Ophiolite Emplacement Research Articles

Eocene and Oligocene basins and ridges of the Coral Sea-New Caledonia region: Tectonic link between Melanesia, Fiji, and Zealandia

This paper presents 34 geochemical analyses, 24 Ar-Ar ages, and two U-Pb ages of igneous rocks from the back-arc basins and submarine ridges in the Coral Sea-New Caledonia region. The D'Entrecasteaux Ridge is a composite structural feature. Primitive arc tholeiites of Eocene age (34–56 Ma) are present along a 200 km length of the ridge and arguably were part of the initial line of subduction inception between Fiji and the Marianas; substantial Eocene arc edifices are only evident at the eastern end where Bougainville Guyot andesite breccias are dated at 40 ± 2 Ma. The South Rennell Trough is confidently identified as a 28–29 Ma (early Oligocene) fossil spreading ridge, and hence, the flanking Santa Cruz and D'Entrecasteaux basins belong in the group of SW Pacific Eocene-Early Miocene back-arc basins that include the Solomon Sea, North Loyalty, and South Fiji basins. The rate and duration of spreading in the North Loyalty Basin is revised to 43 mm/yr between 28 and 44 Ma, longer and faster than previously recognized. The direction of its opening was to the southeast, that is, parallel to the continent-ocean boundary and perpendicular to the direction of coeval New Caledonia ophiolite emplacement. Medium- and high-K alkaline lavas of 23–25 Ma (late Oligocene) age on the northern Norfolk Ridge are an additional magmatic response to Pacific trench rollback.

Fatima suture: A new amalgamation zone in the western Arabian Shield, Saudi Arabia

We describe a new amalgamation zone between Jiddah and Asir juvenile arc terranes in the western Arabian Shield. Ophiolitic rocks in this zone were deformed by a NE-SW oriented belt of opposite-verging overturned folds and thrust faults, whereas two granitic complexes intruded mainly through its axial uplift. Chemical characteristics of these rocks indicate that they formed in an arc suprasubduction zone setting. The amalgamation between Jiddah and Asir terranes is explained mainly in terms of two events followed by two more events related to convergence between eastern and western Arabian superterranes. NW-SE shortenings and dextral transpression of the first three events induced more structural elements and tectonic fabrics than those developed during the youngest shortening event. Tectonic fabrics differentiate between the stress orientations during the oldest deformation events. Variations in attitudes and shear senses throughout these structural and tectonic elements support strain partitioning. Deformation related to assembly of the Jiddah and Asir terranes started during ophiolite emplacement at 812Ma and ended before the deposition of the post-amalgamation Fatima basin. A northwestward shortening inverted this basin and developed NW-verging thrust faults and folds. Tectonic evolution of Fatima suture zone is correlated with the major tectonic settings of the Arabian Shield.

Ophioliticlastic Ihungia igneous conglomerate (Early Miocene), North Island, New Zealand: evidence for an island source related to subduction initiation and deposition within a slump-generated submarine slope re-entrant

In the eastern North Island, the Early Miocene Tolaga Group contains some small isolated outcrops of distinctive basaltic–clast conglomerate and serpentine-bearing sandstone, the Ihungia igneous conglomerate. The shape, texture and composition of ultramafic to mafic gravel and sand components of the conglomerate indicate that they were likely delivered via submarine continental slope canyons from emergent island(s) on which ophiolitic peridotite, gabbro and basalt of the East Coast Allochthon were exposed. We speculatively propose that, following subduction initiation and ophiolite emplacement, and just prior to deposition of these units, eastward (downslope) displacement of part of the allochthon formed a large re-entrant in the continental slope in which the gravel subsequently accumulated. This Miocene Ihungia re-entrant has similarities to modern re-entrants along the continental shelf edge of the Raukumara Peninsula. Thus, subduction-related submarine mass transport processes may have been active along the New Zealand continental margin for the last 20 Ma. This study documents the sedimentary signature of an ophiolite likely created, uplifted and subaerially exposed in association with subduction initiation.

Tectonics of the Musandam Peninsula and northern Oman Mountains: From ophiolite obduction to continental collision

