Island Arc-continent Collision Research Articles

Palaeoweathering Conditions, Provenance, and Tectonic Setting of the Early Silurian Longmaxi Formation in the Upper Yangtze Region (Southern China): Evidence from Geochemistry

The Longmaxi-1 black shales in the Upper Yangtze region are a vital source rocks in southern China. This study investigates the palaeoweathering conditions, provenance, and tectonic setting of the Longmaxi-1 black shale from an elemental geochemical perspective, ultimately revealing its tectonic setting. The results showed that the Longmaxi-1 black shales in the sedimentary period have the characteristics of primary deposition. The Longmaxi-1 black shales were deposited as a primary deposition under a mainly humid climate. However, fluctuations in climatic conditions were recorded from the bottom to the upper part of the formation. The parent rock of the Longmaxi-1 black shales in the Upper Yangtze region is a mixture provenance, mainly composed of intermediate-acid volcanic lithologies (granite and granodiorite), followed by mature quartzite and basalt. Black shale deposition is related to the tectonic setting of active continental margin and island arc-continent collision. The Cathayian orogenic belts and the North Qiangling orogenic belt may have played a role in the genesis of the Longmaxi-1 black shales within the Upper Yangtze region. This study provides significant clues regarding the reconstruction of the palaeoclimatic and palaeogeographical conditions of the Upper Yangtze region during the Early Silurian period.

Tectonic evolution of the Caledonian orogeny in Scotland: a review based on the timing of magmatism, metamorphism and deformation

AbstractClassic tectonic models for the Caledonian orogeny in Scotland involve Ordovician collision of Laurentia–Midland Valley arc (Grampian orogeny), followed by middle Silurian collision of Laurentia–Baltica (Scandian orogeny) and 500–700 km of sinistral displacement along the Great Glen fault separating the Northern Highlands (Moine Supergroup) from the Grampian Highlands (Dalradian Supergroup). A review of the timing of magmatic and metamorphic rocks across Scotland allows a simpler explanation that fits with a classic Himalayan-style continent–island arc–continent collision. Late Cambrian – Early Ordovician NW-directed ophiolite obduction (Highland Border complex) coincided with the ending of stable continental shelf sedimentation along the eastern margin of Laurentia. Following collision between Laurentia and the Midland Valley arc–microcontinent in Early Ordovician time, crustal thickening and shortening led to almost continuous regional metamorphism from c. 470 to 420 Ma, rather than two discrete ‘orogenies’ (Grampian, Scandian). U–Pb monazite and garnet growth ages indicating prograde metamorphism, and S-type granites related to melting of crustal protoliths are coeval in the Grampian and Northern Highlands terranes. There is no evidence that the Great Glen fault was a terrane boundary, and strike-slip shearing post-dated emplacement of Silurian – Early Devonian granites. Late orogenic alkaline granites (c. 430–405 Ma) in both Moine and Dalradian terranes are not associated with subduction. They are instead closely related to regional alkaline appinite–lamprophyric magmatism resulting from simultaneous melting of lower crust and enriched lithospheric mantle. Caledonian deformation and metamorphism in northern Scotland, with continuous SE-directed subduction, show geometry and time scales that are comparable to the Cenozoic India–Kohistan arc–Asia collisional Himalayan orogeny.

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.

ГЕОДИНАМИКА И МАГМАТИЗМ ТРАНСФОРМНЫХ ОКРАИН ТИХООКЕАНСКОГО ТИПА: ОСНОВНЫЕ ТЕОРЕТИЧЕСКИЕ АСПЕКТЫ И ДИСКРИМИНАНТНЫЕ ДИАГРАММЫ

