A model of the Cenozoic evolution of northern New Zealand and adjacent areas of the southwest Pacific

New information from the southwest Pacific indicates that earlier attempts at formulating the evolution of the area assuming a single Upper Cenozoic magmatic arc are untenable. It now appears that there were two arcs during the Miocene and Pliocene, a western Northland/Three Kings Rise arc, and an eastern Tonga-Lau/Kermadec-Colville arc. Both appear to have developed above west-dipping subduction zones. It is suggested that the Norfolk- and Reinga basins formed as back-arc basins to the western arc, and that eastern North Island lay adjacent to Northland and formed the accretionary prism to that arc. Upper Cenozoic evolution of the region involved the simultaneous opening of the Norfolk/Reinga basins, consumption of the western portion of the Oligocene South Fiji Basin by subduction beneath the western arc, and eastwards movement of New Zealand/Three Kings Rise towards the Tonga/Kermadec arc. When the Kermadec and Hikurangi trenches came into line late in the Pliocene, the Tonga/Kermadec arc was able to propagate rapidly southwards into North Island; simultaneously the western arc became extinct, and the tectonic tempo and strike-slip faulting accelerated markedly throughout New Zealand. Eastern North Island was moved dextrally an uncertain distance relative to the western North Island, and rotated 25°–30° clockwise. This accounts for the paradox of a 22-m.y. old accretionary margin lying adjacent to a 2-m.y. old arc (Taupo Volcanic Zone) at the present day.     

The Mount Wright Arc: A Cambrian subduction system developed on the continental margin of East Gondwana,Koonenberry Belt,eastern Australia

The Mount Wright Arc, in the Koonenberry Belt in eastern Australia, is associated with two early to middle Cambrian lithostratigraphic groups developed onto the Late Neoproterozoic volcanic passive margin of East Gondwana. The Gnalta Group includes a calc-alkaline basalt-andesite-dacite suite (Mount Wright Volcanics), interpreted to represent the volcanic component of the arc. Volcaniclastic Gnalta Group rocks now buried in the Bancannia Trough represent the continental back-arc, developed immediately behind the arc in a manner analogous to the modern Taupo Volcanic Zone of New Zealand. East of the Gnalta Group is the Ponto Group, a deep marine sedimentary package that includes tholeiitic lavas (Bittles Tank Volcanics) and felsic tuffs, interpreted as part of a fore-arc sequence. The configuration of these units suggests the Mount Wright Arc developed on continental crust in response to west-dipping subduction along the East Gondwana margin, in contrast with some models for Cambrian convergence on other sections of the Delamerian Orogen, which invoke east-dipping subduction and arc accretion by arc-continent collision.This convergent margin was deformed by the middle Cambrian Delamerian Orogeny, which involved initial co-axial shortening followed by sinistral transpression, and oroclinal folding around the edge of the Curnamona Province.     

Tectonic evolution of the Cretaceous Gyeongsang Back-arc Basin,SE Korea: Transition from sinistral transtension to strike-slip kinematics

The Gyeongsang Basin, the largest Cretaceous nonmarine sedimentary basin in Korea, formed as a continental back-arc basin related to NNW-directed subduction of the (proto-) Pacific Plate underneath the Eurasia Plate. The basin can be divided into an earlier-formed western back-arc depression and a later-formed eastern volcanic arc platform. We investigated the basin evolution and the associated tectonic settings, largely based on an analysis of structures individuated in the field in the back-arc region. From 127 Ma, the basin initiated as a NNE-trending narrow depression bordered by NNE-striking sinistral faults, and then progressively expanded under a transtensional kinematics induced by progressive trench roll-back. Sinistral shearing of inherited NNE-striking structures played an important role in basin subsidence, and secondary WNW- to NW-striking transverse faults acted as normal faults. The NNE-striking principal displacement zone in the west of the basin runs along the western marginal area of the Jinju and Daegu domains and passes through the Uiseong domain from south to north, but most of this zone is now preserved as deep structures. Volcanic activity starting at ca. 115 Ma was characterized mainly by episodic basaltic eruptions occurring contemporaneously with back-arc deposition of a sedimentary sequence. After ca. 90 Ma, a transtensional kinematics changed to a strike-slip one, and the basin expansion and sedimentation in the back-arc region terminated. During the strike-slip event, rhyolitic-dacitic volcanism increased in intensity as a large NE-trending volcanic arc developed close to subduction zone and its loading caused the stratal flexure in the back-arc region, and the orientations of the shortening and stretching axes remained NW–SE and NE–SW, respectively. Additionally, continuing sinistral shear generated local depressions along the faults located in the west of the back-arc region and within the volcanic arc.     

