Showing papers on "Gondwana published in 2009"

Anatomy and global context of the Andes: Main geologic features and the Andean orogenic cycle

Abstract: The Andes make up the largest orogenic system developed by subduction of oceanic crust along a continental margin Subduction began soon after the breakup of Rodinia in Late Proterozoic times, and since that time, it has been intermittently active up to the present The evolution of the Pacifi c margin of South America during the Paleozoic occurred in the following stages: (1) initial Proterozoic rifting followed by subduction and fi nal re-amalgamation of the margin in Early Cambrian times, as depicted by the Puncoviscana and Tucavaca Basins and related granitoids in southern Bolivia and northern Argentina; (2) a later phase of rifting in the Middle Cambrian, and subsequent collisions in Middle Ordovician times of parautochthonous terranes derived from Gondwana, such as Paracas, Arequipa, and Antofalla, and exotic terranes originating in Laurentia, such as Cuyania, Chilenia and Chibcha; (3) fi nal Permian collision between South America and North America to form Pangea during the Alleghanides orogeny, leaving behind rifted pieces of Laurentia as the Tahami and Tahuin terranes in the Northern Andes and other poorly known orthogneisses in the Cordillera Real of Ecuador in the Late Permian–Early Triassic; and (4) amalgamation of the Mejillonia and Patagonia terranes in Early Permian times, representing the last convergence episodes recorded in the margin during the Gondwanides orogeny These rifting episodes and subsequent collisions along the continental margin were the result of changes of the absolute motion of Gondwana related to global plate reorganizations during Proterozoic to Paleozoic times Generalized rifting during Pangea breakup in the Triassic concentrated extension in the hanging wall of the sutures that amalgamated the Paleozoic terranes The opening of the Indian Ocean in Early Jurassic times was associated with a new phase of subduction along the continental margin The northeastward absolute motion of western Gondwana produced a negative trench roll-back velocity that controlled subduction under an extensional regime until late Early Cretaceous times The Northern Andes of Venezuela, Colombia, and Ecuador record a series of collisions of island arcs and oceanic plateaus from the Early Cretaceous to the middle Miocene as a result of interaction with the Caribbean plate The remaining Central and Southern Andes record periods of orogenesis and mountain building alternating with periods of quiescence and absence of deformation as recorded in parts of the Oligocene Based on the generalized occurrence of fl at-slab subduction episodes through time, as recorded in most Ramos, VA, 2009, Anatomy and global context of the Andes: Main geologic features and the Andean orogenic cycle, in Kay, SM, Ramos, VA, and Dickinson, WR, eds, Backbone of the Americas: Shallow Subduction, Plateau Uplift, and Ridge and Terrane Collision: Geological Society of America Memoir 204, p 31–65, doi: 101130/20091204(02) For permission to copy, contact editing@geosocietyorg ©2009 The Geological Society of America All rights reserved

New Zealand phylogeography: evolution on a small continent.

Abstract: New Zealand has long been a conundrum to biogeographers, possessing as it does geophysicalandbioticfeaturescharacteristicofbothanislandandacontinent.Thisschism is reflected in provocative debate among dispersalist, vicariance biogeographic and panbiogeographic schools. A strong history in biogeography has spawned many hypotheses, which have begun to be addressed by a flood of molecular analyses. The time is now ripe to synthesize these findings on a background of geological and ecological knowledge. It has become increasingly apparent that most of the biota of New Zealand has links with othersouthernlands(particularlyAustralia)thataremuchmorerecentthanthebreakupof Gondwana. A compilation of molecular phylogenetic analyses of ca 100 plant and animal groups reveals that only 10% of these are even plausibly of archaic origin dating to the vicariant splitting of Zealandia from Gondwana. Effects of lineage extinction and lack of goodcalibrationsinmanycasesstronglysuggestthattheactualproportionisevenlower,in keeping with extensive Oligocene inundation of Zealandia. A wide compilation of papers covering phylogeographic structuring of terrestrial, freshwater and marine species shows some patterns emerging. These include: east–west splits across the Southern Alps, east– west splits across North Island, north–south splits across South Island, star phylogenies of southern mountain isolates, spread from northern, central and southern areas of high endemism, and recent recolonization (postvolcanic and anthropogenic). Excepting the last ofthese,mostofthesepatternsseemtodatetolatePliocene,coincidingwiththerapiduplift of the Southern Alps. The diversity of New Zealand geological processes (sinking, uplift, tilting, sea level change, erosion, volcanism, glaciation) has produced numerous patterns, making generalizations difficult. Many species maintain pre-Pleistocene lineages, with phylogeographic structuring more similar to the Mediterranean region than northern Europe. This structure reflects the fact that glaciation was far from ubiquitous, despite the topography. Intriguingly, then, origins of the flora and fauna are island-like, whereas phylogeographic structure often reflects continental geological processes.

