Detrital Zircon Provenance Research Articles

Middle-Late Paleozoic geodynamic complexes and structure of Gorny Altai and their record in gravity data

Middle-Late Paleozoic geodynamics and structure of Gorny Altai are studied with reference to gravity data. The northern and central parts of the area belong to the Gorny Altai terrane consisting of Late Precambrian-Paleozoic rocks originated in different tectonic settings on the Siberian continental margin, including Devonian active-margin volcanoplutonic complexes. In the south and east, the Gorny Altai terrane borders the Altai-Mongolia terrane along the Charysh-Terekta-Ulagan shear zone. The Altai-Mongolia terrane is composed of Early Paleozoic turbidites of the Kazakhstan-Baikal continent, Middle Paleozoic collisional garnet-disthene-andalusite schists, and Late Paleozoic zoned andalusite-cordierite schists, with granitic plutons on their periphery. The pattern of these complexes is similar to that of Cenozoic volcanoplutonic and metamorphic domes in the Kamchatka and Chukchi Peninsulas. The Devonian volcanoplutonic complexes from the Gorny Altai terrane and the Middle-Late Paleozoic metamorphic complexes from the Altai-Mongolia terrane are well evident in the gravity field. In general, gravity anomalies in the two terranes strike in different directions: NW in the Gorny Altai terrane and W-E in the Altai-Mongolia terrane, which highlights the structural heterogeneity of the Gorny Altai region. New dates have been obtained for magmatic detrital zircons from Paleozoic sedimentary rocks of the Anui-Chuya basin in the Gorny Altai terrane. The inferred source areas of zircon hosts are igneous rocks of the Precambrian craton basement and the Vendian-Early Ordovician Kuznetsk-Altai island arc. Early Neoproterozoic (1.00-0.75 Ma) detrital zircons are abundant in the Early Paleozoic turbidites of the Altai-Mongolia terrane but are absent from samples of the Gorny Altai terrane. Populations of detrital zircons in the the Gorny Altai terrane contain Devonian and Early Neoproterozoic specimens. The reported data prove that the Kazakhstan-Baikal and Siberian continents amalgamated in the Middle-Late Paleozoic. The resulting Gorny Altai tectonic framework of that time is recorded in the gravity field and in the provenance of detrital zircons.

Provenance and tectonic significance of late Mesoproterozoic detrital zircons from the Tonian system, northern margin of the North China Craton

ABSTRACTThe involvement of the North China Craton (NCC) in the assembly or breakup of Rodinia has long been debated. Studies of palaeomagnetism, mafic sills (dikes), igneous events, and sedimentary records have led to contrasting opinions on this topic. No igneous events related to the late Mesoproterozoic assembly of Rodinia have been reported in the NCC. However, the authors found numerous late Mesoproterozoic zircons in the Tonian system on the northern margin of the NCC. The Tonian Zhulazhagamaodao formation is composed of meta-sandstone, siltstone, slate, carbonate, and dolomine of the littoral to neritic facies and occurs mainly in the western part of the Bayan Obo–Zhaertai–Langshan rift. U–Pb dating of detrital zircons from the Tonian system reveals age peaks at 1079 ± 23 Ma, 1092 ± 22 Ma, 1175 ± 50 Ma, 1175 ± 18 Ma, 1260 ± 45 Ma, 1266 ± 16 Ma, and 1270 ± 26 Ma, which correspond to the timing of Rodinia assembly. Considering that coeval igneous rocks and orogenic belts developed mostly in the Laurentia–Baltica cratons, we propose that these cratons supplied clastic material to the northern margin of the NCC and that they had a close spatial relationship between each other during the Tonian.

Detrital-zircon records of Cenomanian, Paleocene, and Oligocene Gulf of Mexico drainage integration and sediment routing: Implications for scales of basin-floor fans

