Arc-continent Collision Research Articles

Concurrent MORB-type and ultrapotassic volcanism in an extensional basin along the Laurentian Iapetus margin: Tectonomagmatic response to Ordovician arc-continent collision and subduction polarity flip

Arc-continent collision, followed by subduction polarity flip, occurs during closure of oceanic basins and contributes to the growth of continental crust. Such a setting may lead to a highly unusual association of ultrapotassic and mid-ocean ridge basalt (MORB)-type volcanic rocks as documented here from an Ordovician succession of the Scandinavian Caledonides. Interbedded with deep-marine turbidites, pillow basalts evolve from depleted-MORB (εNdt 9.4) to enriched-MORB (εNdt 4.8) stratigraphically upward, reflecting increasingly deeper melting of asthenospheric mantle. Intercalated intermediate to felsic lava and pyroclastic units, dated at ca. 474−469 Ma, are extremely enriched in incompatible trace elements (e.g., Th) and have low εNdt (−8.0 to −6.6) and high Sri (0.7089−0.7175). These are interpreted as ultrapotassic magmas derived from lithospheric mantle domains metasomatized by late Paleoproterozoic to Neoproterozoic crust-derived material (isotopic model ages 1.7−1.3 Ga). Detrital zircon spectra reveal a composite source for the interbedded turbidites, including Archean, Paleo-, to Neoproterozoic, and Cambro-Ordovician elements; clasts of Hølonda Porphyrite provide a link to the Hølonda terrane of Laurentian affinity. The entire volcano-sedimentary succession is interpreted to have formed in a rift basin that opened along the Laurentian margin as a result of slab rollback subsequent to arc-continent collision, ophiolite obduction and subduction polarity flip. The association of MORBs and ultrapotassic rocks is apparently a unique feature along the Caledonian-Appalachian orogen. Near-analogous modern settings include northern Taiwan and the Tyrrhenian region of the Mediterranean, but other examples of strictly concurrent MORB and ultrapotassic volcanism remain to be documented.

Early Neoproterozoic tectonic evolution of northern Yangtze Block: Insights from sedimentary sequences from the Dahongshan area

Precambrian sedimentary strata are widely distributed along the periphery of the Yangtze Block. However, the age, provenance and tectonic setting of the sedimentary successions on the northern margin still remain unclear, which exerted considerable influence on the understanding of Precambrian crustal evolution of the Yangtze Block. Here we report integrated detrital zircon U-Pb dates and Lu-Hf isotopes from the Dahongshan area to the northeast of the nuclei (i.e. the Kongling Complex) of the Yangtze Block. The youngest U-Pb dates of 995 Ma and 810 Ma of detrital zircon grains place constraints on the maximum depositional ages of the underlying Dagushi Group and the overlying Huashan Group, respectively. Both groups show pre-Mesoproterozoic age populations at ca. 2050 Ma and ca. 2700 Ma and corresponding εHf(t) values varying from –24.1 to + 2.3, consistent with counterparts of the Kongling Complex and Yangpo Complex in northern Yangtze Block. The εHf(t) values of Neoproterozoic (1000–800 Ma) detrital zircon grains in the Huashan Group show a decrease after ca. 880 Ma (from + 13.5 to –18.5), possibly indicating a transition from arc-continent collision to continental arc setting on the northern margin of the Yangtze Block. In combination with sedimentary characteristics and the new isotopic results, the Dagushi Group probably formed in a shallow marine basin setting and received dominant detritus from the Kongling and Yangpo complexes. In contrast, the Huashan Group received sediments recycled from the underlying Dagushi Group and contemporary igneous rocks in the Dahongshan and Kongling areas. The changes in provenance and tectonic setting recorded in the two sedimentary sequences suggest a tectonic transition from late Mesoproterozoic passive continental margin to Neoproterozoic subduction and accretion in response to the amalgamation of Rodinia supercontinent. On the basis of distinct location and history, Pre-Nanhua Neoproterozoic sedimentary sequences distributed in the periphery of Yangtze Block are dispersed into four separate domains. Through bivariate kernel density estimates and bootstrap resampling method, we have identified that these domains were characterized by asynchronous igneous impulse and heterogeneous character of igneous activity in early Neoproterozoic along with varying degrees of integration of crustal growth and reworking.

