Early Structures Research Articles

GEOLOGY OF ALAKNANDA BHGIRATHI AND YAMUNA VALLEY, GARHWAL HIMALAYA, PARTS OF CHAMOLI TEHRI UTTAKASHI & PAURI DISTRICTS, UTTRAKHAND STATE, INDIA

The Alaknanda is the trunk stream of Ganga system it drains the eastern part of the area of study .The rocks of Alaknanda valley and adjoining area consist of three units viz Central Cryastalline , Garhwal Group and Dudatoli Groups which from north to south are separated by thrust or fault. The Central Crystalline Group in this area consist of /comprises of northerly dipping sequence of Kyanite schist,Garnet mica schist quartzites and para amphibolites of Tugnath formation and it is intruded by granite at Ragsi,the main Central Thrust seprates it from Garhwal Group.The Dudatoli Groupis represented Pauri Phyllite and Kirsu Quartzite which forms the northern limb of Dudatoil syncline .The north Almora Thrust makes it boundary with Garhwal group. The later is divisiable in to Rudraprayga ,Lamri , Chamoli and Gawangarh and Patrali Formation which occurs in normal stratigraphic order. It is intruded by biotite granite by biotite graninte at Nainidevi and Mohankal , with tourmaline granite around Chirpatikhal and also by basic intrusive . The Rudraprayg , Lameri and Chamoli formations are equivalent to Uttarkashi Shyalnan and Nagnithhank Formation respectively in Bhagirathi valley. The Garhwal Group of has been subjected to three phases of tectonic deformation. The south east to southerly plunging folds such as Marithanasa and Pingapani synclines .Karanprayg anticline were developed during the second phase of movements. The Alaknada fault which cuts off set of the formation and earlier structures between Sunala is the strike slip fault in western part, appears to be the youngest elements. Geologically , the Bhagirathi valley and adjoining areas comprises of four distinct units namely from north to south the Central Crystalline Group , the Deoban Group the Simla Group,and Krol belt rock separating from one another by thrust or faults. The main Central Thrust passing through Sainj in northern part brings the northerly dipping crystalline rocks in sharp contact with under lying Deoban Group (Garhwal Group) sedimentries which comprises a lower Deoban Formation of Phyllite, slate meta basics, minor quartzite and lime stone, the middle Deoban formation of lime stone and upper Deoban formation of Quartzite and basics. The southern contact of Deoban Group is faulted one with comprising mainly siltstone, greywacks and slates dipping south .This fault called Sringar Nalupani fault of fundamental nature. In the southern and eastern part of the area this fault marks the contact between Deoban and Chandpur formation. In the western part south heading Ton Thrust separates the underlying Chanpur formation from the underlying Simla slates which shows abundant development of slump balls rod etc. indicating syndepositional disturbances in the basin of sedimentation while in Chanpur formation, is manly argillaceous, becoming arenaceous towards the top The Tons thrust passes through Laluli in Nagun Gad and is probably truncated by Tehri Nalupani fault at Chandpur in Bhagirathi valley. The full sequence of Krol rocks is exposed beautifully in Mussoorie syncline. The tectonic succession in Yamuna valley is Naogaon sheet comprising more metamorphosed rocks overly the Deoban group rocks separated from the latter by what is called the Naugaon thrust sheet which is folded in a North to Northwest plunging synform. The western limb of the folded thrust crosses Yamuna near the confluence with Kamola Gad and runs along the Kamola Gad. The rocks of the Naugaon sheet can be seen overlying the Deoban formation limestone along this section. The thrust hade towards east in this section. It follows a southerly trend till Tiyan when it takes an easterly swing, heading northward. It closes around Gair. The eastern limb of the synformal thrust sheet, heading westward crosses the Yamuna River at Kisna, Basic intrusive are seen along the thrust sheet near Kisna and around. The complexity of structural and tectonic set up in the area and lack of fossils make the task of correlation extremely difficult. However, on the basis of lithological similarities as well as structural disposition an attempt has been made to correlate the various litho units in the present area.

Hellenistic and early Roman levels at Idalion: a change of identity?

