Dike swarms on Seward Peninsula, Alaska, and their implications for the kinematics of Cretaceous extension in the Bering Strait region

2003 ◽  
Vol 40 (6) ◽  
pp. 865-886 ◽  
Author(s):  
Jeffrey M Amato ◽  
Elizabeth L Miller ◽  
James E Wright ◽  
William C McIntosh
Keyword(s):  
Late Cretaceous ◽  
Tectonic Setting ◽  
Ductile Deformation ◽  
Geochemical Data ◽  
Normal Faults ◽  
Bering Strait ◽  
Shear Sense ◽  
Seward Peninsula ◽  
Dike Swarms ◽  
Shear Sense Indicators

Late Cretaceous dike swarms on Seward Peninsula, northwestern Alaska, represent the youngest local manifestation of a ~115–75 Ma magmatic event in the Bering Strait region. Magmatism accompanied and followed high-grade metamorphism and ductile deformation. A Late Cretaceous extensional tectonic setting for the region is suggested by the thickness and seismic-reflection characteristics of the crust, regional basin development, formation of high-strain tectonites with subhorizontal foliations, bimodal magmatism, and dike swarms. The orientation of the dike swarms is used to address the kinematics of extension. A diabase dike swarm in the Kigluaik Mountains consists of dikes that strike northeast (040°) and dip steeply. Phenocrysts include plagioclase, clinopyroxene, orthopyroxene, and hornblende. Geochemical data indicate that SiO2 ranges from 48% to 56%, and K2O from 1.2% to 4.0%. The dikes are geochemically similar to the mafic to intermediate root of the 90 Ma Kigluaik pluton. Sr- and Nd-isotope data show that initial 87Sr/86Sr ranges from 0.7070 to 0.7077 and initial εNd ranges from –0.85 to –2.90. Field relations and 40Ar/39Ar geochronology bracket the dike ages between 90 and 84 Ma. Diabase dikes in the York Mountains are associated with normal faults that strike east–west to east-northeast. Dikes in the Bendeleben Mountains are both mafic and felsic, but their orientations are unknown. Alkalic dikes in the Darby Mountains strike 030°–050°, similar to those in the Kigluaik Mountains. Regional relationships including the orientation of dikes, normal faults, mineral stretching lineations, and other shear-sense indicators suggest that between 110 and 90 Ma extension on Seward Peninsula was generally oriented north–south to north-northwest–south-southeast.

The petrogenesis and tectonic setting of lavas from the Baft Ophiolitic Mélange, southwest of Kerman, Iran

1994 ◽  
Vol 31 (5) ◽  
pp. 824-834 ◽  
Author(s):  
Mohsen Arvin ◽  
Paul T. Robinson
Keyword(s):  
Late Cretaceous ◽  
Tectonic Setting ◽  
Tholeiitic Basalt ◽  
Ocean Basin ◽  
Plate Motion ◽  
Geochemical Data ◽  
Ophiolite Complex ◽  
Ophiolitic Mélange ◽  
Lut Block ◽  
Mafic Lavas

A Late Cretaceous ophiolite complex in the Baft area, southwest of Kerman, Iran, is characteristic of the Central Iranian Ophiolitic Mélange Belt, which wraps around the Lut Block. Despite the extensive tectonic disruption of the Baft complex, most ophiolitic lithologies are present and many original igneous contacts are preserved. A lack of cumulate gabbros within the sequence suggests that a large and continuous magma chamber did not exist beneath the Baft spreading axis. Geochemical data confirm the presence of two distinct compositional groups in the mafic lavas: (1) tholeiitic basalt and (2) transitional tholeiitic basalt. The tholeiitic lavas are similar to typical mid-ocean-ridge basalt compositions, whereas the transitional tholeiites are similar to intraplate basalts. The available data suggest that the Baft ophiolite complex formed in a small ocean basin, possibly at or near a ridge–transform intersection. Emplacement may have occurred as a result of conversion of the transform fault to a subduction zone during a change in relative plate motion. A ridge–transform setting is compatible with the intraplate character of some of the transitional basalts, which probably represent off-axis (seamount) magmatism, marked by the absence of cumulate gabbros and the presence of a serpentinite mélange cut by basaltic dykes. The ridge–transform model suggests formation of the ophiolite in a narrow ocean basin separating the Sanandaj-Sirjan microcontinent from the Central Iran Block in Late Cretaceous time.

