Columbia Supercontinent Research Articles

Evidence of crustal growth during the Svecofennian orogeny: New isotopic data from the central parts of the Paleoproterozoic Central Finland Granitoid Complex

The Central Finland Granitoid Complex (CFGC) is the Paleoproterozoic core of the Svecofennian orogeny composed mainly of plutonic rocks varying from diorites to granodiorites and granites. Common mixing and mingling textures, synplutonic dykes, and mafic magmatic enclaves highlight the simultaneous nature of mafic, mantle derived magmatism and more evolved felsic magmatism in the CFGC. New U-Pb geochronological data support crustal growth during 1.90–1.87 Ga for the CFGC. Both Sm-Nd (εNd -1.7–+2.5) from whole rocks and Lu-Hf (εHf -8–+9) from zircons point towards relatively juvenile sources for the plutonic rocks without Archean crustal component. On the whole, isotopic evidence collectively points to crustal growth with maturing arc characteristics at 1.90–1.87 Ga, and a possible amalgamation of island arcs during the Svecofennian orogeny. In a larger scale, the CFGC was 1.9 Ga ago located in the active margin of the Great Proterozoic Accretionary Orogen when supercontinent Columbia (Nuna) formed.

Petrogenesis of the Palaeoproterozoic (1.87 Ga) Damyang amphibolites in the north‐western margin of the Yeongnam Massif and tectonic implications of the Korean Peninsula

The Yeongnam Massif is located in the southern part of the Korean Peninsula and holds key elements in understanding the Palaeoproterozoic tectonic evolution of north‐east Asia during the amalgamation of the Columbia supercontinent. In this study, we have conducted geochronological and geochemical studies on the mafic intrusive along the northern margin of the Yeongnam Massif. Sensitive high‐resolution ion microprobe (SHRIMP) U–Pb zircon dating on two amphibolite and one gabbro samples in the Damyang area show that the amphibolites crystallized at ~1.87 Ga and the gabbro crystallized at ~87.6 Ma. The 1.87 Ga Damyang amphibolites are simultaneous with the Muju and Okbang amphibolites along the northern margin of the Yeongnam Massif. They also show similar geochemical characteristics, including tholeiitic basalt composition, enriched Light Rare Earth Elements (LREE) and large ion lithosphile elements (LILEs), depleted high field strength elements (HFSEs), and slightly enriched but various Hf isotopes, indicating that they originated from an enriched but heterogeneous mantle source with fluid addition. Thus, the 1.87 Ga amphibolites along the northern margin of the Yeongnam Massif were probably emplaced in an arc‐related setting. Combined with the 2.02–1.96 Ga magmatism, it is proposed that the subduction might have lasted during the 2.02–1.85 Ga interval and mantle‐derived magma rose up due to the roll‐back process between 1.88–1.85 Ga.

Geochronology and in-situ apatite geochemistry of late Paleoproterozoic A-type granites in the Jiao-Liao-Ji Belt, North China Craton: Implications for petrogenesis and tectonic evolution

A-type granite shows unique geochemical characteristics and refers to specific formation conditions and tectonic environments, and therefore plays an important role in reconstructing orogenic events. In this paper, we systematically investigated the zircon UPb, whole-rock geochemistry, in-situ zircon Hf, apatite trace elements, and in-situ Nd data of the Huanren monzogranite to discuss its petrogenesis and the tectonic evolution of Jiao-Li-Ji belt. The studied zircon and apatite grains show typical oscillatory zoning and subhedral texture as well as obvious internal structure without any fluid/mineral inclusions, referring to a magmatic origin. Therefore, zircon UPb dating results suggest that the Huanren monzogranite was formed in the late Paleoproterozoic (1863–1842 Ma). The studied rocks show typical A-type granite affinities as high SiO2 (64.54–69.06 wt%), Na2O + K2O (8.00–9.34 wt%), and Zr + Nb + Ce + Y (381–598 ppm) concentrations, and FeOT/(FeOT + MgO) (0.82–0.85) and 10000Ga/Al (2.37–2.65) ratios. Their high whole-rock Zr temperature (812–866 °C, generally >840 °C), and low whole-rock Sr (109–157 ppm), apatite Sr (43.4–79.3 ppm) contents, whole-rock Sr/Y (4.79–8.22) and apatite Sr/Y (0.014–0.033) ratios, combined with slightly depleted in-situ zircon Hf (−1.62 to +2.50) and in-situ apatite Nd (−3.22 to −1.65) isotopic compositions, and ancient zircon Hf two-stage model ages (TDM2; 2606–2351 Ma), apatite Nd-TDM2 (2576–2451 Ma), suggest that the studied rocks were formed by partial melting of Neoarchean to Paleoproterozoic granitic gneiss in a high temperature and low-pressure condition. The studied A-type granite, together with regional A-type granite and alkaline syenite in the North China Craton, record the post-collisional event between the Nangrim and Longgang blocks, which combined with coeval worldwide A-type granite magmatisms, representing a response of the initial breakup of Columbia supercontinent.

