Rocks Of Similar Age Research Articles

Paleomagnetic Records From Pulsed Magmatism in the Southwestern Laurentia Large Igneous Province and Cardenas Basalt Support Rapid Late Mesoproterozoic Plate Motion

AbstractMafic intrusions, lava flows, and felsic plutons in southwestern Laurentia have been hypothesized to be associated with the emplacement of a late Mesoproterozoic (Stenian Period) large igneous province. Improved geochronologic data resolve distinct episodes of mafic magmatism in the region. The ca. 1,098 Ma main pulse of southwestern Laurentia large igneous province (SWLLIP) magmatism is recorded by mafic intrusions across southeastern California to central Arizona. A younger episode of volcanism resulted in eruptions that formed the ca. 1,082 Ma Cardenas Basalt, which is the uppermost unit of the Unkar Group in the Grand Canyon. With the updated geochronological constraints, we develop new paleomagnetic data from mafic sills in the SWLLIP. Overlapping poles between the Death Valley sills and rocks of similar age in the Midcontinent Rift are inconsistent with large‐scale Cenozoic vertical axis rotations in Death Valley. We also develop a new paleomagnetic pole from the ca. 1,082 Ma Cardenas Basalt (pole longitude = 183.9°E, pole latitude = 15.9°N, = 7.4°, N = 18). The new paleomagnetic data are consistent with the pole path developed from time‐equivalent rocks of the Midcontinent Rift, supporting interpretations that changing pole positions are the result of rapid equatorward motion. These data add to the record of Laurentia's rapid motion from ca. 1,110 to 1,080 Ma that culminated in collisional Grenvillian orogenesis and the assembly of Rodinia.

A review of small-bodied theropod dinosaurs from the Upper Cretaceous of India, with description of new cranial remains of a noasaurid (Theropoda: Abelisauria)

ABSTRACT Small-bodied theropod dinosaurs are rare on southern landmasses but have been known from India for a century. Excavations by Charles Matley and Durgansankar Bhattacharji in uppermost Cretaceous sediments at Bara Simla, central India in 1917–1919 recovered small theropod vertebral and limb elements originally interpreted as coelurosaurians and separated into at least three species (Compsosuchus solus, Laevisuchus indicus, Jubbulpuria tenuis) based on features that can now be attributed to their serial position in the vertebral column. The comparatively recent discoveries of Noasaurus leali and Masiakasaurus knopfleri from similar-aged rocks in South America and Madagascar, respectively, and advances in basal theropod systematics led to a revised interpretation of most small-bodied Indian theropods as noasaurid abelisauroids. Here we review and redescribe Laevisuchus, Jubbulpuria, and Compsosuchus, including several elements that until now were thought lost, and describe a new partial noasaurid dentary from central India. The dentary bears the characteristic procumbent dentition of Masiakasaurus, which apparently is absent in Noasaurus. Likewise, cervical vertebrae of Laevisuchus more closely resemble those of Masiakasaurus than those of Noasaurus. Despite these similarities, phylogenetic analyses indicate that the balance of character data supports the Indian noasaurid species outside the sister-taxon pairing of South American and Malagasy species. Bones of small-bodied theropods have been recovered exclusively from the youngest Mesozoic localities in India (e.g., Pisdura, Bara Simla); to date they have not been reported from the slightly older localities in western and central India, from southern Indian sites in the Cauvery Basin, nor from the Vitakri Formation of Pakistan.

Early Cretaceous volcanic-arc magmatism in the Dalat-Kratie Fold Belt of eastern Cambodia: implications for the lithotectonic evolution of the Indochina terrane

Mesozoic granitic plutons are found throughout the Indochina terrane of eastern Cambodia and southern Vietnam. The granitic rocks range in age from Early Triassic (240 Ma) to Late Cretaceous (80 Ma) and record distinct tectonomagmatic periods associated with subduction of the Paleotethys and Paleo-Pacific oceans. Samples collected from the Snoul pluton, eastern Cambodia are composed of silicic and intermediate dioritic rocks, and basalt. The quartz diorites and diorites are magnesian, metaluminous, calcic to calc-alkalic, and similar to volcanic-arc granitoids whereas the basaltic rocks are compositionally similar to within-plate basalt. Zircon U-Pb geochronology and Lu-Hf isotopes and whole rock Sr-Nd isotopes show that the silicic rocks are Albian and isotopically juvenile (107.5 ± 0.3 Ma, 109.1 ± 0.4 Ma; εHf(t) = +7.0–+17.0; 87Sr/86Sri = 0.704313–0.707681; εNd(t) = +3.1–+4.9). Fractional crystallization modeling using a dioritic composition as the parental magma demonstrates that it is possible to generate the quartz diorite compositions under oxidizing (ΔFMQ +1) and hydrous (H2O = 2 wt%) conditions suggesting that they are consanguineous. The isotopically juvenile nature of the dioritic rocks and their compositional similarity (SiO2 ≥ 56 wt%, Al2O3 ≥ 15 wt%, Sr ≥ 400 ppm, Y ≤ 18 ppm, Yb ≤ 1.9 ppm) to adakitic rocks indicates that the parental magmas of the Snoul pluton were likely derived by partial melting of juvenile mafic basement rocks of the Indochina terrane. Moreover, Early Cretaceous plutonic rocks of Cambodia are isotopically distinct from plutonic rocks of similar age and tectonic setting from Vietnam suggesting that there could be a lithotectonic domain boundary within the Southern Indochina terrane. In contrast, the basaltic rocks likely record a temporally distinct period of magmatism associated with Late Cenozoic tensional plate stress.