Substantial parts of the Idalion city-kingdom site from the first millennium BCE were excavated under the direction of Dr Pamela Gaber from 1987 to 2017. These excavations revealed physical changes in the layout of parts of the ancient city that allow us to identify the cultural change that occurred in the Hellenistic and Roman periods. The American expedition began excavations on the terrace of the eastern acropolis in a sacred grove that later became known as the “Adonis Temenos”, revealing late Hellenistic and early Roman structures just below the topsoil. These structures were oriented more or less N‑S / E‑W. When further excavation reached the underlying Hellenistic, Classical and Archaic levels, it revealed a different orientation. The earlier structures were oriented N‑W / S‑E. Excavations in the Lower City South “City Sanctuary” from 1998 to 2017 revealed a much more marked change in structural orientation. The question of when the transition took place became clear during the 2017 season of excavations in the “City Sanctuary,” Lower City South, revealing continuous occupation from Hellenistic to Roman levels, but a striking shift in orientation towards N‑S / E‑W structures in the 1st century BCE.

Оконное стекло с поселения Горзувиты и Мангупского городища в Крыму: химический состав, происхождение и хронология в историко-культурном контексте

Chemical composition of 39 window panes of the Early and Middle Byzantine periods was studied with SEM-EDS technique. They originate from the Gorzuvity settlement in the Crimea Southern coast with the ruins of two churches, and Mangup, the largest medieval fortress in the SW Crimea. The presence of glass of groups Foy-3.2/2.1 and HIMT suggests that the earliest structures with glazed windows could have emerged on Mangup in the 5th century at the latest — i. e., before the construction of the Byzantine fortress. A homogenous composition of glass from Gorzuvity suggests a single period of glazing windows of structures existing here — the “lower” church with a shrine dated probably to the 11th century (terminus ante quem for the church construction) and some stone structures at the settlement. 37 samples represent natron glass of the Egyptian origin. Most of window panes are related to the 9th—10th/11th cc. Their glass belongs to the series Foy-2.2, the result of the recycling of the earlier glass of the 2nd half of the 5th/6th — mid-7th centuries (series Foy-2.1). It suggests that the remains of monumental structures of the early Byzantine period (window panes and probably tesserae) were used as raw materials during the construction campaign at Gorzuvity and Mangup in the middle Byzantine period. Two fragments from Mangup of mixed-alkali composition originate from the contexts of the 15 th c., where they could get from disturbed earlier deposits.

A modified configuration of high step‐up non‐isolated DC‐DC converter with low voltage stress: Analysis, design, and implementation

SummaryThis study develops a novel DC‐DC converter with an extremely high voltage conversion ratio that utilizes just one switch, a voltage multiplier circuit (VMC), and a coupled‐inductor. Two diodes and two capacitors comprise the VMC, employed to reach high voltage gain. Consequently, the conduction loss is minimized by using a low voltage rated switch with lower RDS(on). Due to the coupled inductor's leakage inductance, the output diodes' reverse recovery trouble is solved. Moreover, the passive clamp technique stores and recycles leakage energy at the output. The proposed DC‐DC converter features are high conversion ratio, low maximum voltage on semiconductors, remarkable efficiency, the existence of only one active low voltage switch, and simple circuit topology with common ground between the input and the output. This paper outlines CCM, BCM, and DCM's operating concept and steady‐state analysis in great detail. Furthermore, the suggested structure's capability is indicated by mathematical analysis and comparative findings with other earlier structures. Eventually, experimental findings with 210 W output power and 25 kHz switching frequency demonstrates that the proposed converter can be used successfully.

A galaxy group candidate at z ≈ 3.7 in the COSMOS field

We report a galaxy group candidate HPC1001 at z ≈ 3.7 in the COSMOS field. This structure was selected as a high galaxy overdensity at z > 3 in the COSMOS2020 catalog. It contains ten candidate members, of which eight are assembled in a 10″ × 10″ area with the highest sky density among known protoclusters and groups at z > 3. Four out of ten sources were also detected at 1.2 mm with Atacama Large Millimeter Array continuum observations. Photometric redshifts, measured by four independent methods, fall within a narrow range of 3.5 < z < 3.9 and with a weighted average of z = 3.65 ± 0.07. The integrated far-IR-to-radio spectral energy distribution yields a total UV and IR star formation rate SFR ≈ 900 M⊙ yr−1. We also estimated a halo mass of ∼1013 M⊙ for the structure, which at this redshift is consistent with potential cold gas inflow. Remarkably, the most massive member has a specific star formation rate and dust to stellar mass ratio of Mdust/M* that are both significantly lower than that of star-forming galaxies at this redshift, suggesting that HPC1001 could be a z ≈ 3.7 galaxy group in maturing phase. If confirmed, this would be the earliest structure in maturing phase to date, and an ideal laboratory to study the formation of the earliest quiescent galaxies as well as cold gas accretion in dense environments.