AbstractThis paper uses detrital zircon (DZ) provenance and geochronological data to reconstruct paleodrainage areas and lengths for sediment-routing systems that fed the Cenomanian Tuscaloosa-Woodbine, Paleocene Wilcox, and Oligocene Vicksburg-Frio clastic wedges of the northern Gulf of Mexico (GoM) margin. During the Cenomanian, an ancestral Tennessee-Alabama River system with a distinctive Appalachian DZ signature was the largest system contributing water and sediment to the GoM, with a series of smaller systems draining the Ouachita Mountains and discharging sediment to the western GoM. By early Paleocene Wilcox deposition, drainage of the southern half of North America had reorganized such that GoM contributing areas stretched from the Western Cordillera to the Appalachians, and sediment was delivered to a primary depocenter in the northwestern GoM, the Rockdale depocenter fed by a paleo–Brazos-Colorado River system, as well as to the paleo–Mississippi River in southern Louisiana. By the Oligocene, the western drainage divide for the GoM had migrated east to the Laramide Rockies, with much of the Rockies now draining through the paleo–Red River and paleo–Arkansas River systems to join the paleo–Mississippi River in the southern Mississippi embayment. The paleo–Tennessee River had diverted to the north toward its present-day junction with the Ohio River by this time, thus becoming a tributary to the paleo-Mississippi within the northern Mississippi embayment. Hence, the paleo-Mississippi was the largest Oligocene system of the northern GoM margin.Drainage basin organization has had a profound impact on sediment delivery to the northern GoM margin. We use paleodrainage reconstructions to predict scales of associated basin-floor fans and test our predictions against measurements made from an extensive GoM database. We predict large fan systems for the Cenomanian paleo–Tennessee-Alabama, and especially for the two major depocenters of the early Paleocene paleo–Brazos-Colorado and late Paleocene–earliest Eocene paleo-Mississippi systems, and for the Oligocene paleo-Mississippi. With the notable exception of the Oligocene, measured fans reside within the range of our predictions, indicating that this approach can be exported to other basins that are less data rich.

Depositional ages and provenance of the Neoproterozoic Damara Supergroup (northwest Namibia): Implications for the Angola-Congo and Kalahari cratons connection

The Damara Orogen is composed of the Damara, Kaoko and Gariep belts developed during the Neoproterozoic Pan-African Orogeny. The Damara Belt contains Neoproterozoic siliciclastic and carbonate successions of the Damara Supergroup that record rift to proto-ocean depositional phases during the Rodinia supercontinent break up. There are two conflicting interpretations of the geotectonic framework of the Damara Supergroup basin: i) as one major basin, composed of the Outjo and Khomas basins, related to rifting in the Angola-Congo-Kalahari paleocontinent or, ii) as two independent passive margin basins, one related to the Angola-Congo and the other to the Kalahari proto-cratons. Detrital zircon provenance studies linked to field geology were used to solve this controversy. U-Pb zircon age data were analyzed in order to characterize depositional ages and provenance of the sediments and evolution of the succession in the northern part of the Outjo Basin. The basal Nabis Formation (Nosib Group) and the base of the Chuos Formation were deposited between ca. 870Ma and 760Ma. The upper Chuos, Berg Aukas, Gauss, Auros and lower Brak River formations formed between ca. 760Ma and 635Ma. It also includes the time span recorded by the unconformity between the Auros and lower Brak River formations. The Ghaub, upper Brak River, Karibib and Kuiseb formations were deposited between 663Ma and 590Ma. The geochronological data indicate that the main source areas are related to: i) the Angola-Congo Craton, ii) rift-related intrabasinal igneous rocks of the Naauwpoort Formation, iii) an intrabasinal basement structural high (Abbabis High), and iv) the Coastal Terrane of the Kaoko Belt. The Kalahari Craton units apparently did not constitute a main source area for the studied succession. This is possibly due to the position of the succession in the northern part of the Outjo Basin, at the southern margin of the Congo Craton. Comparison of the obtained geochronological data with those from the literature shows that the Abbabis High forms part of the Kalahari proto-craton and that Angola-Congo and Kalahari cratons were part of the same paleocontinent in Rodinia times.

An early bird from Gondwana: Paleomagnetism of Lower Permian lavas from northern Qiangtang (Tibet) and the geography of the Paleo-Tethys

The origin of the northern Qiangtang block and its Late Paleozoic–Early Mesozoic drift history remain controversial, largely because paleomagnetic constraints from pre-Mesozoic units are sparse and of poor quality. In this paper, we provide a robust and well-dated paleomagnetic pole from the Lower Permian Kaixinling Group lavas on the northern Qiangtang block. This pole suggests that the northern Qiangtang block had a paleolatitude of 21.9±4.7°S at ca. 296.9±1.9 Ma. These are the first volcanic-based paleomagnetic results from pre-Mesozoic rocks of the Qiangtang block that appear to average secular variation accurately enough to yield a well-determined paleolatitude estimate. This new pole corroborates the hypothesis, first noted on the basis of less rigorous paleomagnetic data, the presence of diamictites, detrital zircon provenance records, and faunal assemblages, that the northern Qiangtang block rifted away from Gondwana prior to the Permian. Previous studies have documented that the northern Qiangtang block accreted to the Tarim-North China continent by Norian time. We calculate a total northward drift of ca. 7000 km over ca. 100 myr, which corresponds to an average south-north plate velocities of ∼7.0 cm/yr. Our results do not support the conclusion that northern Qiangtang has a Laurasian affinity, nor that the central Qiangtang metamorphic belt is an in situ Paleo-Tethys suture. Our analysis, however, does not preclude paleogeographies that interpret the central Qiangtang metamorphic belt as an intra-Qiangtang suture that developed at southernly latitudes outboard of the Gondwanan margin. We emphasize that rigorous paleomagnetic data from Carboniferous units of northern Qiangtang and especially upper Paleozoic units from southern Qiangtang can test and further refine these paleogeographic interpretations.

