Tight Folds Research Articles

Compromised 2-start zigzag chromatin folding in immature mouse retina cells driven by irregularly spaced nucleosomes with short DNA linkers.

The formation of condensed heterochromatin is critical for establishing cell-specific transcriptional programs. To reveal structural transitions underlying heterochromatin formation in maturing mouse rod photoreceptors, we apply cryo-EM tomography, AI-assisted deep denoising, and molecular modeling. We find that chromatin isolated from immature retina cells contains many closely apposed nucleosomes with extremely short or absent nucleosome linkers, which are inconsistent with the typical two-start zigzag chromatin folding. In mature retina cells, the fraction of short-linker nucleosomes is much lower, supporting stronger chromatin compaction. By Cryo-EM-assisted nucleosome interaction capture we observe that chromatin in immature retina is enriched with i±1 interactions while chromatin in mature retina contains predominantly i±2 interactions typical of the two-start zigzag. By mesoscale modeling and computational simulation, we clarify that the unusually short linkers typical of immature retina are sufficient to inhibit the two-start zigzag and chromatin compaction by the interference of very short linkers with linker DNA stems. We propose that this short linker composition renders nucleosome arrays more open in immature retina and that, as the linker DNA length increases in mature retina, chromatin fibers become globally condensed via tight zigzag folding. This mechanism may be broadly utilized to introduce higher chromatin folding entropy for epigenomic plasticity.

On the Billefjorden fault zone in Garmdalen, central Spitsbergen: implications for the mapping of major fault zones during geological fieldwork and for the tectonic history of Svalbard.

The present contribution reexamines the geometry of a segment of a presumably long-lived fault in Svalbard, the Balliolbreen Fault segment of the Billefjorden Fault Zone, along which presumably two basement terranes of Svalbard accreted in the early-mid Paleozoic after thousands of kilometers strike-slip displacement. We performed structural fieldwork to Billefjorden in central Spitsbergen and interpreted satellite images. Field observations demonstrate that the Balliolbreen Fault formed as a top-west thrust fault in the early Cenozoic and that weak sedimentary units such as shales of the Lower Devonian Wood Bay Formation and coals of the uppermost Devonian-Mississippian Billefjorden Group partitioned deformation, resulting in significant contrast in deformation intensity between stratigraphic units. For example, tight early Cenozoic folds are localized in shales of the Wood Bay Formation and contemporaneous top-west brittle-ductile thrusts within coals of the Billefjorden Group, whereas Pennsylvanian deposits of the Hultberget (and/or Ebbadalen?) Formation are simply folded into gentle open folds. Rheological contrasts also resulted in the development of décollements locally, e.g., between tightly folded strata of the Wood Bay Formation and Billefjorden Group and flat-lying, brecciated limestone-dominated strata of the Wordiekammen Formation. Despite the limited quality and continuity of outcrops in the area, the eastward-thickening character (i.e., away from the fault) of Pennsylvanian deposits of the Hultberget, Ebbadalen, and Minkinfjellet formations suggests that the fault did not act as a normal fault in Pennsylvanian times. The study suggests that strain partitioning of early Cenozoic Eurekan contraction alone may explain the deformation patterns in Paleozoic rock units in central Spitsbergen, i.e., that Late Devonian Svalbardian contraction is not required, and that a major segment of the Billefjorden Fault Zone formed in the early Cenozoic. The present work illustrates the crucial need for interdisciplinary approaches and composite educational backgrounds in science.

Early Precambrian eclogites in the Belomorian Province, eastern Fennoscandian Shield

