Paleoproterozoic Orogenic Belt Research Articles

Paleoproterozoic ultrahigh‐temperature mafic granulites with a high‐pressure prograde path from the Alxa Block: Implications on the tectonic evolution of the Khondalite Belt, North China Craton

AbstractUltrahigh‐temperature (UHT) granulites, a prominent feature of Paleoproterozoic orogenic belts, preserve a record of geodynamic processes during the Precambrian (Archean–Paleoproterozoic). Quantitative pressure–temperature–time (P–T–t) paths of these UHT granulites can constrain the tectonic processes and metamorphic evolution in such a tectonic regime. Here, UHT mafic granulites with a high‐pressure (HP) prograde path are first reported in the Diebusige Complex in the Alxa Block, western part of the Khondalite Belt (KB), North China Craton (NCC). The detailed petrographic studies show that two mafic granulite samples preserve corona textures around relict garnet or garnet pseudomorphs (completely replaced by plagioclase), and a third mafic granulite sample has a relatively simple mineralogy with a granoblastic‐polygonal texture. These mafic granulites have similar peak (Tmax) assemblages of clinopyroxene + orthopyroxene + plagioclase + ilmenite ± garnet ± amphibole ± quartz + melt. Phase equilibrium modelling and Ti‐in‐amphibole and rare earth element (REE)‐based thermometries all constrain similar peak conditions of ~880–950°C/~8.5–10 kbar implying an ~100°C/kbar apparent geothermal gradient for these mafic granulites. Based on the corona textures or pseudomorphs of garnet and mineral assemblages, we identified a Pmax (~14 kbar) prograde stage before the Tmax stage. Thus, a clockwise P–T path with heating and decompression followed by near‐isobaric cooling (IBC) is recorded from these UHT mafic granulites. In addition, zircon and apatite SHRIMP or LA–ICP–MS U–Pb dating yields an age interval of ~1.81–1.7 Ga, which is interpreted as representing the cooling time from ~900–800°C to ~575°C at the middle‐upper crustal levels (<25 km deep) for these mafic granulites, with an ~1.5–2.5°C/Myr cooling rate. The new P–T–t path of these rocks includes high‐pressure prograde, UHT peak, and slow cooling retrograde processes, which implicates a post‐collisional tectonic setting for UHT metamorphism in the KB and the processes of collision, exhumation, and cooling of the KB.

Genetic mechanism of meta-igneous rocks in the Co-bearing Li'eryu Formation, Liaohe Group: Constraints on the tectonic evolution of the Jiao-Liao-Ji Paleoproterozoic orogenic belt

Genetic mechanism of meta-igneous rocks in the Co-bearing Li'eryu Formation, Liaohe Group: Constraints on the tectonic evolution of the Jiao-Liao-Ji Paleoproterozoic orogenic belt

Progress of mineralization of key metal and non-metal in the Paleoproterozoic orogenic belts from the North China Craton

Progress of mineralization of key metal and non-metal in the Paleoproterozoic orogenic belts from the North China Craton

The petrogenesis of the Xiaonvzhai metamorphic gabbro-diorite in the Liaoji Paleoproterozoic orogenic belt and its constraints on Co-Ni enrichment

The petrogenesis of the Xiaonvzhai metamorphic gabbro-diorite in the Liaoji Paleoproterozoic orogenic belt and its constraints on Co-Ni enrichment

The processes of ultra-enrichment and mineralization of the Ni-Co in the Shansonggang Co-Ni-Cu deposit from the Liao-Ji Paleoproterozoic orogenic belt

The processes of ultra-enrichment and mineralization of the Ni-Co in the Shansonggang Co-Ni-Cu deposit from the Liao-Ji Paleoproterozoic orogenic belt

Metamorphic evolution of high-pressure and ultrahigh-temperature granulites from the Alxa Block, North China Craton: Implications for the collision and exhumation of Paleoproterozoic orogenic belts

