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Detrital zircon provenance analysis plays a key role in reconstructions of past tectonic and sedimentary environments. However, non-unique (or even erroneous) interpretations can be introduced due to the inherent limitations of both zircon provenance analysis (fertility bias, recycling) and those of single-proxy provenance systems in general. Apatite crystallizes in a wider range of lithologies than zircon, and can thus facilitate more detailed source reconstructions. In this study, detrital apatite analysis of Cryogenian to Ordovician sandstones in the Cathaysia Block was carried out in comparison with detrital zircon data for a better understanding of the source-sink process on the northern margin of Gondwana. In contrast to the abundant Grenvillian (1300-900 Ma) detrital zircons of igneous origin, detrital apatites show major Pan-African (650-500 Ma) age peaks that are mostly derived from metamorphic rocks (52%-72%). The apatite data show that the Cathaysia Block mainly received detritus from western Australia and India during the late Neoproterozoic to early Paleozoic, with much lower affinities to East Antarctica and the terranes of Iran-Turkey. Provenance variations include a shift with time in the major age populations from ca. 900 Ma to 600 Ma with a decrease in metamorphic apatite (from 72% to 52% of all grains) in the late Cryogenian, an increase in high-grade metamorphic apatite (from 27% to 56%) in the late Ediacaran-Cambrian, and an increase in igneous apatite (from 33% to 45% of all grains) in the Early Ordovician. In contrast, detrital zircon data could only reveal the source change in the late Ediacaran. These provenance switches were likely caused by the unroofing of Pan-African orogens (640-490 Ma) and subsequent erosion of their exposed cores, due to the rapid uplift of source rocks formed in the Pan-African orogens during the Gondwana assembly. [ABSTRACT FROM AUTHOR]

An early Paleozoic eclogite belt extends discontinuously for ~500 km in the East Kunlun Orogen, northwestern China, which provides insight into the evolution of the Proto-Tethys Ocean. However, the nature and age of the eclogite protoliths and subsequent metamorphism are unclear. Here, we report mineral chemical, zircon, and titanite geochronological; whole-rock major and trace elemental; and Sr-Nd isotopic data for eclogites from the Xiarihamu area in the western East Kunlun Orogen. At a minimum, these eclogites underwent peak eclogite-facies metamorphism at 27-28 kbar and 630-650 °C, post-peak decompression, and retrograde amphibolite-facies overprinting. Geochemically, eclogites have characteristics typical of enriched mid-oceanic-ridge basalts and oceanic-island basalts. Inherited magmatic zircon cores yielded a protolith age of 828 Ma, and metamorphic zircons yielded peak and post-peak decompression ages of 443 Ma and 422 Ma, respectively. A titanite U-Pb age of 413 Ma constrains the timing of later amphibolite-facies overprinting. The protoliths of the Xiarihamu eclogites were the products of continental rift-related basaltic magmatism, which was generated during the initial breakup of Rodinia. The protoliths experienced eclogite-facies metamorphism in a continental subduction/collisional setting during the early Paleozoic. The formation of the Xiarihamu eclogites suggests that the Proto-Tethys Ocean had closed by 443 Ma. Given the spatio-temporal relationship between the Xiarihamu magmatic Cu-Ni sulfide deposit and the eclogites studied, the former may have formed in a post-collisional extensional setting. The eclogites and magmatic Cu-Ni sulfide deposit from the Xiarihamu area jointly reveal the evolution of the East Kunlun Orogen from Neoproterozoic supercontinent breakup to early Paleozoic tectonic transitions from collisional convergence to post-collisional extension. [ABSTRACT FROM AUTHOR]

There is general agreement that a series of East Asian blocks has always lain outboard of both India and Australia along the North Indo--Australie peripheral orogen. However, whether the East Asian blocks were involved in the interior orogens of East Gondwana remains equivocal. The geochronology and geochemistry of Neoproterozoic--Late Triassic rocks in the Russian Far East, together with existing paleontological and detrital zircon data, offer an opportunity to determine the tectonic origin and drift history of the Bureya--Jiamusi--Khanka superterrane. Biotite and amphibole 40Ar/39Ar dating results define a distinctive episode of Late Pan-African (ca. 550 Ma) metamorphism and a local Late Triassic (ca. 219-200 Ma) episode of deformation for the Bureya--Jiamusi--Khanka superterrane. Zircon U--Pb ages and whole-rock geochemical data indicate that the Early Ordovician (483 ± 3 Ma) highly fractionated I-type monzogranites were emplaced in a post-collisional setting linked to the collapse of a Late Pan-African orogen, while the Late Triassic (ca. 234-223 Ma) A-type quartz syenites and I-type granite aplite dikes were formed in a slabpull--induced passive continental margin of the subducting Mudanjiang oceanic plate. These crucial archives, complemented by data from the literature, reveal that the Bureya--Jiamusi--Khanka superterrane made up the northernmost Kuunga-Pinjarra interior orogen during the final assembly of East Gondwana. As a result of Devonian rifting after Early Ordovician orogen collapse, the Bureya--Jiamusi--Khanka superterrane escaped from the Kuunga-Pinjarra interior orogen and subsequently migrated to Northeast Asia by the Late Triassic to Jurassic due to the subduction and closure of the Paleo-Tethys and Paleo-Pacific oceans. [ABSTRACT FROM AUTHOR]

