Andean-type Continental Margin Research Articles

Mid-Cretaceous to early Eocene Neo-Tethyan subduction records in West Sulawesi, Indonesia

Situated in the heart of the Indonesian archipelago, Sulawesi records well-developed Cenozoic magmatism, yet its Cretaceous magmatic evolution remains enigmatic. Here, we report new U-Pb-Hf isotopic data of detrital zircons from West Sulawesi, Indonesia to constrain its Cretaceous to Eocene magmatic tempo. Detrital zircons aged at ca. 105−80 Ma and ca. 70−45 Ma occur as the most dominant age populations and show high positive εHf(t) values, indicating derivation from juvenile sources with limited continental crustal contamination. Our new data, combined with available results, support the existence of an Andean-type continental margin in West Sulawesi during mid-Cretaceous to early Eocene times. Importantly, the magmatic tempo of West Sulawesi is also consistent with those of southern Lhasa (Tibet) and Sumatra (Indonesia), but contrasts with those of Paleo-Pacific subduction-related arcs in SE China, SE Vietnam, East Malaysia, and NW Borneo. Therefore, we put forward that West Sulawesi may be the southeasternmost component of the Neo-Tethyan arc system that spreads over 7500 km, from southern Tibet to SE Sundaland. Such a huge arc system with concurrent magmatic flare-ups and lulls in South Asia may have played a significant role in global-scale plate reorganization.

Development of a Modern-Style Trench-Arc-Backarc System in the Proto-Tethys Ocean (Qilian Orogenic Belt, NW China)

Abstract The development of trench-arc-backarc (TABA) systems is uniquely associated with modern-style plate tectonics on Earth. The Qilian orogenic belt in NW China records the evolution history of the Proto-Tethys Ocean at the transition time from the Proterozoic to Phanerozoic. This paper presents systematic studies of petrography, U–Pb chronology and geochemistry on various rocks from a middle-ocean ridge (MOR)-type ophiolite belt, active continental margin and back-arc basin in the Qilian orogenic belt to address the development of a modern-style TABA system. Arc magmas include felsic intrusions with ages of 531 to 477 Ma and felsic-mafic arc volcanic rocks with ages of 506 to 439 Ma, showing distinctive features of typical magmatic rocks formed at an Andean-type continental margin. The back-arc basin is recorded by a 490- to 448-Ma suprasubduction zone (SSZ)-type ophiolite with boninite, and Silurian turbidite flysch formation. We establish a three-stage tectonic history from the initiation of subduction to the formation of a mature Japan-Sea-type back-arc basin at the active continental margin in the Early Paleozoic era. (1) Northward subduction of Proto-Tethys Ocean initiated and the Andean-type continental arc developed at ~530 to 500 Ma with continual crustal thickening; (2) a tectonic transition occurred from an Andean-type active continental margin to a West Pacific-type active continental margin at ~500 to 490 Ma with rapid thinning of crust to ~35 km; and (3) mature ocean basins and back-arc-basin (BAB) ophiolites were formed in the back-arc extensional environment at ~490 to 450 Ma.

U-Pb zircon ages from metasedimentary and plutonic rocks in the Bras d'Or terrane of Cape Breton Island, Nova Scotia, Canada: insights into the Ediacaran–Cambrian tectonomagmatic evolution of Ganderia

The Bras d'Or terrane of central Cape Breton Island, Nova Scotia, Canada, contains a well-preserved record of the Ediacaran to early Cambrian evolution of Ganderia, a Gondwana-derived terrane in the northern Appalachian orogen. A complex assemblage of low- to high-grade metasedimentary rocks has varied detrital zircon signatures from laser ablation inductively coupled plasma mass spectrometry U-Pb zircon dating, but combining three or more samples yielded representative age spectra that support correlation of the low- and high-grade metasedimentary rocks throughout the Bras d'Or terrane and the corresponding Ganderian Brookville terrane of southern New Brunswick. In quartzite samples from the McMillan Flowage Formation in the northwestern Bras d'Or terrane, the youngest detrital zircons have ages >900 Ma, in contrast to previously studied psammitic and semipelitic samples from correlative units in the eastern Bras d'Or terrane in which youngest detrital ages are 620–600 Ma. Both quartzite and semipelitic samples from the McMillan Flowage Formation contain Neoproterozoic dates from zircon rims, which reflect metamorphic overgrowths during peak metamorphism at ca. 550 Ma, providing a robust age for peak metamorphism in the Bras d'Or terrane that supports similar, albeit sparse, ages reported previously from monazite and titanite samples. This metamorphism is coeval with the emplacement of voluminous dioritic to granitic plutons that occur throughout the Bras d'Or terrane and form in an Andean-type continental margin subduction zone. New U-Pb zircon ages presented here from plutons in the northern Bras d'Or terrane, combined with previously published ages, are consistent with subduction-related magmatism and associated metamorphism between ca. 575 and 540 Ma.