High-pressure (HP) and ultrahigh-temperature (UHT) granulites with a high geothermal gradient (greater than 500 °C/GPa) are prominent features of Paleoproterozoic orogenic belts and may represent paired metamorphic belts present during the early stages of plate tectonics. Understanding their pressure−temperature−time (P-T-t) paths and metamorphic evolutionary relationships could provide valuable constraints on the tectonic processes of Paleoproterozoic orogenic belts. Here, we describe garnet mafic and clinopyroxene-orthopyroxene (Cpx-Opx) granulites from the Diebusige area of the Alxa Block in the western part of the Khondalite Belt, North China Craton. Through detailed petrographic, phase equilibrium modeling, and Ti-in-amphibole thermometric studies, we obtained the preserved peak mineral assemblages of two types of mafic granulites: garnet + clinopyroxene + amphibole + plagioclase + quartz + ilmenite, and clinopyroxene + orthopyroxene + plagioclase + amphibole + garnet (rare) + ilmenite. The preserved peak P-T conditions were determined to be 850−890 °C/11.4−13.2 kbar (HP granulite-facies) and 950−970 °C/8.2−9.2 kbar (UHT conditions), with thermal gradients of ∼70 °C/kbar (moderate differential temperature/differential pressure, dT/dP) and ∼110 °C/kbar (high dT/dP), respectively. Using sensitive high-resolution ion microprobe U-Pb dating and rare earth element analysis of zircons, we found that the garnet mafic granulite recorded an HP granulite-facies metamorphic age of ca. 1.95 Ga and a retrograde cooling age of ca. 1.8 Ga, while the Cpx-Opx granulite recorded a consistent retrograde cooling age of ca. 1.8 Ga. By combining these results with the metamorphic evolution and timing (ca. 1.92−1.91 Ga) of UHT rocks from the Khondalite Belt, we suggest that the garnet (HP) mafic and Cpx-Opx (UHT) granulites may represent different stages of the same metamorphic event, shedding light on the processes involved in the collision and subsequent exhumation of Paleoproterozoic orogenic belts.

Tectonic Evolution of the JLJB, North China Craton, Revisited: Constraints from Metamorphism, Geochemistry and Geochronology of the Ji’an Group and Related Granites

The Jiao-Liao-Ji Belt (JLJB) is the most representative Paleoproterozoic orogenic belt in the North China Craton (NCC). The sedimentation, metamorphism and magmatism of the Ji’an Group and associated granites provide significant insights into the tectonic evolution of the JLJB. In this study, we have synthesized published geochemistry and geochronology data on metasedimentary, metavolcanic and igneous rocks. According to the available data, the protoliths of the metasedimentary rocks are sets of shale, wacke, arkose, quartz sandstone and carbonate, while the protoliths of the metavolcanic rocks are calc-alkaline basalt, basaltic andesite, andesite, dacite and rhyolite. The rock assemblages indicate a transformation of the tectonic environment from a passive margin to an active continental margin following the onset of plate convergence and subduction. The A2-type gneissic granite (Qianzhuogou pluton) is formed in a subsequent back-arc basin extension setting at 2.20–2.14 Ga. The Ji’an Group was finally deposited in an active continental margin during the closure of a back-arc basin at 2.14–2.0 Ga. Then, the sediments were involved in a continent–arc–continent collision between the Longgang and Nangrim blocks at ~1.95 Ga. This process was accompanied by HP granulite-facies metamorphism at ~1.90 Ga. The subsequent exhumation and regional extension resulted in decompression melting during 1.90–1.86 Ga, producing metamorphism with an isothermal decompression clockwise P–T path. The resulting metapelites are characterized by perthite + sillimanite, and mafic granulites are characterized by orthopyroxene + clinopyroxene. The S-type porphyritic granite (Shuangcha pluton) is formed during the crustal anatexis. Meanwhile, extensive anatexis produced significant heating and triggered prograde to peak metamorphism with an anticlockwise P–T path. Cordierite-bearing symplectites around the garnet in the metapelites indicate a superposed isobaric cooling metamorphism. The ages of monazites and anatectic zircons suggest that the post-exhumation cooling occurred at 1.86–1.80 Ga. The Paleoproterozoic magmatism, sedimentation and metamorphism suggest a process of subduction back-arc basin extension and closure, collision and exhumation for the tectonic evolution of the JLJB.

Metamorphic P-T paths and zircon U-Pb ages of Paleoproterozoic metabasic dykes in the Jiapigou area, South Jilin Province: Implications for the tectonic evolution of the North China Craton