Tectonic and climatic controls on the Plio-Pleistocene evolution of sediment discharge from Papua New Guinea

This study presents a detailed sedimentary geochemical record of International Ocean Discovery Program (IODP) Site U1489, which was drilled off the northeast margin of Papua New Guinea (PNG). Focusing on the geochemical characteristics and the extent of chemical weathering of siliciclastic component, a total of 183 samples from the upper 84 m of Site U1489 are used to reconstruct the PNG sediment supplies to the tropical western Pacific over the last 4 Ma. Our geochemical results show a 3-stage variability in Site U1489 sediment composition, which are well related to regional tectonic and climatic changes. Stages III (~4.0–3.5 Ma) and II-A (~2.9–1.7 Ma) are characterized by more enhanced and variable contributions from mafic-rock sources than that of felsic-origin. This interval is shown to be accompanied by relatively rapid sediment delivery and more dynamic depositional environments that are possibly related to marginal mixing, coinciding with more frequent PNG tectonic events. In particular, increased contributions derived from ultra-mafic/mafic rocks are recorded between ~3.5 and 2.9 Ma, which is attributed to increased ophiolite input due to arc-continent collision. Accordingly, these results give a consistent but refined timing for an accelerated plate suturing at the eastern margin of PNG. By contrast, Stage I (~1.7–0 Ma) is characterized by a relatively constant background supply of finer particles, showing a persistent increase over time in the intensity of chemical weathering. This increased weathering trend is reported for the first time for the tropical regions of western Pacific, and it is interpreted as indicating a strengthening of the Walker Circulation in the past ~1.7 Ma. Overall, the interpretations of the siliciclastic fraction from Site U1489 presented in this paper provides crucial clues to distinguish the tectonic and climatic influences on the PNG sediment inputs during the Plio-Pleistocene.

Review on geology and mineralization of North Korea (I: Precambrian)

AbstractIn this review, we introduce the geology and mineralization of the northern part of the Korean Peninsula based on recently published data in North Korea. Geological characteristics and events are described in order of geological period and the representative mineral deposits are presented according to the geologic period to show the relationship between the geology and mineralization. In particular, we rearrange the stratigraphy of the Precambrian basement and reset the timing of intrusion and mineralization based mainly on the reported zircon U–Pb age data. The Precambrian geotectonic provinces of North Korea contain continental cores and massifs, active continental margins, and rift zones. The Precambrian strata between the eastern North China Craton (NCC) and North Korea are newly correlated considering rearranged stratigraphy in this review. The Precambrian strata of North Korea are characterized by the depletion of the Paleoproterozoic to Mesoproterozoic strata compared to the NCC from 1.8 to 1.5 Ga. It may indicate that the northern part of the Korean Peninsula was the passive continental margin environment during this period. The common occurrences of bimodal igneous suites (mafic‐felsic and alkaline‐subalkaline) are also characteristic of North Korea. The bimodal magmatism is well explained by the progressive tectonic evolution from oceanic crust‐continent subduction (2.0–2.2 Ga) and island arc–continent collision (~1.9 Ga) to post collisional extension (1.82–1.87 Ga) in the NCC including North Korea. The Precambrian geological similarities between Northeastern China and North Korea would have resulted in the same or similar mineralization. For example, Algoma type banded iron formations of the Fe deposits of the Anshan–Benxi area in China and Musan Fe deposit in North Korea were formed during the Neoarchean and Paleoproterozoic. Sedimentary exhalative type Pb–Zn and metasedimentary type magnesite deposits were formed within the Jiao‐Liao‐Ji belt extending from the Liaoning Rift Zone of China (Pb–Zn deposits in the Qingchenzi orefield and magnesite deposits in Dashiqiao magnesite belt) to the Macheollyeong Rift Zone of North Korea (Geomdeok Pb–Zn deposit and Daeheung–Ryongyang magnesite deposits) during Paleoproterozoic. The geotectonic, geological and metallogenic similarities between Northeastern China and North Korea indicate that the Precambrian continental massifs of North Korea might be evolved in accordance with the NCC evolution. This review is expected to be helpful for understanding the geotectonics, geology, and related mineralization of the northern part of Korean Peninsula and correlating with those of the NCC.

Variable vertical movements and their deformation behaviors at convergent plate suture: 14-year-long (2004–2018) repeated measurements of precise leveling around middle Longitudinal Valley in eastern Taiwan

• We provide 14-year-long leveling results across plate suture of Philippine Sea and Eurasia. • Along the LVF, shallow locked in north, and rapid creeping without locking in south. • The leveling data imply blind slip on the deeper part of the Central Range fault. • Active creeping occurs on a nearly vertical contact along the Chimei fault. To better characterize the vertical movements and the deformation behaviors across the plate suture of an arc-continent collision, we conducted annual repeated measurements on two precise leveling routes in a length of 34 and 37 km, respectively, across the middle part of the Longitudinal Valley in eastern Taiwan in 2004–2018. The 14-year-long results showed that the Longitudinal Valley fault (LVF) dominates the surface deformation: a) the middle LVF (Juisui fault) exhibited partially locked in the upper few kilometers, with a cumulative uplift rate of 9–10 mm/yr in a distance of 4 km; b) the southern LVF (Chihshang fault) showed a creeping behavior with a vertical rate of 24–27 mm/yr. In addition, we are able to characterize other features, including 1) tilting upward to the west in the eastern Central Range, suggesting activity on the west-dipping Central Range fault; 2) the hanging wall of the LVF showed tilting downward behavior to the east; 3) the Chimei fault, a suspected active fault, revealed active slip on the sub-vertical fault plane, that caused a vertical rate of 8–9 mm/yr. Putting the results under global ITRF system, the whole Juisui route was moving downward, supporting the notion that NNW subduction of the Philippine Sea plate starts around the latitude of the middle of the Longitudinal Valley. Finally, the co-seismic vertical deformation of the 2013 M L 6.4 Juisui earthquake was characterized by tilting upward to the west, consistent with stick–slip on the deeper part of a west-dipping interface of the forearc basement.

