Remnant Ocean Basin Research Articles

Silurian ocean island basalt magmatism and Devonian−Carboniferous polymetamorphism: 100 million years in the Western Blue Ridge, USA

The tectonic configuration and evolution of southern Appalachian orogenic episodes are constrained, to a large extent, by knowledge of the timing and environment of pre- or syn-orogenic sediment deposition along with their subsequent thermal and deformational histories. The orogenic events that gave rise to regional folding and Barrovian metamorphism of the Western Blue Ridge (WBR) terrane are a classic example. We present new U-Pb and 40Ar-39Ar results bearing on the timing of magmatism and subsequent metamorphism of the Marble Hill Hornblende Schist (MHHS) of the WBR (southeastern USA). The schist is a key marker unit in the Murphy synclinorium, a central structure in the tectonic configuration of the WBR. The MMHS originated as basaltic volcanics overlying the Murphy Marble at the base of the Mineral Bluff Group. Ocean island basalt geochemistry and a zircon U-Pb age of ca. 437 Ma for the MHHS is consistent with plume-related volcanism in a Silurian remnant ocean basin of the Iapetus Ocean. Hornblende 40Ar-39Ar and rutile U-Pb ages for the MHHS are ca. 380−340 Ma and ca. 320 Ma, respectively, and record subsequent amphibolite facies metamorphism during Devonian Acadian orogeny and the deformation through regional folding and thrusting during the Carboniferous Alleghanian orogeny. The new age constraints for the MHHS require that “isograds” mapped in the region of the Murphy Belt are actually polymetamorphic mineral distributions that developed at least in part through post-Silurian tectonic events.

Dispersion of sandy sediments during marine–continental transition: An integrated study from the Late Paleozoic western Ordos Basin

The western Ordos Basin is located at the intersection of multiple tectonic units and is a key area in the restoration of the palaeogeographic pattern of the East Asia region. The stability of the area and well-developed Paleozoic strata in the basin provide ideal conditions for revealing the relationships among the tectonic processes apparent there. However, within the constraints of extensive post-depositional modification, poor-quality seismic data, and a lack of wells, sediment dispersion differences, source attribution, and source-to-sink processes are still unclear. In this study, we integrated sedimentology, mineral, and geochemical data obtained from marine, continental, and marine-continental transition sedimentary environments in the study area in order to reveal the evolution from source-to-sink. The results show that the western Ordos Basin was predominantly supplied by the Alxa block, Yinshan orogenic belt, Qilian orogenic belt, and the North Qinling orogenic belt during the Late Paleozoic era. As a result of the closure of the Paleo Asian Ocean, the Alxa block and Yinshan orogenic belt became the primary source areas to the north, being composed of granite and alkaline basalt and some sedimentary rocks. In the southern area, the Qilian and the Northern Qinling orogenic belts were subjected to the PaleoTethys remnant ocean basin subduction during the Early Permian. Granite and alkaline basalt were the source rocks of the North Qinling orogenic belt, which became the source area during the Shanxi period. The Qilian orogenic belt contains some sedimentary rocks. The continuous uplift of the southern and northern orogenic belts. The tectonic setting of the northern source area transitions from a passive continental margin to an active continental margin with a mixture of continental arc. The tectonic setting of the southern source area transitions from a mixture of passive continental margin and active continental margin to an active continental margin and continental island arc. The climate changes gradually from humid to semi-arid and then to arid, and meanwhile, the sea level shows a decreasing trend, leading to an increasing distance of advancement for each source-to-sink system, and gradually converged in the central and eastern regions of the basin. Tidal and fan delta sandy sediments in the study area were transformed into fluvial delta sandy sediments in the northern two source-to-sink systems. The southern source-to-sink systems gradually changed from scattered sandbarrier and coastal sandy sediment to fluvial sandy sediment after the Shanxi Formation.