The 132 Ma Comei-Bunbury large igneous province: Remnants identified in present-day southeastern Tibet and southwestern Australia

Abstract: We report 11 new U-Pb zircon ages obtained by sensitive high-resolution ion microprobe (SHRIMP) and laser ablation–inductively coupled plasma–mass spectrometry (LA-ICP–MS) for a large province of Early Cretaceous Comei igneous rocks consisting of basaltic lavas, mafi c sills and dikes, and gabbroic intrusions together with subordinate layered ultramafi c intrusions and silicic volcanic rocks exposed in the Tethyan Himalaya, southeastern Tibet. Available zircon U-Pb ages obtained from various rocks in this province, which has an areal extent of ~40,000 km 2 (~270 km × 150 km), indicate that the magmatism occurred ca. 132 Ma ago, coeval with the Bunbury Basalt in southwestern Australia. Such a striking similarity in emplacement age, in combination with the tectonic reconstruction of eastern Gondwana ca. 132 Ma ago, allows us to propose that the extensive Comei igneous rocks in southeastern Tibet and the Bunbury Basalts in southwestern Australia may represent the erosional and/or deformational remnants of a large igneous province, which we call the Comei-Bunbury LIP. We argue that this newly identifi ed LIP was likely caused by the Kerguelen mantle plume, which started in the Early Cretaceous and may have played a role in the breakup of eastern Gondwana and the development of the 132 Ma old Weissert oceanic anoxic event.

Significant achievements and open issues in study of orogenesis and metallogenesis surrounding the North China continent

Abstract: The significant achievements in past four-year study of Orogenesis and Metallogenesis Surrounding the North China Continent,which is a huge project granted by the National 973-Program,are briefly summarized in this paper.The concepts of ultramafic-mafic rock-hosted hydrothermal Cu-Ni-precious metals deposit and epizonogenism are defined;and consequently,the hydrothermal ore-systems can be classified into three series,i.e.magmatic,metamorphic and epizonogenic.On the basis of discovery and identification of numerous orogenic-type Ag,Pb-Zn,Cu and Mo deposits in the interest area,a new term of orogenic-type deposits and a new element zoning model for orogenic-type ore-system have been introduced to renew the concept of orogenic-type gold and its crustal continuum model,respectively.Indosinian mineralizations,especially intrusion-related hypothermal Mo mineralization,were determined to have occurred in both southern and northern margins of the North China continent.Intra-continental intrusion-related hypothermal ore-systems are rich in CO_2,K and F,which differ from those developed in island arcs.The Carlin-type and Carlin-like gold deposits in compressive orogenic areas usually contain CO_2-H_2O fluid inclusions which cannot be observed the same kind oresystems developed in back-arc Basin-and-Range provinces.The Central Asian and Central China orogenic belts have been from strongly continental accretion and weakly continental collision and weakly continental accretion and strongly continental collision,respectively, which leads them to have quite different type ore-systems and metallic commodities.The eastern portions of the North China continent and its adjacent orogenic belts accommodate large-scale Yanshanian mineralization gradiently younging eastward,with differing genetic types and metal inventories,which possibly resulted from their tectonic evolution combined with interaction with Pacific plate.Precollision hydrothermal ore-systems were reworked more or less,of which some re-mobilized and re-emplaced as other genetic types of ore deposits.Intrusion-related hypothermal Mo mineralizations of ca 1.9 Ga and 1.75 Ga and orogenic type Ag-Au-Mo mineralization of ca 430 Ma were recently discovered in Qinling Mountains,whilst the Mongolia-Hinggan Mountains were reported to have Devonian orogenic Cu-Au lodes,indicating the exploration potential for pre-Mesozoic ore deposits.Ore-system is evidenced to be an ideal probe to geodynamics,and by this way the post-120Ma erosion total of Qinling-Dabie-SuLu orogen is estimated less than 10 km with an average rate of 0.04 mm per year,suggesting that the rapid uplift must occur before 130 Ma if there is.It is constrained that the Paleo-Asian Ocean closed from west to east along the Solonker-Yanji geosuture during the period of from 260 to 250 Ma;while the northern branch of the Paleo-Tethys Ocean was finally closed at ca 220 Ma.The North China craton is revealed to have been involved in supercontinent cycles including Kenor,Columbia,Rodinia,Gondwana and Pangea,as well as the Lomagundi Event which is characterized by positiveδ~(13) Ccarb excursion;and deposition of the khondalite series in North China craton was dated to be2.3 Ga. Suggested key open issues include:duration and geologic marker of onset and end of continental collision orogenesis;identification and targeting of pre-Mesozoic ore-systems;regional regularities and differences of Yanshanian large-scale mineralizations;and detailed process and mechanism of transition and/or combination of tectonic domains or regimes.