This study focuses on a boudin of Archean amphibolite that occurs in the Gridino eclogite-bearing mélange (Belomorian Province, eastern Fennoscandian Shield) and contains two varieties of eclogite. Eclogite-1 is banded, retrogressed (omphacite is totally replaced by clinopyroxene-plagioclase symplectite), and deformed by recumbent tight folds identical to those in the TTG-amphibolite host. Zircon groups are dated at 2721 ± 26 Ma (Zrn-I, fir-tree zoning, no or small negative Eu anomalies, flat HREE patterns, 700–730 °C, 14–15 kbar), ca. 2.70 Ga (Zrn-II, rims around Zrn-I, grains, 750–900 °C, 11–14 kbar, high-P granulite facies), and ca. 2.70 Ga (Zrn-III, rims around Zrn-II). Newly formed Paleoproterozoic zircon crystals are lacking. Retrogressed eclogite-1 in which amphibolization and epidotization totally obliterated garnet and plagioclase-clinopyroxene symplectites is intruded by 2646 ± 46 Ma old granodiorite. Eclogite-2 is massive, contains preserved omphacite-garnet-quartz-rutile assemblages, and comprises two patches whose boundaries truncate folds in eclogite-1. A Paleoproterozoic age of eclogite-2 is evidenced by previously published 1.90 Ga ages of zircon rims around Archean zircon and newly formed crystals with omphacite inclusions. The largest patch contains tabular enclaves of three varieties of amphibolites. One variety is identical to some bands of totally retrogressed eclogite-1 changed into monomineral amphibolites in both the Neoarchean and Paleoproterozoic. The orientation and attitude of these tabular enclaves are coherent with those of the banding on limbs of recumbent tight folds in eclogite-1 within the boudin and later drag folds at its margins and form one and the same structural carcass or skeleton. These data along with recent findings of inherited 2.68 Ga old zircon with inclusions of omphacite in eclogite-2 indicate that this eclogite developed after Neoarchean eclogite-1 due to fluid infiltration along reactivated Neoarchean shear zones enveloping the boudin. These results favor the idea that the transition to the modern-style plate tectonics started not later than in the Neoarchean.

Revised geologic map and structural interpretation of the Mineral King pendant, southern Sierra Nevada, California (USA): Evidence for kilometer-scale folding and structural imbrication of a Permian to mid-Cretaceous volcanosedimentary assemblage

Abstract The Mineral King pendant is an ~15-km-long, northwest-striking assemblage of Permian to mid-Cretaceous metavolcanic and metasedimentary rocks that form a steeply dipping wall-rock screen between large mid-Cretaceous plutons of the Sierra Nevada batholith (California, USA). Pendant rocks are generally well layered and characterized by northwest-striking, steeply dipping, layer-parallel cleavage and flattening foliation and steeply northwest-plunging stretching lineation. Northwest-elongate lithologic units with well-developed parallel layering and an absence of prominent faults or shear zones suggests a degree of stratigraphic continuity. However, U-Pb zircon dating of felsic metavolcanic and volcanosedimentary rocks across the pendant indicates a complex pattern of structurally interleaved units with ages ranging from 277 Ma to 101 Ma. We utilize a compilation of 39 existing and new U-Pb zircon ages and four reported fossil localities to construct a revised geologic map of the Mineral King pendant that emphasizes age relationships rather than lithologic or stratigraphic correlations as in previous studies. We find that apparently coherent lithologic units are lensoidal and discontinuous and are cryptically interleaved at meter to kilometer scales. Along-strike facies changes and depositional unconformities combine with kilometer-scale tight folding and structural imbrication to create a complex map pattern with numerous discordant units. Discrete faults or major shear zones are not readily apparent in the pendant, although such structures are necessary to produce the structural complications revealed by our new mapping and U-Pb dating. We interpret the Mineral King pendant to be structurally imbricated by a combination of kilometer-scale tight to isoclinal folding and cryptic faulting, accentuated by, and eventually obscured by, pervasive flattening and vertical stretching that preceded and accompanied emplacement of the bounding mid-Cretaceous plutons. Deformation in the Mineral King pendant represents a significant episode of pure-shear-dominated transpression between ca. 115 Ma and 98 Ma that adds to growing evidence for a major mid-Cretaceous transpressional orogenic event affecting the western U.S. Cordillera.

State Transitions and Crystalline Structures of Single Polyethylene Rings: MD Simulations.

This study investigates the structural changes of cyclic polyethylene (PE) single chains during cooling through molecular dynamics simulations. The influence of topological constraint on a ring is examined by comparing it with the results of its linear counterpart. A pseudo phase diagram of state transition for PE rings based on length and temperature is constructed, revealing a consistent chain-folding transition during cooling. The shape anisotropy of short crystallized cyclic chains exhibits oscillations with chain length, leading to a more pronounced odd-even effect in single cyclic chains compared with the linear ones. A honeycomb model is proposed to elucidate the odd-even effect of chain folding in crystalline structures of single linear and cyclic chains, and we discuss its potential to predict surface tension. Analyses of the tight folding model and the re-entry modes demonstrate that a cyclic chain possesses a shorter average crystalline stem length and a more compact folded structure than its linear counterpart. The findings highlight the impact of topological change on crystallization and the odd-even effect of chain length, providing valuable insights for understanding polymer crystallization with different topologies.

Characterization of Polyphenol Composition and Starch and Protein Structure in Brown Rice Flour, Black Rice Flour and Their Mixtures.