ABSTRACT The tectonics of the Musandam Peninsula in northern Oman shows a transition between the Late Cretaceous ophiolite emplacement related tectonics recorded along the Oman Mountains and Dibba Zone to the SE and the Late Cenozoic continent-continent collision tectonics along the Zagros Mountains in Iran to the northwest. Three stages in the continental collision process have been recognized. Stage one involves the emplacement of the Semail Ophiolite from NE to SW onto the Mid-Permian–Mesozoic passive continental margin of Arabia. The Semail Ophiolite shows a lower ocean ridge axis suite of gabbros, tonalites, trondhjemites and lavas (Geotimes V1 unit) dated by U-Pb zircon between 96.4–95.4 Ma overlain by a post-ridge suite including island-arc related volcanics including boninites formed between 95.4–94.7 Ma (Lasail, V2 unit). The ophiolite obduction process began at 96 Ma with subduction of Triassic–Jurassic oceanic crust to depths of > 40 km to form the amphibolite/granulite facies metamorphic sole along an ENE-dipping subduction zone. U-Pb ages of partial melts in the sole amphibolites (95.6– 94.5 Ma) overlap precisely in age with the ophiolite crustal sequence, implying that subduction was occurring at the same time as the ophiolite was forming. The ophiolite, together with the underlying Haybi and Hawasina thrust sheets, were thrust southwest on top of the Permian–Mesozoic shelf carbonate sequence during the Late Cenomanian–Campanian. Subduction ended as unsubductable cherts and limestones (Oman Exotics) jammed at depths of 25–30 km. The Bani Hamid quartzites and calc-silicates associated with amphibolites derived from alkali basalt show high-temperature granulite facies mineral assemblages and represent lower crust material exhumed by late-stage out-of-sequence thrusting. Ophiolite obduction ended at ca. 70 Ma (Maastrichtian) with deposition of shallow-marine limestones transgressing all underlying thrust sheets. Stable shallow-marine conditions followed for at least 30 million years (from 65–35 Ma) along the WSW and ENE flanks of the mountain belt. Stage two occurred during the Late Oligocene–Early Miocene when a second phase of compression occurred in Musandam as the Arabian Plate began to collide with the Iran-western Makran continental margin. The Middle Permian to Cenomanian shelf carbonates, up to 4 km thick, together with pre-Permian basement rocks were thrust westwards along the Hagab Thrust for a minimum of 15 km. Early Miocene out-of-sequence thrusts cut through the shelf carbonates and overlying Pabdeh foreland basin in the subsurface offshore Ras al Khaimah and Musandam. This phase of crustal compression followed deposition of the Eocene Dammam and Oligocene Asmari formations in the United Arab Emirates (UAE), but ended by the mid-Miocene as thrust tip lines are all truncated along a regional unconformity at the base of the Upper Miocene Mishan Formation. The Oligocene–Early Miocene culmination of Musandam and late Cenozoic folding along the UAE foreland marks the initiation of the collision of Arabia with Central Iran in the Strait of Hormuz region. Stage three involved collision of Arabia and the Central Iran Plate during the Pliocene, with ca. 50 km of NE-SW shortening across the Zagros Fold Belt. Related deformation in the Musandam Peninsula is largely limited to north and eastward tilting of the peninsula to create a deeply indented coastline of drowned valleys (rias).

Late Cretaceous Conglomerates of the Qahlah Formation, north Oman

Abstract Conglomerate sequences over 700 m thick were deposited subsequent to ophiolite emplacement during Late Cretaceous time in north Oman. The conglomerates were deposited by streams draining the allochthonous ophiolite and Hawasina complex after their obduction onto autochthonous Mesozoic and older Oman shelf sequences and subsequent uplift. The conglomerates belong to the Qahlah Formation of Late Cretaceous age, which is sandwiched between the Semail Ophiolite/Hawasina complex and Maastrichtian–Palaeogene carbonate rocks. The siliciclastics of the Qahlah Formation are the first sediments deposited over the obducted oceanic crust sequence of ophiolite and Hawasina lithologies. In five locations studied in north Oman, the thickness of the formation varies from 140 m to over 700 m and comprises interbedded conglomerate, sandstone and siltstone. The sediments were deposited in isolated segmented depressions each characterized by its source terrain depending on lithologies exposed in the source area. Lithofacies associations, clast sorting and grain roundness suggest deposition in stream-dominated alluvial fans. Clasts in the conglomerates range from subangular to subrounded pebbles to boulders with both grain and matrix (sandstone) support. Cross-bedded fining-upwards sequences in channelized conglomerate and sandstone suggest deposition by high-energy flows in the proximal to distal reaches of alluvial fans. High proportions of chert and ophiolite fragments in the conglomerates suggest rapid erosion of obducted oceanic crust. The presence of Loftusia -bearing carbonate beds and bivalve-bearing conglomerate beds in different sections indicates occasional interruption of alluvial deposition by marine transgressions.