Geochemical classification of Palaeoproterozoic oceanic volcanic front and backarc basin remnants of the Granites-Tanami Orogen, Australia

The Granites-Tanami Orogen (GTO) is a lower-greenschist to amphibolite facies succession of >1840 Ma backarc basalts and volcaniclastic-sedimentary rocks that was metamorphosed (~1850–1840 Ma), and later intruded by granites and granodiorites (~1825–1791 Ma) during assembly of the Kimberley Craton, proto-Northern Australia Craton, and the Arunta Region.The data presented here show geochronological, sedimentological, petrographic, and geochemical evidence for the existence of a volcanic arc (‘Tanami Arc’) in the GTO at ~1912 Ma. Furthermore, the combination of volcanic structures, including fiamme and hyaloclastites, and a mafic HFSE geochemical signature of the pyroclastic and volcaniclastic-sedimentary turbidite successions suggests a syndepositional volcanic front within an oceanic arc-backarc system during deposition of the Dead Bullock Formation (and equivalents). Geochemical vectors applied to existing stratigraphic interpretations indicate a trend towards more felsic composition with younging, providing an alternative proxy for relative stratigraphy and a tool for exploration and correlation across the GTO. The localisation of the volcanic arc within the N-NNE dipping arc-continent collision zone has important implications for the debated Palaeoproterozoic amalgamation of the North Australia Craton.

Global chemical weathering dominated by continental arcs since the mid-Palaeozoic

Earth’s plate-tectonic activity regulates the carbon cycle and, hence, climate, via volcanic outgassing and silicate-rock weathering. Mountain building, arc–continent collisions and clustering of continents in the tropics have all been invoked as controlling the weathering flux, with arcs also acting as a major contributor of carbon dioxide to the atmosphere. However, these processes have largely been considered in isolation when in reality they are all tightly coupled. To properly account for interactions among these processes, and the inherent multi-million-year time lags at play in the Earth system, we need to characterize their complex interdependencies. Here we analyse these interdependencies over the past 400 million years using a Bayesian network to identify primary relationships, time lags and drivers of the global chemical weathering signal. We find that the length of continental volcanic arcs—the fastest-eroding surface features on Earth—exerts the strongest control on global chemical weathering fluxes. We propose that the rapid drawdown of carbon dioxide tied to arc weathering stabilizes surface temperatures over geological time, contrary to the widely held view that this stability is achieved mainly by a delicate balance between weathering of the seafloor and the continental interiors.

Ocean Plate Stratigraphy of a long-lived Precambrian subduction-accretion system: The Wutai Complex, North China Craton

Ocean Plate Stratigraphy (OPS) is the travelogue of the oceanic lithosphere from its birth at the Mid Ocean Ridge to its demise at the subduction zone in convergent plate margins. Here we present an OPS succession preserved onland in the Wutai Complex of the North China Craton (NCC), representing a prolonged subduction-accretion-collision system and continental growth during the Neoarchean-Paleoproterozoic. The OPS succession in Wutai includes metabasalts and banded iron formation representing the pelagic sequences together with intercalated metacarbonates. Phyllite, greenschist, and mica schist represent the hemipelagic sequence. Quartzite and conglomerate correspond to the turbidite sequence, with a progressive southward accretion towards a magmatic arc in the north. We present results from petrological, geochemical, zircon U-Pb, REE, and Lu-Hf studies from representative rocks in the OPS sequence of the Wutai Complex. The trace elements including the rare-earth element (REE) data of the metabasalt show transitional features between normal mid-ocean ridge basalt (N-MORB) and enriched mid-ocean ridge basalt (E-MORB). The REY (lanthanide elements and Y) data of the banded iron formation (BIF), greenschists, and phyllite suggest the interaction of high-temperature hydrothermal fluids and seawater. Magmatic zircon grains from the quartzite show 206Pb/207Pb upper intercept age of 2443 ± 21 Ma, whereas zircon grains in the phyllite show upper intercept age of 2494 ± 32 Ma, with minor xenocrysts with older ages of 2726 ± 46 Ma and 2672 ± 48 Ma. Zircon grains in the metaconglomerate show upper intercept age of 2569 ± 32 Ma. Those from the siliceous and intercalated bands in the BIF yield upper intercept ages of 2583 ± 34 Ma and 2524 ± 49 Ma. The zircon Lu-Hf data on zircon grains from the BIF, phyllite, quartzite, and metaconglomerate all show positive εHf(t) values (+1.3 to +7.4) in the range of depleted mantle to new crust, suggesting Neoarchean intra oceanic arc subduction. Combined with the zircon U-Pb and Hf isotopic data previously reported from the Wutai Complex, we infer the following four tectonic evolution stages: ca. 2800 Ma subduction initiation, ca. 2750–2300 Ma arc-accretionary complex, ca. 2300–2100 Ma back-arc rifting, and ca.1900–1750 Ma arc-continent collision. The metavolcanics and part of the metasedimentary rock assemblages in the Wutai Complex represent a deformed and dismembered OPS sequence generated through northward subduction and closure of the Wutai Ocean.