The distribution and tectonic evolution of the Paleoproterozoic orogenic belts in the North China Craton (NCC) remain controversial. Especially, the extent of the Paleoproterozoic magmatic and metamorphic influences on the Archean Longgang Block needs further demonstration. This paper presents detailed petrographic and mineralogical analyses, phase equilibria modeling and zircon dating for three metabasic dyke samples in the Jiapigou area, South Jilin Province, in order to discuss their metamorphic evolution and tectonic implications. Petrographic observation and phase modeling using THERMOCALC suggest that these metabasic dykes have experienced the metamorphism with clockwise P-T paths under low-amphibolite facies, high-amphibolite facies and high-pressure granulite facies. Their peak P-T conditions were constrained to be 0.6–0.9 GPa/580–650 °C (JN1929), ∼0.95 GPa/757 °C (JN1918) and ∼1.15 GPa / 820 °C (JN1932), according to the stability fields of mineral assemblage and isopleths of Ti content in amphibole, anorthite component (XAn) in plagioclase, pyrope content (XPy) and grossular content (XGrs) in garnet. The peak conditions correspond to apparent geothermal gradients of 19–22℃/km, being medium-pressure type. Zircon U-Pb dating shows that the metabasic dykes have a protolith crystallization age of 2199 ± 5 Ma (MSWD = 0.43), and a metamorphic age of 1855 ± 41 Ma (MSWD = 0.21). The protolith ages, metamorphic characteristics and ages of the metabasic dykes in South Jilin can be well compared with those for metabasic dykes in East Hebei and North Liaoning, indicating that the northern part of the Longgang Block was extensively affected by the mid Paleoproterozoic magmatism, and was involved in an orogen to be metamorphically reworked during the late Paleoproterozoic (1.82–1.85 Ga). In addition, this orogeny mainly occurred along the northern margin of the craton, which is different from the ∼1.95 Ga orogeny in the NCC.

Recognition of late Paleoproterozoic gold mineralization in the North China craton: Evidence from multi-mineral U-Pb geochronology and stable isotopes of the Shanggong deposit

Abstract The North China craton was stabilized in the late Paleoproterozoic but experienced significant removal of ancient lithospheric keel in the late Mesozoic that resulted in the formation of numerous world-class gold deposits with combined reserves of more than 7000 t of gold. However, it remains uncertain whether the North China craton contains older gold deposits formed during generation and final stabilization of the craton. Here, we show that the Shanggong gold deposit (105 t Au at 5.31 g/t) on the southern margin of the North China craton formed in the late Paleoproterozoic during the collision between the Eastern and Western blocks that led to formation of the Trans–North China orogen and final stabilization of the craton. The Shanggong deposit is hosted in amphibolite-facies rocks of the Neoarchean to early Paleoproterozoic Taihua Group and overlying volcanic rocks of the late Paleoproterozoic Xiong’er Group. Gold mineralization is structurally controlled by NE-striking faults and occurs in four segments: the Liuxiugou, Hugou, Shanggong, and Qiliping segments. The ores consist mainly of quartz-ankeritesulfide stockworks and sulfide disseminations in hydrothermally altered wall rocks. Gold is mostly contained in arsenian pyrite that is variably associated with minor sphalerite, galena, and chalcopyrite. Ore-related alteration assemblages comprise mainly quartz, ankerite, K-feldspar, sericite, and tourmaline. Both the stockworks and mineralized alteration assemblages contain hydrothermal accessory minerals, including monazite, apatite, and rutile. Paragenetic relations and textural data show that these accessory phases precipitated synchronously with gold-bearing sulfides. Laser ablation–inductively coupled plasma–mass spectrometry spot analyses of monazite and apatite from the Shanggong segment yielded reproducible U-Pb dates of 1747 ± 20 Ma (2σ, mean square of weighted deviates [MSWD] 0.46) and 1788 ± 200 Ma (2σ, MSWD = 11.3), respectively. These dates are indistinguishable within errors from an apatite U-Pb date of 1743 ± 79 Ma (2σ, MSWD = 1.6) at the Liuxiugou segment and a rutile U-Pb date of 1804 ± 52 Ma (2σ, MSWD = 0.77) at the Hugou segment. These new dates suggest that the Shanggong deposit formed at ca. 1.80–1.74 Ga, coeval with or immediately after formation of the Trans–North China orogen and final stabilization of the North China craton. Sulfides from the Shanggong gold deposit have δ34S values ranging from −18.5‰ to −6.9‰, whereas the coexisting ankerite has δ13CPDB of −6.81‰ to −1.61‰ and δ18OSMOW of 15.70‰–17.62‰. The stable isotope data are distinctively different from values of the Early Cretaceous gold deposits in the southern North China craton, indicating contrasting hydrothermal systems responsible for these two categories of gold deposits. The results presented here, combined with independent geologic evidence, allow Shanggong to be the first confirmed Paleoproterozoic orogenic gold deposit in the North China craton. Recognition of Paleoproterozoic orogenic gold mineralization provides significant new insights into the gold metallogeny of the well-endowed North China craton and has implications for future gold exploration along the three Paleoproterozoic orogenic belts in this craton.

