Intense Magmatic Activity Research Articles

3-D crustal shear wave velocity and azimuthally anisotropic structure of the Pearl River Delta onshore-offshore area and its tectonic implications

The Pearl River Delta (PRD) onshore-offshore area lies in the transition zone between South China and northern continental margin of the South China Sea. To better understand the tectonic and deformation patterns at depth, we developed a 3-D high-resolution crustal shear wave velocity (Vs) and azimuthal anisotropy model by ambient noise tomography in this region. The data sets comprise ∼30 days of seismic ambient noise recorded by 124 land seismic stations and 28 Ocean Bottom Seismometers (OBS). Our results reveal a significant lateral contrast in azimuthal anisotropy in the crust. The fast axes of the azimuthal anisotropy in land show an approximately NW-SE direction, which may be mainly controlled by the regional stress field. In the offshore PRD, however, the fast axes of anisotropy strike nearly in the NE-SW direction, likely dominated by the shearing of the littoral fault zone. Combined with other previous results, the anisotropic model reveals three major crustal deformation processes in this region since the Yanshanian. Furthermore, an upper-middle crustal frozen mafic magma chamber with high Vs (∼3.85–4.0 km/s) is imaged beneath Shenzhen, Zhuhai, and Hong Kong. It is interpreted as a source of intense magmatic activities in and around Hong Kong during the late Mesozoic. Our new model provides important constraints for understanding the crustal architecture and the multistage deformation processes in and around the PRD onshore-offshore area.

A Deformed Wedge‐Top Basin Inverted During the Collapse of the Variscan Belt: The Permo‐Carboniferous Lorraine Basin (NE France)

AbstractA new structural model is presented for the Permo‐Carboniferous Lorraine Basin (NE France), a major intramountain basin that developed during the latest stages of the Variscan orogeny (ca. 315–270 Ma). Digitalized well logs and reprocessed seismic data were used to decipher the kinematic evolution of this basin located along the Rhenohercynian orogenic suture zone. The basin was initiated during the late collision stage (Early to Middle Pennsylvanian) in a wedge‐top position upon the Saxothuringian retro‐wedge. The syn‐orogenic sequence is delimited to the north by the major SE‐verging Metz Thrust, which is part of the backthrust system that propagated during Middle Pennsylvanian (Late Westphalian). Seismic data provide evidence of negative tectonic inversion, allowing the formation of syn‐rift depocenters (Late Pennsylvanian‐Early Permian) above the former anticlines. Erosion of these anticlines results in a major unconformity marking the onset of post‐orogenic collapse. The late Early Permian shortening (Saalian phase) is suggested to reactivate former thrusts and normal faults, thus generating late uplift of the basin. The post‐orogenic phase is complex and diachronous at basin scale, and both compression and extension can be recorded in the same area over a short period (<10 Myr). The Late Carboniferous negative tectonic inversion along the Rhenohercynian suture zone is proposed to result from the lithospheric delamination of the Variscan orogenic roots. The associated upwelling of asthenospheric material is recorded by intense magmatic activity, and can be, in turn, considered as the main trigger for the subsequent thermal subsidence of the Mesozoic Paris Basin.

Tracing the sedimentary response to the rifting and opening of the Meso‐Tethys Ocean

ABSTRACTKnowledge of the rifting and opening process of the Meso‐Tethys Ocean is important for understanding the evolution of the Tethys tectonic domain and for an in‐depth understanding of Tethys dynamics. Sedimentary rocks are faithful recorders of surface expressions of tectonic events and are thus expected to have recorded the rifting and opening of the Meso‐Tethys Ocean. This study presents petrography, sedimentology, zircon U–Pb geochronological data and Hf isotope data for the Carboniferous–Permian Shiquanhe stratigraphic succession in the Lhasa Terrane of the Tibetan Plateau. The data indicate that the 300 to 273 Ma Lagar and Angjie formations in the lower section of the Carboniferous–Permian Shiquanhe succession were deposited in the stable passive margin of northern Gondwana with sediment sources in Gondwanaland. However, the 273 to 252 Ma Xiala Formation in the upper section of the Carboniferous–Permian Shiquanhe succession was deposited in a tectonically active setting characterized by intense magmatic activity. Considering the transition from the Lagar and Angjie formations to the Xiala Formation, a significant change in depositional setting from tectonically stable to tectonically active occurred at ca 273 Ma. Similar Early–Middle Permian changes in depositional setting have also been identified in the South Qiangtang, Baoshan and Oman regions in the Tethyan tectonic domain. These widespread changes in depositional setting, together with Early–Middle Permian tectonic uplift and episodes of subsidence, as well as rift‐related magmatism in the South Qiangtang, Baoshan, Himalayan, Zagros, Oman and Turkey regions once located in northern Gondwana, constitute a complete record of continental rifting–ocean opening associated with the diachronous opening of the Meso‐Tethys Ocean during the Early–Middle Permian.

