Precambrian Geology

Sulphur isotope data from early Archaean rocks suggest that microbes with metabolisms based on sulphur existed almost 3.5 billion years ago, leading to suggestions that the earliest microbial ecosystems were sulphur-based 1-5 . However, morphological evidence for these sulphur-metabolizing bacteria has been elusive. Here we report the presence of microstructures from the 3.4-billion-year-old Strelley Pool Formation in Western Australia that are associated with micrometre-sized pyrite crystals. The microstructures we identify exhibit indicators of biological affinity, including hollow cell lumens, carbonaceous cell walls enriched in nitrogen, taphonomic degradation, organization into chains and clusters, and δ 13 C values of −33 to −46 Vienna PeeDee Belemnite (VPDB). We therefore identify them as microfossils of spheroidal and ellipsoidal cells and tubular sheaths demonstrating the organization of multiple cells. The associated pyrite crystals have 33 S values between −1.65 and +1.43 and δ 34 S values ranging from −12 to +6 Vienna Canyon Diablo Troilite (VCDT) 5 . We interpret the pyrite crystals as the metabolic by-products of these cells, which would have employed sulphate-reduction and sulphur-disproportionation pathways. These microfossils are about 200 million years older than previously described 6 microfossils from Palaeoarchaean siliciclastic environments.

At ∼1.1 Ga, the North American Craton began to rift, resulting in flood-style basaltic volcanism. During the phase of active tectonism, some of that basalt was weathered and redistributed by fluvial processes. New observations near the northwestern shore of Lake Superior have also revealed the presence of seven paleosols formed on weathered, immature sediments derived from the basalt that are described here for the first time. Only three other paleosols have previously been described from this part of the geologic record, so these new paleosols represent a significant new discovery. The paleosols are weakly developed and exhibit physical and chemical characteristics similar to Phanerozoic Entisols. In contrast to many Precambrian paleosols, the Keweenawen paleosols have been subject to minimal postburial alteration. Among the paleosols, three distinct pedofacies are recognized: (1) waterlogged/gleyed fluvial-proximal paleosols, (2) dry fluvial-distal paleosols, and (3) cumulative fluvial-proximal paleosols. Despite these facies differences, using a combination of physical and chemical measures of weathering it is found that the paleosols are all derived from the same parental basalt, with one of the paleosols showing an additional extra-basinal rhyolitic component. By considering the mass-balance behaviour of a variety of alkali and alkaline earth elements, it is possible to rule out significant potassium metasomatism, suggesting that these paleosols may be particularly useful for paleoatmospheric and paleobiologic reconstructions, and that they form an important new source of data about Mesoproterozoic weathering.

The Neoproterozoic Wadi Kid metamorphic belt in southeastern Sinai in Egypt represents a structurally and metamorphically complex assemblage of metasedimentary and metavolcanic rocks folded into a series of ENE-WSW-trending antiforms and synforms. Geological mapping in this region is challenging, primarily due to difficult access, complexity of structures, and lack of resolution and areal integrity of lithological differentiation using conventional mapping techniques. Spectral ratioing of selected bands of Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) data of the area, in synergy with geological field observation, proved effective in resolving geological mapping problems in the region. A new ASTER band-ratio image 4/7-4/6-4/10 is applied successfully for lithological mapping in the Wadi Kid area, showing improvement over previous techniques in detailing the main rock units. These are gneiss and migmatite, amphibolite, volcanogenic sediments with banded iron formation, meta-pelites, talc schist, meta-psammites, meta-acidic volcanics, meta-pyroclastics volcaniclastics, albitites and granitic rocks. Validating the use of the new ASTER band-ratio image relied on both calculating statistical optimum index factor (OIF) and matching interpreted lithological boundaries to field data and previously published geologic maps. The adopted ASTER band-ratio image demonstrates the benefit of using ASTER remote sensing data in lithological mapping of the Wadi Kid area and therefore for lithological mapping in the Arabian-Nubian shield and other arid areas.

Komatiites are ultramafic volcanic rocks that occur mainly in Archean and Paleoproterozoic greenstone belts. These olivine-rich rocks are assumed to have crystallized from magmas that
have about 28–30 wt % MgO. They are characterized by spinifex texture - platy or skeletal crystals of olivine set in a
glassy matrix. Chemically, komatiites resemble peridotites and have high MgO but low SiO2, TiO2 (<1 wt %), K2O (<0.5 wt %) and incompatible trace element contents. Most of their
compositional variations can be accounted for by olivine fractionation. Komatiites are conventionally considered
to be derived from high temperature melts that have eruption temperatures of about 1600oC and are produced by high degrees of anhydrous melting of mantle plumes. The abundance of Archean komatiites, their decrease through the Proterozoic and extreme rarity in the Phanerozoic have
been taken as evidence for secular cooling of the mantle. However, the plume model has recently been challenged.
In marked contrast, it has been proposed that komatiites originate via hydrous melting at a shallow depth in subduction environments at significantly lower melting temperatures than
those invoked by the plume hypothesis. This new model thus challenges traditional views of the early evolution of the Earth. Nevertheless, it appears that many komatiites are plume-related. In addition to the information they provide about the tectonics and the thermal evolution of Archean Earth,
komatiites are economically important because they host locally significant magmatic Ni-sulfide (Ni-Cu-PGE) mineralization.

A group of less disturbed and unmetamorphosed ‘Proterozoic’ platformal sediment package lying over deformed and metamorphosed Archean to Paleoproterozoic basement in several parts of Peninsular India is informally termed as ‘Purana’ basins in Indian stratigraphy. The trend shift in the understanding of these basin fills in last two decades, often supported by international collaborations, has made significant advancements in respect to unconformity and ‘Sequence’ development, relationship with accretion and break-up of the supercontinents, initiation and evolution of the basins in different tectonic set ups, nature of sediment provenance, paleoclimate and paleo-weathering patterns and basin water chemistry. Geophysical backups encompassing the basins, occasionally extending up to the craton and adjacent mobile belts helped in refining the understanding on the basement structure and tectonic forcings. The present paper is an attempt towards the collation of the database generated in last two decades in order to present the status of current understanding on different ‘Purana’ basins with regard to interactions of physical, chemical and biological parameters of the Proterozoic Earth.