Greater India's northern margin prior to its collision with Asia

AbstractGreater India's northern edge prior to collision with Asia is typically modelled as a rifted passive margin. We argue for a quite different geometry as a consequence of two tectonic episodes that happened sometime before the main impact. Whilst the western segment of India's northern boundary had formed in the Late Triassic as a rifted margin, the central and eastern portions developed between 132 and 110 Ma when the sub‐continent separated from Australia–Antarctica as the inner wall of a dextral ‘scything’ transform fault along the Wallaby–Zenith Fracture Zone off western Australia. Key features would have been (i) the very narrow (20–30 km wide) ocean–continent transition zone marking the sub‐continent's eastern northern boundary, and (ii) similar to the region offshore South Africa's Garden Route coast, Greater India's NE corner may have developed a series of ‘perched’ half grabens due to shearing related to its motion along the Wallaby–Zenith Fracture Zone, from initial break‐up until it passed the Zenith Plateau (ca. 110 Ma). Differences in the development of NW Greater India may be reflected in restriction of ultra‐high pressure metamorphic rocks to the western Himalaya where late Paleocene subduction of the rifted passive margin occurred at sub‐equatorial latitudes beneath the intra‐Tethyan arc. Further east, where the margin developed along the scything transform, the continent–ocean boundary would have been more abrupt and probably less strongly welded. Ophiolite emplacement appears to have been penecontemporaneous along the margin. A subsequent slab break‐off episode then eliminated the original plate boundary. Thereafter, remaining oceanic lithosphere north of the arc sutured to the sub‐continent, albeit rather weakly, was consumed beneath Eurasia, culminating in India–Asia collision.

Palaeoproterozoic (1.83 Ga) zircons in a Bajocian (169 Ma) granite within a Middle Jurassic ophiolite (Rubiku, central Albania): a challenge for geodynamic models

Two distinct zircon populations, 1,827 ± 17 and 169 ± 2 Ma in age, have been found in the Rubiku granite dyke in the Middle Jurassic Mirdita ophiolite in central Albania. The old inherited zircons represent a homogeneous population formed during a discrete Palaeoproterozoic, likely magmatic, zircon crystallization event. These older zircons were likely incorporated, in large part, into the granite magma that crystallized broadly at the time of the ophiolite emplacement (around 169 Ma). The limited data available do not allow for the construction of an unequivocal petrogenetic model, though several palaeotectonic scenarios are discussed as possible settings for the granite formation. The models refer to recent findings of old inherited zircons in rocks at recent mid-ocean ridge settings, but also consider likely contributions of crustal materials to primary basic ophiolitic magmas within supra-subduction settings and subsequent accretion/collision circumstances. The presence of old zircons in much younger rocks within ophiolite successions runs counter to geodynamic models of interaction between the oceanic lithosphere and continental crust, but constraining their genesis would require further systematic studies on these old inherited zircons, both in mafic (if present) and in felsic rocks of the ophiolites.

Middle to Late Cenozoic tectonic events in south and central Palawan (Philippines) and their implications to the evolution of the south-eastern margin of South China Sea: Evidence from onshore structural and offshore seismic data

Using recently gathered onland structural and 2D/3D offshore seismic data in south and central Palawan (Philippines), this paper presents a new perspective in unraveling the Cenozoic tectonic history of the southeastern margin of the South China Sea. South and central Palawan are dominated by Mesozoic ophiolites (Palawan Ophiolite), distinct from the primarily continental composition of the north. These ophiolites are emplaced over syn-rift Eocene turbidites (Panas Formation) along thrust structures best preserved in the ophiolite–turbidite contact as well as within the ophiolites. Thrusting is sealed by Early Miocene (∼20 Ma) sediments of the Pagasa Formation (Isugod Formation onland), constraining the younger limit of ophiolite emplacement at end Late Oligocene (∼23 Ma). The onset of ophiolite emplacement at end Eocene is constrained by thrust-related metamorphism of the Eocene turbidites, and post-emplacement underthrusting of Late Oligocene – Early Miocene Nido Limestone. This carbonate underthrusting at end Early Miocene (∼16 Ma) is marked by the deformation of a seismic unit corresponding to the earliest members of the Early – Middle Miocene Pagasa Formation. Within this formation, a tectonic wedge was built within Middle Miocene (from ∼16 Ma to ∼12 Ma), forming a thrust-fold belt called the Pagasa Wedge. Wedge deformation is truncated by the regionally-observed Middle Miocene Unconformity (MMU ∼12 Ma). A localized, post-kinematic extension affects thrust-fold structures, the MMU, and Late Miocene to Early Pliocene carbonates (e.g. Tabon Limestone). This structural set-up suggests a continuous convergent regime affecting the southeastern margin of the South China Sea between end Eocene to end Middle Miocene. The ensuing structures including juxtaposed carbonates, turbidites and shallow marine clastics within thrust-fold belts have become ideal environments for hydrocarbon generation and accumulation. Best developed in the Northwest Borneo Trough area, the intensity of thrust-fold deformation decreases towards the northeast into offshore southwest Palawan.