AGE OF THE KINTEREP FORMATION OF THE NORTHWESTERN SALAIR: CHEMOSTRATIGRAPHY AND U-Pb ZIRCON DATING

A comprehensive study of the stratotype section of the Kinterep formation of the North-Western Salair was carried out, including geochemical and isotope (Sr, C, O) studies of carbonate rocks, and U-Pb dating (LA-ICP-MS) of igneous zircon crystals from tuffites. The studied carbonate rocks are pure limestones with Mg/Ca less than 0.007 and a low proportion of insoluble residue (average 5 %). Kinterep limestones are characterized by δ 18 O SMOW values from 19.8 to 23.8 ‰ and δ 13 С PDB values from –0.7 to +0.9. The Sr isotope composition in limestones of the Kinterep formation varies in a narrow range of 87 Sr/ 86 Sr values between 0.70851 and 0.70859. Comparison of the obtained isotopic characteristics ( 87 Sr/ 86 Sr and δ 13 С PDB ) of Kinterep formation limestones with the generalized global 87 Sr/ 86 Sr variation curve and δ 13 С PDB values in the pale-ocean suggests two equally probable interpretations of the time of accumulation of Kinterep formation limestones: 550–540 and 525–510 Ma. U-Pb dating of magmatic zircon crystals from tuffite, which forms an interlayer among limestones of the Kinterep formation, showed the age at the boundary of ~515 Ma. Thus, using a combination of isotope (Sr, C) chemostratigraphy of carbonate rocks and U-Pb dating of igneous zircon crystals from tuffites syngenetic to limestones, the age limit of 525–510 Ma was established for the time of the formation of the Kinterep formation of the Salair basin. Carbonate rocks of similar age and similar features of the isotopic composition are known in neighbouring areas (for example, the Kuznetsk Alatau) and in regions of the Siberian Platform and microcontinents of Central Asia (Tuva-Mongolian and Dzabkhan) spatially distant from the Salair basin.

Thermal evolution of onshore West Iberia: A better understanding of the ages of breakup and rift-to-drift in the Iberia-Newfoundland Rift

The age of breakup which formed the Central-North Atlantic has been debated for many decades and is still subject to debate: from ca. 150 Ma to 110 Ma. To address this issue, we have carried out a thermochronological study of the eastern margin of the rifted Iberia-Newfoundland sector. New apatite fission-track (AFT) data acquired on samples from the footwall (Variscan basement) and one sample (Triassic of the Lusitanian Basin) from the hanging wall of the principal normal fault bounding the basin. Thermal history of western Iberia can be then reconstructed since ca. 250 Ma. Fission-track ages of Variscan granitoids (whose crystallization age is >275 Ma) range between 191 ± 8 Ma and 75 ± 5 Ma, indicating that significant thermal events affected the study area during that period. Thermal inversion supports two main cooling events that we attribute to a major uplift and denudation of the Variscan basement, consistent with widespread basement-derived siliciclastic rocks of similar ages: Late Jurassic/Early Cretaceous (ca. 150–145 Ma) and late Early Cretaceous (ca. 110 Ma). From the sedimentary record in the Lusitanian Basin and the new AFT data, we deduce that: (1) temperatures >70–110 °C affected west Iberia between ca. 190 and 150 Ma, which can be explained partly by a subsiding basement in both foot and hanging walls; (2) the main cooling event at ca. 150–145 Ma is interpreted as major rift flank uplift; (3) the ca. 110 Ma cooling event may be linked to the final evolution of the margin and onset of oceanic spreading. We infer that the AFT main cooling event at ca. 150–145 Ma reflects the break of the elastic core of the lithosphere (whole lithosphere failure = breakup) with significant rift shoulder uplift (end of Rift 1), which was followed by hyper-extension and mantle exhumation (Rift 2) and finally, by oceanic spreading (rift-to-drift) at ca. 110 Ma (onset of Rift 3).