This paper reviews the state of our current knowledge of the Cryogenian glacial and deglacial sedimentary records of South Australia. Two, distinct, glacial intervals are recognised within rocks of Cryogenian (850-630 Ma) age, separated by an interglacial succession that by definition lacks glacial facies. The glacial successions were laid down during the Sturt and Elatina glaciations. Each of these glaciations is arguably of global extent under the Snowball Earth hypothesis (Hoffman and Schrag, 2002). Evidence for glaciation has been known for over one hundred years from the Sturt Tillite (Howchin, 1900). When compared like-for-like in a systematic facies analysis, both glacial successions show some similarities, notably the occurrence of diamictites representing glacial deposition and slope reflux, and dropstone-bearing intervals, but also show some dramatic differences. Notably, deposition of the Sturt succession was strongly influenced by extensional tectonics, for which evidence is provided by dramatic thickness variations either side of major faults and palaeocurrent data. Sub-basins formed during regional extension contain diamictites 4-6000 m thick (e.g. the Yudnamutana and Baratta “troughs” in the northern and central Flinders Ranges respectively). Deposition of the younger, Elatina glacial deposits was locally influenced by diapirism in the central Flinders Ranges, but otherwise these younger deposits seem to maintain a relatively constant thickness of <100 m, although exceptionally, thicknesses of up to 1500 m occur in basinal sections (Williams et al., 2008). The emergence of South Australia from the Sturt and Elatina glaciations culminated in black, silty shale and rather complex “cap-dolostones” respectively- two contrasting styles of deglaciation.

Neoproterozoic BIFs occur in Tonian, Cryogenian, and Ediacaran successions, and are not restricted
to the middle Cryogenian (c. 715 Ma) glaciation. Many Neoproterozoic BIFs (North and South
America, southern Africa, and Australia) were deposited in glacially influenced settings, and are
traditionally assigned to the Rapitan type. Other occurrences in South America, Africa, and Asia,
however, bear no indications of glacial processes and can be assigned to the Algoma and Lake Superior
types.
Chemostratigraphy is a powerful tool for unraveling the depositional setting of Neoproterozoic
BIFs. Some of the most useful methods are REE distribution, especially the Eu and Ce normalized
concentrations, iron speciation, Nd and Cr isotopes (δ53Cr). Whereas Rapitan type BIFs exhibit no Eu
or Ce anomalies, Algoma type Neoproterozoic BIF show both. Positive δ53Cr values characterize glacially
influenced BIFs, and differentiates them from nonfractionated, mantle-like δ53Cr values of
Algoma type BIFs. The latter are also characterized by high Cr concentrations. The most positive δ53Cr
values occur in the open-shelf, Lake Superior type BIFs, especially those of Ediacaran age. Given the
consistent secular variations exhibited by δ53Cr, it is envisaged that it may be used for correlation and
geochronology once the available database grows sufficiently.
It is demonstrated clearly that glaciation was not the main mechanism responsible for deposition of
BIFs in the Neoproterozoic. Hydrothermal activity related to the rifting of Rodinia probably played the
key role in their reappearance after the Mesoproterozoic gap, and promoted a return to ferruginous
conditions after the demise of Mesoproterozoic euxinic oceans.

Bolivia cubre en la parte oriental una región con una superficie de 220,000 km2 que corresponde a una pequeña parte del gran cratón Amazónico con afloramientos de rocas Meso-Proterozoicas (1.8-1.0 Ga). Aproximadamente diez por ciento de este regolito consiste de “esquistos” de metamorfismo bajo a medio. Investigaciones de los últimos veinticinco años demostraron que estos se presentan en Guarayos y la Chiquitania con características de cinturones de rocas verdes con potencial geológico importante para depósitos de oro orogénico y yacimientos de sulfuros masivos volcanogénicos (VMS). En este contexto el descubrimiento del depósito VMS “Miguela” hace veinte años representa un hallazgo bastante importante en la exploración minera del oriente Boliviano. Está hospedado en una secuencia volcano-sedimentar con afinidad toleítica dentro del cinturón de rocas verdes de Guarayos. Los estudios regionales del pasado no tomaron en cuenta la búsqueda sistemática para este tipo de depósitos, tampoco la aplicación de métodos innovadores de exploración para permitir el descubrimiento de cuerpos mineralizados que no afloran y no dejan rasgos en superficie. Los sulfuros masivos de “Miguela” están ligados a la formación “La Pastora”, que se extiende sobre una distancia de por lo menos doce kilómetros. Los tres lentes mineralizados son ricos en cobre y oro. La mineralización se formó como precipitación submarina e impregnación dentro de los sedimentos y rocas volcánicas con un control por una falla sin-volcánica.

The Bastar Craton of India is composed of Archaean nuclei of tonalite–trondhjemite–granodiorite gneisses, enveloped by an older granite–greenstone belt (~3000 Ma) with banded iron formation (BIF), and an auriferous younger granite–greenstone belt with BIF. Available geological, geochemical and geochronological data indicate multiple episodes of orogeny with high-grade metamorphism at 3200–3300, 2600–2700, 2100–2200, 1900–2000, 1800–1850, 1500–1600 and 1400–1450 Ma, and continental rifting and basin development marked by emplacement of mafic dyke swarms at c. 2900 (subalkaline mafic dykes; BD-1A), 2480 (high-Mg mafic dykes; BD-1B), 2100 (Fe–tholeiite dykes; BD-2A), 1880 (Fe–tholeiites dykes; BD-2B), 1776 and 1422 Ma. Associations of extensive bimodal volcanics and riftogenic sediments are found in the Neoarchaean and Palaeoproterozoic basins of the craton. Evidence of Palaeoproterozoic (Huronian) glaciation and associated ‘cap carbonate’ followed by deposition of fine clastics with manganese ore is found in the Palaeoproterozoic Sausar Group. The lithological association of the Sausar Group is comparable to the carbonate–tillite association of the Huronian Supergroup, Snowy Pass Supergroup, Transvaal Supergroup and Turee Creek Group. The geological evolution of the Bastar Craton matches that of Western Australia and South Africa. Such similarities can be analysed to develop a unified Palaeoproterozoic assembly for these provinces.