Late-stage structural evolution from near-bottom topographic and magnetic Surveys of Suda Seamount (West Pacific)

The late-stage evolution of seamounts is widespread in the West Pacific and may control the distribution of manganese nodules on the lower seamount flanks and adjacent debris aprons. However, due to the paucity of near-bottom observational data, little research exists specifically focused on the late-stage evolution of seamount structures. To fill this knowledge gap, we systematically investigated the tectonic features and evolution of Suda Seamount based on rock samples, satellite gravity data, and high-resolution magnetic and topographic data surveyed by Autonomous Underwater Vehicle (AUV). We found that the central area of the seamount summit exhibits a negative magnetic anomaly related to a group of minor volcanic structures, while the collapse of volcanic structures on the northeast seamount flank is associated with an extensive positive magnetic anomaly. Surprisingly, a late-stage intrusive dyke with significantly high magnetic susceptibility originates from the lower part of a minor group of volcanic structures but cannot be clearly distinguished below the main summit volcanic structure (hereinafter referred to as the main mound complex). These results demonstrate that at least two late-stage periods of intense magmatic activity occurred during the evolution of the seamount, one centered on the main mound complex and one on the margin of the summit platform. By combining fine-scale topographic and satellite gravity data, we deduce that gravitational slip caused by magma intrusion along a fracture was the main cause of the seamount flank collapse. The late-stage processes resulted in a change in the seamount morphology and distributed clastic rock debris widely along the flanks, which contributed to the uneven distribution of manganese nodules along the lower seamount flanks and determined the distribution of subsequently formed nodules.

Quantification and Restoration of the Pre‐Drift Extension Across the NE Atlantic Conjugate Margins During the Mid‐Permian‐Early Cenozoic Multi‐Rifting Phases

AbstractThe formation of the NE Atlantic conjugate margins is the result of multiple rifting phases spanning from the Late Paleozoic and culminating in the early Eocene when breakup was accompanied with intense magmatic activity. The pre‐breakup configuration of the NE Atlantic continental margins is controlled by crustal extension, magmatism, and sub‐lithospheric processes, all of which need to be quantified for the pre‐breakup architecture to be restored. Key parameters that need to be extracted from the analysis of crustal structures and sediment record include stretching factors, timing of rifting phases, and nature of the deep crustal structures. The aim of this study is to quantify the pre‐drift extension of the NE Atlantic conjugate margins using interpreted crustal structure and forward basin modeling. We use a set of eight 2D conjugate crustal transects and corresponding stratigraphic models, constrained from an integrated analysis of 2D and 3D seismic and well data. The geometry and thickness of the present‐day crust is compared to a reference thickness which has experienced limited or no crustal extension since Permian time allowing the quantification of crustal stretching. Based on the eight conjugate crustal transects, the total pre‐drift extension is estimated to range between 181 and 390 km with an average of 270–295 km. These estimates are supported by the results of forward basin modeling, which predict total extension between 173 and 325 km, averaging 264 km. The cumulative pre‐drift extension estimates derived from basin modeling are in turn used to calculate the incremental crustal stretching factors at each of the three main rifting phases between the conjugate Greenland‐Norwegian margins. The mid‐Permian early Triassic rifting phase represents 32% of the total extension, while the equivalent values are 41% for the mid‐Jurassic to mid‐Cretaceous and 27% for the Late Cretaceous‐Paleocene rifting phases. These values are used to establish and present at first, a full‐fit palinspastic plate kinematic model for the NE Atlantic since the mid‐Permian and will be the base for future work on more elaborated models in order to build accurate paleogeographic and tectonic maps.

