Khondalite Belt Research Articles

Magmatism and thermal effect of the Late Paleoproterozoic layered complex in the Jining terrane, North China Craton: Evidence from magmatic cooling duration and crust-mantle interaction

The Paleoproterozoic Khondalite Belt from the northwestern North China Craton (NCC) is characterized by a wide distribution of high-temperature/ultrahigh-temperature (UHT) metamorphism and extensive magmatic events in its eastern segment, the Jining terrane. Although it has been proven that UHT metamorphism is related to large-scale thermal perturbation at the crustal level, the ultimate heat source has been kept unclear and the reliable interrelationship between the formation of UHT metamorphism and mantle-derived magmatism has not been established yet. We report data of two-layered complexes emplaced in duration over 100 Ma, as the candidates of the heat source of the UHT metamorphism. The samples include 1929 ± 23 Ma Sanchakou amphibole-gabbro (ZK0-3) and 1824 ± 2 Ma Hulu norite-gabbro(HL1517). Based on the published geochronological data of basic intrusive rocks in the Jining terrane, it is found that the Late Paleoproterozoic magmatism appears as two stages of ∼1.95 Ga (M1) and ∼1.85 Ga (M2). We calculated that the duration of M1-magmatism can reach ∼71 Myr through Monte Carlo simulation. The sample ZK0-3 is formed in M1-magmatism, coupled with the peak period of metamorphism and the slow cooling process of UHT pelitic granulite/gneiss. We used the “Magma Chamber Simulator (MCS_PhaseEQ_2019AC)” to simulate the genesis of these basic intrusive rocks. It is found that they have experienced the magmatic process of assimilationand fractional crystallizationunder energy constraints(EC-AFC). The augite, pargasite, and zircon record the crystallization temperatures during the slow cooling process of magma. Therefore, mantle-derived magmatism might have supplied heat to generate the UHT metamorphism in the Jining terrane.

Mantle magmatism, metamorphism and anatexis: evidence from geochemistry and zircon U–Pb-Hf isotopes of Paleoproterozoic S-type granites, Khondalite Belt of the North China Craton

ABSTRACT S-type granites constitute an important component of the Paleoproterozoic Khondalite Belt in the North China Craton. Here we present results from petrography, geochemistry and isotope geochronology on the porphyritic garnet-bearing syenogranite and garnet-bearing monzogranite samples in the Jining-Liangcheng area. The geochemical characteristics of these samples indicate formation through partial anatexis of the khondalites, with heat and material input from mantle-derived magma. Geochemical similarities between the porphyritic garnet-bearing syenogranite, garnet-bearing monzogranite, and metapelitic gneiss suggest their broad affinity. Sensitive high-resolution ion microprobe zircon U–Pb dating revealed that the S-type granites formed at ca. 1.92–1.90 Ga and were subsequently metamorphosed at ca. 1.85 Ga. The ca. 1.92–1.91 Ga porphyritic garnet-bearing syenogranite shows zircon εHf(t) values of −1.94–+3.38 with two-stage Hf crustal model ages (TDM2) ages of ca. 2.42–2.59 Ga. The 1.91–1.90-Ga garnet-bearing monzogranites show zircon εHf(t) values ranging from −4.36 to +0.38, with TDM2 ranging from ca. 2.57 to ca. 2.82 Ga. The geochemical isotopic compositions suggest that the porphyritic garnet-bearing syenogranite and garnet-bearing monzogranite originated from the partial melting of pre-existing crust of heterogeneous compositions with the addition of mantle-derived material. On the basis of our results, combined with geological data on the Paleoproterozoic structural evolution of the Khondalite Belt, we assume that the timing of the metamorphism and anatexis in the Jining–Liangcheng area is correlated with a regional metamorphism and mantle-derived magmatism.

Precambrian Tectonic Affinity of the Southern Langshan Area, Northeastern Margin of the Alxa Block: Evidence from Zircon U‐Pb Dating and Lu‐Hf Isotopes

AbstractThe Alxa Block is the westernmost part of the North China Craton (NCC), and is regarded as one of the basement components of the NCC. Its geological evolution is of great significance for the understanding of the NCC. However, the Precambrian basement of the Alxa Block is still poorly studied. In this study, we present new in situ LA‐ICP‐MS zircon U‐Pb and Lu‐Hf isotope data from the Diebusige Metamorphic Complex (DMC) which located in the eastern Alxa Block. Field and petrological studies show that the DMC consists mainly of metamorphic supracrustal rocks and minor metamorphic plutonic rocks and has experienced amphibolite‐granulite facies metamorphism. Zircon U‐Pb dating results suggested that the amphibolite sample yields a crystallization age of 2636 ± 14 Ma and metamorphic ages of 2517–2454 Ma and 1988–1952 Ma, proving the existence of exposed Archean rocks in the Langshan area and indicating that late Neoarchean to Paleoproterozoic metamorphic events existed in the Alxa Block. Two paragneiss samples show that the magmatic detrital zircons from the DMC yield 207Pb/206Pb ages ranging from 2.48 Ga to 2.10 Ga with two youngest peaks at 2.13 Ga and 2.16 Ga, respectively, and they were also overprinted by metamorphic events at 1.97–1.90 Ga and 1.89–1.79 Ga. Compilation of U‐Pb ages of magmatic detrital and metamorphic zircons suggested that the main part of the DMC may have been formed at 2.1–2.0 Ga. Zircon Lu‐Hf isotope data show that the source materials of the main part of the DMC were originated from the reworking of ancient Archean crust (3.45–2.78 Ga). The Hf isotope characteristics and the tectonothermal event records exhibit different evolution history with the Khondalite Belt and the Yinshan Block and the other basements of the Alxa Block, indicating that the Langshan was likely an independent terrain before the middle Paleoproterozoic and was subjected to the middle to late Paleoproterozoic tectonothermal events with the Khondalite Belt as a whole.