Macedonian ruby, a unique local raspberry-pink variety of this beautiful gemstone is arriving to be steadily exploited in Macedonia as well. The Republic of Macedonia is actually the only country in mainland Europe to have naturally occurring rubies. Macedonian rubies have a unique pale-raspberry color, characteristically pink and red colored corundum crystals. Prismatic crystals of the blue colored variety are rarely found in Macedonia.

This "flipbook", which illustrates the plate tectonic development of the continents and ocean basins during the past 750 million years, was assembled to commemorate the scientific career of Professor Rob van der Voo.  The flipbook consists of 34 plate tectonic reconstructions that map the past location of subduction zones (barbed lines), mid-ocean ridges, (dashed lines), and collision zones (marked x's). The tectonic reconstructions are based on the global plate tectonic model developed by the PALEOMAP Project. 
The latitudinal orientation of the continents is derived largely from paleomagnetic data collected by Professor van der Voo (xref).  Hot spots tracks and sea floor spreading isochrons (Seton et al., 2012) were used to constrain the longitudinal position of the continents back to  ~200 million years.  Plate tectonic reconstructions older than 200 million years are necessarily more speculative and have been derived by combining diverse lines of evidence from the tectonic histories of the continents (e.g., timing of continent-continent collisions or ages of rifting), the distribution of paleoclimatic indicators (i.e coals, tillites, salt deposits, and bauxites, see Boucot et al., 2013), and in some case, the biogeographic affinities of fossil faunas and floras.
Though a diverse data has been used to produce these reconstructions, this data, itself, is not  enough.  So much time has passed and so little direct evidence is preserved that guidance must also be sought from the "Rules of Plate Tectonics".
Plates do not move randomly but evolve in a manner that is consistent with the forces that drive them.  The principal driving forces are: slab pull, ridge push and trench rollback.  These forces shape the plates and provide important insights into how plate boundaries will evolve.  Simply said, plates will only move if they are pulled by a subducting slab or pushed by the forces exerted by a mature ridge system. The evolving plate boundaries have been drawn to follow this maxim.  It is also important to note that plate tectonics is a "catastrophic" system.  Though "slow and steady" is the general rule, once every hundred million years or so, a major plate tectonic reorganization occurs. These "plate tectonic catastrophes" most often occur when mid-ocean ridges are subducted or when major continents collide. (For a more complete listing of the "Rules of Plate Tectonics", the reader is referred to XXXXXX.
The first "continental drift" flipbook was pushed as an undergraduate research project (Scotese, 1974; 1975abc). Subsequent editions have followed (1976ab; 1978; 1979; 1980;  1990, 1991, 1997, 2004). A more complete description of the data and information that is used to produce the flipbooks can be found in Scotese (2004).  These maps could not have been produced without the GPlates plate modelling software and the tectonic data sets published by Dietmar Müller and his team at Earthbytes.
Special thanks to Maggie Geiger, and Robert and Jonathan Scotese for their help assembling this flipbook.

Time Scale
The age given next to each map represents age in millions of years.  The corresponding geological ages (Ogg et al., 2008)  are:
0    Modern World
20 Ma  Early Miocene
40 Ma  late Middle Eocene
60 Ma  Paleocene
80 Ma  Late Cretaceous - Campanian
100 Ma  Early Cretaceous - late Albian
120 Ma  Early Cretaceous - early Aptian
140 Ma  Early Cretaceous - Berriasian
160 Ma  Late Jurassic - Oxfordian
180 Ma  Early Jurassic - Toarcian
200 Ma  Triassic/Jurassic boundary
220 Ma  Late Triassic - Carnian
240 Ma  Middle Triassic - Anisian
260 Ma  Middle Permian - Capitanian
280 Ma  Early Permian - Artinskian
300 Ma  Late Pennsylvanian
320 Ma  Late Mississippian
340 Ma  Middle Mississippian
360 Ma  Devono-Carboniferous
380 Ma  Late Devonian - Frasnian
400 Ma  Early Devonian - Emsian
420 Ma  Late Silurian - Ludlow
440 Ma  Early Silurian - Llandovery
460 Ma  Middle Ordovician
480 Ma  Early Ordovician
500 Ma  Late Cambrian
520 Ma  Middle Cambrian
540 Ma  Cambrian-Precambrian
560 Ma  Neoproterozoic - lt. Ediacaran
600 Ma  Neoporterozoic - m. Ediacaran
630 Ma  Neoproterozoic - e. Ediacaran
660 Ma  Neoproterozoic - e. Ediacaran
690 Ma  Neoproterozoic - lt. Cryogenian
720 Ma  m. Cryogenian
750 Ma  m. Cryogenian


References Cited

Ogg, J., Ogg, G., and Gradstein, F.M., 2008. The Concise Geologic Time Scale, Cambridge University Press, 177 p.
Scotese, C.R. 1974. First Flip Book Images (from 35mm film from PLATO System), Unpublished.
Scotese, C.R., and Baker, D.W., 1975a. Continental drift reconstructions and animation, Journal of Geological Education, 23: 167-171.
Scotese, C.R., 1975b.  Continental Drift Flip Book, 1stedition.Chicago, Illinois. (single page version