Deformation characteristics of the high-grade metamorphic and anatectic rocks in the Daqingshan Paleoproterozoic orogenic belt, Inner Mongolia: A case study from the Shijiaqu-Xuehaigou area

The high-grade granulite-phase metamorphic and anatectic rocks are widespread in the Daqingshan area, which is an archetypical of the Early Paleoproterozoic Orogenic Belt (POB) in the North China Carton (NCC), providing an ideal object to delineate the rheology of partially molten lower crust. The multiple approaches of SEM-EBSD fabric analysis, electron probe microanalyses (EPMA) and LA-ICP-MS zircon U-Pb geochronology have been carried out on the metamorphic and anatectic rocks from the Shijiaqu-Xuehaigou area in the Daqingshan. The results of zircon U-Pb dating show that the anatexis process in the POB took place more or less prior to ca. 1920 Ma, subsequently, the main plastic deformation event occurred at ca. 1915–1870 Ma. The macro- and microscopic structures suggest that the Xuehaigou and Shijiaqu areas show the characteristics of the diatexite and metatexite zones, respectively. In the diatexite zone, appearance of abundant melts tends to form schollen and schlieren structures in the high-grade metamorphic and anatectic rocks. The deformation mechanism of plagioclase is mainly represented by diffusion creep and particle flow. In contrast, in the metatexite zone, the deformation pattern is represented by stromatic structure with light-colored bands paralleling to the main gneissosity, and the deformation mechanism of plagioclase is characterized by dislocation creep. Besides, the deformation mechanism of amphibole in the lower crustal rocks from both zones is mostly dominated by dislocation creep. Significantly, the presence of melts in the high-grade metamorphic and anatectic rocks probably weaken their strength, and may have aided to form the sub-horizontal channel, contributing significantly to the subsequent exhumation of the lower crustal rocks in the orogenic belt.

Late Paleoproterozoic orogenic evolution of the northern Tarim Craton, NW China: Insights from phase equilibrium modeling and zircon U-Pb geochronology of metapelitic granulite in the Kuluketage area

Global Paleoproterozoic orogenic evolution can provide important constraints on the Columbia (Nuna) supercontinent assembly. Zircon U-Pb chronology studies on the northern Tarim reveal that a paleoproterozoic tectono-thermal event was developed, which is related to the assembly of the Columbia supercontinent. However, limited metamorphic investigations have hindered the recognition of Paleoproterozoic orogenic evolution in the northern Tarim, further affecting the understanding of the relationship between Tarim Craton and the Columbia supercontinent. The Xingditage Group in northern Tarim is the result of Paleoproterozoic orogeny which can shed light on the Paleoproterozoic orogenic evolution of the northern Tarim Craton. Our study conducted petrography, zircon U-Pb geochronology, and phase equilibria modeling of metapelitic granulite collected from the Xingditage Group. Petrographic and phase equilibria modeling indicate a clockwise P-T path involving the peak metamorphic stage (M1) at ∼840 °C/7 kbar, the near-isothermal decompression stage (M2) at ∼840 °C/3 kbar and followed near-isobaric cooling stage (M3) at ∼785 °C/2.5 Kbar. The ages of metamorphic zircons in metapelitic granulite range continuously from 1831 ± 13 Ma to 1782 ± 16 Ma. Petrographic observation shows almost all zircons grow in quartz and biotite (Bi-2), indicating they were recrystallized during the isobaric cooling stage (M3) after decompression. Thus, the ca. 1.85–1.80 Ga metamorphic age in northern Tarim records a regional post-Tmax cooling event after exhumation rather than a collisional event of crustal thickening. We further propose a tectonic evolution scenario of the northern Tarim Paleoproterozoic orogenic belt and suggests the northern Tarim has collided with an unknown block (perhaps Sharyzhalgai uplift in southwestern Siberia Craton) and became a peripheral part of the Columbia supercontinent prior to ∼1.85 Ga.

Petrogenesis and tectonic significance of Paleoproterozoic metavolcanic rocks in the Khondalite Belt, North China Craton

As a typical continent–continent collision belt, the Khondalite Belt (KB) of the North China Craton (NCC) represents a Paleoproterozoic orogenic belt that underwent subduction and collision. Although many high-grade metamorphic rocks have been well studied, the low to medium grade metamorphic rocks well preserved in KB are less studied, which hinders a better understanding of the initiation of Paleoproterozoic subduction and collision processes. The Erdaowa Group is a representative of such a metamorphic rock series. Zircon U-Pb dating of the metavolcanic rocks in the Erdaowa Group yields the eruption ages of 2465 ± 24 Ma and 2350 ± 34 Ma, and the metamorphic ages of 1933 ± 32 Ma and 1844 ± 30 Ma. The geochemical results show that the metavolcanic rocks of the Erdaowa Group belong to tholeiitic basalts series. The enrichment of large ion lithophile elements (LILEs) such as Rb and Ba, and the depletion of high field strength elements (HFSEs) such as Ta, Nb and Ti indicate that the metavolcanic rocks have arc geochemical affinities and may have been formed at an active continental margin associated with subduction. Zircon Lu-Hf isotopic analysis shows that εHf(t) values are −0.15 – + 8.72, and the single-stage depleted mantle model age is 2448 – 2707 Ma, indicating that the primary magma originated from partial melting of the depleted lithospheric mantle and experienced slight crustal contamination. The results further prove that the low and medium grade rocks were directly involved in the subduction and collision between the Yinshan Block and the Ordos Block.