U–Pb detrital zircon ages from the Paleozoic Marbella Conglomerate of the Malaguide Complex (Betic Cordilleras, Spain). Implications on Paleotethyan evolution

The Marbella Conglomerate (Betic Cordilleras, SW Spain) is a poorly sorted and polymictic rock of vaguely constrained Late Carboniferous age interlayered within a sandy sequence. It contains variable amounts of pebbles of quartzite, gneiss, deformed granitoid, schist, aplite, dacite and other volcanic rocks among others, which makes it a potential target for detrital zircon provenance studies. In order to decipher provenance we combined U–Pb SHRIMP and LA–ICP-MS analyses on zircons obtained from single pebbles of deformed rocks (schist, granitoids) and detrital zircons from the sandy sequence, respectively. The age spectra of the detrital zircons indicates that at least the sedimentation took place soon after the start of the Permian according to the youngest detrital zircon age (≈286Ma), and it involved the denudation of terranes with rocks bearing Paleoproterozoic, Neoproterozoic, Cambro-Ordovician, Devonian and Carboniferous zircon age clusters. In contrast with the Permian age of the detrital zircons from the sandstones, igneous (ca. 532 and 516Ma) and metamorphic (ca. 356Ma) U–Pb SHRIMP Concordia ages were obtained from the pebbles. The different age clusters observed could be correlated to igneous, metamorphic and detrital rocks from an already eroded terrane similar to the Ossa-Morena Zone of the Iberian Variscan Belt. Therefore, we propose that most of the sedimentation of the Marbella Conglomerate took place along the western border of the Paleotethys at the north margin of Gondwana during the dismantling of the Variscan orogenic edifice and/or the Neotethys ocean opening and the birth of the Cimmerian ribbon continent.

New insights on the Triassic tectonic development of South China from the detrital zircon provenance of Nanpanjiang turbidites

New insights on the Triassic tectonic development of South China from the detrital zircon provenance of Nanpanjiang turbidites

East Anatolian plateau constructed over a continental basement: No evidence for the East Anatolian accretionary complex

The East Anatolian plateau (Turkey) is extensively covered by Neogene to Quaternary volcanic-sedimentary rocks, and is characterized by an attenuated lithospheric mantle. Its pre-Neogene basement is commonly considered to consist entirely of Late Cretaceous to Oligocene oceanic accretionary complexes, formed at the junction of several continental blocks. Here we report on three main exposures of the pre-Neogene basement in this region. The exposed areas consist mainly of amphibolite-to granulite-facies metamorphic rocks, including marble, amphibolite, metapelite, metagranite, and metaquartzite. An upper amphibolite-to granulitefacies domain is equilibrated at similar to 0.7 GPa and similar to 800 degrees C at 83 +/- 2 Ma (2 sigma). U-Pb dating of magmatic zircons from the metagranite yielded a Late Ordovician-early Silurian protolith age (444 +/- 9 Ma, 2 sigma). The detrital zircons from one metaquartzite point to a Neoproterozoic-early Paleozoic provenance. Ophiolitic rocks tectonically sit on the metamorphic rocks. Both the metamorphic and ophiolitic rocks are in turn unconformably covered by lower Maastrichtian clastic rocks and reefal limestones, suggesting that the whole exhumation process and juxtaposition with the ophiolitic rocks had occurred by the early Maastrichtian. Several lines of evidence, such as (1) the absence of any indication of a former high-pressure metamorphism in the metamorphic rocks, (2) the allochthonous nature of the ophiolitic rocks, (3) the presence of metagranite with a Late Ordovician-early Silurian protolith age, and (4) the Neoproterozoic- early Paleozoic provenance of detrital zircons in the metaquartzite (in contrast to the dominance of late Paleozoic-Mesozoic crystalline rocks in the adjacent continental blocks) indicate a substantial component of continental basement beneath the Neogene to Quaternary cover. Thus, the loss of the lithospheric mantle probably resulted from lithospheric foundering processes beneath the plateau, rather than just slab steepening and break-off.