The termination of the Paleo-Asian Ocean, including duration and architecture, is controversial and has led to different reconstructions of the Central Asian orogenic belt. Deep-marine turbidites are of great significance in constraining the evolution of the oceanic basin. The youngest marine turbidites in the Beishan orogen in the central part of the southern Central Asian orogenic belt are separated by the Liuyuan mélange into two sections, the South turbidites and North turbidites. Detrital zircon grains from South turbidites yielded a maximum depositional age of 255 Ma. Those from North turbidites yielded a maximum depositional age of 254 Ma. Most of the Precambrian zircons of South turbidites have concentrated εHf(t) values (-6 to -2.6), whereas those of North turbidites range from -12.6 to +10.4, indicating different provenances. The North turbidites also have more positive whole-rock εNd(t) values (-0.5 to +1.1) than the South turbidites (-4.2 to -2.4), suggesting more juvenile or less evolved crustal components in the source. Detailed comparison of the detrital zircon ages and Hf-Nd isotopic characteristics with igneous and metamorphic rocks in the south Beishan area distinguishes two sources. These findings constrain the Liuyuan suture as the latest suture in the Beishan region, occurring no earlier than 254 Ma. The youngest peak age of detrital zircons of the youngest marine sedimentary rocks in the southern Central Asian orogenic belt becomes younger eastward from 288 Ma to 247 Ma, characterizing the closure duration of the Paleo-Asian Ocean from west to east in ~40 m.y. This study finds that the youngest turbidites in the Beishan orogen not only record sedimentary processes in response to the final episode of orogenic evolution in the southern Central Asian orogenic belt, but they also constrain how and when an archipelago-type accretionary orogen terminated. [ABSTRACT FROM AUTHOR]

Accretionary orogens function as major sites for the generation of continental crust, but the growth model of continental crust remains poorly constrained. The Central Asian Orogenic Belt, as one of the most important Phanerozoic accretionary orogens on Earth, has been the focus of debates regarding the proportion of juvenile crust present. Using published geochemical and zircon Hf-O isotopic data sets for three belts in the Eastern Tianshan terrane of the southern Central Asian Orogenic Belt, we first explore the variations in crustal thickness and isotopic composition in response to tectono-magmatic activity over time. Steady progression to radiogenic zircon Hf isotopic signatures associated with syn-collisional crustal thickening indicates enhanced input of mantle-derived material, which greatly contributes to the growth of the continental crust. Using the surface areas and relative increases in crustal thickness as the proxies for magma volumes, in conjunction with the calculated mantle fraction of the mixing flux, we then are able to determine that a volume of ~14-22% of juvenile crust formed in the southern Central Asian Orogenic Belt during the Phanerozoic. This study highlights the validity of using crustal thickness and zircon isotopic signatures of magmatic rocks to quantify the volume of juvenile crust in complex accretionary orogens. With reference to the crustal growth pattern in other accretionary orogens and the Nd-Hf isotopic record at the global scale, our work reconciles the rapid crustal growth in the accretionary orogens with its episodic generation pattern in the formation of global continental crust. [ABSTRACT FROM AUTHOR]

Neoproterozoic to Paleozoic sedimentation shows systematic temporal-spatial variations within South China, which must be considered in reconstructing geological evolution of South China in response to global plate reorganization from the breakup of Rodinia to the assembly of Gondwana. We use >1000 new U-Pb and Hf isotopic data for detrital zircons from Neoproterozoic--Cambrian strata across the western (i.e., Longmenshan) and eastern (i.e., Wuyishan) margins of South China, coupled with compiled stratigraphic and magmatic information, to constrain change in provenance through time. First-order conclusions are as follows: (1) detrital zircons from the Neoproterozoic strata of the two margins were mainly sourced from the Panxi-Hannan arc and the Jiangnan orogen, signaling a rough self-sufficient sedimentary system; (2) newly identified Cambrian molasse-like sediments in the western margin, in which abundant detrital zircons are 550-500 Ma old with positive εHf(t) values, were mainly derived from the 580-500 Ma Cadomian arc belt along the Iran-Turkey margin; and (3) the Cambrian sediments in the eastern margin document more increased contributions from the Grenvillian-age provinces most possibly in Australia. Such spatial-temporal provenance variations signal the northward drifting of South China, from a position connecting with Iran-Turkey and northern India to that approaching Australia during the late Neoproterozoic--Cambrian period. We highlight that the activity of oblique oceanic-continental convergence accreted Asian terranes onto the northern margin of Gondwana, hence contributing to the ultimate Gondwana architecture under global plate reorganization. [ABSTRACT FROM AUTHOR]