Multi-phase metamorphism in the northern margin of the North China Craton: Records from metapelite in the Hongqiyingzi Complex

It is controversial about the tempo–spatial distribution and tectonic attributes of the Paleoproterozoic orogenic belts in the North China Craton (NCC). The Hongqiyingzi Complex in the northern margin of the NCC, comprising orthogneiss, supracrustal sequence and an ophiolitic mélange, was investigated to have experienced multiple tectonic evolution from Paleoproterozoic to Mesozoic. However, the depositional age and metamorphic P–T path of the supracrustal sequence have not been well addressed. Garnet mica schists are investigated on the basis of petrography, mineral chemistry, phase equilibria modelling and zircon and monazite dating, which record an extreme case with four phases of metamorphism. The first-phase is characterized by high pressure (HP) granulite facies with the peak conditions of 10–11 kbar/>780 °C, which occurred at ~1.95 Ga. It is considered to correspond to a collisional orogeny with crust thickening widespread in the Paleoproterozoic orogenic belts of the NCC, followed by an exhumation with heating at ~1.92 Ga. The second-phase is marked by the overprinting of staurolite-bearing assemblages with the peak conditions of 6–7 kbar/610–630 °C, which occurred at ~1.85 Ga. It may correlate a separate orogeny occurred along the northern margin of the NCC, following a ~1.90 Ga oceanic subduction. Phase modelling suggests this overprinting over the first-phase HP granulites is mainly controlled by water infiltration. The third-phase andalusite-type and the fourth-phase greenschist facies metamorphism are confined to local equilibrium domains and their ages have not been well constrained. With a comparison of regional geology, the third-phase metamorphism is inferred to be related with the 320–290 Ma extension in the northern part of the NCC during Late Paleozoic, and the fourth-phase metamorphism is correlated with the 250–230 Ma collision occurred along the Solonker Suture Zone in the Central Asia Orogenic Belt during Early Mesozoic. Moreover, detrital magmatic zircons yield ages of 2.0–2.1 Ga, providing a definite upper limit on the deposition of the Hongqiyingzi supracrustal sequence.

Detrital zircon constraints on tectonic evolution of the Liaodong Paleoproterozoic orogenic belt, North China Craton

The Liaodong Paleoproterozoic orogenic belt (LPOB), as part of the eastern North China Craton (NCC), is the result of global collision during the amalgamation of the Columbia supercontinent. Tectonics of the LPOB thus becomes the key to the understanding of the tectonic evolution of the NCC, and may provide important information on the assembly of the supercontinent. Detailed geochronological and geochemical analysis on detrital zircons from the Liaohe group is conducted to unravel the tectonic attribute of the major constituent, i.e., the Liaohe group within the LPOB. The results show that the U-Pb ages of detrital zircons from the Langzishan, Li’eryu, Gaojiayu and Dashiqiao formations at the middle-lower parts of the Liaohe group are mainly characterized by peaks at ~ 2500 and 2200–2100 Ma. However, the ages of detrital zircons from the Gaixian formation at the upper part are peaked at 2100–2000 Ma. The age data indicate that the Archean basement rocks and Paleoproterozoic magmatic activities at 2200–2100 Ma variably provide sources for sediments of the middle-lower Liaohe group. However, sediments of the Gaxian formation at the upper part of the Liaohe group are mainly derived from magmatic activities from the Nangrim and North Gyeonggi blocks at 2100–2000 Ma . The source characteristics of the Liaohe group highlight the importance of back-arc extension in the evolution of the LPOB. The tectonic evolution of the LPOB is, therefore, subdivided into four stages, i.e. early back-arc extension stage (2200–2080 Ma), transitional stage (2080–1940 Ma), main orogenic deformation (1940–1840 Ma) and post-orogenic plutonic emplacement (after 1840 Ma).