The study investigates the structural and chemical properties of brown rice flour (WRF), black rice flour (BRF) and their mixtures in ratios of 25%, 50% and 75% to provide reference information for the gluten-free bakery industry. BRF contains higher concentrations of proteins, lipids, total minerals, crude fiber, total polyphenols, proanthocyanidins and flavonoids than WRF. A higher amylose content in BRF than in WRF resulted in flour mixtures with slower starch digestion and a lower glycemic response depending on the BRF ratio added. Differences in the chemical composition of WRF and BRF led to improved composition of the flour mixtures depending on the BRF ratio. The presence of anthocyanidins and phenolic acids in higher concentrations in the BRF resulted in a red-blue color shift within the flour mixtures. The deconvoluted FTIR spectra showed a higher proportion of α-helixes in the amide I band of BRF proteins, indicating their tighter folding. An analysis of the FTIR spectra revealed a more compact starch structure in BRF than in WRF. By processing reflection spectra, nine optically active compound groups were distinguished in rice flour, the proportion in BRF being 83.02% higher than in WRF. Due to co-pigmentation, the bathochromic shift to higher wavelengths was expressed by the proanthocyanins and phenolic acids associated with the wavelengths 380 nm to 590 nm and at 695 nm. Anthocyanins, protein-tannin complexes, methylated anthocyanins and acylated anthocyanins, associated with wavelengths 619, 644 and 668 nm, exhibited a hypsochromic effect by shifting the wavelengths to lower values. This research represents a first step in the development of rice-based products with increased nutritional value and a lower glycemic index.

Differential deformation mechanism of E–W‐trending Weiningbeishan fold‐thrust belt from central Ningxia, NW China

The Weiningbeishan fold‐thrust belt (WFTB), located in the transitional zone of the Tibetan Plateau, Alxa Block and Ordos Basin, is an ancient intracontinental orogenic belt. In this article, structural analysis is conducted to more finely reveal differential deformation between the Devonian and Carboniferous strata in the WFTB. We found that the E–W‐trending open folds are mainly developed in the Upper Devonian Zhongning Formation (D3z), while the E–W‐trending close and tight folds are mainly developed in the Carboniferous strata. The N–S minimum shortening strain of the bottom boundary of Member 2 of the Upper Devonian Zhongning Formation (D3z2) is 21.1%, whereas the N–S minimum shortening strain of the bottom boundary of Member 2 of the Upper Carboniferous Danliangshan Formation (C2d2) is 64.1%. We propose that the E–W‐trending open folds in the Upper Devonian Zhongning Formation (D3z) and E–W‐trending close and tight folds in the Carboniferous strata were formed under the N–S compression during the Middle–Late Triassic. The Zhangyigou and Laoyagou faults are the main tear faults to accommodate differential displacement on the surface between the Upper Devonian Zhongning Formation (D3z) in the east and Carboniferous strata in the middle, which change into a décollement fault in the deep part of the Dafosigou fold area in the middle to accommodate differential deformation between the deep Upper Devonian Zhongning Formation (D3z) and Carboniferous strata. This study enables us to better understand the Mesozoic intracontinental deformation in response to far‐field plate‐boundary convergence in NW China.

Structural Analysis and Petrography of High-Grade Gneisses and Associated Mafic / Ultramafic Dikes Around Salem, Southern India

Southern Granulite Terrane (SGT) of India preserves extensive high-grade granulite facies rocks of Archaean and Proterozoic age. The SGT is divided into number of blocks by several suture/shear zone. Structural investigations on the basement gneisses and younger mafic/ultramafic dikes have been carried out within the Salem block which is part of Northern Granulite Block (NGB), north of the Cauvery Suture Zone (CSZ). The present work emphasizes various scale fold styles and other structural patterns of the area, which includes regionally metamorphosed high-grade rocks as basement for the multiple ultramafic intrusions to the north of Cauvery Suture Zone (CSZ) which highlights the finite strain geometry, complex deformation pattern and high-grade metamorphism. Structural map of the study area is prepared showing two generations of folding, namely F1 whose axial trend is NE-SW, subparallel with general trend of gneissic foliation and are tight isoclinal folds while F2 which are open folds with axial trend NW-SE.E-W structural cross section across the foliation planes, characterizes antiformal and synformal fold patterns of the basement due to varying dip directions which also reflects type-3 interference pattern of folding. Mesoscopic scale shear zones of dextral kinematics in response to E-W collision during Paleo-Meso Archean time, delta type porphyroclasts, S-C fabrics with the dextral movement of CSZ system, Riedel shear, thrust imbricates implying duplex structures, rotation of mafic boudins along shear zones are the most prominent ductile structural features of this area. Brittle structures like different sets of cross cutting joints and faults indicate younger deformation as well. Petrography of major lithologies has classified them into amphibolite gneiss, migmatite gneiss, charnockites, granulites and mylonites as basement rocks to the younger pyroxenite intrusions. Typical textures like, perthite, granulose, reaction rims, sieve textures and microstructures like S-C fabrics, kink bands, rotated porphyroclasts, etc are observed within the basement rocks. Coarse grained textures with fractured porphyroclasts of garnets indicating the water interactions and retrogradations within the granulite facies rocks. Reaction rims observed in charnockites and granulites are indicative of retrogression during shearing. The coarse grained cummulate nature of pyroxenites neither represent deformation nor metamorphism. Keywords: Southern Granulite Terrane, Salem, Structural Analysis, Mafic/Ultramafics, Dikes, Petrography