Scotese, C.R., 1975c.  Continental Drift Flip Book, 1st edition. Chicago, Illinois. (double page version)
Scotese, C.R., 1976a. Continental
Drift “Flip Book”,  edition 1.5, Department of Geological Sciences, University of Illinois. ResearchGate  Academia
Scotese, C.R., 1976b. A continental drift “flip book", Computers & Geosciences, 2:113-116.
Scotese, C.R., and Ziegler, A.M., 1978. Paleozoic continental drift reconstructions and animation, American Geophysical Union, 1978 Spring Annual Meeting, Eos, v. 59. Issue 4, p. 263.
Scotese, C.R., 1979. Continental Drift (flip book), 2nd edition.
Scotese, C.R., Snelson, S.S., and Ross, W.C., 1980. A computer animation of continental drift, J. Geomag. Geoelectr., 32: suppl. III, 61-70.
Scotese, C.R., 1990. Atlas of Phanerozoic Plate Tectonic Reconstructions, PALEOMAP Progress 01-1090a, Department of Geology, University of Texas at Arlington, Texas, 57 pp.
Scotese, C.R., 1991. Continental Drift Flip Book, 4th edition, PALEOMAP Project, Arlington, TX, 49 pp.
Scotese, C.R., 1997.  Continental Drift Flip Book, 7th edition, PALEOMAP Project, Department of Geology, University of Texas at Arlington, Texas, 80 pp.

Scotese, 2004.
Seton et al., 2012.
Van der Voo,  R., 1993. Paleomagnetism of the Atlantic, Tethys, and Iapetus Oceans, Cambridge University Press, 411 p.

Deciphering the tectonic evolution of Proterozoic Eastern Ghats Mobile Belt (EGMB) is important in the context of modelling the reconstruction of Rodinia and other ancient supercontinents. The polyphase intense ductile deformation in the belt and consequent development of major shear zones, a pervasive strong fabric, regional granulite facies metamorphism locally reaching up to UHT conditions and generation of migmatites is a reflection of its complex tectono metamorphic history. The causative multiple orogenic movements range in age from late Archaean to early Phanerozoic. A general gravity high over the belt and a steep gravity gradient across its boundary with the adjoining Bastar and Singhbhum cratons is one of its characteristic features. Detailed study of meso-to microscopic structural features, thermobarometric estimates and precise dating of tectonic events is limited to only a few sectors. The mobile belt is regarded as a composite high-grade terrane with many subterranes or domains of different geologic and tectonic history which are separated from each other by tectonic boundaries. Major ductile shear zones were described from the western boundary and from within the belt. MEMOIR GEOLOGICAL SOCIETY OF INDIA No. 74, 2008, pp. 63 -87 J.K. NANDA 6 4

An Archaean continent ‘SIWA’, an acronym for South India–Western Australia, comprising the Bastar–Dharwar craton, the Yilgarn craton, the Napier Complex, and the Vestfold Hills has been identified from palaeomagnetic and spatio-temporal data. This assembly was dispersed in three phases with the development of the proto-Indian ocean. The first and second events ~2350 and ~2000 Ma were related to the separation of the Yilgarn craton and the Napier Complex, respectively, to form a proto-Indo-Antarctic ocean and the Cuddapah basin. The proto-ocean was closed ~1650 Ma by the collision of the Lambert Terrane of East Antarctica and the Bastar–Dharwar craton. This collision, associated with ultra-high temperature (UHT) granulite facies metamorphism, is identified in the southern domain of the Eastern Ghats and the Oygardens domain of East Antarctica. The third extensional event between 1500 and 1200 Ma was associated with the separation of the Vestfold Hills block and a second phase of opening of the proto-Indian ocean, and the development of a series of basins on the western side of the Eastern Ghats (the Chhatisgarh, Khariar, Ampani, Indravati, and Sabari basins). The closing of this ocean basin during the Eastern Ghats–Rayner orogeny at ~950 Ma was related to the amalgamation of India and East Antarctica to form the supercontinent Rodinia. During the Neoproterozoic, this part of Rodinia was involved in orogenic collapse/extension and deposition of the Sodruzhesvo Group. The Pan-African Prydz Bay orogeny at ~550 Ma caused the closing of the basin to form East Gondwanaland.

The Precambrian rocks of the Mansar area, Nagpur district, Maharashtra, belong to the Sausar Group and the Tirodi Gneiss. Both these lithological units show an unconformable relation in the area, marked by a conglomerate at the base of the Sausar Group. The metasediments of the Sausar Group bear imprints of polyphase deformation. The folds of the first generation (F1) are isoclinal with high amplitude to wavelength ratios and pervasive axial planar cleavage (S1). The structures of the second generation are represented by WNW-ESE trending upright isoclinal folds (F2) and axial planar crenulation cleavage (S2). Gentle upright folds with NE-SW striking axial planes represent structures of the third generation (F3). Superposition of F2 folds on F1 folds is marked by mushroom shaped interference pattern in small-scale. Because of upright isoclinal nature of F2 folds on WNW-ESE striking axial planes, the metasedimentary bands extend in E-W direction. Slight arcuate geometry of the metasedimentary bands is the result of superposition of F3 folds on F1 /F2 folds.

The Great Oxidation Event (GOE) is one of the most significant changes in seawater and atmospheric chemistry in Earth history. This rise in oxygen occurred between ca. 2.4 and 2.3 Ga and set the stage for oxidative chemical weathering, wholesale changes in ocean chemistry, and the evolution of multicelluar life. Most of what is known about this important event and the subsequent oxygenation history of the Precambrian Earth is based on either geochemistry or "data mining" published literature to understand the temporal abundance of bioelemental sediments. Bioelemental sediments include iron formation, chert, and phosphorite, which are precipitates of the nutrient elements Fe, Si, and P, respectively. Because biological processes leading to their accumulation often produce organic-rich sediment, black shale can also be included in the bioelemental spectrum. Thus, chemistry of bioelemental sediments potentially holds clues to the oxygenation of the Earth because they are not simply recorders of geologic processes, but intimately involved in Earth system evolution.

