Late Cretaceous Paleocene Research Articles

Structural evolution and exhumation events recorded in the Huingancó Granodiorite, Cordillera del Viento, Southern Central Andes, Argentina

This study seeks to unravel the exhumation history of Permian granodiorites corresponding to the Huingancó volcano-plutonic Complex in the southern sector of the Cordillera del Viento (∼37°S), located within the Chos Malal fold-thrust belt. In this context, mineral chemistry analyses were conducted on the granodiorites using electron microprobe data to infer the P-T conditions of emplacement, resulting in 700–900 °C and pressures ranging between 1 and 2.4 kbar. Employing a geostatic gradient of 3.7 km/kbar, these values give an estimate of emplacement depths between 4 and 9 km. In order to understand their exhumation path, five samples from the Huingancó Granodiorite were taken along the Huaraco creek on the western flank of the Cordillera del Viento anticline to perform apatite fission track (AFT) analysis. This analysis yielded new cooling ages for the study area ranging between 50 and 80 Ma. Furthermore, inverse thermal modeling using the fission track data revealed two significant exhumation events during the Andean cycle: one during the Late Cretaceous-Paleocene and the other in Miocene times, separated by a period of gradual cooling or stability during Eocene-Oligocene times. These important cooling events are associated with the main construction phases of the Cordillera del Viento. Finally, to characterize its deformation evolution, a structural kinematic model is proposed based on a balanced structural section and its reconstruction to its non-deformed pre-Cretaceous state. The resulting model allows us to identify the structures and mechanisms of uplift rising the Cordillera del Viento, and their association with the main exhumation events depicted in the inverse thermal modeling. The main structure of the Cordillera del Viento corresponds to a fault bending fold that involves the basement in the deformation. Subsequently, its insertion as an intracutaneous wedge is related with the development of the thin-skinned structures at the internal sector of the Chos Malal fold and thrust belt.

Unraveling deformation mechanism of the Fukang fold-and-thrust belt: Insight into intracontinental orogenesis of the Bogda Mountain, NW China

Characterized by the superposition of well-developed thick-skinned and thin-skinned structures, the Fukang fold-and-thrust belt is an ideal place for understanding the intracontinental orogenic process of the Bogda Mountain in the Tianshan orogenic belt, China. This study comprehensively examines the geological architecture, structural evolution, and deformation mechanism of the Fukang fold-and-thrust belt using high-resolution seismic reflection data, apatite-fission track analysis, and discrete element simulation. Seismic profile reveals that the Fukang fold-and-thrust belt exhibits superimposed tectonic styles, including a thrust duplex involving Carboniferous strata and an overlapping thrust imbricate structure. Stratigraphic unconformities and thermochronological results from apatite fission track suggest that this belt experienced five main episodes of compressional deformation in the Late Permian, Middle-Late Triassic, Middle-Late Jurassic, Late Cretaceous-Paleocene, and Late Miocene-present. The discrete element simulation results indicate that the Late Permian initial compressional deformation was triggered by reactivation of the pre-existing extensional faults. Subsequent episodic deformation was primarily controlled by thrusting along the Upper Carboniferous and Middle Permian decollement layers. This study highlights the predominant roles of the pre-existing faults and the decollement layers in the formation and evolution of the piedmont fold-and-thrust belt of the Bogda Mountain at distinct stages, serving as critical factors in determining the extent and amplitude of an intracontinental orogenic belt.

Geochemistry and fluid inclusion study of the Jbel Tirremi fluorite-baryte deposit, Morocco: New insights into the genetic model in relation to Mesozoic tectonics

The highly fractured Jurassic carbonates at Jbel Tirremi in northeastern Morocco host fluorite-baryte deposit. The mineralization occurs both as stratabound in marl-limestone contact and as fault-hosted veins (N-S- and NNW-SSE). The mineral paragenesis consists of two fluorite and baryte generations and calcite with subordinate amounts of quartz, dolomite, traces of sulfides (chalcopyrite, pyrite, galena), and oxidized minerals. Fluid inclusion data reveal that hot moderately saline fluids derived from the Paleozoic basement mixed with Triassic brines and cooler, meteoric waters. The REY inventory, C-O-S-Pb-Sr-Nd isotope, and crush-leach data point to the Paleozoic basement as the primary source of metals with a contribution from the Triassic red beds. The refined ore genetic model developed in this study from our new geological and geochemical data includes the downward movement of Triassic-Jurassic evaporated seawaters along normal faults, followed by the leaching of metals from Paleozoic and Triassic rocks, and the subsequent upward flow of these metalliferous fluids. During the Late Cretaceous-Paleocene basin inversion, the deep-seated ore-forming fluids migrated upward, which eventually mixed with Triassic brines and cooler meteoric waters. This fluid mixing caused the precipitation of multiple generations of fluorite and baryte.