Late Cretaceous−early Paleogene rise of the Gangdese magmatic arc (south Tibet) from sea level to high mountains

Recognition of the existence of an Andean-type continental margin in southern Tibet prior to its collision with India has provided crucial constraints on the formation of the Tibetan Plateau and South Asian climate evolution. Here, we focused on well-dated Late Cretaceous successions in the Linzhou Basin and determined the elevation changes from sea level to high mountains in the Gangdese magmatic arc in southern Tibet. Our results show that the Linzhou Basin was still submerged in the Tethyan Sea at around 92 Ma when it accumulated Cenomanian (ca. 105−92 Ma) shallow-marine orbitolinid-bearing limestones (Takena Formation); these limestones are unconformably overlain by Campanian (83−78 Ma) fluvial-lacustrine deposits (Shexing Formation) after an ∼9 m.y. depositional hiatus. A prominent unconformity between the tightly folded Shexing Formation and gently tilted overlying Paleocene−Eocene Linzizong successions represents the formation of the regional Lhasaplano ca. 70 Ma, which may have been linked to the rise of an Andean-type Gangdese mountain range along the southern margin of the Lhasa terrane. Using carbonate oxygen isotope and clumped isotope thermometry data from the Shexing Formation paleosols, we quantitatively documented the rise of the Andean-type Gangdese Mountains with a peneplain surface at an elevation of 2.7 +0.5/−0.9 km above sea level prior to onset of the India-Asia collision ca. 65−63 Ma. This scenario of surface gain may have been an isostatic compensation response to the crust thickening to over 50 km during the Late Cretaceous. Subsequently, the surface isostatically rose to its near-present elevation of ∼4.6 km due to the removal of overthickened mantle lithosphere and revival of intense Gangdese magmatism by 56 Ma.

Neoproterozoic bimodal magmatism in the eastern Himalayan orogen: Tectonic implications for the Rodinia supercontinent evolution

Neoproterozoic magmatism associated with the assembly and configuration of the Rodinia supercontinent is widely distributed in the India-Himalayan terrane. However, its petrogenesis and tectonic settings remain controversial. This study provides new geochronological and geochemical data on the Neoproterozoic bimodal magmatism from the eastern Himalayan orogen. In situ zircon UPb dating revealed that the protoliths of amphibolites were emplaced at ca. 826 Ma and the granitic gneisses have crystallization ages of 825–820 Ma. The granitic gneisses exhibit geochemical features of A-type granites, with high initial (87Sr/86Sr)i ratio (0.7182–0.7394), low whole-rock εNd(t) (−8.4 to −6.6), and variable zircon εHf(t) (−7.4 to +1.0) values. They were probably generated by partial melting of the ancient lower crust with minor input of mantle components. The amphibolite samples are enriched in light rare earth elements (LREEs) and depleted in heavy rare earth elements (HREEs), suggesting an arc affinity. They have relatively high initial (87Sr/86Sr)i ratios (0.7113–0.7136), low whole-rock εNd(t) (−1.1 to 1.4) and a wide range of zircon εHf(t) (−4.1 to 8.3) values, indicating that the protoliths of amphibolites were likely generated by partial melting of an enriched subduction-modified continental lithospheric mantle. Their geochemical signatures are similar to typical back-arc basin basalts. The presence of coeval A-type granites and arc-related mafic rocks is probably due to the existence of a back-arc system. We argue that the Neoproterozoic bimodal magmatism is a product of back-arc extension initiated at an early stage, resulting from the rollback of the Mozambique Oceanic slab. Combined with previous studies on Neoproterozoic magmas from India and the Himalayas, we suggest that an extensive Neoproterozoic back-arc system may have existed along the northwestern margin of the Rodinia supercontinent. This theory supports a scenario of an Andean-type continental margin for the India-Himalayan terrane during the middle Neoproterozoic.