Stratigraphy and tectosedimentary evolution of the late Paleozoic Ancestral Andes between 33° and 25° SL

The presence and evolution of a late Paleozoic mountain chain with a paleogeographic disposition similar to the present-day Andean Cordillera is analyzed in this paper. This mountain range, here named Ancestral Andes, was formed during the Gondwanan orogeny (Permian) and separated the Paleopacific Sea from the eastern retroarc basins in this part of South America. Three basement types are involved in the roots of the Ancestral Andes: 1. poorly exposed Mesoproterozoic-Neoproterozoic high-grade metamorphic rocks probably remains of the Chi-Cu terrane, 2. Cambrian-Silurian sedimentary and metamorphic rocks formed during the Famatinian orogeny, and 3. Neoproterozoic to early Carboniferous sedimentary and metamorphic rocks originated during the Chanic orogenic cycle. According to tectonic activity, sedimentary facies, and magmatic record, the Gondwanan cycle comprises seven tectosedimentary stages: 1) Late Mississippian-Early Pennsylvanian (post-Chanic orogeny marine sedimentation), 2) late Early Pennsylvanian (sea-level fall and progradation of sandy wedges in an extensional pre-orogenic period), 3) Middle-Late Pennsylvanian (sea level fluctuations at the end of the pre-orogenic phase), 4) latest Pennsylvanian-early Cisuralian (active tectonism during the beginning of the uplift of the Ancestral Andes, 5) middle Cisuralian (continental and shallow marine sedimentation during the main phase of the Ancestral Andes uplift), 6) late Cisuralian-Guadalupian (continental sedimentation and beginning of the post-orogenic volcanism), 7) late Guadalupian-Lopingian (most active post-orogenic volcanism). The stages 1, 2, and 3 correspond to the pre-orogenic phase of the Gondwanan cycle recorded in the Agua Negra Formation, which is mainly marine with thin continental intercalations. Stages 4 and 5 represent the orogenic conditions that promoted the uplift of the Ancestral Andes and a sudden change from mainly marine (Agua Negra Formation) to continental (San Ignacio Formation) facies. Finally, stages 6 and 7 show the intense magmatic activity developed during the Guadalupian-Lopingian and probably early Triassic times (Choiyoi Group, anaorogenic conditions).The late Paleozoic paleofloras recovered from different stratigraphic intervals into the Ancestral Andes allow establishing that stages 1, and 2, bear remains of the Nothorhacopteris-Botrychiopsis-Ginkgophyllum (NBG) Biozone (latest Mississippian-Early Pennsylvanian). Stage 3 yielded Late Pennsylvanian plant remains and invertebrates while the Stage 5 provided silicified trunks of Cuyoxylon (San Ignacio Formation) and palynofloras characterized by Lueckisporites (La Puerta Formation) of Cisuralian age.

Opening and closure of Cadomian peri-Gondwanan oceans: age and evolution of the Mérida Ophiolite (SW Iberia)

ABSTRACT In the SW Iberian Massif, the Ossa-Morena Complex contains a stack of units of different origin and tectonothermal evolution. Individual terranes of the complex record a Cadomian history, traditionally interpreted in relation to the dynamics of a peri-Gondwanan volcanic arc. The interpretation of the Cadomian terranes is a key issue in the reconstruction of the Ediacaran margin of Gondwana in NW Africa. In the Mérida Massif, a mafic – ultramafic unit stacked between two units of continental or arc affinity is interpreted as a Cadomian ophiolite, the Mérida Ophiolite. Within it, mafic lithologies dated at c. 596 Ma (U-Pb in zircon) have calc-alkaline or tholeiitic affinity, indicating generation in a supra-subduction zone setting. The ophiolite shows a main event of Cadomian metamorphism (c. 590 Ma, U-Pb garnet dating) with a prograde P-T path and peak conditions at c. 700°C and 8 kbar. The mafic rocks show Nd isotopic compositions clearly different from those characteristics of the mafic rocks formed in the axial zone of the volcanic arc. Hence, the Mérida Ophiolite probably represents oceanic lithosphere of a back-arc basin, opened between the volcanic arc and the outer margin of Gondwana. Closure of the back-arc occurred during collision of the volcanic arc with the margin of Gondwana (starting at c. 590 Ma), which caused rapid accretion of the back-arc oceanic lithosphere beneath the arc and prograde metamorphism typical of subduction inception. The Mérida Ophiolite was finally obducted above the continental margin of Gondwana, presently preserved in gneissic unit piled beneath the ophiolite. Cadomian evolution of this peri-Gondwanan arc section continued with new tectonothermal events dated in the range 560–540 Ma that alternated with episodes of intense magmatic activity and preceded the collapse of the magmatic arc and its erosive levelling, followed by the generation of a new episode of intense magmatic activity in the arc and the unconformable deposition of the Ediacaran-Cambrian Malcocinado Formation.