Linking the NE Anatolian and Lesser Caucasus ophiolites: evidence for large-scale obduction of oceanic crust and implications for the formation of the Lesser Caucasus-Pontides Arc

In the Lesser Caucasus and NE Anatolia, three domains are distinguished from south to north: (1) Gondwanian-derived continental terranes represented by the South Armenian Block (SAB) and the Tauride–Anatolide Platform (TAP), (2) scattered outcrops of Mesozoic ophiolites, obducted during the Upper Cretaceous times, marking the northern Neotethys suture, and (3) the Eurasian plate, represented by the Eastern Pontides and the Somkheto-Karabagh Arc. At several locations along the northern Neotethyan suture, slivers of preserved unmetamorphozed relics of now-disappeared Northern Neotethys oceanic domain (ophiolite bodies) are obducted over the northern edge of the passive SAB and TAP margins to the south. There is evidence for thrusting of the suture zone ophiolites towards the north; however, we ascribe this to retro-thrusting and accretion onto the active Eurasian margin during the latter stages of obduction. Geodynamic reconstructions of the Lesser Caucasus feature two north dipping subduction zones: (1) one under the Eurasian margin and (2) farther south, an intra-oceanic subduction leading to ophiolite emplacement above the northern margin of SAB. We extend our model for the Lesser Caucasus to NE Anatolia by proposing that the ophiolites of these zones originate from the same oceanic domain, emplaced during a common obduction event. This would correspond to the obduction of non-metamorphic oceanic domain along a lateral distance of more than 500 km and overthrust up to 80 km of passive continental margin. We infer that the missing volcanic arc, formed above the intra-oceanic subduction, was dragged under the obducting ophiolite through scaling by faulting and tectonic erosion. In this scenario part of the blueschists of Stepanavan, the garnet amphibolites of Amasia and the metamorphic arc complex of Erzincan correspond to this missing volcanic arc. Distal outcrops of this exceptional object were preserved from latter collision, concentrated along the suture zones.

Jurassic to Cenozoic tectonics of the Zagros Orogen in northwestern Iran

The Zagros Mountains of Iran formed by continental collision from closure of the Neo-Tethyan Ocean. The Zagros Orogen underlying the mountain range reflects a much longer history with the Pan-African basement and Phanerozoic successions. New mapping, radiometric ages, and stratigraphic analyses have enabled advances in our understanding of the Jurassic to Cenozoic tectonic history. The northwestern Zagros Orogen consists of three belts: (1) the Zagros Fold and Thrust Belt, divided into the outer Zagros Simply Folded Belt and the inner High Zagros Belt; (2) the Zagros Suture Zone including radiolarite, ophiolite, and Bisotun limestone thrust sheets; and (3) the Sanandaj–Sirjan Zone, which contains abundant metamorphic rocks. Late Cretaceous ophiolites of the Kermanshah region are part of the outer ophiolite belt of the Zagros Orogen and have formed in passive margin and supra-subduction zone settings. Major events include early Mesozoic rifting, Jurassic subduction followed by a more cryptic interval of subduction in the Cretaceous, multiple ophiolite emplacement on the Arabian margin in the Late Cretaceous to Eocene, and collision of central Iran and the Arabian margin in the Oligocene with final closure of the shallow Tethyan seaway in the mid-Miocene. A Middle to Late Jurassic plutonic belt, the Qorveh–Aligodarz Plutonic Belt, formed a magmatic arc with subdued topography related to a moderately NE-dipping subduction zone under the Sanandaj–Sirjan Zone. An Early Cretaceous unconformity reflects limited uplift followed by widespread marine deposition with intercalated volcanic rocks in the Sanandaj region. Subduction continued with a low-lying arc that underwent trenchward advance. In the Late Cretaceous to Oligocene interval, the Neo-Tethyan Ocean closed with ophiolite obduction over the Arabian Peninsula margin and major shortening affected the Sanandaj–Sirjan Zone with uplift and plutonism. Much of the forearc of the Jurassic to Cretaceous arc system has been lost by tectonic erosion along a low-angle Eocene subduction zone prior to collision. Flattening of the subducting slab in the Late Cretaceous and Palaeogene explains the inland retreat of the arc to central Iran. Continental collision initiated in the Oligocene but the Tethyan seaway remained open until the mid-Miocene.

Late Triassic and Lower Jurassic Foraminifera of the carbonate platform of the Beyaz Aladağ Group (Eastern Taurus, Turkey): New stratigraphic implications

Foraminifera have proven to be reliable biostratigraphic indicators. Accordingly, Triassic and Early Jurassic benthic Foraminifera allow us to define a biostratigraphic zonation within the carbonate platform of Kayseri (Yahyalı), Göksun (Kahramanmaraş) and Sivas (Deliktaş) regions in the Eastern Taurus (Ceviz, Aladağ, Kaman and Felfan Mountains). Seven new stratigraphic sections are described in detail and the first precise inventory and illustration of the benthic foraminifer assemblages from the Triassic successions are presented over a large geographic area. The stratigraphic and palaeontological features of the Lower Mesozoic carbonate units of these mountains include several synchronous transgressive–regressive events that suggest continuity of the Lower Mesozoic environments over a large parautochthonous Taurus zone. Palaeogeographic considerations about the Eastern Taurus carbonates are given, evidencing three stages of development underwent by the studied area: 1) a stable continental margin from Lower Triassic to Lower Cretaceous; 2) a dismantling of the continental margin and first emplacement of ophiolites in the Upper Cretaceous; and 3) a deformation of the continental margin and emplacement of the Peridotite Nappe in the uppermost Cretaceous (Maastrichtian).