Reconstruction of the Neoproterozoic supercontinent Rodinia shows near neighbour positions of the South Indian Cratons and Western Australian Cratons. These cratonic areas are characterized by extensive Paleoproterozoic tectonism. Detailed analysis of the spatio-temporal data of the Satpura Mountains of India indicates presence of at least three episodes of Proterozoic orogeny at ~2100-1900 Ma, ~1850 Ma and ~1650 Ma, and associated basin development and closing. A subdued imprint of the Grenville orogeny (~950 Ma) is also found in rock records of this Mountain Belt. The Capricorn Orogen of Western Australia also shows three episodes of orogeny: Opthalmian-Glenburgh Orogeny (2100-1950 Ma), Capricorn Orogeny (~1800 Ma) and Mangaroon Orogeny (~1650 Ma), and basin opening and closing related to these tectonic movements. These broad similarities suggest their joint evolution possibly in a near neighbour position during Paleoproterozoic Era. In view of juxtaposition of the Western Australia along the east coast of India, at the position of the Eastern Ghats, during Archean, it is suggested that the breaking of this Archean megacraton at ~2400 Ma led to northward movement of the broken components and formation of the Satpura-Capricorn Orogen (at ~2100 and ~1800 Ma) due to the collision of cratonic blocks with the pre-existing northern cratonic nuclei of India and Western Australia. This is also the time of formation of the supercontinent Columbia. A phase of basin opening followed the ~1800 Ma event, followed by another phase of collisional event at ~1600 Ma at the site of the Satpura-Capricorn Orogen. Subsequent evolutions of the Satpura and the Capricorn Orogens differ slightly, indicating separate evolutional history.

The Satpura Mountain Belt (also referred as Central Indian Tectonic Zone in recent literature) forms an important morphotectonic unit in the central part of India. Some of the recent workers have reported an orogenic event at ~1000–900 Ma (termed ‘‘Sausar orogeny”) which led to amalgamation of the North Indian Block and the South Indian Block and formation of the Satpura Mountain Belt. In this model the stratigraphic relations of two important lithostratigraphic units on either side of the Satpura Mountain Belt (the Sausar Group in the south and the Vindhyan Supergroup on the north) are suggested to be revised from previously held ideas. Critical analyses of available published work in the region to assess the status of the Sausar Group vis a vis the Vindhyan Supergroup was carried out. It is found that the ideas proposed by the recent workers stem from an earlier interpretation that the Sausar Group has monocyclic evolution and the earliest fabric in the Sausar Group is marked by a schistosity with EW strike. Re-mapping of the gneissic rocks and adjacent matasedimentary rocks of Khawasa, Deolapar, and Kandri–Mansar areas revealed presence of gneissic rocks and granulites of two generations, and of four phases of superposed deformations in the metasediments and gneisses. The older gneisses and granulites constitute the basement over which the rocks of the Sausar Group were deposited; and the younger gneisses developed by metamorphism and migmatisation of the rocks of the Sausar Group. The latter types are found in the Khawasa–Ramakona areas. Contrary to the belief of the recent workers that no volcanic activity is present in the Sausar Group, volcanic rocks marked by amygdular basic flows and tuffs have been mapped from different parts of the Sausar Group. Migmatisation and metamorphism of these volcanic rocks (of the Sausar Group) have given rise to amphibolites and granulites in Khawasa and Ramakona areas. Therefore, the use of fabric patterns in these areas to suggest that the granulite facies metamorphism in the Ramakona–Katangi granulite domain was pre-Sausar in age is debatable. Available geochronological data of the Satpura Mountain Belt and its eastward continuation into the Chhotanagpur Gneiss terrain indicate that the basement and cover rocks of these areas were subjected to multiple deformation and metamorphic episodes of similar style and nature. The earliest deformation and metamorphism of the rocks of the Sausar Group and its equivalent rocks to the east took place at ~2100–1900 Ma. The regional EW trend of the belt developed during the second deformation at ~1800–1700 Ma and again at ~1600–1500 Ma. This deformation was accompanied by migmatisation and granulite facies metamorphism in the northern domain of the Sausar Belt and in the Chhotanagpur Gneiss region. Late phase low intensity deformations in the region were associated with thermal events at ~1100–1000 Ma and ~900–800 Ma. The ~EW trending fabric, referred as ‘‘Satpura orogenic trend” in Indian literature marks a major compressional tectonic event, developed during the second deformation of the Sausar Group. This has its counter part in Western Australia as the Capricorn orogeny (~1780–1830 Ma). The development of the Satpura Mountain Belt during the Grenvillian orogeny is ruled out from the synthesis of event stratigraphic data of the region and from its comparison with the Western Australian Craton.

Detailed mapping of the Sausar Group around Kandri Mines, Nagpur district, Maharashtra, shows that the rocks of the area have been involved in folding of three generations. The metasedimentary bands in the Kandri Mines and the surrounding area show an arcuate outcrop that closes northwest. The bedding and schistosity strike ~ E-W in the northern part of the mine. The orientation gradually changes from E-W through NE-SW to N-S in the central part and NW-SE to NE-SW in the southern part of the mine. This variation defines a synformal fold of second (F2) generation (syncline near Kandri Mines), with WNW-ESE axial trace. The axial trace of the regional F2 fold of the Kandri area coincides with that of the Ramtek area when extrapolated over the soil cover. The terminations of the manganese-ore bands of the Kandri Mines and Mansar Mines are the result of original sedimentary facies change.

The emergent salt domes of the United Arab Emirates (UAE) have been investigated in detail and examples from central Oman have been studied for comparison. The salt domes contain exotic clasts of igneous, sedimentary and low-grade metamorphic rocks of the Arabian basement that have been brought to the surface from depths of over 8 km. The clasts thus provide an opportunity to examine the lithology, geochemical composition and age of the "basement" underlying this part of eastern Arabia, where no other outcrops are available for direct study. Five volcanic rocks give consistent latest Ediacaran U-Pb zircon crystallisation dates of ca. 560-545 Ma, with Neoproterozoic, Palaeoproterozoic and Neoarchaean ages of inherited zircons. These rocks, although strongly altered, preserve geochemical characteristics compatible with formation in a within-plate, extensional setting along the northern edge of Gondwana, adjacent to Prototethys. U-Pb analyses of detrital zircons in sedimentary and low-grade metamorphic rocks indicate deposition younger than ca. 597 Ma in UAE and <734 Ma in Oman. The two UAE sedimentary rocks may correlate with the Shuram and Khufai Formations of the Nafun Group (Huqf Supergroup) in Oman. Like the volcanic rocks, the two sedimentary samples from the UAE show derivation from the erosion of Neo-, Palaeoproterozoic and Neoarchaean sources. These sources could be from the Arabian basement itself or from other basement blocks such as those embedded in present-day Iran and Afghanistan, the precise whereabouts of which in Neoproterozoic times remains somewhat uncertain. The zircon age spectra of samples from the UAE show Neoproterozoic age peak characteristics of sources from both the western and eastern Arabian basement blocks, indicating that the two segments were juxtaposed by about 597 Ma, the maximum age of their deposition.