Depositional history and provenance of Paleogene strata in the Sage Creek basin, southwestern Montana

In southwestern Montana (SWMT), Paleogene strata that are preserved in the Sage Creek basin were deposited during the transition from late-stage Sevier-Laramide compressional tectonism to extensional reactivation of the northern Rocky Mountain region. Similar to correlative deposits across the Cordillera, Sage Creek basin strata host diverse paleoclimate and paleoenvironmental proxies such as mammal fossil assemblages, paleobotanical fossil assemblages, and thick paleosol successions. As such, Sage Creek basin strata have been the focus of recent paleoclimate and paleoenvironmental studies, which have yielded results that indicate significant tectonic, climatic, and topographic evolution of the northern Cordillera during Paleogene time. This study revisits a succession of Paleocene to Oligocene terrestrial deposits in the Sage Creek basin of SWMT that have recently been at the forefront of Cenozoic paleoclimate studies in the northern Rocky Mountains. We present detailed physical stratigraphic trends, cobble and detrital zircon provenance data, and detrital zircon–based age constraints for the Paleocene to Oligocene basin fill that reveal the evolution of depositional systems, sediment routing, and approximate rates of deposition in the basin. The new data are compared with regional trends in structural deformation and volcanism to interpret a detailed depositional and tectonic history of the SWMT region. Specifically, the Paleogene strata record (1) the final pulse of Sevier-Laramide deformation in the region; (2) widespread erosional exhumation of the Sevier fold-thrust belt and Laramide intraforeland uplifts during Paleocene and early Eocene time; (3) middle Eocene onset of localized, bimodal volcanism and volcaniclastic sedimentation associated with gravitational collapse of the Cor­di­lleran complex; and (4) middle Eocene to Oligocene extensional reactivation of the Sevier fold-thrust belt and Laramide intraforeland province. Constraints on the timing, duration, and sedimentary response to such events provide a more complete understanding of the tectonic and topographic evolution of SWMT, which provides an essential framework for interpreting the suites of terrestrial paleoclimate and paleoenvironmental data in the northern Cordillera.

The onset of flysch sedimentation in the Kaoko Belt (NW Namibia) – Implications for the pre-collisional evolution of the Kaoko–Dom Feliciano–Gariep orogen

Detrital zircon provenance study of a metamorphosed sedimentary succession in the eastern part of the Kaoko Belt in Namibia has revealed two distinct sources for the Neoproterozoic sedimentation along the southwestern Congo Craton margin. The lower part of the succession shows detrital zircon ages consistent with erosion of Paleoproterozoic basement of the Congo Craton with an inferred Mesoproterozoic volcano-sedimentary cover. Within the middle part of the succession, which includes glaciogenic sediments correlated with the Sturtian (717–660Ma) glaciation, the Mesoproterozoic zircon grains disappear and the signal is dominated by ages known from the Congo Craton basement. The sedimentation in these parts of the succession is interpreted as related to the early Neoproterozoic rifting.The sedimentary rocks in the top part of the profile contain only subordinate proportion of the Paleoproterozoic–Archaean zircon grains and the populations are dominated by three age groups of ca. 1.0–1.2Ga, ca. 800–750Ma and ca. 650Ma, consistent with erosion of the Punta del Este–Coastal Terrane exposed in the centre of the Kaoko–Dom Feliciano–Gariep orogen. An associated glaciogenic horizon interpreted as reflecting the Marinoan (645–635Ma) glaciation constrains the sedimentation in the upper part of the succession and suggests a short time span between the high-grade metamorphism/magmatism in the Punta del Este–Coastal Terrane and its exhumation. Sedimentary rocks with such detrital zircon pattern appear also in the Damara and Gariep belts. Their source in the western part of the Kaoko–Dom Feliciano–Gariep orogen suggests that they represent an early orogenic flysch that originated during early collision in the western part of the orogen.The short time span between the metamorphism/magmatism in the Punta del Este–Coastal Terrane and deposition of the early orogenic flysch derived from it suggests that the Coastal Terrane was never separated from the Congo Craton by an oceanic domain. The estimated time span between the end of lithospheric stretching and sedimentation of the early flysch suggests that the hypothetical Adamastor Ocean separating the western and eastern forelands of the Kaoko–Dom Feliciano–Gariep orogen must have been small.