The impact of structural inversion on the hydrocarbon system, northwest Mosul area, Case study Sasan (Sarjoon) Oil Field.

Sasan field is in Nineveh governorate, 46 Km northwest Mosul city. The present Sasan structure was discovered from surface mapping and 2D seismic defined the Upper Cretaceous reservoir but due to poor data quality, any estimate of oil in places are highly uncertain. Sasan structure from seismic shows Block-Faulted anticline covering a small area (Sasan East). Several normal faults appear to separate SA-2 from SA-1 affected the hydrocarbon system in these two wells. The more possible realistic interpretation is an inverted graben, thick Shiranish Formation in Sasan wells support this interpretation.The model suggest that normal faults created the accommodation during Late Cretaceous (Sinjar trough) and subsequent Tertiary compression uplifted the depocenter creating the topographic depression which interpretated as a fault propagation fold. The last compressional structures can only have been filled with remigrated petroleum from breached, older traps, earlier structures could have been filled by migration from an actively generating source rocks. The exploration potential in the old Sasan structure configuration is good but it is still an exploration play not a commercial oil discovery, although oil is present in Shiranish, Hartha/Mushora and Wajnah formations but not clear if it is recoverable.Gas present in deeper formations, both the oil and gas traps are breaching traps. The best exploration targets should, therefore, be old structures, produced by Late shoulders of Sinjar basin contain many such leads as the prospective leads nominated A, B, C and D.Second best are old structures which have been partially restructured and whose closure has been modified, but not breached. The prospective reservoirs will be at Late Cretaceous, Early Cretaceous and Late Triassic.

Thermophysical properties of helium and hydrogen mixtures under high pressure predicted by ab-initio calculations: Implications for Saturn and Jupiter planets

The thermodynamic and physical properties of Helium (He) and Hydrogen (H) mixtures are crucial form an astrophysical perspective. Nowadays, it is well known that these two elements constitute roughly 95% of the matter in the solar system. The high-pressure equation of He state doped with H is calculated in the framework of density functional theory (DFT) for three crystallographic structures. Namely, the Body Centered Cubic (BCC), Face Centered Cubic (FCC), and hexagonal close packed (HCP) structures have been studied. The equations of state (EOS) are provided for the He 0.90 H 0.10 and He 0.70 H 0.30 mixtures and the energy of the same mixtures are calculated with the earlier structures. The band structure for pressures of 0, 75 and 150 GPa were estimated by our calculations for the presumed crystal structures in the case of pure He and He 0.70 H 0.30 mixture for comparison. The k x − k y cuts of the Bloch Spectral Functions (BSF) are presented for the pure He and He 0.70 H 0.30 mixture for the three structures to explore the impact of doping on electronic properties. In addition, electrical resistivity calculations of the mentioned structures were carried out for mixtures with 10, 15, 20 and 30% of H. At final stage, the enthalpy (ΔH) of these latest mixtures have been deduced for the three crystal structures.

From 2D and 3D documentation to 4D interpretation. Building archaeological conclusions and workflow strategies gained by remote study of Insula V 1, Pompeii

The text describes new methods elaborated for and used in the building archaeological assessment of a city block, studied first on site, then remotely by members of the Swedish Pompeii Project. Use of a digital platform, with collected wall observations and analysis, systematic photographic documentation of all standing structures, and 3D models, allowed discussion to proceed after the fieldwork came to an end. The models provided new possibilities and new angles of approach, e.g. examining walls at any given point, studying boundary walls as wall-strings in their full extent, allowing all kinds of sectioning at will, introducing bird’s-eye views as a new perspective in study, and measuring wherever needed. The joint results obtained are summed up in a four-phase development of the use of space: the earliest structures; the late Samnite building boom (2nd century BC); the colony (second half of 1st century BC); the imperial era (until AD 79). This narrative includes conclusions concerning building process and development of masonry techniques and on changes in way of life. Many results affect Pompeian archaeology in general. Results of particular importance concern the character of the early plot division and the understanding of the building process creating the double-atrium house of Caecilius Iucundus, including an anchorage in time for this creation in the Claudian period. The relatively small impact in terms of damage that may be ascribed the literary recorded earthquake of AD 62/63 is also worth noting. The text ends with a suggestion of a new workflow for insula studies.