Early Devonian ultrapotassic magmatism in the North China Craton: geochemical and isotopic evidence for subcontinental lithospheric mantle metasomatism by subducted sediment-derived fluids

AbstractWe report new U–Pb zircon age data, zircon in situ oxygen isotope, mineral chemistry, whole-rock geochemistry and Sr–Nd isotopic compositions from the Early Devonian ultrapotassic Gucheng pluton in the North China Craton, and discuss its petrogenesis. The Gucheng pluton is exposed in the northern part of the North China Craton and forms a composite intrusion, consisting of K-feldspar-bearing clinopyroxenite, clinopyroxene-bearing syenite and alkali-feldspar syenite. Mineral phases in these lithologies include clinopyroxene (Wo43–48En19–35Fs18–38), sanidine (An0Ab3–11Or89–97), and subordinate titanite, andradite and Na-feldspar. These rocks show homogeneous Sr but variable Nd isotopic compositions, and have relatively high zircon in situ oxygen isotopes (δ18O = 5.2–6.7). The Gucheng plutonic rocks formed through fractional crystallization and accumulation from ultrapotassic magmas, which were originated from partial melting of metasomatic vein systems in the subcontinental lithospheric mantle of the North China Craton. These vein networks developed as a result of the reactions of fluids derived from subducted pelitic sediments on the downgoing Palaeo-Asian ocean floor with the enriched, subcontinental lithospheric mantle peridotites. Sensitive high-resolution ion microprobe (SHRIMP) U–Pb zircon dating has revealed a crystallization age of 415 Ma for the timing of the emplacement of the Gucheng pluton that marks the early stages of alkaline magmatism associated with the Andean-type continental margin evolution along the northern edge of the North China Craton facing the Palaeo-Asian Ocean.

The Sr–Nd–Pb–Hf Isotopic Composition of Late Paleozoic Granitoids in Central Chukotka

Results of the study of Sr–Nd–Pb–Hf isotopic composition of Late Paleozoic granitoids of Central Chukotka are represented on the example of Kibera and Kuekvun plutons. The age of granitoids of these plutons and granites from pebbles in conglomerates in the base of overlying Lower Carboniferous deposits is 351–363 Ma (U–Pb zircon, TIMS, SIMS, LA–ICP–MS). Thus, granitoid magmatism corresponds in time to tectonic events of Elsmerian orogeny in Arctic region. Sr–Nd–Pb–Hf isotopic composition of granitoids indicate participation of mantle and crustal components in the source of granite melts. Granitoids formation probably occurred in geodynamic setting of Andean type continental margin during the interaction between mantle melts, forming at the mantle wedge melting in suprasubduction conditions, and continental crust.

Slab break-off triggered lithosphere - asthenosphere interaction at a convergent margin: The Neoproterozoic bimodal magmatism in NW India

The Neoproterozoic Malani Igneous Suite (MIS) is described as the largest felsic igneous province in India. The linearly distributed Sindreth and Punagarh basins located along eastern margin of this province represent the only site of bimodal volcanism and associated clastic sediments within the MIS. The in-situ zircon U-Pb dating by LA-ICPMS reveals that the Sindreth rhyolites were erupted at 769–762Ma. Basaltic rocks from both the basins show distinct geochemical signatures that suggest an E-MORB source for Punagarh basalts (low Ti/V ratios of 40.9–28.2) and an OIB source (high Ti/V ratios of 285–47.6) for Sindreth basalts. In the absence of any evidence of notable crustal contamination, these features indicate heterogeneous mantle sources for them. The low (La/Yb)CN (9.34–2.10) and Sm/Yb (2.88–1.08) ratios of Punagarh basalts suggest a spinel facies, relatively shallow level mantle source as compared to a deeper source for Sindreth basalts, as suggested by high (La/Yb)CN (7.24–5.24) and Sm/Yb (2.79–2.13) ratios. Decompression melting of an upwelling sub-slab asthenosphere through slab window seems to be the most plausible mechanism to explain the geochemical characteristics. Besides, the associated felsic volcanics show A2-type granite signatures, such as high Y/Nb (5.97–1.55) and Yb/Ta (9.36–2.57) ratios, consistent with magma derived from continental crust that has been through a cycle of continent-continent collision or an island-arc setting. A localized extension within an overall convergent scenario is interpreted for Sindreth and Punagarh volcanics. This general convergent setting is consistent with the previously proposed Andean-type continental margin for NW Indian block, the Seychelles and Madagascar, all of which lay either at the periphery of Rodinia supercontinent or slightly off the Supercontinent.