A Possible Influence of Tethyan Ophiolite Emplacement on North and Central Atlantic Spreading

A Possible Influence of Tethyan Ophiolite Emplacement on North and Central Atlantic Spreading

Study on the Tectonic Setting for the Ophiolites in Xigaze, Tibet

Abstract:The Xigaze ophiolite is located in the middle section of the Yarlung Zangbo River ophiolite belt and includes a well‐preserved sequence section of seven ophiolite blocks. The relatively complete ophiolitic sequence sections are represented by Jiding, Dejixiang, Baigang, and Dazhuqu ophiolites and consist of three–four units. The complete ophiolite sequence in order from the bottom to top consists of mantle peridotite, cumulates, sheeted sill dike swarms, and basic lavas±radiolarian chert. These cumulates are absent in the remaining blocks of Dejixiang and Luqu. The age of radiolaria in the radiolarian chert is Late Jurassic–Cretaceous. The basalt and ultramafic rock of the ophiolite also are overlaid by Tertiary Liuqu conglomerate, which contains numerous pebble components of ophiolite, indicating that the Tethys Ocean began to close at the end of Cretaceous Period. The isotopic data of gabbro, diabase, and albite granite in the Xigaze ophiolite are approximately 126–139 Ma, which indicates that the ophiolite formed in the Early Cretaceous. The K‐Ar age of amphibole in garnet amphibolite in the ophiolite mélange is 81 Ma, indicating that tectonic ophiolite emplacement occurred at the end of Late Cretaceous. Research in petrology, petrological chemistry, mineralogy, and geochemistry of volcanic rocks and dikes of the Xigaze ophiolite indicate the following characteristics: (1) They are mainly composed of basalt, basaltic andesite, dolerite, and diabase and are characterized by high TiO2 (0.7–1.47%), low MgO (mostly less than 8%), and low SiO2 (mostly less than 53%). (2) The volcanic rocks and dikes of the Xigaze ophiolite show light rare earth element (LREE)‐depleted rare earth element (REE) patterns. (3) The spider diagrams of the volcanic rocks and dikes of the Xigaze ophiolite exhibit LILE depletion relative to high‐field‐strength element (HFSE) patterns with left oblique features. (4) No protogenetic olivine and clinoenstatite was detected. (5) Some dikes show low TiO2 and high MgO, in which a few of Cr‐enriched spinels and a very few pseudomorphs of olivine, orthopyroxene can be seen. They show more distinctive affinity as boninitic rock and canbe classified to boninite series rock. The previously mentioned features of the volcanic rocks and dikes in the Xigaze ophiolite implies that these ophiolites formed in a mid‐ocean ridge (MOR) in the earlier stage and than forearc extension of subduction initiation occurred once at the later stage of the evolution of the Xigaze ophiolite. The forearc extention caused further melting of the residue‐depleted mantle, resulting in the formation of melts with lower TiO2 and higher MgO. These melts formed as dikes and intruded into the oceanic crust formed in the earlier stage, resulting in a close association of mid‐ocean ridge basalt and the boninite rock of the Xigaze ophiolite.

Proterozoic orogens in southern Peninsular India: Contiguities and complexities

The Precambrian terranes of southern Peninsular India have been central to discussions on the history of formation and breakup of supercontinents. Of particular interest are the Proterozoic high grade metamorphic orogens at the southern and eastern margins of the Indian shield, skirting the 3.4Ga Dharwar craton which not only preserve important records of lower crustal processes and lithospheric geodynamics, but also carry imprints of the tectonic framework related to the assembly of the major Neoproterozoic supercontinents – Rodinia and Gondwana. These Proterozoic orogens are described as Southern Granulite Terrane (SGT) in the southern tip and the Eastern Ghats Mobile Belt (EGMB) in the eastern domains of the peninsula. The contiguity of these orogens is broken for a distance of ∼400km and disappears in the Bay of Bengal. These orogens expose windows of middle to lower crust with well-preserved rock records displaying multiple tectonothermal events and multiphase exhumation paths.Recent studies in these orogens have led to the recognition of discrete crustal blocks or terranes separated by major shear zone systems, some of which represent collisional sutures. The SGT and EGMB carry several important features such as fold-thrust tectonics, regional granulite facies metamorphism of up to ultrahigh-temperature conditions in some cases, multiple P–T paths, development of lithospheric shear zones, emplacement of ophiolites, presence of alkaline and anorthositic complexes, development of crustal-scale “flower structures”, transpressional strains, and reactivation tectonics. A heterogeneous distribution of different metamorphic and magmatic assemblages with distinct spatial and temporal strain variations in shaping the fabric elements in different blocks is identified. Both EGMB and SGT share a common transpressional deformation history during the latest Neoproterozoic characterized by the steepening of the initial low angle crustal scale structures leading to a subvertical grain conducive to reactivation tectonics. Our synthesis of the spatial distribution, geometry, kinematics and the transpressional strain of the shear zone systems provides insights into the tectono-metamorphic history of the Proterozoic orogens of southern India and their contiguity and complexities. Recent understanding of subduction, accretion and collisional history along these zones together with a long lived transpressional tectonic regime imply that these orogens witnessed identical tectonic regimes at different times in Earth history, although the major and common structural architecture was built during the final assembly of the Gondwana supercontinent.