Deformation, Magmatism, and Sulfide Mineralization in the Archean Golden Mile Fault Zone, Kalgoorlie Gold Camp, Western Australia

AbstractThe Golden Mile fault zone is a key controlling structure to the estimated 75 Moz gold endowment of the Kalgoorlie gold camp in the Yilgarn craton of Western Australia. The earliest structures in the fault are F1 folds that developed during D1 recumbent-fold and thrust deformation (<2685 ± 4 Ma). These F1 folds are overprinted by a pervasive NW- to NNW-striking S2 cleavage related to sinistral shearing beginning with 2680 ± 3 Ma D2a sinistral strike-slip and culminating with ca. 2660 Ma D2c sinistral-reverse movement. The majority of deformation in the fault zone correlates to ca. 2675 Ma D2b deformation, which is characterized by sinistral-normal kinematic indicators. Late, ca. 2650–2640 Ma D3 dextral-reverse kinematic indicators overprint the earlier D2 structures. Pyrrhotite-chalcopyrite-pyrite-sphalerite-galena assemblages were emplaced throughout the D2 event within NE-trending D2a tensile fractures, NW- to NNW-striking D2b normal faults and associated breccias, and NW- to NNW-striking D2c low-angle veins, with the latter D2b and D2c structures correlating to the Fimiston and Oroya mineralization types, respectively. All D2a-, D2b-, and D2c-related sulfides in the Golden Mile fault zone show similarly restricted δ34S (~1.0–4.5‰) and elevated Δ33S (~2.0–3.0‰) values that reflect strong local sulfur contribution from shales of the Lower Black Flag Group and host-rock buffering of hydrothermal fluids related to the Fimiston and Oroya mineralization events. This host-rock buffering decreased fluid fO2, favoring the development of pyrrhotite-pyrite stable sulfide assemblages and causing respective decreases and increases in fluid Au-Te and Pb-Bi-Sb concentrations. At the camp scale, the Golden Mile fault zone exerted a primary control on the distribution of porphyry dikes and gold deposits; however, magma and hydrothermal fluid circulation was favored in adjacent, higher-order structural sites due to the fault zone’s incompetent rheology and tendency for ductile deformation and diffuse fluid flow. Other Archean examples such as Au deposits of the Larder Lake-Cadillac deformation zone in the Superior craton illustrate that this type of diffuse fluid flow in large-scale crustal fault zones can result in disseminated economic mineralization. However, this study highlights that host-rock effects on fluid chemistry in large-scale crustal fault zones exercises a strong control on a fluid’s propensity to form ore. The results of this study emphasize that both the rheology and chemistry of rocks within and adjacent to large-scale deformation zones act as important controls on the formation of gold ore in Archean terranes.

St Lawrence, Alton, Hampshire: the Romanesque crossing and the origins of the Anglo-Saxon minster

The earliest architectural details of the church of St Lawrence, Alton are the Romanesque crossing arches which date from c.1095-1110. A survey of the crossing, however, suggests the arches were inserted into an earlier structure: a minster church indirectly implied in the grant of William I of the church at Alton to New Minster. The 1984 excavations at Amery House immediately south of the church revealed two ditches, one of probable 7th-century date, which may relate to a minster enclosure. This possibly succeeded an early Anglo-Saxon cemetery, though there is no evidence for direct continuity. Alton’s dependent chapel at Holybourne was axially aligned on springs which the place-name suggests were of ritual significance, but this was also a hundredal meeting place, the focus purveying both religious and political power.

La Roundele, Berwick-upon-Tweed

A late 13th-century survey of Berwick-upon-Tweed includes an entry entitled ‘la Roundele’. It has not previously been interpreted satisfactorily but this paper shows it to have been a large circular site, in a secondary use by the time of the survey, at the head of the town’s early beachside marketplace. It is argued that the site’s shape, size and ability to survive in the changing townscape means that it originated in a substantial earlier structure – such as a broch or similar complex Atlantic roundhouse. The proposition accords with what is known of the early history of the Tweed estuary and southern brochs in general. Archaeological evidence for the structure may survive beneath later buildings.
 