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.

Reworking of ancient tectonic amalgamation belt beneath the central north of North China Craton revealed by dense seismic observations

The North China Craton (NCC) is one of the oldest cratons in the world, and its internal tectonic belt is often used to investigate the earth’s tectonic evolution events. During the late Mesozoic and Cenozoic, the western Pacific subduction zone caused the restructuring of NCC by damaging the craton beneath eastern NCC, resulting in the distinct lateral differences between western and eastern NCC, which ultimately formed the current NCC. Furthermore, the subsequent tectonic events activated the ancient tectonic weak zones, and their traces are imprinted in the deep earth. Here, we investigated the crust structures with a high-density seismic array beneath the splice position of the eastern margin of the Khondalite Belt and the northern part of the central orogenic belt in NCC. The array included 140 short-period seismographs spaced at 2–3 km intervals, which recorded teleseismic three-component waveforms over a one-month period. P-wave receiver functions calculated from 25 teleseismic events provided an image of the crustal structure. The weak Moho and Moho offset under the study area are visible in the migration image of receiver functions. The geological investigations and the rock outcrops were combined to establish the strong coupling relationship between the present surface fault-depression system and deep structures. The deep material circulation, which governs the surface extension of the basin-range structure, is controlled by the deep material circulation which is ultimately derived from the continuous subduction of the western Pacific. The study’s findings indicate that the ancient amalgamative belt might have transformed into a weak zone easily susceptible to modification by plate tectonic movements.

Petrogenesis and tectonic implications of 1.86–1.80 Ga A-type granites in the Daqingshan Complex, Khondalite Belt, North China Craton

The Khondalite Belt is regarded as a Paleoproterozoic continent–continent collisional belt along which the Yinshan Block and the Ordos Block amalgamated to form the Western Block in the North China Craton. Associated with the collision of the Yinshan and Ordos Blocks was granitic magmatism represented by quartz monzogranites in the Khondalite Belt, whose petrology, geochemistry and petrogenesis will provide important insights into understanding of the crustal evolution of the Khondalite Belt in the late Paleoproterozoic. In this paper, we carried out a detailed study on the petrography, geochronology, whole-rock geochemistry, and zircon Lu-Hf isotope of quartz monzogranites exposed in the Daqingshan Complex of the Khondalite Belt. Zircon LA-ICP-MS U-Pb dating results show that the Daqingshan quartz monzogranites were formed at 1.86–1.80 Ga, at some time posterior to the ∼ 1.95 Ga collision of the Yinshan and Ordos Blocks. Geochemically, the Daqingshan quartz monzogranites belong to ferroan, metaluminous to peraluminous, calc-alkalic to alkalic-calc series, exhibiting high SiO2, Na2O, K2O and FeOT / (FeOT + MgO), low Al2O3, MgO and CaO, and high Zr, Nb, Ce and Y, low Cr and Ni contents, with an affinity of A-type granites. In terms of REE and trace elements, the Daqingshan quartz monzogranites have right dipping patterns and negative Eu anomalies, enriched large ion lithophile elements (LILEs) (e.g. Rb, Zr and Hf), and depleted high field strength elements (HFSEs) (e.g. Ta, P and Ti). Zircon Lu-Hf isotopic characteristics (εHf(t) = -9.63 – −4.31, TDMC = 2744–3050 Ma) indicate that the Daqingshan quartz monzogranites were most likely originated from the partial melting of a Neoarchean ancient crust. Combining new results presented in this paper with previous data, we propose that the quartz monzogranites in the Daqingshan Complex were derived from the partial melting of Neoarchean TTG rocks under high temperatures caused by the upwelling of mantle magmas under a post-collision extensional setting. Meanwhile, it indicates that the Khondalite Belt completed collision at 1.86–1.80 Ga to form the Western Block.