Paleocene to Pliocene low-latitude, high-elevation basins of southern Tibet: Implications for tectonic models of India-Asia collision, Cenozoic climate, and geochemical weathering

The elevation history of the Tibetan Plateau promises insight into the mechanisms and dynamics that develop and sustain high topography over tens of millions of years. We present the first nearly continuous Cenozoic elevation history from two sedimentary basins on the southern Tibetan Plateau within the latest Cretaceous to Eocene Gangdese arc. Oxygen-isotope and Δ47 clumped-isotope compositions of nonmarine carbonates allow us to constrain carbonate formation temperature and reconstruct the paleoprecipitation record of the Eocene to Pliocene Oiyug Basin and Paleocene to Eocene Penbo Basin. We exploit the systematic decrease of surface temperature and meteoric water δ18O values with elevation to derive paleoelevation estimates for these basins. Minimally altered and unaltered pedogenic and lacustrine carbonates from the Oiyug Basin yield Δ47, CDES (relative to the carbon dioxide equilibrium scale [CDES]) values of 0.625‰ to 0.755‰, which correspond to temperatures of 1−30 °C using a Δ47 thermometer for low-temperature carbonates. Similarly, the Penbo Basin yielded Δ47, CDES values of 0.701‰ to 0.726‰, corresponding to temperatures of 6−12 °C. The apparent evidence for survival of primary clumped-isotope values in the face of substantial burial and heating is an important result for the field of carbonate clumped-isotope thermometry. Our paleoelevation estimates for the Eocene to Pliocene Oiyug Basin (∼6.5−4.1 km) support previous evidence that high elevations were attained in southern Tibet by at least ca. 30 Ma. Stable-isotope results allow for the possibility of significant topographic subsidence during the Miocene as a result of regional extension. In the Penbo Basin, our paleoelevation estimates for the Paleocene to Eocene Nianbo Formation (4.4 +1.3/−1.7 km) and Eocene Pana Formation (4.1 +1.2/−1.6 km) extend the altitude record of the southern Tibetan Plateau to pre−India-Asia collision. These results support the “Lhasaplano” model of an Andean-type continental margin tectonic system. The rise of the Himalayas and Tibet is often invoked to understand isotopic proxies for global chemical weathering in the Cenozoic and has constrained the debate on the nature of CO2−climate−weathering feedbacks. The nature of the Tibetan paleoelevations from pre- to postcollision, as presented here, indicates that high relief at low latitude prevailed on the Asian margin much earlier than previously thought. Thus, high topography alone at low latitude is not sufficient to account for the Cenozoic weathering proxy record.

Geochronological and sedimentological evidences of Panyangshan foreland basin for tectonic control on the Late Paleozoic plate marginal orogenic belt along the northern margin of the North China Craton

There is a wide support that the Inner Mongolia Palaeo-uplift on the northern margin of the North China Craton has undergone an uplifting history. However, when and how did the uplift occurred keeps controversial. Extensive field-based structural, metamorphic, geochemical, geochronological and geophysical investigations on the Inner Mongolia Palaeo-uplift, which suggested that the Inner Mongolia Palaeo-uplift was an uplifted region since the Early Precambrian or range from Late Carboniferous–Early Jurassic. The geochemical characteristics of the Late Paleozoic to Early Mesozoic intrusive rocks indicated that the Inner Mongolia Palaeo-uplift was an Andean-type continental margin that is the extensional tectonic setting. To address the spatial and temporal development of the Inner Mongolia Palaeo-uplift, we have carried out provenance analysis of Permian sedimentary rocks which collected from the Panyangshan basin along the northern margin of the North China Craton. The QFL diagram revealed a dissected arc-recycled orogenic tectonic setting. Moreover, the framework grains are abundant with feldspar (36–50%), indicating the short transport distance and unstable tectonic setting. Detrital zircon U–Pb analysis ascertained possible provenance information: the Precambrian basement (~2490 and ~1840 Ma) and continental arc magmatic action (~279 and ~295 Ma) along the northern margin of the North China Craton. The projection in rose diagrams of the mean palaeocurrent direction, revealing the SSW and SSE palaeoflow direction, also shows the provenance of the Panyangshan basin sources mainly from the Inner Mongolia Palaeo-uplift. The andesite overlying the Naobaogou Formation has yielded U–Pb age of 277.3 ± 1.4 Ma. The additional dioritic porphyry dike intruded the Naobaogou and Laowopu Formations, which has an emplacement age of 236 ± 1 Ma. The above data identify that the basin formed ranges from Early Permian to Middle Triassic (277–236 Ma). Accordingly, the Inner Mongolia Palaeo-uplift also was developed in the Early Permian to Middle Triassic (277–236 Ma), related to the final closure of the Paleo-Asian Ocean. Furthermore, we advocate that the tectonic setting of Inner Mongolia Palaeo-uplift probably belonged to the plate marginal orogenic belt during Early Permian–Middle Triassic.