Investigating the stratigraphy and palaeoenvironments for a suite of newly discovered mid-Cretaceous vertebrate fossil-localities in the Winton Formation, Queensland, Australia

The Winton Formation of central Queensland is recognized as a quintessential source of mid-Cretaceous terrestrial faunas and floras in Australia. However, sedimentological investigations linking fossil assemblages and palaeoenvironments across this unit remain limited. The intent of this study was to interpret depositional environments and improve stratigraphic correlations between multiple fossil localities within the preserved Winton Formation in the Eromanga Basin, including Isisford, Lark Quarry, and Bladensburg National Park. Twenty-three facies and six repeated facies associations were documented, indicating a mosaic of marginal marine to inland alluvial depositional environments. These developed synchronously with the final regression of the Eromanga Seaway from central Australia during the late Albian-early Turonian. Investigations of regional- and local-scale structural features and outcrop, core and well analysis were combined with detrital zircon provenance signatures to help correlate stratigraphy and vertebrate faunas across the basin. Significant palaeoenvironmental differences exist between the lower and upper portions of the preserved Winton Formation, warranting informal subdivisions; a lower tidally influenced fluvial-deltaic member and an upper inland alluvial member. This work further demonstrates that the Isisford fauna is part of the lower member of the preserved Winton Formation; whereas, fossil localities around Winton, including Lark Quarry and Bladensburg National Park, are part of the upper member of the Winton Formation. These results permit a more meaningful framework for both regional and global comparisons of the Winton flora and fauna.

Evidence for transition from a continental forearc to a collisional pro-foreland basin in the eastern Trans-Hudson Orogen: Detrital zircon provenance analysis in the Labrador Trough, Canada

The New Quebec Orogen (NQO) is the best preserved supracrustal belt of the deeply eroded Paleoproterozoic Trans-Hudson Orogen and thus constitutes an exceptional window to investigate one of the most ancient Wilson cycle sedimentary records within the Manikewan paleo-ocean. It consists of a Paleoproterozoic supracrustal belt that underwent reworking when the Superior Craton collided with an Archean to Paleoproterozoic microcontinent (Core Zone terrane), during the Trans-Hudsonian orogeny.Within the NQO, the western and central parts of the Labrador Trough comprise greenschist-facies sedimentary and volcanic sequences (Kaniapiskau Supergroup) inferred to represent the rifted margin of the Superior Craton, whereas the Laporte Group (eastern part), composed of similar successions but metamorphosed to higher grades, remains of unclear origin. Competing models purport that the Laporte Group is either a deeper, higher-grade exposure of the Kaniapiskau Supergroup, or an exotic terrane. Large-scale sampling, petrography and SHRIMP U-Pb detrital zircon geochronology provide insights to elucidate the sedimentary provenance and depositional environments for both zones.Kaniapiskau Supergroup detrital zircons yield ages older than 2.5Ga, showing a signature typical of the Archean Superior Craton with a main peak at ∼2.72Ga. There is a gap of more than 150Ma between detrital zircon ages and the interpreted depositional age, suggesting a divergent environment like a rift and passive margin.In contrast, detrital zircons from the Laporte Group yield ages as young as 1834±2.4Ma and a dominant age peak at 1.84Ma. The presence of age peaks at 2.2–2.4Ga suggests that the Core Zone exotic terrane is the main source area, and the metamorphic monazite ages previously dated at 1793±2Ma point to a relative short depositional time.The presence of an Andean-type magmatic arc in the western part of the Core Zone terrane supports the interpretation of an eastward subduction at 1860–1830Ma. Furthermore, a lag time between crystallization and deposition ages within the Laporte Group points to convergent and collisional settings, with a 40Ma transition from continental forearc basin to collisional pro-foreland basin, marking the consolidation of the Columbia Supercontinent in northeastern Laurentia.

Neoproterozoic backarc basin on the southeastern margin of the Yangtze block during Rodinia assembly: New evidence from provenance of detrital zircons and geochemistry of mafic rocks

Several tectonic models have been proposed for the Neoproterozoic amalgamation of the South China block during the assembly of Rodinia. However, the timing of the end of arc magmatism between the two subblocks in the South China block (i.e., the Yangtze and Cathaysia blocks) remains controversial because it is unclear whether the 860−820 Ma magmatic rocks and coeval sedimentary basins in this area are related to subduction or plume activity. Here, we present new detrital zircon U-Pb and Hf isotopic data for the sediments directly overlying early Neoproterozoic arc volcanic rocks in this region. These data reveal a rhythmic change in source coincident with a progressive increase in the amount of juvenile and old crustal detritus within these sediments. This result, combined with the presence of a fining-upward grain-size trend and horizontal bedding within these sediments, provides evidence of bidirectional sources that are consistent with a backarc setting. The juvenile crustal material within these sediments was sourced from adjacent arc terranes to the east, whereas the old crustal detritus was derived from the Yangtze block to the west. In addition, sensitive high-resolution ion microprobe zircon U-Pb dating of mafic rocks within equivalent sedimentary sequences yielded ages of ca. 860−840 Ma, and these mafic rocks have arc- or mid-ocean-ridge basalt−like geochemical features that indicate the initiation of backarc spreading associated with Neoproterozoic NW-directed subduction. The data from the sediments and mafic rocks suggest the presence of a backarc basin system at ca. 860−820 Ma within the southeastern margin of the Yangtze block. This in turn indicates that Rodinia assembly was not completed until ca. 820 Ma, with the South China block possibly acting as a connection between a Neoproterozoic Andean-type active continental margin and Grenvillian belts on the paleo−western margin of the Rodinia supercontinent.