Arc-related peridotite blocks exhumed to the Eastern Block of the North China Craton prior to 2.47 Ga

AbstractThe Songling and Majiayu peridotite blocks occur in the Eastern Block, North China Craton (NCC). Geothermobarometry data show that the Songling peridotites began exhumation from a depth of c. 70 km (c. 23 kbar). During exhumation, the Songling peridotites were intruded by an upper-crust-derived, high-δ18O (up to +7.28‰ in zircon) trondhjemitic dyke at 2.47 Ga and experienced granulite-facies metamorphism. The Songling peridotites have hybrid mantle wedge (HMW) -like high SiO2 (> 45 wt%), high FeOt (c. 10 wt%) content, high modal orthopyroxene abundance (> 35%) and high ϵNd(t) (+18.4 to +21.4), which were generated by the reaction between peridotite and eclogite-derived melts. The clinopyroxenes from the Songling peridotites were in equilibrium with a Nb-, Zr- and Ti-depleted arc-like magma. The Majiayu peridotites are characterized by depletion of Nb, Zr and Hf and are highly enriched in FeOt, Th and light rare earth elements (LREEs), which can be interpreted as an open system reaction between hydrous melts and fore-arc mantle peridotites. These two peridotite blocks are considered to be arc-related mantle peridotites that experienced melt extraction and metasomatism in different styles. They were exhumed to the north margin of the North China Craton during the c. 2.47 Ga arc–continent collision along the Zunhua structural belt.

Middle–late Permian high-K adakitic granitoids in the NE Alxa block, northern China: Orogenic record following the closure of a Paleo-Asian oceanic branch?

How and when the Paleo-Asian Ocean was finally closed still is a hot topic open to debate. Here we presented geochronological (laser ablation inductively coupled plasma mass spectrometry, LA–ICP–MS, and 40Ar/39Ar), geochemical, and Sr–Nd–Hf isotopic data for the granitoids from the NE Alxa block in the southern margin of the Central Asian Orogen Belt, northern China, in an attempt to constrain the closure of the Paleo-Asian oceanic branch in this region. These granitoids were dated at 268–255 Ma. They show distinct adakitic signatures of high Sr/Y (19–100) and (La/Yb)N (13–50) ratios, and low Y (3.98–16.50 ppm) and Yb (0.24–1.46 ppm) concentrations. They are also characterized by relatively high K2O/Na2O ratios (0.7–1.37), and low MgO (0.22–0.75 wt%), Cr (1.41–9.96 ppm), and Ni (0.36–6.31 ppm) contents and variable Mg# values (26–50). In addition, they display negative εHf(t) (−16.46 to −7.48) and εNd(t) (−14.2 to −9.83) and high (87Sr/86Sr)i (0.7072–0.7196) and Th (7.33–14.10 ppm), indicating that they were most likely generated by partial melting of thickened continental lower crust up to ~59 km thick. This thickened crust was built on the early Permian transitional Alxa crust (~32 km thick), likely caused by the rifting related to the upwelling of mantle plume. Consequently, the NE Alxa block could have witnessed a tectonic transition during the mid-Permian from rifting to arc–continent collision and resultant crustal thickening following the closure of the Paleo-Asian oceanic branch. The subsequent upwelling of asthenosphere in response to the delamination of the orogen during the middle–late Permian provided thermal source for the adakitic magmatism.

