Tectonic Connection Research Articles

When did the Dead Sea fault become a transform?

This study re-evaluates the ~20 Myr development of the Dead Sea Fault System (DSFS) and its tectonic definition as a transform plate boundary. The DSFS conveys sinistral displacement between the Arabian-Sinai plates: ~105 km along its ~400 km-long southern segment (Gulf of Aqaba-Eilat to the Hula basin); ~90 km and 4–16 km along the central and northern segments (~190 km long each, across Lebanon, western Syria, and southern Turkey). A review of previous studies, combined with new seismological data analysis, associates the northward displacement decline with obstacles along the DSFS propagation path. During the Miocene, DSFS propagated up to the NW-trending Irbid rift (1st obstacle) and splayed NW towards the Mediterranean and NE along the Late Cretaceous Palmyra fold-thrust belt (2nd obstacle). Its reactivation uplifted the Hermon and the Anti-Lebanon mountain ranges. Northward DSFS propagation into the cold and rigid Aleppo plateau lithosphere (3rd obstacle) was stalled until the early Pliocene (~5 Ma), when volcanism and ongoing regional tectonic forcing enabled the DSFS to shift to the Yammouneh fault and rupture through the Missyaf-Ghab branch farther north (central and northern segments, respectively). During the Pleistocene-recent, connection of the DSFS with the ophiolite belt and East Anatolian Fault System (EAFS) along the Bitlis suture zone (4th obstacle) has not yet been established. Seismological data show a clear separation between the EAFS and the DSFS, while seismicity is scattered across the Aleppo plateau and the central and northern DSFS segments. In contrast, seismicity is localized along the southern DSFS segment. Our findings suggest that, at present, the DSFS has still not made a structural, seismologic, and tectonic connection with the EAFS. Hence, we redefine the DSFS as a pre-transform and suggest its interaction with the EAFS is a world-class example of a fault-fault-fault triple junction in the making.

Sedimentary provenance supports a mid-paleozoic tectonic connection between the Junggar and Altai terranes in central Asia

The provenance of Precambrian detritus in the Junggar and Altai terranes provides crucial constraints on the peri-Siberian accretionary tectonic evolution in the middle Paleozoic. The Precambrian detrital zircons have no coeval magmatic equivalents in the Junggar terrane but show U–Pb age spectra and εHf(t) values comparable to those in the Altai terrane. The correlations suggest that the old detrital materials in the Junggar and Altai terranes were most likely derived from the Siberia craton and adjacent Tuva-Mongolian microcontinent. Paleozoic zircons in the Junggar terrane display a εHf(t) pattern from large spread to dominantly positive values at ca. 420–410 Ma. Such an abrupt change points to an accretionary tectonic transition from an advancing to retreating mode during mid-Paleozoic time, synchronous with similar tectonic switch occurring in the Altai terrane. Taking into account the temporal and spatial relations in sedimentation, tectonism and arc magmatism, we propose that the Junggar terrane had once collided onto the peri-Siberian Altai terrane to receive abundant old detritus from the Siberian continent in the Silurian–early Devonian. They were subsequently separated at ca. 420–410 Ma, possibly due to the slab rollback of the subducting Paleo-Asian Ocean (PAO) plate. These results constrain an Early Paleozoic tectono-paleogeographic boundary of the CAOB along the North Tianshan–Solonker suture zone, and also imply a long-lived PAO subduction was responsible for the Neoproterozoic to Paleozoic accretionary orogenesis at the margins of southern Siberia, eastern Kazakhstan, and northern Gondwana.

Rift and plume: a discussion on active and passive rifting mechanisms in the Afro-Arabian rift based on synthesis of geophysical data

