Sensitive High-Resolution Ion Microprobe (SHRIMP) U-Pb analyses of zircons from Paleoarchean (~3.4 Ga) tonalite-gneiss called the Older Metamorphic Tonalitic Gneiss (OMTG) from the Champua area of ...the Singhbhum Craton, India, reveal 4.24-4.03 Ga xenocrystic zircons, suggesting that the OMTG records the hitherto unknown oldest precursor of Hadean age reported in India. Hf isotopic analyses of the Hadean xenocrysts yield unradiogenic
Hf/
Hf
compositions (0.27995 ± 0.0009 to 0.28001 ± 0.0007; ɛHft = -2.5 to -5.2) indicating that an enriched reservoir existed during Hadean eon in the Singhbhum cratonic mantle. Time integrated ɛHft compositional array of the Hadean xenocrysts indicates a mafic protolith with
Lu/
Hf ratio of ∼0.019 that was reworked during ∼4.2-4.0 Ga. This also suggests that separation of such an enriched reservoir from chondritic mantle took place at 4.5 ± 0.19 Ga. However, more radiogenic yet subchondritic compositions of ∼3.67 Ga (average
Hf/
Hf
0.28024 ± 0.00007) and ~3.4 Ga zircons (average
Hf/
Hf
= 0.28053 ± 0.00003) from the same OMTG samples and two other Paleoarchean TTGs dated at ~3.4 Ga and ~3.3 Ga (average
Hf/
Hf
is 0.28057 ± 0.00008 and 0.28060 ± 0.00003), respectively, corroborate that the enriched Hadean reservoir subsequently underwent mixing with mantle-derived juvenile magma during the Eo-Paleoarchean.
Thirty-seven granitoids from Scotland have been dated using the sensitive high-resolution ion microprobe zircon method. Granitoids were intruded during: (1) crustal stretching at c. 600 Ma after ...Rodinia broke up (A-types); (2) the Grampian event of crustal thickening when the Midland Valley Arc terrane collided with Laurentia at c. 470 Ma (S-types); (3) erosion and decompression of the over-thickened Laurentian margin at c. 455 Ma (S-types); (4) subduction of Iapetus Ocean lithosphere under Laurentia starting at 430 Ma (I-types); (5) roll-back beginning at 420 Ma (I-types); (6) bilateral slab break-off and lithospheric delamination at 410 Ma (I- and S-type granites) when Baltica hard-docked against the Northern Highland terrane and Avalonia soft-docked against the Grampian Highland terrane. Far-field Acadian events at 390 Ma were recorded by I-type granites intruded along active sinistrally transpressive faults. I-types formed in lower crustal hot zones above subduction zones, whereas S-types formed in lower crustal hot zones above lithospheric windows through which hot asthenosphere had risen.
•Major lithologies of the Northern Liaoning Complex were formed at 2.57–2.50Ga.•The Northern Liaoning Complex experienced intensive metamorphism at ∼2.50Ga.•Major crustal growth of the Northern ...Liaoning Complex occurred at 2.9–2.7Ga.•The Northern Liaoning Complex underwent strong crustal reworking during 2.6–2.5Ga.
The Northern Liaoning Complex in northeastern China constitutes an important component of the Eastern Block in the North China Craton. The major lithologies consist of Archean granitoid gneisses with minor supracrustal rocks occurring as tectonic lenses. This study presents zircon Lu–Hf isotopic data for the first time as well as new SHRIMP zircon U–Pb data of the major lithologies from the Northern Liaoning Complex, in order to elucidate the crustal evolution of the complex and provide new constraints on the Neoarchean crustal evolution of the Eastern Block in the North China Craton. Magmatic zircon U–Pb data from this study show that the protolith magmas of the supracrustal rocks and granitoid gneisses were generated during ∼2.55–2.50Ga. Metamorphic zircons document consistent metamorphic ages at 2.49–2.48Ga, suggesting a regional metamorphic event immediately after the magmatism at the end of the Neoarchean in the Northern Liaoning Complex. Inherited/detrital zircons of 2.79–2.60Ga suggest possible existence of ancient crust in this region. Zircon Lu–Hf isotopic compositions show that the magmatic zircons have variable ɛHf(t) values from −4.0 to +9.0 with depleted mantle model ages of 3.6–2.5Ga, of which most ɛHf(t) values are positive with a model age peak at 2.9–2.7Ga. These zircon Hf signatures reveal major juvenile crustal growth with additions of older crustal materials during 2.9–2.7Ga, and a crustal reworking event with minor juvenile additions at 2.6–2.5Ga in the studied area. Integrated with previous data from other Neoarchean complexes in the Eastern Block, both the major juvenile crustal growth during 2.9–2.7Ga and the strong crustal reworking at 2.6–2.5Ga contribute to the extensive Neoarchean crust formation of the Eastern Block in the North China Craton. The North China Craton share similar Neoarchean continental crustal evolution to other cratons in the world, though it is distinctively featured by intensive tectonothermal overprinting at the end of the Neoarchean.