Transform margins represent lithospheric plate boundaries with horizontal sliding of oceanic plate, which in time and space replaced the subduction related convergent margins. This happened due to: spreading ridge–trench intersection (California; Queen Charlotte–Northern Cordilleran, West of the Antarctic Peninsula, and probably the Late Miocene–Pleistocene Southernmost South America) or ridge death along continental margin (Baja California); change in the direction of oceanic plate movement (Western Aleutian–Komandorsk; Southernmost tip of the Andes); and island arc-continent collision (New Guinea Island). Post-subduction magmatism is related to a slab window that resulted either from the spreading ridge collision (subduction) with a continental margin or slab tear formation, or slab break-off after subduction cessation due to other reasons. Igneous magmatic series formed in consequence of these events show diversity of tholeiitic (sub-alkaline), alkaline or calc-alkaline, high-alumina and adakitic rocks. The comprehensive geochemical dataset (more than 2400 analyses) on igneous rocks of the model transform and convergent geodynamic settings allowed to substantiate the most informative triple diagrams for the petrogenic oxides TiO2 × 10 – Fe2O3Tot – MgO and trace elements Nb – La– Yb. Mostly approved for the rock compositions with SiO2 < 63 wt. %, the new plots are capable of distinguishing igneous rocks formed above zones of subduction at an island arc and continental margin (related to convergent margins), from those formed in the tectonic setting of transform margins along continents or island arcs.

Study of overthrust nappe structure and its geodynamic mechanism along the southeastern margin of Nansha Trough

ABSTRACT On the basis of interpretation of comprehensive geophysical data and foreign data analysis, there existed a lot of overburden detachment shear thrust faults along the southeastern margin of Nansha Trough, which composed imbricated overthrust nappe structure. Thrust-faulted nappe structure pattern is determined in this area, which consists of frontal fault zone, thrust fault-folded zone and root zone structures, and presents regularly zonation on plane. The detail description of the structural geometrical characteristics is given in shallow thrust fault zone, and the kinematical mechanism of thrust fault nappe structure is furtherly discussed. Overthrust nappe structure in this area is resulted from island arc-continent collision and orogenic activities.

Electromagnetic constraints for subduction zones beneath the northwest Borborema province: Evidence for Neoproterozoic island arc–continent collision in northeast Brazil

The Borborema province in northeast Brazil occupies a crucial position in the complex Neoproterozoic West Gondwana reconstruction puzzle. However, correlation attempts between northeast Brazil and West Africa have been hampered because key links in the internal structure of the Borborema province have yet to be identifi ed. To aid such an correlation, a magnetotelluric study was undertaken along two subparallel profi les to image the deep electrical structure in the northwestern part of the province. Despite the occurrence of recurrent tectonothermal episodes that affected the region in the past, two-dimensional models show that a large-scale signature of the assembled terrane during the Neoproterozoic accretion and collision is plausibly preserved in the area. Two resistive features dipping from the upper crust into the upper mantle in downward convergence (opposite directions) are defi ned beneath one of the profi les that are interpreted to be related to remnants of former subduction slabs, since the observed high-resistivity zone is consistent with a dehydrated oceanic lithosphere depleted of sediments. On the basis of geological and geochemical information, a model of collision of an intraoceanic magmatic arc coalesced into an earlier passive margin is proposed for the Neoproterozoic tectonic evolution of the province, involving processes of reversal of subduction polarity and oceanic slab breakoff.

Age and structure of the Crevice pluton: overlapping orogens in west-central Idaho?

