Mesoarchean accretionary mélange and tectonic erosion in the Archean Dharwar Craton,southern India: Plate tectonics in the early Earth

Accretionary orogens are hallmarks of subduction tectonics along convergent plate margins. Here we report a sequence of low-grade metasediments carrying exhumed blocks of ultramafic, mafic and felsic rocks from Sargur in the Western Dharwar Craton in India. These rocks occur along the southern domain of the Chitradurga Suture Zone, which marks the boundary between the Western and Central Dharwar Cratons and thus provide a window to explore Archean convergent margin processes. We present zircon U-Pb and Lu-Hf data from Sargur metasediments including quartz mica schist, fine-grained quartzite, and pelitic schist, as well as from blocks/layers of trondhjemite, garnet amphibolite, and chromite-bearing serpentinite occurring within the metasedimentary accretionary belt. The detrital zircon grains from the metasediments show multiple age groups, with the oldest age as 3482 Ma and an age peak at 2862 Ma. Magmatic zircons in trondhjemite show ²⁰⁷Pb/²⁰⁶Pb weighted mean age of ca. 2972 Ma, whereas those in the chromite-bearing serpentinite display multiple age populations of ca. 2896, 2750, 2648, 2566 and 2463 Ma, tracing zircon crystallization in an evolving mantle wedge adjacent to a subducting oceanic plate. Metamorphism is dated as ca. 2444 Ma from zircon grains in the garnet amphibolite. Zircon εHf(t) in the mafic-ultramafic rocks and trondhjemite are mostly positive, suggesting a juvenile (depleted mantle) source. The detrital zircon Lu-Hf data suggest that the sediment source involved Paleoarchean juvenile and reworked components. Based on our findings, we propose that the Sargur sequence represents an accretionary mélange which forms part of a major Mesoarchean accretionary orogen that witnessed multiple stages of tectonic erosion at least during three periods at ca. 3200–3000 Ma, 3000–2800 Ma and 2800–2500 Ma removing a large part of the accretionary prism along the convergent margin. We correlate the processes with prolonged subduction-accretion cycle culminating in the final collision between the Western and Central Dharwar cratonic blocks.     

Detrital zircon U–Pb ages and Hf-isotope systematics from the Gadag Greenstone Belt: Archean crustal growth in the western Dharwar Craton,India

The Western Dharwar Craton in peninsular India comprises a typical Meso- to Neo-Archean granite-greenstone terrain. Detrital zircons from two metagreywackes in a late basin from the Gadag Greenstone Belt preserve at least eight age populations ranging in age from ca 3.34 to 2.55 Ga, and grains as old as ca 3.54 Ga. The zircon provenances for the two samples appear to be the same up to ca 3.25 Ga, with relatively juvenile ε_Hf values largely between zero and depleted mantle values. After 3.25 Ga, one sample has similar ε_Hf values whereas the other has only negative values indicative of Hf-evolution in a crustal environment. After ca 3.25 Ga the source regions for the two samples were distinctly different.The detrital zircons reflect the age and evolution of the upper crust of the Western Dharwar Craton. Modeling of Hf isotopic evolution of the detrital zircons suggests two major crust-forming events at ca. 3.6 and 3.36 Ga, and some indication of juvenile addition to the crust at ca 2.6 Ga. The maximum sedimentation age of the greywackes is constrained by the youngest detrital zircon population at 2547 ± 5 Ma. Gold mineralization in the belt is dated at 2522 ± 6 Ma and constrains greywacke sedimentation, deformation and metamorphism to a ca 25 my interval.     

Genesis of the Late Archean granitoids of the northern part of the Dharwar foreland (Dharwar Craton), south India – Insights from field,crystal size distribution,thermobarometry, microgeochemical and bulk-rock geochemical studies