► In eastern Hebei the North China Craton is dominated by Neoarchean igneous rocks. ► In the west are 2550–2530
Ma tonalites, quartz diorites and mafic rocks ► In the east are 2530–2510
Ma granites ...with 2550–2530
Ma inclusions. ► They formed in a complex arc with distinct pulses of plutonism. ► ∼2500
Ma granulite facies metamorphism marked extension in this arc.
The eastern part of the North China Craton in eastern Hebei Province contains metamorphosed and deformed Neoarchaean to earliest Palaeoproterozoic rocks (∼2550–2490
Ma) with some older Archaean rocks. Numerous precise U–Pb zircon ages, structural observations, Nd and Hf isotopic data and whole rock geochemistry (our new data with reassessment and integration of previous work) show that there is not a single protracted event at the end of the Archaean lasting ∼60 million years, but that from east to west there are several separate events with their own unique character.
The eastern coastal region is dominated by weakly deformed 2530–2510
Ma granites with subordinate granodiorites, diorites and magnesian-gabbros. This suite has inclusions of older 2550–2540
Ma plutonic rocks. ∼80
km inland to the west, there are amphibolite facies biotite-rich schists, lenses of BIF, siliceous fuchsite bearing rocks with 3880–3540
Ma zircons, peridotites and orthogneisses, all intruded by younger granites and monzonites. Three amphibolite–granulite facies gneisses and schists with volcano-sedimentary protoliths have 2548–2534
Ma igneous zircon populations, rare inheritance back to >3600
Ma and 2506
±
6
Ma zircon equated with granulite facies metamorphism. Older tonalitic to granitic polyphase orthogneisses contain 3287
±
11
Ma to ∼2940
Ma igneous components. Late kinematic high Fe/Mg gabbros, monzonites and granites have ages of 2499
±
7 to 2491
±
13
Ma. 160–100
km inland, gneissose 2550–2530
Ma quartz-diorite to tonalitic rocks occur as intrusions into, or intercalations with, mafic rocks. These were affected by granulite facies metamorphism but then widely retrogressed. Abundant syn-granulite facies neosome and later shear zones disrupt the early geological relationships. The granulite facies metamorphism is dated at 2503
±
5
Ma from several samples, including a syn-granulite facies pegmatite.
The Neoarchaean igneous rocks show marked negative Nb, Ti anomalies, LIL enrichment and enrichment of the light REE relative to the heavy REE across the entire ultramafic, basaltic, tonalitic and granitic compositional spectrum: 2550–2530
Ma tonalites and quartz diorites are most important in the west and 2530–2510
Ma granites are most important in the east. Their composition resembles those formed at various stages of magmatic arc evolution at a convergent plate boundary, rather than being plume products. The eastern Hebei rocks thus formed in a complex arc with distinct pulses of plutonism at 2550–2540 and 2530–2510
Ma, with local incorporation of older continental crust. The 2500–2490
Ma thermal event with its associated higher Fe/Mg magmas involved interaction of underplated fractionated gabbroic melt with deep crustal melts, possibly during extension of an already ∼50 million years old arc.
We report SHRIMP U‐Pb, rare earth element, Hf isotope, and laser Raman spectroscopic data on zircons from ultrahigh‐temperature (UHT) granulites from the Jining Complex of the Khondalite Belt in the ...Western Block of the North China Craton (NCC). These UHT rocks form part of an ultrahot orogen that formed along the collisional margin of the NCC associated with the tectonics of assembly of the Paleoproterozoic supercontinent Columbia. Despite the core‐rim textures displayed by some of the UHT zircons, their age values sharply converge within error, yielding weighted mean207Pb/206Pb ages of ca. 1.92 Ga, indicating growth by recrystallization under extreme thermal conditions. In general, the zircons show moderate heavy rare earth element enrichment with sharp positive Ce and negative Eu anomalies. The Hf isotope data from the UHT zircons also display a fairly uniform character, with the majority of them characterized by positive εHfvalues, without any indication of mixing between reworked crust and juvenile material. The majority of mineral inclusions in the UHT zircons, as revealed by laser Raman study, also support a magmatic source. Our results confirm extreme crustal metamorphism in the NCC and suggest asthenospheric upwelling, magmatic underplating, and plume activity in response to the collision‐extension events during the final assembly of the Paleoproterozoic supercontinent Columbia.