Late Palaeozoic and Mesozoic tectonic and palaeogeographical evolution of SE Asia

Abstract: SE Asia comprises a collage of continental terranes derived directly or indirectly from the India–Australian margin of eastern Gondwana The Late Palaeozoic and Mesozoic evolution of the region involved the rifting and separation of three elongate continental slivers from eastern Gondwana and the successive opening and closure of three ocean basins, the Palaeo-Tethys, Meso-Tethys and Ceno-Tethys The Sukhothai Island Arc System, including the Linchang, Sukhothai and Chanthaburi terranes, is identified between the Sibumasu and Indochina–East Malaya terranes in SE Asia and was formed by back-arc spreading in the Permian The Jinghong, Nan–Uttaradit and Sra Kaeo sutures represent the closed back-arc basin The Palaeo-Tethys is represented to the west by the Changning–Menglian, Chiang Mai/Inthanon and Bentong–Raub suture zones The West Sumatra and West Burma blocks rifted and separated from Gondwana, along with Indochina and East Malaya in the Devonian, and together with South China formed a composite terrane ‘Cathaysialand’ in the Permian They were translated westwards to their positions outboard of the Sibumasu Terrane by strike-slip tectonics in the Late Permian–Early Triassic at the zone of convergence between the Meso-Tethys and Palaeo-Pacific plates SW Borneo is tentatively identified as possibly being the missing ‘Argoland’ that separated from NW Australia in the Jurassic Palaeogeographical reconstructions for the Late Palaeozoic and Mesozoic illustrating the tectonic and palaeogeographical evolution of SE Asia are presented SE Asia is a unique natural laboratory for studying collisional plate tectonics, suture formation and mountain building (Hall 2002, 2009) The region is also one of the best for studying long-lived terrane dispersion and accretion processes (Metcalfe 1999) and the effects of rapid changes in continent– ocean configurations on biogeographical patterns and ecosystems (Hall & Holloway 1998; Kershaw et al 2001; Metcalfe et al 2001) The tectonic evolution, terrane accretion, and assembly of SE Asia during the Late Palaeozoic and Mesozoic has resulted in complex changes in the palaeogeography of SE Asia and in the juxtaposition of contrasting but temporally coincident palaeo-ecosystems in the region Changing continent–ocean configurations, palaeogeography and climate changes in the Late Palaeozoic and Mesozoic of what is now SE Asia have resulted in complex patterns of both marine and terrestrial ecosystems of SE Asia both in space and time This paper presents an overview of the tectonic and palaeogeographical evolution of SE Asia in the Late Palaeozoic and Mesozoic Tectonic framework of SE Asia SE Asia is located at the zone of convergence between the Eurasia, Pacific and Indo-Australian plates (Fig 1) The region comprises a complex assemblage of continental terranes (bounded by suture zones or other major tectonic features), island arcs and small ocean basins The older Palaeozoic and Mesozoic portions of the region comprise allochthonous continental terranes (small to medium-sized allochthonous continental blocks that have distinctive tectonostratigraphic histories) that were assembled prior to the current collision of Australia with the region The Cenozoic evolution of the region has been well studied, and the evolution and reconstruction models of Hall (2002) are considered the most reliable This paper focuses on the Late Palaeozoic and Mesozoic evolution Continental terranes and their origins The principal continental terranes and sutures of SE Asia are shown in Figures 2 and 3 Terranes are grouped according to their interpreted origins and are discussed