Description: Publication date: Available online 23 December 2014 Source: Precambrian Research Author(s): Dewashish Upadhyay , Sabyasachi Chattopadhyay , Ellen Kooijman , Klaus Mezger , Jasper Berndt

Description: Publication date: Available online 19 December 2014 Source: Precambrian Research Author(s): Rajat Mazumder , Martin J. Van Kranendonk , Wlady Altermann Although no unambiguous biogenic criteria exist to discriminate Precambrian shallow-marine succession s from fluvial deposits, physical sedimentological evidence, including an association of primary sedimentary structures and texture s , stratigraphic position, and comparison with Phanerozoic and Modern examples has been found useful in identifying these deposit types. Our high resolution sedimentary facies analysis coupled with new mapping clearly indicates shallow-marine to beach-aeolian to fluvial sedimentation in the Paleoproterozoic Koolbye Formation of the Turee Creek Group, Western Australia. A falling stage systems tract within the Koolbye Formation has been documented. Our sedimentary facies analysis in combination with sedimentological analysis of the underlying Kungarra Formation indicates development of at least three falling stage systems tracts within the Turee Creek Group across the rise of atmospheric oxygen (the Great oxidation event). Graphical abstract

Description: Publication date: Available online 18 December 2014 Source: Precambrian Research Author(s): Alfredo Camacho , Richard Armstrong , Donald W. Davis , Andrey Bekker The Centralian Superbasin is a concept connecting Neoproterozoic successions that presently occur in separate structural basins in central Australia into a once-continuous depositional system. The superbasin is thought to have been initiated ∼830 Ma, coevally with the breakup of Rodinia, by a mantle plume centred under the central Adelaide Geosyncline, South Australia. The superbasin is thought to deepen towards the south with the basal sediments mainly sourced from the Arunta Region in the north, and blanketing the crystalline Musgrave Block to the south. Our results suggest that deposition in the Amadeus Basin, the most studied of these intraplate basins that made up the superbasin, began ∼1040 Ma ago (assembly of Rodinia; about 200 Ma earlier than previously suggested) in association with a mantle plume that formed the Warakurna large igneous province. Moreover, we argue for a two stage opening of the Amadeus Basin, one starting at ∼1040 and the other at ∼800 Ma, and a long stratigraphic break(s) within supersequence 1. The basal units of Supersequence 1 in the southern Amadeus Basin yield detrital zircon U-Pb age populations consistent with derivation from the Musgrave Block, which must have been emergent at the time. Our data support the correlation between the basal Neoproterozoic units of the Amadeus Basin (Heavitree Quartzite and Bitter Springs Formation) and the Succession B in western North America, consistent with paleogeographical reconstructions placing Australia to the west of North America after the assembly of Rodinia and before its breakup. Furthermore, our study brings into question the existence of the Centralian Superbasin because Supersequence 1 sedimentary rocks do not belong to a single depositional system.

Description: Publication date: January 2015 Source: Precambrian Research, Volume 256

Description: Publication date: Available online 12 December 2014 Source: Precambrian Research Author(s): Henry C. Halls , Alan Lovette , Mike Hamilton , Ulf Söderlund A paleomagnetic study of the western end of the ∼585 Ma Grenville dyke swarm shows that individual dykes are characterized by high coercivity and unblocking temperature magnetizations that can differ in direction by as much as 90°. Field tests including baked contact studies and the continuity of paleomagnetic direction along dyke strike, suggest that the magnetizations are primary. Precise U-Pb baddeleyite dating on these dykes indicates that changes in magnetization direction of ∼90° occur in less than 4 million years, and their close temporal association with reversals of the axial dipole field suggest that certain dykes are recording an equatorial dipole field as a transitional field between opposite polarity states. The documented instability in the Earth's field occurs less than 10 Myr before the first recorded appearance of macroscopic multi-cellular organisms on Earth, inviting speculation that an extended period of frequent magnetic reversals may play a part in faunal evolution.