An intrusive granitoid pluton into TTG-Dharwar Supergroup greenstone sequence is being reported for the first time from the Dharwar Foreland region. Based on field and petrographic characteristics, these granitoids are classified as - quartz-monzodiorites and granites. Occasional mafic bodies of dioritic-granodioritic composition with size ranging from small microgranular magmatic enclaves to bodies of several centimeters are common in these granitoids.The granitoids are devoid of any crystal-plastic fabric as well as high-strain characteristics. The textural (CSD) studies indicate that the quartz-monzodiorites are derived from magma mixing whereas the granites are derived from equilibrium crystallization of the magma derived from the reworking of quartz-monzodiorites. The P-T estimates indicate that the quartz-monzodiorites were crystallized at higher temperature (>950 °C) and pressure (3.09–4.36 kbar) conditions in a reducing environment at mid-crustal levels. However, the granites indicate lower temperature (<750 °C) and pressure (0.89–1.88 kbar) conditions of crystallization in an oxidizing environment at shallow-crustal levels. The bulk rock chemical characteristics indicate that the quartz-monzodiorites were derived from the melt generated by the mixing of two melts - a melt derived from the differentiation of sanukitoids senso lato (s.l.) and a melt derived from the partial melting of TTG. On the other hand, reworking of the hot crystallizing quartz-monzodiorite due to its rapid upliftment to shallow crustal levels resulted in a decompression melting which gave rise to granitic melts.The relative age of the Dharwad granitoids is estimated to be ∼2580–2560 Ma and unlike the other older granitoids (> 2.61 Ga) reported from the northern part of the Shimoga greenstone belt, the studied granitoids marks the final stage of cratonization in the Foreland region.     

A petrogenetic relationship between 2.37 Ga boninitic dyke swarms of the Indian Shield: Evidence from the Central Bastar Craton and the NE Dharwar Craton

The Indian Shield is cross-cut by a number of distinct Paleoproterozoic mafic dyke swarms. The density of dykes in the Dharwar and Bastar Cratons is amongst the highest on Earth. Globally, boninitic dyke swarms are rare compared to tholeiitic dyke swarms and yet they are common within the Southern Indian Shield. Geochronology and geochemistry are used to constrain the petrogenesis and relationship of the boninitic dykes (SiO₂ = 51.5 to 55.7 wt%, MgO = 5.8 to 18.7 wt%, and TiO₂ = 0.30 wt% to 0.77 wt%) from the central Bastar Craton (Bhanupratappur) and the NE Dharwar Craton (Karimnagar). A single U-Pb baddeleyite age from a boninitic dyke near Bhanupratappur yielded a weighted-mean ²⁰⁷Pb/²⁰⁶Pb age of 2365.6 ± 0.9 Ma that is within error of boninitic dykes from the Dharwar Craton near Karimnagar (2368.5 ± 2.6 Ma) and farther south near Bangalore (2365.4 ± 1.0 Ma to 2368.6 ± 1.3 Ma). Rhyolite-MELTS modeling indicates that fractional crystallization is the likely cause of major element variability of the boninitic dykes from Bhanupratappur whereas trace element modeling indicates that the primary melt may be derived from a pyroxenite mantle source near the spinel-garnet transition zone. The Nd isotopes (ε_Nd(t) = −6.4 to +4.5) of the Bhanupratappur dykes are more variable than the Karimnagar dykes (ε_Nd(t) = −0.7 to +0.6) but they overlap. The variability of Sr-Nd isotopes may be related to crustal contamination during emplacement or is indicative of an isotopically heterogeneous mantle source. The chemical and temporal similarities of the Bhanupratappur dykes with the dykes of the Dharwar Craton (Karimnagar, Penukonda, Chennekottapalle) indicate they are members of the same giant radiating dyke swarm. Moreover, our results suggest that the Bastar and Dharwar Cratons were adjacent but likely had a different configuration at 2.37 Ga than the present day. It is possible that the 2.37Ga dyke swarm was related to a mantle plume that assisted in the break-up of an unknown or poorly constrained supercontinent.     