Geochronological and geochemical comparison of Precambrian meta-mafic volcanics in Zhongtiaoshan and Lüliangshan Regions in Shanxi, North China Craton

To unravel the geochemical heterogeneity and its origin in different terranes of North China, we conducted geochronological and geochemical analyses of the meta-mafic rocks from the Luliang–Zhongtiao rift zone (Shanxi Province). LA-ICP-MS zircon U–Pb dating yielded mostly End-Neoarchean to Proterozoic ages for the basement rocks (Sushui Complex: 2516 ± 26 Ma; Meta-mafic rocks: 2494 ± 31 Ma), Jiangxian Group (~ 2213 Ma), Zhongtiao Group (2077 ± 29 Ma), Jiehekou Group (1998 ± 23 Ma), and Luliang Group (2152 ± 52 Ma). Petrographic characteristics show that the meta-mafic rocks from the Neoarchean–Paleoproterozoic Zhongtiaoshan (Sushui Complex) have similar geochemical characteristics to the overlying Jiangxian and Zhongtiao Groups. The Paleoproterozoic Luliang and Yejishan Group meta-mafic rocks from Luliangshan also have similar geochemical characteristics but are geochemically different from similar-age rocks from Zhongtiaoshan. This shows that the late-stage rocks have a geochemical inheritance from the early-stage rocks in the same region and that the geochemical heterogeneity of rocks from different areas was originated from the inherited heterogeneity of the magma source.

Ordovician metamorphism and magmatism preserved in the Ossa Morena Complex: SHRIMP geochronology, geochemistry and Sr[sbnd]Nd isotopic signatures of the Sierra Albarrana Domain (SW Iberian Massif)

This study integrates SHRIMP UPb zircon geochronology and whole-rock and SrNd isotope geochemistry data from migmatites and granitic rocks of the Sierra Albarrana Domain. We provide new information on the magmatic and metamorphic events of this domain of the Ossa-Morena Complex. The metasedimentary succession, nowadays corresponding to a migmatite dome, was probably deposited during the Ediacaran and Cambrian. SHRIMP UPb ages of magmatic and zoned metamorphic zircon grains indicate that the main tectono-magmatic event in the Sierra Albarrana Domain is Late Cambrian (granite emplacement; 481.2 ± 2.3 Ma) to early Ordovician (migmatization; 477.8 ± 2.4 Ma), supported by the intrusion of La Cardenchosa Pluton, by the low-pressure partial melting and by the ductile deformation of the host metasedimentary rocks. We suggest that the granitic magmatism, the migmatization and the main regional fabrics are part of a single Ordovician event, only slightly modified by Variscan reworking.Geochemical and isotopic data are compatible with an extensional environment in the middle-upper crustal levels, related to a continental rift development. This setting and timing are compatible with the latest magmatic event of the Early Paleozoic rifting (535–460 Ma), well documented in the Ossa Morena Complex. The geochemical characteristics of the subalkaline rift-related rocks of the Ossa Morena Complex and of the Central Iberian Zone partly coincide. As a result, it is not possible to discriminate between them and favor a correlation between both terranes based on the geochemical affinities of magmatic rocks of similar age.

Formation and evolution of the Eastern Kunlun Range, northern Tibet: Evidence from detrital zircon U-Pb geochronology and Hf isotopes

The Eastern Kunlun Range, as a high-elevation and granitoid-rich tectonic element in northern Tibet, records Paleozoic–Mesozoic amalgamation process of the East Asia continent and Cenozoic uplift of the Tibetan Plateau. However, Precambrian evolution of the Eastern Kunlun remains poorly understood and relations between Eastern Kunlun and adjacent terranes (e.g., Qaidam and Qilian) during the Phanerozoic accretion process are still highly controversial. We use detrital zircon U-Pb geochronological and Hf isotopic data of Proterozoic and Paleozoic metasedimentary rocks from the Eastern Kunlun Range, to reconstruct its origin and subsequent evolutionary history. Detrital zircons of the Proterozoic rocks are dominated by early–middle Neoproterozoic ages (700–1000 Ma), with two age peaks at ca. 800 Ma and ca. 920 Ma and εHf(t) values ranging from −10 to 5. The youngest detrital zircon ages (648–788 Ma) demonstrate that these investigated Proterozoic strata, which were previously mapped as Paleoproterozoic to Mesoproterozoic, were most likely deposited in the middle–late Neoproterozoic. Abundant 0.9–1.0 Ga detrital zircon crystals are consistent with those crystalline rocks of similar ages across the Kunlun-Qaidam and Qilian terranes, which are generally interpreted as the product of Grenvillian orogenesis. These findings support the hypothesis that these terranes were probably within a single continental landmass (named as KQQ block) during the Neoproterozoic. The high similarity of detrital zircon ages, Hf isotopes and Neoproterozoic lithostratigraphy between western Yangtze and KQQ blocks, supports a temporary connection of the KQQ block to western Yangtze in Rodinia supercontinent. Detrital zircons of the analyzed Paleozoic rocks are characterized by 390–490 Ma age populations. These results, in combination with published granitoids data of the northern Tibet, favor a scenario in which the Kunlun-Qaidam and Qilian terranes underwent separated subduction and accretion processes during the late Cambrian–Devonian, but together formed an upper plate to northward subduction of the Paleo-Tethys during the Permian–Triassic.