Rhyacian‐Orosirian Khondalite Belt in the Borborema Province (NE Brazil): An active margin setting based on U–Pb zircon and monazite constraints

Khondalite belts are of special importance is delimiting old suture zones and in palaeocontinental reconstruction of Precambrian terrains. In the South‐American Platform, khondalitic rocks surround cratonic areas and Archean blocks reworked in the Neoproterozoic, an example of which being the Ceará Khondalite Belt (CKB). Located in the northern portion of the Borborema Province in NE Brazil, CKB is here described by means of its petrographic, structural, and LA‐SF‐ICP‐MS zircon and monazite U–Pb geochronological characteristics. CKB constitutes an E‐W to NE–SW striking belt comprising migmatitic spinel (hercynite)‐ and graphite‐bearing cordierite‐garnet‐sillimanite‐biotite gneisses, small granulitic boudins, garnet‐biotite quartzite, lenses of garnet amphibolite, calc‐silicate rock, gondite, and mylonitized leucogneiss. Relicts of Palaeoproterozoic island and continental arcs surrounding CKB are represented by tonalitic and dioritic gneiss, respectively. The contact between CKB and the Neoproterozoic Independência Unit is marked by a transpressional shear zone to the north, whereas the contact between CKB and Archean and Palaeoproterozoic rocks to the south is via a N‐verging thrust fault. The metamorphic peak is given by the parageneses: spinel (hercynite)‐quartz, spinel (hercynite)‐cordierite, and cordierite‐sillimanite‐garnet, possibly stable under UHT conditions. Crystallization ages of 2,086 ± 8 Ma and 2,063 ± 9 Ma were obtained by dating CKB migmatitic dioritic orthogneisses using the zircon U–Pb method. The CKB para‐derived rocks yielded detrital zircon U–Pb age peaks at 2,190, 2,130, and 2,060 Ma. Three metamorphic stages are identified in the Palaeoproterozoic via U–Pb dating of zircon rims and monazite at 2,094 ± 4 Ma, 2,055 ± 5 Ma, and 1,958 ± 3 Ma. A fourth metamorphic event with associated migmatization in shear zones took place in the Neoproterozoic between 595 ± 6 Ma and 573 ± 15 Ma, as indicated by dating zircon rims and monazite, respectively. Our study shows that the metamorphic events occurring in CKB in the Palaeoproterozoic share similarities with those that affected the khondalitic rocks bordering the São Francisco and the North China cratons, which suggests the existence of a continuous orogen during the Rhyacian‐Orosirian related to the Columbia Supercontinent amalgamation.

Thermal regime of the lower crust in the eastern Khondalite Belt, North China Craton, constrained by Zr-in-rutile thermometry mapping

Ultrahigh temperature (UHT) metamorphism represents the thermally extreme metamorphic conditions in the mid- to lower crust, and its generation is significant for our understanding of crustal differentiation and crust-mantle interaction. Several Paleoproterozoic UHT metamorphic localities have been reported from the eastern Khondalite Belt, North China Craton. However, the precise spatial scale that was affected by this UHT metamorphism is still unknown, and therefore the mechanism to generate UHT metamorphism is broadly debated. Zr-in-rutile thermometry is regarded as a valid tool to estimate the near-peak metamorphic temperature of UHT granulites. Here we establish the thermal regime of the lower crust in the eastern Khondalite Belt using large-scale (∼10,000 km2) Zr-in-rutile thermometry mapping. Thirty-eight rutile-bearing garnet-sillimanite gneisses were collected, and rutile that is far from zircon and lacks ilmenite reaction rims was selected for electron probe microanalysis. Results show that the size of UHT metamorphism in the eastern Khondalite Belt is at least 3000 km2. UHT rocks closely correspond with large-scale charnockites, and small exposed mafic rocks imply that UHT metamorphism is not caused by intrusion of mafic magma. UHT metamorphism likely developed during post-collisional extension in which anomalous heat reflects both the radiogenic heating of an overthickened orogen and additionally elevated mantle flux due to subsequent lithosphere extension and asthenosphere upwelling. Nearly all large-scale UHT metamorphic terranes formed prior to ∼550 Ma, but their drivers are probably not simply the same.

The first identification of early Paleoproterozoic (2.46–2.38 Ga) supracrustal rocks in the Daqingshan area, northwestern North China Craton: Geology, geochemistry and SHRIMP U-Pb dating