Syn-tectonic Dipilto batholith (NW Nicaragua) linked to arc-continent collision: High- and room-temperature AMS evidence

The northern Central America region (Honduras and Nicaragua) is characterized by geotectonic units delimited by strike-slip fault systems and shortening zones of poorly constrained ages. The eastern portion of the Chortís block, named the “Dipilto micro-block” or “Patuca” is one of these units that besides with the Siuna Serpentinite Mélange, provides evidence for Early Cretaceous arc-continent collision. Nevertheless, within the Dipilto micro-block is the Early Cretaceous Dipilto batholith (NW Nicaragua), an Ilmenite-Series granitoid suites whose emplacement tectonic setting is unknown.We document the room- and high-temperature anisotropy of magnetic susceptibility (RT-AMS and HT-AMS) and hysteresis cycles from 31 sites in the Dipilto batholith and cross-cutting dikes as well as the oxide mineral microscopy of main lithologies. This is to investigate the magmatic fabric in the granitoids and dikes, and the relation to the emplacement dynamics. The RT-AMS and HT-AMS results show magnetic lineation and foliation (Kmax and Kmax–Kint plane) dominated by paramagnetic minerals (biotite and hornblende). The central parts of the intrusion show a NE-SW Kmax distribution and sites near to boundary of the country-rock a Kmax–Kint plane sub-parallel to the contact. These results and previous structural data in the surrounding Nueva Segovia Schist country-rock support an intrusion emplaced in a contractional setting concurrent with the batholith's NE-SW regional geometry. The Dipilto batholith age (119–112 Ma) implies a syn-collisional origin that together with our results indicate an Early Cretaceous progressive shortening in the region associated with the Siuna Intraoceanic Arc collision (~134–113 Ma). Furthermore, they indicate that the shortening azimuth (i.e., the direction of tectonic transport) is ~127°–137° in its current geographical position, but was 227°–237° in its Early Cretaceous paleo-position, probably related to the final stage of shortening and collision events of the southwestern Mexican paleocontinent.

Meso-Neoproterozoic arc-related sediments of the Xiahe Group in the Qinling block, central China: Implications for the paleogeographic reconstruction of Rodinia

The Meso-Neoproterozoic Rodinia supercontinent formed a coherent large landmass, which was later dispersed over all current major continents and a number of microcontinents. The Qinling block is a Precambrian continental mass, located in the Qinling orogenic belt, which marks the junction of the North China and South China cratons. In this paper, we present a systematic study of the petrology, whole-rock geochemistry and geochronology of metasedimentary rocks from the Xiahe Group, which is a key unit of the Precambrian basement in the Qinling block, to constrain the paleogeographic reconstruction of Rodinia. The studied metasedimentary rocks have detrital zircon ages of 3054–1082 Ma that peak at 1172 Ma and 1582 Ma. The protoliths of the metasedimentary rocks are mainly shales and wackes with maximum depositional ages from 1147 to 1082 Ma, representing a part of a continental arc-related sedimentary sequence. Combining our results with existing data, we propose that their protoliths constituted a sedimentary series including an older sequence of basement and a younger sequence with depositional ages between 1262 and 840 Ma. The detritus that is older than 1266 Ma was sourced from the continental margin of the Indian craton, which was part of the Columbia supercontinent. There was a Paleo-Mesoproterozoic continental nucleus in the Qinling block that split from the margin of the Indian craton during the breakup of Columbia. The source rocks for the younger detritus were arc magmatic rocks in the Qinling block, which formed in a continental arc by oceanic lithosphere subduction during the assembly of Rodinia. A sequence of oceanic subduction beneath the continental nucleus of the Qinling block (1262–981 Ma), arc-continent collision between the continental nucleus and the Indian craton (981–911 Ma), continuous subduction of oceanic crust beneath the block with formation of a mature volcanic arc (929–833 Ma), and continental rifting (833–774 Ma) during the formation of the Qinling block was identified. The block faced the Neoproterozoic ocean during the assembly of Rodinia, and finally rifted off the supercontinent during its breakup to form an isolated arc terrane

Timing and magnitude of progressive exhumation and deformation associated with Eocene arc-continent collision in the NE Caribbean plate

Abstract Puerto Rico and the northern Virgin Islands together preserve a unique archive of island arc construction and plate margin deformation along the northeastern edge of the Caribbean plate. In Eocene times, arc-continent collision of the Caribbean plate and the North American plate led to transpressional deformation along two major fault systems in Puerto Rico, resulting in an island-wide depositional hiatus. Although styles and kinematics of this deformational event are seemingly well understood, the lack of chronologic constraints have left uncertainties related to the timing of inception and activity, the magnitude of crustal exhumation, and the character of deformation (i.e., progressive or polyphase). New zircon and apatite (U-Th)/He ages reveal that deformation associated with arc-continent collision started in the early Eocene (ca. 52 Ma) and ended in the early Oligocene (ca. 29 Ma). Over this 23 m.y. time frame, deformation was not restricted to major faults, instead it propagated gradually eastward, with punctuated episodes of vertical exhumation in the early Eocene (ca. 52–34 Ma) and late Eocene (ca. 36–29 Ma). In contrast, the northern Virgin Islands experienced rapid cooling and exhumation in the early Miocene (ca. 24–21 Ma) associated with the extensional opening of the Anegada Passage. The modeled thermal histories for the central and northeastern part of Puerto Rico indicate collision-related peak transpressional deformation between 36 and 29 Ma and an average exhumation rate 0.9 ± 0.6 km/m.y. These results represent the first direct constraints on the timing and magnitude of collisional exhumation and offer insights into the deformational evolution of the northeastern edge of the Caribbean plate.