scholarly journals CONTRASTING GEOMETRY BETWEEN ALPINE AND LATE- TO POSTALPINE TECTONIC STRUCTURES IN ANAFI ISLAND (CYCLADES)

2004 ◽  
Vol 36 (4) ◽  
pp. 1688 ◽  
Author(s):  
Konstantinos I. Soukis ◽  
Demetrios J. Papanikolaou
Keyword(s):  
Normal Faults ◽  
Thrust Faults ◽  
High Angle ◽  
Backarc Basin ◽  
Tectonic Structures ◽  
Extensional Deformation ◽  
Upper Miocene ◽  
Deformation Phase ◽  
Shear Sense ◽  
Shear Sense Indicators

A significant change is observed in the geometry of the major faults in Anafi Island from Ν to NE dip in the alpine structures to S to SW dip in the late to post-alpine. Several thrust faults dipping to the NE preserved at the central-eastern part of the island form a nappe pile of Cretaceous HT/LP metamorphic units emplaced over a parautochthonous nonmetamorphic flysch of partly Eocene age without development of metamorphic structures (deformation phase Di). The development of detachment normal faults dipping to the SW (deformation phase D2) deformed the previous thrusts together with the post alpine continental sedimentary sequence of Miocene age, occurring in the northern and western part of Anafi. Asymmetric to the SW folds are observed at the lower part of the Upper Miocene sediments as well as numerous shear sense indicators along the undulating surface of the detachment above the underlying alpine units. The deformation weakens towards the upper part of the Upper Miocene sediments. An intensely sheared molassic type formation of probable ?Oligocene-Early Miocene age was distinguished between the alpine units and the detached Upper Miocene sediments. High angle normal faults dipping to the SW deform all previous structures (D3). The extensional deformation phases D2 and D3 are related to the opening of the Cretan backarc basin during Tortonian - Early Pliocene.

scholarly journals Structural evolution and tectonic setting of the Porongos belt, southern Brazil

2006 ◽  
Vol 143 (1) ◽  
pp. 59-88 ◽  
Author(s):  
K. SAALMANN ◽  
M. V. D. REMUS ◽  
L. A. HARTMANN
Keyword(s):  
Continental Crust ◽  
Tectonic Setting ◽  
Structural Evolution ◽  
Sedimentary Basins ◽  
Passive Margin ◽  
Ductile Deformation ◽  
Geochemical Data ◽  
Northwestern Part ◽  
Metavolcanic Rocks ◽  
Significant Contamination

The SW–NE-striking Porongos belt, located between juvenile Neoproterozoic rocks in the west and the Dom Feliciano belt, characterized by intense reworking of older crust, in the east, comprises a greenschist to amphibolite-facies metavolcano-metasedimentary succession (Porongos sequence) of unknown age with some exposures of Palaeoproterozoic gneisses (Encantadas gneisses). High-temperature ductile deformation of the basement gneisses comprises at least two magmatic events followed by three deformational phases including folding and shearing (DT1–DT3) and can be attributed to the Palaeoproterozoic Trans-Amazonian orogeny. The deformation of the Porongos sequence occurred during the Neoproterozoic Brasiliano orogeny and comprises four ductile deformation phases (DB1–DB4), including two phases of isoclinal folding associated with shearing recorded in mylonitic layers, followed by closed NW-vergent folding and thrusting leading to formation of a thrust stack. Uplift of the basement and formation of late tectonic sedimentary basins occurred as a result of semi-ductile to brittle block faulting in a sinistral strike-slip regime. The Porongos sequence can be subdivided into a southeastern and a northwestern part. Trace element analyses as well as Sm–Nd and Rb–Sr geochemical data indicate partial melting and significant contamination by old continental crust for the metavolcanic rocks. The metavolcanic rocks show εNd(t=780 Ma) values of −20.64 and −21.72 (northwestern units) and −6.87 (southeastern sequence). The metasedimentary rocks were derived from late Palaeoproterozoic to Archaean sources, and the data indicate different sources for the northwestern and southeastern rock units of the Porongos sequence. εNd(t=780 Ma) are −6.25 and −6.85 in the southeastern units, with TDM model ages between 1734 and 1954 Ma, and vary between −14.72 and −17.96 in the northwestern parts, which have TDM model ages between 2346 and 2710 Ma. High 87Sr/86Sr(t) values between 0.7064 and 0.7286 confirm reworking of older crust. Isotopic signatures of the Porongos sequence do not show indications for a significant contribution from a Neoproterozoic juvenile source. A passive margin or continental rift environment is suggested for the tectonic setting of the Porongos belt, which is compatible with both deposition of shallow marine to deep marine sediments and stretching of continental crust leading to volcanism which is characterized by significant contamination by old continental crust.