briefly under these origin groupings below Descriptions of the terranes have been given by Metcalfe (2006) All the continental terranes of East and SE Asia are interpreted to have been directly or indirectly derived from the eastern Gondwana margin at different times and some small terranes were subsequently derived indirectly from larger Gondwana-derived terranes or composite terranes (see Metcalfe 1986, 1988, 1990, 1991, 1993, 1996a, b, 1998, 2001, 2002, 2005, 2006; Table 1) I have previously described the successive rifting and northwards drift of three From: BUFFETAUT, E, CUNY, G, LE LOEUFF, J & SUTEETHORN, V (eds) Late Palaeozoic and Mesozoic Ecosystems in SE Asia The Geological Society, London, Special Publications, 315, 7–23 DOI: 101144/SP3152 0305-8719/09/$1500 # The Geological Society of London 2009 Gondwana-derived continental slivers (now disrupted into various terranes), with the successive opening and closure of the Palaeo-Tethys, Meso-Tethys and Ceno-Tethys ocean basins This broad scenario is still advocated here (Fig 4), but recent new data demand modification of the terrane make-up of these continental slivers, and also reinterpretations of the origins and boundaries of some of the terranes in the region Terranes derived from Gondwana in the Devonian A group of East and SE Asian terranes are interpreted to have rifted and separated from Gondwana as an elongate continental sliver in the Devonian (Fig 4) and comprise North China, South China (including Hainan), Indochina–East Malaya (including the Qamdao–Simao/Simao and disrupted West Sumatra and West Burma terranes) and Tarim (including the disrupted Kunlun, Qaidam and Ala Shan terranes) The West Sumatra terrane was proposed by Hutchison (1994) and Barber & Crow (2003), and is interpreted to have been translated westwards from ‘Cathaysialand’ (combined South China–Indochina–East Malaya composite terrane in Permo-Triassic times) as suggested by Barber et al (2005) and Metcalfe (2005) A Devonian separation of these terranes from Gondwana is still advocated here based on palaeomagnetic and biogeographical data from the terranes themselves and also from Devonian age data for oceanic radiolarian cherts in the Palaeo-Tethys (for details, see Metcalfe 1988, 1990, 1998, 2005) Jablonski & Saitta (2004) have, however, on the basis of transgressive–regressive sequences in western Australian basins, argued for a later Early Carboniferous (Visean) separation of South China, Indochina and Simao terranes This timing seems too young in view of the fact that the Palaeo-Tethys suture zone includes oceanic sediments of Devonian age and no post-Devonian Gondwana biota is reported from the terranes in question Terranes derived from Gondwana in the Early Permian The second continental sliver that rifted and separated from Gondwana in the Early Permian (with opening of the Meso-Tethys) was the Cimmerian continent of Sengor (1979, 1984), which included the Sibumasu terrane (Metcalfe 1984) of SE Asia and the Baoshan and Tengchong terranes of Yunnan in western China I have presented evidence for the NW Australian origin and Early Permian rifting and separation of the Sibumasu portion of the Cimmerian continent from Gondwana in a series of papers (eg Metcalfe 1986, 1988, 1990, 1991, 1993, 1996a, b, 1998, 2001, 2002, 2005, 2006) and this will not be repeated here Recent studies (Sone & Metcalfe 2008) have led to the recognition of an island arc system, the Sukhothai Island Arc system, through SE Asia (Fig 5) situated between Sibumasu and Indochina–East Malaya (from which it was derived by back-arc spreading) This interpretation, Fig 1 Principal tectonic plates of SE Asia Arrows show plate motions relative to Eurasia I METCALFE 8