Origin of the Songpan–Garzê terrane, Tibetan Plateau: a perspective from the tectonic evolution of the Palaeo-Tethys Ocean

Abstract The Songpan–Garzê terrane is the largest Triassic remnant flysch basin on Earth and formed as the Palaeo-Tethys Ocean closed during the final amalgamation of the Pangaea supercontinent. However, the origin of the Songpan–Garzê terrane is highly controversial. A synthesis of the tectonic evolution of the Palaeo-Tethys Ocean and its branches surrounding the Songpan–Garzê terrane is presented, which clarifies the nature and relationships among the many Palaeo-Tethys sutures. Provenance analyses suggest that branches of the Palaeo-Tethys near the Songpan–Garzê terrane closed before the Early Triassic. In contrast, the main Palaeo-Tethys Ocean (Longmu Co-Shuanghu) did not close until the beginning of the Late Triassic. This study argues against the Songpan–Garzê terrane being a remnant ocean basin, and proposes that it was a back-arc basin of the main Palaeo-Tethys Ocean. It initially underwent extension by the combined effects of the main Palaeo-Tethys Ocean subduction and the Emeishan mantle plume in the Late Permian, and subsequently developed into a back-arc basin in the Triassic, into which huge turbiditie units were deposited derived from all surrounding terranes and orogens. The final closure of the main Palaeo-Tethys Ocean in the beginning of the Late Triassic and subsequent continent–continent collision led to basin inversion in the Late Triassic.

Late Paleozoic Evolution of the Anadarko Basin: Implications for Laurentian Tectonics and the Assembly of Pangea

AbstractInterplay between marginal and intraplate late Paleozoic tectonics in southeastern Laurentia is a subject of debate. In southern Laurentia, intraplate deformation has been attributed to combinations of compressive forces from orogenic belts in the west, southwest, and southeast. While left‐lateral transpression is generally an accepted mechanism for formation of uplifts in the Southern Oklahoma Aulacogen (SOA), to date no studies have explained the driving mechanisms of these kinematics. Here, we analyze the Southern Oklahoma Transpressional System (SOTS), a ∼500 km long ∼50 km wide fault zone that extends from the southeastern Laurentian margin into the plate interior along Cambrian lithospheric weaknesses inherited from the SOA. We use a compilation of published studies to present detailed, time‐integrated sedimentary thickness maps of SOTS‐related basins. We combine these maps with a new interpretation of three 2D seismic reflection lines to constrain timing and kinematics of all major late Paleozoic SOTS fault zones. We show that the SOTS kinematics evolved from contraction to left‐lateral strike‐slip during Mississippian‐Pennsylvanian time. Tectonic activity and fault kinematics in the SOTS are explained by a model in which a remnant ocean basin closed diachronously from northeast to southwest along the Southern Appalachian and Ouachita‐Marathon orogens. Left‐lateral transpression during diachronous closure of the Rheic oceanic basin along the Ouachita‐Marathon margin is related to rotation of the stress field due to changes in slab‐pull and eastward drift of Laurentia toward Gondwana. We speculate that the SOTS acted in part as a STEP (subduction‐transfer edge propagator) fault that followed the pre‐existing SOA.

Middle Triassic remnant of the Palaeo‐Tethys Ocean, central Tibet: Constraints from the Pianshishan retrograded eclogite‐type rocks

The high-pressure and low-temperature metamorphic rocks constitute the important parts of the Longmu Co-Shuanghu suture zone (LSS) in Tibet, providing a natural window for unveiling the tectonic evolution of the Palaeo-Tethys Ocean. In this contribution, geochemical studies, including the whole-rock geochemistry, Sr-Nd isotopes and zircon U–Pb geochronology, were performed on the Pianshishan garnet amphibolites and retrograded eclogites, to reconstruct the genesis of the protoliths and to reveal tectonic evolution of the Longmu Co-Shuanghu Palaeo-Tethys Ocean (LSPTO). The garnet amphibolites show characteristics similar to the retrograded eclogites, representing different degrees of retrograde metamorphism of the Pianshishan eclogites. The protoliths of garnet amphibolites and retrograded eclogites are alkaline basalts, with geochemical characteristics similar to ocean island basalts (OIB) without Nb, Ta or Ti negative anomalies. Furthermore, geochemical data imply that the protoliths were formed by fractional crystallization of the magma derived from partial melting of garnet lherzolites without crustal contamination. The parental magma was probably generated in a relatively depleted but heterogeneous asthenosphere mantle source. Their protoliths erupted as a seamount within the LSPTO. Garnet amphibolites and retrograded eclogites yielded zircon U–Pb weighted mean ages of 240.2 ± 1.7 Ma and 239.1 ± 2.7 Ma, respectively. Combining with previous studies, we suggest that the LSPTO remained open in the Pianshishan area during the Middle Triassic, and the whole ocean might be gradually closed during the Early to Late Triassic. The small remnant ocean basin during the Middle Triassic can well explain a rapid evolution of the Pianshishan eclogite-type rocks, that is, from generation to eclogite-facies metamorphism and then to exhumation-related retrograde metamorphism within ~19 Myr.