 Canmore ID 25990

AN ARCHITECTURAL ANALYSIS OF THE SEALAND BUILDING AT TELL KHAIBER, SOUTHERN IRAQ

This paper analyses the architecture of the large fortified building excavated at Tell Khaiber in southern Iraq, the first known example of monumental architecture from the Sealand Kingdom. It examines the development of this highly unusual building, analyses the spatial properties and apparent functions of the structure, reviews possible architectural parallels, and considers what the architecture might reveal about Tell Khaiber's role in the context of the Sealand state. The outer form and organisation of the building indicate a fortified structure with a high priority afforded to defence. The interior of the Tell Khaiber building is divided between a smaller, earlier structure, enclosing conventionally arranged architecture with apparently executive and administrative functions, and a larger extension, densely packed with accommodation for a large number of personnel. When considered alongside textual sources on the Sealand state, which provide evidence about the geo-political context in which the Tell Khaiber building was constructed, it is possible to suggest the role such a building may have had in the development of the Sealand Kingdom. The form of the Tell Khaiber building may also be important in understanding the nature of the contested border between the Sealand Kingdom and its Babylonian neighbours.

THE ANGLO-NORMAN ABBEY CHURCH OF ST ALBANS AND THE AISLELESS NAVE OF ITS CRUCIFORM PREDECESSOR: THE MATERIAL EVIDENCE

Within the Romanesque abbey church at St Albans (Hertfordshire), the vestiges of an earlier structure have been identified for the first time. A hitherto unrecorded feature in the transept, noted by the author in 2017, indicates that, at some stage, the nave lacked its existing arcade piers and instead had solid walls. The implications of this are considerable, calling for a thorough reassessment of the building’s history. For now, it is important to record the primary evidence, so as to make it available for further research. This article aims to provide a concise account of the evidence and a summary of what it might mean.According to the thirteenth-century chronicler, Matthew Paris, the existing church was begun in 1077 and completed in 1088. New evidence indicates, however, that the Romanesque building, with its aisled nave and presbytery, was preceded by a cruciform structure without aisles. The inference is that the existing building contains the fabric of this unaisled predecessor. The obvious conclusion – that it therefore represents the lost Anglo-Saxon abbey church – does not follow without question; as yet, excavation has yielded no conclusive evidence of an earlier church on the site.The critical diagnostic feature presented here for the first time adds substance to the view that the remodelling of unaisled buildings was not uncommon in the post-Conquest period, including large as well as minor churches, as identified long ago at York Minster and, more recently, at Worksop Priory.

The Marfa Kurgan in the Stavropol Territory: An Example of an Ancient Architectural Structure

This study focuses on the analysis of structural elements of the Marfa kurgan in the Stavropol Territory. We list and examine terms referring to such elements, and suggest our own. A description of the kurgan, its natural environment, excavation techniques, sampling, and analytical methods is provided. The material of which the kurgan was made is assessed, and its advantages over other materials are demonstrated. We studied mud blocks (or “bricks”), their clay coatings, and a striped adobe element from the kurgan. Results of chemical and granulometric analyses are outlined, along with those of the micromorphological analysis of soils underlying the kurgan, of the material of which the “bricks” and the coatings were made. The blocks were molded by thoroughly kneading and compacting a moistened material consisting of loess with the addition of river silt, without plant admixture. Clay coatings were much denser, as it consisted of a coherent finely dispersed clay-carbonate material. Clay mortar, similar to coatings in composition and properties, was used to connect the blocks and the stones of the crepidoma. The same mortar was used for foundations of clay “bricks” buildings. The adobe element with thinnest variously colored stripes resulted from a destruction of an earlier structure.

Optimization and biological evaluation of thiazole-bis-amide inverse agonists of RORγt

The nuclear receptor retinoic acid receptor-related orphan receptor gamma t (RORγt) is a transcription factor that drives Th17 cell differentiation and IL-17 production in both innate and adaptive immune cells. The IL-23/IL-17 pathway is implicated in major autoimmune and inflammatory diseases. RORγt lies at the core of this pathway and represents an attractive opportunity for intervention with small molecule therapeutics. Despite diverse chemical series having been reported, combining high potency and nuclear receptor selectivity with good physicochemical properties remains a challenging endeavor in the field of RORγt drug discovery. We recently described the discovery and evaluation of a new class of potent and selective RORγt inverse agonists based on a thiazole scaffold. Herein we describe the successful optimization of this class by incorporation of an additional amide moiety at the 4-position of the thiazole core. In several optimization cycles, we have reduced human PXR activation, improved solubility, and increased potency while maintaining nuclear receptor selectivity. X-ray crystallographic analysis of compound 1g bound in the sterol binding site of the ligand binding domain of RORγt was largely consistent with an earlier structure, guiding further insight into the molecular mechanism for RORγt inhibition with this series. Compound 1g is orally bioavailable, potent in a human whole blood assay and proved to be efficacious in an ex-vivo IL-17A assay, and was selected for preclinical evaluation.