Linking the Jehol Biota Evolution to the Early Cretaceous Volcanism During the North China Craton Destruction: Insights From F, Cl, S, and P

AbstractThe Early Cretaceous Jehol Biota evolution has remarkable spatiotemporal correlation with the destruction of the North China craton though the coupling mechanism remains enigmatic. The craton destruction was accompanied by intense magmatic activity and the released volatiles and nutrients might have had climatic and environmental impacts on the biotic evolution. In this study, we investigated the mentioned hypothetical causal link by determining concentrations and total emissions of volatile elements (S, F, Cl) and bulk‐rock P contents of volcanic rocks that were erupted during the pre‐flourishing, flourishing and post‐flourishing stages of the Jehol Biota. Our results show that the volcanism near the flourishing stage has lower S (1,083–2,370 ppm), Cl (1,277–5,608 ppm) and higher P2O5 contents (0.48–0.84 wt.%) than that in the non‐flourishing stages with S of 1,991–3,288 ppm, Cl of 7,915–12,315 ppm and P2O5 of 0.17–0.23 wt.%. Fluorine contents in the three stages vary from 893 to 3,746 ppm. The total volatile emissions are minor in the flourishing stage (1–14 Gt S, 0.6–10 Gt Cl, 0.6–9 Gt F) but elevated in the non‐flourishing stages (2–766 Gt S, 4–1,168 Gt Cl, 1–175 Gt F). Our data suggest that regional climatic and environmental impacts of volcanism in the non‐flourishing stages probably hindered the species diversification. The high P flux released from lithospheric mantle‐derived lavas during the peak time of craton destruction might have enhanced primary productivity and contributed to the flourishing of the Jehol Biota. Our study provides insights into the relationship between the biosphere and deep geodynamic processes driven by volcanism.

The Limpopo Magma‐Rich Transform Margin, South Mozambique: 1. Insights From Deep‐Structure Seismic Imaging

AbstractA variety of structures results from the interplay of evolving far‐field forces, plate kinematics, and magmatic activity during continental break‐up. The east Limpopo transform margin, offshore northern Mozambique, formed as Africa and Antarctica separated during the mid‐Jurassic period break‐up of the Gondwana supercontinent. The nature of the crust onshore has been discussed for decades in an effort to resolve issues with plate kinematic models. Two seismic refraction profiles with coincident multichannel seismic reflection profiles allow us to interpret the seismic velocity structures across the margin, both onshore and offshore. These seismic profiles allow us to (a) delineate the major regional crustal domains; (b) identify widespread indications of magmatic activity; and (c) map crustal structure and geometry of this magma‐rich transform margin. Careful examination of the profiles allows us to make the following observations and interpretations: (a) on land, continental crust is overlain by a >10‐km thick volcano‐sedimentary wedge related to an early rifting stage, (b) offshore, thick oceanic crust formed due to intense magmatic activity, and between the two (c) a 50–60‐km wide transform zone where the crustal structures are affected by intense magmatic activity and faulting. The prominent presence of intrusive and extrusive igneous units may be attributed to the combination of a deep‐seated melting anomaly and a trans‐tensional fault zone running through thinned lithosphere that allowed melt to reach the surface. A comparison of the crustal thinning along other transform margins shows a probable dependence with the thermal and/or tectonic history of the lithosphere.

The Limpopo Magma‐Rich Transform Margin, South Mozambique – 2: Implications for the Gondwana Breakup

AbstractThe rifted continental margins of Mozambique provide excellent examples of continental passive margins with a significant structural variability associated with magmatism and inheritance. Despite accumulated knowledge, the tectonic structure and nature of the crust beneath the South Mozambique Coastal Plain (SMCP) are still poorly known. This study interprets high‐resolution seismic reflection data paired with data from industry‐drilled wells and proposes a structural model of the Limpopo transform margin in a magma‐rich context. Results indicate that the Limpopo transform margin is characterized by an ocean‐continent transition that links the Beira‐High and Natal valley margin segments and represents the western limit of the continental crust, separating continental volcano‐sedimentary infilled grabens from the oceanic crust domain. These basins result from the emplacement of the Karoo Supergroup during a Permo‐Triassic tectonic event, followed by an Early Jurassic tectonic and magmatic event. This latter led to the establishment of steady‐state seafloor spreading at ca.156 Ma along the SMCP. A Late Jurassic to Early Cretaceous event corresponds to formation of the Limpopo transform fault zone. Which accommodated the SSE‐ward displacement of Antarctica with respect to Africa. We define a new type of margin: the magma‐rich transform margin, characterized by the presence of voluminous magmatic extrusion and intrusion coincident with the formation and evolution of the transform margin. The Limpopo transform fault zone consists of several syn‐transfer and ‐transform faults rather than a single transform fault. The intense magmatic activity was associated primarily with mantle dynamics, which controlled the large‐scale differential subsidence along the transform margin.