Composition and geodynamic setting of Late Paleozoic magmatism of Chukotka

The paper reports the results of petrogeochemical and isotope (Sr-Nd-Pb-Hf) study of the Late Paleozoic granitoids of the Anyui–Chukotka fold system by the example of the Kibera and Kuekvun massifs. The age of the granitoids from these massifs and granite pebble from conglomerates at the base of the overlying Lower Carboniferous rocks is within 351–363 Ma (U-Pb, TIMS, SIMS, LA-MC-ICP-MS, zircon) (Katkov et al., 2013; Luchitskaya et al., 2015; Lane et al., 2015) and corresponds to the time of tectonic events of the Ellesmere orogeny in the Arctic region. It is shown that the granitoids of both the massifs and granite pebble are ascribed to the I-type granite, including their highly differentiated varieties. Sr-Nd-Pb-Hf isotope compositions of the granitoids indicate a contribution of both mantle and crustal sources in the formation of their parental melts. The granitic rocks of the Kibera and Kuekvun massifs were likely formed in an Andean-type continental margin setting, which is consistent with the inferred presence of the Late Devonian–Early Carboniferous marginal-continental magmatic arc on the southern Arctida margin (Natal’in et al., 1999). Isotope data on these rocks also support the idea that the granitoid magmatism was formed in a continental margin setting, when melts derived by a suprasubduction wedge melting interacted with continental crust.

A ca.2.1 Ga Andean-type margin built on metasomatized lithosphere in the northern Yangtze craton, China: Evidence from high-Mg basalts and andesites

We report for the first time the presence of a suite of Paleoproterozoic (2.12Ga) metamorphosed high-Mg basalts and andesites in the Huangling dome, northern Yangtze craton, China, which provide new insights into crustal growth processes in the craton during the Paleoproterozoic era. The high-Mg basalts and andesites are mineralogically and texturally amphibolites and quartz-bearing amphibolites, respectively, and occur as deformed layers within the metasedimentary rocks of the Shuiyuesi Group in the northern Huangling dome. We present new field and petrographic observations, zircon U-Pb ages, in situ zircon Hf isotope and whole-rock major and trace element and Nd isotope data, to assess the petrogenetic origin and geodynamic setting of these high-Mg rocks. The igneous zircons from the andesites yield a weighted age of ca. 2.12Ga that is interpreted to be the formation age of the magmatic protolith. The basalts are characterized by moderate SiO2 (49wt.%), low TiO2 (0.63–0.65wt.%), high MgO (13.7–14.6wt.%) and high Mg-numbers (58–59). The andesites have 53–60wt.% SiO2, 0.45–0.50wt.% TiO2 and 6.6–9.5wt.% MgO contents, yielding high Mg-numbers (63–76). Both the basalts and andesites are enriched in LILE and LREE, but depleted in Nb, Ta, and HREE. Zircons in the andesites have εHf (t) values between −0.2 and +3.3 and corresponding Hf isotopic model age (TDM1) of 2.4Ga, reflecting various degrees of crustal input. They have negative εNd (t) values, ranging from −4.4 to −2.7. Geochemical characteristics of the basalts and andesites indicate that they are equivalent to high-Mg basalts and andesites, respectively, occurring in Phanerozoic suprasubduction zones. The Nd and Hf isotope compositions of the high-Mg rocks suggest that they were derived from partial melting of subarc lithospheric mantle above a subducting oceanic slab. The formation age and general geochemical characteristics of the high-Mg rocks reveal the presence of a Paleoproterozoic (2.1–2.2Ga) Andean-type continental margin developed on metasomatized lithospheric mantle in the northern Huangling dome. The geochemical and geochronological data presented in this study provide important insights into Paleoproterozoic evolution of the Yangtze craton.