scholarly journals Statherian (ca. 1714–1680 Ma) Extension-Related Magmatism and Deformation in the Southwestern Korean Peninsula and Its Geological Significance: Constraints from the Petrological, Structural, Geochemical and Geochronological Studies of Newly Identified Granitoids

Minerals ◽  
2021 ◽  
Vol 11 (6) ◽  
pp. 557
Author(s):  
Byung-Choon Lee ◽  
Weon-Seo Kee ◽  
Uk-Hwan Byun ◽  
Sung-Won Kim
Keyword(s):  
Korean Peninsula ◽  
Tectonic Setting ◽  
Alkali Feldspar ◽  
Ductile Deformation ◽  
Southwestern Part ◽  
The North ◽  
Deformation Event ◽  
Geochemical Analyses ◽  
A Minor ◽  
T Values

In this study, petrological, structural, geochemical, and geochronological analyses of the Statherian alkali feldspar granite and porphyritic alkali feldspar granite in the southwestern part of the Korean Peninsula were conducted to examine petrogenesis of the granitoids and their tectonic setting. Zircon U-Pb dating revealed that the two granites formed around 1.71 Ga and 1.70–1.68 Ga, respectively. The results of the geochemical analyses showed that both of the granites have a high content of K2O, Nb, Ta, and Y, as well as high FeOt/MgO and Ga/Al ratios. Both granites have alkali-calcic characteristics with a ferroan composition, indicating an A-type affinity. Zircon Lu-Hf isotopic compositions yielded negative εHf(t) values (−3.5 to −10.6), indicating a derivation from ancient crustal materials. Both granite types underwent ductile deformation and exhibited a dextral sense of shear with a minor extension component. Based on field relationships and zircon U-Pb dating, it was considered that the deformation event postdated the emplacement of the alkali feldspar granite and terminated soon after the emplacement of the porphyritic alkali feldspar granite in an extensional setting. These data indicated that there were extension-related magmatic activities accompanying ductile deformation in the southwestern part of the Korean Peninsula during 1.71–1.68 Ga. The Statherian extension-related events are well correlated with those in the midwestern part of the Korean and eastern parts of the North China Craton.

scholarly journals Geology of the orogenic Cheminis gold deposit along the Larder Lake – Cadillac deformation zone, Ontario

2015 ◽  
Vol 52 (12) ◽  
pp. 1093-1108 ◽  
Author(s):  
Bruno Lafrance
Keyword(s):  
Deformation Zone ◽  
Volcanic Rocks ◽  
Tholeiitic Basalt ◽  
Hydrothermal Fluids ◽  
South Side ◽  
Shear Sense ◽  
Abitibi Subprovince ◽  
Deformation Features ◽  
Shear Sense Indicators ◽  
Host Rocks

The Larder Lake – Cadillac deformation zone (LLCDZ) is one of two major, auriferous, deformation zones in the southern Abitibi subprovince of the Archean Superior Province. It hosts the Cheminis and the giant Kerr Addison – Chesterville deposits within a strongly deformed band of Fe-rich tholeiitic basalt and komatiite of the Larder Lake Group (ca. 2705 Ma). The latter is bounded on both sides by younger, less deformed, Timiskaming turbidites (2674–2670 Ma). The earliest deformation features are F1 folds affecting the Timiskaming rocks, which formed either during D1 extensional faulting or during early D2 north–south shortening related to the opening and closure, respectively, of the Timiskaming basin. Continued shortening during D2 imbricated the older volcanic rocks and turbidites and produced regional F2 folds with an axial planar S2 cleavage. D2 deformation was partitioned into the weaker band of volcanic rocks, producing the strong S2 foliation, L2 stretching lineation, and south-side-up shear sense indicators, which characterize the LLCDZ. Gold is present in quartz–carbonate veins in deformed fuchsitic komatiites (carbonate ore) and turbiditic sandstone (sandstone-hosted ore), and in association with disseminated pyrite in altered Fe-rich tholeiitic basalts (flow ore). All host rocks underwent strong mass gains in CO2, S, K2O, Ba, As, and W, during sericitization, carbonatization, and sulphidation of the host rocks, suggesting that they interacted with the same hydrothermal fluids. Textural relationships between alteration minerals and S2 cleavage indicate that mineralization is syn-cleavage. Thus, gold was deposited as hydrothermal fluids migrated upward along the LLCDZ during contractional, D2 south-side-up shearing. The gold zones were subsequently modified during D3 reactivation of the LLCDZ as a dextral transcurrent fault zone.