Linking ∼1.4–0.8 Ga volcano-sedimentary records in eastern Central Asian orogenic belt with southern Laurentia in supercontinent cycles

The record of Meso- to Neoproterozoic magmatism and sedimentation from the western Xing’an-Airgin Sum Block (XAB), eastern Central Asian Orogenic Belt (CAOB), provides the first key evidence for the close affinity between XAB and southern Laurentia, as well as the linkage with the supercontinent cycles. The ∼ 1.4 Ga calc-alkline granite-rhyolite association within the western XAB was probably the product of extension on a long-lived retreating convergent margin during the Columbia breakup, remarkably similar to the coeval Granite-Rhyolite Province in the southern Laurentia. Siliciclastic, mixed clastic and carbonate sequences of the Airgin Sum Group accumulated on the western XAB during two stages at 1.00–0.92 and 0.87–0.75 Ga, which were comparable with the syn- to post-orogenic successions on the southern Laurentia margin representing two dominant phases of the Grenville orogenic cycle in the Rodinia assembly. The Columbia breakup to Rodinia assembly also correlated well with the shift of zircon Hf isotope from a long-term juvenile crustal growth (1.6–1.2 Ga) to the rapid crustal reworking (1.1–0.8 Ga), and with the changes of zircon trace elements over time in the western XAB. The ever-growing new discovery of predominant 1.5–1.3, 0.9–0.8 Ga detrital zircon age peaks and coeval magmatism in many blocks worldwide suggests that they recorded much more intense magmatic activity, exhumation and deposition than previous thought. Juvenile crustal growth underestimated in previous researches, occurred extensively in blocks within the CAOB and Columbia at ∼ 1.5–1.3 Ga, and crust reworking significantly dominated the crustal evolution during the Rodinia assembly in 1.1–0.8 Ga.

Cenozoic temporal variation of crustal thickness in the Urumieh-Dokhtar and Alborz magmatic belts, Iran

We present regional variations of whole-rock Sr/Y and (La/Yb)N ratios of magmatic rocks along the Cenozoic Urumieh-Dokhtar and Alborz magmatic belts, Iran. Both the magmatic belts are located at the north of the main Zagros Neo-Tethyan suture. The Urumieh-Dokhtar magmatic belt (UDMB), which trends NW-SE for 1000 km across Iran, was characterized by the intensive volcanism and plutonism, and defined the magmatic front (MF) of the Zagros orogenic belt. The Alborz magmatic belt (AMB) is situated to the north, and characterized by less intense magmatic activity. The Alborz magmatic belt was formed behind it in the rear-arc (RA) domain. A striking feature of the both magmatic belts is the transition from normal calc-alkaline arc magmatism during the Eocene–Oligocene to adakite-like calc-alkaline magmatism during the Middle to Late Miocene–Pliocene. The late-Cenozoic magmatism of the UDMB and AMB shows higher Sr/Y and (La/Yb)N. However, it should be noted that crustal thickening event is intensive in the UDMB than AMB during Late Cenozoic. Using the composition of the Lale-Zar zircons from the SE UDMB we determined the oxygen fugacity (fO2) during zircon crystallization to be between FMQ (fayalite–magnetite–quartz buffer) -0.69 to +2.41, whereas those of the Hashroud-Teckmdash-Gormolla zircons from NW AMB range from −1.22 to +5.99. The fO2 estimates suggest relatively more oxidized conditions for the Late Cenozoic igneous rocks of the AMB. Compiled data from the UDMB and AMB intrusions show an increase in average zircon crystallization temperatures with decreasing age. These outcomes have been interpreted in terms of variation of the crustal thickness, from 30 to 35 km during Eocene-Oligocene to 40–55 km during the middle-late Miocene. We propose the increase in crustal thickness is associated with the collision between the Arabian plate and Iran and subsequent convergence during the middle-late Miocene.