Abstract. The causal relationship between the activity of mantle plumes and continental break-up is still elusive. The Afro-Arabian rift system offers an opportunity to examine these relationships, in which an ongoing continental break-up intersects a large Cenozoic plume-related flood basalt series. In the Afar region, the Gulf of Aden, the Red Sea, and the Main Ethiopian Rift form an R-R-R triple junction within plume-related flood basalt series. We provide an up-to-date synthesis of the available geophysical and geological data from this region. We map the rift architecture in the intersection region by applying the difference in Gaussians to the topography and the bathymetry and interpreting vertical gravity gradients and Bouguer anomalies. With the aid of these methods we review the spatiotemporal constraints in the evolution of the different features of the plume–rift system. Our results show rough and irregular morphologies of the Gulf of Aden and the Red Sea arms in contrast to the symmetric, continuous, and smooth Main Ethiopian Rift. The triple junction formed by the northeastward propagation of the Main Ethiopian Rift and developed simultaneously with the abandonment of the tectonic connection between the Red Sea and the Gulf of Aden through Bab al Mandab Strait. The triple junction was the last feature to develop in the plume–rift system and marked a tectonic reorganization. By this time, all rift arms were sufficiently evolved and the break-up between Africa and Arabia was already accomplished. We argue that the classical active and passive rifting mechanisms cannot simply explain the progressive development of the Afro-Arabian rift. Instead, we propose a plume-induced plate rotation, which includes an interaction between active and passive mechanisms. In this tectonic scenario, the arrival of the Afar plume provided a push force that promoted the rotation of Arabia around a nearby pole located to the northwest of the plate boundary, enabling the rifting and, ultimately, the break-up of Arabia from Africa.

Seismically-induced changes in sea-level markers: Jolly Buoy Island, South Andaman

Sea-level markers like coastlines, landforms, tidal notches and coral reefs can unveil the seismic behaviour of subduction processes. Jolly Buoy Island, South Andaman, has undergone a remarkable change in shape and orientation due to rising sea levels and active tectonics. Involving integrated field, remote sensing and GIS techniques, we systematically estimated shoreline change rate, reef uplift and morphometry of tidal notches to track inter-, co- and postseismic periods. We quantified higher subsidence rates in the SW coast (−0.227m) than in the NE coast (−0.128m) during the coseismic period from geomorphology and biological resource mapping. The uplift was evident during the postseismic period in the NE and Eastern part of the Island compared to the SW and Western coast. The shoreline change analysis corroborates the results of the seaward migration of the northeast coastline. A gradual fading of uplift towards the southwest coast cause erosion in that part. The tidal notches identified during fieldwork also suggest similar subsidence and uplift patterns. Finally, here we proposed a model of geomorphological evolution of Jolly Buoy with possible local tectonic connections. More seismic data and geomorphic evidence from other islands can reveal regional significance.

A Single Dras‐Kohistan‐Ladakh Arc Revealed by Volcaniclastic Records

AbstractTectonic interpretations of arc remnants in the Himalayan orogen remain uncertain, despite their important implications for the overall convergence history between India and Eurasia. Provenance results from deep‐water volcaniclastic rocks of the Indus Suture Zone in Ladakh provide new constraints on the Mesozoic tectonic evolution of the Dras and Kohistan‐Ladakh arcs. Detrital zircon (DZ) U‐Pb ages and whole‐rock geochemistry of the fault‐bounded Upper Cretaceous Nindam and Paleocene Jurutze formations present age patterns and compositions that are consistent with those of the Dras and Kohistan‐Ladakh arcs, respectively. The combination of DZs of the Nindam and Jurutze formations with the igneous zircons of the Dras and Kohistan‐Ladakh arcs shows similar age distributions that support a Late Jurassic to Paleocene tectonic connection between all these units. We argue that the secular trends in geochemical composition of DZs and volcaniclastic material are consistent with the magmatic evolution of one convergent margin, which shifted from a primitive to a mature stage during the Late Cretaceous. The recognition of a single Dras‐Kohistan‐Ladakh arc sets the stage for reevaluating competing scenarios of the Mesozoic evolution of the India–Eurasia convergent system. We find that the most likely scenario is that of a Jurassic arc formed above a south‐dipping intraoceanic subduction zone and accreted to Eurasia during the Early Cretaceous, after which it evolved above a north‐dipping subduction zone.