The mechanisms of growth and destruction of continental lithosphere have been long debated. We define
and test a unifying plate tectonic driving mechanism that explains the numerous petrological, geophysical,
and geological features that characterize the destruction of cratonic lithospheric roots. Data from three
Archean cratons demonstrate that loss of their roots is related to rollback of subducted flat slabs, some
along the mantle transition zone, beneath the cratons. During flat slab subduction dehydration reactions
add water to the overlying mantle wedge. As the subducting slabs roll back, they suck in mantle material
to infill the void space created by the slab roll back, and this fertile mantle becomes hydrated. The roll-back
causes concomitant lithospheric thinning of the overlying craton so the flux of newly hydrated mantle material
inevitably rises causing adiabatic melting, generating new magmas that gradually destroy the roots of the
overlying craton through melt–peridotite reactions. Calculated fluxes of new mantle material beneath cratons
that have lost their roots range from 2.7 trillion to 70 million cubic kilometers, which is sufficient to generate
enough melt to completely replace the affected parts of the destroyed cratons. Cratonic lithosphere may be
destroyed in massive quantities through this mechanism, warranting a re-evaluation of continental growth
rates with time.

Sedimentological insights underpin many of the important recent advances in understanding of Earth system behaviour in the Neoproterozoic Era. This article reviews three main areas: (i) chemical proxies and their preservation, with emphasis on carbonate facies; (ii) glacial and post-glacial facies, including their age constraints; (iii) sedimentary evidence for biotic innovations and responses. Chemostratigraphy plays an important role in ordering Neo-proterozoic events and defining disturbances to the carbon cycle. There is increasing attention being paid to assessing the role of diagenetic origination or modification of chemostratigraphic signals. Alongside this, new criteria for identifying primary dolomite and precursor metastable phases such as ikaite have been developed. In respect of oxygenation, geochemical proxies substantiate the concept of a Neoproterozoic Oxygenation Event as a very gradual transition, the ocean being at any one time a heterogeneous assemblage of ferruginous, sulphidic and oxic conditions, with some evidence of increasing deep-sea oxidation through the Ediacaran Period. Techniques such as Fe-speciation need to be supplemented with proxies sensitive to suboxic conditions. More generally, it is predicted that petrographically constrained microanalytical studies will also become more important in reconstructing palaeoenvironmental conditions. The global distribution of Neoproterozoic glacial deposits combined with palaeomagnetic evidence supports the concept of panglaciations in which ice sheets reached sea-level in the tropics. Advances in radiometric dating have demonstrated the synchronous onset of global (Sturtian) glaciation at 717 Ma and the demise of a second (Marinoan) glaciation at 635 Ma, and plausibly indicate long durations for each (55 Myr for Sturtian and 5 to 15 Myr for Marinoan). However, a compilation of radiometric dates indicates ambiguities indicating the need for further improvements to the radiometric and Sr-isotope database to understand events within the Sturtian time frame, the timing of onset of Marinoan glaciations, and the age and synchroneity of individual negative d 13 C anomalies. Sturtian deposits are typically thick, rift-related successions containing a range of environments influenced or dominated by dynamic glaciers , as well as ice-free marine intervals. Marinoan glacial deposits, by contrast , tend to be thin and continental. During the latter interval, oxygen isotope systematics of sulphate demonstrate that atmospheric CO 2 was high, as predicted by Snowball Earth theory, and that sedimentation was influenced by orbital forcing. The Sturtian record, by comparison, needs to be searched for evidence of cold-climate hiatuses on the one hand and orbital forcing on the other. Cap carbonate formation appears to have coincided with rising sea-levels following panglaciations. Snowball theory considers that they formed rapidly in the postglacial greenhouse, but an alternative 253

New geologic mapping, lithofacies and granulometric analysis, and geochemistry from the volcano-sedimentary
successions of the central part of the Bas Draâ inlier, Western Anti-Atlas, constrain the Ediacaran
Ouarzazate Supergroup evolution during the post-collisional stage of the Pan-African orogeny.
Volcanosedimentary facies analysis is the key aspect of the present contribution. We distinguished sixteen
terrestrial volcanosedimentary lithofacies in the Bas Draâ succession (BDS), which reaches a total
thickness of 2000 m. BDS evolution can be grouped into four units (Aouinet Aït Oussa I to IV, AO I–AO
IV). The earliest volcanic activity produced rhyolitic ignimbrite sheets (AO I), which had been considered
as lava flows by previous workers, and which were presumably related to caldera system(s). During AO II,
a complex of high-silica andesitic and rhyolitic lavas formed, punctuated by the explosive eruption of a
high-temperature silica-rich magma leading to the formation of parataxitic ignimbrite. AO III consists of
basalt and andesite lava fields and small explosive, in parts phreatomagmatic volcanic vents. It is dissected
by fluvial systems depositing external non-volcanic and local volcanic debris. BDS evolution terminated
with the formation of a large SiO2-rich lava dome complex (AO IV), accompanied by small
basalt effusive event. Volcanosedimentary facies analysis infers that the BDS evolved in a continental
extensional setting developing in a low topography under humid paleoclimatic conditions. Alteration
textures are dominated by a piemontite–calcite–albite–quartz (+ iron oxides) assemblage.
Chemical analysis of BDS volcanic and subvolcanic rocks belongs to high-k calc-alkaline and alkali-calcic
to alkaline magmatic trend typical for a post-collision setting. Trace elements spidergrams show a pattern
typical for subduction-related suites of orogenic belts. REE patterns show moderate enrichment in
LREE relative to flat HREE, with strong negative Eu anomaly in rhyolitic rocks. Geotectonic diagrams suggest
an affinity transitional between subduction- and within-plate settings. BDS magmatism can be
explained by a magma source enriched in inherited components from Pan-African subduction. Volcanosedimentary
facies, structural features, geochemical composition and radiometric data of BDS suggests
correlation with the upper Ouarzazate Supergroup of the Anti-Atlas. Geodynamic evolution of the BDS
was an expression of an extensional setting that operated in northern Gondwana margin precursory to
the Cambrian anorogenic volcanic activity