Nature and Evolution of Pre‐Neoproterozoic Continental Crust in South China: A Review and Tectonic Implications

AbstractSouth China as an amalgamation of the Yangtze and Cathaysia blocks is composed of Archean to Mesoproterozoic basement overlain by Neoproterozoic and younger cover. Both the constituent Yangtze and Cathaysia blocks contain well‐preserved Neoproterozoic rocks that have been extensively studied in terms of the age and tectonic nature, but less is known about their earlier crustal history due to the incomplete rock record. Recent efforts in investigating the yet survived crustal nature based on isotopic and elemental signatures preserved in igneous and sedimentary rocks have steadily improved our knowledge about the pre‐Neoproterozoic continental crustal evolution in South China. In this paper, we summarize the up‐to‐date pre‐Neoproterozoic records, including petrological, geochronological, geochemical and geophysical data, across South China, and discuss its spatiotemporal patterns of the pre‐Neoproterozoic crust and the relevant tectonic events. While the xenocrystic/inherited and detrital zircon records suggest widespread Archean (mainly ca. 2.5 Ga) crustal components within both the Yangtze and Cathaysia blocks, exposed Archean rocks are only limited to isolated crustal provinces in the Yangtze Block. These Archean rocks are dominated by TTGs (tonalite‐trondhjemite‐granodiorite) with varied ages (3.3–2.5 Ga) and zircon Hf isotopes, indicating a compositionally heterogeneous nature of the Archean Yangtze Block and, by inference, the development of multiple ancient terranes. The early Paleoproterozoic (2.4–2.2 Ga) tectonomagmatic events characterize the western Yangtze Block and are supportive of an east‐west subdivision of the Yangtze basement, whereas the late Paleoproterozoic (2.1–1.7 Ga) orogeneses may have affected a larger area covering both the western and eastern parts of the Yangtze Block, and also the Cathaysia Block. The eastern Yangtze Block with generally northeastward‐younging late Paleoproterozoic magmatism and metamorphism likely experienced a prolonged 2.05–1.75 Ga orogenic process welding the various Archean proto‐continents, consistent with the documentation of a buried late Paleoproterozoic orogenic belt imaged by deep seismic profiling from its central part and of a slightly older ophiolitic mélange in the northern part. The Cathaysia Block was probably involved in a short‐lived 1.9–1.8 Ga orogenic event. The two orogeneses overlapped in time and may have contributed to the cratonization of a possible unified South China, and are referred to be linked with the assembly of the Nuna Supercontinent. The subsequent late Paleoproterozoic to early Mesoproterozoic rift successions and intrusions (1.7–1.5 Ga) in the southwestern Yangtze Block, and the ca. 1.43 Ga rifting in Hainan Island of the Cathaysia Block could be responses to the Nuna break‐up. Late Mesoproterozoic (1.2–1.0 Ga) magmatism of varied age and nature in different localities of the Yangtze Block is reflective of a complex tectonic process in the context of the assembly of the Rodinia Supercontinent. Similar‐aged metamorphism (1.3–1.0 Ga) is recorded in Hainan Island, reflecting the Grenvillian continental collision during the Rodinia assembly, but further studies are necessary to better constrain the late Mesoproterozoic tectonic framework of South China.

Juxtaposition of diverse, subduction-related tectonic blocks with contrasting metamorphic features and ages in the Paleoproterozoic Aketashitage orogen, NW China: Implications for Precambrian orogeny

Abstract The comprehensive investigation of orogenic-related litho-structural assemblages, metamorphism, and geochronology in early Precambrian orogens can help us better understand the features of plate tectonics in early Earth. The Paleoproterozoic Aketashitage orogenic belt is located at a key position in northwestern China and connects the North China craton, Tarim craton, Altaids orogen, and Tethys orogen. Garnet-bearing mafic and paragneissic granulite occur as interlayers or blocks preserved within paragneissic matrix, and two to three generations of metamorphic mineral assemblages were identified. Geothermobarometry and pseudosection modeling yielded clockwise metamorphic P-T paths passing from 7.5–8.6 kbar/575–715 °C (M1) through 7.4–12.2 kbar/715–895 °C (M2) and finally to 5.2–7.3 kbar/710–800 °C (M3) for the mafic and paragneissic granulite as well as amphibolite, which is indicative of metamorphic features of subduction/collision zones. Peak metamorphic P-T conditions of all the samples lie in the medium P/T facies series, suggesting that the thermal gradient (∼20–31 °C/km) of this Paleoproterozoic orogenic belt was obviously higher than most of the Phanerozoic subduction zones. Secondary ion mass spectrometry (SIMS) and laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) U-Pb dating of zircon and monazite yielded metamorphic ages of ca. 1.98–1.96 Ga in the eastern part of the orogen, ca. 1.86–1.85 Ga in the western part, and a maximum depositional age of ca. 2.06 Ga for paragneiss. Compared with previous studies, the Aketashitage orogen is composed of unordered juxtaposition of diverse, subduction-related tectono-metamorphic blocks with different protoliths, metamorphic grades, and ages preserved within the paragneissic matrix deposited in the Paleoproterozoic, which is highly similar to Phanerozoic mélange. A Paleoproterozoic subduction-metamorphic-exhumation-accretionary process was deciphered, similar to that found in accretionary/orogenic wedge in Phanerozoic orogens. The juxtaposition of diverse, subduction-related tectonic blocks with contrasting ages and metamorphic features can serve as a marker of early Precambrian orogens and plate tectonics.