Neocene and Quaternary extent and geometry of the subducted Pacific Plate beneath North Island, New Zealand: Implications for Kaikoura tectonics

The extent and geometry of the obliquely subduced oceanic Pacific Plate beneath North Island, New Zealand, for five million year intervals through the mid-Miocene to Quaternary, are presented in a series of maps and cross-sections. These show that the subducted plate progressively increased its extent from NE to SW beneath the North Island, and in the more northern regions where it was first emplaced, concomitantly increased its dip from 10° to 50°.The changing extent and geometry of the subducted slab has been established from the age pattern of orogenic andesites and from the geochemical K₂O-h parameter of depth of magma generation. The radiometric dates show a migration of the volcanic front back towards the trench at an average rate of 20 km/My. The trenchward migration is explained by a model of increasing slab dip which is corroborated by the K₂O data calibrated against the presently active arc (Taupo Volcanic Zone). With the exception of northern Coromandel Peninsula, the andesitic magmas were generated at 85–100 km depth. The interpretation of the dates adopted here indicates that the subducted slab originated at the NE-SW trending Kermadec-Hikurangi Trench, and implies a different and much simpler evolution of the Australia-Pacific plate boundary in the vicinity of North Island than other recent models.Subduction geometry has been found elsewhere to be a principal influence upon the state of stress and deformational style in an over-riding plate. The possibility is explored that the timing, nature and pattern of the Neogene to Quaternary Kaikoura Orogeny in North Island is due to this influence. Apart from the effect of oblique subduction in eastern North Island, there is an accord between the onset of deformation and the emplacement sequence of the shallow slab beneath North Island, and between the change in subduction geometry and a progressive north to south change in northern North Island from compression to extension.     

Ocean trench blocked and obliterated by Banda forearc collision with Australian proximal continental slope

The bathymetry and abrupt changes in earthquake seismicity around the eastern end of the Java Trench suggest it is now blocked south–east of Sumba by the Australian, Jurassic-rifted, continental margin forming the largely submarine Roti–Savu Ridge. Plate reconstructions have demonstrated that from at least 45 Ma the Java Trench continued far to the east of Sumba. From about 12 Ma the eastern part of the Java Trench (called Banda Trench) continued as the active plate boundary, located between what was to become Timor Island, then part of the Australian proximal continental slope, and the Banda Volcanic Arc. This Banda Trench began to be obliterated by continental margin-arc collision between about 3.5 and 2 Ma.The present position of the defunct Banda Trench can be located by use of plate reconstructions, earthquake seismology, deep reflection seismology, DSDP 262 results and geological mapping as being buried under the para-autochthon below the foothills of southern Timor. Locating the former trench guides the location of the apparently missing large southern part of the Banda forearc that was carried over the Australian continental margin during the final stage of the period of subduction of that continental margin that lasted from about 12 Ma to about 3.5 Ma.Tectonic collision is defined and distinguished from subduction and rollback. Collision in the southern part of the Banda Arc was initiated when the overriding forearc basement of the upper plate reached the proximal part of the Australian continental slope of the lower plate, and subduction stopped. Collision is characterised by fold and thrust deformation associated with the development of structurally high decollements. This collision deformed the basement and cover of the forearc accretionary prism of the upper plate with part of the unsubducted Australian cover rock sequences from the lower plate. Together with parts of the forearc basement they now form the exposed Banda orogen. The conversion of the northern flank of the Timor Trough from being the distal part of the Banda forearc accretionary prism, carried over the Australian continental margin, into a foreland basin was initiated by the cessation of subduction and simultaneous onset of collisional tectonics.This reinterpretation of the locked eastern end of the Java Trench proposes that, from its termination south of Sumba to at least as far east as Timor, and probably far beyond, the Java-Banda Trench and forearc overrode the subducting Australian proximal continental slope, locally to within 60 km of the shelf break. Part of the proximal forearc's accretionary prism together with part of the proximal continental slope cover sequence were detached and thrust northwards over the Java-Banda Trench and forearc by up to 80 km along the southwards dipping Savu Thrust and Wetar Suture. These reinterpretations explain the present absence of any discernible subduction ocean trench in the southern Banda Arc and the narrowness of the forearc, reduced to 30 km at Atauro, north of East Timor.     