New U–Pb zircon geochronology from the Riggins region of west-central Idaho refines the timing of contractional deformation across the Salmon River suture zone (SRSZ), a broad north- to northeast-striking belt (>25 km wide) of high strain recording Jura-Cretaceous island-arc–continent collision. Laser ablation – inductively coupled plasma – mass spectrometry (LA–ICP–MS) yields mid-Cretaceous crystallization ages on formerly undated plutonic rocks sampled from the Salmon River canyon. In the Crevice pluton (∼105 Ma), the development of steep to moderate northerly striking gneissic foliation (S1) was followed by tops-to-the-west slip on shallow mylonitic shear zones (S2) and brittle overprinting via systematic joints (Jn) of regional extent. Together, these structures form the pluton’s internal architecture. Subvertical gneissic foliation in the adjacent Looking Glass pluton (∼92 Ma) indicates ductile deformation was ongoing in the Late Cretaceous. Prior to this investigation, penetrative fabrics in local arc volcanogenic, plutonic, and continental rocks have been unequivocally linked to post-collisional dextral transpression on the narrow (<10 km wide) western Idaho shear zone (WISZ). As an alternative to this model which requires spatially overlapping but temporally distinct orogenic belts (WISZ–SRSZ), we consider a protracted history whereby regional synmetamorphic structures accumulated over a pre-118 Ma to post-92 Ma interval without an overprinting orogen-scale ductile shear zone. In our view, a progressive deformation history more accurately accounts for the time-transgressive nature and structural continuity of fabrics observed across the arc–continent transition. This tectonic history proposed for western Idaho may be analogous to other long-lived accretionary margins in the North American Cordillera (e.g., Omineca Belt of southeastern British Columbia).

Ophiolites in European Variscides and Uralides: Geodynamic settings and metamorphism

The most important tectonic and magmatic events in the history of ophiolites in the Uralides and the European Variscides occurred almost sinchronously. The rocks of paleooceanic complexes in the both regions have similar paleontological and isotopic ages. The formation of the Ural and Variscan ophiolites is brought into correlation with a wide range of geodynamic settings. The Ural ophiolites mainly correspond to the suprasubduction setting, whereas the Variscan ophiolites are commonly related to rifts and mid-ocean spreading centers of the oceanic crust. The main difference is related to the origin of metamorphic rocks associated with ophiolites. The high-pressure-low-temperature metamorphism of the Ural ophiolites mainly related to the island arc-continent collision, whereas the Barrow-type metamorphism of ophiolites in the European Variscides developed at a higher temperature under medium-low pressure.

Tectonics of the Ural paleozoides in comparison with the Tien Shan

The main differences and similarities between the tectonic features of the Urals and the Tien Shan are considered. In the Neoproterozoic and Early and Middle Paleozoic, the Ural and Turkestan oceanic basins were parts of one oceanic domain, with several distinct regions in which tectonic events took different courses. The Baltic continental margin of the Ural paleoocean was active, whereas the Tarim-Alay margin of the Turkestan ocean, similar in position, was passive. The opposite continental margin in the Urals is known beginning from the Devonian as the Kazakh-Kyrgyz paleocontinent. In the Tien Shan, a similar margin developed until the Late Ordovician as the Syr Darya block with the ancient continental crust. In the Silurian, this block became a part of the Kazakh-Kyrgyz paleocontinent. The internal structures of the Ural and Turkestan paleooceans were different. The East Ural microcontinent occurred in the Ural paleoocean during the Early and Middle Paleozoic. No microcontinents are established in the Turkestan oceanic basin. Volcanic arcs in the Ural paleoocean were formed in the Vendian (Ediacarian), at the Ordovician-Silurian boundary, and in the Devonian largely along the Baltic margin at different distances from its edge. In the Turkestan paleoocean, a volcanic arc probably existed in the Ordovician at its Syr Darya margin, i.e., on the other side of the ocean in comparison with the Urals. The subduction of the Turkestan oceanic crust developed with interruptions always in the same direction. The evolution of subduction in the Urals was more complicated. The island arc-continent collision occurred here in the Late Devonian-Early Carboniferous; the continent-continent collision took place in the Moscovian simultaneously with the same process in the Tien Shan. The deepwater flysch basins induced by collision appeared at the Baltic margin in the Famennian and Visean, whereas in the Bashkirian and Moscovian they appeared at the Alay-Tarim margin. In the Devonian and Early Carboniferous, the Ural and Turkestan paleooceans had a common active margin along the Kazakh-Kyrgyz paleocontinent. The sudduction of the oceanic crust beneath this paleocontinent in both the Urals and the Tien Shan started, recommenced after interruptions, and finally ceased synchronously. In the South Ural segment, the Early Carboniferous subduction developed beneath both Baltica and the Kazakh-Kyrgyz paleocontinent, whereas in the Tien Shan, it occurred only beneath the latter paleocontinent. A divergent nappe-fold orogen was formed in the Urals as a result of collision of the Kazakh-Kyrgyz paleocontinent with the Baltic and Alay-Tarim paleocontinents, whereas a unilateral nappe-fold orogen arose in the Tien Shan. The growth of the high divergent orogen brought about the appearance of the Ural Foredeep filled with molasse beginning from the Kungurian. In the Tien Shan, a similar foredeep was not developed; a granitic axis similar to the main granitic axis in the Urals was not formed in the Tien Shan either.