The uplift of Fuping Complex and its implications for the late Paleoproterozoic evolution of the North China Craton

The Paleoproterozoic is a key period in the evolution of the North China Craton, involving major tectonic events such as the cratonization and the transition of the tectonic regime. Previous study showed that the continent–continent collision occurred during the late Paleoproterozoic (∼1.85 Ga), which is related to the amalgamation of the Eastern and Western blocks. However, the anorogenic magmatism and intra-continental rifts indicated the extensional setting after the collision. Therefore, the tectonic regimes of the North China Craton underwent the transition from compression to extension during the late Paleoproterozoic. In this paper, it is proposed by authors that the uplift of the Fuping Complex occurred under the extensional setting during the late Paleoproterozoic, which probably indicate the original manifestation and initial time of the Meso- to Neoproterozoic extension in the North China Craton. Main evidences suggested by author are listed as follows. (1)The low-angle deformation zone developed on the northwest margin of the Fuping Complex, including the Longquanguan shear zone, Wangmaoshan folded deformation layer and Xiaomai shear zone. Various asymmetrical indicators in these structures showed the top-to-the-NW or W sense of shearing. (2) Based on constraints from different kinds of dating results, the deformation time of Longquanguan shear zone is constrained in period 1.83 ∼ 1.78 Ga, which is later than the collision along the Trans-North China Orogen (∼1.85 Ga), while earlier than the occurrence of the Xiong’er Group (1.78 ∼ 1.75 Ga) in the Xiong’er rift. Meanwhile, the Pingshan shear zone on the southeastern margin of Fuping Complex showed the top-to-the-SE shearing which deformed synchronously with Longquanguan shear zone. The uplift of Fuping complex is confirmed by the fact that it was sandwiched by two low-angle shear zones with different shearing orientation on its northwest and southeast margins. The author proposed that the uplift process is probably the result of the magma diapirism, which is related to the lithospheric dissociation of North China Craton along with the breakup of the Columbia Supercontinent.

Early Mesoproterozoic (1.72–1.68 Ga) convergence between Bastar and Eastern Dharwar cratons along the Bhopalpatnam orogen, southcentral India and implication for paleogeography of supercontinent Columbia

Temporal constraints on orogen initiation and duration are critical for the Paleoproterozoic reconstruction of cratons presently constituting India. Recent late Paleoproterozoic paleomagnetic pole data indicate proximity of Eastern Dharwar, Bastar and Singhbhum cratons and in view of global Mesoproterozoic-aged final Columbia assembly, reconstruction sequence of Indic cratons is critical to assess whether they constituted Columbia. The initiation time and duration of the Bhopalpatnam orogen, developed between the Eastern Dharwar and Bastar cratons, range from earliest Mesoproterozoic to Neoarchean. Therefore, in order to constrain the earliest stages of cratonic convergence and crustal thickening, the time of peak metamorphism was established on tectonites, sampled from > 300 km along newly classified longitudinal domains representative of the entire Bhopalpatnam orogen, by precise combined garnet Lu-Hf and Sm-Nd chronology of amphibolite-and granulite-facies rocks. Interpreting the Lu-Hf and Sm-Nd isochron weighted mean ages, an orogenic duration of 38 ± 19 Myr is inferred between the high-pressure amphibolite-facies through to granulite-facies event at 1721 ± 14 Ma and a post-peak cooling to ≤ 650 °C at 1683 ± 6 Ma, being the Sm-Nd garnet weighted mean age. Archean two-stage depleted mantle model ages (at 1.7 Ga) of tectonites and rotated dyke swarm orientations support the reactivation and reworking of the Paleo- to Neoarchean Bastar craton marginal rocks in response to the early Mesoproterozoic orogeny. Based on the clockwise P-T path involving an early high-pressure amphibolite-facies stage (Pmax ≥ 12 kbar at ∼ 750 °C) followed by a granulite-facies stage (Tmax ≤ 850 °C at lower pressures), we interpret the orogen to represent deeply exhumed thrust slices of the reworked Bastar craton leading edge underthrusted beneath the Eastern Dharwar craton. As paleomagnetic data indicates proximity or contiguity of Bastar and Eastern Dharwar cratons by 1.79 Ga, the Bhopalapatnam orogen could represent site of early Mesoproterozoic cratonic collision or locus of post amalgamation reactivation due to convergence.