Late Palaeozoic–Cenozoic tectonic development of carbonate platform, margin and oceanic units in the Eastern Taurides, Turkey

Abstract Continental margin-type, ophiolitic and mélange units are exposed throughout central eastern Turkey (e.g. Gürün, Hekimhan and Pınarbaşı areas). These restore as a north-verging Triassic-rifted continental margin that underwent Jurassic–Early Cretaceous passive margin subsidence. Chemically ‘enriched’ basaltic lavas of seamount type are interbedded with and overlain by Middle Jurassic–Early Cretaceous ribbon cherts. Ophiolitic rocks (e.g. Pınarbaşı, Dağlıca, Kuluncak, Hekimhan, Divriği) formed by spreading above a Late Cretaceous northwards-dipping intra-oceanic subduction zone. Emplacement of continental margin units, mélanges and ophiolites onto the East Tauride platform was driven by trench-margin collision during latest Cretaceous. The northern part of the East Tauride neritic carbonate platform detached and overthrust the continent to the south (Malatya Metamorphics) which was deeply underthrust, metamorphosed at least to greenschist facies and exhumed by latest Cretaceous. Collision-related Mid-Eocene southwards thrusting strongly affected the western part of the region (e.g. Pınarbaşı), whereas areas further east (e.g. Darende, Hekimhan, Divriği, Sivas) mainly experienced folding. Taking account of the regional tectonic setting, we infer that the Gürün platform, with its distinctive unbroken up to Lutetian-aged succession, represents a small exotic terrane that was translated from a relatively southerly (‘internal’) part of the Tauride platform (Geyik Dağ), related to strike-slip displacement (syn/post-Eocene to pre-Pliocene). Supplementary material: Two supplementary tables giving the GPS coordinates of the samples of basic intrusive and extrusive igneous rocks that were analyzed during this work are available at www.geolsoc.org.uk/SUP18569

Revised Late Campanian-Danian age of the melange-related turbiditic sequence in the Mersin area (Central Taurides, S. Turkey)

A planktonic foraminiferal assemblage obtained from the Yavca stratigraphic section north of Mersin shows that the age of a melange-related turbiditic sequence extends to the Danian (Early Palaeocene). Previously, this turbiditic sequence, termed the Yavca Formation, was considered to be of Late Cretaceous or Campanian-Maastrichtian age. The formation is either depositionally overlain by the Fındıkpınarı ophiolite-related melange or tectonically by Mersin Ophiolite slices or Jurassic-Cretaceous platform carbonates. Clayey limestone and mudstone samples collected from the type area of the Yavca Formation yielded planktonic foraminiferal assemblages, which include Parasubbotina pseudobulloides (Plummer), P. varianta (Subbotina), Praemurica pseudoinconstans (Blow), P. inconstans (Subbotina), Globanomalina compressa (Plummer), G. ehrenbergi (Blow), Subbotina triloculinoides (Plummer), S. triangularis (White), Morozovella praeangulata (White), and Eoglobigerina spiralis (Bolli). These assemblages range from the late Danian P1c subzone to the basal P3a subzone. Basal red pelagic limestones are assigned here to the late Campanian-Maastrichtian, based on the presence of Radotruncana cf. R. calcarata (Cushman) and Contusotruncana cf. C. walfischensis (Todd). The age of the melange-related turbiditic sequence is revised to be late Campanian (Late Cretaceous) to Danian (Early Paleocene). This revised age provides a new insight into the evolution of the Central Taurides and helps refine palaeogeographical interpretation during this time. The timing of the ophiolite emplacement in the Central Taurides is interpreted as post-Danian to pre-Miocene (Late Palaeocene or Late Eocene).