A tale of two basins? Stratigraphy and detrital zircon provenance of the Palaeoproterozoic Turee Creek and Horseshoe basins of Western Australia

The 2445–2010Ma tectonic evolution of the southwestern Pilbara Craton is recorded by two depositional basins, but considering the time span involved it is pertinent to question whether only two are preserved and others have vanished. The first, the Turee Creek Basin, developed conformably on an ∼2450Ma back-arc volcanic province, and was closed long before ∼2208Ma. It was a retroarc basin sited in front of a magmatic fold-thrust belt on the southwestern margin of the craton. Its folded strata were intruded by ∼2208Ma dolerite sills that are the preserved rock record of a large igneous province. The basin and dolerites were deformed by the N-verging ∼2195–2145Ma Ophthalmia Fold-Thrust Belt. The second, the Horseshoe Basin, formed at ≤2050Ma, unconformably truncating folded strata of the Turee Creek Basin and the ∼2208Ma dolerites, and was closed prior to intrusion of ∼2008Ma dolerite dykes. It was an intracontinental rift basin sited on the inverted fold-thrust belt. Detrital zircon age-spectra for the basins have poor fit to the zircon age-spectrum of the Pilbara, and differ significantly in their youngest modes. The youngest mode for the Turee Creek Basin is ∼2442Ma, whereas the youngest mode for the Horseshoe Basin decreases upwards from ∼2276Ma to ∼2206Ma. Although differing in youngest detrital zircon age-modes, zircon age-spectra of the basins are otherwise similar, and broadly match the Glenburgh Terrane on the southwestern margin of the craton. While Turee Creek sediments were derived from the southwest, Horseshoe sediments were derived from the north and northeast. This conundrum is resolved by the Ophthalmia Fold-Thrust Belt, which tectonically loaded the craton to the north and northeast to form a now-vanished Ophthalmia foreland basin that derived sediment from the south and southwest, thereby emplacing zircon with an exotic age-spectrum on the North Pilbara. Inversion of tectonic elements occurred during formation of the Horseshoe Basin, with the fold-thrust belt subsiding beneath the rift while the foreland basin was uplifted. Recycling of the foreland basin inverted its detrital zircon age-spectrum, explaining why the youngest detrital zircon age-mode of the Horseshoe Basin decreases in age upwards.

The zircon evidence of temporally changing sediment transport—the NW Gondwana margin during Cambrian to Devonian time (Aoucert and Smara areas, Moroccan Sahara)

Detrital zircon provenance studies are an established tool to develop palaeogeographic models, mostly based on zircon of siliciclastic rocks and isotope data. But zircon is more than just istopes and features well definable morphological characteristics. The latter may indicate single grain transport histories independent of the individual grade of concordance. This additional tool for palaeogeoraphic reconstructions was tested on zircon from siliciclastic and carbonate sedimentary rocks of Palaeozoic age from the Aoucert and Smara areas of the Souttoufides, while findings of zircon in limestone generally open new archives for sedimentary provenance analysis. The morphologies—length, width, roundness, grain surfaces—of 834 detrital zircons from sediments of allochthonous Cambrian, and (par-)autochthonous Ordovician, and Devonian units were studied, while 772 of them were analysed for their U–Th–Pb isotopes by LA-ICP-MS. Mesoproterozoic zircon contents of more than 10% in the Cambrian sediments exclude the West African Craton (WAC) as exclusive source area. Thus, at least one additional external source is suggested. This is likely the western Adrar Souttouf Massif with its significant Mesoproterozoic zircon inheritance, or comparable, yet unknown sources. Decreasing Mesoproterozoic zircon age populations in Ordovician sediments are thought to be linked to the rifting of the terranes in the course of the Rheic Ocean opening and a predominant supply of WAC detritus. The Devonian sediments likely contain reworked material from the Cambrian siliciclastics, which is shown by the zircon age distribution pattern and the zircon morphologies. Therefore, multiple shifts in the direction of sedimentary transport are indicated.