Early Paleoproterozoic supracrustal rocks are relatively rare worldwide and only a few have been reported in the North China Craton (NCC). Daqingshan is a typical area of the Khondalite Belt, northwestern NCC, where early Precambrian supracrustal and intrusive rocks are widely distributed, although the precise age of all units remains unconfirmed. The Lower Wulashan Group is mainly composed of acidic to mafic volcanic and volcano-sedimentary rocks that have undergone amphibolite to granulite facies metamorphism; it was previously considered to be of Mesoarchean age. This study utilized integrated field and petrographic work, whole-rock geochemistry, and Nd whole-rock and zircon U-Pb-Hf isotopic analyses on the Lower Wulashan Group and related intrusive rocks. SHRIMP U-Pb dating of eight samples from the supracrustal rocks, interpreted as metavolcanics, yielded magmatic zircon ages of 2455–2382 Ma, thus for the first time identifying early Paleoproterozoic supracrustal rocks in the Daqingshan area. Thus it is of great importance for understanding the Precambrian evolution of the NCC as well as the Earth because this is within the period when magmatism was globally weak. Six samples from a variety of intrusive rocks have zircon U-Pb ages of 2436–2362 Ma, thus further confirming the depositional ages of the supracrustal rocks. These rocks include meta-alkali basalt, and are high in total rare earth element contents and have magmatic zircon εHf(t) values of −3.00 to +6.62 and crustal model ages of 3.12–2.52 Ga (38 analyses), and whole-rock εNd(t) of +1.0 to +2.6 with crustal model ages of 2.74–2.60 Ga (5 analyses). It is considered that the early Paleoproterozoic supracrustal rocks of the Lower Wulashan Group and related intrusive rocks formed in a continental environment, but more work is required to determine the tectonic regime (extension or subduction).

Anatexis of late Neoarchean-Early Paleoproterozoic and late Paleoproterozoic garnet-bearing leucogranite from the Khondalite Belt in the North China Craton

ABSTRACT Two episodes of late Neoarchean-early Paleoproterozoic and late Paleoproterozoic garnet-bearing leucogranite, named the Baotou and Jining–Liangcheng garnet-bearing leucogranite are recognized from the Khondalite Belt in the North China Craton. Geochemical studies show that garnet-bearing leucogranite has high Al2O3 content and FeOT/MgO ratio, with a large variation in the CaO content and K2O/Na2O ratio. Additionally, the garnet-bearing leucogranite is enriched in light rare earth elements and large ion lithophile elements and depleted in Nb, Ta, P, and Ti. However, there are some variations in Eu anomalies, as indicated by the Eu-enriched and Eu-depleted patterns. The sensitive high-resolution ion microprobe (SHRIMP) zircon U-Pb dating of the Baotou garnet-bearing leucogranite and Jining–Liangcheng garnet-bearing leucogranite show that their anatectic ages were 2.35–2.43 Ga and 1.90–1.92 Ga, respectively, with zircon εHf (t) values of −0.01–3.93 and −4.36–1.99, and two-stage model ages (TDM2) of 2.76–3.02 Ga and 2.57–2.83 Ga, respectively. U-Th-Pb SHRIMP analyses on zircon reveal ages of ca. 2.35–2.47 Ga for the Baotou metapelite gneiss and ca. 1.90–1.91 Ga for the Jining–Liangcheng metapelite gneiss, which represent the ages of tectonic metamorphic events related to the anatexis. Our results, combined with geological and petrographical observations, geochemistry, and geochronology, suggest that (1) Garnet-bearing leucogranites formed as a result of anatexis of metapelite gneisses; (2) They are mixtures of leucosomes, residual minerals and mantle-derived materials; (3) Two episodes of garnet-bearing leucogranites have been identified; (4) Both two episodes of garnet-bearing leucogranites corresponded to late Neoarchean-early Paleoproterozoic and late Palaeoproterozoic tectonothermal events, respectively.

A syn- to post-collisional tectonic transition in the Khondalite Belt, North China Craton: Constraints from 1.95 - 1.93 Ga adakitic granitoids in the Daqingshan Complex

As one of the important orogenic belts connecting the Columbia supercontinent in the late Paleoproterozoic, the Khondalite Belt (KB) of the North China Craton (NCC) is a typical continent-continent collisional orogenic belt formed through the collision between the Yinshan and Ordos Blocks at ca. 1.95 Ga. However, very few collision-related magmatic rocks have been recognized in this orogenic belt, which hampers our understanding of the crustal thickening process during this orogeny. In this study, we present new petrological, geochronological, geochemical, and zircon Lu-Hf isotopic data for the late Paleoproterozoic granitoids in the Daqingshan Complex of the KB. Zircon U–Pb dating results reveal that the granitoids were formed at ca. 1.95–1.93 Ga, which was contemporaneous with the metamorphic ages of mafic and pelitic granulites in the KB. Geochemically, these granitoids contain high Sr/Y (34.49–654.88) and (La/Yb)N (23.47–65.11) ratios, low Y (0.59–4.29 ppm) and Yb (0.10–0.42 ppm) contents, coupled with the enrichment in LREE and LILE, all of which are consistent with adakitic affinity. Such signatures along with their strong enrichment in zircon Hf isotopes (εHf(t) = −5.9 – −13.6, TDMC = 2928–3398 Ma) indicate that these granitoid rocks were derived from the partial melting of the thickened ancient lower crust. Our new results, combined with previous data, shed light on that the late Paleoproterozoic tectonic transition from syn-collisional to post-collisional regimes developed in the time interval of 1.95–1.93 Ga in the KB. This improves our understanding of the continent-continent collision process between the Yinshan and Ordos Blocks during the late Paleoproterozoic time.