柴北缘赛坝沟增生杂岩组成与变形特征

柴北缘构造带由高压-超高压变质岩、蛇绿岩、增生杂岩、火山-岩浆弧及前寒武纪中-高级变质岩共同构成。该构造带内的"滩间山群"岩石组合与构造属性复杂,其岩性包括中基性火山岩、碎屑沉积岩以及超基性岩和中酸性侵入岩,普遍遭受低绿片岩相变质作用和强烈构造变形。结合区域资料和地质填图结果,综合分析认为该构造带东段赛坝沟地区的"滩间山群"由火山-岩浆弧、增生杂岩、蛇绿岩三个不同构造单元岩石组成。其中增生杂岩主要是一套深海-半深海沉积组合,夹玄武岩、灰岩、硅质岩等块体,自南而北总体呈现出来自洋壳、海山和海沟环境的大洋板块地层的岩石组合特征,同时呈现与日本西南部增生杂岩极为相似的岩石组合类型。该套组合构造变形强烈,主要表现为2期构造变形。其中第一期构造变形(D1)主要表现为双冲构造和同斜紧闭褶皱,断层和褶皱轴面主体倾向为NE,形成于大洋俯冲阶段;第二期构造变形(D2)主要表现为不对称褶皱和S-C组构,可能是晚期柴达木与祁连地块发生陆-陆碰撞过程中形成的,形成时间为440～400Ma。空间上,该增生杂岩与出露于其北侧的蛇绿岩、火山-岩浆弧共同构成了相对完整的沟-弧系统,指示了寒武-奥陶纪时期,柴北缘地区曾发生古洋盆向北俯冲造山作用。     

西太平洋俯冲带的演变:来自东北亚陆缘增生杂岩的制约

本文系统总结了东北亚陆缘晚古生代和中生代增生杂岩的构成与形成时代,并结合同时代火成岩组合及其时空变异以及沉积建造组合,重塑了西太平洋板块俯冲带的演变历史.结果表明:①位于佳木斯地块东缘的跃进山杂岩代表了二叠纪俯冲带,它是古亚洲洋构造体制的产物;②侏罗纪增生杂岩代表了侏罗纪俯冲带,与陆缘同期钙碱性火成岩组合以及含煤建造一...     

Middle Miocene to present plate tectonic history of the southern Central American Volcanic Arc

New mid Miocene to present plate tectonic reconstructions of the southern Central American Volcanic Arc (CAVA) reveal that the inception of Cocos Ridge subduction began no earlier than 3 Ma, and possibly as late as 2 Ma. The Cocos Ridge has been displaced from the Malpelo Ridge to the southeast since 9 Ma along the Panama Fracture Zone (PFZ) system. Ambiguous PFZ and Coiba Fracture Zone (CFZ) interaction since 9 Ma precludes conclusively establishing the age of initial Cocos Ridge subduction. Detailed reconstructions based on magnetic anomalies offshore reveal several other variations in subduction parameters beneath southern Central America that preceded subduction of the Cocos Ridge, including southeastward migration of the Nazca–Cocos–Caribbean triple junction along the Middle America Trench (MAT) from 12 Ma to present, and subduction of ≤2 km high scarps both parallel and perpendicular to the trench from 6 to 1 Ma.The timing of changes in subduction processes has commonly been determined by (and correlated with) geologic changes in the upper plate. However, reliable ⁴⁰Ar/³⁹Ar dating of these events has become available only recently [Abstr. Programs-Geol. Soc. Am. (2002)]. These new dates better constrain the magmatic and structural history of southern Costa Rica. Observations from this data set include: a gap in the volcanic record from 11 to 6 Ma, which coincides temporally with emplacement of most plutons in southern Costa Rica, normal arc volcanism ceased after 3.5 Ma in southern Costa Rica, and Pliocene (mostly 1.5 Ma) adakite volcanism was widely distributed from central Panama to southern Costa Rica (though volumetrically insignificant).This new data reveals that many geologic phenomena, commonly attributed to subduction and underplating of the buoyant Cocos Ridge, in fact precede inception of Cocos Ridge subduction and seem to correlate more favorably in time with earlier tectonic events. Adakite volcanic activity corresponds in space and time with the subduction of a large scarp associated with a tectonic boundary off southern Panama. Regional unconformities and an 11–6 Ma gap in arc volcanism match temporally with oblique subduction of the Nazca plate beneath central and southern Costa Rica. Cessation of volcanic activity, low-temperature cooling of plutons in the Cordillera de Talamanca (CT), and rapid increases in sedimentation in the fore-arc and back-arc basins coincide with passage of the Nazca–Cocos–Caribbean triple junction and initiation of subduction of “rough” crust associated with Cocos–Nazca rifting 3.5 Ma, closely followed by initial subduction of the Cocos Ridge 2–3 Ma. None of the aforementioned geologic events occurred at a time that would allow for underplating by the Cocos Ridge. Rather they are probably related to complex interactions with subduction of complicated plates offshore. All of the aforementioned events indicate that the southern Central American subduction system has been in flux since at least 12 Ma.     