Mesoarchean TTG magmatism from the northeastern margin of the Kaapvaal Craton, southern Africa: Arguments for an exotic terrane (remnant of Pilbara Craton?)

High-grade terranes along Archean cratonic margins either represent remobilized equivalents of the adjacent low-grade domain or an exotic entity which accreted to the developing craton. This study addresses this debate for the Southern Marginal Zone high-grade terrane along the northeastern margin of the Kaapvaal Craton. The Hout River shear zone separates the high-grade terrane from the adjacent low-grade Pietersburg block of the Kaapvaal Craton. Tonalite-trondhjemites of the Baviaanskloof gneiss unit constitute the dominant rock in the Southern Marginal Zone. Both pyroxene-bearing and pyroxene-absent variants occur. Locally, the granitoids are affected by anatectic and metasomatic overprints. Magmatic textures are better preserved in the massive granitoids. U-Pb zircon analyses of two orthopyroxene-bearing granitoids gave Mesoarchean crystallization ages [3088 ± 11 Ma (massive), 3121 ± 9 Ma (banded)]. However, overprint ages differ, with 2706 + 50/−34 Ma from the massive variety, and 1925 ± 19 Ma, 1976 ± 11 Ma from the banded variety. The syn-tectonic ~2.71 Ga is interpreted as metamorphic overprint age, while the post-tectonic ~2 Ga represent age of local overprint. Available geochemical data on the Baviaanskloof granitoids are similar to Archean TTGs. A possible spatial-temporal transition from ~3.13 Ga low-pressure through ~3.12–2.98 Ga medium-pressure to ~2.92 Ga high-pressure TTG is delineated from the northwest towards the southeastern Southern Marginal Zone. This trend is compatible with the southward directed polarity of accretion events recognised in the adjacent low-grade Pietersburg block. We argue that the northeastern margin of the Kaapvaal Craton, north of the Hout River shear zone, is an exotic terrane because 1) the Baviaanskloof granitoid event (~3.1–2.9 Ga with peak at ~3.1 Ga) is older than the accretion episodes (~2.97–2.92 Ga with peak at ~2.95 Ga, and ~2.87–2.84 Ga with peak at ~2.86 Ga) in the adjacent Pietersburg block, 2) the younger ~2.86 Ga event occurs closer to the Hout River shear zone, while the older ~2.95 Ga event was away from it, and 3) contemporaneous (~3.1–3.0 Ga) detrital zircons are absent in greenstone belts of the Pietersburg block that are proximal to the Hout River shear zone. Possible connection to rocks of similar age from the Pilbara Craton as part of the Vaalbara supercraton is explored.

Prey fractionation in the Archaeocyatha and its implication for the ecology of the first animal reef systems

AbstractArchaeocyaths are the most abundant sponges from the Cambrian period, having formed the first animal reef communities more than 500 million years ago. The Archaeocyatha are index fossils for correlating rocks of similar ages globally because of their abundance, extensive geographic distribution, detailed anatomy, and well-established taxonomy. Their ecological significance remains incompletely explored, yet they are known to have strongly competitively interacted, unlike modern sponges. This study examines the feeding ecology of the fossil remains of Siberian archaeocyath assemblages. As suspension feeders, archaeocyaths filtered plankton from the water column through pores in their outer wall. Here we outline a new method to estimate the limit on the upper size of plankton that could be consumed by an archaeocyath during life. The archaeocyaths examined were predominantly feeding on nanoplankton and microplankton such as phytoplankton and protozooplankton. Size-frequency distributions of pore sizes from six different Siberian archaeocyath assemblages, ranging from Tommotian to Botoman in age, reveal significantly different upper limits to the prey consumed at each locality. Some of the assemblages contain specimens that could have fed on larger organisms extending into the mesoplankton, including micro-invertebrates as a possible food resource. These results show that during the establishment of the first animal reef systems, prey partitioning was established as a way of reducing competition. This method has applicability for understanding the construction and the functioning of the first reef systems, as well as helping to understand modern reef systems and their development though time and space.