Møre–Vøring Composite Tectono-Sedimentary Element, Norwegian Rifted Margin, Norwegian Sea

Abstract The Møre and Vøring basins at the mid-Norwegian margin were affected by a series of rift phases separated by periods of tectonic quiescence from Caledonian collapse in the Devonian to final continental break-up in the earliest Eocene. The tectonic phases were mostly extensional in nature, and the pre-drift extension across the Møre and Vøring basins since mid-Permian time has been estimated to be of the order of 200–250 km. The pre-Cretaceous basin configuration is poorly constrained due to limited seismic resolution at great depths and a lack of borehole control. A fundamental change occurred in the crustal deformation regime: from Late Jurassic distributed stretching of the upper crust to Early Cretaceous thinning at lower-crustal levels located along the axis of the Møre and Vøring basins. A westward migration of Late Cretaceous–Paleocene depocentres in the Vøring Basin reflects the focus of deformation towards the time and line of break-up. The basin architecture and evolution are summarized in relation to tectono-sedimentary elements corresponding to the main tectonic and depositional phases, and represent characteristic megasequences in the seismic data. Finally, the exploration history and main petroleum systems of the Møre and Vøring basins are presented.

Early development of the Patagonian fold and thrust belt and the onset of foreland sedimentation in the Austral-Magallanes basin

Retroarc basins register the onset of compressional exhumation during the Cretaceous in the Andes, evidenced by sequences showing sedimentary provenance from the orogen. We present U–Pb detrital zircon geochronology from the Austral-Magallanes basin in the Southern Patagonian Andes (∼47–48°SL), where the foreland stage began in the Early Cretaceous. The littoral sandstones from basal foreland sequences of the Río Belgrano Formation yield ∼123 Ma maximum depositional ages, confirming previous studies that the basin infill is early Aptian. The detrital zircon ages showed two main clusters of 129-115 Ma and 151 -140 Ma, that are derived from the coetaneously exhumed Andean arc and earlier Jurassic magmatic sources. The zircons which overlap with ages of Upper Jurassic Andean synrift volcanics, confirms orogenic exhumation coeval with sedimentation. A sequence of retroarc volcanism dated between 119 and 97 Ma overlies the basal foreland littoral-continental deposits, and it is followed by a Late Cretaceous-Paleocene hiatus. Further analysis of detrital zircons ages distribution and geological considerations, indicates that the studied northern depocenter was a source region of sedimentary supply after its Cenomanian exhumation.

Reconstruction of the topographic evolution of the Nanling Range in South China and its implications for the East Asian Monsoon evolution

The East Asian monsoon is the largest periodic airflow on Earth and significantly affects the climate of East Asia. However, considerable controversy exists about the onset timing of the East Asian monsoon. As one of the southern barriers blocking the northward movement of the warm and humid airflow, the Nanling Range has likely recorded key topographic information related to the East Asian monsoon onset and development. We used apatite and zircon (UTh)/He data obtained from the Shaoguan–Guidong horizontal cross-section to reconstruct the two-dimensional (2-D) paleotopography of the Nanling Range on a long-term scale. Four vertical profiles in Shulouqiu, Erjian, Sanfenshi, and Leiwangdian were used to constrain the exhumation history of the Nanling Range. The result revealed the following: 1) The drainage divide began to move from south to north at 80 Ma. At 80 Ma, the south segment of the cross-section reached a peak elevation of ∼3.6 km. The asymmetric topography experienced a rapid elevation (and relief) decrease from 80 Ma to 40–30 Ma. The four vertical profiles also experienced increased cooling and high exhumation rates from 100 Ma to 40–30 Ma. 2) The south segment experienced more rapid exhumation than the north segment from 80 Ma to 40–30 Ma. The rapid exhumation of the south segment during the Late Cretaceous–Paleocene is probably related to the activity of the Nanxiong Fault, and the rapid exhumation of the south segment during the Eocene probably results from the onset of the East Asian Monsoon.