Oligocene to Recent tectonic history of the Central Solomon intra-arc basin as determined from marine seismic reflection data and compilation of onland geology

Systematic analysis of a grid of 3450 km of multichannel seismic reflection lines from the Solomon Islands constrains the late Tertiary sedimentary and tectonic history of the Solomon Island arc and its convergent interaction with the Cretaceous Ontong Java oceanic plateau (OJP). The OJP, the largest oceanic plateau on Earth, subducted beneath the northern edge of the Solomon arc in the late Neogene, but the timing and consequences of this obliquely convergent event and its role in the subduction polarity reversal process remain poorly constrained. The Central Solomon intra-arc basin (CSB), which developed in Oligocene to Recent time above the Solomon arc, provides a valuable record of the tectonic environment prior to and accompanying the OJP convergent event and the subsequent arc polarity reversal. Recognition of regionally extensive stratigraphic sequences—whose ages can be inferred from marine sedimentary sections exposed onland in the Solomon Islands—indicate four distinct tectonic phases affecting the Solomon Island arc. Phase 1: Late Oligocene–Late Miocene rifting of the northeast-facing Solomon Island arc produced basal, normal-fault-controlled, asymmetrical sequences of the CSB; the proto-North Solomon trench was probably much closer to the CSB and is inferred to coincide with the trace of the present-day Kia-Kaipito-Korigole (KKK) fault zone; this protracted period of intra-arc extension shows no evidence for interruption by an early Miocene period of convergent “soft docking” of the Ontong Java Plateau as proposed by previous workers. Phase 2: Late Miocene–Pliocene oblique convergence of the Ontong Java Plateau at the proto-North Solomon trench (KKK fault zone) and folding of the CSB and formation of the Malaita accretionary prism (MAP); the highly oblique and diachronous convergence between the Ontong Java plateau and the Solomon arc terminates intra-arc extension first in the southeast (Russell subbasin of the CSB) during the Late Miocene and later during the Pliocene in the northwest (Shortland subbasin of the CSB); folds in the CSB form by inversion of normal faults formed during Phase 1; Phinney et al. [Sequence stratigraphy, structural style, and age of deformation of the Malaita accretionary prism (Solomon arc-Ontong Java Plateau convergent zone)] show a coeval pattern of southeast to northwest younging in folding and faulting of the MAP. Phase 3: Late Pliocene–early Pleistocene arc polarity reversal and subduction initiation at the San Cristobal trench. Effects of this event in the CSB include the formation of a chain of volcanoes above the subducting Australia plate at the San Cristobal trench, the formation of the broad synclinal structure of the CSB with evidence for truncation at the uplifted flanks, and widespread occurrence of slides and “seismites” (deposits formed by seismic shaking). Phase 4: Pleistocene to Recent continued shortening and synclinal subsidence of the CSB. Continued Australia-Pacific oblique plate convergence has led to deepening of the submarine, elongate basin axis of the synclinal CSB and uplift of the dual chain of the islands on its flanks.     