2.2 ga mafic sills in the central part of the Karelian Сraton: U-Pb dating of zircons and geochemistry of gabbro-dolerites in the lake Bolshozero area

New age and compositional data for mafic igneous intrusions in the Bolshozero area, western Karelia, are reported. In this area, Jatulian gabbro-dolerites form several bodies that cut through the host Archean and Paleoproterozoic supracrustal and granitoid rocks. Paleoproterozoic mafic igneous rocks vary in composition from melanogabbr to leucocratic gabbro-dolerites and gabbro-pegmatites. Such variations are probably caused by in situ fractional crystallization of the mafic melt, and point to a gently sloping primary orientation of the bodies. The gabbro-dolerites were altered under greenschist –epidote-amphibolite facies, which caused the replacement of primary magmatic minerals by amphibole, epidote, and titanite. According to the results of U-Pb SIMS (SHRIMP II, VSEGEI) dating of zircons extracted from the gabbro-pegmatites, the age of their magmatic crystallization is considered to be 2225 ± 20 Ma. This dating supports the assumption about the Jatulian age of magmatic crystallization of gabbro-dolerites in Bolshozero area. In their chemical composition, the gabbro-dolerites of Bolshozero area show a subalkaline series affinity, with the exception of gabbro-pegmatites, which are strongly enriched in Na2O, LILE, and LREE. Trace element distribution, LREE enrichment and Nb depletion suggest that crustal contamination has contributed significantly to the evolution of the primary melts. This assumption is supported also by the Nd isotopic composition data (εNd2200 = –0.3). The analysis of the available geochemical and age data and comparison with mafic igneous rocks of similar age located in the western part of the Karelian Craton suggest that mafic sills in Bolshozero area belong to the large igneous province aged ca. 2.22 Ga, which marks the termination of the Paleoproterozoic endogenic lull.

Adakite Volcanism at the Continental Margin and Associated Problems. Part I. Adakites from the Upper Reaches of the Valovayam River: New Age, Mineral, and Chemical Data and Petrological Modeling

The paper presents new age and petrological–geochemical data on the rocks of the Valovayam River area (Kamchatka Isthmus) and some areas of the Sredinny Range of Kamchatka (Orlov Volcano, Polovinnaya, Stolbovaya, and Matera mountains). Analysis of the obtained data shows that the spatial and temporal association of the intraplate and island-arc volcanism in the Valovayam River area is not accidental, but resulted from melting of a common source related to the mantle diapir. Additional data on the composition of the mantle xenoliths and the traces of their melting in the form of residual glasses make it possible to relate the formation of different rock series into a single process. A two-stage petrogenetic model is proposed: (1) formation of “black pyroxenites” as a result of melting of mantle lherzolites and (2) formation of the whole rock assemblage through melting of the same lherzolites and newly formed pyroxenites. The concurrent study of the rocks of similar age from the Valovayam River area and the Sredinny Range allows us to distinguish two types of adakites: high-Si adakites (HSA) in the former area and low-Si adakites (LSA) in the latter. The formation of the first type is related to the fractionation, melting, and breakdown of amphibole, while the formation of the second type was controlled by the fractionation and melting of pyroxene.

Spatial and temporal links between shawinigan accretionary orogenesis and massif anorthosite intrusion, southern grenville province, New York, U.S.A.

Synthesis of new and existing field, structural, geochemical, isotopic, and geochronologic data in the Adirondack Highlands of the southern Grenville Province indicate a suite of arc plutonic rocks (Piseco Lake granite suite) was intruded into basement rocks from ca. 1205–1180 Ma due to northward subduction beneath the Laurentian margin. Although rocks of similar age and origin are found in the Adirondack Lowlands and elsewhere in the Highlands, they occur in the greatest volume and are most intensely deformed in the Piseco Lake Shear Zone (PLSZ). This structure separates the Adirondack Highlands from ca. 1350-1300 Ma tonalitic gneisses in the southern Adirondacks. Tectonites in the PLSZ record the deformation of a continental arc batholith during collision with an outboard terrane which was accreted to Laurentia during the Shawinigan Orogeny. Internal to the PLSZ, a 10–15 km wide, subvertical zone of subhorizontally lineated L-S and L-tectonites (Piseco Lake gneisses) was derived primarily from megacrystic arc plutonic protoliths and documents sinistral relative motion. Intrusion of the arc granitoids, deformation and anatexis (ca. 1180–1160 Ma) throughout the entire Adirondack region immediately preceded and overlapped the intrusion of the anorthosite-mangerite-charnockite-granite (AMCG) suite at ca. 1165-1145 Ma in the Adirondack Highlands. We hypothesize that delamination or slab detachment, in combination with an irregular Laurentian margin, triggered disruption of the underlying lithosphere, allowed ascent of enriched asthenosphere, and facilitated the intrusion of voluminous AMCG rocks in the Adirondacks north of the PLSZ. Other large anorthosite massif complexes in the southern Grenville Province, including the Morin and Lac St. Jean bodies near the Laurentian margin, have also been linked to Shawinigan convergent structures and were an important part of accretionary processes documented in the Grenville Orogen.