Calcareous Nannofossils Biostratigraphy of Late Cretaceous–Paleocene Successions from Northern Jordan and Their Implications for Basin Analysis

Local geological and tectonic processes have been pivotal in shaping the diverse sedimentation patterns observed in Jordan, forming sub-basins characterized by elevated organic matter content (TOC). This study aims to characterize the Maastrichtian basin, focusing on sedimentation rates using calcareous nannofossils and understanding paleoecological and paleo-oceanic conditions. It offers insights into the paleoenvironmental factors impacting oil shale deposition in the late Maastrichtian–Paleocene period. It employs classical biostratigraphical, semi-quantitative, and statistical methodologies to achieve its objectives of age determination and paleoecological insights. A total of 116 smear slides from two sites were obtained: the first, consisting of WA-1 (23 samples), WA-2 (18 samples), and WA-3 (11 samples), and the second, with 60 samples. Notably, the sites exhibit varying topography. WA-1 and WA-2, situated at lower elevations, have the highest Total Organic Carbon (TOC) levels, while areas with higher elevations in section four are visually identified by a light color. The study revealed varying patterns of calcareous nannofossil richness in the two investigated sites. These patterns were instrumental in defining biozones, with the utilization of marker species such as Lithraphidites quadratus, Micula murus, Micula prinsii, and Cruciplacolithus tenuis. Chronologically, these sections were classified as Maastrichtian–Paleogene, encompassing the following biozones in sequential order: UC-20a, UC-20b, UC-20c, UC-20d, and NP-2. Furthermore, the study identified two hiatus intervals, observed in sections WA-1 and KAS-1. The absence of certain biozones in the analyzed sections suggests that these sections correspond to distinct geological blocks within the basin, underscoring the role of tectonic forces during the deposition period. The sedimentation rate initially commenced at low levels but gradually increased due to topographic alterations. Notably, the biozone UC-20c demonstrated a clear trend toward warming and enhanced nutrient availability. In this context, the abundance and diversity of species were associated with increased continental influx into the sub-basin, resulting in rising nutrient levels and the number of calcareous nannofossils. This study enhances the understanding of the local and global effects such as tectonic and climates of the continuity of basins by deciphering calcareous nannofossil patterns and their correlation with sedimentation factors.

Mesozoic-Cenozoic Exhumation Processes of the Harlik Mountain (East Tianshan), NW China: Evidence from Apatite (U-Th)/He Thermochronology

Abstract The Tianshan Mountains, which formed through the prolonged and complex subduction-accretion of the paleo-Asian ocean, experienced multiple widespread erosions and reactivations during the Mesozoic-Cenozoic period. Thus, the Tianshan has become a crucial area to explore the process and mechanism of intracontinental orogeny. The Harlik Mountain located in the easternmost part of Tianshan has special significance in revealing crustal deformation and far-field stress propagation. In this study, we use the apatite (U-Th)/He method to investigate the near-surface exhumation process of Harlik Mountain, which is the result of tectonic events and erosion. The apatite (U-Th)/He data and thermal history modeling reveal three enhanced exhumation events in the Harlik Mountain, i.e., the early Cretaceous, the late Cretaceous-Paleocene, and the middle Eocene. These events are consistent with the exhumation patterns observed throughout the entire Tianshan. Notably, the exhumation rate and amplitude in the early Cenozoic period were significantly higher in the Harlik Mountain compared with the Mesozoic period. Our findings reveal that the exhumation of the Harlik Mountain and the entire Tianshan displayed pronounced spatial-temporal variations throughout the Mesozoic-Cenozoic period. These variations can be attributed to the combined effect of uneven northward compression of the southern Asian margin, the heterogeneous rheological properties of the lithosphere, and the complex structure of the Tianshan.

The Generation of Eocene Mafic Dike Swarms During the Exhumation of a Core Complex, Biarjmand Area, NE Iran

