Early Cretaceous Tectonics Research Articles

Geochemistry of high‐Nb basalt‐andesite in the Erguna Massif (NE China) and implications for the early Cretaceous back‐arc extension

This paper presents new zircon laser ablation–inductively coupled plasma–mass spectrometry U–Pb age and whole‐rock geochemical data for the high‐Nb basalts‐andesites (HNBs) from the Meiletu Formation in NE China. In comparison with common arc basalts and Nb‐enriched basalts, the Meiletu HNBs (140 Ma) show high TiO2 (1.7–3.2 wt.%), P2O5 (0.7–1.7 wt.%), Nb (14.6–34.0 ppm), and Zr (314–600 ppm) contents, and high (Nb/Th)PM (0.26–0.91), (Nb/La)PM (0.22–0.36), Nb/U (8.2–24.8) ratios. They show strongly light rare earth element (REE) enriched chondrite‐normalized REE patterns with unusually high total REE contents [(TREE)cn = 978–1802]. Unlike adakite‐associated HNBs derived from a mantle wedge metasomatized by adakites, the Meiletu HNBs were derived from low degree (<2%) partial melting of the garnet peridotite at considerable depth (>80 km). The Meiletu HNBs were generated in an intracontinental back‐arc extension setting. Combined with previous geological observations, it is argued that Early Cretaceous tectonics of the Erguna Massif is dominated by the Mongol–Okhotsk oceanic slab‐rollback and back‐arc extension.

Early Cretaceous Tectonics and Evolution of the Tibetan Plateau

AbstractSelected geological data on Early Cretaceous strata, structures, magmatic plutons and volcanic rocks from the Kunlun to Himalaya Mountains reveal a new view of the Early Cretaceous paleo‐tectonics and the related geodynamic movement of the Tibetan Plateau. Two major paleo‐oceans, the Mid‐Tethys Ocean between the Qiangtang and Lhasa blocks, and the Neo‐Tethys Ocean between the Lhasa and Himalayan blocks, existed in the Tibetan region in the Early Cretaceous. The Himalayan Marginal and South Lhasa Seas formed in the southern and northern margins of the Neo‐Tethys Ocean, the Central Tibet Sea and the Qiangtang Marginal Sea formed in the southern and northern margins of the Mid‐Tethys Ocean, respectively. An arm of the sea extended into the southwestern Tarim basin in the Early Cretaceous. Early Cretaceous intensive thrusting, magmatic emplacement and volcanic eruptions occurred in the central and northern Lhasa Block, while strike‐slip formed along the Hoh‐Xil and South Kunlun Faults in the northern Tibetan region. Early Cretaceous tectonics together with magmatic K2O geochemistry indicate an Early Cretaceous southward subduction of the Mid‐Tethys Oceanic Plate along the Bangoin‐Nujiang Suture which was thrust ∼87 km southward during the Late Cretaceous‐Early Cenozoic. No intensive thrust and magmatic emplacement occurred in the Early Cretaceous in the Himalayan and southern Lhasa Blocks, indicating that the spreading Neo‐Tethys Oceanic Plate had not been subducted in the Early Cretaceous. To the north, terrestrial basins of red‐beds formed in the Hoh‐Xil, Kunlun, Qilian and the northeastern Tarim blocks in Early Cretaceous, and the Qiangtang Marginal Sea disappeared after the Qiangtang Block uplifted in the late Early Cretaceous.

A multidisciplinary study of the emplacement mechanism of the Qingyang–Jiuhua massif in Southeast China and its tectonic bearings. Part II: Amphibole geobarometry and gravity modeling