Latest Neoproterozoic to Cambrian detrital zircon facies of western Laurentia

Abstract Late Neoproterozoic to Cambrian sandstone units are common in western Laurentia and record initial transgression of the craton after the formation of the western passive margin during the latest Neoproterozoic to earliest Cambrian. Detrital zircon measurements from 42 latest Neoproterozoic to Cambrian basal Sauk sequences and five older Neoproterozoic sandstone samples from a region extending from the Mexico–United States border to central British Columbia, Canada, are combined with previous results to characterize sediment source areas and dispersal systems. Detrital zircon populations in Neoproterozoic and Cambrian sedimentary rocks are divided into six facies based on a statistical comparison using multidimensional scaling. Detrital zircon facies are found in unique geographical regions reflecting proximity to the major tectonic provinces of Laurentia. Samples from northern regions are dominated by Archean and Paleoproterozoic zircons derived from Archean tectonic provinces and the orogenic belts that record the assembly of the Laurentian craton. More southerly sample locations show an increase in detrital zircons derived from younger Paleoproterozoic orogenic belts and early Mesoproterozoic intrusive suites. Detrital zircons from Grenville-aged sources are common in the south. The Transcontinental Arch, a feature interpreted to have controlled large-scale sediment dispersal patterns in the mid- to late Cambrian, likely played a major role in isolating the southern and northern signatures. Our data set can be used to test tectonic models for the Cordilleran orogen that invoke Jurassic or Cretaceous collision of a ribbon continent as the driving mechanism for orogenesis. Cambrian rocks of the Cassiar-Antler platform juxtaposed with North America during the hypothetical ribbon continent collision show the same geographic distribution of detrital zircon facies as similar-aged rocks from autochthonous and parautochthonous locations on the Laurentian margin. The concordance of detrital zircon facies across the proposed suture is a negative result for models that predict large dextral displacements, on the order of 2000 km, across the suture.

Implications of Late Cretaceous U–Pb zircon ages of granitic intrusions cutting ophiolitic and volcanogenic rocks for the assembly of the Tauride allochthon in SE Anatolia (Helete area, Kahramanmaraş Region, SE Turkey)

An assemblage of NE–SW-trending, imbricate thrust slices (c. 26 km E–W long × 6.3 km N–S) of granitic rocks, basic-felsic volcanogenic rocks (Helete volcanics), ophiolitic rocks (Meydan ophiolite) and melange (Meydan melange) is exposed near the Tauride thrust front in SE Anatolia. The volcanogenic rocks were previously assumed to be Eocene because of associated Nummulitic limestones. However, ion probe U–Pb dating of zircons extracted from the intrusive granitic rocks yielded ages of 92.9 ± 2.2–83.1 ± 1.5 Ma (Cenomanian–Campanian). The Helete volcanic unit and the overlying Meydan ophiolitic rocks both are intruded by granitic rocks of similar age and composition. Structurally underlying ophiolite-related melange includes similar-aged, but fragmented granitic intrusions. Major, trace element and rare earth element analyses coupled with electron microprobe analysis of the granitic rocks show that they are metaluminus to peraluminus and calc-alkaline in composition. A magmatic arc setting is inferred from a combination of tectonomagmatic discrimination, ocean ridge granite-normalized multi-element patterns and biotite geochemistry. Sr–Nd–Pb isotope data further suggest that the granitoid rocks were derived from variably mixed mantle and crustal sources. Granitic rocks cutting the intrusive rocks are inferred to have crystallized at ~5–16 km depth. The volcanogenic rocks and granitic rocks originated in a supra-subduction zone setting that was widely developed throughout SE Anatolia. Initial tectonic assembly took place during the Late Cretaceous probably related to northward subduction and accretion beneath the Tauride continent (Keban and Malatya platforms). Initial tectonic assembly was followed by exhumation and then transgression by shelf-depth Nummulitic limestones during Mid-Eocene, as documented in several key outcrops. Final emplacement onto the Arabian continental margin took place during the Early Miocene.