From arc-continent collision to ocean closure: Lower Cretaceous Shamuluo Formation in the western segment of the Bangong–Nujiang suture zone, central Tibet

One of most hotly debated topics concerning the Late Mesozoic evolution of Tethyan and the Tibetan Plateau is the timing of the closure of the Meso-Tethys ocean, which is represented by the Bangong–Nujiang suture zone. The Upper Jurassic–Lower Cretaceous Shamuluo Formation, which unconformably overlies the older Mugagangri Group accretionary complex, provides important information on the closure of the Meso-Tethys Ocean. This paper precisely confines the depositional age of the Shamuluo Formation in the western segment of the Bangong–Nujiang suture zone, extending it from the Late Jurassic to the Albian. Combined with the results of previous studies, we suggest that the Shamuluo Formation in the Awengco–Baerqiong region mainly contains a bathyal Berriasian–Hauterivian subunit and a shallow-marine Albian subunit. Provenance analysis indicates that the Berriasian–Hauterivian subunit was mainly derived from the Jurassic southern Qiangtang magmatic arc, while the Albian subunit was derived from the coeval volcanic rocks and the Upper Carboniferous–Upper Permian strata in the southern Qiangtang terrane. Thus, the two subunits of the Shamuluo Formation have significant distinct sedimentary facies and provenances, indicating that they were deposited in different tectonic settings. Based on the regional geological data, we suggest that the bathyal Berriasian–Hauterivian subunit and the shallow-marine Albian subunit of the Shamuluo Formation should be interpreted as a record of the oceanic arc-continent collision and the Lhasa–Qiangtang soft-collision, respectively. Thus, the closure time of the Meso-Tethys Ocean is at least limited to the Albian.

Geochronology and petrogenesis of the TTG gneisses and granitoids from the Central Bundelkhand granite-greenstone terrane, Bundelkhand Craton, India: Implications for Archean crustal evolution and cratonization

In this contribution we present field relations, U-Pb zircon geochronology, in-situ Lu-Hf isotopes, bulk-rock Sm-Nd isotopes and geochemistry of the tonalite-trondhjemite-granodiorite (TTG) gneiss, sanukitoid and anatectic granites from the Central Bundelkhand granite-greenstone terrane (CBGGT). The present study provides a comprehensive insight into the crust-mantle evolution, reworking, and cratonization of the Bundelkhand Craton (BC) during the Archean Eon. We report two discrete episodes of Neoarchean TTG magmatism at ~ 2.71 and ~ 2.68 Ga from the BC for the first time. Additionally, we identify a TTG gneiss that is significantly older (~3.34 Ga) than thus far assumed in the eastern part of the area. Furthermore, zircon U-Pb ages of the sanukitoids and the anatectic granites suggest synchronous emplacement at 2.58–2.50 Ga. Zircon of Paleoarchean TTG, Neoarchean TTG, sanukitoid, and anatectic granites show εHf(t) values in the following ranges: +1.7 to −0.9, +4.1 to −10.7, −3.6 to −6.2, and −5.9 to −7.8, respectively, which are indicative of significant crustal reworking. Neoarchean TTG gneiss shows εNd(t) and εHf(t) value of + 4.5 and + 10.0 to −6.8, respectively, indicating a juvenile crustal source and probably formed by the partial melting of deep-seated mafic crust in the garnet stability field. Neoarchean TTGs formed in arc creation/collision to the Paleoarchean nucleus of the BC. The amalgamation of diverse micro-blocks occurred by the arc-continent collision and probable breakoff of the descending slab between crustal blocks of the BC during Neoarchean. This event generated anatectic granites by intense partial melting of the existing crust, which resulted as closing of subduction and marked as final stabilization and cratonization of the BC. This event also shows evidence that the BC did not amalgamate until ~2.50 Ga.