The Late Mesozoic geology of the Lower Yangtze area is characterized by extensional sedimentary basins, numerous granitic plutons and several world-class ore deposits. Regionaly, the coeval tectonic and geodynamic framework remains inadequately investigated. In order to provide a more comprehensive understanding of the regional tectonic context, we performed a multidisciplinary study of the emplacement mechanism of the Qingyang–Jiuhua massif. It consists of the granodioritic Qingyang and the monzogranitic Jiuhua plutons, U–Pb dated at 142±1.0Ma and 131±2.6Ma, respectively. Biotite and amphibole cooling ages are 5–8myr younger. Results deduced from field structural observation, petrographic and magnetic fabrics, paleomagnetism show that this massif was probably vertically emplaced by permissive intrusion coeval with weak regional extension. However, detailed information on the characteristics of this tectonic event and its emplacement depth was not documented. Therefore, we carried out an investigation of amphibole geobarometry and gravity modeling in order to address the emplacement mode of the plutons within their regional tectonic framework. Amphibole data show that the Qingyang–Jiuhua massif was emplaced in the upper crust at a depth between 5 and 12km. Gravity modeling indicates that the massif is laccolithic. It is characterized by several NE–SW-striking linear thickening zones that we interpret as the feeder roots of the massif. These results led us to conclude that (1) the Qingyang–Jiuhua massif was fed by vertical, NE–SW striking tension gashes; (2) consequently the late Early Cretaceous tectonics in the study area was characterized by NW–SE extension.

Deposition of serpentine-bearing conglomerate and its implications for Early Cretaceous tectonics in northern Japan

The discovery of serpentinite-bearing conglomerate including detrital blue amphibole grains in Cretaceous forearc basin sediments in the northern part of Japan supports large tectonic movement in the forearc basin during the Early Cretaceous. Conglomerate and sandstone are intercalated in the Lower Cretaceous offshore mudstone sequence and contain serpentinite clasts, chromian spinels, blue amphiboles, and oolitic grains with chromian spinel nuclei. The conglomerate and sandstones were deposited as a debris flow consisting of an admixture of siliciclastic terrigenous sediments and calcareous biogenic material with serpentinite-derived sediments. The sandstones consist of feldspathic–lithic arenites and wackes, and their composition suggests that most of the terrigenous material was derived from the Cretaceous volcanic terrane and the Jurassic accretionary complex located to the west of the depositional basin. However, the serpentinite body correlated with the provenance of the sediments is not distributed in these terranes. Because the oolitic grains in the matrix of the conglomerate include only angular chromian spinels and serpentine clasts without quartz and feldspar grains, most of the serpentinite-derived sediments are considered to have been supplied primarily from a serpentinite body exposed along the shallow marine environments near the sedimentary basin. Therefore, the serpentine-derived sediments and feldspathic and lithic materials have essentially different sources. Thus, we may infer that the examined sediments are due to large slope failure affecting a relatively wide area of shallow coast involving the place where the serpentine body was emplaced and the place where river-fed terrigenous siliciclastic sediments accumulated. The stratigraphic range of the serpentinite-derived sediments, which are sporadically distributed in the Cretaceous forearc basin of northern Japan, suggests that the serpentinite-derived material was actively supplied to the forearc basin in Albian times. Recent tectono-stratigraphy of the Late Mesozoic accretionary complex in Japan reveals a strike–slip movement in the subduction zone around northeastern Asia. Large earthquakes affected by active strike–slip motion of the oceanic plate are inferred to be the trigger of tectonic movement, such as large slope failure following serpentine intrusion in the forearc region. Another possibility is that subduction of a large number of seamount on the oceanic plate might also cause a large change in basin morphology, bringing about large slope failure.

The Lower Cretaceous King Lear Formation, northwest Nevada: Implications for Mesozoic orogenesis in the western U.S. Cordillera