Celotno besedilo
Dostopno za:
BFBNIB, DOBA, IZUM, KILJ, NMLJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
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► Late Neoarchean syenogranites are widely distributed in the North China Craton. ► Two phases (2.53–2.52Ga and 2.52–2.50Ga) of syenogranite magmatism are recognized. ► There are ...three types of syenogranites in terms of element and isotope compositions. ► They mark a tectono-magmatic event resulting in stabilization of the craton.
At the end of the Neoarchean continental evolution, voluminous syenogranites were emplaced in the North China Craton, together with other magmatic rocks (trondhjemite–tonalite–granodiorite (TTG), monzogranite, diorite, gabbro). Syenogranites are widely distributed in Anshan-Benxi, Qinhuangdao and western Shandong, and also occur in southern Jilin, northern Liaoning, northwestern Hebei and central Henan. Based on geological relationships, degree of metamorphism, deformation and magmatic zircon ages, two phases of syenogranite magmatism are recognized. Rocks produced during the first phase show a gneissic texture and were formed between 2.53 and 2.52Ga and locally comprise abundant TTG. Rocks of the second phase cut late Neoarchean TTG and supracrustal rocks, display a massive structure, and mainly formed between 2.52 and 2.50Ga. All syenogranites share the same features in major element compositions, being high in SiO2 and low in CaO, total FeO, MgO, TiO2 and P2O5. However, they are different in trace and REE compositions and can be subdivided into three types. (1) Type 1 shows a large variation in total REE contents, low (La/Yb)n ratios, strong negative Eu*/Eu anomalies and Ba depletion; (2) Type 2 is similar to Type 1 but has higher (La/Yb)n ratios. (3) Type 3 shows a large variation in total REE and (La/Yb)n ratios and significantly do not show strongly negative Eu*/Eu anomalies and Ba depletion. Whole-rock Sm–Nd isotopic compositions show large variations in ɛNd(t) values and tDM(Nd) modal ages, ranging from −9.49 to −4.72 and 3.70 to 3.25Ga (Type 1), 0.55–1.03 and 2.77–2.71Ga (Type 2) and −2.35 to 1.23 and 2.93–2.66Ga (Type 3), respectively. Hf isotopic compositions of zircons from three samples have ɛHf(t) values and tDM1(Hf) ages of 0.7–7.2 and 2.84–2.56Ga (Type 1), 2.6–7.4 and 2.74–2.56Ga (Type 2) and 2.1–6.3 and 2.76–2.60Ga (Type 3). It is concluded that syenogranites were generated by melting of continental crust with different mean crustal residence ages, and most of them were emplaced during the second phase (2.52–2.50Ga) in an extensional tectonic regime. The formation of these voluminous syenogranites marks a tectono-magmatic event resulting in stabilization of the North China Craton at the end of the Neoarchean.
•∼2.7 Ga rocks have been identified in eight areas of the North China Craton.•They are mainly tonalitic in composition and frequently underwent late alteration.•Their formation was a result of ...juvenile additions to the continental crust.•The North China Craton is similar in main period of crustal growth to other cratons.
The North China Craton (NCC) is characterized by major ∼2.5 Ga tectono-thermal events and is thus different from many other cratons worldwide where ∼2.7 Ga events are well developed. However, whole-rock Nd and Hf-in-zircon isotopic compositions of ∼2.5 Ga crustally derived granitoids reveal that they mainly formed through reworking of late Mesoarchean to early Neoarchean continental material. We review the spatial distribution, rock types, geochemical and Nd–Hf isotopic compositions of ∼2.7 Ga granitiods that are widely identified in the NCC, including eastern Shandong, western Shandong, Huoqiu, Hengshan, Fuping, Zanhuang, Zhongtiao and Wuchuan. These granitoids are mainly tonalitic in composition and frequently underwent strong metamorphism, deformation and anatexis. They show large variations in SiO2, total FeO, MgO and CaO, and can be subdivided into two types in terms of their REE patterns. More importantly, whole-rock Nd and Hf-in-zircon isotopic compositions indicate that the strong ∼2.7 Ga tectono-thermal event mainly involved juvenile additions to the continental crust. The early Neoarchean was the most important period for rapid production of new continental crust in the NCC. The main difference of the NCC from many other cratons worldwide is a strong and widespread superimposed tectono-thermal event at ∼2.5 Ga that stabilized the cratonic assemblage.