Structural development and tectonostratigraphic evolution of the Sylhet Trough (northeastern Bengal Basin) in the context of Cenozoic Himalayan Orogeny: Insights from geophysical data interpretation

The Sylhet Trough of the Bengal Basin in the northeastern Indian Plate had started to develop since the Late Mesozoic Gondwana break-up and subsequent onset of the Cenozoic Himalayan Orogeny. However, very little is known about evolution of the Cenozoic Sylhet Trough in response to the latter tectonic event. Therefore, we aim at providing insights into the nature of basement, variations in structural style, kinematics and possible timing of structural activation(s) and tectonostratigraphic evolution of the Sylhet Trough based on geophysical data interpretation. Results show that the Sylhet Trough is mostly underlain by an attenuated continental or oceanic crust, bounded by a NE-SW-trending geophysical feature in the northwest that corresponds to the boundary with the Precambrian continental crust. The overlying Cenozoic sediments show variations in style of deformations and can be divided into three structural domains. Domains 1 and 2 in the southeastern and northeastern parts of the Sylhet Trough, respectively, are characterized by anticlines that are highly deformed to the east and are mostly associated with west- or northwest-dipping reverse faults. However, the anticlinal trends are deviated from a generalized NS-orientation in the Domain 1 to a dominant NE-SW-orientation in the Domain 2. Many of these anticlines resemble positive flower structures, indicating possible impacts of regional transpression associated with the Dauki and Kaladan faults to the north and east; respectively. In contrast, the Domain 3 to the west shows NE-SW-trending extensional structures. A southward thickening of the Oligocene to Miocene pre-kinematic packages indicates an early episode of foreland basin subsidence, although there is no evidence of a major structural activation. Rather, the presence of the Pliocene syn-kinematic packages indicates a major structural reactivation in response to the E-W and N-S crustal shortening since the Pliocene. This younger episode of structural activation can be directly linked with the late Cenozoic subduction related processes of the Indian Plate to the north and to the east, which is also responsible for the transformation of the Sylhet Trough into a remnant ocean basin. This latter (i.e., Pliocene and onward) episode of crustal shortening played a significant role in structural trap formation and preservation of hydrocarbons in the Sylhet Trough.

Evolution of Sediment Gravity Flows in Response to the Subduction and Closure of the West Junggar (China) Remnant Ocean Basin During the Early Carboniferous

Evolution of Sediment Gravity Flows in Response to the Subduction and Closure of the West Junggar (China) Remnant Ocean Basin During the Early Carboniferous

Identification and geological significance of the Early Paleozoic Tianjunnanshan remnant ocean basin in the Zongwulong belt, NE Tibetan Plateau

Identification and geological significance of the Early Paleozoic Tianjunnanshan remnant ocean basin in the Zongwulong belt, NE Tibetan Plateau

Peperites Associated Pillow Lavas within Ophiolites and New Insight to Tectonic Setting: Comparative Study between Oman and West Junggar of China