Paleoproterozoic multiple magmatic-metamorphic events in the Dunhuang Block, eastern Tarim Craton: Implications for assembly of the Columbia supercontinent

The evolution of the Dunhuang Block associated with the assembly of the Columbia supercontinent is poorly constrained. The geochemical composition and temporal evolution of magmatic and metamorphic rocks may hold key information regarding critical geodynamic processes that occurred during the evolution of the Dunhuang Block. In this paper, we present a systematic petrographic, geochemical, and zircon U-Pb and Hf isotopic investigation on tonalitic gneiss, carbonatite, granitic dyke, mafic granulite and A-type granite in the Dunhuang Block. The results suggest that tonalitic gneiss was derived from partial melting of a thickened oceanic plateau crust or island-arc crust at ~3.67 Ga and then it recorded an important subduction-collision orogenesis in the Paleoproterozoic (~2.02 Ga to ~1.96 Ga). The ~1.94 Ga carbonatite and ~1.85 Ga granitic dyke were formed by partial melting of marble and Meso- to Neoarchean basement rocks, respectively. Both of them were formed in post-collisional setting. The ~1.82 Ga mafic granulite recorded high-pressure granulite facies metamorphism followed by a medium–low pressure granulite facies metamorphic overprint, suggesting a clockwise P-T path and implying an environment of collisional orogenesis. The ~1.76 Ga A-type granite resulted from the reworked Neoarchean crust and was most likely related to a post-collisional episode. Combined with previous studies, we identify two Paleoproterozoic orogenic belts of the Dunhuang Block: the ~2.00–1.96 Ga South Orogen and ~1.85–1.80 Ga North Orogen. According to the coupling of these two orogenies with the Columbia orogeny, we conclude that the Dunhuang Block was associated with the assembly of the Columbia supercontinent.

Tectonic evolution of the Dadongcha Formation, Ji'an group, Qinghe area, Tonghua, NE China: Implications from geochronological and geochemical evidence of metapelites

The Jiao–Liao–Ji Belt (JLJB) is an important Paleoproterozoic orogenic belt that has been a focus of research to understand the Precambrian evolution of the North China Craton (NCC). The widespread Paleoproterozoic Ji’an group, which was exposed in the northern margin of JLJB, is the key to solving controversies in the tectonic setting of this special belt. An intensive study on metamorphic reactions, zircon U–Pb ages, mineral thermobarometry, geochemistry, and quantitative phase equilibria modeling (pressure–temperature pseudosections) of typical metapelites from the Dadongcha Formation of the Ji’an group provides important insight to understand the tectonic setting and processes of the Paleoproterozoic JLJB. The analyzed metapelites are exposed in Toudao and Qinghe towns in NE China, include garnet–biotite schist, garnet–biotite–plagioclase gneiss, garnet–sillimanite–cordierite–biotite gneiss, and hypersthene-spinel–cordierite–biotite gneiss. Garnets contain mineral inclusions such as sillimanite, biotite, feldspar, and quartz and retain the typical cordierite reactive edge structures. The protoliths of metapelites are sets of claystone or miscellaneous sandstone with an average chemical composition that is close to that of the upper continental crust (UCC). Chemical Index of Alteration (CIA) and Index of Compositional Variability (ICV) values suggest a high degree of weathering of their sources and low compositional maturity of clastic sediments. The chondrite-normalized rare earth element (REE) pattern of analyzed samples displays characteristics of medium fractionation in light and heavy REEs, and strong enrichment in light REEs. The primitive mantle-normalized trace element pattern shows enrichment of large ion lithophile elements (LILEs) such as Ba, and the content of high field strength elements (HFSEs) such as Zr and Hf is relatively low; furthermore, Nb, Ta, P, and Ti are distinctly depleted. The emphasis is on the metamorphism of metapelites, which shows a clockwise P–T path. In combination with zircon U–Pb dating, a general evolution model for the metapelites was drawn. The metapelites were formed in an active continental margin environment where the evolved island arcs developed around 1.95–2.02 Ga, then were involved in the collision between the Longgang and Langrim blocks in the eastern part of the NCC, and returned to the surface after undergoing regional metamorphism with widespread anatexis around 1.8–1.95 Ga.