Plume and Plate Tectonics Model for Formation of some Proterozoic Basins of India along Contemporary Mobile Belts: Mahakoshal – Bijawar, Vindhyan and Cuddapah Basins

Abstract Proterozoic basins in India mostly belong to two periods, viz. Paleo-Mesoproterozoic (~1.9-1.6 Ga) and Meso-Neoproterozoic (1.1-0.7 Ga) periods that show a long hiatus of ~0.5 Ga between the upper and the lower groups. We have considered Mahakoshal – Bijawar, lower Vindhyan and lower Cuddapah (Cuddapah Supergroup) basins in the former group while the latter consists of upper Vindhyan, and upper Cuddapah (Kurnool) basins. They mostly occur along the contemporary Proterozoic collision zones and are sub parallel to them. The Mahakoshal and Bijawar Supergroups occur along the Satpura Mobile Belt (SMB) and Bundelkhand craton, respectively with Bundelkhand craton as basement and are overlain by the Vindhyan Supergroup of rocks along the SMB. They are almost sub-parallel to the mobile bet, SMB. The Cuddapah Supergroup of Paleoproterozoic period and the Kurnool Group of Neoproterozoic period of Cuddapah basin occur along the Eastern Ghat Mobile Belt (EGMB). Based on the exposed contemporary dyke swarms and sills of mafic and ultramafic rocks that are exposed far apart and their extent sub-surface based on geophysical data, it is suggested that a large plume/superplume existed during Paleoproterozoic period (~1.9 Ga) under the Indian continent. It was responsible for the breakup (rifting) of the then cratons and provided margins for deposition of the former older group of rocks with shelf type of sediments and large scale mafic/ultramafic intrusives. The latter younger groups formed during subsequent convergence in Meso-Neoproterozoic period (~1.1-0.7 Ga) as foreland basins on the stable platform of the rifted cratons. That largely explains their undisturbed nature and absence of magmatic rocks. This convergence also caused large scale deformation as folds and faults in the former group of rocks as they collided with adjoining cratons and formed orogenic belts of that time. In the above examples, the Mahakoshal, Bijawar, lower Vindhyan and lower Cuddapah basins of Paleoproterozoic period formed during the rifting phase due to the plume/superplume while the upper Vindhyan and upper Cuddapah (Kurnool) basins of Neoproterozoic period formed during subsequent convergence as foreland basins. As they formed during different stages of plate tectonics viz. rifting and convergence, they show long hiatus of 0.5-0.6 Ga between the older and the younger groups. The same plume/superplume at 1.9 Ga might also be responsible for the breakup of the contemporary Columbia supercontinent as rocks of similar ages have been reported from other parts of this supercontinent.

The Appledore Island pluton of the Rye Complex, coastal New Hampshire and Maine, USA: geochronological and chemical evidence for the affinity of an enigmatic terrane

The Rye Complex of coastal New Hampshire and Maine is a peri-Gondwanan terrrane that up to now had an uncertain origin. An offshore portion of the complex, Appledore Island of the Isles of Shoals, hosts a mainly dioritic intrusion that yielded an U-Pb zircon age of 361.09 ± 0.14 Ma, allowing comparison of its geochemical characteristics with mafic rocks of similar age across the northern Appalachian orogen. The Appledore Island diorite has similar major, trace, and isotopic compositions as continental rift tholeiite in the Narragansett Basin in southern New England and in the Maritimes Basin of Canada. These intraplate volcanic rocks range from 375 to 330 Ma, bracketing the age of the Appledore Island diorite. Their intraplate tectonic setting reflects regional extension during the Late Devonian to Early Carboniferous which produced successor basins after the Acadian orogeny. The geochemical and age similarities of the Appledore Island diorite and the mafic rocks of the successor basins suggest that the Rye Complex is a basement fragment of a successor basin block. Further evidence of the identity of the Rye Complex is provided by the isotopic composition of intermingled, comagmatic granitic rocks associated with the Appledore Island diorite. The granite has a Ganderian isotopic signature, suggesting that the Rye Complex is a Ganderian basement block that was transposed by movement along the Norumbega Fault System to its position adjacent to the Merrimack Trough of New Hampshire and Maine.

Sourcing sandstone cobble grinding tools in southern California using petrography, U–Pb geochronology, and Hf isotope geochemistry

Procurement strategies for grinding tool lithic material among mobile societies are thought to rely on opportunistic selection of resources locally available at habitation sites and along migratory routes. In San Diego County, California, non-local appearing quartzarenite cobble handstones were identified in the ground stone assemblages of some hunter-gatherer archaeological sites dating from ca. 7000 years ago. Due to the nature of the cobble material, both natural and cultural processes may have played a role in the spatial distribution of the artifacts recovered by archaeologists. In this study we employ three techniques to investigate the geological origins and source location(s) of the quartzarenite cobbles: thin section petrography, U–Pb geochronology, and Hf isotope geochemistry. Results confirm the Neoproterozoic-lower Paleozoic age of the cobbles, while metamorphism of southern California basement rocks of similar age indicates that the cobbles must have been transported into the area, probably during Eocene times. People collected the cobbles from source locations and carried them at least 4–10 km and possibly farther. We consider the diagnostic value of the three techniques for characterizing resource distributions of sedimentary cobble material and related procurement strategies, and more broadly, their global applicability for sourcing other archaeological materials made of sedimentary and metasedimentary rock.