New Insight From the First Application of Ti-in-Quartz (TitaniQ) Thermometry Mapping in the Eastern Khondalite Belt, North China Craton

The thermal regime of the lower crust is a critical factor that controls crustal anatexis, high-grade metamorphism, and granite formation, which finally results in crustal differentiation. However, the large-scale thermal regime in the Precambrian continental crust is generally not well established. In this study, we first applied Ti-in-quartz (TitaniQ) thermometer to map the temperature variation in the lower crust within an area of ∼10,000 km2 in the Paleoproterozoic eastern Khondalite Belt, North China Craton. The studied rocks are aluminous gneisses/granulites, which contain abundant quartz that generally coexists with rutile. The results show that matrix-type quartz with substantial rutile exsolution generally contains the maximum Ti concentration, which is <300 ppm higher than that of inclusion-type quartz. This result suggests that two quartz types probably formed at the prograde and near-peak to early cooling metamorphic stages, respectively. Therefore, the temperature mapping result based on the maximum Ti concentrations of the matrix-type quartz can better represent the thermal regime than inclusion-type quartz. Our regime shows that the hottest Paleoproterozoic lower crust is underneath the Liangcheng-Heling’er-Zhuozi area, where ultrahigh-temperature (UHT) metamorphism is closely associated with abundant charnockite. The hottest region may represent the root of an ancient large hot orogeny. Our study provides a new insight into the formation of UHT metamorphism.

Paleoproterozoic ultrahigh‐temperature metamorphism in the Alxa Block, the Khondalite Belt, North China Craton: Petrology and phase equilibria of quartz‐absent corundum‐bearing pelitic granulites

AbstractAn Al‐rich, quartz‐absent corundum‐bearing pelitic granulite is reported for the first time at the Diebusige complex in the Alxa Block in the western part of the Khondalite Belt (KB), North China Craton (NCC). A detailed petrographic study shows that a quartz‐present domain occurs in porphyroblastic garnet cores from the corundum‐bearing pelitic granulite, with a prograde metamorphic mineral assemblage (M1) of garnet + plagioclase + quartz + biotite + spinel + rutile ± melt, and a quartz‐absent domain occurs in the matrix of this rock, with a preserved peak mineral assemblage (M2) of garnet + corundum + spinel + biotite + plagioclase + K‐feldspar + rutile + melt and a retrograde metamorphic mineral assemblage (M3) of garnet + sillimanite + corundum + biotite + plagioclase + K‐feldspar ± rutile. Phase equilibrium modelling and Zr‐in‐rutile and ternary feldspar thermometry all reveal similar peak conditions of 890–940°C at 7.5–9.8 kbar, which indicate a high geothermal gradient of ~110°C/kbar and ultrahigh‐temperature (UHT) conditions. Combining this information with the detailed analysis of metamorphic zircons, we obtain the metamorphic evolution of the corundum‐bearing pelitic granulite. Specifically, the corundum‐bearing pelitic granulite experienced granulite‐facies metamorphism at ~1950 Ma. Then, this rock was slowly uplifted with heating and partial melting until it achieved UHT conditions. Finally, it cooled to the solidus at ~1830 Ma. Thus, we propose that the UHT metamorphic conditions of a corundum‐bearing pelitic granulite from the Diebusige complex of the Alxa Block may be the result of long‐term slow uplift with heating under a high geothermal gradient.

Paleoproterozoic tectonic evolution of the Khondalite Belt in the North China Craton: Constraints from the geochronology and geochemistry of 1.9–2.3 Ga felsic and basic intrusive rocks in the Jining area

Although the Paleoproterozoic Khondalite Belt is one of the most important delineation boundaries in the North China Craton, its tectonic evolution remains controversial. Here, we present new geochronological and geochemical data for Paleoproterozoic granodiorite gneiss, amphibolite, and gabbro and monzogranite dykes in the Jining area in order to constrain the tectonic evolution of the Khondalite Belt. Zircon U–Pb dating indicates that the granodiorite gneiss, amphibolite and monzogranite were emplaced at ca 2.3 Ga, 2.0 Ga and 1.9 Ga, respectively. The 2.3 Ga granodiorite gneisses have positive εNd(t) values (+0.6 to +1.3) and high zircon saturation temperatures (864–873 °C), and show geochemical characteristics of A2-type granites, probably indicating extension background related to subduction. The 2.0 Ga amphibolites have high Nb contents and their protoliths display geochemical features of Nb-enriched basalts. The low MgO, Cr, Ni, LREE-enriched patterns, and negative εNd(t) values (−5.5 to −6.3) with relatively old Nd model ages suggest that the protoliths were derived from a fertile mantle source metasomatized by slab-derived melts. The distinct geochemical characteristics suggest that the formation of the amphibolites were attributed to the upwelling asthenosphere triggered by the opening of slab window. Based on the U-Pb ages of zircons and the contact relationship in the outcrops, the intrusive age of the gabbros was constrained to be 2.0–1.9 Ga. These gabbro dykes have high Mg#, Cr, and Ni contents, and show E-MORB-like REE patterns with high contents of large ion lithophile elements and negative Nb-Ta anomalies, indicating a subducting tectonic setting. Their high Ba/Th and Rb/Y ratios, low Th/Ta and Nb/Y ratios imply a mantle source metasomatized by slab-derived fluids. The 1.9 Ga monzogranite dykes have high Sr and Sr/Y ratios, low Yb and HREE, similar to those of typical adakitic rocks. Their low MgO, Cr, Ni, Mg# and negative εNd(t) suggest that the dykes were generated by partial melting of thickened lower continental crust. These different rocks, therefore, indicate a convergent margin occurred along the Khondalite Belt before the collision between the Yinshan Block and the Ordos Block, followed by extension event at ca. 2.3 Ga and closed with a collision at ca. 2.0–1.9 Ga, and then changed to post-collisional tectonic setting with the adakitic monzogranite dykes formed at ca. 1.9 Ga.