Did satellite imagery supersede aerial imagery? A perspective from 3D geopositioning accuracy

In this study, the geometric accuracy comparison of aerial photos and WorldView-2 satellite stereo image data is evaluated with the different number and the distribution of the ground control points (GCPs) on the basis of large scale map production. Also, the current situation of rivalry between airborne and satelliteborne imagery was mentioned. The geometric accuracy of Microsoft UltraCam X 45 cm ground sampling distance (GSD) aerial imagery and WorldView-2 data both with and without GCPs are also separately analyzed. The aerial photos without any GCP by only using global navigation satellite system (GNSS) and inertial measurement unit (IMU) data with tie points give an accuracy of ±1.17 m in planimetry and ±0.71 m in vertical that means nearly two times better accuracy than the rational polynomial coefficient (RPC) of stereo WorldView-2. Using one GCP affects the accuracies of aerial photos and WorldView-2 in different ways. While this situation distorts the aerial photo block, it corrects the shift effect of RPC in WorldView-2 and increases the accuracy. By using four or more GCPs, ½?pixel (～0.23 m) accuracy in aerial photos and 1 pixel (～0.50 m) accuracy in WorldView-2 can be achieved in horizontal. In vertical, aerial photos have 1 pixel (～0.55 m) and WorldView-2 has 1.5 pixels (～0.85 m) accuracy. These results show that Worldview-2 imagery can be used in the production of class I 1:5000 scale maps according to the ASPRS Accuracy Standards for Digital Geospatial Data in terms of geometric accuracy. It is concluded that the rivalry between aerial and satellite imagery will continue for some time in the future.     

Hydrothermal H?gbomite Associated with Vanadiferous-Titaniferous (V-Ti) Bearing Magnetite Bands in Bhakatarhalli Chromite Mine, Nuggihalli Greenstone Belt, Western Dharwar Craton, Karnataka, India

Hogbomite,a rare exotic mineral,is found to be associated with the vanadiferous-titaniferous （V-Ti） bearing magnetite bands at Bhakatarhalli,Nuggihaifi greenstone belt,western Dharwar Craton,India.We report on a second occurrence of hogbomite from the Dharwar craton in Karnataka,which is the sixth documented occurrence of this mineral from India.We evaluate the chemical characteristics of hogbomite and associated Fe-Ti-minerals in an attempt to identify its formation as a primary hydrothermal mineral in a metamorphosed magnetite layer.We report here the presence of hogbomite as a complex oxide of Fe,Mg,Al and Ti with accessory of Zn,V and Sn.Petrographic studies suggest the （V-Ti） bearing magnetite （Mt） contain spinel,hogbomite,chlorite,martite,ilmenite （Ⅱ） and minor amounts of diaspore.The hogbomite displays euhedral to subhedral textures,and is up to 250 μm along the grain boundaries of magnetite and ilmenite.In the samples studied,hogbomite is prismatic,irregular and elongated in shape.The genesis of hogbomite in veins between magnetite and ilmenite implies its precipitation from fluids without involving complicated reactions.Several models were proposed for the formation of hogbomite; however,the subject is still debatable.     

Petrology, geochemistry and genesis of newly discovered Mesoproterozoic highly magnesian, calcite-rich kimberlites from Siddanpalli, Eastern Dharwar Craton, Southern India: products of subduction-related magmatic sources?

The Siddanpalli kimberlites constitute a newly discovered cluster (SKC) of Mesoproterozoic (1090 Ma) dykes occurring in the granite-greenstone terrain of the Gadwal area in the Eastern Dharwar Craton (EDC), Southern India. They belong to coherent facies and contain serpentinized olivines (two generations), phlogopite, spinel, perovskite, ilmenite, apatite, carbonate and garnet xenocrysts. A peculiar feature of these kimberlites is the abundance of carbonate and limestone xenoliths of the eroded platformal Proterozoic (Purana) sedimentary cover of Kurnool/Bhima age. Chemically, the Siddanpalli dykes are the most magnesium-rich (up to 35 wt.% MgO) and silica-undersaturated (SiO₂?<?35 wt.%) of all kimberlites described so far from the Eastern Dharwar Craton. The La/Yb ratio in the Siddanpalli kimberlites (64–105) is considerably lower than that in the other EDC kimberlites (108–145), primarily owing to their much higher HREE abundances. Since there is no evidence of any crustal contamination by granitic rocks we infer this to be a specific character of the magmatic source. A comparison of the REE geochemistry of the Siddanpalli kimberlites with petrogenetic models for southern African kimberlites suggests that they display involvement of a wide range in the degree of melting in their genesis. The different geochemical signatures of the SKC compared to the other known kimberlites in the EDC can be explained by a combination of factors involving: (i) higher degrees of partial melting; (ii) relatively shallower depths of derivation; (iii) possible involvement of subducted component in their mantle source region; and (iv) previous extraction of boninitic magmas from their geological domain.     