Paleoarchean sulfur cycle and biogeochemical surface conditions on the early Earth, Barberton, South Africa

This study presents the first multiple sulfur isotope dataset on sulfides from the ca. 3.5–3.2 Ga Onverwacht Group in the Paleoarchean Barberton Greenstone Belt (BGB) of South Africa. In situ δ34SCDT and Δ33S values of pyrite (n=568) are reported from a wide range of hydrothermal, volcanic and sedimentary environments and are used to explore Mid-Archean biogeochemical sulfur cycling. Samples are from fresh drill core collected by the Barberton Scientific Drilling Project that intercepted cherts, metabasalts and sheared ultramafics of the ∼3.3–3.35 Ga Kromberg Formation; the sedimentary units of the ∼3.432 Ga Noisy formation; and the unconformably underlying metabasaltic pillow lavas of the ∼3.472 Ga Hooggenoeg Formation.Pyrite in quartz-carbonate-veins in the lower diamictite of the Noisy sequence records the largest range and most negative δ34SCDT values so far reported from an Archean terrain (δ34SCDT=−55.04 to +27.46‰). The Noisy sediments also contain detrital and diagenetic pyrites with a significant variation in Δ33S of between −0.62 to +1.4‰ and δ34SCDT of between −7.00 and +12.6‰, interpreted to reflect tectonic exposure of these early sediments to atmospheric – shallow marine conditions. Early marine pyrites from the Kromberg Cherts also display strong positive Δ33S values up to +2.50‰ with narrow range in δ34SCDT values (−6.00 to +1.50‰), whereas hydrothermal veins in the basal ultramafic shear zones preserve magmatic values (∼0‰). This study reveals a potential proto-tectonic control on atmospheric, geodynamic and hydrothermal environments available for early sulfate reducing and/or methanogenic microbes in the Paleoarchean.No evidence for microbial sulfate reduction or disproportionation was identified in the Kromberg Cherts, despite previous morphological claims for microbial life. Highly variable and negative δ34SCDT values were found in the Noisy turbidites and Hooggenoeg pillow lava breccia supporting the presence of microbial sulfate reduction in early tectono-sedimentary basins and in the Paleoarchean sub-seafloor, respectively. In light of current controversies surrounding sulfur isotope studies in similar-aged rocks of the Pilbara Craton (West Australia), we argue that microbial elemental sulfur disproportionation was not a preferred metabolic pathway on the Paleoarchean earth.

Late Cenozoic basalt and gabbro in the subsurface in the Phetchabun Basin, Thailand: Implications for the Southeast Asian Volcanic Province

Fragments of basaltic and gabbroic rocks were obtained in cuttings from 15 exploration wells in the Na Sanun area of the Wichian Buri Sub-basin of the Phetchabun Basin in central Thailand. The samples represent flows and sills in lacustrine and fluvial sedimentary rocks of the Lower to mid-Miocene Wichian Buri Group. Mafic igneous units were identified in the sections based on their typically high-amplitude seismic reflections, confirmed by the examination of several hundred well cuttings and magnetic susceptibility measurements. Cross-sections of the sub-basin were constructed on the basis of previously published subsurface interpretations, seismic and well data, and petrological observations. Basaltic flows A, B, E, and F have ages of ca. 2Ma, 16Ma, 24Ma and 18Ma, based on inferred stratigraphic position. Gabbroic sill C and dioritic sill G are inferred to be correlative at ca. 11.6Ma, and differ petrologically from ca. 12.8Ma gabbroic sill D. Major minerals in both basaltic and gabbroic samples are plagioclase (ca. An50), anorthoclase, and augite, with pervasive alteration to Na- and Ca- zeolite minerals and analcime. Leucodioritic sill G also contains amphibole and high Ti-phlogopite. Overall, the rocks show within-plate tholeiitic to alkalic characteristics, and show similarities to basaltic surface outcrops of similar ages in the Wichian Buri-Lop Buri area. No evidence was seen in the subsurface for the andesitic to rhyolitic rocks of similar ages that occur at surface, but their presence cannot be precluded based on our limited data.