Konrad Wachsman’s Grapevine Structure: Timber Variations on a Pre-Existing Concept

This paper offers a speculative reflection on the structural concept developed by Konrad Wachsmann in 1953 and built in timber by burkhalter sumi together with Marko Pogacnik IUAV at the Venice Biennale in 2018. The resulting construction, entitled the “Grapevine,” is analyzed according to changing, fragmentary viewpoints that aim to expand the field of its understanding. The Gestalt (shape)—to a certain extent the “aesthetic culmination” of the construction—is examined with regard to the object’s immediate perception. In contrast, a semantic approach questions and interprets the “Grapevine” according to its overriding meaning as a “modern totem.” The object is then brought into relation to sculptures by Joel Shapiro. “Figure” (1989) raises the question of the unstable balance as an artistic intention, while the detail of “étude” (2006) questions the fragility of the joint, in contrast to the rigidity of tectonic connections as assumed by Gottfried Semper. The argument thus comes closer to the conceptual orientation of the Wachsmann construction, namely the knot subjected to tensile stress. Centered on the “Grapevine” installation, this paper illustrates how timber knowledge is formed outside the academy, in dialogues between architects, engineers and timber contractors.

Lithospheric Formation and Evolution of Eastern North American Continent

AbstractLithospheric layering contains critical information about continental formation and evolution. However, discrepancies on the depth distributions of lithospheric layers have significantly limited our understanding of possible tectonic connections among the layers. Here, we construct a high‐resolution shear velocity model of eastern North America using full‐wave ambient noise simulation and inversion by integrating onshore and offshore seismic datasets. Our new model reveals large lateral variations of lithosphere thickness approximately across the major tectonic boundaries, strong low‐velocity anomalies underlying the thinner lithosphere, and multiple low‐velocity layers within the continental lithosphere. We suggest that the present mantle lithosphere beneath eastern North America was formed and modified through multiple stages of tectonic processes, among which metasomatism may have significantly contributed to the observed intralithospheric low‐velocity layers. The sharp thickness variation of lithosphere promoted edge‐driven mantle convection, which has been consequently modifying the overlying mantle lithosphere and further sharpening the gradient of lithosphere thickness

Analysis and interpretation of geophysical data to delineate the geologic structures of Abu Dabbab area, South Eastern Desert, Egypt

ABSTRACT The present study aims to identify the geologic structure of the Abu Dabbab area. The previous work state that the study area contains different ore minerals such as Tantalum, Niobium, Cassiterite, Gold, and sulphides. Processing, analysis, and interpretation of aeromagnetic and recorded seismic events data of the study area were to define the seismic activity zones and the main trend in the study area and its relation with ore deposits distribution. The area is controlled by different structural elements of trends NE-SW, NNW-SSE, and E-W. The results indicated that most of ore deposits are located at an active fault zone which is characterised by high seismic activity. There are high deformation zone trends NE-SW. There is a high value zone located approximately at the centre of the northern portion of the study area. This high energy zone is oriented towards NE and extends to the Red Sea. The energy map shows that the energy released from the study area is considered as a part of the energy release of the Red Sea area suggesting a tectonic connection between this region and the Red Sea.

Tectonomagmatic evolution of a Jurassic Cordilleran flare-up along the Korean Peninsula: Geochronological and geochemical constraints from granitoid rocks

This study used new and published U-Pb geochronological, chemical, and Sr-Nd-Hf-O isotopic data (n > 2500) from Jurassic granite-granodiorite-diorite-monzonite-gabbro plutons in the southern part of the Korean Peninsula to assess the spatiotemporal evolution of a flare-up magmatism, its tectonic connection, and specific contributions of mantle and crustal reservoirs to the magmas generated. After a ~15 m.y. magmatic gap in the Late Triassic, calc-alkaline granitoids intruded into the outboard Yeongnam Massif, then magmatic activity migrated systematically toward the inboard Gyeonggi Massif. The early phase of the Jurassic magmatism is represented by relatively sodic plutons showing distinctly primitive isotopic signatures. The crustal signature of the plutons became increasingly prominent with decreasing age. Voluminous inboard plutons in the Gyeonggi Massif and the intervening Okcheon Belt are dominated by Middle Jurassic peraluminous granites that show isotopic compositions conspicuously shifted toward old crustal values. The Nd-Hf isotopic compositions of the inboard plutons are distinctly less radiogenic than those of Jurassic plutons in Southwest Japan and southeastern China, which corroborates the North China affinity of the Yeongnam and Gyeonggi massifs. The geochronological and geochemical data compiled in this study suggest a tectonomagmatic model consisting sequentially of (1) an extension-dominated arc system in the margin of the Yeongnam Massif (ca. 200–190 Ma); (2) low-angle subduction and the development of an advancing arc system (ca. 190–180 Ma); (3) continued low-angle subduction, extensive underthrusting of fertile crustal materials to the arc root, and consequent magmatic flare-up (ca. 180–170 Ma); and (4) flat subduction and the development of the Honam Shear Zone (ca. 170–160 Ma). The subsequent magmatic lull and previous dating results for synkinematic rocks and minerals indicate that the compressional arc system was maintained until the Early Cretaceous.