Polygenetic mélange in the retrowedge foredeep of an active arc-continent collision, Coastal Range of eastern Taiwan

The Plio-Pleistocene Lichi Mélange in the Coastal Range of eastern Taiwan offers an excellent opportunity to study processes of mélange development at the continent-ocean interface of an active arc-continent collision. This paper presents new results of detailed geologic mapping, lithofacies analysis, magneto-biostratigraphy, paleocurrent, and paleoslope analyses in the southern Coastal Range to investigate the origins and significance of this mélange. The results show that the Lichi Mélange consists of mass-transport deposits including well-stratified block-in-matrix beds (olistostromes), extra-formational blocks (olistoliths), and broken formation with abundant soft-sediment deformation features that transition laterally into distal mega-slump beds and pebbly mudstones (subaqueous debrites). Abundant observations of depositional contacts and interbedding of mélange with contemporary (ca. 4–1 Ma) flysch units of the Fanshuliao and Paliwan formations confirm their sedimentary origin. Compacted sedimentological shear fabrics in olistostromal facies are broadly parallel to internal stratification and bedding, and are readily distinguishable from cross-cutting brittle fault zones related to post ~1 Ma west-vergent thrust faults. Paleoslope and paleocurrent analyses record down-slope gravity-driven transport toward the east and southeast.The data provide evidence for a polygenetic origin of the Lichi Mélange, in which sedimentary mass-wasting deposits are overprinted by younger tectonic shear zones. Slide blocks, conglomerate clasts, and detrital sand were all derived from an eroding source in the east-vergent eastern retrowedge of the Taiwan collisional orogen. The source area included tectonically accreted fragments of the two converging plates that represent shallow-crustal equivalents of the Miocene Yuli Belt and Eastern Slates exposed in the modern Central Range. Reconstructed stratigraphic panels record eastward progradation of olistostromal facies over distal basinal flysch deposits, which we infer resulted from eastward (oceanward) migration of a steep submarine slope at the leading edge of the retrowedge orogenic front. Thus, the Coastal Range basin evolved as a migrating retro-foredeep basin that formed on top of older, pre-collisional volcanic arc and forearc crust. These results demonstrate a unique type of sedimentary basin that is formed and then rapidly inverted at a convergent continent-ocean interface during the transition from intra-oceanic subduction to arc-continent collision. This revised history of the Lichi Mélange provides a new perspective on the dynamics of rapid crustal mixing and tectonic recycling at the convergent suture of an active arc-continent collision system.

Remarkably fresh abyssal peridotites from Sibuyan island, Romblon Island Group, Philippines: Markers of young arc-continent collision

The bulk of Sibuyan island in the Romblon Island Group, Philippines is underlain by remarkably fresh spinel lherzolites, harzburgites and dunites collectively called as the Sibuyan Ultramafics. Based on petrographic and geochemical characteristics, the Sibuyan Ultramafics can be classified into: (1) Group I peridotites composed of spinel lherzolites and harzburgites with spinel Cr# < 0.35, (2) Group II harzburgites and dunites with intermediate spinel Cr# = 0.40–0.65, and (3) Group III dunites with very high spinel Cr# (>0.75). Increase in spinel Cr# is accompanied by decreasing Al2O3 contents and increasing Mg# in the pyroxenes from the Group I to Group II and Group III peridotites. Chondrite-normalized clinopyroxene data revealed various trace-element patterns for the three groups suggestive of different processes (e.g. anhydrous and hydrous melting, mantle-melt interaction) involved in their formation. The Sibuyan Ultramafics is closely associated with the similarly fresh Calaton Hill metamorphic/plutonic complex in Tablas island which is thought to be representative of the lower crust of the Philippine island arc. At a more regional context, the Sibuyan Ultramafics and the Calaton Hill metamorphic/plutonic complex can be used as markers for the young arc-continent collision in western Philippines. Rapid uplift and emplacement due to the collision of the Philippine Mobile Belt and the Palawan Microcontinental Block during the Miocene or even later may have led to the remarkably fresh state of these lithologies. This occurrence is similar to the Horoman peridotite complex in the Hidaka metamorphic belt in Northern Japan. The Sibuyan Ultramafics and the Calaton Hill metamorphic/plutonic complex therefore provide a rare and fresh glimpse into the upper mantle and lower crust in the Philippines due to their young ages of emplacement.

The mid-Cretaceous Peninsular Ranges orogeny: a new slant on Cordilleran tectonics? I: Mexico to Nevada