Crustal growth and reworking of Archean crust within the Rhyacian domains of the southeastern Guiana Shield, Brazil: Evidence from zircon U–Pb–Hf and whole-rock Sm–Nd geochronology

The southeastern Guiana Shield, northern Amazonian Craton, is part of a Paleoproterozoic orogenic belt that was built up during the Transamazonian orogenic cycle (2.26–1.95 Ga). This cycle includes large segments of Rhyacian juvenile crust and some reworked Archean terranes. The geology in this region consists mainly of Paleoproterozoic granulitic-migmatitic-gneissic complexes, deformed and metamorphosed metavolcanic and metasedimentary rocks, and granitoids (granitic and TTG magmatism). Three tectonic domains are distinguished in the Brazilian territory of the southeastern Guiana Shield. They are known as the Amapá Block, Lourenço Domain, and Carecuru Domain. The Amapá Block is a Meso–Neoarchean continental block that was intensely reworked during the Transamazonian orogeny. The other two domains represent Rhyacian landmasses, the evolution of which involved several stages of subduction of oceanic lithosphere in magmatic arc environments. There are also relics of reworked Archean continental crust, the formation of which was followed by a collisional stage of tectonic accretion of the magmatic arcs. Whole-rock Sm–Nd and U–Pb zircon geochronology have confirmed the juvenile character of much of this Transamazonian orogenic belt. However, for the Lourenço and Carecuru domains, Nd isotopic signatures indicate the participation of Meso–Neoarchean crustal material in the sources of the magmatic rocks. Combined zircon U–Pb and Lu–Hf isotopic analyses by LA-ICP-MS were performed on eleven Rhyacian granitoids and orthogneisses from the Lourenço and Carecuru domains. The aim was to verify the extension of the influence of the Archean continental crust in the adjacent Paleoproterozoic domains. The main magmatic episodes were identified in the Lourenço Domain (~2.17–2.18, 2.14 and 2.12–2.09 Ga) and Carecuru Domain (2.14 Ga) by U–Pb zircon geochronology. The Lu–Hf isotope data point to the predominance of crustal reworking processes (ƐHf(2.2–2.1 Ga) < 0; 67% of zircon crystals) during the formation of Lourenço and Carecuru domains. Hf model ages were found to be mostly Archean (98.4%), even for zircon grains that have positive ƐHf(2.2–2.1 Ga) values. For the terrane at the border of the Lourenço and Carecuru domains with the Amapá Block, assimilation of Archean crust of different ages and proportions in a magmatic arc environment accounts for the Hf–Nd isotopic signatures and Hf model ages of Rhyacian magmatism. In the northwestern part of the Lourenço Domain, more than 100 km north of the Amapá Block, the Hf–Nd isotopic signatures and Hf model ages indicate the participation of Archean crustal material, either as continental fragments and/or through incorporation of continental sediments in island arc environments, similar to what has been recorded for some Birimian terranes of the West African Craton in Ghana.

Multi-stage Paleoproterozoic structural evolution of the southern Liaodong orogenic belt: A case study of the Hadabei granite gneiss dome

A group of Paleoproterozoic gneiss domes are well preserved in the southern Liaodong segment of the Jiao-Liao-Ji Orogenic Belt (JLJOB), eastern North China Craton. Similar to the domes in many other orogenic belts, they may provide important clues to our understanding of the orogenic processes and related middle-lower crustal mass flow during the tectonic evolution of the orogenic belt. This paper conducted detailed structural analysis of the Hadabei dome, a typical example in the dome group to unravel the Paleoproterozoic structural styles and deformation history of the southern Liaodong orogenic belt. Three stages of deformation (D1-D3) are reconstructed for the structural evolution of the dome. The D1 deformation is characterized by meso- to micro-scale intrafolia folds (F1), penetrative foliations (S1) and mineral lineations (L1) in the metamorphosed volcanic-sedimentary rocks. The D2 deformation intensively transformed S1 foliations to form asymmetrical folds (F2) and crenulation cleavages (S2). The D3 deformation is mainly evidenced by occurrence of open folds (F3) at various scales. U-Pb zircon geochronological dating of syn-tectonic leucogranitic dykes shows that the D2 deformation occurred from >1860 Ma to 1822 Ma. It is also shown that the D2 deformation is the peak stage of deformation that contributed to the formation of the overall tectonic framework of the Hadabei dome, and therefore, the orogenic belt. At this stage, subhorizontal mass flow contributed to the widely developed shear structures. The formation of the Hadabei dome was ascribed to early diapirism (D1), subhorizontal shearing and doming (D2) and fold superposition (D3). The multi-stage structural evolution was resulted from successive E-W oriented rifting, extension and contraction, and subsequent superimposition by N-S shortening in the southern Liaodong Paleoproterozoic orogenic belt. These conclusions provide a better understanding of the mechanisms of doming, regional structural deformation, and tectonic evolution of the JLJOB.