Exhumation of an Archean Granulite Terrane by Paleoproterozoic Orogenesis: Evidence from the North China Craton

Abstract Granulites represent high-grade metamorphic rocks of the deep continental crust. The metamorphism and exhumation of granulites from Archean terranes provide insights into the crustal evolution of Archean cratons and shed light on the formation and reactivation of cratons. We present petrology, U–Pb geochronology (zircon, rutile, and titanite), and pressure–temperature (P–T) paths for metadiabase dikes in an Archean granulite terrane of the North China Craton. Garnet (Grt) coronae in the metadiabase dikes are developed between plagioclase (Pl) and clinopyroxene (Cpx) via the reaction Pligneous + Cpx → Pl1 + Grt ± quartz. The reaction proceeds inward within the plagioclase, progressively consuming Pligneous (XAn = 0.65–0.69) and leaving Ca-poor Pl1 (XAn = 0.46–0.53) as the residue. Geothermobarometry and P–T pseudosections suggest peak conditions for garnet formation at ~800°C and 10–13 kbar. During retrograde metamorphism, Grt broke down to Ca-rich Pl2 (XAn = 0.73–0.74), and ilmenite replaced rutile. Geothermobarometry and Zr-in-titanite temperatures constrain the P–T conditions of retrograde metamorphism at 700–750°C and 4.5–7.5 kbar. Zircon and titanite U–Pb geochronology shows that the protolith of the metadiabase dike was formed at 2.4 Ga and underwent granulite-facies metamorphism at 1.86 Ga. The intrusion of mafic dikes into the Archean granulite terrane indicates that the Archean basement was also heated and buried in the Paleoproterozoic. The metadiabase dikes and the hosting Archean basement underwent Paleoproterozoic granulite-facies metamorphism at a depth of ~40 km, followed by near-isothermal decompression and subsequent near-isobaric cooling (cooling rate of 1–3°C Myr−1) at depths of 15–25 km. Crustal shortening and thickening may have been caused by the underplating of the Khondalite series beneath the Archean basement during the amalgamation of supercontinent Columbia. The Paleoproterozoic orogeny induced a second generation of metamorphism of the Archean basement along the margin of the craton and drove the exhumation of the Archean granulite terranes to the middle crust (~15 km).

Geochemical constraints on the petrogenesis of mafic rocks (metadolerites) from the Proterozoic Shillong Basin, Northeast India: implications for growth of the Greater Indian Landmass

AbstractThe Paleo-Mesoproterozoic Shillong Basin of the Assam-Meghalaya Gneissic Complex is exposed in parts of Northeast India. The studied metadolerites are from the volcano-sedimentary sequence of Shillong Basin from the Borjuri area in the Mikir Massif. This episode of mafic magmatism can be correlated with the Columbia supercontinent formation and bears significance to its reconstruction. The present work discusses the field, petrography and geochemical characteristics of the metadolerites, which occur in close association with the quartzites of the Shillong Group of rocks (metasedimentary rocks of the Shillong Basin). Our data show distinctive characteristics of subduction-related magmatism exhibiting high LREE/HREE, large ion lithophile element/high field strength element ratios and pronounced negative Nb anomaly. Elemental ratios such as Zr/Ba (0.21–0.46), La/Nb (1.23–2.32) and Ba/Nb (30.08–56.90) point to a fluid-enriched lithospheric mantle source in a subduction regime. Metadolerites plot in the field of ‘back-arc basin basalts’ in tectonic discrimination diagrams reinforcing a subduction zone tectonic setting. The mafic rocks correspond to a 6–10 % partial melting of a mantle source incorporating spinel+garnet lherzolite. The metamorphic P-T of the metadolerites estimated from plagioclase-hornblende geothermobarometer (7–8 kbar, 664 °C) is indicative of amphibolite facies metamorphism in a medium P-T zone. Based on the comparative analysis of field observation, petrography, geochemistry and geological ages given by previous workers, we infer that the Shillong Basin represents a back-arc rift region and is the eastern continuation of the Bathani volcano-sedimentary sequence of the Chotanagpur Granite Gneiss Complex marking continuation of the Central Indian Tectonic Zone to the Mikir Massif.