Precambrian metasediments of Parseoni area belong to the Sausar Group. These comprise of quartzite, mica schist with manganese ore and marble. The metasediments of the area show evidence of three phases of folding. The early folds (F1) are isoclinal with an axial planar cleavage (S1). The second folds (F2) are tight to isoclinal with axial planar crenulation cleavage (S2). These F2 folds have EW striking vertical axial planes and congruous pucker axis lineations. The third folds (F3) are open upright with NS striking axial planes. An antiformal F2 fold plunging E is mapped in the area. In the absence of any primary top-and-bottom criteria the stratigraphic succession for the area suggested by earlier workers is debatable.

The Neoproterozoic basement of Wadi Al-Baroud area located at the northern Eastern Desert (ED) of
Egypt, at the northernmost segment of the Arabian–Nubian Shield (ANS), is comprised of two different
granite suites. A large batholith ascribed to the Older Granite suite, extends across the boundary between
the northern and central ED, and is intruded by two isolated plutons of the Younger Granite suite. The
Older Granite suite includes gray-colored, massive to gneissose, granodiorites to tonalites typically containing
microgranular mafic enclaves. These are calc-alkaline, magensian, metaluminous I-type granitoids,
with high Sr contents, and depleted in Rb, Nb, Y and REE. The Younger Granite suite plutons are
pink to red, biotite and two-mica monzogranites. These are peraluminous A-type granites exhibiting a
high-K calc-alkaline nature, and varying between ferroan and magnesian type granites. The A-type granites
of the Younger Granite suite are enriched in Ga, Y, HFSE and REE elements, and depleted in the LILE
elements Ba, Sr and Rb and transition metals Cr, Ni, Co, Sc and V. Magmatic saturation temperatures indicate
early crystallization of apatite at high temperature in the metaluminous I-type Older Granite suite,
while in the peraluminous A-type Younger Granites its crystallization occurs later after separation of zircon
and monazite. The plutons of the Younger Granite suite were generated during the post-collisional
stage of the northern ANS, following collision between the juvenile ANS crust and the pre-Neoproterozoic
continental blocks of west Gondwana. The emplacement of the Older Granite suite took place earlier,
within a normally mature continental arc prior to the collision. These pre-collision granitoids evolved
through assimilation-fractional crystallization processes from mantle-derived parental magmas, which
have interacted with crustal materials during ascent and storage. The post-collisional Younger Granite
suite seems to have been derived by high degree, partial melting of metasedimentary sources, particularly
psammitic and pelitic metasediments.

Around Salumbar in the Udaipur district, Rajasthan, the Banded Gneissic Complex (BGC), the Aravalli metasedimentary rocks, the Dudar Gneiss and the Lakapa Granite Gneiss have been involved in the same style and sequence of multiple deformation. The oldest rocks are the migmatites forming the BGC, which underlie the Aravalli metasediments with an unconformity marked by a conglomerate. Rare relict pre-Aravalli structures in the BGC, and the conglomerate containing gneissic pebbles provide incontrovertible evidence for a part of the BGC being the original basement. Identical structural style and sequence of the basement gneisses with those of the meta-sedimentary cover rocks, however, point to mobilization so that they could take part in the earliest deformation affecting the metasediments in a ductile manner. The Dudar Gneiss has formed by migmatization of the Aravalli rocks synkinematically with the first deformation, whereas the Lakapa Granite Gneiss has been emplaced as a syn-to late-tectonic intrusion.

A review and comparison of the tectonic history of the North China and Slave cratons reveal that the two cratons have
many similarities and some significant differences. The similarities rest in the conclusion that both cratons have a history of a
Wilson Cycle, having experienced rifting of an old continent in the late Archean, development of a rift to passive margin
sequence, collision of this passive margin with arcs within 100–200 Ma of the formation of the passive margin, reversal of
subduction polarity, then eventual climactic collision with another arc terrane, microcontinental fragment, or continent. This
cycle demonstrates the operation of Paleozoic-style plate tectonics in the late Archean. The main differences lie in the later
tectonic evolution. The Slave’s post-cratonization history is dominated by subduction dipping away from the interior of the
craton, and later incorporation into the interior of a larger continent, whereas the North China Craton has had a long history of
subduction beneath the craton, including presently being located above the flat-lying Pacific slab resting in the mantle transition
zone, placing it in a broad back-arc setting, with multiple mantle hydration events and collisions along its borders. The hydration
enhances melting in the overlying mantle, and leads to melts migrating upwards to thermochemically erode the lithospheric
root. This major difference may explain why the relatively small Slave craton preserves its thick Archean lithospheric root,
whereas the eastern North China Craton has lost it.