AbstractPeperites are generated by magma intruding and mingling with wet unconsolidated or poorly consolidated sediments. Late Paleozoic peperites have been identified in the Darbut and Baijiantan ophiolitic belts at West Junggar, NW China. The peperites form successions up to 500 m thick interbedded with basaltic lava (sometimes pillow lava) and sedimentary rocks (i.e. limestones). The peperites are described and interpreted as resulting from basaltic lava bulldozed into wet, unconsolidated sediments at their basal contacts. The peperite‐bearing units are generally undeformed, occurring in continuous stratigraphic sections distributed regionally over a distance of 100 km on either side of the Darbut and Baijiantan ophiolitic belts, in contrast to the highly deformed slices of ophiolite. They demonstrate that the Darbut and Baijiantan ophiolitic belts should not be interpreted as significant plate boundaries and represent the underlying ocean crust uplifted along tectonic lineaments within a continuous shallow remnant ocean basin. Jordan et al. (2008) reported an occurrence of peperite in the Oman—United Arab Emirates (UAE) border region. In this border area the field relations of the pillow lavas surrounded by limestone with deformed bedding and peperite boundaries between the pillows and the limestone are consistent with the pillow lavas forming directly within carbonate sediments. The pillow lavas in Oman‐ UAE border area likely have formed as intrusions into water‐saturated carbonate sediments deposited along the edges of seamounts. Based on the comparative study on the peperites associated pillow lavas within ophiolites between West Junggar and Oman, this paper proposes that the ophiolites with peperites associated pillow lavas surrounded by limestone were not formed in a typical ocean basin, but a shallow remnant ocean basin.

Palaeogene stratigraphy and chronology of the western Sivas Basin, central Anatolia (Turkey): Tectono‐sedimentary evolution of a well‐preserved basin along the northern Neotethys suture zone

AbstractThe Sivas Basin overlaps the northern Neotethys suture zone in central Anatolia (Turkey) and contains a ca. 12‐km thick succession of Cenozoic strata that provides an exceptional record of major tectonic transitions from subduction to continental assembly and tectonic escape. Consensus regarding the tectonic and palaeogeographic evolution of this segment of the Arabia‐Eurasia collision zone has been hindered by uncertainty in the tectonic setting of the early (Palaeogene) Sivas Basin, which has been variably interpreted as a remnant ocean, forearc, foreland, wedge‐top or intracontinental extensional basin. Here we integrate new geologic mapping (>5,000 km2), stratigraphy, facies analysis and U‐Pb geochronology from the western Sivas Basin to produce a detailed time‐stratigraphic framework and a refined Palaeogene tectono‐sedimentary model for the Sivas Basin. Earliest marine sedimentation occurred during the Maastrichtian‐Palaeocene in a remnant ocean setting due to incomplete closure of the northern Neotethys Ocean. Rapid accumulation of >2 km of basin floor turbidites during the middle to late Eocene reflect a transition to a foreland setting. A major late Eocene unconformity (ca. 38–34 Ma) coincides with the initiation of the north‐vergent southern Sivas fold‐thrust belt, which inverted and structurally partitioned the basin into a southern wedge‐top and a northern evaporitic foreland basin; the entire basin was dominantly nonmarine after this unconformity. Published palaeomagnetic data integrated with a newly discovered tuff dated at 31.9 Ma reveal that the 2.8‐km thick Altinyayla Formation was deposited from ca. 34 to 26 Ma in an unconfined braided fluvial system. Close stratigraphic correlations between the western, central and northern Sivas Basin suggest that the entire basin evolved from a remnant ocean to peripheral retro‐foreland basin during the middle to late Eocene, and finally a fragmented foreland basin since the Oligocene. This general evolution may be a characteristic of such sedimentary basins formed on suture zones across Anatolia and in other collisional orogens globally.