Middle Paleoproterozoic tectonic setting of Khondalite Belt: Evidence from ~2.2Ga charnockite in Zhuozi

麻粒岩-紫苏花岗岩杂岩在华北克拉通孔兹岩带内分布较广但研究程度较低，本文对孔兹岩带东部卓资地区大什字紫苏碱长花岗岩进行了详细的岩相学、地球化学和地质年代学研究，探讨了其形成时代、岩石成因及构造背景，为孔兹岩带构造演化及孔兹岩系沉积环境提供约束。SHRIMP锆石U-Pb测年结果表明大什字紫苏碱长花岗岩形成于古元古代中期（~2.2Ga），并经历了古元古代晚期构造热事件及~1.89Ga变质作用叠加改造。岩石具有铁质、钙碱性至碱钙性、准铝质至弱过铝质特征，具有较高SiO₂、Na₂O+K₂O、Ga、Zr含量及FeO^T/（FeO^T+MgO）值，低Al₂O₃、CaO、MgO、Sr、Cr含量及较高的全岩锆石饱和温度（835~887℃，平均860℃），与A型花岗岩指标相近。样品呈现平坦的右倾型稀土元素配分模式和弱的负Eu异常，富集K、Rb、Ba、Zr、Hf，亏损Sr、Nb、Ta、P、Ti。综合研究表明大什字紫苏碱长花岗岩是在弧后伸展背景下幔源岩浆上涌导致英云闪长质、花岗闪长质地壳岩石部分熔融形成，熔体可能经历了斜长石、含钛矿物相及磷灰石分离结晶作用。孔兹岩带东部在古元古代中期（~2.2Ga）可能处于弧后伸展背景，孔兹岩带是否存在古元古代中期陆内裂解事件有待进一步研究。;The granulites-charnockites complex is widely distributed in the Khondalite Belt, North China Craton. Despite its significance, relatively little attention is paid to its further research. This paper makes a detailed study on the petrography, geochemistry, and geochronology of the Dashizi charnockite in Zhuozi of eastern Khondalite Belt, and reveals its formation age, petrogenesis, and tectonic setting, which provides constraints for the tectonic evolution of the Khondalite Belt and sedimentary environment of the khondalite series. SHRIMP zircon U-Pb dating shows that Dashizi charnockite formed in middle Paleoproterozoic (~2.2Ga), and was subjected to late Paleoproterozoic tectono-thermal events and~1.89Ga metamorphism. The samples are ferroan, calc-alkalic to alkali-calcic, and metaluminous to slightly peraluminous, they exhibit high SiO₂, Na₂O+K₂O, Ga, Zr contents and FeO^T/(FeO^T+MgO) value, low Al₂O₃, CaO, MgO, Sr, Cr contents, and relatively high whole-rock zircon saturation temperature (835~887℃, average 860℃), which is similar to A-type granites. They show flat right dipping REE patterns and slightly negative Eu anomalies, enriching K, Rb, Ba, Zr and Hf, depleting Sr, Nb, Ta, P, and Ti. The Dashizi charnockite was formed by partial melting of tonalitic and granodioritic crustal rocks triggered by upwelling of mantle-derived magma under the back-arc extension setting, and the magma may experience fractional crystallization of plagioclase, Ti-bearing mineral and apatite. The eastern segment of the Khondalite Belt may be in a back-arc extensional tectonic setting in the middle Paleoproterozoic (~2.2Ga), whether there was a middle Paleoproterozoic intracontinental rift event in the Khondalite Belt remains to be further studied.