Recognition of an Early Triassic accretionary complex in the Nedamo Belt of the Kitakami Massif, Northeast Japan: New evidence for correlation with Southwest Japan

AbstractThe Kitakami Massif of the Tohoku district, Northeast Japan, consists mainly of the South Kitakami Belt (Silurian–Cretaceous forearc shallow‐marine sediments, granitoids, and forearc ophiolite) and the North Kitakami Belt (a Jurassic accretionary complex). The Nedamo Belt (a Carboniferous accretionary complex) occurs as a small unit between those two belts. An accretionary unit in the Nedamo Belt is lithologically divided into the Early Carboniferous Tsunatori Unit and the age‐unknown Takinosawa Unit. In order to constrain the accretionary age of the Takinosawa Unit, detrital zircon U–Pb dating was conducted. The new data revealed that the youngest cluster ages from sandstone and tuffaceous rock are 257–248 Ma and 288–281 Ma, respectively. The Early Triassic depositional age of the sandstone may correspond to a period of intense magmatic activity in the eastern margin of the paleo‐Asian continent. A 30–40 my interval between the youngest cluster ages of the sandstone and the tuffaceous rock can be explained by the absence of syn‐sedimentary zircon in the tuffaceous rock. The new detrital zircon data suggest that the Takinosawa Unit can be distinguished as an Early Triassic accretionary complex distinct from the Early Carboniferous Tsunatori Unit. This recognition establishes a long‐duration northeastward younging polarity of accretionary units, from the Carboniferous to Early Cretaceous, in the northern Kitakami Massif. Lithological features and detrital zircon spectra suggest that the Early Triassic Takinosawa Unit in the Nedamo Belt is comparable with the Hisone and Shingai units in the Kurosegawa Belt in Shikoku. The existence of this Early Triassic accretionary complex strongly supports a pre‐Jurassic geotectonic correlation and similarity between Southwest and Northeast Japan.

Geological process of Late Paleozoic shale gas generation in the eastern Ordos Basin, China: Revelations from geochemistry and basin modeling

During the Meso-Cenozoic, the eastern Ordos Basin (EOB) underwent a complex tectonothermal process influenced by the destruction of North China Craton, significantly affecting the thermal maturation of the Late Paleozoic source rocks. Tectonothermal modeling and maturation of coal-bearing shales were performed in the EOB to reveal the geological process of shale gas generation. Organic geochemical data for shales show that TOC values vary from 0.96 wt% to 21.36 wt% and Ro values range from 1.56% to 2.47%, as well as that organic matter mainly consists of type III kerogen—indicating excellent potential, and sufficient maturity, for gas generation. Thermal modeling suggests that heat flow in the EOB significantly increased as a result of intense magmatic activities during the Yanshanian orogeny, with peak values of 108 and 128 mW/m2 in the northern and southern regions, respectively. Consequently, great variations in maturation history are seen in different regions of the EOB, with the Taiyuan and Shanxi shales reaching the wet gas and dry gas stages, respectively, in the northern region and all shales reaching the dry gas stage in the southern region. Hydrocarbons were generated at 237 Ma and peaked around 162 Ma, whereas hydrocarbon expulsion began at 230 Ma and peaked at 131 Ma. Rapid subsidence in the Triassic brought the shales to the oil generation window and Early Cretaceous magmatic activities led to rapid maturation of shales, again reaching the gas generation stage. Accordingly, extremely high levels of thermal maturity are well documented in hydrocarbons' alkane composition and stable carbon isotope ratio. Gas geochemical data (δ13C1 vs. C1/C2+3, δ13C1 vs. C2+) imply that that hydrocarbons are from highly mature thermogenic gas generated mainly from humus, and this offers great support for thermal maturation modeling. Regionally, coal-bearing shales have been steadily uplifted and eroded since the Late Cretaceous, causing partial destruction of gas reservoirs. The tectonothermal evolution and hydrocarbon generation of EOB were controlled primarily by magmatic thermal effects resulting from the westward subduction of the Pacific plate.

Inhomogeneous thinning of a cratonic lithospheric keel by tectonic extension: The Early Cretaceous Jiaodong Peninsula–Liaodong Peninsula extensional provinces, eastern North China craton