Geology, geochronology and geochemistry of large Duobaoshan Cu–Mo–Au orefield in NE China: Magma genesis and regional tectonic implications

Duobaoshan is the largest porphyry-related Cu–Mo–Au orefield in northeastern (NE) Asia, and hosts a number of large-medium porphyry Cu (PCDs), epithermal Au and Fe–Cu skarn deposits. Formation ages of these deposits, from the oldest (Ordovician) to youngest (Jurassic), have spanned across over 300 ​Ma. No similar orefields of such size and geological complexity are found in NE Asia, which reflects its metallogenic uniqueness in forming and preserving porphyry-related deposits. In this study, we explore the actual number and timing of magmatic/mineralization phases, their respective magma genesis, fertility, and regional tectonic connection, together with the preservation of PCDs. We present new data on the magmatic/mineralization ages (LA–ICP–MS zircon U–Pb, pyrite and molybdenite Re–Os dating), whole-rock geochemistry, and zircon trace element compositions on four representative deposits in the Duobaoshan orefield, i.e., Duobaoshan PCD, Tongshan PCD, Sankuanggou Fe–Cu skarn, and Zhengguang epithermal Au deposits, and compiled published ones from these and other mineral occurrences in the orefield.In terms of geochronology, we have newly summarized seven magmatic phases in the orefield: (1) Middle–Late Cambrian (506–491 ​Ma), (2) Early and Middle Ordovician (485–471 ​Ma and ~462 ​Ma), (3) Late Ordovician (450–447 ​Ma), (4) Early Carboniferous and Late-Carboniferous to Early Permian (351–345 and 323–291 ​Ma), (5) Middle–Late Triassic (244–223 ​Ma), (6) Early–Middle and Late Jurassic (178–168 ​Ma and ~150 ​Ma), and (7) Early Cretaceous (~112 ​Ma). Three of these seven major magmatic phases were coeval with ore formation, including (1) Early Ordovician (485–473 ​Ma) porphyry-type Cu–Mo-(Au), (2) Early–Middle Triassic (246–229 ​Ma) porphyry-related epithermal Au-(Cu–Mo), and (3) Early Jurassic (177–173 ​Ma) Fe–Cu skarn mineralization. Some deposits in the orefield, notably Tongshan and Zhengguang, were likely formed by more than one mineralization events.In terms of geochemistry, ore-causative granitoids in the orefield exhibit adakite-like or adakite-normal arc transitional signatures, but those forming the porphyry-/epithermal-type Cu–Mo–Au mineralization are largely confined to the former. The varying but high Sr/Y, Sm/Yb and La/Yb ratios suggest that the ore-forming magmas were mainly crustal sourced and formed at different depths (clinopyroxene-/amphibole-/garnet-stability fields). The adakite-like suites may have formed by partial melting of the thickened lower crust at 35–40 ​km (for the Early Ordovician arc) and >40 ​km (for the Middle–Late Triassic arc) depths. The Early Jurassic Fe–Cu skarn ore-causative granitoids show an adakitic-normal arc transitional geochemical affinity. These granitoids were likely formed by partial melting of the juvenile lower crust (35–40 ​km depth), and subsequently modified by assimilation and fractional crystallization (AFC) processes.In light of the geological, geochronological and geochemical information, we proposed the following tectonometallogenic model for the Duobaoshan orefield. The Ordovician Duobaoshan may have been in a continental arc setting during the subduction of the Paleo-Asian Ocean, and formed the porphyry-related deposits at Duobaoshan, Tongshan and Zhengguang. Subduction may have ceased in the latest Ordovician, and the regional tectonics passed into long subsidence and extension till the latest Carboniferous. This extensional tectonic regime and the Silurian terrestrial-shallow marine sedimentation had likely buried and preserved the Ordovician Duobaoshan magmatic-hydrothermal system. The south-dipping Mongol-Okhotsk Ocean subduction from north of the orefield had generated the Middle–Late Triassic continental arc magmatism and the associated Tongshan PCD and Zhengguang epithermal Au mineralization (which superimposed on the Ordovician PCD system). The Middle Jurassic closure of Mongol-Okhotsk Ocean in the northwestern Amuria block (Erguna terrane), and the accompanying Siberia-Amuria collision, may have placed the Paleo-Pacific subduction system in NE China (including the orefield) under compression, and formed the granodiorite-tonalite and Fe–Cu skarn deposits at Sankuanggou and Xiaoduobaoshan. From the Middle Jurassic, the consecutive accretion of Paleo-Pacific arc terranes (e.g., Sikhote-Alin and Nadanhada) onto the NE Asian continental margin may have gradually distant the Duobaoshan orefield from the subduction front, and consequently arc-type magmatism and the related mineralization faded. The minor Late Jurassic and Cretaceous unmineralized magmatism in the orefield may have triggered mainly by the far-field extension led by the post-collisional (Siberia-Amuria) gravitational collapse and/or Paleo-Pacific backarc-basin opening.