How global is U.S. Major League Baseball? A historical and geographic perspective

This article explores the globalization of U.S. Major League Baseball (MLB), measured by the participation of foreign-born players in the sport from 1876 to 2005. Data show that the number of non-native athletes has been increasing since the end of World War II, suggesting that MLB is becoming a more globalized organization. An investigation at regional and country levels reveals that most foreign participants in the 1990s and early 21st century are from Latin America, especially the Dominican Republic. In contrast, most African, European, and Asian countries have shown little sign of participation. This implies that the global reach of MLB is limited. An empirical study of 2005 data suggests that prosperous countries, neighboring countries, or countries having a close political relationship with the U.S. tend to provide more athletes to MLB. In other words, the globalization of MLB is reliant on America’s economic, cultural, and geographic proximity to the rest of the world.     

Late Neoarchean reworking of the Mesoarchean crustal remnant in northern Liaoning,North China Craton: A U–Pb–Hf–O–Nd perspective

How the earth's crust formed and evolved during the Precambrian times is one of the key questions to decipher the evolution of the early Earth. As one of the few cratons containing well-preserved Eoarchean to Neoarchean basement on Earth, the North China Craton is an ideal natural laboratory to unravel the early crustal evolution. It is controversial whether the Archean tectonothermal events in this area represents reworking or growth of the continental crust. To solve this issue, we have compelled field-based mapping, zircon U–Pb dating by SHRIMP RG and LA–ICP–MS U–Pb, zircon SHRIMP SI oxygen and LA–MC–ICP–MS Hf isotope, and whole-rock Nd–O isotope analyses from the Archean granitoids in northern Liaoning, North China Craton. On the basis of zircon U–Pb isotopic dating and measured geological section investigation, two distinct magmatic suites as enclaves in the Jurassic granites are recognized, viz. a newly discovered 3.0 Ga crustal remnant and a 2.5 Ga granitoid. The Mesoarchean zircons from the 3.0 Ga granodioritic gneisses exhibit heterogeneous Hf isotopic compositions, with the most radiogenic analysis (ε_Hf(t) = +3.8) following the depleted mantle evolution array and the most unradiogenic ε_Hf(t) extending down to −3.4. This implies that both ancient continental crust at least as old as 3.4 Ga and depleted mantle contributed to the magma source of the protoliths of the Mesoarchean gneisses. The ε_Hf(t) values of the Neoarchean zircons from these gneisses overlap the 3.4–3.0 Ga zircon evolution trend, indicating that the ancient crustal materials have been reworked during the late Neoarchean. The Neoarchean zircons from the 2.5 Ga granitoids have a relatively small variation in the Hf isotope and are mainly plotted in the 3.0–2.8 Ga zircon evolution field. However, taking all the ε_Hf(t) values of the Neoarchean zircons into the consideration, we find that the Hf model age of the Neoarchean zircon does not represent the time of crustal growth or reworking but are artifacts of magma mixing. The interaction between the magmas derived from the ancient crustal materials and the depleted mantle is also supported by zircon O isotopic data and Hf–O isotopic modeling of the Neoarchean granitoids. Both Mesoarchean and late Neoarchean tectonothermal events involved synchronous crustal growth and reworking, which may be applicable to other parts of the world.     

A thousand years of loneliness? Globalization from the perspective of a city in a European periphery

Most cities face the challenge of increasing global and local change. Much of what has been said about cities in a globalized world has been concerned with large metropolitan cites. It has been postulated that increased competitiveness is the relevant response, and that urban governance has to change from managerialism to entrepeneurialism in order to cope with this challenge. The first part of the paper discusses some aspects of this body of theory, and the relevance for sub-national regional capitals. It also discusses how the scope of strategies depend on changing national and regional policies. The second part uses the case of Trondheim to discuss how these cities perceive and deal with globalization. Four policy options are discussed; the clientist strategy, the competitive strategy, the isolationist strategy and finally the option of doing nothing at all. The article concludes that global challenges will force local government in small cities to forge new strategies, but the preferred option is a clientist strategy rather than an entrepreneurial one, and the scope of strategy is national rather than global. Thus, when dealing with small peripheral cities and globalization, the range of perspectives must be extended beyond entrepreneurialism and competitiveness.     