THE GENESIS OF PYROXENITE-RICH PERIDOTITE AT CABO ORTEGAL (NW SPAIN). INFERENCES FROM GEOCHEMICAL, MINERAL AND PB-SR ISOTOPIC DATA

THE GENESIS OF PYROXENITE-RICH PERIDOTITE AT CABO ORTEGAL (NW SPAIN). INFERENCES FROM GEOCHEMICAL, MINERAL AND PB-SR ISOTOPIC DATA

Deformations of the coastal Pilbara Terrane, Western Australia

The middle Archean (3.25-3.20Ga) coastal Pilbara Terrane was formed by an immature oceanic island arc-continent collision [D1: 3.15-3.05Ga] and was deformed by regional intraplate strike-slip deformations [D2: 3.0-2.95Ga; D3: 2.90-2.80Ga] (Kiyokwa and Taira, 1999; Kiyokawa et al., submit). The immatured oceanic island arc unit of the Cleaverville-Roebourne Supercomplex tectonically overthrusts the granitecontinental shelf metasedimentary Karratha Supercomplex (see cross section) (Kiyokawa and Taira, 1998). D1 thrust deformation evidences, such as klippen structure, imbricated thrust piles and a basal decollement with quartz mylonite, are well preserved in the complexes boundary. On the other hand, the D2 event identified regional strike-slip deformations (eg. reactivated quartz mylonite, steep axis asymmetric fold) and the D3 deformation locally preserved at the terrane boundary with mylonite shear zone [Sholl shear zone]. These deformations are identified as formation of a juvenile continent and stabilization of early continent in Middle Archean.

U-series, SrNdPb isotope and trace-element systematics across an active island arc-continent collision zone: Implications for element transfer at the slab-wedge interface

We present U-series, SrNdz.sbnd;Pb isotope and trace-element results of a regional study of geochemical systematics across an island arc-continent collision zone in the East Sunda Arc of Indonesia. Samples from four active volcanoes exhibit a striking compositional range from low-K tholeiitic to ultrapotassic, but all are characterised by high 87 Sr 86 Sr (0.7053–0.7067), radiogenic lead isotope ratios ( 206 Pb 204 Pb = 18.99–19.15), low ( 230 Th) ( 232 Thz) (0.66–0.85), and low 143 Nd 144 Nd (0.51255–0.51272), except for high 143 Nd 144 Nd (>0.51286) at the volcanic front. Low ( 230 Th) ( 232 Th) ratios are also found in terrigenous sediments in front of the arc, which, in combination with Srz.sbnd;Ndz.sbnd;Pb isotopic constraints, indicates that subducted continental material contributes to magma sources in this arc sector. The volcanoes close to the trench show a large excess of 238U over . 230Th (up to 80%) and of 226Ra over 230Th (up to 800%). In addition, they are enriched in elements thought to be mobile in hydrous fluids during slab-wedge transfer, such as Ba, Pb, and Sr. In contrast, Uz.sbnd;Thz.sbnd;Ra systematics are close to equilibrium in the volcanoes behind the front. Abundance patterns of incompatible trace elements in these rocks are similar to those of the terrigenous sediments, so that, in comparison with the arc-front lavas, they possess low Ba/La, Ba/Th, La/Th, Pb/Ce, and Zr/Nb. Higher concentration levels and less interelement fractionation form conspicuous differences with the front volcanics. Our combined isotopic and trace element data are consistent with three-component mixing whereby a slab-derived hydrous fluid and a siliceous melt are both added to the sub-arc mantle source. The hydrous fluid largely controls the input in the shallow part of the subduction zone, whereas the siliceous melt dominates the flux at deeper levels. Sedimentary material is considered to be the primary source of both. The large U-Th-Ra disequilibria at the front suggests that element transfer is a currently active process associated with present-day subduction of continental material.