Cretaceous paleogeography of the U.S. Cordillera west of the Sevier fold-and-thrust belt is poorly known due to the scarcity of Cretaceous supracrustal rocks in the arc and backarc regions. The Lower Cretaceous King Lear Formation, exposed in the Jackson Mountains and the Krum Hills of northwest Nevada, provides a rare and important record of Early Cretaceous tectonism and paleogeography. Our work shows that the King Lear Formation everywhere overlies deformed and metamorphosed Triassic-Jurassic rocks across a major unconformity. The King Lear Formation is dominated by conglomerates and sandstones deposited in subaerial alluvial-fan and gravelly braided river systems, and it can be divided into three new members based on differences in clast provenance: a lower member derived from local arc and backarc rocks; a middle member dominated by externally derived quartzite and chert clasts; and an upper member derived largely from an intrabasinal volcanic complex. Sedimentary features and provenance analysis indicate that clasts in the middle member were derived from nearby exposures of Paleozoic rocks such as the Roberts Mountains and Golconda allochthons, which must have formed a topographically elevated area in central Nevada during the Early Cretaceous. The stratigraphic record provides evidence of deposition in a tectonically active basin. In contrast with some prior studies inferring that deposition was synchronous with contractional deformation, our new field observations, structural data, and a shallow seismic-reflection profile confirm that the King Lear Formation was deposited in an active half-graben in the Jackson Mountains. These results provide new upper age constraints on the timing of shortening deformation in the arc and backarc regions: shortening must have been complete not only before deposition of the King Lear Formation in the middle Early Cretaceous, but also prior to several kilometers of exhumation of its depositional basement. Possible driving forces for extension leading to development of the King Lear basin include relaxation of thick crust in the hinterland of thrust belts to the east, stresses associated with regional tilting and development of dynamic topography, and stresses related to dextral strike-slip deformation to the west.

Review of geology of the New Siberian Islands between the Laptev and the East Siberian Seas, North East Russia

Abstract. The New Siberian Islands comprise De Long Islands, Anjou Islands, and Lyakhov Islands. Early Paleozoic, Mesozoic and Cenozoic sediments and igneous rocks are known on the De Long Islands. Cambrian slate, siltstone, mudstone and silicified limestone occur on Bennett Island. Ordovician volcanogenic turbidites, lavas, and small intrusions of andesite-basalt, basalt, dolerite, and porphyritic diorite were mapped on Henrietta Island. The igneous rocks are of calc-alkaline island arc series. The Ordovician age of the sequence was defined radiometrically. Early Paleozoic strata were faulted and folded presumably in the Caledonian time. Early Cretaceous sandstone and mudstone are known on Bennett Island. They are overlain by a 106–124 Ma basalt unit. Cenozoic volcanics are widespread on the De Long Islands. Zhokhov Island is an eroded stratovolcano. The volcanics are mostly of picrite-olivine type and limburgite. Radiometric dating indicates Miocene to Recent ages for Cenozoic volcanism. On the Anjou islands Lower-Middle Paleozoic strata consist of carbonates, siliciclastics, and clay. A Northwest-southeast syn-sedimentary facies zonation has been reconstructed. Upper Paleozoic strata are marine carbonate, clay and siliciclastic facies. Mudstone and clay predominate in the Triassic to Upper Jurassic section. Aptian-Albian coal bearing deposits uconformably overlap lower strata indicating Early Cretaceous tectonism. Upper Cretaceous units are mostly clay and siltstone with brown coal strata resting on Early Cretaceous weathered rhyolite. Cenozoic marine and nonmarine silisiclastics and clay rest upon the older units with a transgressive unconformity including a weathering profile in the older rocks. Manifestations of Paleozoic and Triassic mafic and Cretaceous acidic magmatism are also found on these islands. The pre-Cretaceous structure of the Anjou islands is of a block and fold type Late Cimmerian in age followed by faulting in Cenozoic time. The Lyakhov islands are located at the western end of the Late Cimmerian South Anyui suture. Sequences of variable age, composition, and structural styles are known on the Lyakhov Islands. These include an ancient metamorphic sequence, Late Paleozoic ophiolitic sequence, Late Mesozoic turbidite sequence, Cretaceous granites, and Cenozoic sediments. Fold and thrust imbricate structures have been mapped on southern Bol'shoi Lyakhov Island. North-northwestern vergent thrusts transect the Island and project offshore. Open folds of Jurassic–Early Cretaceous strata are characteristic of Stolbovoi and Malyi Lyakhov islands. Geology of the New Siberian Islands supports the concept of a circum Arctic Phanerozoic fold belt. The belt is comprised of Caledonian, Ellesmerian, Early Cimmerian and Late Cimmerian fold systems, manifested in many places on the mainland and on islands around the Arctic Ocean. Knowledge of the geology of the New Siberian Islands has been used to interpret anomalous gravity and magnetic field maps and Multi Channel Seismic (MCS) lines. Two distinguishing structural stages are universally recognized within the offshore sedimentary cover which correlate with the onshore geology of the New Siberian Islands. Dating of the upper structural stage and constituent seismic units is based on structural and stratigraphic relationships between Late Mesozoic and Cenozoic units in the archipelago. The Laptev Sea–western East Siberian Sea seismostratigraphic model for the upper structural stage has much in common with the seismostratigraphic model in the American Chukchi Sea.