Paleozoic convergence processes in the southwestern Central Asian Orogenic Belt: Insights from U–Pb dating of detrital zircons from West Junggar, northwestern China

The West Junggar orogen, located in the southwestern Central Asian Orogenic Belt (CAOB), preserves an abundant record of tectonic processes associated with the evolution of the Junggar Ocean. In this study, we use detrital zircon U–Pb age data from Ordovician to Carboniferous sandstones in the southern and central West Junggar domains, complemented by literature data, to better constrain the tectonic evolution of the southwestern CAOB. The Kekeshayi, Qiargaye, and Laba formations in the southern West Junggar domain were deposited during the Darriwilian-Sandbian, Katian-Aeronian, and Homerian-Emsian, respectively. Detrital zircon provenances of these formations display a marked shift from the southern West Junggar domain to the Paleo-Kazakhstan Continent (PKC). This suggests that the southern West Junggar intra-oceanic arc might have gradually accreted to the northern margin of the PKC prior to the Emsian, which has significantly contributed to the lateral growth of the PKC. The Carboniferous strata, Xibeikulasi, Baogutu, and Tailegula formations, in the central West Junggar domain represent a coherent sequence of volcaniclastic turbidites and were deposited in a progressively shrinking remnant oceanic basin during the Visean to Moscovian. They contain unimodal detrital zircon distributions and are derived from the local and coeval magmatic rocks in the central West Junggar domain. We propose that the final closure of the Junggar Ocean likely occurred in the end of the Late Carboniferous in response to regional amalgamation events in the southwestern CAOB, which marks the final assembly of the Kazakhstan Orocline. The central and southern West Junggar domains underwent individual evolution in the Paleozoic, and were recombined by the significant intra-continental reworking along the large-scale strike-slip faults.

Silurian Sedimentation in the South Qilian Belt: Arc‐Continent Collision‐related Deposition in the NE Tibet Plateau?

AbstractThe South Qilian belt mainly comprises an early Paleozoic arc‐ophiolite complex, accretionary prism, microcontinental block, and foreland basin. These elements represent accretion‐collision during Cambrian to Silurian time in response to closure of the Proto‐Tethyan Ocean in the NE of the present‐day Tibet Plateau. Closure of the Proto‐Tethyan Ocean between the Central Qilian block and the Oulongbuluke block and the associated collision took place from NE to SW in a zipper‐like style. Sediment would have been dispersed longitudinally SW‐ward with a progressive facies migration from marginal alluvial sediments toward slope deep‐water and deep‐sea turbidites. This migration path indicates an ocean basin that shrank toward the SW. The Balonggongga'er Formation in the western South Qilian belt represents the fill of a latest Ordovician‐Silurian remnant ocean basin that separated the Oulongbuluke block from the Central Qilian block, and records Silurian closure of the Proto‐Tethyan Ocean and subduction beneath the Central Qilian block. However, alluvial deposits in the Lajishan area were accumulated in a retro‐foreland basin, indicating that continent‐continent collision in the eastern South Qilian belt occurred at c. 450–440 Ma. These results demonstrate that the Proto‐Tethyan Ocean closed diachronously during early Paleozoic time.

Competing sediment sources during Paleozoic closure of the Marathon-Ouachita remnant ocean basin

AbstractThe Paleozoic construction of Pangea advanced southwestward from the Appalachian system to the Marathon fold-and-thrust belt in west Texas and progressively closed a remnant ocean basin between Laurentia and Gondwana. The resulting collisional orogen was a potential driver of Ancestral Rocky Mountain tectonism and impacted continental-scale sediment routing. New detrital zircon U-Pb geochronologic and heavy mineral provenance data from Ordovician–Pennsylvanian strata in the Marathon fold-and-thrust belt, and Permian strata in the Guadalupe Mountains of west Texas record changes in sediment provenance during the tectonic development of southwestern Laurentia and the Delaware Basin. In the Marathon fold-and-thrust belt, Ordovician rocks (Woods Hollow and Marathon Formations) record peri-Gondwanan sediment sources prior to continent collision. Syncollisional Mississippian and Pennsylvanian rocks (Tesnus, Haymond, Gaptank Formations) record contributions from distal Appalachian sources, recycled material from the active continental suture, and volcanic arc material from Gondwana. Near the Guadalupe Mountains, postcollisional Permian strata (Delaware Mountain Group) from the northern Delaware Basin margin suggest a dominantly southern catchment that was sourced from the deforming suture and Gondwanan arc. The results demonstrate that both plates and the active suture zone were sources for the siliciclastic wedge, but their proportions differed through time. These results also suggest that the delay between initial late Mississippian suturing in the Marathon region and increased mid-Permian siliciclastic deposition into the northern Delaware Basin may have been linked to a southward catchment expansion that integrated the collisional belt and southern volcanic arc into a broadly north-directed sediment dispersal system.