Proterozoic evolution of Eastern Dharwar and Bastar cratons, India – An overview of the intracratonic basins, craton margins and mobile belts

Based on critical analysis of stratigraphic succesions in the Proterozoic intracratonic basins, geochronological data and possible connections or disconnections with adjacent fold belts and craton margin mobile belts, an overview of the Proterozoic evolution of the Eastern Dharwar and Bastar cratons in India is presented. The Chattisgarh and Cuddapah basins in these cratons with Archean nuclei host sedimentary successions ranging in age from the Paleoproterozoic to the Ediacaran period, and representing several silicilastic and carbonate cycles. The Proterozoic successions of the Pranhita–Godavari valley (PGV) basin along the Dharwar–Bastar join, record multiple rifting since late Neoarchean suturing of the two cratons. We postulate a first order stratigraphic correlation across the cratons and their join and discuss how major sea level fluctuations coupled with regional tectonic events shaped the development of unconformity bound successions, adjoining fold belts and the mobile belts with supposed global tectonic connections. The oldest Paleoproterozoic intracratonic sedimentation is preserved in the Cuddapah and PGV basins, while sedimentation in the Bastar craton is largely Mesoproterozoic. The fluviodeltaic to shallow marine Neoproterozoic sedimentation followed emplacement of end-Mesoproterozoic kimberlites and lamproites indicating thermal rejuvenation of the Indian continental crust. The allochthonus Nallamalai fold belt in eastern Cuddapah basin and the early Mesoproterozoic fold belt in PGV basin point to craton margin crustal convergences which punctuated the Paleoproterozoic sedimentation. Widespread development of carbonate bearing sequences in the Mesoproterozoic to Neoproterozoic successions point to peneplanation of the cratons and stable platformal sedimentation. The Neoproterozoic sedimentation was terminated following the docking of the Eastern Ghats belt to the eastern margin of the Dharwar–Bastar ensemble and possible final tectonic hiccups in the Central Indian Tectonic zone bordering the Bastar craton. The available data and their analysis rule out any foreland basin type connection between the Eastern Ghats belt and cratonic sedimentation in Bastar and Eastern Dharwar.