Understanding the geologic history and position of the North China craton in the Paleoproterozoic Columbia supercontinent has proven
elusive. Paleoproterozoic orogenic episodes (2.00–1.85 Ga) are temporally associated with ultimate stabilization of the North China craton (NCC),
followed by the development of extensive craton-wide rift systems at 1.85–1.80 Ga. The age difference between the sedimentary cover and the
metamorphic basement is up to 500–700 Ma, suggesting that uplift and doming of cratonic basement occurred in the latest Paleoproterozoic.
Mafic dike swarms (1.80–1.77 Ga) and anorogenic magmatism (1.80–1.70 Ga) record the extensional breakup and dispersal of the North China
craton during this stage. The late Paleoproterozoic tectonic framework and geological events documented provide important constraints for
reconstruction of the NCC within the Late Paleoproterozoic supercontinent of Columbia.
An east-west striking thousand kilometer long belt of khondalites (granulite faciesmetapelites) stretches along the northernmargin of the North China
craton, on the cratonward side of the Northern Hebei orogenic belt. This granulite belt includes Mg–Al (sapphirine bearing) granulites that reached
ultrahigh-temperature “peak” metamorphic conditions of ∼1000 °C at 10 kbars at 1927±11 Ma. Following peak ultrahigh-temperature conditions, the
rocks underwent initial isobaric cooling and subsequent isothermal decompression, and these trajectories are interpreted to be part of an overall anticlockwise
P-Tevolution indicating that the northernmargin of the craton experienced continental collision at 1.93–1.92 Ga. The position of the khondalite
belt south of the Northern Hebei orogenic belt makes it analogous to Tibet, a continental collision-related plateau characterized by double crustal
thicknesses and granulite facies metamorphism at depth.We suggest that the tectonic evolution of the NCC during this period was closely related to the
assembly and break-up of the Columbia supercontinent, and that the NCC was adjacent to the Baltic and Amazonian cratons in the period 2.00–1.70 Ga.
Craton-wide extension occurred within 100–150 Ma of collision along the northern margin of the craton at 1.93–1.92 Ga. It is concluded that mantle
upwellings are chiefly responsible for the breakup of the NCC from the Paleoproterozoic supercontinent.

Soapstone deposits on the Belcher Islands are a product of intrusion of the Haig gabbro sills as part of 1960 ±160Ma plume-related volcanic events. Multiple sills intruded into wet sedimentary units underlying the Flaherty pillow basalts. Evidence of autohydration of sills include the uralitization and chloritization of pyroxene, epidotization, saussuritization and calcite replacement of plagioclase, and leucoxenization of ilmenite. Autohydration accompanied subsolidus cooling of 1000°C gabbro sills to under 400°C under low 2kbar pressure conditions.

The Sausar Group of Palaeoproterozoic age comprises a thick sequence of carbonate-quartzite-psammopelitic rocks. These rocks have undergone polyphase deformation. The regional E-W to ENE¬-WSW alignment of the belt is found to be the effect of second deformation. Synthesis of published geological, geophysical and geochronological data indicates extensive weathering and erosion of a basement complex, Tirodi Gneiss, with development of palaeosol between 2.5 to 2.2 Ga. The deposition of the sediments forming Sausar Group took place during the period 2.2 to 1.8 Ga, with evidence of glaciogenic condition at the basal part. Earliest deformation and metamorphism of the Sausar Group took place during Satpura Orogeny at ~1.8 Ga. Subsequent deformation, metamorphism and remobilisation of the entire Satpura belt took place during the period 1.5-1.4 Ga, 1.0-0.9 Ga and 0.6-0.5 Ga.

A detailed examination of lithostratigraphic, tectonothermal, geochronologic and palaeomagnetic database of the Dharwar–Bastar cratons of South India, the Yilgarn craton of Western Australia and the East Antarctic shield has shown broad similarity. Two palaeomagnetic key poles of ~2400 Ma age from the Dharwar and Yilgarn cratons suggest near neighbor positions. Matching patterns of craton outlines, orientation of mafic dyke swarms and palaeo–north direction for ~2400 Ma have established a continental assembly of “SIWA”, an acronym for South India (SI) and Western Australia (WA), at ~2400 Ma. In this assembly the Yilgarn craton fits against the Bastar craton and the Singhbhum craton. The available geological data from the Napier Complex of the Eastern Antarctica and the Dharwar craton of South India were used to prepare the barcode style reconstruction of Archaean tectonostratigraphic events of both the cratons. The method of matching continental outlines, the internal features of two continental blocks and the palaeomagnetic data demonstrate that the Napier Complex was also a part of “SIWA” during the period 2200–1900 Ma and was located at the position of the Cuddapah basin of India adjacent to the Dharwar craton and the Yilgarn craton. The separation of the Napier Complex from the south Indian block led to the development of the Cuddapah basin at ~1950 Ma.

Geological history from the late Palaeoproterozoic to early Neoproterozoic is dominated by the formation of the supercontinent Columbia, and its break-up and re-amalgamation into the next supercontinent, Rodinia. On a global scale, major orogenic events have been tied to the formation of either of these supercontinents, and records of extension are commonly linked to break-up events. Presented here is a synopsis of the geological evolution of southwest Fennoscandia during the ca. 1.9–0.9 Ga period. This region records a protracted history of continental growth and reworking in a long-lived accretionary orogen. Three major periods of continental growth are defined by the Transscandinavian Igneous Belt (1.86–1.66 Ga), Gothian (1.66–1.52 Ga), and Telemarkian (1.52–1.48 Ga) domains. The 1.47–1.38 Ga Hallandian–Danopolonian period featured reorganization of the subduction zone and over-riding plates, with limited evidence for continental collision. During the subsequent 1.38–1.15 Ga interval, the region is interpreted as being located inboard of a convergent margin that is not preserved today and hosted magmatism and sedimentation related to inboard extensional events. The 1.15–0.9 Ga period is host to Sveconorwegian orogenesis that marks the end of this long-lived accretionary orogen and features significant crustal deformation, metamorphism, and magmatism. Collision of an indenter, typically Amazonia, is commonly inferred for the cause of widespread Sveconorwegian orogenesis, but this remains inconclusive. An alternative is that orogenesis merely
represents subduction, terrane accretion, crustal thickening, and burial and exhumation of continental crust, along an
accretionary margin. During the Mesoproterozoic, southwest Fennoscandia was part of a much larger accretionary orogen
that grew on the edge of the Columbia supercontinent and included Laurentia and Amazonia amongst other cratons. The
chain of convergent margins along the western Pacific is the best analogue for this setting of Proterozoic crustal growth and
tectonism.