Emplacement of the ophiolitic mélanges in the west Karamay area: Implications for the Late Paleozoic tectonic evolution of West Junggar, northwestern China

The Darbut and Karamay ophiolitic mélanges in the west Karamay area at the southeastern margin of West Junggar, southern Altaids, represent the relict fragments of the Paleozoic Junggar ocean basin. The mélanges contain structurally complex tectonic blocks of ultramafic rocks, gabbro, basalt, and chert that are dispersed within an extensively sheared serpentinite matrix. This study presents new field observations, structural analyses, geochronological and geophysical data for the mélanges and the overlying Carboniferous strata. Three stages of deformation (D1–D3) have been identified. D1 is only locally preserved in the mélanges and is characterized by thrust-imbricated faults, recording the subduction and accretion of the paleo-oceanic crust in the Early Carboniferous. D2 mainly consists of map-scale upright folds (F1) in the Carboniferous strata and NE-SW-striking sub-vertical right-lateral shear zones in the mélanges. D3 is characterized mainly by NE-SW-striking transcurrent left-lateral strike-slip faults and “S-shaped” drag folds (F2). The extensive tectonic reworking during D2 and D3 deformations eradicated most of the D1 structures. Our structural observations, combined with geophysical data, suggest that the basement of the west Karamay area consists of trapped oceanic crust or dismembered ophiolitic fragments and that the Darbut and Karamay ophiolitic mélanges were extruded through right-lateral shear zones. Our results and the published data further suggest that the emplacement of the mélanges and the formation of F1 folds represent regional-scale amalgamation processes between different tectonic blocks and/or plates in the Late Carboniferous. These processes resulted in the closure of the West Junggar remnant ocean basin and other sub-oceanic basins in the Paleo-Asian Ocean, leading to the formation of the Kazakhstan orocline. Furthermore, the D3 deformation was associated with anticlockwise rotation of the West Junggar region in a post-collisional setting in the Permian.

Characteristics and genesis of diachronous Carboniferous volcano-sedimentary sequences: insights from geochemistry, petrology and U–Pb dating in the North Junggar basin, China

ABSTRACTThe subduction of oceanic lithosphere during the Carboniferous Period contributed to the formation of widely distributed subduction-related volcanic rocks within the Junggar basin. These volcanic rock associations contain significant clues for understanding the subduction of the Keramaili oceanic lithosphere and the filling of the remnant oceanic basin. Here, we report regional gravity and magnetic data, petrology, geochemistry, and U–Pb dating for Carboniferous volcanic rocks from the North Junggar basin (NJB). Using samples from well Y-1, we distinguish upper and lower volcanic sequences on the basis of selected geochemical data. An isochronous stratigraphic framework of Carboniferous volcano-sedimentary sequences is then constructed and the petrogenesis of these volcanic rocks is discussed. Finally, we propose an explanation for the genesis of these diachronous Carboniferous volcano-sedimentary sequences. The results show that various volcanic rocks are distributed in different areas of the NJB, and mainly consist of calc-alkaline basalt–andesite–dacite assemblages and alkaline basalt–basaltic andesite–andesite assemblages. The geochemical data also demonstrate a binary nature of the Carboniferous volcanic rocks. In the eastern NJB, the lower and upper volcanic sequences are formed during the early and late Carboniferous, respectively. However, all of these volcano-related sequences in the western of the NJB are formed during the late Carboniferous. These volcano-sedimentary sequences exhibit a ‘ladder-style’ of temporospatial evolution from east to west. The geochemical results also indicate that the upper volcanic rocks include island arc components formed in an extensional setting, whereas the lower volcanic rocks were derived from deep crustal cycling metasomatism by various mantle components in a continental arc environment. Earlier closure of the Keramaili oceanic basin and slab roll-back of the Junggar oceanic lithosphere in eastern versus western Junggar basin led to the formation of these diachronous volcano-sedimentary sequences.