Abstract Several swarms of parallel E–W dikes cuts late Neoproterozoic- to early Paleozoic (540 Ma) basement in the Biarjmand area, NE Iran. The microgabbroic to doleritic dike are several hundred meters long and 0.5 to 3 meters wide. U–Pb dating of their zircon grains yields a crystallization age of 46.0 ± 7.1 Ma for the dike swarms. The dikes have SiO2 contents of 46.0–49.3 wt%, and Fe2O3 contents of 9.80–14.8 wt% with variable MgO (4.92–9.16 wt%), TiO2 (1.47–2.65 wt%), and K2O contents (0.33–1.13 wt%). The dikes have low contents of high field strength elements (HFSEs), and have some similarities to transitional mid-ocean ridge basalts (T-MORB) based on their chemical composition. Positive ${\varepsilon}_{Nd}(t)$ values of +5.2 to +6.0 for the dike samples imply that the basaltic magma was generated from depleted lithospheric mantle. After the closure of the Sabzevar ocean and obduction of the large mantle peridotite body over the continental crust in the late Cretaceous-Paleocene, the gravitational instability in the central Iran/Eurasia plate collision zone triggered exhumation of old basement coeval with injection of the mafic magma. During exhumation, mylonitic deformation with brittle-ductile structures affected the basement metagranite and the host rocks. The metagranite and dike swarms cut the Cretaceous Sabzevar ophiolite, and the disparting of ophiolite members probably occurred during basement exhumation in the Cenozoic. The similar ages of the mafic dike swarms and other Eocene magmatic rocks of the Urumiah (Urmia) Dokhtar magmatic arc (UDMA), western Iran, is consistent with a rapid extensional regime over the Sabzevar suture zone on an earlier collision zone in NE Iran. This process provided a suitable setting for the exhumation of the old basement, the emplacement of the parallel dike swarm, and the development of shallow basins in this area.

Океаническая кора, трансрегиональные зоны сдвига и Амеразийская микроплита в мел-кайнозойской геодинамике формирования океана в Арктике

The author has reconstructed the structural-tectonic setting of the Late Cretaceous-Early Cenozoic stage of the geodynamic evolution of the Arctic Ocean. It is shown that the oceanic crust in the Eurasian and Canadian basins occupies a much smaller area than previously thought and was formed in both on blocks of the continental basement strongly stretched by Cretaceous rifting. Due to the processes, large and extended transregional shear zones were set in motion: the Chukchi-Canadian during the opening of the Canadian basin in the Early Cretaceous, and the continental marginal ones — Khatanga-Lomonosov and Northern Greenland-Canadian, the activation of shear movements in which is associated with the Late Cretaceous-Paleocene time, when the consistent formation of the Makarov and Eurasian basins took place. As a result new composite Amerasian microplate was detached and set in motion, which combined the blocks of Arctic Alaska, the Canadian Basin, the Chukchi Rise, the Alpha–Mendeleev Rise, the Podvodnikov and Makarov Basins, and the Lomonosov Ridge. The movement of the microplate along approximately parallel large shear zones at the edges of the Canadian Arctic and Siberian-Chukotka shelves was directed towards the Pacific subduction zone. The movement of the Amerasian microplate was accompanied by rifting and detachment of the Lomonosov Ridge from the Barents-Kara margin, opening of the Eurasian Basin in the rear of the ridge, and transform displacements — right-sided along the Khatanga-Lomonosov zone and left-sided along the North Greenland-Canadian fault zone. At the same time, as a result of the movement of the Amerasian microplate, the previously unified area of Cretaceous plateau basalts (HALIP) was broken, and the Central Arctic province of magmatism was separated and moved away from the Barents Sea province.

Global impact and selectivity of the Cretaceous-Paleogene mass extinction among sharks, skates, and rays.

The Cretaceous-Paleogene event was the last mass extinction event, yet its impact and long-term effects on species-level marine vertebrate diversity remain largely uncharacterized. We quantified elasmobranch (sharks, skates, and rays) speciation, extinction, and ecological change resulting from the end-Cretaceous event using >3200 fossil occurrences and 675 species spanning the Late Cretaceous-Paleocene interval at global scale. Elasmobranchs declined by >62% at the Cretaceous-Paleogene boundary and did not fully recover in the Paleocene. The end-Cretaceous event triggered a heterogeneous pattern of extinction, with rays and durophagous species reaching the highest levels of extinction (>72%) and sharks and nondurophagous species being less affected. Taxa with large geographic ranges and/or those restricted to high-latitude settings show higher survival. The Cretaceous-Paleogene event drastically altered the evolutionary history of marine ecosystems.