Evolutionary stasis during the Mesoproterozoic Columbia-Rodinia supercontinent transition

The transition between the supercontinents Columbia and Rodina coincided with a delay in eukaryote expansion during the Mesoproterozoic, however, the cause for this association is uncertain. Here, we use statistical geochemical analyses of igneous and fine-grained siliciclastic rocks to demonstrate that extensive crustal differentiation occurred during this transition interval. The results show a relative increase in abundance of phosphorus-poor felsic volcanic and plutonic rocks and a prevailing low weathering intensity between ∼ 1.8 and 1.2 Ga (billion years ago). The decelerated weathering of phosphorus-poor felsic volcanic and plutonic rocks could have maintained the low flux of bio-essential nutrients to the oceans that sustained low primary productivity and atmospheric O2 levels, which inhibited biologic radiation during the Columbia-Rodinia supercontinent transition period.

Insights into the Crustal Evolution and Tungsten Mineralization of the West Cathaysia Block: Constraints from the Inherited Zircons from the Mesozoic Dengfuxian and Paleozoic Tanghu Plutons, South China

The formation and evolution of the ancient continental crust are crucial issues in solid-earth geology which are commonly associated with global tectonic events and the formation of economically valuable magmatic-hydrothermal ore deposits. The Cathaysia Block, one of the ancient continents in Southeast Asia, can be subdivided into two parts: the West Cathaysia Block and the East Cathaysia Block. Unlike the East Cathaysia Block, no Precambrian rocks are exposed in the West Cathaysia Block, constraining further understanding of the formation and evolution of this block. In this study, a total of four hundred and thirty-three zircon U-Pb dating analyses and two hundred and eighteen Lu-Hf isotopic analyses on zircon grains from the Jurassic Dengfuxian granites and Ordovician Tanghu granites, Nanling Range, were carried out. LA-ICP-MS zircon U-Pb dating yields mean average 206Pb/238U ages of 152.6 ± 2.2 Ma (MSWD = 1.6) and 442.4 ± 1.7 Ma (MSWD = 3.8), which are regarded as the rock-forming age for the Jurassic Dengfuxian granites and Ordovician Tanghu granites, respectively. The 207Pb/206Pb ages of the inherited zircons from the Jurassic Dengfuxian granites and Ordovician Tanghu granites range from 522 Ma to 3395 Ma, hosting two major peaks at the 0.9–1.0 Ga and 2.4–2.5 Ga. In contrast to the East Cathaysia Block, the West Cathaysia Block lacks the age peak of 1.8–1.9 Ga, indicating that the West Cathaysia Block was not influenced by the assembly of the Columbia supercontinent in the Paleo-Proterozoic. In combination with the Lu-Hf isotopes, we proposed that the crust evolution of the West Cathaysia Block in Archean is dominated by juvenile crustal growth events, and dominated by the crustal reworking since the Proterozoic. The long duration of crustal reworking in the West Cathaysia Block resulted in the enrichment of lithophile elements (e.g., W, Sn, Nb, and Ta) in the crust of that region. Therefore, the Jurassic granites in the Nanling Range, which are mainly derived from the partial melting of Proterozoic basement rocks, became associated with large-scale tungsten polymetallic mineralization.