Paleoproterozoic A1- and A2-type coexisting monzogranites in the Daqingshan Complex, Khondalite Belt, North China Craton and its tectonic implications

Paleoproterozoic granitoids, widely exposed in the Daqingshan Complex in the Khondalite Belt of North China Craton (NCC), are of great significance for understanding the magmatic evolution and tectonic setting of the blet. Zircon LA-ICP-MS U-Pb dating results of four monzogranite samples are 2385 ± 18 Ma, 2358 ± 24 Ma, 2437 ± 32 Ma, and 2338 ± 24 Ma. Zircon Lu-Hf isotopic analysis shows that the monzogranites have positive εHf(t) values of +0.5 to +4.5, with two-stage Hf model ages (TDMC) range from 2859 to 2617 Ma, indicating that these rocks were mainly produced from ancient crust through the process of assimilation-fractional crystallization. The Daqingshan monzogranites are high-K calc-alkaline to shoshonite series, metaluminous to peraluminous series, enriched in large-ion lithophile elements (LILEs, such as Rb, Ba, La, and Ce) and depleted in high field strength elements (HFSEs) such as Nb, Ta, and Ti. They have low Sr/Y (3.48–35.72) and (La/Yb)N (4.79–46.50) ratio and weakly Eu negative anomalies (δEu = 0.14–1.23), indicating that they were formed in the continental magmatic arc environment. In addition, the monzogranites have high alkaline (Na2O + K2O) and SiO2 components, and high Ga/Al and HFSE values, showing the coexistence of A1- and A2-type granitoids. Combined with previous studies, our new results provide that the Khondalite Belt underwent magmatic events from 2.44 to 2.34 Ga during a long-lived arc-continental accretion process along the southern margin of the Yinshan Block. However, the Daqingshan monzogranites do not preserve records of Paleoproterozoic collisional event at 1.95–1.85 Ga in the Khondalite Belt, indicating that they did not experience subduction-related metamorphism and subsequent collision. Thus, the Daqingshan monzogranites may represent the post-collisional to late orogenic granitoids during the transition from compressive to rift tectonics following collision between the Yinshan and Ordos blocks.

Mesoproterozoic (∼1.3 Ga) S–type granites in Shangdu area, Inner Mongolia of the North China Craton (NCC): Implications for breakup of the NCC from the Columbia supercontinent

Mesoproterozoic (∼1.3 Ga) magmatism in the North China Craton (NCC) was characterized by diabase sills, while contemporary granitic magmatism was relatively rare, limiting our understanding of the NCC’s evolution during this period. In this manuscript, we report newly identified ∼1.3 Ga S–type granitic plutons in the Shangdu area, the western part of the northern NCC. Based on the results of geochemical, geochronological and zircon in–situ Lu–Hf isotope analyses, we discussed the petrogenesis, tectonic setting of the granitic plutons and the regime that drove the break–up of the NCC from the Columbia supercontinent. The zircon laser ablation inductively coupled plasma mass spectrometry (LA–ICP–MS) U–Pb dating results indicate that these granites were emplaced at some time between 1315 ± 21 Ma and 1307 ± 32 Ma. Moreover, the geochemical results show that they have high contents of SiO2 (75.34–76.97 wt%), Al2O3 (12.90–13.61 wt%) and Na2O + K2O (6.21–8.31 wt%), but low MgO (0.09–0.25 wt%) and Mg# (14–34). The A/CNK ratios varied between 1.10 and 1.28, indicating that the granites belong to the peraluminous series. Furthermore, the existence of Al–rich minerals (e.g., muscovite and garnet) suggests that they are the S–type granites. The ∼1.3 Ga zircon display negative to slightly positive εHf(t) values (−9.28–3.1) and old two–stage model ages (TDM2) (3.3–2.1 Ga). The ages of the inherited zircon and Lu–Hf isotope compositions of the ∼1.3 Ga zircon in the granite are consistent with those of the detrital zircon from Jining complex, the eastern part of the Khondalite Belt. Based on these facts, we infer that the granites in this study derived from the partial melting of the Jining complex. The coeval mafic dykes (in the Yanliao large igneous province) and the Shangdu granite in the north margin of the NCC strongly suggest an extensional setting, which was related to the break–up of the NCC from the Columbia supercontinent. A mantle plume was likely the dominant driver of the break–up and it should have provided heat for the partial melting of Jining complex.

Episodic metamorphism and anatexis within the Khondakite Belt, North China Craton: Constraint from Late-Paleoproterozoic fluid-fluxed melting of the Daqingshan Complex

The metamorphism and anatexis of the Khondalite Belt may provide key information for the Late-Paleoproterozoic collisional orogeny of the North China Craton (NCC). Migmatites formed by anatexis are widely developed in the Daqingshan Complex, central Khondakite Belt. However, the timing and anatectic regime of these migmatites have not been constrained. In this paper, we present systematic petrographic, whole-rock geochemical, Sr-Nd isotopic, zircon U-Pb and Hf isotopic investigation of the Baibuziwan stromatic migmatite and different types of leucosome in the northwestern Daqingshan Complex. The results show that: (1) the metamorphic rocks in Baibuziwan underwent in-situ to in-source partial melting, and the anatectic melts migrated and gathered in different degrees; (2) the ∼2.37 Ga Bt-Hbl-Pl gneiss in the Daqingshan Complex is possible protolith of the Baibuziwan migmatites; (3) the Baibuziwan migmatites have experienced three stages of metamorphism and anatexis in the Late-Paleoproterozoic, i.e., ∼1.95 Ga, ∼1.90 Ga, ∼1.85 Ga; (4) the anatectic regime of the Baibuziwan migmatites is fluid-fluxed melting, which has been proposed for the first time in Daqingshan Complex. Combined with previous studies, we suggest that following the collisional orogeny, the thinned lithosphere of the Khondalite Belt may have experienced asthenospheric upwelling. The lower crust of the Daqingshan complex was heated and dehydrated repeatedly, and the generated fluid poured into the overlying crust, which eventually led to the episodic metamorphism and fluid-fluxed melting in the Baibuziwan area.