Exhumation mechanisms of the Himalayan metamorphic core in the Bhagirathi Valley, NW India: Insights from an integrated structural and metamorphic analysis

The Himalayan metamorphic core in the Bhagirathi valley (NW India) consists of low-grade rocks belonging to the Lesser Himalayan Sequence to the south, and of high-grade rocks of the Greater Himalayan Sequence (GHS), to the north. The contact between these two units is a 2–3 km thick high-strain zone known as the Main Central Thrust zone (MCTz). Structural studies in the GHS identify the superposition of foliation (S2) related to tight isoclinal fold (F2) on a pre-existing foliation (S1). S2 was further overprinted by D3 crenulations, and a set of conjugate fractures (D4) overprinted these ductile fabrics. Deformation in the GHS was characterized by top-to-the-SW shearing, which, in its upper structural level, was overprinted by top-to-the-NE extensional shear. Metamorphic analysis shows a moderate T/high P inverted metamorphic sequence with pre-to syn-kinematic, inclusion-rich garnet in the structurally lower part of the GHS and high T-moderate P prograde metamorphism with post-tectonic inclusion-free garnet and evidence of partial melting, in its upper structural level. We envisage that the uppermost part of the GHS and the lower part of the GHS, including the MCTz, are two distinct tectonic slices, separated by a tectono-metamorphic discontinuity.

Deformation Sequence and Paleofluids in Carbonate Buckle Folds Under Transpression (Pag Anticline, External Dinarides, Croatia)

AbstractContractional deformation structures at the front of transpressional orogens display complex three‐dimensional geometries deviating from the interpretative templates commonly applied in thrust belts. Accordingly, detailed constraints on deformation patterns and associated paleofluid circulation are desirable, especially for fracture geometry and permeability predictive purposes. The Pag anticline, which is located in the Dinaric fold and thrust belt, provides an appropriate field site for studying fold‐ and fault‐related deformation structures in a transpressive setting. We performed a multiscale structural analysis together with petrographic and stable isotope characterization of the deformation‐related calcite cements. Structural mapping suggests that the Pag anticline is a detachment fold developed mainly by buckling, since large‐scale thrust faults are absent. Fold tightening in a transpressive setting produced a complex deformational structure including two sets of N‐S right‐lateral and E‐W left‐lateral late‐stage strike‐slip fault sets trending oblique to the NW‐SE fold axis. The pre‐folding deformation pattern includes incipient normal faults likely related to the forebulge stage, veins and stylolites coherent with NE‐SW layer parallel shortening contraction in a strike‐slip regime, and metric to decametric scale conjugate thrusts coherent with layer parallel shortening in a compressive regime. Buckle folding preceded propagation of a series of accommodation structures during fold tightening. Petrographic and isotopic data indicate meteoric alteration of the Cretaceous platform carbonates in the prefolding stage, likely due to forebulge subaerial exposure. Layer parallel shortening and early syn‐folding veins involved formational fluids resulting from mixed marine and meteoric fluids during folding at shallow burial conditions. Eventually, meteoric fluid infiltrated again along strike‐slip faults, acting as cross‐formational conduits in the postfolding stage.