The statherian anorogenic magmatism in the Paramirim Aulacogen, são Francisco-Congo paleoplate: New data, synthesis and regional correlations

Fragmentation of continental masses is usually associated with anorogenic magmatism, and in this context, major silicic magmatic events may be associated with Large Igneous Provinces (LIPs). The Paramirim Aulacogen evolves between 1.77 and 0.67 Ga, filling anorogenic siliciclastic and acidic volcanic rocks with subordinate carbonates. A rhyolite from the Algodão Formation, the oldest unit of the Aulacogen, was dated in this work using the U–Pb method (LA-ICPMS), finding a crystallization age of 1777±1 Ma, with a model age (TDM) of 3.10 Ga and εNd (t) equals −10.4. The anorogenic plutonic magmatism is represented by the Lagoa Real Intrusive Suite, with over 5000 km2. New geochemical and geochronological data are presented, and the integration with the literature allowed the interpretation of four plutonic magmatism cycles: (i) Cycle 1: represented by Lagoa do Barro granitoids (1762 ± 9 Ma) and the metavolcanic rocks of the Algodão Formation (1775 ± 77–1777±1 Ma); (ii) Cycle 2: with the São Timóteo (1741 ± 4–1746 ± 5 Ma) and Caetité (1743 ± 5 Ma) granitoid and syenitoid, in addition to charnockitic rocks (1742±7 Ma); (iii) Cycle 3: is related to phonotephrite, tephriphonolite and phonolite. Trachyte, trachyandesite and trachydacite of São Simão Formation (1731 ± 5 Ma) and tuff layer of Ouricuri do Ouro Formation (1722 ± 13 Ma), as well as rhyolites and dacites that ocurr in the basement of Paramirim Aulacogen. The Caldeirão granitoid and syenitoid (1724 ± 5 Ma) is associated with this cycle; and (iv) Cycle 4: with the Suçuarana intusive rocks (1686 ± 6 Ma) and pyroclastic rocks of trachyandesitic composition. The Sm–Nd model ages (TDM) obtained in this work and the literature varies between 3.1 and 2.2 Ga, with values of εNd (t) between −15.8 and −8.6. The formation of the Statherian magmas possibly occurred by melting the enriched mafic mantle, followed by underplating in the continental crust and assimilation of Archean crustal rocks, with fractionation of hornblende, biotite, apatite, and Fe–Ti oxides during magma evolution. The Lagoa Real Intrusive Suite, and their volcanic correlates, represent part of a Statherian Silicic Large Igneous Province (SLIP) developed in a crust of the Archean-Rhyacian-Orosirian age of the São Francisco-Congo Paleoplate. This magmatism marks the attempt at the breakup of the Columbia supercontinent, with correlates in other regions of Brazil and the world.

Hot orogenesis in the Paleoproterozoic: Insights from granitic gneiss domes within the Jiao-Liao-Ji belt, North China craton

As a part of the Columbia supercontinent, the North China craton is an ideal object for studying the evolution of supercontinent assembly and the mechanism of orogenesis in the Paleoproterozoic. The Jiao-Liao-Ji belt, located in the eastern part of the North China craton, provides important clues for our understanding of Paleoproterozoic orogenic processes. A series of Paleoproterozoic granitic gneiss domes is preserved in the Liaodong segment of the Jiao-Liao-Ji belt. These domes are cored by the Liaoji granitic gneisses (emplaced at 2250−2150 Ma) and mantled by metamorphosed volcanic-sedimentary rocks (deposited at 2200−1940 Ma). Combining multiple lines of evidence from mesostructures and microstructures, kinematics, magnetic fabrics, and crystallographic fabrics, we suggest that the granitic gneiss domes reflect inhomogeneous shearing of the middle to lower crust during Paleoproterozoic orogenic processes. Intensive layer-paralleling shearing characterized subhorizontal flow during nearly E-W−oriented compression. As a hot orogen formed in the Paleoproterozoic, the orogenic deformation in the Jiao-Liao-Ji belt was characterized by extensive doming due to dominant subhorizontal flow and subsidiary vertical flow in the middle to lower crust.