Correlations and reconstruction models for the 2500–1500 Ma evolution of the Mawson Continent

Abstract: Continental lithosphere formed and reworked during the Palaeoproterozoic era is a major component of pre-1070 Ma Australia and the East Antarctic Shield. Within this lithosphere, the Mawson Continent encompasses the Gawler–Adelie Craton in southern Australia and Antarctica, and crust of the Miller Range, Transantarctic Mountains, which are interpreted to have assembled during c. 1730–1690 Ma tectonism of the Kimban– Nimrod–Strangways orogenies. Recent geochronology has strengthened correlations between the Mawson Continent and Shackleton Range (Antarctica), but the potential for Mesoto Neoproterozoic rifting and/or accretion events prevent any confident extension of the Mawson Continent to include the Shackleton Range. Proposed later addition (c. 1600–1550 Ma) of the Coompana Block and its Antarctic extension provides the final component of the Mawson Continent. A new model proposed for the late Archaean to early Mesoproterozoic evolution of the Mawson Continent highlights important timelines in the tectonic evolution of the Australian lithosphere. The Gawler–Adelie Craton and adjacent Curnamona Province are interpreted to share correlatable timelines with the North Australian Craton at c. 2500–2430 Ma, c. 2000 Ma, 1865–1850 Ma, 1730–1690 Ma and 1600–1550 Ma. These common timelines are used to suggest the Gawler–Adelie Craton and North Australian Craton formed a contiguous continental terrain during the entirety of the Palaeoproterozoic. Revised palaeomagnetic constraints for global correlation of proto-Australia highlight an apparently static relationship with northwestern Laurentia during the c. 1730–1590 Ma time period. These data have important implications for many previously proposed reconstruction models and are used as a primary constraint in the configuration of the reconstruction model proposed herein. This palaeomagnetic link strengthens previous correlations between the Wernecke region of northwestern Laurentia and terrains in the eastern margin of proto-Australia. This chapter outlines the Palaeoproterozoic to early Mesoproterozoic tectono-thermal evolution of the Mawson Continent of Australia and Antarctica (Fig. 1). The Mawson Continent comprises the Gawler Craton, South Australia, and the correlative coastal outcrops (e.g. Cape Hunter and Cape Denison) of Terre Adelie and George V Land in Antarctica and various other terrains of East Antarctica (Fig. 1, Oliver & Fanning 1997; Goodge et al. 2001; Fitzsimons 2003). Perhaps the most notable feature of the Mawson Continent is its lack of exposure. Excluding the flat-lying c. 1590 Ma Gawler Range Volcanics, the Gawler Craton portion is estimated to contain ,5% basement exposure in an area approximately 530 800 km (slightly smaller than France). The Antarctic component of the Mawson Continent contains even less exposure. Despite the impediment of limited basement exposure, numerous tectonic reconstruction models have been proposed to account for the evolution of the Mawson Continent and its interaction with other Proterozoic terrains, particularly other portions of the current Australian continent (Borg & DePaolo 1994; Daly et al. 1998; Betts et al. 2002; Dawson et al. 2002; Fitzsimons 2003; Giles et al. 2004; Betts & Giles 2006; Wade et al. 2006). From: REDDY, S. M., MAZUMDER, R., EVANS, D. A. D. & COLLINS, A. S. (eds) Palaeoproterozoic Supercontinents and Global Evolution. Geological Society, London, Special Publications, 323, 319–355. DOI: 10.1144/SP323.16 0305-8719/09/$15.00 # Geological Society of London 2009. In attempting to reconstruct the evolution of the Mawson Continent, a particularly intriguing aspect of the geology of the Mawson Continent, and the Australian Proterozoic in general, is the comparative lack of evidence for subduction-related magmatism. The few Australia-wide examples of documented late Palaeoproterozoic and early Mesoproterozoic subduction-related magmatism can be summarized as follows: c. 1850 Ma magmatism associated with the accretion of the Kimberley Craton (Sheppard et al. 1999); volumetrically minor granites of the 1770–1750 Ma Fig. 1. Map of East Gondwana (modified from Collins & Pisarevsky 2005) displaying pre-Gondwana terrain locations in Antarctica (after Boger et al. 2006) and pre-1 Ga crustal provinces of Australia (after Betts et al. 2002; Payne et al. 2008). East Antarctica terrains are: BG, Beardmore Glacier; BH, Bunger Hills, DML, Dronning Maud Land; NC, Napier Complex, sPCM, southern Prince Charles Mountains; VH, Vestfold Hills, WI, Windmill Islands; WL, Wilkes Land. Bold abbreviations are MR, Miller Range; SR, Shackleton Range; and TA, Terre Adelie Craton, which have all experienced c. 1700 Ma tectonism (see text). Australian pre-1070 Ma terrains are: AR, Arunta Region, CI, Coen Inlier; CmB, Coompana Block; CO, Capricorn Orogen; CP, Curnamona Province; GI, Georgetown Inlier; HC, Halls Creek Orogen; KC, Kimberley Craton; MI, Mt Isa Inlier; MP, Musgrave Province; NoC, Nornalup Complex; PC, Pilbara Craton; PcO, Pine Creek Orogen; RC, Rudall Complex; TC, Tennant Creek Region; and TR, Tanami Region. J. L. PAYNE ET AL. 320

The drift history of Iran from the Ordovician to the Triassic

Abstract: New Late Ordovician and Triassic palaeomagnetic data from Iran are presented. These data, in conjunction with data from the literature, provide insights on the drift history of Iran as part of Cimmeria during the Ordovician-Triassic. A robust agreement of palaeomagnetic poles of Iran and West Gondwana is observed for the Late Ordovician-earliest Carboniferous, indicat- ing that Iran was part of Gondwana during that time. Data for the Late Permian-early Early Tri- assic indicate that Iran resided on subequatorial palaeolatitudes, clearly disengaged from the parental Gondwanan margin in the southern hemisphere. Since the late Early Triassic, Iran has been located in the northern hemisphere close to the Eurasian margin. This northward drift brought Iran to cover much of the Palaeotethys in approximately 35 Ma, at an average plate speed ofc. 7-8 cm year 21 , and was in part coeval to the transformation of Pangaea from an Irvin- gian B to a Wegenerian A-type configuration.