Paleoproterozoic tectonic evolution from subduction to collision of the Khondalite Belt in North China: Evidence from multiple magmatism in the Qianlishan Complex

This study presents detailed petrology, major and trace element chemistry, Sr-Nd isotope, and in-situ zircon U-Pb dating and Hf-O isotopes on granites from the Qianlishan Complex of the Khondalite Belt in North China. Zircon SIMS U-Pb data indicate three episodes of Paleoproterozoic magmatism at ca. 2.06 Ga, 1.95 Ga and 1.92 Ga. Of those, the ca. 2.06 Ga hornblende monzogranites and fine-grained potassic granites display typical features of A-type granite, represented by metaluminous affinity, high FeOT/MgO ratios (3.29–5.63), and high Ga/Al and Zr + Nb + Ce + Y values with high zircon saturation temperatures (916–1000 °C). Moreover, they have positive zircon εHf values of +0.29 to +5.01 and homogenous δ18O values of 5.11–5.87 ‰, probably derived from the partial melting of calc-alkaline granitoids without addition of supracrustal rocks. The ca. 1.95 Ga garnet-bearing granites contain peraluminous minerals of garnet and muscovite and have high ASI index (>1.1) and δ18O values (7.14–9.18 ‰), indicating S-type granite. Their negative whole-rock εNd(t) values (−2.87 to −2.81) and zircon εHf(t) values (−4.06 to +1.29) suggest a source of ancient supracrustal rocks. The ca. 1.92 Ga coarse-grained potassic granites present metaluminous and magnesian signatures of I-type granite, including low A/CNK and FeOT/MgO ratios. Their negative εHf(t) values (−5.00 to −1.64) and homogenous δ18O values (5.20–6.00%) suggest that the original magma was derived primarily from enriched lower crust. The results, combined with regional geology and previous studies, establish a prolonged magmatic-metamorphic evolution of the Khondalite Belt from subduction to collision, involving ca. 2.3–2.0 Ga subduction-related arc magmatism, ca. 1.95 Ga syn-collisional high-pressure high-temperature crustal anatexis, and ca. 1.92 Ga post-collisional magmatism and synchronous ultrahigh temperature metamorphism.

Paleoproterozoic polyphase deformation in the Helanshan Complex: Structural and geochronological constraints on the tectonic evolution of the Khondalite Belt, North China Craton

The Khondalite Belt is widely regarded as a Paleoproterozoic collisional orogen between the Yinshan and Ordos Blocks in the Western Block of the North China Craton. However, the deformation history of the Khondalite Belt is poorly understood, and many aspects of the tectonic processes involved in the collision remain enigmatic. In this paper, we carried out detailed field-based structural analyses integrated with geochronological studies in the Helanshan Complex, one of the multiply deformed high-grade gneiss terrains in the Khondalite Belt. Three major phases of deformation (D1-D3) were identified in the Helanshan Complex. D1 mainly produced S(SW)-verging recumbent to overturned intrafolial isoclinal folds F1, originally sub-horizontal penetrative transposition foliations S1 and SSW-plunging mineral lineations L1. D1 deformational fabrics occurred coevally with the granulite-facies peak metamorphism. D2 dominantly generated steeply SE(E)-plunging asymmetrical upright open folds F2 that successively refolded the previous D1 structures. D3 gave rise to a series of NE- to E-trending ductile shear zones, featured by top-to-the-(N)NW oblique thrusting with a component of sinistral strike-slip movement. LA-ICP-MS U-Pb zircon dating results of seven deformation-related samples reveal that D1 occurred at some time from 1954 Ma to 1911 Ma, most likely at 1954–1949 Ma. D2 successively happened in the period of 1911–1870 Ma, and D3 had broadly taken place at ∼ 1870 Ma. The D1-D3 deformation sequences recorded tectonic processes including the initial top-to-the-SSW thrusting and crustal thickening, subsequently followed by exhumation of the khondalites in the Paleoproterozoic. Combined with previous studies, these new structural and geochronological data indicate that the Khondalite Belt underwent a long-term (>100 Myr) orogenic history and developed polyphase deformation, high-grade metamorphism as well as magmatism in response to the NNE-SSW-directed oblique collision between the Yinshan and Ordos Blocks at ∼ 1.95 Ga.