Gondwana-derived microcontinents — the constituents of the Variscan and Alpine collisional orogens

The European Variscan and Alpine mountain chains are collisional orogens, and are built up of pre-Variscan “building blocks” which, in most cases, originated at the Gondwana margin. Such pre-Variscan elements were part of a pre-Ordovician archipelago-like continental ribbon in the former eastern prolongation of Avalonia, and their present-day distribution resulted from juxtaposition through Variscan and/or Alpine tectonic evolution. The well-known nomenclatures applied to these mountain chains are the mirror of Variscan resp. Alpine organization. It is the aim of this paper to present a terminology taking into account their pre-Variscan evolution at the Gondwana margin. They may contain relics of volcanic islands with pieces of Cadomian crust, relics of volcanic arc settings, and accretionary wedges, which were separated from Gondwana by initial stages of Rheic ocean opening. After a short-lived Ordovician orogenic event and amalgamation of these elements at the Gondwanan margin, the still continuing Gondwana-directed subduction triggered the formation of Ordovician Al-rich granitoids and the latest Ordovician opening of Palaeo-Tethys. An example from the Alps (External Massifs) illustrates the gradual reworking of Gondwana-derived, pre-Variscan elements during the Variscan and Alpine/Tertiary orogenic cycles.     

Growth of accretionary wedges and pulsed ophiolitic mélange formation by successive subduction of trench‐parallel volcanic elevations

Fault‐bounded coherent belts alternating with belts of mélanges are common in accretionary wedges and are usually interpreted as a result of imbrication along subduction zone megathrusts. Using the Neoproterozoic/early Cambrian Blovice accretionary complex (BAC), Bohemian Massif, as a case example, we present a new model for the origin of alternating belts through the repetition of several cycles of (1) offscraping and deformation of trench‐fill sediments to form the coherent units, interrupted by (2) arrival and subduction of linear, trench‐parallel volcanic elevations. The latter process leads to an increase in the wedge taper, triggering mass‐wasting and formation of olistostromes. At the same time, ophiolitic mélanges form by disruption of an upper part of the volcanic ridge and incorporation of the disrupted ocean‐floor succession into the olistostromes. Specifically, the BAC represents a complete section across an accretionary wedge and records three such major pulses of ophiolitic mélange formation through subduction of an outboard back‐arc basin.     

The Keepit arc: provenance of sedimentary rocks in the central Tablelands Complex,southern New England Orogen,Australia, as recorded by detrital zircon

Detrital zircon from the Carboniferous Girrakool Beds in the central Tablelands Complex of the southern New England Orogen, Australia, is dominated by ca 350–320 Ma grains with a peak at ca 330 Ma; there are very few Proterozoic or Archean grains. A maximum deposition age for the Girrakool Beds of ca 309 Ma is identified. These data overlap the age of the Carboniferous Keepit arc, a continental volcanic arc along the western margin of the Tamworth Belt. Zircon trace-element and isotopic compositions support petrographic evidence of a volcanic arc provenance for sedimentary and metasedimentary rocks of the central Tablelands Complex. Zircon Hf isotope data for ca 350–320 Ma detrital grains become less radiogenic over the 30 million-year record. This pattern is observed with maturation of continental volcanic arcs but is opposite to the longer-term pattern documented in extensional accretionary orogens, such as the New England Orogen. Volcanic activity in the Keepit arc is inferred to decrease rapidly at ca 320 Ma, based on a major change in the detrital zircon age distribution. Although subduction continues, this decrease is inferred to coincide with the onset of trench retreat, slab rollback and the eastward migration of the magmatic arc that led to the Late Carboniferous to early Permian period of extension, S-type granite production and intrusion into the forearc basin, high-temperature–low-pressure metamorphism, and development of rift basins such as the Sydney–Gunnedah–Bowen system.     

Mid–Cretaceous Episodic Magmatism and Tin Mineralization in Khingan-Okhotsk Volcano–Plutonic Belt, Far East Russia