Subduction of Indian continental lithosphere during the Asia-India collision played an important role in the formation and evolution of the Himalaya-Tibetan orogen. However, the geometry of early Indian continental subduction remains debated. Given that the Indian continent is characterized by enriched isotope ratios (87Sr/86Sr > 0.730, εNd(t) < -10), relative to those in subducted oceanic materials (87Sr/86Sr < 0.704, εNd(t) ≈ +8), changes in the composition of magmatic rocks with time, in particular their radiogenic isotope ratios, is used to constrain the timing and nature of continental subduction. This study reports the field relations, zircon U-Pb ages and geochemical composition of a syn-collisional batholith that crosscuts the central Indus-Yarlung Zangbu suture in the Saga area of southern Tibet. Zircon U/Pb ages for the batholith mainly range from 50 to 46 Ma. Samples from the Lopu Range batholith have enriched zircon Hf (εHf(t) = -0.4 to -8.6) and whole rock 87Sr/86Sri = 0.7094-0.7121 and εNd(t) = -7.3 to -9.8, suggesting that they were derived from a mixture of juvenile Gangdese and isotopically enriched Indian crustal materials. This result indicates that subduction of Indian crustal rocks occurred before 50 Ma in the central Himalaya. The geochemical composition and distribution of high volume ca. 51 Ma magmatism in the Gangdese belt, combined with thermal models of the subduction zone, suggests a steepening of the subducted Indian continental lithosphere occurred between the onset of India-Asia collision (59 Ma) and 46 Ma in the central-eastern Himalaya. [ABSTRACT FROM AUTHOR]

As a main part of the North China craton collage system, the tectonic origin of the Bainaimiao arc terrane is still hotly debated, especially its relationship with the North China craton. Thus, we report on a field-based petrological and zircon U-Pb-Hf isotopic study of (meta-)sedimentary and volcanic rocks from the Bainaimiao arc terrane and northern margin of the North China craton in the Damao region. The lower and middle successions of the Bayan Obo Group from the northern North China craton, including the Dulahala, Jianshan, Halahuogete, and Bilute Formations, were deposited ca. 1.81-1.35 Ga and show age peaks at 1.85, 1.90, 2.0, and 2.5 Ga. This age pattern is in accordance with the coeval and extensively outcropped metamorphosed basement rocks of the northern North China craton. The upper succession, including the Bayinbaolage and Hujiertu Formations, deposited ca. 1.19-0.92 Ga, shows age peaks at ca. 1.35, 1.57, and 1.69 Ga, and sediments were derived from coeval rift-related magmatism characterized by a significant increase in positive εHf(t) values in detrital zircons. Thus, the Bayan Obo Group can be subdivided into North China craton basement-derived sediments and Mesoproterozoic to Neoproterozoic rift-derived sediments, and the change of the provenance was probably caused by the ca. 1.35-1.30 Ga rifting event related to the breakup of the Nuna supercontinent. In the Bainaimiao arc terrane, zircon U-Pb geochronological results of (meta-)sedimentary rocks indicate they were formed in the Neoproterozoic and Paleozoic and have mainly late Paleoproterozoic to Neoproterozoic ages (ca. 0.6-0.9, 1.1-1.2, 1.4-1.7, and 1.8-2.0 Ga) with peaks at ca. 0.86, 0.96, 1.15, 1.47, 1.66, 1.75, 1.80-1.87, and 1.94 Ga. The abundant Neoproterozoic ages for the Bainaimiao arc terrane detrital zircons are distinct from the scarcity of these ages in the northern North China craton, southern Siberia (age peaks at ca. 1.87, 1.92, and 2.0 Ga), and Mongolia (age peak at ca. 0.62, 0.83, 0.93, 1.84, and 2.0 Ga), but they are similar to the features of the Tarim craton (age peaks at ca. 0.62, 0.85, 1.15, 1.47, 1.66, 1.75-1.80, 1.85, and 1.94 Ga). Together with the recognition of a possible preexisting Proterozoic basement (ca. 0.7-2.0 Ga) in the Bainaimiao arc terrane, as evidenced by the Hf model ages of continental arc magmatism in the Bainaimiao arc terrane, this late Paleoproterozoic to Neoproterozoic detritus probably resulted from local recycled sedimentation, and the preexisting Bainaimiao arc terrane basement rifted away from a continent with Tarim craton affinity. The rifting probably occurred between ca. 0.6 and 0.52 Ga, because the reworking of the Precambrian rocks in the North China collage system occurred between ca. 520 and 230 Ma. [ABSTRACT FROM AUTHOR]