Basin stratigraphy, sea‐level fluctuations and their global tectonic connections—evidence from the Proterozoic Cuddapah Basin

The Cuddapah Supergroup succession can be divided into four unconformity‐bound sequences, namely, the Papaghni, Chitravati, Srisailam and Kurnool groups and formation representing four major cycles of sedimentation. The oldest sequence, the Papaghni Group is represented by fan‐delta, prodelta and shallow shelf deposits. The rifting stage of the basin evolution is attested by the immature delta succession deposited as a major fault‐controlled basin evolution, and was followed by the early subsidence stage. Basement uplift and a hiatus in deposition follows the first cycle of sedimentation. The Chitravati Group, representing the second cycle of sedimentation, consists of mature sandstones separated by a heterogeneous shale–sandstone–dolomite interval. The third cycle starts with the deposition of widespread coastal fluvial to shallow marine sandstone of the Srisailam Formation, and the fourth cycle is represented by the Kurnool Group consisting of conglomerates, feldspathic sandstones, supermature quartzarenites, minor shale and carbonates. Each cycle represents a rifting phase followed by a stable subsidence stage when the basin evolved into a large epicontinental sea. The supermature Gandikota Quartzite of the Chitravati Group and the Paniam Quartzite of the Kurnool Group represent relative sea‐level fall and forced regression. The siliciclastics in each of the sequences display signatures of macrotidal sedimentation pointing to open ocean connection. The sequences further display signatures of passive margin sedimentation with multiple events of carbonate‐shale rhythmite deposition. Mafic flows and dykes in the Papaghni and Chitravati groups reflect thermal anomalies associated with phased crustal extension; successive extensional phases were punctuated by basin inversion. Extensive and pulsed development of epicontinental seas as recorded in the Cuddapah sequences in the south Indian craton, possibly reflect global sea‐level changes associated with supercontinent (eg. Columbia in the Palaeoproterozoic) break‐up and assembly. Copyright © 2012 John Wiley & Sons, Ltd.

Connecting the Yakima fold and thrust belt to active faults in the Puget Lowland, Washington

[1] High-resolution aeromagnetic surveys of the Cascade Range and Yakima fold and thrust belt (YFTB), Washington, provide insights on tectonic connections between forearc and back-arc regions of the Cascadia convergent margin. Magnetic surveys were measured at a nominal altitude of 250 m above terrain and along flight lines spaced 400 m apart. Upper crustal rocks in this region have diverse magnetic properties, ranging from highly magnetic rocks of the Miocene Columbia River Basalt Group to weakly magnetic sedimentary rocks of various ages. These distinctive magnetic properties permit mapping of important faults and folds from exposures to covered areas. Magnetic lineaments correspond with mapped Quaternary faults and with scarps identified in lidar (light detection and ranging) topographic data and aerial photography. A two-dimensional model of the northwest striking Umtanum Ridge fault zone, based on magnetic and gravity data and constrained by geologic mapping and three deep wells, suggests that thrust faults extend through the Tertiary section and into underlying pre-Tertiary basement. Excavation of two trenches across a prominent scarp at the base of Umtanum Ridge uncovered evidence for bending moment faulting possibly caused by a blind thrust. Using aeromagnetic, gravity, and paleoseismic evidence, we postulate possible tectonic connections between the YFTB in eastern Washington and active faults of the Puget Lowland. We suggest that faults and folds of Umtanum Ridge extend northwestward through the Cascade Range and merge with the Southern Whidbey Island and Seattle faults near Snoqualmie Pass 35 km east of Seattle. Recent earthquakes (MW ≤ 5.3) suggest that this confluence of faults may be seismically active today.

Zircon U-Pb age and o isotope evidence for neoproterozoic low-18O magmatism during supercontinental rifting in South China: Implications for the snowball earth event