Abstract: Age of magmatism and tin mineralization in the Khingan‐Okhotsk volcano–plutonic belt, including the Khingan, Badzhal and Komsomolsk tin fields, were reviewed in terms of tectonic history of the continental margin of East Asia. This belt consists mainly of felsic volcanic rocks and granitoids of the reduced type, being free of remarkable geomagnetic anomaly, in contrast with the northern Sikhote‐Alin volcano–plutonic belt dominated by oxidized‐type rocks and gold mineralization. The northern end of the Khingan‐Okhotsk belt near the Sea of Okhotsk, accompanied by positive geomagnetic anomalies, may have been overprinted by magmatism of the Sikhote‐Alin belt. Tin–associated magmatism in the Khingan‐Okhotsk belt extending over 400 km occurred episodically in a short period (9510 Ma) in the middle Cretaceous time, which is coeval with the accretion of the Kiselevka‐Manoma complex, the youngest accretionary wedge in the eastern margin of the Khingan‐Okhotsk accretionary terranes. The episodic magmatism is in contrast with the Cretaceous‐Paleogene long–lasted magmatism in Sikhote–Alin, indicating the two belts are essentially different arcs, rather than juxtaposed arcs derived from a single arc. The tin‐associated magmatism may have been caused by the subduction of a young and hot back‐arc basin, which is inferred from oceanic plate stratigraphy of the coeval accre‐tionary complex and its heavy mineral assemblage of immature volcanic arc provenance. The subduction of the young basin may have resulted in dominance of the reduced‐type felsic magmas due to incorporation of carbonaceous sediments within the accretionary complex near the trench. Subsequently, the back‐arc basin may have been closed by the oblique collision of the accretionary terranes in Sikhote–Alin, which was subjected to the Late Cretaceous to Paleogene magmatism related to another younger subduction system. These processes could have proceeded under transpressional tectonic regime due to oblique subduction of the paleo‐Pacific plates under Eurasian continent.     

Structural evolution and strike-slip tectonics off north-western Sumatra

Based on new multi-channel seismic data, swath bathymetry, and sediment echosounder data we present a model for the interaction between strike-slip faulting and forearc basin evolution off north-western Sumatra between 2°N and 7°N. We examined seismic sequences and sea floor morphology of the Simeulue- and Aceh forearc basins and the adjacent outer arc high. We found that strike-slip faulting has controlled the forearc basin evolution since the Late Miocene. The Mentawai Fault Zone extends up to the north of Simeulue Island and was most probably connected farther northwards to the Sumatran Fault Zone until the end of the Miocene. Since then, this northern branch jumped westwards, initiating the West Andaman Fault in the Aceh area. The connection to the Mentawai Fault Zone is a left-hand step-over. In this transpressional setting the Tuba Ridge developed. We found a right-lateral strike-slip fault running from the conjunction of the West Andaman Fault and the Tuba Ridge in SSW-direction crossing the outer arc high. As a result, extrusion formed a marginal basin north of Simeulue Island which is tilted eastwards by uplift along a thrust fault in the west. The shift of strike-slip movement in the Aceh segment is accompanied by a relocation of the depocenter of the Aceh Basin to the northwest, forming one major Neogene unconformity. The Simeulue Basin bears two major Neogene unconformities, documenting that differences in subsidence evolution along the northern Sumatran margin are linked to both forearc-evolution related to subduction processes and to deformation along major strike-slip faults.     

Post-collisional crustal extension setting and VHMS mineralization in the Jinshajiang orogenic belt, southwestern China

The Jinshajiang orogenic belt (JOB) of southwestern China, located along the eastern margin of the Himalayan–Tibetan orogen, includes a collage of continental blocks joined by Paleozoic ophiolitic sutures and Permian volcanic arcs. Three major tectonic stages are recognized based on the volcanic–sedimentary sequence and geochemistry of volcanic rocks in the belt. Westward subduction of the Paleozoic Jinshajiang oceanic plate at the end of Permian resulted in the formation of the Chubarong–Dongzhulin intra-oceanic arc and Jamda–Weixi volcanic arc on the eastern margin of the Changdu continental block. Collision between the volcanic arcs and the Yangtze continent block during Early–Middle Triassic caused the closing of the Jinshajiang oceanic basin and the eruption of high-Si and -Al potassic rhyolitic rocks along the Permian volcanic arc. Slab breakoff or mountain-root delamination under this orogenic belt led to post-collisional crustal extension at the end of the Triassic, forming a series of rift basins on this continental margin arc. Significant potential for VHMS deposits occurs in the submarine volcanic districts of the JOB. Mesozoic VHMS deposits occur in the post-collisional extension environment and cluster in the Late Triassic rift basins.     