Caribbean–South America interactions since the Late Cretaceous: Insights from zircon U–Pb and Lu–Hf isotopic data in sedimentary sequences of the northwestern Andes

The Northern Andes in Colombia developed along an active, convergent margin with a complex subduction-accretion/collision history since Triassic times. Sedimentary basins that developed within, or close to, the evolving margin provide an important record for the tectonic history. Here we present U–Pb and Hf isotopic data of detrital zircons from Late Cretaceous and Miocene sedimentary strata. Two sedimentary sequences deposited in an active margin setting are analyzed in this study along two roughly E–W trending transects. Targeted sedimentary sequences are the Late Cretaceous-Paleocene siliciclastic member of the Penderisco Formation outcropping in the Western Cordillera and the hemipelagic Miocene Beibaviejo Formation overlying the suture zone between the Western Cordillera and the Panama-Chocó Block (PCB). Provenance and Hf isotopic signatures for sediments and volcaniclastic sandstones associated with the Penderisco Formation indicate a maximum depositional age of ca. 57 Ma with input of detrital material from mixed sources from two major domains: an eastern ancient continental domain, and a western Cretaceous oceanic domain that defines the present Western Cordillera. The record from continental sources suggests a para-autochthonous to autochthonous syn-tectonic history. For the Beibaviejo Formation provenance and Hf isotopic data suggest the Penderisco Formation and Eocene rocks with oceanic affinity within the PCB as the main sources and define a middle Miocene maximum depositional age (∼16 Ma). Our results provide a new insight into the evolution of volcaniclastic sequences at the northwestern margin of South America and provide a new constraint on the timing of collision between the PCB and the Andean margin during the middle Miocene.

Late extension of a passive margin coeval with subduction of the adjacent slab: The Western Alps and Maghrebides files

The evolution of the Alpine Tethys margins during the beginning of the African-Eurasian convergence was little studied compared to their evolution during the post-Pangea rifting and oceanic expansion,i.e., from the Early Jurassic to the early Late Cretaceous. The present work firstly aims to make up for this shortcoming in the case of the distal European margin of the Alpine Tethys, namely the Briançonnais domain of the Western Alps. We show that this margin was affected by strong post-rifting extension mainly in Late Cretaceous-Paleocene times and propose to make it the type of the (rare) “Late Extension Passive Margins”. Remarkably, this extension shortly preceded Lutetian times, when Briançonnais margin encroached the SE-dipping subduction zone under the Adria microplate. Secondly, we assess the post-rifting evolution of the north-Tethyan paleomargin in the Maghrebides transects,i.e., south-west of the Briançonnais transect along the same European-Iberian paleomargin. For this purpose, we consider the Triassic-Eocene series of the “Dorsale Calcaire” in the Alkapeca Blocks located along southeastern Iberia until the Eocene then transported onto the North African margin. Examination of the literature shows that the Tethyan margin of the Alboran block was strongly affected by normal faulting as early as Late Jurassic-Early Cretaceous times whereas post-rifting extension of the Kabylian blocks mainly occurred in the Late Cretaceous-Paleocene like in the Briançonnais. We propose that post-rifting extension of the Alboran block southern margin resulted from the sinistral movement of Africa relative to Iberia while the later extension of the Kabylian blocks can be related to the further convergence kinematics. Subduction of the Ligurian-Maghrebian slab under the North African margin would have occurred at that time in the southward continuation of the Alpine subduction. The overriding Adria and North African margins did not experience significant compression at that time. During the Eocene, a subduction polarity reversal occurred, which was associated with the relocation of the subduction zone along the Alkapeca block. This was the beginning of the Apenninic subduction, which triggered the back-arc opening of the Mediterranean basins.

Evaluation of Re–Os geochronology and Os isotope fingerprinting of Late Cretaceous terrestrial oils in Taranaki Basin, New Zealand