Are we going to live in a post-NATO world? A critical perspective on trends,obstacles and possibilities

The main research question investigated in this paper is the following: will a post-NATO world emerge during the next decades? The relevance of such a question is a consequence of the political and economic changes that have seen the light as a result of the power shift of international relations after the end of the Cold War. In spite of this, some contradictory tendencies, such as the weakening of the European pole within the NATO block, the US-NATO enlargement and its military aggressiveness, are generating a number of significant obstacles to the emergence of a post-NATO world. We will argue that the existence of these obstacles could be interpreted as some steps toward the historical downsizing of the US-EU-NATO hegemony. A “post-NATO” world does not necessarily imply the end of NATO, but rather the end of its hegemonic military presence on the global stage. Firstly, we will put the question into context mentioning the debates around NATO’s future and underlining the path undertaken by the Alliance in the frame of the redefinition of the aims of its “strategic concepts”. In this perspective, we will underline the direct link which exists between US strategic needs and NATO’s evolution in the post-Cold war era. Secondly, we will argue that the recent process of military expansionism led by NATO is remarkably de-legitimizing its actions on the global stage. Such a process, along with the current world system shift toward the end of unipolarity, is likely to provoke dramatic consequences in terms of international insecurity and the spreading of war. Thirdly, we will briefly compare the US and Chinese foreign actions, arguing that the space of international legitimacy is radically changing. This fact represents another brick supporting the idea of the emergence of a post-NATO world system in the future of international relations.     

Geology,mineralogy, and geochemistry of magnetite-associated Au mineralization of the ultramafic–basalt greenstone hosted Crusader Complex,Agnew Gold Camp,Eastern Yilgarn Craton,Western Australia; a Late Archean intrusion-related Au deposit?

The Crusader Complex, part of the Agnew gold camp of the Lawlers Anticline of the Yilgarn Craton, Western Australia, is located close to or along the contact between the Lawlers Basalt and Agnew Ultramafics units. Au mineralization within the four orebodies that form the Crusader Complex is dominated by very pure Au, containing less than 1 wt.% Ag, with Au variably associated with scheelite, Bi-tellurides and minor chalcopyrite within a magnetite and titanite gangue assemblage. Hydrothermal alteration associated with this style of mineralization is characterized by increasing concentrations of Mo, Be, Li, Sn and Fe and depletions in Na, Cu, Ba, Pb, Mn, Zn, Si, and K relative to protolith concentrations; these enrichments are more typical in orebodies associated with felsic intrusive-related mineralizing systems rather than the more well-known orogenic Au deposits found elsewhere within the Lawlers Anticline (e.g. at Waroonga) and within the greater Yilgarn Craton.We propose that flexures of the contact between the Lawlers Basalt and Agnew Ultramafic units acted as conduits for Au-bearing felsic intrusive-derived fluids and generated structural traps that enhanced fluid flow. The mineralizing fluids that formed the Crusader deposits were derived from the Lawlers granitoid pluton that intruded into the study area. Enhanced fluid flow promoted interaction between hydrothermal fluids and the reactive mafic–ultramafic rock sequence, augmenting the amount of Au that was precipitated during formation of the orebodies at Crusader. The magnetite-dominated quartz- and sulfide-poor intrusion-related mineralization at Crusader contrasts sharply with other late Archean intrusion-related deposits of the Yilgarn Craton that are usually sulfide- and/or quartz-rich. This may in turn suggest that the Crusader deposit represents a new class of under-explored intrusion-derived deposits, possibly opening new mineral exploration opportunities for the Agnew region, and potentially the wider Eastern Goldfields Superterrane. Enrichments in Mo and Sn and significant depletions in Cu suggest that other parts of the Lawlers batholith may also be prospective for base metal mineralization.Integration of stratigraphic interpretation with the identification of key structural fluid pathways and the presence of felsic intrusive bodies, as presented in this study, enables the delineation of the key elements that underlie mineralization at the Crusader Complex. We propose that these key elements provide vital information for future gold exploration models that can be used within other Archean terranes and within the Eastern Yilgarn Craton in particular.