The Misis–Andırın Complex: a Mid-Tertiary melange related to late-stage subduction of the Southern Neotethys in S Turkey

The Mid-Tertiary (Mid-Eocene to earliest Miocene) Misis–Andırın Complex documents tectonic-sedimentary processes affecting the northerly, active margin of the South Tethys (Neotethys) in the easternmost Mediterranean region. Each of three orogenic segments, Misis (in the SW), Andırın (central) and Engizek (in the NE) represent parts of an originally continuous active continental margin. A structurally lower Volcanic-Sedimentary Unit includes Late Cretaceous arc-related extrusives and their Lower Tertiary pelagic cover. This unit is interpreted as an Early Tertiary remnant of the Mesozoic South Tethys. The overlying melange unit is dominated by tectonically brecciated blocks (>100 m across) of Mesozoic neritic limestone that were derived from the Tauride carbonate platform to the north, together with accreted ophiolitic material. The melange matrix comprises polymict debris flows, high- to low-density turbidites and minor hemipelagic sediments.The Misis–Andırın Complex is interpreted as an accretionary prism related to the latest stages of northward subduction of the South Tethys and diachronous continental collision of the Tauride (Eurasian) and Arabian (African) plates during Mid-Eocene to earliest Miocene time. Slivers of Upper Cretaceous oceanic crust and its Early Tertiary pelagic cover were accreted, while blocks of Mesozoic platform carbonates slid from the overriding plate. Tectonic mixing and sedimentary recycling took place within a trench. Subduction culminated in large-scale collapse of the overriding (northern) margin and foundering of vast blocks of neritic carbonate into the trench. A possible cause was rapid roll back of dense downgoing Mesozoic oceanic crust, such that the accretionary wedge taper was extended leading to gravity collapse. Melange formation was terminated by underthrusting of the Arabian plate from the south during earliest Miocene time.Collision was diachronous. In the east (Engizek Range and SE Anatolia) collision generated a Lower Miocene flexural basin infilled with turbidites and a flexural bulge to the south. Miocene turbiditic sediments also covered the former accretionary prism. Further west (Misis Range) the easternmost Mediterranean remained in a pre-collisional setting with northward underthrusting (incipient subduction) along the Cyprus arc. The Lower Miocene basins to the north (Misis and Adana) indicate an extensional (to transtensional) setting. The NE–SW linking segment (Andırın) probably originated as a Mesozoic palaeogeographic offset of the Tauride margin. This was reactivated by strike-slip (and transtension) during Later Tertiary diachronous collision. Related to on-going plate convergence the former accretionary wedge (upper plate) was thrust over the Lower Miocene turbiditic basins in Mid–Late Miocene time. The Plio-Quaternary was dominated by left-lateral strike-slip along the East Anatolian transform fault and also along fault strands cutting the Misis–Andırın Complex.     

Jurassic Subduction of the Paleo-Pacific Ocean in NE China: Zircon U–Pb and Sr-Nd-Hf isotopic Evidence from the Huashan and Taili Monzogranites

The Qilian orogen along the NE edge of the Tibet‐Qinghai Plateau records the evolution of Proto‐Tethyan Ocean that closed through subduction along the southern margin of the North China block during the Early Paleozoic. The South Qilian belt is the southern unit of this orogen and dominated by Cambrian‐Ordovician volcano‐sedimentary rocks and Neoproteozoic Hualong complex that contains similar rock assemblages of the Central Qilian block. Our recent geological mapping and petrologic results demonstrate that volcano‐sedimentary rocks show typical rock assembles of a Cambrian‐early Ordovician arc‐trench system in Lajishan Mts. along the northern margin of the Hualong Complex. Island arc rocks including basalt, andesite, dacite, rhyolite, and breccia is in fault contact with ophiolite complex consisting of mantle peridotite, serpentinite, gabbro, dolerite, plagiogranite, and basalt. Accretionary complexes are tectonically separated from the ophiolite‐arc rocks, with various rock assemblages spatially. They consist of pillow basalt, basalt breccia, tuff, chert, and limestone blocks with a seamount origin within the scaly shale in Dingmaoshan and Donggoumeikuang areas, and basalt, chert, and sandstone blocks within muddy shale matrix and mélange at Lajishankou area. Abundant radiolarians occur in red chert, and trilobite, brachiopod, and coral fossils occur within Dingmaoshan limestone blocks. Although partial basalt or chert blocks are highly disrupted, duplex, thrust fault, rootless intrafolial fold, tight fold, and penetrative foliation are well‐developed at Donggoumeikuang area. Spatially, accretionary complexes lie structurally beneath ophiolite complex and above the turbidites of the Central Qilian block. Ophiolite and accretionary complexes are also overlapped by late Ordovician molasse deposits sourced from Cambrian arc‐trench system and the Central Qilian block. These observations demonstrate that a Cambrian‐early Ordovician trench‐arc system within the South Qilian belt formed during the early Paleozoic southward subduction of the South Qilian Ocean collided with the Central Qilian block prior to the late Ordovician.     