Early Cretaceous Tectonism and Diatoms in Korea

Abstract: The Early Cretaceous Sindong Group, a non‐marine molasse, unconformably overlies the folded earliest Cretaceous Myogok Formation. The tectonism that folded the Jaseong Synthem including the Myogok and other formations is here called the Nakdong‐Jaeryeonggang (N‐J) tectonism. The Oknyeobong and Dabokni Formations are discussed to show that they belong to the Jaseong Synthem. The Dabokni Formation yielded fossil diatoms whose age has been referred as the “earliest Cretaceous” based on the geologically constrained age of the fossil‐bearing deposit. The age of the N‐J tectonism appears Barremian as it is between the Hauterivian Myogok Formation and the Aptian Sindong Group with the TPN (Trigonioides‐Plicatounio‐Nippononaia) fauna. The N‐J tectonism, an orogeny, quite deformed pre‐Aptian strata in Korea, but can hardly find its reported equivalent in NE China. A revised correlation table shows that the Jaseong‐Sindong sequence corresponds to the Jehol Group of China. The Sindong‐Hayang transition was characterized by basin migration and dextral rotation probably caused by the Tan‐Lu fault system in a broad sense.

Hydrocarbon prospectivity in the Irish Sea area: insights from recent exploration of the Central Irish Sea, Peel and Solway basins

Abstract Compared with the prolific success of the Triassic play in the East Irish Sea Basin (EISB) the lack of hydrocarbon discovery in neighbouring Permo-Triassic basins of the Irish Sea has been an enigma. However, recent exploration of the Peel, Solway and Central Irish Sea basins has provided new insights into the geology of these basins and the controls upon hydrocarbon prospectivity in the Irish Sea area. Regional seismic interpretation suggests that 12 of the 15 exploration wells drilled in the basins adjacent to the EISB tested valid structural closures at top Triassic reservoir level. Re-evaluation of the Irish Sea petroleum system reveals that, although effective reservoirs occur in the Lower-Middle Triassic Ormskirk Sandstone Formation, and evaporites in the Middle-Upper Triassic Mercia Mudstone Group provide a regional top seal, the major factor controlling hydrocarbon prospectivity is the limited presence of effective source rocks in the underlying Carboniferous section. A further control upon prospectivity is the timing of hydrocarbon migration, from those areas where Carboniferous source rocks were deposited and preserved. The Namurian basinal marine oil- and gas-prone shales, which form the principal source of hydrocarbons for the Triassic play in the EISB, are restricted to an east-west fairway extending from the EISB into the Kish Bank Basin. Rocks of this age are absent from the Peel and Solway basins as a result of Variscan uplift and erosion. However, palaeogeographical reconstructions based on well and outcrop data suggest that, even if preserved, the depositional environment was not conductive to the formation of marine oil-and gas-prone source rocks. Well and seismic data suggest that rocks of Namurian age were not deposited in the Central Irish Sea area, which remained high during much of Dinantian and Namurian time. Potential source rock development in the Central Irish Sea area is therefore limited to the Westphalian section, which is organically lean and dominated by intertinitic kerogens. Potential hydrocarbon traps in the Central Irish Sea, Peel and Solway basins formed largely as a result of Early Cretaceous tectonism and were subsequently modified by fault reactivation during Tertiary uplift phases. Trap formation appears to postdate the most likely timing of hydrocarbon charge, which this study suggests would have occurred in Late Triassic and Jurassic time. Hydrocarbon entrapment in the EISB may have been favoured by limited Early Cretaceous uplift, coupled with renewed hydrocarbon generation and re-migration during Early Tertiary time. It is concluded that the remaining prospectivity of the Triassic play in the Irish Sea area is likely to be restricted to the proven play fairway within the EISB.