U-Pb Ages and Sedimentary Provenance of Detrital Zircons from Eastern Hayfork Meta-argillites, Sawyers Bar Area, Northwestern California

In the central Klamath Mountains, the Eastern Hayfork terrane (EHF) accreted directly seaward of the North Fork ophiolitic arc. The EHF trench mélange consists of very fine-grained, quartzose meta-argillite + boudinaged metachert layers as well as scattered blocks derived from both oceanic and inboard arc-margin sources. Among the exotic blocks are coarse-grained feldspathic metasandstones. Detrital zircon SHRIMP U-Pb ages ranging from the latest Archean to the early Proterozoic were reported by Scherer and colleagues in 2010 for five metasandstone blocks from the central and southern Klamaths; Phanerozoic zircons were totally lacking. It was concluded that the blocks were olistostromal and that erosion of a nearby thrust sheet outlier of the Proterozoic Antelope Mountain Quartzite of the Eastern Klamath belt, Yreka subterrane, was a likely source. To determine the provenance and time of deposition of the EHF muddy matrix host of the metasandstone blocks, we separated zircons from three very fine-grained, intimately interstratified, feldspar-poor meta-argillites from the Sawyers Bar map area. New laser ablation multicollector inductively coupled plasma mass spectrometry zircon U-Pb data indicate maximum sedimentary ages for the meta-argillites as ∼272, ∼211, and ∼201 Ma. Thus, the muddy strata were deposited near the end of Triassic time. The meta-argillites contain scattered Proterozoic and Paleozoic–early Mesozoic detrital zircons, indicating local inboard Klamath sources, including the Antelope Mountain Quartzite thrust sheet. St. Clair Creek distal turbidites in the landward North Fork terrane contain Paleozoic and Triassic–Early Jurassic (∼188 Ma) zircons as well as scattered Precambrian grains similar to those in the EHF. The EHF surficially docked against the North Fork terrane by ∼174–173 Ma because the amalgamated but unmetamorphosed terrane contact was invaded by the English Peak plutonic complex beginning at ∼172 Ma. Regional metamorphism and deformation took place throughout the central Klamath Mountains during the Siskiyou transpressive accretionary event at ∼170–168 Ma.

Magnetostratigraphy, age and depositional environment of the Lobo Formation, southwest New Mexico: implications for the Laramide orogeny in the southern Rocky Mountains

AbstractThe Lobo Formation of southwestern New Mexico consists of spatially variable continental successions attributed to the Laramide orogeny (80–40 Myr), although its age and provenance are virtually undocumented. This study combines sedimentological, magnetostratigraphical and geochronological data to infer the timing and origin of the Lobo Formation. Measured sections of Lobo strata at two locations, Capitol Dome in the Florida Mountains and in the Victorio Mountains, indicate significant differences in depositional environments and sediment provenance. At Capitol Dome, where Lobo strata were deposited above a syncline developed in Palaeozoic strata, deposition took place in fluvial, palustrine and marginal lacustrine settings, with alluvial‐fan deposits only at the top of the formation. Combined magnetostratigraphy and a young U–Pb detrital zircon age suggest deposition of the section at Capitol Dome from ~60 to 52 Ma. The Lobo Formation in the Victorio Mountains was deposited in alluvial‐fan and fluvial settings; the age of deposition is poorly bracketed between 66 ± 2 Ma, the weighted‐mean age of two young zircons, and middle Eocene (~40 Ma), the approximate age of overlying volcanic rocks. U–Pb zircon ages from sandstones at the Victorio and Capitol Dome localities indicate that different source rocks provided sediment to the Lobo Formation. Local Proterozoic basement (~1.47–1.45 Ga) dominated the source of the Lobo Formation in the Victorio Mountains, consistent with abundant granitic clasts that are present in the proximal facies there; a diverse range of grain ages suggest that recycled Lower Cretaceous strata provided the dominant source for Lobo Formation sediment at the Capitol Dome locality. The U–Pb data suggest that the depositional systems at the two sites were not connected. Contrasts in depositional setting and detrital zircon provenance indicate that the Palaeogene Lobo Formation in southwest New Mexico was deposited in an assemblage of local depositional settings, possibly in separate structural basins, as a consequence of Laramide tectonics in the region.