The rhenium-osmium (Re–Os) isotope system has been applied to several marine and lacustrine petroleum systems worldwide, showing good potential for dating crude oils and correlating them to their source rocks. Here we explore the applicability of the Re–Os geochronometer and Os isotope fingerprinting to terrestrial oils by comparing the Re and Os systematics of Late Cretaceous terrestrial oils from Taranaki Basin, New Zealand, and their correlated coaly source rocks. Comparison is also made with selected Late Cretaceous–Paleocene marine oils and source rocks with varying levels of terrestrial organic matter input.The asphaltene fractions of nine genetically related terrestrial oils from the Maui, Maari-Manaia and Tui Area fields in offshore Taranaki Basin contain low concentrations of Re (0.18–0.45 ppb) and 192Os (1.3–12.7 ppt) comparable to their correlated Late Cretaceous coaly source rocks (Rakopi and North Cape formations; Re 0.19–0.37 ppb, 192Os 5.3–9.6 ppt). The Re and 192Os concentrations in these terrestrial oils are generally one to two orders of magnitude lower than those in marine-sourced oils from the Kora Field in offshore Taranaki Basin and surface seeps in East Coast Basin.The 187Re/188Os and 187Os/188Os ratios of the terrestrial oils failed to yield a precise Re–Os isochron age. We attribute this to: (1) insufficient homogenisation of oils with widely variable initial 187Os/188Os (Osi) values inherited from thick, coaly source rock intervals (up to about 2700 m) within the Maui sub-basin and northern Kahurangi Trough kitchens; (2) insufficient spread of 187Re/188Os values (only 275 units); (3) insufficient time since oil expulsion (modelled to be from approximately 10 Ma to the present day) for the evolution of an isochron; and (4) possible effects of water washing of the oil columns. Although all of the studied oils are water-washed to varying degrees, there is no definitive evidence that water washing has disturbed the Re–Os systematics.The Osi values for the studied terrestrial oils inherited at the modelled time of oil expulsion (approximately 10 Ma) display a wide range (0.47–1.14) and do not provide a unique fingerprint of their Late Cretaceous coaly source rock formations. Osmium isotope compositions therefore appear to have limited potential for broad oil-source rock correlation within the predominantly coal-sourced petroleum systems of Taranaki Basin. The Osi values may, however, provide useful distinction of the terrestrial oils emanating from the Kahurangi Trough (Tui Area oils) from those of the Maui sub-basin (Maui and Maari-Manaia oils) based on the significantly more radiogenic values of the Tui Area oils (0.84–1.14 compared with 0.47–0.65 from Maui and Maari-Manaia oils). Overall, this study has provided useful insights into the potential application of the Re–Os isotope system to terrestrial, coal-sourced petroleum systems.

U-Pb geochronology and geochemistry of the Torud igneous rocks: Implications for post-collision Eocene magmatism in northeast Iran

New geochemical and U-Pb isotopic data from the Torud volcanic and subvolcanic rocks and their associated dikes exposed along the southern margin of the Sabzevar-Torud zone provide new evidence for Early-Middle Eocene, post-collision magmatism in northeast Iran. The 52–46 Ma (late Ypresian-Lutetian) U-Pb age interval of zircons separated from these rocks confirm the paleontological age of nummulite-bearing limestone interlayers. Inherited zircons separated from these igneous rocks have a much wider range of U-Pb ages that include Archean, Paleoproterozoic, Mesoproterozoic, Carboniferous, Permian, Triassic, Middle Jurassic, and Late Cretaceous. Most volcanics and subvolcanic rocks display high-K calcalkaline and shoshonitic trends. Distinct crystal fractionation patterns of the volcanic and subvolcanic rocks suggest magmatic differentiation in separate magma chambers. The studied rocks, depleted in the HFSE and enriched in the LILE, display nearly homogeneous isotopic Sr (0.7039–0.7055) and Nd (0.5126–0.5129) ratios and positive ɛNd values (0.08–0.56) indicating partial melting from an enriched lithospheric mantle source that was slightly contaminated with crustal material. Fluids, especially those released from the subducted slab, affected the composition of the source for the studied rocks. The magmatism occurred in the Torud area after the Late Cretaceous-Paleocene collision of the Central Iran microcontinent and Binalud-Kopeh-Dagh blocks and the Early-Middle Eocene break-off of the subducted slab.

Geochemistry and Petrogenesis of Late Cretaceous–Paleocene Granites from the Tengchong Block, Western Yunnan: Implications for Angle‐switching of Subducting Slab

AbstractThe Cenozoic geological hallmark of Western Yunnan is the characteristic voluminous Late Cretaceous‐Eocene granites; however, their geological background and petrogenesis have not been well constrained and elucidated. In this study, we present new zircon U‐Pb dating, along with geochemical and Sr‐Nd‐Hf isotopic data for granites from the Tengchong–Lianghe granitoid belt (as abbreviated to Tengliang belt) and West Yingjiang batholiths from the Tengchong block. The mineralogical and geochemical features of the Tengliang granites and the West Yingjiang batholiths are ascribed to aluminous S‐type granites and weak peraluminous I‐type, respectively. Zircon U‐Pb analyses yielded consistent ages ranging from 67.5 Ma, 68.4 Ma and 66.2 Ma from the Tengliang granitoid belt and 50.4 Ma to 60.8 Ma for three samples from the west Yingjiang batholiths. The Tengliang granites were emplaced during the Late Cretaceous (68–66 Ma) and demonstrate negative εHf(t) values (–24 to –4) and initial 87Sr/86Sr ratios of 0.7101–0.7139 and significant negative εNd(t) values from –8.91 to –13.2, indicating a Proterozoic sedimentary source or enriched components. The hornblende‐bearing I‐type granites from West Yingjiang are characterized by lower initial 87Sr/86Sr ratios of 0.7076–0.7106, compared to Tengliang granite and negative whole‐rock εNd(t) values from –4.0 to –11.9. The early Eocene west Yingjiang gneissic granites show wide ranges of εHf(t) values from +7.4 to –8.5 and T2DM of 1.30–0.65 Ga, indicating partial melting of ancient crust with contributions of depleted mantle materials. In combination with the regional background and previous studies, we propose that such a spatio‐temporal distribution of the Tengchong granitoid belt might be related to the rollback or angle‐switching of the Neo‐Tethyan subducting slab. This study sheds new light on the evolutionary history of the Tengchong block.