Geochronology and geochemistry of the TTG and potassic granite of the Taihua complex, Mts. Huashan: Implications for crustal evolution of the southern North China Craton

Tonalite-trondhjemite-granodiorite (TTG) suite and potassic granite volumetrically expose in the Neoarchean to Paleoproterozoic Taihua complex, Mts. Huashan region, southernmost segment of the Trans-North China Orogen (TNCO). Zircon U–Pb dating on the trondhjemite, granitic gneiss, K-feldspar granite and coarse-grained granite samples show three episodes of magmatism (2.55–2.49Ga, 2.33–2.25Ga and 1.87–1.80Ga) with distinct geochemical features in this area during the Paleoproterozoic. The trondhjemite samples have high SiO2 (67.46–71.73wt%), Na2O (4.83–5.95wt%), low Mg# (31–40) and HREE contents, with moderate (La/Yb)N values (16.8 to 35.3) and Sr/Y ratios (15.8 to 34). The potassic granite samples show high SiO2 (65.2–75.43wt%), K2O (3.9–8.6), low Na2O (1.74–4.17wt%), Mg# (2–46) and HREE contents, with moderate to high (La/Yb)N values (10.3 to 226) and Sr/Y ratios (12.8 to 208). All these granitoid samples are characterized by high SiO2 and low Mg#, Cr, Ni with moderate to high (La/Yb)N values and Sr/Y ratios. The absence of evidence of any pre-existing high Sr/Y and La/Yb sources in this region led to that the granitoids probably generated from partial melting of hydrous mafic rocks with garnet and amphibole in the residue. Therefore, partial melting of thickened lower curst is the most likely origin. Combined with previous studies, the first episodic magmatism (2.55–2.49Ga) represented by TTG and granitic gneisses with positive whole rock ƐNd(t) and zircon ƐHf(t) values is interpreted as melts from partial melting of juvenile thickened lower crust. The second episodic magmatism (2.33–2.25Ga) represented by TTG, granitic gneisses and K-feldspar granite with positive to negative whole rock ƐNd(t) and zircon ƐHf(t) values is suggested as the product of partial melting of both juvenile and pre-existing crustal material. The third episodic magmatism (1.87–1.80Ga) is represented by these potassic granites, which is synchronism with the metamorphism recorded in this region and probably resulted from partial melting of pre-existing crustal materials in a syn-orogenic or post-orogenic setting during the collision between the Eastern and Western Blocks of the North China Craton. Multistage continental accretion (at 2.84–2.72Ga, 2.57–2.43Ga and 2.36–2.25Ga) and reworking (at 2.36–2.25Ga, 2.19–2.07Ga and 1.87–1.80Ga) occurred in the southern segment of the TNCO from Neoarchean to Paleoproterozoic. Transformation from an Andean-type continental margin arc setting on the western margin of the Eastern Block to continent-arc-continent collision in the southern TNCO during Late Neoarchean to Late Paleoproterozoic is suggested in this paper.

Field relations, age, and tectonic setting of metamorphic and plutonic rocks in the Creignish Hills – North Mountain area, southwestern Cape Breton Island, Nova Scotia, Canada

The Creignish Hills and North Mountain areas of southwestern Cape Breton Island consist mostly of Neoproterozoic rocks typical of the Ganderian Bras d’Or terrane. U-Pb ages presented here for detrital zircon in the Blues Brook Formation of the Creignish Hills confirm a depositional age no greater than about 600 Ma. Although it is possible that some components of the formation are much older, similarities in rock types and field relations suggest that this is not the case. It is likely that the equivalent Malagawatch Formation of the North Mountain area, as well as high-grade metasedimentary rocks of the Melford Formation and Chuggin Road complex in the Creignish Hills and Lime Hill gneiss complex in the North Mountain area, represent the same or stratigraphically equivalent units as the Blues Brook Formation. The minimum ages of all of these units are constrained by cross-cutting syn- and post-tectonic plutons with ages mostly between 565 and 550 Ma, indicating that sediments were deposited, regionally metamorphosed, deformed, and intruded by plutons in less than 40–50 million years. The assemblage of pelitic, psammitic, and carbonate rocks indicates that a passive margin in a tropical climate was quickly changed to an active Andean-type continental margin in which voluminous calcalkaline dioritic to granitic plutons were emplaced. This sedimentary and tectonic history is characteristic of the Bras d’Or terrane and is shared by its likely correlative, the Brookville terrane in southern New Brunswick.