Abstract The mechanisms of lithospheric thinning and craton destruction have been hotly debated in the last decades. The Early Cretaceous Jiaodong and Liaodong extensional provinces (JEP and LEP, respectively) of the eastern North China craton are typical areas where the cratonic Archean lithosphere has been intensely extended and thinned. Various extensional structures, e.g., metamorphic core complexes (MCCs), low-angle detachment faults, and extensional basins, characterize the Early Cretaceous crustal deformation of the two provinces. However, profound differences exist in structural development and related magmatic activities between the two provinces. Distributed small-scale extensional basins were formed in association with exhumation of the Liaonan and Wanfu MCCs in the LEP, whereas the major Jiaolai Basin was developed coevally with exhumation of the Wulian, Queshan, and Linglong MCCs in the JEP. Sr-Nd isotope compositions of volcanic rocks from the basins of the two provinces are compatible with syntectonic magmatic activities of evolving magma sources in the LEP, but multiple and hybrid magma sources in the JEP. It is shown, from variations in structural styles, plutonic and volcanic activities, and thermal evolution of the two extensional provinces, that two stages (ca. 135–120 Ma and 120–100 Ma) of tectonic extension affected the JEP and LEP in the Early Cretaceous. We demonstrate that regional tectonic extension (parallel extension tectonics, or PET) is responsible for the formation of major extensional structures and the occurrence of the magmatic associations. Progressive wide rifting by coupled crust-mantle detachment faulting of a hot LEP lithosphere was accompanied by evolving magma sources from dominant ancient crust and enriched mantle to juvenile crust. Two stages of narrow rifting of a cold JEP lithosphere led to early crustal detachment faulting transitioning to late crust-mantle faulting, which resulted in intense magmatic activity from hybrid to multiple magma sources. These processes contributed to destruction of the craton, with thinning of its lithospheric keel and local transformation of the nature of the lithospheric mantle. It is expected that such a model is also applicable to interpretation of tectonic extension of contiguous areas of the North China craton and the remobilization of other cratons.

Large environmental disturbances caused by magmatic activity during the Late Devonian Hangenberg Crisis

Abstract A wide range of various proxies (e.g., mineralogy, organic carbon, inorganic geochemistry, C and Mo isotopes, and framboidal pyrite) were applied for interpretation of changing oceanic redox conditions, bioproductivity, and the regional history of magmatic activity. This resulted in internally consistent interpretation of the late Famennian Hangenberg Crisis in subtropical deepest water sites of the epeiric Rhenohercynian and Saxo–Thuringian basins, as well as more open sites of the Paleo-Tethys Ocean. High mercury concentrations were detected in all of the studied sections, with the highest values strata in the Carnic Alps (up to 20 ppm) and Thuringia (up to 1.5 ppm). The beginning of the Hg anomaly and the presence of pyroclastic material, indicate that local magmatic activity was initiated before the deposition of the Hangenberg Black Shale (HBS). The onset of the HBS deposition coincided with the expansion of phosphate-enriched, anoxic to euxinic waters during short-lived CO2-greenhouse spike of a warm–humid climate. Intensive magmatic activity was a trigger for climatic changes, an excessive eutrophication, and an accelerated burial of organic carbon during the Hangenberg transgressive pulse. The injection of catastrophic amounts of CO2, toxic elements and acids from volcanic activity could have led to acidification, mutation of spores, and episodes of mass mortality of marine plankton.

The characteristics of granites in the Gaofeng and Baocheng areas, Hainan Province, China: response to subduction of the Tethyan South China Sea

During the early Mesozoic Era there was intense magmatic activity near Hainan Island, South China. As a result, the granites of Hainan Island provide information on, and are suitable material to potentially improve understanding of the Cretaceous tectonic environment of the northern margin of the South China Sea. The Gaofeng and Baocheng intrusions are composed mainly of medium- to fine-grained biotite adamellite (Baocheng) and granodiorite (Gaofeng). The two intrusions yielded U–Pb LA-ICP-MS zircon ages of 107.7 ± 6.1 Ma (Gaofeng) and 105.8 ± 2.4 Ma (Baocheng). Regarding the major elements, the Gaofeng and Baocheng intrusions had medium Si and alkali contents and high Ca, Mg, and Al contents, with an aluminum saturation index of 0.95–1.03 and 1.05–1.30. The trace element and rare earth element (REE) characteristics showed that the two intrusions have intense heavy REE/light REE (HREE/LREE) fractionation, LREE enrichment, HREE depletion, and weak negative Eu anomalies. The intrusions were enriched in high field-strength elements and depleted in large ion lithophile elements. These geochemical characteristics indicate that the Hainan Province was in a tectonic subduction environment in the late Yanshanian period. Multiple geochemical characteristics demonstrate that the granites in the Hainan Province were formed by a different mechanism and in a different setting from those in Fujian and Zhejiang. The late Mesozoic granites of Fujian and Zhejiang were formed by the Western Pacific subduction. However, Hainan Island was under an arc environment formed by the northward subduction of the Tethyan-South China Sea during the Cretaceous leading to emplacement of the Gaofeng and Baocheng intrusions.