scholarly journals Polyphase evolution of Pelagonia (northern Greece) revealed by geological and fission-track data

Solid Earth ◽  
2015 ◽  
Vol 6 (1) ◽  
pp. 285-302 ◽  
Author(s):  
F. L. Schenker ◽  
M. G. Fellin ◽  
J.-P. Burg
Keyword(s):  
Early Cretaceous ◽  
Late Cretaceous ◽  
Fission Track ◽  
Regional Scale ◽  
Normal Faults ◽  
Recent Sediment ◽  
Northern Greece ◽  
Rapid Cooling ◽  
Fission Track Ages ◽  
Pelagonian Zone

Abstract. The Pelagonian zone, situated between the External Hellenides/Cyclades to the west and the Axios/Vardar/Almopias zone (AVAZ) and the Rhodope to the east, was involved in late Early Cretaceous and in Late Cretaceous–Eocene orogenic events whose duration and extent are still controversial. This paper constrains their late thermal imprints. New and previously published zircon (ZFT) and apatite (AFT) fission-track ages show cooling below 240 °C of the metamorphic western AVAZ imbricates between 102 and 93–90 Ma, of northern Pelagonia between 86 and 68 Ma, of the eastern AVAZ at 80 Ma and of the western Rhodope at 72 Ma. At the regional scale, this heterogeneous cooling is coeval with subsidence of Late Cretaceous marine basin(s) that unconformably covered the Early Cretaceous (130–110 Ma) thrust system from 100 Ma. Thrusting resumed at 70 Ma in the AVAZ and migrated across Pelagonia to reach the External Hellenides at 40–38 Ma. Renewed thrusting in Pelagonia is attested at 68 Ma by abrupt and rapid cooling below 240 °C and erosion of the gneissic rocks. ZFT and AFT in western and eastern Pelagonia, respectively, testify at ~40 Ma to the latest thermal imprint related to thrusting. Central-eastern Pelagonia cooled rapidly and uniformly from 240 to 80 °C between 24 and 16 Ma in the footwall of a major extensional fault. Extension started even earlier, at ~33 Ma in the western AVAZ. Post-7 Ma rapid cooling is inferred from inverse modeling of AFT lengths. It occurred while E–W normal faults were cutting Pliocene-to-recent sediment.

Mesozoic Tectonic Setting of SE Sundaland After Magmatism and Suture Evidences in JS-1 Ridge Area

2021 ◽  
Keyword(s):  
Early Cretaceous ◽  
Late Cretaceous ◽  
Tectonic Setting ◽  
Plate Boundary ◽  
Early Jurassic ◽  
The South ◽  
Magmatic Arc ◽  
Plate Convergence ◽  
Ridge Area ◽  
Cretaceous Subduction

Mesozoic plate convergence in SE Sundaland has been a source of debate for decades. A determination of plate convergence boundaries and timing have been explained in many publications, but not all boundaries were associated with magmatism. Through integration of both plate configurations and magmatic deposits, the basement can be accurately characterized over time and areal extents. This paper will discuss Cretaceous subductions and magmatic arc trends in SE Sundaland area with additional evidence found in JS-1 Ridge. At least three subduction trends are captured during the Mesozoic in the study area: 1) Early Jurassic – Early Cretaceous trend of Meratus, 2) Early Cretaceous trend of Bantimala and 3) Late Cretaceous trend in the southernmost study area. The Early Jurassic – Early Cretaceous subduction occurred along the South and East boundary of Sundaland (SW Borneo terrane) and passes through the Meratus area. The Early Cretaceous subduction occurred along South and East boundary of Sundaland (SW Borneo and Paternoster terranes) and pass through the Bantimala area. The Late Cretaceous subduction occurred along South and East boundary of Sundaland (SW Borneo, Paternoster and SE Java – South Sulawesi terranes), but is slightly shifted to the South approaching the Oligocene – Recent subduction zone. Magmatic arc trends can also be generally grouped into three periods, with each period corresponds to the subduction processes at the time. The first magmatic arc (Early Jurassic – Early Cretaceous) is present in core of SW Borneo terrane and partly produces the Schwaner Magmatism. The second Cretaceous magmatic arc (Early Cretaceous) trend is present in the SW Borneo terrane but is slightly shifted southeastward It is responsible for magmatism in North Java offshore, northern JS-1 Ridge and Meratus areas. The third magmatic arc trend is formed by Late Cretaceous volcanic rocks in Luk Ulo, the southern JS-1 Ridge and the eastern Makassar Strait areas. These all occur during the same time within the Cretaceous magmatic arc. Though a mélange rock sample has not been found in JS-1 Ridge area, there is evidence of an accretionary prism in the area as evidenced by the geometry observed on a new 3D seismic dataset. Based on the structural trend of Meratus (NNE-SSW) coupled with the regional plate boundary understanding, this suggests that both Meratus & JS-1 Ridge are part of the same suture zone between SW Borneo and Paternoster terranes. The gradual age transition observed in the JS-1 Ridge area suggests a southward shift of the magmatic arc during Early Cretaceous to Late Cretaceous times.