Structure of Sumatra and its implications for the tectonic assembly of Southeast Asia and the destruction of Paleotethys

Abstract: It is now generally accepted that Southeast Asia is composed of continental blocks which separated from Gondwana with the formation of oceanic crust during the Paleozoic, and were accreted to Asia in the Late Paleozoic or Early Mesozoic, with the subduction of the intervening oceanic crust. From east to west the Malay peninsula and Sumatra are composed of three continental blocks: East Malaya with a Cathaysian Permian flora and fauna; Sibumasu, including the western part of the Malay peninsula and East Sumatra, with Late Carboniferous–Early Permian ‘pebbly mudstones’ interpreted as glaciogenic diamictites; and West Sumatra, again with Cathaysian fauna and flora. A further unit, the Woyla nappe, is interpreted as an intraoceanic arc thrust over the West Sumatra block in the mid Cretaceous. There are varied opinions concerning the age of collision of Sibumasu with East Malaya and the destruction of Paleotethys. In Thailand, radiolarites have been used as evidence that Paleotethys survived until after the Middle Triassic. In the Malay peninsula, structural evidence and the ages of granitic intrusions are used to support a Middle Permian to Early Triassic age for the destruction of Paleotethys. It is suggested that the West Sumatra block was derived from Cathaysia and emplaced against the western margin of Sibumasu by dextral transcurrent faulting along a zone of high deformation, the Medial Sumatra Tectonic Zone. These structural units can be traced northwards in Southeast Asia. The East Malaya block is considered to be part of the Indochina block, Sibumasu can be traced through Thailand into southern China, the Medial Sumatra Tectonic Zone is correlated with the Mogok Belt of Myanmar, the West Burma block is the extension of the West Sumatra block, from which it was separated by the formation of the Andaman Sea in the Miocene, and the Woyla nappe is correlated with the Mawgyi nappe of Myanmar.

Hidden levels of phylodiversity in Antarctic green algae: further evidence for the existence of glacial refugia

Abstract: Recent data revealed that metazoans such as mites and springtails have persisted in Antarctica throughout several glacial–interglacial cycles, which contradicts the existing paradigm that terrestrial life was wiped out by successive glacial events and that the current inhabitants are recent colonizers. We used molecular phylogenetic techniques to study Antarctic microchlorophyte strains isolated from lacustrine habitats from maritime and continental Antarctica. The 14 distinct chlorophycean and trebouxiophycean lineages observed point to a wide phylogenetic diversity of apparently endemic Antarctic lineages at different taxonomic levels. This supports the hypothesis that long-term survival took place in glacial refugia, resulting in a specific Antarctic flora. The majority of the lineages have estimated ages between 17 and 84 Ma and probably diverged from their closest relatives around the time of the opening of Drake Passage (30–45 Ma), while some lineages with longer branch lengths have estimated ages that precede the break-up of Gondwana. The variation in branch length and estimated age points to several independent but rare colonization events.

Breakup of Pangaea and plate kinematics of the central Atlantic and Atlas regions

Abstract: SUMMARY A new central Pangaea fit (type A) is proposed for the late Ladinian (230 Ma), together with a plate motions model for the subsequent phases of rifting, continental breakup and initial spreading in the central Atlantic. This model is based on: (1) a reinterpretation of the process of formation of the East Coast Magnetic Anomaly along the eastern margin of North America and the corresponding magnetic anomalies at the conjugate margins of northwest Africa and the Moroccan Meseta; (2) an analysis of major rifting events in the central Atlantic, Atlas and central Mediterranean and (3) a crustal balancing of the stretched margins of North America, Moroccan Meseta and northwest Africa. The process of fragmentation of central Pangaea can be described by three major phases spanning the time interval from the late Ladinian (230 Ma) to the Tithonian (147.7 Ma). During the first phase, from the late Ladinian (230 Ma) to the latest Rhaetian (200 Ma), rifting proceeded along the eastern margin of North America, the northwest African margin and the High, Saharan and Tunisian Atlas, determining the formation of a separate Moroccan microplate at the interface between Gondwana and Laurasia. During the second phase, from the latest Rhaetian (200 Ma) to the late Pliensbachian (185 Ma), oceanic crust started forming between the East Coast and Blake Spur magnetic anomalies, whereas the Morrocan Meseta simply continued to rift away from North America. During this time interval, the Atlas rift reached its maximum extent. Finally, the third phase, encompassing the time interval from the late Pliensbachian (185 Ma) to chron M21 (147.7 Ma), was triggered by the northward jump of the main plate boundary connecting the central Atlantic with the Tethys area. Therefore, as soon as rifting in the Atlas zone ceased, plate motion started along complex fault systems between Morocco and Iberia, whereas a rift/drift transition occurred in the northern segment of the central Atlantic, between Morocco and the conjugate margin of Nova Scotia. The inversion of the Atlas rift and the subsequent formation of the Atlas mountain belt occurred during the Oligocene–early Miocene time interval. In the central Atlantic, this event was associated with higher spreading rates of the ridge segments north of the Atlantis FZ. An estimate of 170 km of dextral offset of Morocco relative to northwest Africa, in the central Atlantic, is required by an analysis of marine magnetic anomalies. Five plate tectonic reconstructions and a computer animation are proposed to illustrate the late Triassic and Jurassic process of breakup of Pangaea in the central Atlantic and Atlas regions.