Interactions of gulf cordgrass, Spartina spartinae (Trin.) Merr. ex Hitchc., habitat with ixodids on the South Texas coastal plain

Many ixodid species on the South Texas coastal plain can transmit pathogens to their hosts. Substantial areas are dominated by gulf cordgrass, Spartina spartinae (Trin.) Merr. ex Hitch. The S. spartinae habitat was examined in terms of abiotic and biotic factors that likely impinge upon ixodids using the plant for questing. Natural enemies, temperature, humidity, and plant structure were investigated as possible mortality factors and improving ixodid survival. Spartina spartinae (soil and foliage) harbored few natural enemies of ixodids, and soil salinity was nonlethal. Conditions were cooler and more humid inside S. spartinae clumps than in the canopies; hence, questing ixodids can rehydrate inside the clump when threatened by desiccation. Leaves were mostly “V” shaped in cooler months and, during warm months, the tightly folded leaf slot predominated, into which larvae crawled. Immature ixodids were more abundant in the concave side of the “V”-shaped leaves than on the exposed convex side. Larvae sought refuge from potential lethal ambient air conditions by entering tight warm season leaf folds. The leaf “V” and fold offer opportunities for rehydration on the leaf without moving to the clump’s base. In addition to five other species collected on the grass, a relatively heavy larval southern cattle fever tick, Rhipicephalus (Boophilus) microplus (Canestrini), population was detected, suggesting that abundances in the South Texas cattle fever tick eradication quarantine zone are increasing and might spread further into Texas.

Precise U-Pb dating of incremental calcite slickenfiber growth: Evidence for far-field Eocene fold reactivation in Ireland

Abstract The Variscan orogen in southern Ireland and Britain is characterized by an intensely deformed, E-W–trending fold-and-thrust belt. Farther north in Ireland, the Carboniferous North Dublin Basin exhibits tight chevron folds and kinematically linked en echelon vein sets, along with bedding-parallel veins with slickenfibers. This deformation is assumed to be Variscan in age, despite lying 150 km north of the supposed Variscan “front.” The laser ablation–inductively coupled plasma–mass spectrometry (LA-ICP-MS) U-Pb dating of these calcite veins undertaken for this study showed that relict Variscan U-Pb ages are very poorly preserved. Instead, late Eocene ages were obtained from many calcite veins, including fold hinge breccias and bedding-parallel slickenfiber veins associated with N-S shortening (flexural slip). Also, U-Pb ages from one bedding-parallel vein showed protracted flexural slip over ~5 m.y. during late Eocene times. Detection of the growth domains within this vein was facilitated by the imaging approach to LA-ICP-MS U-Pb dating adopted in this study, which can identify age-homogeneous domains by integrating spatial U-Pb isotopic information with maps of petrogenetically diagnostic major and trace elements. The late Eocene fold reactivation phase was hitherto undetected on the Irish mainland, but regional Cenozoic N-directed shortening has been documented in Mesozoic–Cenozoic sequences of the southern Irish Sea, Celtic Sea, southern England, and the Paris Basin. We attribute late Eocene fold reactivation to far-field, N-directed shortening associated with the Alpine/Pyrenean orogenies. It is likely that many Variscan or Caledonian folds, particularly in southern onshore Ireland, were reactivated during Eocene–Oligocene shortening, which has not been recognized to date because of the lack of post-Variscan markers (e.g., dikes, Mesozoic–Cenozoic cover sequences).

The Dugald River-type, shear zone hosted, Zn-Pb-Ag mineralisation, Mount Isa Inlier, Australia

The Dugald River Zn-Pb-Ag mine is situated in the Mount Isa Inlier, a globally significant base metal province. Zn-Pb deposits in the Mount Isa Inlier are stratabound with four main genetic models, including SEDEX-style, remobilised SEDEX, epigenetic and Broken Hill-type mineralisation applied to interpret their formation. We propose that the Zn-Pb-Ag mineralisation at Dugald River represents a unique, shear zone hosted deposit type that formed through a series of successive deformation events during the Paleoproterozoic Isan Orogeny that concentrated the mineralisation within the Dugald River Shear Zone during two main mineralising phases. The first phase of mineralisation occurred during regional D2 shortening, which is associated with the formation of large-scale F2 folds and a regionally penetrative S2 fabric. During this phase, progressive tightening of upright F2 folds resulted in several sets of secondary space accommodating quartz-carbonate veins that were progressively rotated into parallelism with the pervasive, steep, W-dipping S2 cleavage. The quartz-carbonate veins were coevally replaced by sulphides, which migrated to extensional sites (boudin necks and fold hinges) in tight folds. Thereby creating a sulphide-rich horizon within a developing high strain zone, which during D4 developed into the Dugald River Shear Zone. The second phase of mineralisation occurred during the regional D4 transpressional deformation event and resulted in significant metal enrichment and the current geometry of the ore bodies. The significant enrichment of the mineralisation during D4 resulted from further fold tightening within the high strain zone, which resulted in the attenuation and dismembering of folds and produced a transposed fabric (S4). The sulphide veins were transposed into parallelism with S4 forming sulphide-rich planar ore textures. Strain partitioning at the contact between the ductile deforming sulphide horizon and the brittle deforming slates resulted in the development of an anastomosing shear zone, known as the Dugald River Shear Zone. A right-handed releasing bend in the shear zone produced a dilational jog and a thick, high-grade ore body. The mobilisation of sulphides within the dilational jog involved fragmentation of sulphides and wall rock, brecciation, rotation and rolling of fragments, and the formation of durchbewegung texture.