Structural features and proto-type basin reconstructions of the Bay of Bengal Basin: A remnant ocean basin model

Remnant ocean basin is a key to understand the plate suturing and subsequent uplift and erosion of orogen. The Bay of Bengal Basin (BOBB) provides a typical example to analyze the remnant ocean basin structures, evolution, and relationships between depositional filling and uplifting of the Himalayan Orogen. Thirty-nine seismic profiles as well as interval velocities of well BODC3 were used to compile isopach maps of the basin. Among the seismic data, 26 seismic profiles were applied to establish 8 cross sections. The cross sections suggest the basin is asymmetric, bounded to the west by the eastern continental margin of India (ECMI) with graben-horst and to the east by the Sunda convergence margin dominated by trench-arc system. The BOBB is characterized by a prominent down flexure structures caused by huge amount of Bengal fan turbidite sediments accumulation. Our isopach maps and chronology data collected from adjacent regions reveal the initial development and fast southward growth of the Bengal fan were related to the early and major stage uplift and erosion of the Himalayan Orogen, respectively. The BOBB has experienced a critical transition from an ocean basin to a remnant ocean basin at Late Oligocene. Such basin structures and evolution features indicate the BOBB provides whole records of oblique convergence of the India and Asia plates, and the early and major stage evolution of the Himalayan Orogen.

The Ophiolitic Mélanges in Strike‐slip Fault Zones in West Junggar, Xinjiang, NW China

The Ophiolitic Mélanges in Strike‐slip Fault Zones in West Junggar, Xinjiang, NW China

Confirmation of the southwest continuation of the Cat Square terrane, southern Appalachian Inner Piedmont, with implications for middle Paleozoic collisional orogenesis

Detailed geologic mapping, U-Pb zircon geochronology and whole-rock geochemical analyses were conducted to test the hypothesis that the southwestern extent of the Cat Square terrane continues from the northern Inner Piedmont (western Carolinas) into central Georgia. Geologic mapping revealed the Jackson Lake fault, a ∼15 m-thick, steeply dipping sillimanite-grade fault zone that truncates lithologically distinct granitoids and metasedimentary units, and roughly corresponds with a prominent aeromagnetic lineament hypothesized to represent the southern continuation of the terrane-bounding Brindle Creek fault. Results of U-Pb SHRIMP geochronology indicate Late Ordovician to Silurian granitoids (444–439 Ma) occur exclusively northwest of the fault, whereas Devonian (404–371 Ma) granitoids only occur southeast of the fault. The relatively undeformed Indian Springs granodiorite (three individual bodies dated 317–298 Ma) crosscuts the fault and occurs on both sides, which indicates the Jackson Lake fault is a pre-Alleghanian structure. However, detrital zircon signatures from samples southeast of the Jackson Lake fault reveal dominant Grenville provenance, in contrast to Cat Square terrane detrital zircon samples from the northern Inner Piedmont, which include peri-Gondwanan (600–500 Ma) and a prominent Ordovician-Silurian (∼430 Ma) signature. We interpret the rocks southeast of the Jackson Lake fault to represent the southwestern extension of the Cat Square terrane primarily based on the partitioning of granitoid ages and lithologic distinctions similar to the northern Inner Piedmont. Data suggest Cat Square terrane metasedimentary rocks were initially deposited in a remnant ocean basin setting and developed into an accretionary prism in front of the approaching Carolina superterrane, ultimately overridden by it in Late Devonian to Early Mississippian time. Burial to >20 km resulted in migmatization of lower plate rocks, forming an infrastructure beneath the Carolina superterrane suprastructure. Provenance patterns support ∼250 km of Devonian dextral translation of the composite Inner Piedmont, which places the northern portion of the Inner Piedmont adjacent to a suite of ∼430 Ma plutons in the Virginia Blue Ridge during deposition. The megascopic thrust-nappe structural style of the northern Inner Piedmont, combined with southwest-directed lateral extrusion at mid-crustal depths, may reconcile differences in timing of metamorphism between the Carolina and central Georgia Inner Piedmont and structural contrasts between the Brindle Creek and Jackson Lake faults.