Cretaceous felsic volcanism in New Zealand and Lord Howe Rise (Zealandia) as a precursor to final Gondwana break-up

Abstract: Abstract We report new, highly precise, U–Pb and Ar/Ar ages for seven Cretaceous rhyolites, tuffs and granites from across Zealandia spanning a 30 Ma period from arc magmatism to continental break-up. Combined with previously published data, these reveal a strong episodicity in Cretaceous silicic magmatism outside the Median Batholith. 112 Ma tuffs are known only from the Eastern Province in association with a Cretaceous normal fault system. Both 101 and 97 Ma groups of rhyolites and tuffs occur across the entire width and half the length of Zealandia from near the palaeotrench to the continental interior, indicating widespread and effectively instantaneous extension. We attribute an increase in A-type character with time (112–101–97–88–82 Ma) to the progressive thinning of the Zealandia continental crust whereby, with time, there is less opportunity for crustal contamination. Extension directions associated with 101, 97 and 82 Ma magmatism and associated core complex exhumation across Zealandia are all oriented c. 30° oblique to the margin. These observations suggest Zealandia rifting was controlled by either >83 Ma capture of Zealandia by the Pacific Plate and/or <83 Ma Zealandia–West Antarctica spreading, rather than by laterally migrating triple junctions, slab windows or plume heads.

Tectonomagmatic evolution of Western Amazonia: Geochemical characterization and zircon U-Pb geochronologic constraints from the Peruvian Eastern Cordilleran granitoids

Abstract: The results of a coupled, in situ laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) U-Pb study on zircon and geochemical characterization of the Eastern Cordilleran intrusives of Peru reveal 1.15 Ga of intermittent magmatism along central Western Amazonia, the Earth's oldest active open continental margin. The eastern Peruvian batholiths are volumetrically dominated by plutonism related to the assembly and breakup of Pangea during the Paleozoic-Mesozoic transition. A Carboniferous-Permian (340-285 Ma) continental arc is identified along the regional orogenic strike from the Ecuadorian border (6 degrees S) to the inferred inboard extension of the Arequipa-Antofalla terrane in southern Peru (14 degrees S). Widespread crustal extension and thinning, which affected western Gondwana throughout the Permian and Triassic resulted in the intrusion of the late- to post-tectonic La Merced-San Ramon-type anatectites dated between 275 and 220 Ma, while the emplacement of the southern Cordillera de Carabaya peraluminous granitoids in the Late Triassic to Early Jurassic (220-190 Ma) represents, temporally and regionally, a separate tectonomagmatic event likely related to resuturing of the Arequipa-Antofalla block. Volcano-plutonic complexes and stocks associated with the onset of the present Andean cycle define a compositionally bimodal alkaline suite and cluster between 180 and 170 Ma. A volumetrically minor intrusive pulse of Oligocene age (ca. 30 Ma) is detected near the southwestern Cordilleran border with the Altiplano. Both post-Gondwanide (30-170 Ma), and Precambrian plutonism (691-1123 Ma) are restricted to isolated occurrences spatially comprising less than 15% of the Eastern Cordillera intrusives. Only one remnant of a Late Ordovician intrusive belt is recognized in the Cuzco batholith (446.5 +/- 9.7 Ma) indicating that the Famatinian arc system previously identified in Peru along the north-central Eastern Cordillera and the coastal Arequipa-Antofalla terrane also existed inboard of this parautochthonous crustal fragment. Hitherto unknown occurrences of late Mesoproterozoic and middle Neoproterozoic granitoids from the south-central cordilleran segment define magmatic events at 691 +/- 13 Ma, 751 +/- 8 Ma, 985 +/- 14 Ma, and 1071-1123 +/- 23 Ma that are broadly coeval with the Braziliano and Grenville-Sunsas orogenies, respectively. Our data suggest the existence of a continuous orogenic belt in excess of 3500 km along Western Amazonia during the formation of Rodinia, its "early" fragmentation prior to 690 Ma, and support a model of reaccretion of the Paracas-Arequipa-Antofalla terrane to western Gondwana in the Early Ordovician with subsequent detachment of the Paracas segment in form of the Mexican Oaxaquia microcontinent in Middle Ordovician. A tectonomagmatic model involving slab detachment, followed by underplating of cratonic margin by asthenospheric mantle is proposed for the genesis of the volumetrically dominant Late Paleozoic to early Mesozoic Peruvian Cordilleran batholiths