Evidence of Eocene high-temperature/high-pressure metamorphism of ophiolitic rocks and granitoid intrusion related to Neotethyan subduction processes (Doğanşehir area, SE Anatolia)

Abstract New data for regionally important granulite facies metaophiolitic rocks and cross-cutting granitoids rocks are presented and discussed. The high-temperature/high-pressure Berit metaophiolite is cut by unmetamorphosed Eocene (51–45 Ma) granitoid rocks. The highest metamorphic grade occurs in blocks of mafic granulites. Enveloping amphibolite facies rocks reflect retrograde metamorphism related to exhumation. Sm–Nd (pyroxene–garnet–amphibole–whole rock) isochron ages of 52–50 Ma for the granulite facies rocks are interpreted to represent the time of cooling of the granulite facies rocks. The over-riding Malatya metamorphic unit to the north is also intruded by Eocene granitoid rocks. The granulite facies metamorphism of the meta-ophiolitic rocks is inferred to have formed in the roots of an Eocene magmatic arc, with accentuated heat flow being provided by subduction of a spreading ridge, or rupture of the subducting slab. The high-temperature/high-pressure metamorphism was followed by exhumation, as indicated by field structural relations and the evidence of retrograde metamorphism. The Eocene arc magmatism can best be explained by northward subduction of the Southern Neotethys, which persisted after the time of latest Cretaceous regional ophiolite emplacement until the collision of the Eurasian (Anatolian) and Arabian continents during the Early–Mid Miocene. Subsequent Plio-Quaternary left-lateral strike-slip strongly affected the area. Supplementary-material: Four supplementary tables giving the whole rock geochemistry of the granitoids, mineral geochemistry of the granulite facies rocks, LA-MC-ICP-MS zircon U–Pb data belonging to granitoids and Sm–Nd data belonging to granulite facies rocks and two documents giving the detailed analytical procedures and detailed petrography of the granitoids are available at www.geolsoc.org.uk/SUP18588

Episodic arc-ophiolite emplacement and the growth of continental margins: Late accretion in the Northern Irish sector of the Grampian-Taconic orogeny

Research Article| November 01, 2012 Episodic arc-ophiolite emplacement and the growth of continental margins: Late accretion in the Northern Irish sector of the Grampian-Taconic orogeny Steven P. Hollis; Steven P. Hollis 1Ocean and Earth Science, National Oceanography Centre Southampton, University of Southampton, Waterfront Campus, European Way, Southampton, SO14 3ZH, UK †Current address: CSIRO Earth Science and Resource Engineering, 26 Dick Perry Avenue, Kensington, Western Australia, 6151, Australia; e-mail: steven.hollis@csiro.au Search for other works by this author on: GSW Google Scholar Stephen Roberts; Stephen Roberts 1Ocean and Earth Science, National Oceanography Centre Southampton, University of Southampton, Waterfront Campus, European Way, Southampton, SO14 3ZH, UK Search for other works by this author on: GSW Google Scholar Mark R. Cooper; Mark R. Cooper 2Geological Survey of Northern Ireland, Colby House, Stranmillis Court, Malone Lower, Belfast BT9 5BJ, UK Search for other works by this author on: GSW Google Scholar Garth Earls; Garth Earls 316 Mill Road, Ballygowan, Newtownards, County Down, BT23 6NG, UK Search for other works by this author on: GSW Google Scholar Richard Herrington; Richard Herrington 4Department of Mineralogy, Natural History Museum, London SW7 5BD, UK Search for other works by this author on: GSW Google Scholar Daniel J. Condon; Daniel J. Condon 5Natural Environment Research Council Isotope Geosciences Laboratory, British Geological Survey, Kingsley Dunham Centre, Keyworth, Nottingham NG12 5GG, UK Search for other works by this author on: GSW Google Scholar Matthew J. Cooper; Matthew J. Cooper 1Ocean and Earth Science, National Oceanography Centre Southampton, University of Southampton, Waterfront Campus, European Way, Southampton, SO14 3ZH, UK Search for other works by this author on: GSW Google Scholar Sandy M. Archibald; Sandy M. Archibald 6Aurum Exploration Services, Unit S/C, Kells Business Park, Kells, County Meath, Ireland Search for other works by this author on: GSW Google Scholar Stephen J. Piercey Stephen J. Piercey 7Department of Earth Sciences, Memorial University of Newfoundland, St. John’s, Newfoundland A1B 3X5, Canada Search for other works by this author on: GSW Google Scholar GSA Bulletin (2012) 124 (11-12): 1702–1723. https://doi.org/10.1130/B30619.1 Article history received: 09 Oct 2011 rev-recd: 03 May 2012 accepted: 18 May 2012 first online: 08 Mar 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation Steven P. Hollis, Stephen Roberts, Mark R. Cooper, Garth Earls, Richard Herrington, Daniel J. Condon, Matthew J. Cooper, Sandy M. Archibald, Stephen J. Piercey; Episodic arc-ophiolite emplacement and the growth of continental margins: Late accretion in the Northern Irish sector of the Grampian-Taconic orogeny. GSA Bulletin 2012;; 124 (11-12): 1702–1723. doi: https://doi.org/10.1130/B30619.1 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGSA Bulletin Search Advanced Search Abstract In order to understand the progressive growth of continental margins and the evolution of continental crust, we must first understand the formation of allochthonous ophiolitic and island-arc terranes within ancient orogens and the nature of their accretion. During the early Paleozoic closure of the Iapetus Ocean, diverse sets of arc terranes, oceanic tracts, and ribbon-shaped microcontinental blocks were accreted to the passive continental margin of Laurentia during the Grampian-Taconic orogeny. In the northern Appalachians in central Newfoundland, Canada, three distinct phases of arc-ophiolite accretion have been recognized. New field mapping, high-resolution airborne geophysics, whole-rock and Nd-isotope geochemistry, and U-Pb zircon geochronology within the Tyrone Volcanic Group of Northern Ireland have allowed all three episodes to now be correlated into the British and Irish Caledonides. The Tyrone Volcanic Group (ca. 475–469 Ma) is characterized by mafic to intermediate lavas, tuffs, rhyolite, banded chert, ferruginous jasperoid, and argillaceous sedimentary rocks cut by numerous high-level intrusive rocks. Geochemical signatures are consistent with formation within an evolving peri-Laurentian island-arc/backarc, which underwent several episodes of intra-arc rifting prior to its accretion at ca. 470 Ma to an outboard peri-Laurentian microcontinental block. Outriding microcontinental blocks played a fundamental role within the orogen, explaining the range of ages for Iapetan ophiolites and the timing of their accretion, as well as discrepancies between the timing of ophiolite emplacement and the termination of the Laurentian Cambrian–Ordovician shelf sequences. Accretion of the Tyrone arc and its associated suprasubduction-zone ophiolite represents the third stage of arc-ophiolite emplacement to the Laurentian margin during the Grampian-Taconic orogeny in the British and Irish Caledonides. You do not have access to this content, please speak to your institutional administrator if you feel you should have access.