Detrital zircon provenance of upper Cambrian-Permian strata and tectonic evolution of the Ellsworth Mountains, West Antarctica

Detrital zircons from the upper Cambrian-Devonian sandstones (Crashsite Group; n=485) and Carboniferous tillite (Whiteout Conglomerate; n=81) of the Ellsworth Mountains, Antarctica record a steady supply of Neoproterozoic (“Pan-African”) orogeny (~550–600Ma), Grenville (~1000Ma) and Neoarchean (~3000–3500Ma) zircons into the northern marginal basin of Gondwana. The overlying Permian Glossopteris-bearing Polarstar Formation shales (n=85) have the same zircon provenance as underlying units but also include a dominance of depositional-age (263Ma) euhedral zircons which are interpreted to be of local, volcanic arc origin. Modeling of detrital zircon provenance suggests that source areas were present in Pan-African and Laurentian crust throughout the Paleozoic. We also report calcite twinning strain results (12 strain analyses; n=398 twins) for the Cambrian Minaret Fm. in the Heritage range which is predominantly a layer-parallel shortening strain in the direction (WSW-ENE) of Permian Gondwanide orogen thrust transport. There is a secondary, sub-vertical twinning strain overprint. The initiation of localized lower-middle Cambrian rifting (Heritage Group deposition) in Grenville-aged crust as Gondwana amalgamated and the subsequent Jurassic counterclockwise rotation of the Ellsworth-Whitmore terrane out of the Permian Gondwanide belt into central Antarctica each remain tectonic curiosities.

Relict basin closure and crustal shortening budgets during continental collision: An example from Caucasus sediment provenance

Comparison of plate convergence with the timing and magnitude of upper-crustal shortening in collisional orogens indicates both shortening deficits (200-1700 km) and significant (10-40%) plate deceleration during collision, the cause(s) for which remain debated. The Greater Caucasus Mountains, which result from post-collisional Cenozoic closure of a relict Mesozoic back-arc basin on the northern margin of the Arabia-Eurasia collision zone, help reconcile these debates. Here we use U-Pb detrital zircon provenance data and the regional geology of the Caucasus to investigate the width of the now-consumed Mesozoic back-arc basin and its closure history. The provenance data record distinct southern and northern provenance domains that persisted until at least the Miocene. Maximum basin width was likely ~350-400 km. We propose that closure of the back-arc basin initiated at ~35 Ma, coincident with initial (soft) Arabia-Eurasia collision along the Bitlis-Zagros suture, eventually leading to ~5 Ma (hard) collision between the Lesser Caucasus arc and the Scythian platform to form the Greater Caucasus Mountains. Final basin closure triggered deceleration of plate convergence and tectonic reorganization throughout the collision. Post-collisional subduction of such small (102-103 km wide) relict ocean basins can account for both shortening deficits and delays in plate deceleration by accommodating convergence via subduction/underthrusting, although such shortening is easily missed if it occurs along structures hidden within flysch/slate belts. Relict-basin closure is likely typical in continental collisions in which the colliding margins are either irregularly shaped or rimmed by extensive back-arc basins and fringing arcs, such as those in the modern South Pacific.

Detrital-Zircon Mixing and Partitioning In Fluvial To Deep Marine Systems, Central California, U.S.A.

The increasing use of detailed detrital-zircon provenance data calls for an understanding of the controls that sedimentary processes exert on changing detrital-zircon provenance signatures in time and space in addition to the well-established influence of tectonics. Our U-Pb detrital-zircon data from seventeen samples taken across a series of modern second-order rivers to deep-marine depositional systems in central California show that marine mixing processes and sediment pathway partitioning exert important controls on detrital-zircon provenance signatures. The second-order rivers that input sediment into this system produce differentiable detrital-zircon provenance signatures as a function of the unique geology of their drainage areas. The mixing of sediment through the marine realm can be traced through the evolution of distinct detrital-zircon signatures as sediment is transported from rivers down system through longshore drift into submarine canyons. Sediment input from second-order streams is mixed in the littoral and upper submarine-canyon environments, yielding provenance signatures that are not thoroughly mixed until the lower reaches of submarine canyons. Sediment partitioning in these dispersal systems results in distinct detrital-zircon provenance signatures for different dispersal systems over short length scales (< 50 km). These data suggest that sediment mixing in the marine realm is likely an important control on detrital-zircon provenance signatures in any system in which sediment is transported through longshore drift and sediment pathways are distinctly partitioned. Changes in the way sediment pathways are partitioned through time has the potential to create heterogeneous detrital-zircon provenance signatures in stratigraphic successions through time and between closely spaced deposits of the same age. When seen in an ancient system, this heterogeneity may be mistakenly attributed to tectonic controls without the recognition of the influence of sedimentary process.