Hot, Wide, Continental Back-arcs Explain Earth’s Enigmatic mid-Proterozoic Magmatic and Metamorphic Record

Higher than average thermobaric ratios (temperature/pressure) of metamorphic rocks and abundant ‘dry’ ferroan magmatism including massif anorthosite suites are two enigmatic features of the mid-Proterozoic (1.85–0.85 Ga) that have unclear origins. It has been proposed that elevated mantle temperatures due to insulation under the Columbia supercontinent, and/or to plate slowdown, combined with thin lithosphere, led to high continental geothermal gradients, high-temperature metamorphism, and an increase in dry, ferroan magmatism. Geodynamic modelling predicts that continental subduction zones at mid-Proterozoic mantle potential temperatures (80–150 °C hotter than at present) would exhibit key differences to the Phanerozoic, critically, extensive slab rollback combined with greater volumes of decompression melting of the asthenosphere would lead to wide regions of back-arc magmatism. We posit that these hot, wide continental back-arcs can effectively explain the abundance of ferroan magmatism, anorthosite suites, and high T/P metamorphism. Our model negates the need for extra mantle heating from supercontinental insulation or plate slowdown and shows that the tectonic regime of the mid-Proterozoic was a transitional phase between those of the Archean (likely comprising peel-back tectonics and episodic subduction) and the Phanerozoic (comprising deep continental subduction), and which could have resulted solely from secular cooling of the mantle.

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

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

Far from boring: A new Grenvillian perspective on Mesoproterozoic tectonics

The “boring billion” (1.8 to 0.8 billion years ago) is an enigmatic period of Earth's evolution viewed by some as a time of tectonic quiescence reflecting secular changes in our planet's convection regime, either from sluggish global plate tectonics regime or from a wholly different regime. The confusion about this time-span stems from diverging interpretations of an ambiguous geological record, which points to a Mesoproterozoic world dominated by volcanic arcs, but also includes the formation of the massive Grenville Orogen. Here we present a compilation of multidisciplinary geological datasets, that are incompatible with the current tectonic paradigm, whereby the Grenville Orogen developed as an Andean-like arc at the margin of the Laurentia continent (now North America) and was reworked during a collision with the Amazonia continent (now South America). We argue, instead, that the geological record and proxies, with emphasis on those from the main exposure of the Grenville Orogen in the Grenville Province of eastern Canada, are consistent with the assembly of a distinct continent, which we coin Shawiniga (1.2-1.15 Ga), through the amalgamation of mature oceanic arcs/back-arcs offshore of Laurentia followed by a Shawiniga-Laurentia collision (∼1.03 Ga). This new model reveals that the transition from the supercontinent Columbia to Rodinia involved long-lived passive margins and subduction zones, as well as continental assembly through arc collisions, resolving the longstanding contradiction between tectonic proxies and the geological record and confirming the Mesoproterozoic was actually an exciting Era.

High magnesian schist, granitic gneiss, amphibolite and monzogneiss in the eastern Ama Drime Massif in South Tibet (China): A rifted Paleoproterozoic arc fringed the western Columbia supercontinent?

Understanding the Paleoproterozoic tectonic setting of the north Indian Craton—as either continental rifting or continent arc—is vital for locating the Indian Craton in the Columbia supercontinent. Herein, we present new petrological, geochemical, Nd–Hf isotopic, and geochronological data of high magnesian schist, granitic gneiss, amphibolite and biotite monzogneiss in the south-eastern margin of the Ama Drime Massif of South Tibet (China). The high magnesian schist contains 20.4 %–31.3 % phlogopite, 12.2 %–17.8 % clinochlorite, 10.5 %–13.4 % cordierite and 5.5 %–5.6 % loss on ignition, implying its protolith of Mg-rich clays and later alteration in the fault zone. Its medium-silicic composition and concentrative magmatic zircon age of ca. 1859 Ma indicates the origin of the clays from locally deposited mafic rocks. Moreover, its negative values of ƐNd(t) (−3.0 to −2.6) and zircon ƐHf(t) (−8.6 to +2.4) correspond to the metavolcanic rock in the same outcrop as well. Granitic gneiss, amphibolite and biotite monzogneiss exhibit their protolith of crystal ages between 1870 and 1849 Ma with characteristics of negative anomalies of Nb, Ta, and Ti in subduction zone setting. They have similar negative values of ƐNd(t) (−3.0 to −1.3) and zircon ƐHf(t) (−8.6 to +4.0), indicating various degrees of contamination in the continental crust. The geochemical characteristics of the granitic gneiss and amphibolite signify the generation of their protolith via various degrees (1.5–2.5 %) of partial melting of spinel lherzolite inside the shallow mantle. As the high alkalinity of biotite monzogneiss implies a greater contribution of water from the subduction plate, and the trace elements of zircons manifest their affinity of continent arc toward island arc, we interpret the origin of the protolith of these rocks in a setting of continental arc-related rifting at the north of the Indian Craton. The finding of this arc reinforces that the reconstruction of the western Columbia supercontinent was fringed with an active margin.