Identification of Neoproterozoic low δ¹⁸O igneous rocks is a key to demonstrate that high-T water-rock interaction and low-¹⁸O magmatism in rift tectonic zones can serve as an efficient interface to transport heat and material from the Earth9s interior to exterior at the onset of the snowball Earth event. Low δ¹⁸O values of −10.9 to +4.4 permil characteristic of meteoric origin were observed, on an areal extent over 30,000 km², for mid-Neoproterozoic metaigneous zircons from the ultrahigh-pressure eclogite-facies metamorphic belt of Triassic ages along the Dabie-Sulu orogenic belt, China. Although the zircon O isotope system could be reset to acquire its low δ¹⁸O values by exchange with matrix minerals during “wet” eclogite-facies metamorphism, the abnormal ¹⁸O depletion is confirmed by occurrence of Neoproterozoic low δ¹⁸O zircons in low-grade metaigneous rocks in the same belt. Cathodoluminscence imaging of zircons from low-grade metagranitoid and metavolcanic rocks shows preservation of the internal structures of oscillatory zoning typical of magmatic origin. Hornblende from two granites of low δ¹⁸O zircons gave Ar-Ar plateau ages of 747 ± 6 and 776 ± 12 Ma, ruling out that Phanerozoic metamorphism effected mineral O isotope values. Two groups of U-Pb ages were measured at 756 ± 5 Ma and 782 ± 5 Ma, respectively, for the low δ¹⁸O zircons. This indicates that low δ¹⁸O zircons crystallized during two episodes of low-¹⁸O magmatism in response to tectonic evolution from supercontinental rifting at ∼780 Ma to breakup at ∼750 Ma. The second episode of low-¹⁸O magmatism is contemporaneous with the continental Kaigas iceage. A plate-rift model is advanced to account for the tectonic connection between the low-¹⁸O magmatism, the continental glaciation and the supercontinental rifting during the Cryogenian period. High-T meteoric water-rock interaction occurred prior to low-¹⁸O magmatism in rift tectonic zones, and caldera collapse was responsible for melting of hydrothermally altered low δ¹⁸O rocks during rifting of the South China Block from the Rodinia supercontinent.

The ultimate expanding earth hypothesis

The ultimate expanding earth hypothesis

Significance of earthquake‐related anomalies in fluids of Val D’Agri (southern Italy)

Geochemical investigations carried out at the Campano–Lucano Apennine (Southern Italy) revealed the presence of fluids composed of a mixing between components of shallow and deep origin, where mantle‐derived helium is also detectable. For the gas phase, the deep component is represented by both CH4 and CO2‐rich gases, while the shallow one is N2‐dominated. Coinciding with the 3 April 1996 ML=4.9 earthquake, the CH4‐rich component mixed with the shallow, N2‐dominated one at the Tramutola well (Val d’Agri), displaying wide variations in mixing proportions. In contrast, no significant modifications occurred in relation to the 1998 ML=5.5 event. According to the collected data, an earthquake‐related transient modification of local crustal permeability is suggested for the 1996 event. The different crustal response to the two events may be related to different stress distributions around the epicentres or may suggest a different tectonic connection between the Val d’Agri and the two earthquake locations.

The recognizing of ca. 1.95 Ga tectono-thermal eventin Kongling nucleus and its significance for the evolution of Yangtze Block, South China

Some 1.95 Ga metamorphism of high-grade Archean rocks in Kongling terrain, continental nucleus of Yangtze Block, South China, are recognized by Sm-Nd dating. This event is further confirmed by the ages of single zircon SHRIMP U-Pb and K-Ar analyses of TTG and (or) paragneisses, and intrusions of potassic-granitic batholith in the region. The coincidence in period between the high-grade metamorphism in the Kongling area and the creation of major basement rocks of its neighborhoods of the Yangtze Block around the Kongling Archean nucleus makes it a favorable explanation for their tectonic connections that, in the whole Yangtze Block there was some tectono-thermal event of ca. 2.0-1.8 Ga, which resulted in the formation of unitive Yangtze basement.