Hallandian 1.45 Ga high-temperature metamorphism in Baltica: P–T evolution and SIMS U–Pb zircon ages of aluminous gneisses, SW Sweden

The southernmost Baltic Shield exposes polymetamorphic continental crust that was largely formed and accreted during a series of 1.92–1.66Ga Paleoproterozoic orogenic events and later reworked during the 1.14–0.90Ga Sveconorwegian orogeny. An intermediate period of metamorphism, deformation and magmatism at 1.47–1.38Ga has been attributed to the Hallandian orogeny, but due to overprinting by Sveconorwegian high-grade metamorphism and deformation, the P–T-t evolution and deformation of the Hallandian event have remained obscure. This study presents the first quantitative P–T model of the Hallandian event using high-temperature aluminous gneisses in the south-easternmost marginal part of the Sveconorwegian orogen. The high-grade metamorphism and spatially associated granite magmatism are dated using U–Pb SIMS analysis of zircon. Petrography, bulk and mineral geochemistry, and pseudosection models demonstrate prograde staurolite-sillimanite-grade metamorphism reaching granulite-facies temperatures (700–750°C) at low pressures (4–5kbar), with the formation of Crd+Sil+Grt+K-fsp+Ilm+Melt±Bt. The rocks followed a clockwise P–T path. Later stages involved the formation of sillimanite+biotite at the expense of garnet and cordierite. Local low-temperature and fluid-assisted retrogression also caused the formation of chlorite and muscovite at the expense of cordierite. Both granite and aluminous gneisses contain complex zircon with inherited 1.70Ga igneous cores and high-U, secondary zircon, mainly formed by reworking of protolith cores. The latter date the Hallandian high-grade metamorphism at 1451±6Ma and the granite magmatism at 1445±8Ma. The presence of 1.70Ga igneous zircon cores in both metamorphic and magmatic rocks suggests that they formed from similar protoliths. The protolith ages correlate with the youngest generation of magmatic rocks of the Transscandinavian Igneous Belt. The aluminous gneisses are of supracrustal origin, and may have formed by chemical alteration of magmatic rocks. Hallandian regional metamorphism took place under a strongly elevated geotherm and was associated with granitic magmatism, suggesting an accretionary orogenic setting. The Hallandian event may demonstrate an 1.47–1.38Ga Andean-type continental margin at the SW margin of Baltica.

Early Paleoproterozoic (2.45–2.20 Ga) magmatic activity during the period of global magmatic shutdown: Implications for the crustal evolution of the southern North China Craton

A global database of zircon ages from both granitoids and detrital sediments shows an exceptional and robust age gap between 2.45 and 2.20Ga. The early Paleoproterozoic magmatism dramatically decreased on the Earth, which was proposed to relate to the global plate tectonic shutdown. However, the available data indicate that 2.45–2.20Ga magmatic rocks are widespread in the Taihua Complex during the quiet interval. The Taihua Complex is located in both the Lushan and Xiaoqinling areas along the southern segment of North China Craton (NCC). The Complex is composed mainly of a gneiss series and the Khondalite-dominated supracrustal rocks. There was an original unconformable relationship between the two rock associations. The latter occurs as a linear structural belt and was named the Khondalite Belt. The gneiss series in the Lushan area has an age of 2.85–2.72Ga, whereas the Xiaoqinling region contains widespread tonalitic–trondhjemitic–granodioritic gneisses with ages of 2.45–2.20Ga. Significant variations of Hf isotopes in zircons and whole-rock ɛNd(t) values suggest that these rocks were produced by variable mixing of a juvenile materials with older crust in an Andean-type continental margin arc or island arc setting. The depositional age of the sedimentary protoliths of the khondalite series can be roughly constrained in the period between 2300 and 1970Ma. It has been considered that they were deposited in a stable continental margin environment. The U–Pb dating of metamorphic zircons from the Taihua Complex suggest that the southern NCC underwent a polyphase tectonic evolution during the period 1.97–1.82Ga, and the peak metamorphism coeval with crustal thickening has occurred at ∼1.94Ga.