Description: Publication date: January 2015 Source: Precambrian Research, Volume 256 Author(s): Martin J. Van Kranendonk , Rajat Mazumder , Kosei E. Yamaguchi , Koji Yamada , Minoru Ikehara This paper presents the first, detailed sedimentological analysis of the Paleoproterozoic Kungarra Formation, the lowermost of three formations comprising the Turee Creek Group in Western Australia, which was deposited across the rise in atmospheric oxygen (the Great Oxidation Event, or GOE) and the transition from early to modern Earth. The data show that the Kungarra Formation has a gradational, conformable lower contact with underlying banded iron-formation of the Hamersley Group and predominantly comprises an upward-shallowing succession from deepwater shales and siltstones, through rippled fine-grained sandstones and stromatolitic carbonates, to tidal flat deposits that immediately underlie coastal–fluvial deposits of the overlying Koolbye Formation. At the base of the Kungarra Formation is a gradual transition from alternating units of magnetic green shale and thin units of banded iron-formation that pass upsection to units of non-magnetic shale and ferruginous chert and grey chert, reflecting a gradual loss of iron from the world's oceans accompanying the rise of atmospheric oxygen. A falling stage system s tract is recognised above this transition in the Hardey Syncline area, capped by stromatolitic carbonates and a period of exposure marked by an erosional unconformity and carbonate beachrock. Two glacio-eustatic cycles are recognised within the middle to upper parts of the Kungarra Formation, each of which is marked by the rapid onset of falling systems tracts and characterised by falling systems tracts during and following diamictite deposition. Stratigraphic data are used to infer a depobasin filled by a sediment wedge prograding from southeast to northwest, in contrast to previous models of a north-northeastward deepening foreland basin. The lack of seismites or internal unconformities within the formation precludes a foredeep setting. Rather, deposition is interpreted as having occurred within an intracratonic basin, with detritus sourced from erosion of uplifted bedrock to the southeast.

Description: Publication date: Available online 10 December 2014 Source: Precambrian Research Author(s): Yun Li , Peng Peng , Xinping Wang , Haozheng Wang Several late Paleoproterozoic (1800-1600 Ma) mafic dyke swarms in the North China Craton (NCC), including the ca. 1780 Ma Taihang, ca. 1730 Ma Miyun, ca. 1620 Ma Taishan, and a newly recognized ca. 1680 Ma Laiwu swarm of this study, are compared. The newly defined Laiwu swarm contains tens of NNW-trending dykes, with widths of 10-40 m and lengths of up to 10 km in the Taishan Mts. in the eastern part of the NCC. Baddeleyites from a Laiwu dyke analyzed on a CAMECA SIMS 1280 machine yield a 207 Pb/ 206 Pb weighted average age of 1680 ± 5 Ma. In the Taishan Mts., there are also ca. 1620 Ma dykes, which consist of several ∼30 m-wide NNW- and NE-trending dykes. Both the Laiwu and Taishan dykes have a similar mineral assemblage of mainly clinopyroxene, plagioclase and Fe-Ti-oxides, except that the Laiwu dykes are coarser-grained and contain more volumes of plagioclase and Fe-Ti-oxides. Both swarms are compositionally tholeiitic, and exhibit significant enrichment in light rare earth elements (Laiwu: (La/Yb) N = 5.2-9.2; Taishan: (La/Yb) N = 2.3-3.4) and large ion lithophile elements, but variable depletion in high field-strength elements. Their similarity in ɛ Nd (t = 1680 Ma) values (from -2 to +2) and trace element patterns indicate that they may have originated from a common slightly depleted source with various degrees of fractionation. These features are more or less similar to those of the ca. 1730 Ma Miyun dykes, which were thought to be derived from paleo-plume, but distinguishable from the ca. 1780 Ma Taihang dykes, which were generated from the sub-continental lithospheric mantle (SCLM) of the NCC. Thus the Laiwu-Taishan series was derived either from the SCLM, which was (partially) rejuvenated prior to 1680 Ma, or from a region other than the SCLM. The first possibility is favored as younger mafic igneous products from the SCLM show consistent characteristics with the Laiwu-Taishan series. This rejuvenation of the SCLM could be due to an upwelling of asthenosphere during the delamination of a Paleoproterozoic orogen or alternatively a plume process at ca. 1730 Ma.

Description: Publication date: February 2015 Source: Precambrian Research, Volume 257 Author(s): Renaud Soucy La Roche , Félix Gervais , Alain Tremblay , James L. Crowley , Gilles Ruffet This study investigates the tectono-metamorphic history and exhumation mechanisms of the mid-crustal Mékinac-Taureau domain of the Mauricie area, central Grenville Province. Macro- and micro-structural analyses reveal the top-down-to-the-ESE sense of shear on the eastern Taureau shear zone, a major extensional structure that exhumed the mid-crustal Mékinac-Taureau domain and juxtaposed it against the lower grade rocks of the Shawinigan domain. Peak metamorphism in the Mékinac-Taureau domain, inferred to be the result of northwestward thrusting and regional crustal thickening, took place under P – T conditions of 1000–1100 MPa and 820–880 °C prior to 1082 ± 20 Ma. Retrograde conditions varying from 775 to 675 °C and from 800 to 650 MPa were registered in its upper structural levels prior to and/or during shearing along the eastern Taureau shear zone that was active at 1064 ± 15 Ma. The Shawinigan domain records P – T conditions ranging from 850 to 625 MPa and from 775 to 700 °C, P – T values that are similar to or slightly lower than those for retrogressed samples from the upper structural levels of the Mékinac-Taureau domain, but clearly lower than the peak metamorphism values of the latter domain. Finally, the area cooled below 550–600 °C at ∼1000–1030 Ma and below 450 °C at ∼900–970 Ma on the basis of 40 Ar/ 39 Ar geochronology on amphibole and biotite. Structural and metamorphic characteristics of the Mauricie area are similar to those expected from a metamorphic core complex formed during post-convergence orogenic collapse in a gravity-driven fixed-boundary mode. The Mékinac-Taureau and Shawinigan domains were thus probably exhumed by a similar process, which supports the orogenic collapse model recently proposed to explain the exhumation of mid-crustal metamorphic core complexes in the Grenville Province.