Dendrochronology at the Mission San Xavier del Bac convento (Tucson, Arizona, USA)

The Spanish Colonial Mission San Xavier del Bac near Tucson, Arizona has been studied extensively for its contribution to the origin and development of Tucson as an urban center. While the general timeline of construction is understood from historical documentation, suggestions of timber reuse from earlier structures (Fontana, 2015) have not been scientifically evaluated. Three vigas (horizontal roof support timbers) and an internal wall beam were sampled for tree-ring analysis and compared to tree-ring chronologies from the nearby Santa Rita, Catalina, and Rincon mountain ranges. Dates for the timbers suggest that timber reuse from earlier structures is not supported in the case of one room, the convento. Additionally, chronologies from the Santa Rita, Catalina, and Rincon ranges do cross-date with these and other historic materials from downtown Tucson, demonstrating potential for dating of local structures from the same period.

The Oldest Ceramics Kiln in the Russian Far East

This article analyzes the remains of a pottery kiln excavated at the Chernyatino 2 site in the Primor’e District on the southern mainland of the Russian Far East adjacent to the Korean Peninsula and northeastern China. The kiln’s remains have been assigned to the Krounovskaia culture of the Paleometal period and preliminarily dated to the early 1st millennium CE. The kiln is characterized by: 1) a subrectangular floor plan excavated into the soil and slightly sloped; 2) fuel and firing sections located at different levels and separated by a low step; 3) small size; 4) a tunnel-like clay dome on a stick frame. Many damaged dome fragments were found near the subrectangular kiln excavation. Based on the results of pottery sample examination, in particular scanning electron microscope [SEM] analysis, the firing temperatures in the kiln were 750–900° С. The kiln is the earliest structure for firing pottery so far recorded in the southern Russian Far East. Such kilns were invented on the Korean Peninsula in the 3rd–4th centuries CE.

Controlling Photosynthetic Excitons by Selective Pigment Photooxidation.

As a basis of photosynthesis, photoinduced oxidation of (bacterio)chlorophyll molecules in the special reaction center complexes has been a subject of extensive research. In contrast, the generally harmful photooxidation of antenna chromoproteins has received much less attention. Here, we have established the permanent structural changes in the LH2 antenna bacteriochlorophyll-protein complex from a sulfur photosynthetic purple bacterium Ectothiorhodospira haloalkaliphila taking place at physiological conditions upon intense optical irradiation. To this end, a crystal structure of the LH2 complex from E. haloalkaliphila was first resolved by X-ray diffraction to 3.7 Å, verifying a great similarity with the earlier structure from Phaesporillum molischianum. Analysis of the various steady-state and picosecond time-resolved optical spectroscopy data and related model simulations then confirmed that the major spectral effects observed-bleaching and blue-shifting of the B850 exciton band and correlated emergence of a higher-energy C700 exciton band-are associated with photooxidation of increasing numbers of B850 bacteriochlorophylls into 3-acetyl-chlorophylls, with no noticeable damage to the pigment-binding protein scaffold. A prospective noninvasive method for an in situ optical control of excitons by selective photooxidation of pigment chromophores was thus revealed and demonstrated in a structurally well-defined native system.

