construction stage (1.5–0.01 Ma), and a caldera-forming stage (0.2 Ma-present). Detailed studies on the petrogenesis of the volcanic products between the first two stages and the possible role of geodynamics and local tectonics in controlling the volcanism, however, are lacking. Here, we present structural and whole-rock geochemical and zircon Hf isotopic data on Pleistocene dikes of the Changbai Mountains at the transition from the shield-forming to the Tianchi stage with the aim to constrain their age and the source(s) of their parental magma. The dikes represent the shallower feeding system of monogenetic cones and have a NW-SE strike, which is also the preferred strike of the major fault affecting the area and along which the Changbai Mountains monogenetic scoria cones align. The dikes have a potassic affinity and a trachybasaltic composition. Their zircon U–Pb age is 1.19–1.20 Ma (Calabrian). The trachybasalts are enriched in Rb, Ba, Th, U, Nb, Ta, K, Pb, and LREE and slightly depleted in Sr, Zr, Hf, Ti, and HREE with a weak negative Eu/Eu* (δEu = 0.96–0.97). Trace elements and isotopic compositions are compatible with an OIB-type source with an EMI signature. The calculated (87Sr/86Sr)i(=0.705165–0.705324), (143Nd/144Nd)i(= 0.512552–0.512607, εNd(t) = −0.58 to −1.65), and Hf model ages (TDM2) of 1768–1562 Ma suggest that the trachybasaltic dikes were contaminated by a Mesoproterozoic, relatively basic lower crust. The source of the Calabrian trachybasalts consists of asthenospheric melts modified by a subcontinental lithospheric mantle. These melts upwell from depth and stop at the crust-mantle interface where underplating processes favor the assimilation of ancient lower crust material. During the ascent to the surface along deep-seated crustal discontinuities, these magmas weakly differentiate.

Open-system Evolution of a Crustal-scale Magma Column, Klamath Mountains, California

Abstract This study addresses the question of how and where arc magmas obtain their chemical and isotopic characteristics. The Wooley Creek batholith and Slinkard pluton are a tilted, mid- to upper-crustal part of a vertically extensive, late-Jurassic, arc-related magmatic system in the Klamath Mountains, northern California. The main stage of the system is divided into an older lower zone (c. 159 Ma) emplaced as multiple sheet-like bodies, a younger upper zone (c. 158–156 Ma), which is gradationally zoned upward from mafic tonalite to granite, and a complex central zone, which represents the transition between the lower and upper zones. Xenoliths are common and locally abundant in the lower and central zones and preserve a ghost stratigraphy of the three host terranes. Bulk-rock Nd isotope data along with ages and Hf and oxygen isotope data on zircons were used to assess the location and timing of differentiation and assimilation. Xenoliths display a wide range of εNd (whole-rock) and εHf (zircon), ranges that correlate with rocks in the host terranes. Among individual pluton samples, zircon Hf and oxygen isotope data display ranges too large to represent uniform magma compositions, and very few data are consistent with uncontaminated mantle-derived magma. In addition, zoning of Zr and Hf in augite and hornblende indicates that zircon crystallized at temperatures near or below 800 °C; these temperatures are lower than emplacement temperatures. Therefore, the diversity of zircon isotope compositions reflects in situ crystallization from heterogeneous magmas. On the basis of these and published data, the system is interpreted to reflect initial MASH-zone differentiation, which resulted in elevated δ18O and lowered εHf in the magmas prior to zircon crystallization. Further differentiation, and particularly assimilation–fractional crystallization, occurred at the level of emplacement on a piecemeal (local) basis as individual magma batches interacted with partial melts from host-rock xenoliths. This piecemeal assimilation was accompanied by zircon crystallization, resulting in the heterogeneous isotopic signatures. Magmatism ended with late-stage emplacement of isotopically evolved granitic magmas (c. 156 Ma) whose compositions primarily reflect reworking of the deep-crustal MASH environment.

Petrogenesis of the Pandao granites in the Wutai Mountains area in the North China Craton: Constraints from geochemistry, zircon U–Pb geochronology, and Hf isotopes

The Trans‐North China Orogen (TNCO) is a part of the North China Craton (NCC) and together provides a classic example of lithospheric destruction. The Pandao granites outcropping in the Wutai Mountains area provide a window to investigate the Mesozoic magmatism in the TNCO. Here, this paper presents the new zircon geochronology, whole‐rock geochemistry, and zircon Hf isotope data for the Pandao granites to discuss their petrogenesis and tectonic implications. The Pandao granites are mainly composed of light‐red medium‐ to coarse‐grained biotite granite and light‐grey fine‐ to medium‐grained biotite granite. Zircon U–Pb ages of 110.05 ± 0.67 Ma and 108.35 ± 0.81 Ma suggest that the Pandao granites were crystallized in the Early Cretaceous. The Pandao granites are classified as high‐K calc‐alkaline and weak peraluminous series. The rocks display abundance in large‐ion lithophile elements (LILE) and light rare‐earth elements (LREE) but show depletion in high‐field‐strength elements (HFSE) and heavy rare‐earth elements (HREE), with strong negative Eu anomalies. The classification diagrams indicate that the Pandao granites are A‐type granites and thus belong to the A1 subtype, formed in an intraplate extensional environment. The Pandao granites have homogeneous zircon Hf isotopic compositions. Their zircons have negative εHf(t) values (−19.1 to −17.1) and old Hf isotope crustal model ages (2,250–2,375 Ma), suggesting that the Pandao granites were formed by partial melting of the Paleoproterozoic lower crustal material. Therefore, it is suggested that the Pandao granites were formed under an intraplate extensional tectonic environment of remote effect due to the ancient Pacific Plate subduction and retreat beneath the Eurasian continent. The TNCO was influenced by the subduction and retreat of the ancient Pacific Plate in the late Early Cretaceous.

Earth's new tectonic regime at the dawn of the Paleoproterozoic: Hf isotope evidence for efficient crustal growth and reworking in the São Francisco craton, Brazil

Abstract A zircon Hf isotope data set from Archean and Paleoproterozoic magmatic and metasedimentary rocks of the southern São Francisco craton (Brazil) is interpreted as evidence of accretionary and collisional plate tectonics since at least the Archean-Proterozoic boundary. During the Phanerozoic, accretionary and collisional orogenies are considered the end members of different plate tectonic settings, both involving preexisting stable continental lithosphere and consumption of oceanic crust. However, mechanisms for the formation of continental crust during the Archean and Paleoproterozoic are still debated, with the addition of magmatic rocks to the crust being explained by different geodynamic models. Hf isotopes can be used to quantify the proportion of magmatic addition into the crust: positive εHf values are usually interpreted as indications of magmatic input from the mantle, whereas crust-derived rocks show more negative εHf. We show that the crust of the amalgamated Paleoproterozoic tectonostratigraphic terranes that make up the southern São Francisco craton were generated from different proportions of mantle and crustal isotopic reservoirs. Plate tectonic processes are implied by a consistent sequence of events involving (1) the generation of juvenile subduction-related magmatic arc rocks, followed by (2) collisional orogenesis and remelting of older crust, and (3) post-collisional bimodal magmatism.