The Peninsular Ranges orogeny occurred during the mid-Cretaceous at ∼100 Ma and affected rocks from southern Mexico to Alaska. The event resulted from the closing of an Early Cretaceous marine arc trough, named the Bisbee–Arperos seaway in Mexico and Arizona, and the Cinko Lake arc trough in the Sierra Nevada. The trough was an ocean that formed after the Late Jurassic – Early Cretaceous Nevadan orogeny and associated post-collisional magmatism. It was open for ∼40 million years and closed by westward subduction. Here, we focus initially on the most complete cross section, located in southwestern Mexico, where a west-facing Albian carbonate platform, with subjacent siliciclastic rocks built on the western margin of North America, was pulled down into a trench at 100 Ma, buried in hemipelagic mud and Cenomanian flysch, then overthrust from the west by rocks of the 140–100 Ma Santiago Peak – Alisitos arc and its substrate, the Guerrero Superterrane, which collectively document westerly subduction. This tectonically thickened collision zone was exhumed and intruded by 99–84 Ma distinctive post-collisional tonalite–granodiorite plutonic complexes, all with Sr/Y &gt; 20, Sm/Yb &gt; 2.5, Nb/Y &gt; 0.4, and La/Yb &gt; 10. These geochemical features are typical of slab failure, not arc magmas. The post-collisional plutons, previously considered to represent arc flare-ups, were derived from melting of the descending slab following arc-continent collision. Remnants of the arc, basin, related east-vergent 100 Ma thrusts, flexural foredeep, and 99–84 Ma slab failure plutons are traced from the Peninsular Ranges, through the Mojave Desert to the Sierra Nevada where similar rocks, relations, and ages occur. Along the western, back-arc, side of the orogen after collision and slab break-off, but during exhumation, east-dipping reverse faults with &gt;10 km of east-side up movement shed 100–85 Ma plutonic and other debris westward from the hinterland into troughs such as the Valle and Great Valley. We extend our synthesis northward, from west-central Nevada to Alaska, in Part II.

Origin and tectonic implications of the early Middle Triassic tuffs in the western Yangtze Craton: Insight into whole-rock geochemical and zircon U-Pb and Hf isotopic signatures

The tuff layer steadily distributed in the western Yangtze Craton is a regional marker for the Early–Middle Triassic (Olenekian–Anisian) boundary. Integrated studies of whole-rock geochemistry and zircon geochronology reveal that the parental magma of the tuff is of felsic composition, generated via volcanic eruptions in the continental arc setting along the southwestern margin of the Yangtze Craton at ~247 Ma. The syn-depositional zircons in the tuff layers and in the coeval igneous rocks exhibit uniform negative εHf(t) values of approximately −20 to −6, indicating the significant input of crustal materials. Massive crustal assimilation implies a large-scale remelting of the pre-existing continental crust, triggered by the intensive arc–continental collision during that time. This intensive collisional tectonomagmatic event is an important signal for the closing of the eastern Paleo-Tethys branch and points to the initial collision of the Indochina Block and the Yangtze Craton. Xenocrystic zircons in the Precambrian-age offer insight into the early evolution of the southwestern Yangtze Craton, which shows episodic crustal growth and reworking of ~2.9–2.2 Ga, crustal reworking of ~1.9–1.7 Ga, rifting-related tectonomagmatism of ~1.6–1.4 Ga, and crustal growth of ~1.1–0.8 Ga. The older crystallization ages (3.4–2.5 Ga), lower initial 176Hf/177Hf values (0.2805–0.2813), negative εHf(t) values (−15.7 to −1.6), and two-stage Hf model ages (3.9–2.8 Ga) of zircons further suggest that an unexposed Archean basement exists beneath the southwestern Yangtze Craton. Significant contributions of mantle-derived materials occur at ~1.3–1.0 Ga, implying that the southwestern Yangtze Craton may not be involved in the Grenvillian-aged continental–continental collision orogeny. Comparable age spectrums and Hf isotopic data suggest that the Paleoproterozoic igneous rocks are a non-negligible provenance for Proterozoic metasedimentary in the Kangdian region.

Inherited lithospheric structures control arc-continent collisional heterogeneity

Abstract From west to east along the Sunda-Banda arc, convergence of the Indo-Australian plate transitions from subduction of oceanic lithosphere to arc-continent collision. This region of eastern Indonesia and Timor-Leste provides an opportunity for unraveling the processes that occur during collision between a continent and a volcanic arc, and it can be viewed as the temporal transition of this process along strike. We collected a range of complementary geological and geophysical data to place constraints on the geometry and history of arc-continent collision. Utilizing ∼4 yr of new broadband seismic data, we imaged the structure of the crust through the uppermost mantle. Ambient noise tomography shows velocity anomalies along strike and across the arc that are attributed to the inherited structure of the incoming and colliding Australian plate. The pattern of anomalies at depth resembles the system of salients and embayments that is present offshore western Australia, which formed during rifting of east Gondwana. Previously identified changes in geochemistry of volcanics from Pb isotope anomalies from the inner arc islands correlate with newly identified velocity structures representing the underthrusted and subducted Indo-Australian plate. Reconstruction of uplift from river profiles from the outer arc islands suggests rapid uplift at the ends of the islands of Timor and western Sumba, which coincide with the edges of the volcanic-margin protrusions as inferred from the tomography. These findings suggest that the tectonic evolution of this region is defined by inherited structure of the Gondwana rifted continental margin of the incoming plate. Therefore, the initial template of plate structure controls orogenesis.