Paleozoic Gondwanan structure along the Maule river valley between Toconey and Constitución (35.4°S, Chilean Pacific Coast)

During the late Carboniferous–middle Permian, the basement of the Chilean Coastal Cordillera was deformed by the Gondwanan Orogeny, developed by the subduction of the Paleo-Pacific plate under Gondwana from the early Carboniferous. In the Maule sector (35.4°S), the following metamorphic rock units are distinguished: (i) Western Series, formed by metapelites, metabasites, metacherts, metaconglomerates, and marbles, mixed in a subduction channel, with probably ages between the Cambrian and the Carboniferous; (ii) Eastern Series, consisting of metasediments of a fore-arc basin, Carboniferous in age. In the Eastern Series two units are recognized in terms of lithology and deformation style: the Eastern Pelitic Series and the Eastern Sandy Series. Three Gondwanan deformation episodes have been distinguished, affecting both series unequaly. In the Western Series, D1 structures consist of a foliation (S1) developed under high-pressure and low-temperature conditions, while in the Eastern Series it comprise tight east-verging folds, with the associated S1 developed under low PT metamorphic conditions (greenschist facies). D2 structures are only present in the Western Series and Eastern Pelitic Series and represent the exhumation of the accretionary prism and its emplacement to the east over the fore-arc basin, with the development of east-verging recumbent folds and a thick shear-zone. Difficulties in the propagation of the deformation by the presence of the Coastal Batholith to the east led to the development of the D3 deformation event, only well developed in the Eastern Sandy Series, and represented by the Los Tablones Back-thrust and associated folds, as well as N–S open right folds formed under low PT metamorphic conditions.

Understanding the Relationships between Landscape Eco-Security and Multifunctionality in Cropland: Implications for Supporting Cropland Management Decisions.

Cropland is an essential strategic resource, for which landscape ecological security and multifunctionality evolution are related to regional stability and sustainable social development. However, few studies have explored the spatial heterogeneity of the coupling between the two from a multiregional and systematic perspective, and the interaction mechanisms have still not been thoroughly analyzed. In this study, a typical karst trough and valley area in the mountainous regions of southwest China was selected as the research object, and by establishing a multi-indicator evaluation system using a landscape pattern index, a multifunctional identification model, a coupled coordination model, and a geodetector model, the spatial variability in the evolutionary characteristics and the coupling and coordination of cropland landscape ecological security (CLES) and cropland multifunctionality (CM) in the mountainous regions of the southwest and their driving mechanisms were explored. The main results were as follows: (1) CLES in the mountainous areas of southwest China has undergone an evolutionary process of first declining and then slowly rising, with the characteristics of "fast declining in the high-value areas and slow rising in the low-value areas", while CM showed a spatial distribution of "high in the northwest and low in the northeast", with positive contributions originating from ecological functions. (2) Over the 20 years, the cropland coupling coordination degree (CCCD) values showed significant spatial heterogeneity, which was regionally expressed as ejective folds (EF) > TF (tight folds) > TLF (trough-like folds) > AF (anticlinorium folds). Low CCCD values were primarily found in the east, whereas high levels were primarily found in the west, with a rapidly diminishing trend. (3) There were differences in the driving mechanisms of CCDD in different landscapes, but GDP was still the determining factor and had a limiting effect. Hence, we call for the adoption of a "function over pattern" approach in areas with more development constraints and a "pattern over function" approach in areas with fewer development constraints. Ultimately, this study will contribute to the formation of a coupled cropland mechanism system described as the "multi-mechanisms drive, multi-elements integrated" system. In conclusion, this study can provide a better understanding of the relationship between cropland patterns and multifunctionality, which can help provide a basis for cropland conservation and landscape planning in similar mountainous areas and promote the achievement of sustainable agricultural development goals in the mountainous areas of southwest China.