Chapter 5 Arakan Coastal Ranges in western Myanmar, geology and provenance of Neogene siliciclastic sequences: implications for the tectonic evolution of the Himalaya–Bengal System

Supplementary material : Preparation and analysis of samples with appendices are available at https://doi.org/10.6084/m9.figshare.c.3860926 Neogene clastic sequences preserved in the western part of Indo-Myanmar Ranges provide detrital information that document the erosional and unroofing history of the eastern Himalayas and the Burmese Arc during the Indian–Asian collision. All of the sedimentological and provenance data link the syntectonic sedimentation and sequential evolution of the Bengal Basin, a remnant ocean basin south of the eastern Himalayas and, at the time of formation, a palaeo-incised valley in the eastern trough of the Central Myanmar Tertiary Basin. To the east lies the Sagaing Fault and the Mogok Belt, and further east the Shan–Thai Block. Modal analysis of the Lower Miocene sandstones of the Baronga Islands, Arakan Coastal Ranges shows that they are rich in both monocrystalline and polycrystalline quartz, sub-angular to subrounded feldspars and lithic fragments including metamorphic rock fragments with minor basaltic fragments, suggesting the onset of uplift, erosion and unroofing of the eastern Himalayas and Indo-Myanmar Ranges. Since the Early Miocene, sediments were deposited in twin gulfs separated by the uplifted Indo-Myanmar Ranges. In the Middle Miocene there was a major change in the provenance of the Neogene sediments of the Arakan Basin and the Central Tertiary Basin of Myanmar. Since the Early Miocene, basement uplift of the Mogok Belt in the east and the Gangaw Ranges of the upper Irrawaddy Basin in the western part of the Asian Plate, as well as the initiation of river systems, supplied orogenic detritus to the south (Allen et al. 2008; Kyi Khin et al. 2014; Robinson et al. 2014; Licht et al. 2015). Middle Miocene sandstones from both areas are rich in sub-angular monocrystalline quartz, chert and argillites with small amounts of feldspar and metamorphic lithic fragments, suggesting a relatively low …

Identifying late Carboniferous sanukitoids in Hala’alate Mountain, Northwest China: new constraint on the closing time of remnant ocean basin in West Junggar

ABSTRACTVolcanic rocks in the Hala’alate and Aladeyikesai formations, which are composed of basaltic andesite and pyroxene andesite, are widespread in Hala’alate Mountain, West Junggar, Northwest China. These rocks (plagioclase + clinopyroxene/olivine) formed in the late Carboniferous and show a remarkable geochemical affinity with typical sanukitoids with oversaturated SiO2 (52.9–56.9 wt.%) and high MgO (3.47–6.88 wt.%, Mg# >48) contents. They also exhibit a narrow range of Sr-Nd-Pb isotopes within (87Sr/86Sr)i = 0.7037–0.7041, εNd(t) = 4.4–6.2, 206Pb/204Pb = 18.22–18.41, 207Pb/204Pb = 15.48–15.52, 208Pb/204Pb = 37.99–38.30. Hala’alate Formation volcanic rocks are similar to the sanukitoids of Karamay, with high Sr (633.5–970.1 ppm), Ba (268.7–796.3 ppm), and Sr/Y (61.34–84.28), formed by partial melting of the mantle metasomatized by slab-derived adakitic melts. In contrast, Aladeyikesai Formation volcanic rocks show some affinity with sanukitoids of the Hatu area and the Setouchi Volcanic Belt, with low Sr (442.2–508.7 ppm), Ba (199.2–485.1 ppm), and Sr/Y (25.03–30.28), generated by the partial melting of subducting sediments. Identification of late Carboniferous sanukitoids in Hala’alate Mountain provides important constraints on the closing time of the remnant ocean basin in West Junggar, and implies that multi-stage subduction–accretionary orogeny plays a crucial role in the evolution and growth of the continental crust in the Central Asian Orogenic Belt.