Description: Publication date: Available online 10 December 2014 Source: Precambrian Research Author(s): M.E. Bickford , W.R. Van Schmus , K.E. Karlstrom , P.A. Mueller , G.D. Kamenov The origin and tectonic setting of the Mesoproterozoic (1.50-1.34 Ga) Granite-Rhyolite Provinces of the midcontinent region of the United States, and the coeval A-type granite plutons of the southwestern United States, have been an enigma for decades. In this paper we review the history of this problem, examine the significance of a wealth of previously published U-Pb zircon and whole-rock Sm-Nd data, and present new U-Pb zircon age and Lu-Hf isotopic data from selected zircon samples. Our data show that the initiation of this magmatism spans the interval 1.50 to 1.40 Ga across the continent, but there is a general younging westward. Younger, 1.39 to 1.34Ga magmatism also occurred across the continent, but forms a major magmatic event only in the south-central mid-continent. There is generally a good correlation between Sm-Nd and Lu-Hf isotopic compositions and inferred mantle derivation model ages, except possibly in southeastern Oklahoma. The absence of older cores in zircons is compatible with calculated zircon saturation temperatures of ca. 850 °C, and supports mantle-driven basaltic underplating and resulting crustal partial melting as a petrogenetic model for the A-type magmatism. Our new data compilation refines the existence of the “Nd-line” that extends from southwestern Texas into southeastern Michigan and the western Grenville Province in Canada; it marks an isotopic boundary between granites and rhyolites of cratonal origin to the northwest (1.8-1.6 Ga model ages) and those of more juvenile origin to the southeast (1.5-1.4 Ga model ages). Our suggested tectonic model for the Mesoproterozoic A-type magmatism across eastern and southern Laurentia involves the development of an active Laurentian margin extending from eastern Canada, across what is now the midcontinent region of the United States, and at least into the current southwestern United States. Magmatism along this margin was likely related to asthenosphere-lithosphere interactions associated with the accretion of outboard arcs and possible exotic terranes that caused complex deformational and magmatic responses in the continental interior. This activity evidently spread from northeast to southwest over a period of ca. 70 million years. The occurrence of the younger, ca. 1.39-1.34 Ga event indicates that similar processes occurred some 130 million years later, suggesting a long-lived convergent plate margin and recurring basaltic underplating in some locations, perhaps due to inboard lithospheric delamination and/or mantle upwelling.

Description: Publication date: Available online 10 December 2014 Source: Precambrian Research Author(s): C.L. Kirkland , R.H. Smithies , C.V. Spaggiari Extensive time constrained isotopic (Sm-Nd, Lu-Hf) datasets on samples with well-studied geological context demonstrates that the Musgrave Province of central Australia and the Albany-Fraser Orogen of south Western Australia evolved through temporally similar Mesoproterozoic orogenies — at 1345–1260 and 1215–1140 Ma — but on completely different basement. The West and North Australian Cratons amalgamated before the 1345–1260 Ma event, which saw the convergence and final amalgamation of those combined cratons with the South Australian Craton. Well-defined Nd- and Hf-isotopic evolution arrays for the Musgrave Province reflect a juvenile basement with distinct 1950–1900, 1600–1550 Ma crust formation events. Rare non-radiogenic material is seen only in detritus and in magmas that assimilated this material. This evolved detritus was derived from non-Yilgarn Archean sources, and reworked Archean sources, which were added to sedimentary basins developed over the Musgrave Province basement during and after c. 1400 Ma. To the south of the Musgrave Province, the Madura Province has a similarly radiogenic signature to the Musgrave Province and is likely contiguous with it beneath younger cover sequences. It shows 2.0–1.4 Ma mantle extraction ages and is dominated by juvenile rocks reflecting oceanic crust consumed to the north of the South Australian Craton and east of the West Australian Craton. Available data support the suggestion that the Musgrave Province is simply modified Madura Province crust situated along the edge of the North Australian Craton. Together, the Musgrave Province and the Madura Province represent Proterozoic Australia's most juvenile crustal remnant. In stark contrast to this juvenile remnant, the isotopic evolution array for the Albany-Fraser Orogen reveals a much more evolved signature, charting progressive juvenile input into an Archean source with strong isotopic and age similarity to the Yilgarn Craton of the West Australian Craton.