Birth and decay of an intracontinental magmatic swell: Early Cretaceous tectonics of southern Israel

The Early Cretaceous history of southern Israel is an example of the formation, growth, and decay of an intracontinental swell associated with magmatism. In this paper we document and quantify this process and analyze its geodynamic mechanism. The magmatism and the uplifting continued for about 10 Myr and produced a 150 to 200‐km‐wide dome, from whose crest nearly 1000 m of sediments were removed. Shortly after the magmatism ended, a period of cooling and subsidence began, and sediments started to cover the swell's margins. However, this subsidence was much smaller than the initial uplift and did not bury the swell's crest, which remained elevated for an additional 10 Myr. The fact that most of the uplift remained indicates that the major cause for uplifting was the permanent buoyancy effect of intrusions. Transient effects such as heating at the base of the lithosphere and dynamic support of the asthenosphere may have also occurred, but their contribution to the local uplifting was minor. The distinction between temporal and permanent effects is possible because of the long‐term history provided by the stratigraphic record (a full life cycle of a fossil swell). In currently active swells this distinction is much more complicated, and from this point of view this case provides unique information. The tectonostratigraphic analysis we present illustrates how geological observations can be used to calculate tectonic uplift and to estimate accordingly the volume of magmatism that produced it. Taking into account the sea level rise during uplift and considering the topographic relief that remained after the erosion, the calculated tectonic uplift amounts to about 500 m or 40% higher than the uplift inferred only from the amount of erosion. Thermal‐mechanical modeling indicates that this uplift can be explained by intrusions with a volume equivalent to a 4 to 5‐km‐thick sill, consistent with other geological and geophysical observations.

Paleogeographic and Paleotectonic Models for the New Zealand Geosyncline in Eastern Gondwanaland

New Zealand geosyncline stratigraphy accords with a paleogeographic model whereby late Paleozoic–Mesozoic sedimentation occurred between continental forelands. Such a model fits into a reassembly of eastern Gondwanaland and supports the hypothesis that Late Jurassic–Early Cretaceous tectonism in this region was related to relative motion of the Australian continent.

Espirito Santo--Pattern of Brazilian Marginal Basins: ABSTRACT

The Espirito Santo basin lies in the eastern continental margin of Brazil, as a member of an assemblage of Cretaceous/Tertiary basins correlatable by close stratigraphic and structural analogies. It is considered as the most complete model of this group of basins, and can serve as a pattern for a study of their origin and evolution. The basin originated by Early Cretaceous tectonism that fractured the original cratonic mass into elongated grabens bounded by normal faults. Immature fluviolacustrine sediments were deposited in this tectonically active rift valley. End_Page 601------------------------------ Sea-floor spreading caused the subsequent widening of the basin, and allowed the first marine transgression that formed a long and narrow embayment--the primitive South Atlantic Ocean. Here, due to restrictive conditions, an evaporitic section was deposited. The combined effect of the enlargement of this embryonic ocean by eastward migration of the Mid-Oceanic Ridge since Late Cretaceous time, and basin tilting due to detumescence of the pre-rift arching, determined the deposition of a thick, predominantly marine section with deltaic sedimentation near the Doce River area, and of shallow-platform carbonates in the central and eastern parts of the basin. This upper marine section, although only weakly structured by the progressively decreasing reactivation of the Early Cretaceous faulting, underwent adiastrophic movements by growth faulting and halokinesis. Late Cretaceous to middle Eocene submarine volcanic activity built up the framework of a 30,000-sq km accretion to the preexisting continental shelf. The process of origin and evolution, and the structural and stratigraphic characteristics of the Espirito Santo basin, cause consideration of the basin as potentially petroliferous, and warrant the exploration program that is being carried out. The accumulated knowledge of the Espirito Santo basin, that reflects the regional situation of the whole Brazilian continental margin, affords an important clue to the study of continental drift of South America and Africa. End_of_Article - Last_Page 602------------