Quantifying the late-to post-Variscan pervasive heat flow, central Netherlands, Southern Permian Basin

The Southern Permian Basin is marked by significant Latest Carboniferous-Early Permian magmatism attributed to mantle plume emplacement. This intense magmatic activity is commonly assumed to have impacted the heat flow in this area. In the central Netherlands a large number of wells show evidence of magmatic activity dated as Permo-Carboniferous. In addition, high maturity values have been measured for the Carboniferous and below. Theoretical models for tectonic heat flow and maturity evolution presented in this paper show that mantle upwelling, underplating, and intrusions have a significant effect on maturity-depth trends. Tectonic modelling of five selected wells shows that tectonic subsidence and exhumation can be correlated with a significant heat flow pulse at Latest Carboniferous-Early Permian time. This could well explain the widespread elevated maturity/depth gradient in Carboniferous rocks. Quantitative assessment of heat flow, based on a model of mantle plume emplacement, shows that mantle upwelling and underplating at the base of the crust, proposed by previous studies, provides insufficient heat flow to explain strongly elevated maturity-depth trends. In contrast, widespread Permo-Carboniferous calc-alkaline magmatism at shallow crustal levels provides a mechanism for elevated heat flow with a regional impact, consistent with observed high maturity-depth trends. The model and maturity data demonstrate that elevated maturity at shallow burial-depth levels of 500–1000 m is probably sited in the gas window during a heat pulse, occurring at Late Carboniferous times. • Late-to post-Variscan thermal perturbation related to magmatic event. • High maturity in central Netherlands by deep lithospheric processes. • Distinct, short lived thermal peak in carboniferous sediments. • Result fit with regional geodynamic models and magmatic occurrences across the Southern Permian Basin.

Age and Depositional Settings of the Ordovician Chalovskaya Group in the Argun Massif, Eastern Part of the Central Asian Fold Belt

The results of mineralogical and geochemical studies of the metaclastic rocks of the Grebnev and Magdagachi sequences of the Chalovskaya Group, one of the key lithostratigraphic units of the Argun continental massif in the eastern part of the Central Asian Fold Belt, as well as the results of the U–Pb dating of detrital zircons from these rocks by the LA-ICP-MS method, are presented. It was found that the age of the youngest zircons is ~478 Ma (Early Ordovician) in the metasandstones of the Grebnev Sequence and ~448 Ma (Late Ordovician), in the metasiltstones of the Magdagachi Sequence. Together with the previously determined age of the metadacites of the Isagachi Sequence (476 ± 8 Ma), this suggests the Ordovician age of the Chalovskaya Group, dated previously as Late Precambrian. The available data indicate that the deposits of the Chalovskaya Group accumulated in a setting of an active continental margin or an island arc against the background of intense magmatic activity. Considering that the Early Paleozoic suprasubduction magmatism is manifested in all continental massifs of the eastern part of the Central Asian Fold Belt (Argun, Mamyn, Bureya, Jiamusi, Khanka), one cannot exclude that these continental massifs have a common geodynamic history.

Age and formation features of the Ordovician Chalovskaya sequence in the Argun Massif, eastern part of the Central Asian fold belt

In this paper we present the results of the mineralogical and geochemical studies of metaterrigenous rocks of the Grebnev and Magdagachi formations of the Chalovskaya Sequence – one of the key stratigraphic divisions of the Argun continental Massif in the eastern part of the Central Asian fold belt, and U–Pb geochronological (LA-ICP-MS) data for the detrital zircons from these rocks. It is established that the youngest zircons in the metasandstones of the Grebnev Formation have an age of ~478 Ma, and in the metaalevrolites of the Magdagachi Formation ~448 Ma. Together with the previously obtained data on the age of metadacites from the Isagachi Formation (476 ± 8 Ma), this information indicates the Ordovician age of the Chalovskaya Sequence, previously attributed to the Late Precambrian. It was shown that the accumulation of sediments of the Chalovskaya Sequence took place in an environment of an active continental margin or island arc simultaneously with intense magmatic activity. Taking into account the fact that the Early Paleozoic suprasubduction magmatism manifested within all the continental massifs of the eastern part of the Central Asian fold belt (Argun, Mamyn, Bureya, Jiamusi, Khanka), it cannot be excluded that the mentioned continental massifs have a common geodynamic history.