U-Pb geochronology of mid-Paleozoic plutonism in western New Zealand: Implications for S-type granite generation and growth of the east Gondwana margin

Abstract: New U-Pb isotope-dilution-thermal ionization mass spectrometry (ID-TIMS) ages (371–305 Ma) for 30 granitic plutons along the New Zealand sector of the East Gondwanan active margin reveal a highly episodic emplacement history and crustal growth pattern. The Late Devonian-late Carboniferous ages also establish specific links with both the mostly older, Lachlan and the mostly younger, New England fold belts of eastern Australia. Dated plutons are representative of two S- and I-type suite pairs, the volumetrically predominant Karamea-Paringa (371–360 Ma) and minor Ridge-Tobin (355–342 Ma) pulses, as well as sporadic Foulwind Suite A-type granites (350–305 Ma). Emplacement of the bulk of the dominant ∼3400 km 2 Karamea Suite S-type granite-granodiorite plutons within a 2.11 Ma interval is explained by major and intimate intrusion of mantle-derived magma into largely metasedimentary crust during intra-arc extension of previously overthickened crust. Transient emplacement rates were thus of similar magnitude as some young ignimbrite flare-ups and an order of magnitude greater than long-term averages for Mesozoic-Cenozoic cordilleran batholiths of the western Americas. Extension likely was terminated abruptly by resumption of convergence, possibly associated with amalgamation of the Buller and Takaka terranes, between 368 and 355 Ma. Significant crustal growth occurred during generation of the two S-type suites, where mantle basalt contributed mass, and heat for rapid melting, during transient intra- or backarc extensional episodes. In contrast, the I-type suites were dominated by partial melting of meta-igneous crust, and they are relatively small in volume. The Karamea S-type suite shares striking similarities in terms of age, composition, and extensional tectonic setting with S-type granites of the Melbourne terrane of the Lachlan fold belt. Both regions may have formed in a backarc position with respect to the Late Devonian-early Carboniferous subduction zone in the New England fold belt. Foulwind Suite A-type magmatism in New Zealand overlaps in age with the widespread 320–285 Ma A- and I-type magmatism in the northern New England fold belt. The likely continuation of the New England subduction system must have subsequently been removed from outboard of the New Zealand region after 320–285 Ma magmatism, and prior to Triassic accretion of a Permian oceanic arc terrane to the New Zealand margin.

Global Neoproterozoic petroleum systems: The emerging potential in North Africa

Abstract: The Neoproterozoic Eon is relatively poorly known from a petroleum perspective, despite the existence of producing, proven and potential plays in many parts of the world In tectonic, climatic and petroleum systems terms, the Neoproterozoic to Early Cambrian period can be divided into three distinct phases: a Tonian to Early Cryogenian phase, prior to about 750 Ma, dominated by the formation, stabilization and initial break-up of the supercontinent of Rodinia; a mid Cryogenian to Early Ediacaran phase (c 750-600Ma) including the major global-scale 'Sturtian' and 'Marinoan' glaciations and a mid Ediacaran to Early Cambrian (c post 600Ma) phase corresponding with the formation and stabilization of the Gondwana Supercontinent There is increasing evidence that deposition of many mid to late Neoproterozoic (to Early Palaeozoic) organic-rich units was triggered by strong post-glacial sea level rise on a global scale, following the 'Snowball Earth' type glaciations, coupled with basin development and rifting on a more local scale Fieldwork in North Africa including the Taoudenni Basin in Mauritania, Algeria and Mali; the Anti-Atlas region of Morocco and the Cyrenaica, Kufra and Murzuk basins in Libya has added to the understanding of reservoir, source and seal relationships and confirmed the widespread presence of Precambrian stromatolitic carbonate units of potential reservoir facies Current research on the chronostratigraphy, distribution and quality of source rocks, controls on reservoir quality and distribution of seals in the Precambrian-Early Cambrian hydrocarbon plays through-out South America, North Africa, the Middle East and the Indian Subcontinent is documented in this Special Publication © The Geological Society of London 2009

Provenance of the Meguma terrane, Nova Scotia: rifted margin of early Paleozoic Gondwana

Abstract: Detrital zircon ages from the lower part of the Late Proterozoic(?) to Middle Cambrian Goldenville Group in the Meguma terrane of Nova Scotia suggest derivation from local sources in the Avalonian ...