Latest Cretaceous and Paleocene biostratigraphy and paleogeography of northern Zealandia, IODP Site U1509, New Caledonia Trough, southwest Pacific

ABSTRACT IODP Site U1509 (Expedition 371), New Caledonia Trough, provides a rare latest Cretaceous–Paleocene record from offshore northern Zealandia. We present new palynomorph and benthic foraminiferal assemblage data that show a transition from a latest Cretaceous vegetated sediment source region to a fully oceanic environment in the Paleocene. Latest Cretaceous (c. 68–66 Ma) non-calcareous claystone was deposited in upper bathyal paleodepths, with abundant plant microfossils that were likely transported in a northwest direction through the Aotea Basin region. A 2–3 Myr unconformity is identified at the Cretaceous/Paleogene boundary. Middle early–late Paleocene (c. 63.5–56 Ma) calcareous claystone shows evidence of deepening, deposited in middle bathyal or deeper paleodepths, and terrestrial input is minor. This latest Cretaceous to Paleocene deepening trend is consistent with inferred evolution of the Aotea and Northland basins further to the east, and other sparse northern Zealandia records, which show a common pattern of post-rift transgression consistent with long-term subsidence. Site U1509 allows for biogeographic extension and modification of the New Zealand Paleocene dinoflagellate zonation, description of a new dinoflagellate and pollen species, better inference of regional paleogeography, and may provide insights into the onset of western Pacific subduction initiation.

Meso-Cenozoic growth of the eastern Qilian Shan, northeastern Tibetan Plateau margin: Insight from borehole apatite fission-track thermochronology in the Xiji Basin

The surface uplift of the Tibetan Plateau (TP) is among the most important geological events in Earth's history, but the growth of the eastern TP margin that yielded the thickened crust and abrupt topography remains controversial. In this paper, six sample apatite fission-track (AFT) analyses of three boreholes in the Xiji Basin are applied to constrain the Mesozoic-Cenozoic uplift and exhumation history of the eastern Qilian Shan, northeastern TP. Most of the AFT ages range from 134 ± 8 Ma to 117 ± 6 Ma, except for the shallowest sample, with a younger age of 65.9 ± 3.2 Ma. Thermal history modeling indicates that the eastern Qilian Shan experienced a three-phase differential cooling history: (1) widespread rapid cooling during the Middle Jurassic-Early Cretaceous (ca. 174-120 Ma, Stage 1), (2) regional cooling during the Late Cretaceous-Paleocene (ca. 80-60 Ma, Stage 2) and (3) widespread cooling during the Eocene-early Miocene (ca. 40-20 Ma, Stage 3). We conclude that the Middle Jurassic-Early Cretaceous was the main stage of the growth and thickening of the northeastern TP, which was related to the upper-crustal horizontal shortening of the eastern Qilian Shan. Thermal history modeling of the youngest sample and seismic profile analysis imply significant reactivation of the Liupanshan fault zone during ca. 80-60 Ma. This locally intense uplift and deformation on the eastern margin of the Qilian Shan during the Late Cretaceous was likely induced by the closure of the Neo-Tethys and the continued shortening of the Lhasa-Qiangtang block. Late Eocene-Early Miocene (ca. 40-20 Ma) cooling of the eastern margin of the Qilian Shan records the coeval crustal extension and exhumation of the northeastern margin of the TP as the far-field effect of subduction of the western Pacific plate. Our AFT data detect no intense late Cenozoic reactivation information for the Xiji region, which indicates that the ca. 15-7 Ma rapid uplift triggered by fault reactivation was only located in the Haiyuan-Liupanshan fault zone, along the eastern margin of the Qilian Shan, northeastern TP. This multi-phase exhumation history is not beneficial for regional hydrocarbon exploration.