燕山运动与东亚构造体制的转变

构造体制转变的本质是动力学体系的转变。东亚构造体制的转变是从一个汇聚碰撞的动力学体系转变为一个活动大陆边缘的动力学体系。其核心问题是古太平洋板块开始向新生的亚洲大陆下俯冲。在这一独特的动力学体系转变过程中 ,产生了陆缘俯冲消减增生杂岩带 ,火山弧和相关的表壳变形等一系列标志。文中强调以自然的、显著的、易于识别的标志———火山弧的出现代表东亚构造域动力学体系的转变 ;指出翁文灏命名的燕山运动A幕———髫髻山组火山岩下的不整合 ( ( 16 0± 5 )Ma前 )和B幕———张家口组火山岩下的不整合 ( ( 13 5± 1)Ma前 )代表这一转变。也就是说 ,燕山运动是东亚构造体制转变的产物 ,其出现有着深刻的地球动力学背景     

Seismicity, gravity anomalies and lithospheric structure of the Andaman arc, NE Indian Ocean

The Andaman arc in the northeastern Indian Ocean defines nearly 1100 km long active plate margin between the India and Burma plates where an oblique Benioff zone develops down to 200 km depth. Several east-trending seismologic sections taken across the Andaman Benioff Zone (ABZ) are presented here to detail the subduction zone geometry in a 3-D perspective. The slab gravity anomaly, computed from the 3-D ABZ configuration, is a smooth, long-wavelength and symmetric gravity high of 85 mGal amplitude centering to the immediate east of the Nicobar Island, where, a prominent gravity “high” follows the Nicobar Deep. The Slab-Residual Gravity Anomaly (SRGA) and Mantle Bouguer Anomaly (MBA) maps prepared for the Andaman plate margin bring out a double-peaked SRGA “low” in the range of − 150 to − 240 mGal and a wider-cum-larger MBA “low” having the amplitude of − 280 to − 315 mGal demarcating the Andaman arc–trench system. The gravity models provide evidences for structural control in propagating the rupture within the lithosphere. The plate margin configuration below the Andaman arc is sliced by the West Andaman Fault (WAF) as well as by a set of sympathetic faults of various proportions, often cutting across the fore-arc sediment package. Some of these fore-arc thrust faults clearly give rise to considerably high post-seismic activity, but the seismic incidence along the WAF further east is comparatively much less particularly in the north, although, the lack of depth resolution for many of the events prohibits tracing the downward continuity of these faults. Tectonic correlation of the gravity-derived models presented here tends to favour the presence of oceanic crust below the Andaman–Nicobar Outer Arc Ridge.     

Cretaceous accretionary–collision complexes in central Indonesia

The geology of Cretaceous accretionary–collision complexes in central Indonesia is reviewed in this paper. The author and his colleagues have investigated the Cretaceous accretionary–collision complexes by means of radiolarian biostratigraphy and metamorphic petrology, as well as by geological mapping. The results of their work has revealed aspects of the tectonic development of the Sundaland margin in Cretaceous time. The Cretaceous accretionary–collision complexes are composed of various tectonic units formed by accretionary or collision processes, forearc sedimentation, arc volcanism and back arc spreading. The tectonic units consist of chert, limestone, basalt, siliceous shale, sandstone, shale, volcanic breccia, conglomerate, high P/T and ultra high P metamorphic rocks and ultramafic rocks (dismembered ophiolite). All these components were accreted along the Cretaceous convergent margin of the Sundaland Craton. In the Cretaceous, the southeastern margin of Sundaland was surrounded by a marginal sea. An immature volcanic arc was developed peripherally to this marginal sea. An oceanic plate was being subducted beneath the volcanic arc from the south. The oceanic plate carried microcontinents which were detached fragments of Gondwanaland. Oceanic plate subduction caused arc volcanism and formed an accretionary wedge. The accretionary wedge included fragments of oceanic crust such as chert, siliceous shale, limestone and pillow basalt. A Jurassic shallow marine allochthonous formation was emplaced by the collision of continental blocks. This collision also exhumed very high and ultra-high pressure metamorphic rocks from the deeper part of the pre-existing accretionary wedge. Cretaceous tectonic units were rearranged by thrusting and lateral faulting in the Cenozoic era when successive collision of continental blocks and rotation of continental blocks occurred in the Indonesian region.