Mesoproterozoic basins (Yukon, Canada) in the evolution of supercontinent Columbia

Geochemical and geochronological data from the Pinguicula Group and unit PR1 of the lower Fifteenmile Group (Yukon, Canada) provide information on sediment provenance and timing of break-up of supercontinent Columbia and seaway development on Laurentia’s northwestern margin. The older unit PR1, in the Coal Creek inlier, has a near-unimodal detrital zircon population with an age of 1499 ± 3 Ma. The Pinguicula Group detrital zircon data, in the Wernecke and Hart River inliers, display a polymodal detrital zircon population with a maximum age of <1322 ± 23 Ma. Using detrital zircon signatures, Sm–Nd isotopic data, and C-isotopic signatures, lithostratigraphic correlations between the Pinguicula Group in the Wernecke and Hart River inliers are confirmed, whereas the Pinguicula Group and unit PR1 are no longer considered correlative. The zircon population in unit PR1 requires a proximal source, but sources of this age are not known in western Laurentia. Based on detrital zircon and Sm–Nd data, sediment in unit PR1 was derived from the Mt. Isa inlier in northeastern Australia sometime after 1460 Ma. Unit PR1 correlates with older Mesoproterozoic successions, including the Belt-Purcell, that were deposited during break-up of supercontinent Columbia, and contain sediment from Australia and the Mawson continent. Mesoproterozoic successions deposited after 1.45 Ga, including the Missoula Group, lack North American Magmatic Gap (NAMG)-aged zircon and instead record sediment provenance from southern Laurentia, as north Australia and the Mawson continent rifted from Laurentia’s western margin. The Pinguicula Group has few NAMG-aged grains that were probably recycled from older Mesoproterozoic basins.

PALEOPROTEROZOIC GRAPHITIZATION IN THE CLÁUDIO SHEAR ZONE (SOUTHERN SÃO FRANCISCO CRATON - BRAZIL) INVESTIGATED BY RAMAN SPECTROSCOPY AND X-RAY DIFFRACTION

The southern São Francisco craton hosts some of the largest graphite mines in Brazil, located in the city of Itapecerica. This paper addresses graphite crystals that occur within the regional structure known as the Cláudio shear zone in terms of thermometry. Raman spectroscopy and X-ray diffraction data showed that, on average, graphite crystals of the Cláudio shear zone have high crystallinity and are similar to those from mines in Itapecerica. The average temperature found (702 ºC) in this study is close to the samples from Itapecerica. However, this temperature is still lower than the expected (~900 ºC) from previous studies. The hypothesis for this would be that the graphite devolved high crystallinity, but was modified during the evolution of the metamorphism, or during the post-collisional stage fluid percolation. Thus, the modified crystallinity parameters lead to the relatively low-temperature values found. The proximity and similarity of geological framework suggest correlation between the precursor basins that formed the Itapecerica and the Cláudio shear zone graphite occurrences. From a global perspective, the closure of precursor basins and formation of the Cláudio shear zone are part of the collisions of Archean and Paleoproterozoic crustal blocks that formed the Columbia supercontinent.

Petrogenesis and in situ U-Pb zircon dates of a suite of granitoid in the northern part of the Central Indian tectonic Zone: Implications for prolonged arc magmatism during the formation of the Columbia supercontinent