Gondwana assembly: The view from Southern Africa and East Gondwana

Neoproterozoic-Cambrian tectonism in Africa, Antarctica and formerly adjacent parts of East Gondwana records the final assembly of the Gondwana supercontinent. Here we compile recent data regarding the timing and kinematics of tectonism for critical parts of southern Africa and East Gondwana, focusing on the period between ~ 650-500 Ma, and integrate these data into a regional framework in order to investigate aspects of the assembly of this portion of Gondwana. We use this information to address the following questions. What cratons remained coherent continental blocks between Rodinia break-up and Gondwana assembly? What were the configurations of Neoproterozoic-Cambrian oceans that separated these coherent blocks? When did the cratons reassemble into the Gondwana supercontinent? In southern Africa, the apparent continuity of older terranes across the Neoproterozoic Zambezi belt, together with other evidence, suggest that the Congo and Kalahari cratons have been a coherent block since ~ 1.1 Ga. The Khomas/Adamastor ocean did not transect the Congo/ Kalahari block; instead any tectonic connection with the Neoproterozoic-Cambrian collisional plate boundary in the Mozambique belt must have been via shear zones such as the Mwembeshi dislocation, which was active at ~ 550 Ma. Age and structural data from Queen Maud Land in East Antarctica indicate that this area was also linked with the Congo/Kalahari block and remained attached to it during the breakup of Rodinia. A suture must thus separate this block from the main part of the East Antarctic craton and likely represents the southern continuation of the Mozambique Ocean. Accumulating evidence for Neoproterozoic-Cambrian orogenesis (~ 550-520 Ma) in the Lützow-Holm Bay and Queen Maud Land regions of East Antarctica suggest the postulated continuation of the Mozambique suture zone may lie beneath the ice, where it separates the main part of the East Antarctic craton from the Congo-Kalahari block and contiguous sectors of Queen Maud Lond. There is also increasing evidence for Neoproterozoic-Cambrian tectonism in the Enderby Land and Wilkes Land sectors of East Antarctica, and in formerly adjacent portions of western Australia and India. Although the regional tectonic significance of this activity with regard to Gondwana assembly remains uncertain, its widespread nature is additional evidence that East Gondwana did not remain an entirely coherent, rigid entity since ~ 1.1 Ga. Final assembly of East and West Gondwana occurred in the Cambrian along boundaries that only partially coincide with the Mesozoic continental margins of the southern continents.

Tectonic connection of the Hellenic and Cyprus arcs and related geotectonic elements

The Cyprus Arc System forms part of a well-defined, presently active, plate boundary and is a critical area for understanding the evolution of the Eastern Mediterranean Sea. The available seismic reflection profiles are utilised in order to establish the nature and origin of the main tectonic features of the arc, which include: 1. (a) The Cyprus Trench, displaying evidence of underthrusting and morphostructural features typical of subduction zones. 2. (b) The Pytheus Trench, associated with right-lateral strike-slip movement and connecting the western end of the Cyprus Trench to the Strabo Trench sector of the Hellenic Trench System. 3. (c) A predominantly transtensional fault zone connecting the easternmost part of the Cyprus Trench via the Baer Bassit overthrust zone in Syria to the Dead Sea Transform Fault System. 4. (d) A zone of complex deformation, involving thrust and transform elements, running from the Misis Mountains of southeast Turkey through the Kyrenia Range in Cyprus to the Gulf of Antalya and transected by roughly N-S major shears (notably the Cape Gelidonya-Anaximander Mountains strike-slip zone), which appears to form the western boundary of the present active system of the Cyprus Arc. The nature of the shallow structures associated with the Cyprus Arc is consistent with a geotectonic model involving some post-Miocene rotation of the South Anatolian-Cyprus Block, probably induced by “escape dynamics” resulting from continent-continent collision in eastern Turkey and the development of the Maras triple junction in southeastern Turkey. The alternation of plate boundary sectors respectively characterised by thrusting and strike-slip displacement suggests that the shallow crust in this part of the eastern Mediterranean is in a compartmented and relatively brittle state, allowing accumulated boundary stresses to be accommodated largely by displacements and deformation along secondary features.

Causality between interplate (North Atlantic) and intraplate (Fennoscandia) seismicities

Annual seismic energy release patterns have been calculated, for the time period 1917–1987, for Fennoscandia and the North Atlantic Ridge (NAR) between 40° N and 80° N. A brief visual comparison shows the great similarity between the energy release patterns in Fennoscandia and individual segments along the NAR. To express the observed resemblance quantitatively and to provide an objective test of the phenomenon, systematic cross-correlations between seismicities along various NAR segments and in Fennoscandia were carried out. The cross-correlations obtained are statistically significant and show maximum values for time lags mostly between 0 and −3 years. Negative time lags mean that the energy release in the NAR precedes that in Fennoscandia. The closest similarity is found between Fennoscandia and the ridge segment between Iceland and Jan Mayen (66°–71° N). Periodicities of 8, 13 and 38 years are seen in the energy release from both regions. The significant cross-correlations and consistent periodicities in the temporal patterns of seismic energy release along the NAR and in Fennoscandia serve as an indication of a tectonic connection between the interplate (NAR) and intraplate (Fennoscandia) seismicities.