Tectonometamorphic Evolution of Jutulsessen, Gjelsvikfjella, cDML, East Antarctica

The Jutulsessen area, can provide a vital clue to the supercontinent assembly of Gondwana Land as it is situated within the Circum East Antarctic Mobile Belt just east of the Penksockett rift marking the divide between the central Dronning Maud Land from the Western Dronning Maud Land. This landmass is dominated by migmatitic quartzo-feldspathic rocks intruded by syn to post-tectonic granites. The work highlights the data from western part cDML area with a view to arrive at a more comprehensive model for the cDML and subsequently to the super continent assembly. Granitic and migmatitic gneisses comprising of amphibolitic and biotite rich enclaves. The gneisses show variations from quartzo-felspathic gneiss to amphibolitic gneiss. The area has witnessed complex geological history involving at different deformational episodes with concomitant metamorphism. The pervasive dominant foliation trends NW-SE with shallow to medium dips towards SW. In the Stabben area, a nonfoliated intrusive syenite-gabbro pluton limits the gneissic exposures. Compositionally, the orthogneisses plot in the monzogranitegranodiorite field where as the mafic dykes/enclaves plot in the basalt-andesite-rhyodacite field. The bulk geochemical characteristics suggest significant crustal contamination. Garnet-biotite Fe-Mg exchange thermometry gives peak metamorphic temperature of 483° C for the gneisses and 628° C for the dioritic enclave within gneisses. A peak metamorphic grade of upper amphibolite to granulite facies is deduced from the mineral assemblages. Widespread anatexis has led to extensive occurrence of migmatites in the area. Recent geochronological studies assign an age of 1170 Ma to 970 Ma for the migmatites/gneisses and an emplacement age of 501 Ma for the Stabben gabbro and syenite. The discriminant plots of the Jutulsessen rocks indicate diverse origin ranging from pre-plate collision to post-collision orogenic tectonic setting. The mafic enclaves/dykes show ocean island arc to MORB affinities. Voluminous addition of juvenile crust during the Pan-African orogeny strongly overprints earlier structures.

Structural geometry of orogenic gold deposits: Implications for exploration of world-class and giant deposits

With very few exceptions, orogenic gold deposits formed in subduction-related tectonic settings in accretionary to collisional orogenic belts from Archean to Tertiary times. Their genesis, including metal and fluid source, fluid pathways, depositional mechanisms, and timing relative to regional structural and metamorphic events, continues to be controversial. However, there is now general agreement that these deposits formed from metamorphic fluids, either from metamorphism of intra-basinal rock sequences or de-volatilization of a subducted sediment wedge, during a change from a compressional to transpressional, less commonly transtensional, stress regime, prior to orogenic collapse. In the case of Archean and Paleoproterozoic deposits, the formation of orogenic gold deposits was one of the last events prior to cratonization. The late timing of orogenic gold deposits within the structural evolution of the host orogen implies that any earlier structures may be mineralized and that the current structural geometry of the gold deposits is equivalent to that at the time of their formation provided that there has been no significant post-gold orogenic overprint. Within the host volcano-sedimentary sequences at the province scale, world-class orogenic gold deposits are most commonly located in second-order structures adjacent to crustal scale faults and shear zones, representing the first-order ore-forming fluid pathways, and whose deep lithospheric connection is marked by lamprophyre intrusions which, however, have no direct genetic association with gold deposition. More specifically, the gold deposits are located adjacent to ∼10°–25° district-scale jogs in these crustal-scale faults. These jogs are commonly the site of arrays of ∼70° cross faults that accommodate the bending of the more rigid components, for example volcanic rocks and intrusive sills, of the host belts. Rotation of blocks between these accommodation faults causes failure of more competent units and/or reactivation and dilation of pre-existing structures, leading to deposit-scale focussing of ore-fluid and gold deposition. Anticlinal or antiformal fold hinges, particularly those of ‘locked-up’ folds with ∼30° apical angles and overturned back limbs, represent sites of brittle-ductile rock failure and provide one of the more robust parameters for location of orogenic gold deposits.In orogenic belts with abundant pre-gold granitic intrusions, particularly Precambrian granite-greenstone terranes, the boundaries between the rigid granitic bodies and more ductile greenstone sequences are commonly sites of heterogeneous stress and inhomogeneous strain. Thus, contacts between granitic intrusions and volcano-sedimentary sequences are common sites of ore-fluid infiltration and gold deposition. For orogenic gold deposits at deeper crustal levels, ore-forming fluids are commonly focused along strain gradients between more compressional zones where volcano-sedimentary sequences are thinned and relatively more extensional zones where they are thickened. World-class orogenic gold deposits are commonly located in the deformed volcano-sedimentary sequences in such strain gradients adjacent to triple-point junctions defined by the granitic intrusions, or along the zones of assembly of micro-blocks on a regional scale. These repetitive province to district-scale geometrical patterns of structures within the orogenic belts are clearly critical parameters in geology-based exploration targeting for orogenic gold deposits.