Tectonostratigraphic evolution of the Upper Cretaceous–Cenozoic central Anatolian basins: an integrated study of diachronous ocean basin closure and continental collision

Abstract The Upper Cretaceous–Mid-Eocene Kırıkkale, Tuz Gölü, Haymana and Çankırı basins are bounded by the Pontide (Eurasian) continental margin to the north, the Niğde–Kırşehir microcontinent to the east and the Tauride–Anatolide continental unit to the south. The basins developed during northward subduction/collision of the İzmir–Ankara–Erzincan Ocean (‘northern Neotethys’) in the north and the inferred Inner Tauride Ocean in the south. Subduction of the İzmir–Ankara–Erzincan Ocean resulted in latest Cretaceous collision of the Niğde–Kırşehir microcontinent with the Pontide active margin and ophiolite emplacement. Some mid-ocean ridge-type oceanic crust remained to the SW and formed the basement of the Kırıkkale and Tuz Gölü basins. These basins are partially floored by an accretionary wedge to the west and by the Niğde–Kırşehir microcontinent to the east. Locally volcaniclastic, the sediment infill switched to terrigenous after latest Cretaceous. The Haymana Basin, further NW, developed as a forearc basin on the Mesozoic accretionary wedge and Pontide continental fragments. The Çankırı Basin also developed on an accretionary wedge, bounded by the Eurasian active margin to the north. An extensional setting prevailed during the latest Cretaceous related to subduction of remnant oceanic crust, followed by a switch to regional compression during Late Paleocene–Mid Eocene progressive and diachronous collision.

Geological features of a collision zone marker: The Antique Ophiolite Complex (Western Panay, Philippines)

The Antique Ophiolite Complex exposed along the western side of Panay Island, central Philippines was derived from the Jurassic to Cretaceous proto-South China Sea oceanic leading edge of the Palawan microcontinental block. The subduction and ultimate closure of this ocean basin resulted in the emplacement and exposure of this lithospheric fragment along the collisional boundary of the microcontinental block and the oceanic- to island arc-affiliated Philippine mobile belt. The ophiolite complex has volcanic rocks having normal- to transitional mid-ocean ridge basalt (MORB) to island arc tholeiitic (IAT) geochemistry consistent with the transitional MORB–IAT characteristics of its peridotites. The chromitites manifest subduction signature suggestive of the involvement of water in its generation. All of these would be consistent with generation in a supra-subduction zone environment, specifically in a subduction-related marginal ocean basin. The collision of the Palawan microcontinental block with the Philippine mobile belt along western Panay resulted, aside from ophiolite emplacement, into arc curvature, island rotation, serpentinite diapirism and thrusting along the forearc side. The offshore bathymetric expression of the microcontinental block along the collision zone shows the leading edge of this oceanic bathymetric high to have spread laterally. This is indicative of its being buoyant resulting to non-subduction as supported by available earthquake hypocenter data.