The timing and petrogenesis of magmatic rocks in the Central Indian Tectonic zone (CITZ) have paramount importance in understanding the (a) growth of the Indian shield and (b) formation and disintegration of the Columbia and Rodinia supercontinents. In this study, the petrology, geochemistry and U-Pb in-situ zircon dating of a suite of porphyritic granitoids from the Makrohar Granulite Belt (MKGB) of the CITZ are presented. The studied rock suite develops megacrystic K-feldspar and plagioclase phenocrysts, embedded in medium to fine-grained matrix of biotite ± amphibole + quartz + K-feldspar + plagioclase + ilmenite ± garnet with widely variable phenocryst to matrix ratio. The bulk compositions of the studied rocks overlap with the compositions of the I-type granitoid, emplaced in a continental arc setting. The in-situ U-Pb zircon age fixes the timing of magmatism at 1750 Ma. Systematic geochemical trends combined with the variation in modal mineralogy suggest crystal fractionation to be the dominant process during the evolution of this arc magma. Phase equilibrium modeling in Na2O-CaO-K2O-FeO-MgO-Al2O3-SiO2-H2O-TiO2-O2 system under various physicochemical conditions suggests that both post-emplacement fractionation of a felsic magma and combined fractionation-crustal assimilation of a mafic magma at shallow depths (≤5 kbar) can produce the chemical variation observed in the studied arc granites. Petrography and field evidences negate substantial granite formation from combined fractionation and crustal assimilation of arc basalt in the studied area. Plagioclase and K-feldspar occur as early crystallising phases. Variation of the modeled melt compositions simulates the variations of the major element compositions in the studied granitoid suite. The ca. 1750 Ma old arc magmatism in the MKGB is also reported from the Mahakoshal Supracrustal Belt (MSB). This feature is consistent with the view that both MKGB and MSB, now separated by the Son Narmada South Fault formed a coherent block till 1750 Ma. In combination with the published information, the present study demonstrates southward progression of the arc front in the Indian shield from ca. 1900 Ma to ca. 1600 Ma during growth of the Columbia supercontinent.

A Paradigm Shift: North China Craton's North Margin Orogen Is the Collisional Suture With the Columbia Supercontinent

AbstractIn a new study, Wu, Wang, Zhou, Zhao, Haproff, et al. (2022, https://doi.org/10.1029/2022GC010662) present a comprehensive study of the North Margin Orogen of the North China Craton (NCC), showing that older accreted rocks in this belt preserve a record of active margin magmatism from 2.2 to 2.0 Ga, followed by collisional tectonics, marked by mélange and mylonitic shear zones, then granulite facies metamorphism at 1.9–1.8 Ga, marking the final collision of the NCC with the Columbia Supercontinent. The multidisciplinary studies presented in this work support earlier suggestions that the North China Craton amalgamated during accretionary orogenesis in the Neoarchean to earlier Paleoproterozoic, and that the late widespread 1.85 Ga high‐grade metamorphism is craton‐wide in scale, and not confined to a narrow orogen in the center of the craton. This new understanding creates new possibilities for refining reconstructions of one of Earth's earliest, best documented supercontinents, showing a globally linked plate network at 1.85 Ga, and suggests drastic new correlations and models for mineral resource exploration.

Origin and tectonic evolution of the Langshan (NW China): Insights from Proterozoic magmatic and sedimentary records

The Langshan connects the North China Craton (NCC) with the Alxa Block and occupies a key position to unraveling their Precambrian tectonic affinity. The tectonic origin and evolutionary history of the Precambrian basement of the Langshan is debated. To clarify these issues, we report zircon U-Pb ages and geochemical data for magmatic and metasedimentary rocks in the northern Langshan. The new results combined with previous data indicated that the northern Langshan experienced multistage magmatism at ∼2.53–2.49, ∼2.02, and ∼1.92–1.97 Ga, similar to those in the NCC. Late Paleoproterozoic (∼1.64–1.71 Ga) gneissic alkalic feldspar granite and monzogranite show A-type granite geochemical signatures. Detrital zircon U-Pb-Hf isotopic data indicated that the Baoyintu Group was deposited in the Mesoproterozoic and mainly sourced from the basement rocks and coeval rift-related granites in the northern Langshan and NCC. The A-type gneissic granites and Baoyintu Group were resulted from the breakup of the Columbia supercontinent. In addition, a K-feldspar granite with A-type granite geochemical characteristic was dated at 855 ± 5 Ma. A schist displays detrital zircon age peaks at ∼1577, ∼1443, ∼1348, and ∼1174 Ma with predominantly positive εHf(t) values, and the Alxa Block might provide significant detritus for it. A continental fragment was probably detached from the Alxa Block due to regional back-arc extension along the northern margin of the Rodinia supercontinent during the early Neoproterozoic, which was finally incorporated into an early Paleozoic accretionary complex in the southern Central Asian Orogenic Belt. The available data indicate that the Langshan can be subdivided into the northeastern Langshan and southwestern Langshan, with the former belonging to the NCC and the latter as a part of the Alxa Block. We advocate that the Alxa Block was an independent microcontinent with a different tectono-thermal evolution from the NCC at least during the Neoproterozoic.