Atomic Hydrogen Annealing of Graphene on InAs Surfaces and Nanowires: Interface and Morphology Control for Optoelectronics and Quantum Technologies

Folding two-dimensional graphene around one-dimensional III–V nanowires yields a new class of hybrid nanomaterials combining their excellent complementary properties. However, important for high-quality electrical and optical performance, needed in many applications, are well-controlled oxide-free interfaces and a tight folding morphology. To improve the interface chemistry between the graphene and InAs, we annealed the samples in atomic hydrogen. Using surface-sensitive imaging, we found that the III–V native oxides in the interface can be reduced at temperatures that maintain the graphene and the III–V nanostructures. Transferring both single- and multilayer graphene flakes onto InAs NWs, we found that single layers fold tightly around the NWs, while the multilayers fold weakly with a decline of only a few degrees. Annealing in atomic hydrogen further tightens the folding. Together, this indicates that high-quality morphological and chemical control of this hybrid material system is possible, opening for future devices for quantum technologies and optoelectronics.

Seismic Survey in Lesser Himalayan Thrust Belt, Western Nepal

Two hundred km of 2D seismic survey was carried out at the Lesser Himalayan Thrust Belts in Dailekh district, western Nepal. The main motivation is to elucidate the geologic relationship between the known oil and gas seeps, subsurface structure, and stratigraphy in the area. This is a challenging task which is from its extreme structural and geological complexity such as thrust faulting, tight folding, steep dip layers, and strong lateral variations in seismic velocity. Seismic data were acquired with SERCEL 428XL system and processed by GEOEAST computer software. In order to increase signal-to-noise ratio (SNR), suppress interference, and search for optimum acquisition parameters, a series of comparative tests on the different charge depth and size, group interval, CDP fold, geophone array, and single high-sensitivity geophone were conducted. We also tested 2S3L (two lines shooting and three lines receiving) wide line profiling. The results indicate that single hole with charge depth of 12 m, 4-16 kg charge size (less charge size for the densely populated areas), single high-sensitivity geophone, and 1S2L wide line profiling with 132 folds are the optimum acquisition parameters. On the basis of comparative process experiment, data processing workflow consisting of data preparation, prestack denoising, amplitude compensation, deconvolution, tomography static correction, velocity analysis, residual static correction, CRS stack, poststack migration, prestack time migration (PSTM), and prestack depth migration (PSDM) was selected. Maybe affected by problem of conflicting dip in complex media, CRS stack section does not show satisfactory geological characteristics. PSTM profile has moderate signal-to-noise (S/N) ratio; the shallow, medium, and deep continuous reflections can be observed in section. More details of the geological structures can be observed in PSDM section, especially in medium and shallow layers (less than 3000 ms or 4000 m), but PSDM method is more expensive and highly time consuming than that of CRS stack and PSTM. So, the PSTM section can be reasonably used for geological interpretation. By reference to field mapping, thrust characteristics, and MT data, the final interpretation to the PSTM section identified the interfaces of 6 geological units (Paleoproterozoic Nabhisthan Fm., Paleoproterozoic Dubidanda Fm., Neogene to Late Cretaceous Surkhet group, Late Carboneferous to Early Cretaeous Gondwana group, Mesoproterozoic Upper Lakharpata group, and Lower Lakharpata group) and delineated Main Boundary Thrust (MBT), Ramgarh Thrust (RMT), Padukasthan Thrust (PT), and Dailekh Thrust (DT). The bottom of Surkhet group which is our top target zone is about 4250 meters deep.

Forearc tectonics and volcanism during the Devonian–Carboniferous evolution of the North Patagonian segment, southern Chile (41,3°S)

Late Paleozoic to early Mesozoic subduction complexes formed during the evolution of southwestern Gondwana and extensively crop out along the Chilean continental margin. Recent findings in northern Patagonia (40°–43°S) revealed that accretionary processes were active since the Devonian when enhanced lithosphere stretching in the forearc led to the formation of Chaitenia island arc. The extension in the crust consecutively developed a backarc basin, which culminated during a compressive episode that re-amalgamated the Chaitenia island arc with the margin. This episode produced intermediate grade metamorphism in the sedimentary rocks that were formed throughout the extension. To constrain the tectonic evolution of these processes, we combined petrology, structural analysis, whole-rock geochemical, and whole-rock isotopic tracing (Sr-Nd-Pb) data along with thermodynamic modelling. Two petro-tectonic domains are here defined. The Western Coastal Range Domain is composed of Carboniferous to Permian metapsammopelitic rocks, which are mainly schists with a metasedimentary Carboniferous protolith exhibiting a penetrative northeast to southwest dipping main foliation associated with basal accretion. The Eastern Coastal Range Domain is comprised by garnet micaschists, metabasalts, metarhyolites, and metasandstones. This unit is folded by three ductile structures: The first is related to rootless isoclinal folds, the second is associated with kilometric scale west-verging tight folds, and the third is associated with west-verging cylindrical folds. The volcanic rocks of this domain are comprised by middle Devonian alkaline metarhyolites and metabasalts with enriched-MORB and normal-MORB affinities. Trace element composition suggests that the metabasalts formed through shallow melting in an extensional setting over a supra-subduction zone. Nd and Pb isotope data point to a mantle source change for the basaltic melts from an EM1-like to a DM-like and are interpreted to reflect the embryonic to mature evolution of the early Devonian to Carboniferous backarc system. The calculated P–T evolution of the garnet micaschists follows: 1) a clockwise IP–IT prograde Barrovian path, 2) an isobaric thermal increase at ∼7 kbar and 540°C, and 3) an adiabatic decompression. Finally, after the metamorphism, these rocks were uplifted by thrusting processes that probably occurred during the late Permian.