The Maira-Sampeyre and Val Grana Allochthons (south Western Alps): review and new data on the tectonometamorphic evolution of the Briançonnais distal margin

Here we describe the structure, the high-pressure, low-temperature (HP-LT) metamorphism and tectonic evolution of the Briançonnais distal margin units from the south Western Alps. The studied area extends southwest of the Dora-Maira (U)HP basement units and east-southeast of the classical Briançonnais nappes. A new structural map accompanied by geological profiles shows the thrusting of the oceanic nappes (Monviso and Queyras units) onto the distal Briançonnais units (D1 and D2 late Eocene deformation phases) under blueschist-facies conditions. Subsequent deformation during the Early Oligocene (D3 deformation phase) took place under greenschist-facies conditions and was associated with back-folding and -thrusting in the units overlying the Dora-Maira massif and with exhumation related to normal reactivation of former thrusts within the latter massif. Two large cover units, detached from their former distal Briançonnais basement, are redefined as the Maira-Sampeyre and Val Grana Allochthons (shortly: Maira-Grana Allochthons = MGA) including, (i) the Val Maira-Sampeyre unit involving Lower and Middle Triassic formations, seemingly detached from the Dora-Maira units during the subduction process, and (ii) the Val Grana unit with Middle-Upper Triassic and Early-Middle Jurassic formations, which was probably detached from the Maira-Sampeyre unit and correlates with the “Prepiemonte units” known from the Ligurian Alps to the Swiss Prealps. Three major shear zones involving tectonic mélanges of oceanic and continental rocks at the base of the Val Grana, Maira-Sampeyre and Dronero units testify to an early phase of exhumation within the subduction channel in front of the Adria plate. We present a new metamorphic map based on published and new petrological data, including new thermometric data obtained by Raman spectroscopy of carbonaceous material (RSCM). The TRSCM values range from ~ 400 °C to > 500 °C, going from the most external Val Grana unit and overlying Queyras schists to the uppermost Dora-Maira unit. During the Late Triassic, the width of the Briançonnais s.l. domain can be restored at ~ 100 km, whereas it reached ~ 150 km after the Jurassic rifting. A significant, second rifting event affected the Briançonnais domain during the Late Cretaceous-Paleocene, forming the Longet-Alpet chaotic breccias, which deserve further investigations.

Petrographic and geochemical characteristics of selected coal seams from the Late Cretaceous-Paleocene Guaduas Formation, Eastern Cordillera Basin, Colombia

Petrographic, geochemical and carbon isotopic determinations were conducted on five samples from four seams within the Late Cretaceous-Paleocene of the Guaduas Formation in Colombia. The individual coal seams are thin, ranging from 0.59 to 1.2 m, and occur over a 157 m interval. The average weighted ash yield is 13.7% (dry basis), although one sample presented values >35%. Vitrinite reflectance increases from 1.33% in the stratigraphically uppermost seam (La Cuarta) to 1.44% in the lower most coal seam (Cisquera), indicating their rank to be medium volatile bituminous.The studied sequence of the Guaduas Formation represents a peat environment influenced by shifting depositional settings, particularly in relation to the proximity of marine/brackish water environments as indicated by Sr/Ba values, sulfur, pyrite, δ13C and the proportion of telinite. A decrease in inertinite indicates that the peat mires were becoming relatively ‘wetter’ stratigraphically upwards. This trend, unlike that of Sr/Ba and telinite, may be driven by climatic shifts rather than only changes in depositional environment.Both trace and rare earth elements, plus yttrium (REY) are related to the inorganic fraction of the coal. All rare earth elements are depleted relative to average worldwide hard coals (for trace elements) and average upper continental crust (for REY) with the notable exception of Li and Sb for the high ash yield sample (the La Cuarta lower coal seam). The abundance of some REY elements (i.e. Eu, Gd, Tb, Dy, Y, Ho, Er, Tm, Yb and Lu) may be more influenced by the presence of illite rather than just the quantity of total ash yield. Based on the relationship between SiO2 and Nb/Y, the provenance of the inorganics changed from a rhyolitic source at the lowest seam (Cisquera) to a dacite source in the middle layer (El Tesoro) to an andesite source in the stratigraphically uppermost seams (La Gemela and La Cuarta).