Late Proterozoic colisional orogen and geosuture in Southeastern China: Petrological evidence

The Jiangshan-Shaoxing fracture belt (JSFB) is a Late Proterozoic geosuture due to island arc-continent collision in South China. The Cathaysian Block (CT), lying on the southeast side of JSFB, is composed of green schist-amphibolite complexes in the form of a series of tectonic flakes. On the northwest side of JSFB, which is located in the border area of Zhejiang, Jiangxi and Anhhi provinces ( abbreviated as ZJP-JXP-AHP ), are distributed an ophiolite suite and other rocks, constituting the Jiangnan ancient island arc (JN) on the southeast margin of the Yangtze Block (Y Z). The collision between JN and CT at R∼ 0.9Ga ago led to the folding of JN, followed by the intrusion (∼ 0.9–0.8Ga ago) of many dioritic and ultramafic stitching plutons along the fracture belt. As a result, the basic Precambrian tectonic framework of southeastern China was shaped.

Deformation and metamorphism of the Aileu Formation, north coast, East Timor and its tectonic significance

The large block of metamorphic rocks along the north coast of East Timor is of special interest as it occurs at the boundary between continental and oceanic crust in an island arc-continent collision zone. A detailed study of the structure and metamorphic history of 400 km 2 of this formation showed it has a complex history of penetrative deformation but the structure is coherent. Pelites, psammites and limestones interlayered with dolerites and amphibolites have been metamorphosed in a medium pressure environment. They now form a metamorphic province zoned from low greenschist facies in the southwest to upper amphibolite facies in the east. The earliest recognised deformation phase predated the metamorphism and produced a widespread layer—parallel schistosity but no recognisable folds. The second deformation phase post-dated the metamorphic maximum and micropetrological evidence indicates a gradual cooling during this event. This deformation produced tight folds with an axial plane schistosity and transposed the earlier structures. The progressively weaker third and fourth phases developed crenulation cleavages and related folds, under greenschist facies conditions. Open, fifth phase, macroscopic folds were probably synchronous with strike slip faulting parallel to the north coast. Later dip slip faulting juxtaposed the Aileu Formation with Permian and Mesozoic sediments of very low metamorphic grade. Reconnaissance K/Ar radiometric dating using hornblende and biotite showed the prograde metamorphic maximum occurred before 11 Ma ago and implies that the second, and strongest, deformation phase occurred in the late Miocene. This young age establishes the relationship of the deformation events to the collision between Australia and the Inner Banda Arc. The proposed models for the structure of Timor must be modified to fit the deformation history of the Aileu Formation. If Timor is essentially autochthonous, the Aileu Formation was probably deposited in a Palaeozoic graben and the metamorphic maximum may have occurred in the Jurassic. The overthrusting models must be modified in the light of the close correlation in time between penetrative deformation and emplacement of the proposed thrust sheets. The analogy proposed between Timor and ‘normal’ convergent margins is not supported but it may be possible to draw analogies with the Molucca Sea.

The Grampian Orogeny in Scotland: Arc-Continent Collision and Polarity Reversal

Comparison of the early Ordovician Grampian orogeny in Scotland with Cenozoic collision belts elsewhere suggests that the Grampian event was an island arc-continent collision which followed southeastward subduction of ocean floor, and was succeeded by northwestward subduction of the Caledonian orogeny.