Mud Diapir or Fault‐Related Fold? On the Development of an Active Mud‐Cored Anticline Offshore Southwestern Taiwan

AbstractThere has been a controversial debate about the roles of diapiric folding versus fault‐related folding in mud‐cored anticlines. This study tackles this debate by looking into the structural developments in southwestern Taiwan. Among all the structures, the Liuchiu anticline is the only active structure exposed above sea level and therefore offers a unique opportunity to integrate land and marine data sets. On Liuchiu Island, we obtained the fold core geometry at the surface and identified three terrace groups with age constraints. In the offshore area, we obtained the fold limb geometry from seismic profiles. Given the tight fold shape and the asymmetric terrace tilting, we found that a hybrid fault tip fold‐fault propagation fold model can best explain the geologic and geomorphic features. In this regard, mud diapirism should be a secondary process, possibly along discrete patches of mobile shales to enhance fold amplification. Our model yields decreasing shortening rates from 0.7 mm/yr during the Plio‐Pleistocene to 0.375 mm/yr since 120 ka. The uplift rate however increases since the mid‐Holocene, which we tentatively attribute to larger mobile shale deformation triggered by earthquakes along the fault after the near‐fault fluids are drained. At the regional scale, we further suggest that the remaining plate convergence is absorbed by a few major structures west of Liuchiu Island.

Late Cretaceous–early Palaeogene inversion-related tectonic structures at the northeastern margin of the Bohemian Massif (southwestern Poland and northern Czechia)

Abstract. A brief, regional-scale review of the Late Cretaceous–early Palaeogene inversion-related tectonic structures affecting the Sudety Mountains and their foreland at the NE margin of the Bohemian Massif is presented and complemented with results of new seismic studies. The Sudetes expose Variscan-deformed basement, partly overlain by post-orogenic Permo-Mesozoic cover, containing a wide spectrum of tectonic structures, both brittle and ductile, in the past in this area referred to as young Saxonian or Laramide. We have used newly reprocessed legacy seismics to study these structures in the two main post-Variscan structural units of the area: the North Sudetic and Intra-Sudetic synclinoria. The results were discussed together with regionally distributed examples of tectonic structures from quarries and underground mines as well as those known from the literature. The Late Cretaceous–early Palaeogene tectonic structures in consecutively reviewed Sudetic tectonic units, from the north to the south, typically include gentle to moderately tight buckle folds, locally of detachment type or fault-related and high-angle reverse and normal faults, as well as low-angle thrusts – often rooted in the crystalline basement. The structures termed grabens in the local literature are at the same time frequently interpreted as bounded by reverse faults (hence we use here the term “reverse grabens”) and typically reveal a strongly synclinal pattern of their sedimentary fill. The top of the crystalline basement, as imaged by seismic data in the North Sudetic Synclinorium below the faulted and folded cover, is synformally down-warped with a wavelength of up to 30 km, whereas on the elevated areas, where the basement top is exposed at the surface, it is tectonically up-warped (i.e. antiformally buckled). The compressional structures typically show an orientation that fits the regionally known Late Cretaceous–early Palaeogene tectonic shortening direction of NE–SW to NNE–SSW. The same applies to the regional jointing pattern, typically comprising an orthogonal system of steep joints of ca. NW–SE and NE–SW strikes. All the reviewed structures are regarded as being due to the Late Cretaceous–early Palaeogene tectonic shortening episode, although some of the discussed faults with a strike-slip component of motion may have been modified, or even produced, by late Cenozoic tectonism.