Metagabbros of the Gangdese arc root, south Tibet: Implications for the growth of continental crust

The Gangdese batholith of the southern Tibet is regarded as a principal component of the pre-Himalayan collision, Andean-type continental margin. However, the Gangdese arc root remains poorly understood because most of previous studies concentrated on granitoids from the middle and upper crust of the arc. In this paper, we report new petrochemical and geochronological characteristics of metagabbros occurred as a part of the Late Cretaceous Lilong batholith in the eastern Gangdese arc. The gabbros with protolith ages of ∼82–95Ma, underwent slightly late (68–77Ma) granulite-facies metamorphism and nearly coeval anatexis, typical of lower arc crusts. The metagabbros and diorites of the Lilong batholith show geochemical features of juvenile crust in continental magmatic arcs, and an original magmatic differentiation trend, with gabbros formed as the cumulates, whereas diorites as the crystalline products of evolved magmas. The Lilong batholith forms an arc crustal section with a possible thickness of 20–30km, and may have an overall andesitic composition, providing a support for the “andesite model” of continental crust growth.

The Laurentian Caledonides of Scotland and Ireland

Abstract The Caledonides of Britain and Ireland are one of the most intensively studied orogenic belts in the world. This review considers all the tectonic events associated with the development and closure of the Iapetus Ocean. It first summarizes the tectonic evolution of each segment involved in the Scottish–Irish sector of the Caledonides and then reviews the temporal evolution of the Caledonian Orogeny. Three main tectonic phases are recognized in the Scottish–Irish Caledonides: an Early–Middle Ordovician (475–465 Ma) phase termed the Grampian Orogeny; a phase of Silurian (435–425 Ma) tectonism restricted to the Northern Highland Terrane of Scotland termed the Scandian Orogeny; and an Early Devonian (395 Ma) phase termed the Acadian Orogeny. The Grampian Orogeny was caused by the collision of the Laurentian continental margin with an oceanic arc terrane and associated suprasubduction zone ophiolites during the latest Cambrian–Early Ordovician. Following the Grampian arc–continent collision event, there was a subduction polarity reversal. This facilitated continued subduction of Iapetan oceanic lithosphere and an Andean-type continental margin developed on and adjacent to the Laurentian margin in the Middle Ordovician along with a substantial thickness of accretionary prism sediments (the Southern Uplands–Longford Down Terrane). The Iapetus Ocean is believed to have disappeared by the Late Silurian based on the faunal record and a continent–continent collision ensued. The absence of significant regional deformation and metamorphism associated with the Late Silurian collision between Avalonia and the Scottish–Irish margin of Laurentia suggests that the continental collision in this sector of the Caledonian–Appalachian orogen was ‘soft’ or highly oblique. The exception is the Northern Highlands Terrane of Scotland that was believed to have been situated 500–700 km to the north along orogenic strike. This terrane records evidence for significant Silurian regional deformation and metamorphism attributed to the collision of the Laurentian margin of East Greenland with Baltica (the Scandian Orogeny). Current controversies in the Laurentian Caledonides of Scotland and Ireland are discussed at the end of this review.

Precambrian geology of China

Precambrian geology of China

Late Mesozoic–Cenozoic evolution of the Sanjiang Basin in NE China and its tectonic implications for the West Pacific continental margin

This study uses new seismic reflection profiles and exploratory well data to analyze the structural characteristics and evolution of the Sanjiang Basin in eastern Heilongjiang, NE China. The basin sequence was divided into six stratigraphic units, representing discrete Middle-Upper Jurassic, Lower Cretaceous, Upper Cretaceous, Eocene–Oligocene, Miocene and Quaternary phases of development. The Sanjiang Basin initiated as a passive marginal rift flank to the southern Mongol–Okhotsk Ocean during the Middle Jurassic, and primary basin growth was terminated by orogenic deformation related to the Mongol–Okhotsk suture to the north and the accretion of the Nadanhada terrane to the east. Middle-Upper Jurassic strata are controlled by half-graben structures active during this phase of basin growth, and are limited largely to the west Suibin sub-basin. The wider basin experienced renewed rifting and large-scale sag caused by back arc extension along the Eurasian continental margin in the Early Cretaceous, terminating during the Late Cretaceous in a phase of intense compression at the contemporary Andean-type continental margin. This produced a series of thrust-folds through the Lower and Upper Cretaceous successions, and led to the development of a regional-scale erosional unconformity. Minor subsequent Cenozoic extension is attributed to back-arc extension along the West Pacific continental margin, with Eocene–Oligocene, Miocene, and Quaternary deposits unconformably overlying the Mesozoic sequences in half-graben and extensional fault-demarcated depocenters, most prominently in the east Qianjin sub-basin.