scholarly journals Influence of inherited structural domains and their particular strain distributions on the Roer Valley Graben evolution from inversion to extension

2020 ◽  
Author(s):  
Jef Deckers ◽  
Bernd Rombaut ◽  
Koen Van Noten ◽  
Kris Vanneste
Keyword(s):  
Late Cretaceous ◽  
Fault System ◽  
Normal Faults ◽  
Geological Model ◽  
Structural Domains ◽  
Stress Directions ◽  
Roer Valley Graben ◽  
Western Border ◽  
Border Fault ◽  
As Stress

Abstract. After their first development in the middle Mesozoic, the overall NW-SE striking border fault systems of the Roer Valley Graben were reactivated as reverse faults under Late Cretaceous compression (inversion) and reactivated again as normal faults under Cenozoic extension. In Flanders (northern Belgium), a new geological model was created for the western border fault system of the Roer Valley Graben. After carefully evaluating the new geological model, this study shows the presence of two structural domains in this fault system with distinctly different strain distributions during both Late Cretaceous compression and Cenozoic extension. A southern domain is characterized by narrow ( 10 km) distributed faulting. The total normal and reverse throw in the two domains was estimated to be similar during both tectonic phases. The repeated similarities in strain distribution during both compression and extension stresses the importance of inherited structural domains on the inversion/rifting kinematics besides more obvious factors such as stress directions. The faults in both domains strike NW-SE, but the change in geometry between them takes place across the oblique WNW-ESE striking Grote Brogel fault. Also in other parts of the Roer Valley Graben, WNW-ESE striking faults are associated with major geometrical changes (left-stepping patterns) in its border fault system. This study thereby demonstrates the presence of different long-lived structural domains in the Roer Valley Graben, each having their particular strain distributions that are related to the presence of non-colinear faults.

scholarly journals Structural setting and tectonic evolution of the Bahariya Depression, Western Desert, Egypt

GeoArabia ◽  
2003 ◽  
Vol 8 (1) ◽  
pp. 91-124 ◽  
Author(s):  
Adel R Moustafa ◽  
Ati Saoudi ◽  
Alaa Moubasher ◽  
Ibrahim M Ibrahim ◽  
Hesham Molokhia ◽  
...  
Keyword(s):  
Late Cretaceous ◽  
Tectonic Evolution ◽  
Middle Miocene ◽  
Middle Eocene ◽  
Western Desert ◽  
Normal Faults ◽  
Surface Mapping ◽  
Early Mesozoic ◽  
Hydrocarbon Fields ◽  
Stable Area

ABSTRACT An integrated surface mapping and subsurface study of the Bahariya Depression aided the regional subsurface interpretation. It indicated that four major ENE-oriented structural belts overlie deep-seated faults in this part of the ‘tectonically stable’ area of Egypt. The rocks of the Bahariya area were deformed in the Late Cretaceous, post-Middle Eocene, and Middle Miocene-and subsurface data indicated an early Mesozoic phase of normal faulting. The Late Cretaceous and post-Middle Eocene deformations reactivated the early normal faults by oblique slip and formed a large swell in the Bahariya region. The crest was continuously eroded whereas its peripheries were onlapped by Maastrichtian and Tertiary sediments. The tectonic evolution of the Bahariya region shows great similarity to the deformation of the ‘tectonically unstable’ area of the northern Western Desert where several hydrocarbon fields have been discovered. This similarity may indicate that the same phases of deformation could extend to other basins lying in the ‘tectonically stable’ area, such as the Asyut, Dakhla, Nuqura, and El Misaha basins.

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