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•A new complex, named as the Hujiamiao Complex, was discovered in the Anshan area, NCC.•Trondhjemitic rocks of different ages from 3.79 to 3.11 Ga have been identified.•It is the ...first time in Anshan to identify trondhjemitic rocks with relatively high (La/Yb)n ratios.•Magmatic zircons have εHf(t) of −12.3 to 1.6, tDM(Hf) and tCC(Hf) ages of 4.1 to 3.6 Ga and 4.3 to 3.7 Ga.•All the Anshan 3.8–3.3 Ga complexes are the relics of the same larger complex in the area.
Anshan is located in the northeastern North China Craton and has a long-term geological history back to 3.8 Ga. Four complexes with ages of 3.8–3.1 Ga have been identified previously, namely the Baijiafen, Dongshan, Shengousi and Guodishan complexes. Being similar to the neighbouring Beijiafen Complex, the newly-discovered Hujiamiao Complex extends in a northwest-southeast direction and shows tectonic contacts on one side with the Chengtaigou granite and on the other with the Chengtaigou supracrustal rocks. In the Hujiamiao Complex, trondhjemitic rocks of 3789 Ma, 3786 Ma, 3698 Ma, 3617 Ma, 3566 Ma, 3504 Ma and 3106 Ma have been identified. More work is required to establish if a gabbro also has a formation age of 3.8 Ga. The trondhjemitic rocks show similar compositional features in being high in SiO2 (72.37–76.71 %) and Na2O (5.00–6.47 %) and low in K2O (0.60–1.95 %), ∑REE contents (32.83–91.83 ppm) and (La/Yb)n ratios (11.09–48.64). They have whole-rock εNd(t) values of 0.35–4.43, tDM(Nd) of 3.74–3.46 Ga and tCC(Nd) ages of 3.74–3.43 Ga, and in situ magmatic zircon εHf(t) values of −12.3 to 1.56, tDM(Hf) ages of 4.2 to 3.5 Ga and tCC(Hf) ages of 4.6 to 3.7 Ga. Combined with previous work, it is concluded that all the Anshan area 3.8–3.3 Ga complexes are the relics of a larger complex which was once more widely distributed in the Anshan area. The trondhjemitic rather than tonalitic character of the Anshan Eoarchean rocks shows diversity in the formation and evolution of the earliest continental crust with a range of T/P for crustal anatexis.
The Jiaodong Terrane in eastern Shandong Province is an important part of the Eastern Block of the North China Craton (NCC). In order to better understand the Precambrian crustal evolution of the ...NCC, we conducted a study of zircon geochronology, bulk-rock elemental and Nd-isotope geochemistry on gneisses and granodiorites from the Jiaodong Terrane. Zircon U-Pb SHRIMP analyses on biotite leptites and TTG gneisses yielded two groups of ages, one at Ca. 2.90 Ga, and the other at 2.71 to 2.73 Ga. The new age results establish the existence of Meso. archean and Neoarchean continental crust in the Jiaodong Terrane. The association of leptites, interpreted as metadacitic rocks, and TTG gneisses at 2.9 Ga was likely generated in an island-arc system, hence implying that plate tectonics, similar to the modern regime, was operative during the Mesoarchean. On the other hand, the results also indicate that the period of 2.71 to 2.73 Ga represents the most significant crust-fonning episode in the Jiaodong Terrane. This is in contrast to the general understanding that the most important period of crustal growth and related metamorphism/deformation in the NCC took place in the terminal Archean (∼2.5 Ga). The geochemical and age constraints of the Neoarchean TTG rocks suggest that their formation was not related to subduction of oceanic crust, but to underplating and subsequent partial melting of lower crustal mafic rocks. Nd isotope data indicate that the Mesoarchean and Neoarchean rocks were mainly derived from juvenile sources with a limited amount of old crustal component. Like in other parts of the NCC, these rocks represent a juvenile addition to the late Archean continental crust. Finally, the formation of supracrustal rocks and most TTG gneisses in the period of 2.9 to 2.7 Ga distinguishes the Jiaodong Terrane from other tectonic units of the North China Craton. PUBLICATION ABSTRACT
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