The evolution of the northern margin of Gondwana, especially to the north of India and Australia, remains enigmatic. Much controversy concerns when and where the Tarim craton was amalgamated with northern Gondwana due to final closure of the North and South Altyn Oceans (two branches of the Proto-Tethys Ocean between southeastern Tarim and northern Gondwana). This study addressed these issues through systematic field-based zircon U-Pb dating and Hf-isotope analyses of early Paleozoic sedimentary rocks in the Altyn Tagh orogen. New dating results reveal depositional ages from ca. 494 to 426 Ma. Provenance tracing indicates the ca. 494-477 Ma samples were dominantly sourced from local Altyn Tagh areas to the south of the North Altyn Ocean, whereas the ca. 465-449 Ma samples are characterized by a significant increase in ca. 2.7-2.4 Ga, 2.0-1.7 Ga, and 840-780 Ma detrital zircons, indicating an augmented supply of detritus from the Tarim craton to the north of the North Altyn Ocean. This change indicates a major provenance shift from a single to multiple source regions between ca. 477 and 465 Ma, marking the timing of the final closure of the North Altyn Ocean. Zircon U-Pb and Hf-isotopic data from the ca. 444-426 Ma samples resemble those from the ca. 465-449 Ma samples, suggesting local sediment recycling related to a postcollisional regime. Considering the South Altyn Ocean and other branches of the Proto-Tethys Ocean, we infer that the entire Proto-Tethys Ocean might have been progressively closed at ca. 500-420 Ma, leading to the amalgamation of most East Asian blocks with northern Gondwana. Detrital zircon U-Pb and Hf-isotope comparisons indicate that Tarim shared a North Indian affinity with many East Asian terranes (such as North Qilian, North Qinling, South China, Indochina, South Qiangtang, etc.), rather than with Arabia-Iran or other terranes (e.g., Lhasa and Sibumasu) that were adjacent to western Australia along the northern margin of Gondwana. [ABSTRACT FROM AUTHOR]

A clear insight of the Indo-Burma amalgamation is required for an understanding of the complex processes of the Indo-Asian collision. Where and when the northeastern part of the Indian subcontinent amalgamated with the Burma plate has not yet been well defined. In order to better understand the tectonic affiliations and evolution of the Indo- Burma Ranges (IBR), we report new detrital zircon U-Pb and Hf isotope data of nine sandstone/siltstone samples (late Miocene- Pliocene) from the Chittagong-Tripura Fold Belt, Bangladesh, which is in the Neogene belt of the IBR. Our results show that the zircon ages of all nine samples have three peaks at <200 Ma, ca. 500 Ma, and 800-1000 Ma. The percentage of young (<200 Ma) zircons increase from the Boka Bil Formation (6.9% to 15.2%) to the Tipam Formation (20.3% to 27.6%). The εHf(t) of most young zircons from the Boka Bil Formation suggest derivation from the Gangdese arc, whereas those from the Tipam Formation show an affinity with the Burma magmatic arc. Therefore, we suggest that the increase of young zircons in the Tipam Formation came from the Burma plate. Comparing provenances of the Paleogene and Neogene belts of the IBR, we suggest that they belong to the Burma plate and Indian subcontinent, respectively, and that the Kaladan Fault, separating these two belts, is the suture between the Indian and Burma terranes. The time of amalgamation is constrained by the ca. 2.5-3.9 Ma boundary between the Boka Bil and Tipam formations, and the eastern Indian promontory likely collided with the Burma plate ca. 11-12 Ma. [ABSTRACT FROM AUTHOR]

The tectonic affinity of the terranes and microcontinents within the Central Asian Orogenic Belt (CAOB) remains controversial. The Altai-Mongolian terrane (AMT), as a representative tectonic unit in the Mongolian collage, plays a vital role in reconstructing evolution history of the CAOB. The well-preserved early Paleozoic sedimentary sequence covering in this terrane could be considered as a fingerprint to track its provenance and tectonic affinity. Here, we present new whole-rock geochemistry, detrital zircon U-Pb dating, and Hf isotopic analysis for the metasedimentary rocks from the Mongolian Altai in order to shed new light on the tectonic affinity of the AMT. The youngest detrital zircon ages and the regional intrusions constrain the depositional time of the Mongolian Altai sequence to between Late Silurian and Early Devonian, which is consistent with the Habahe group in the western Chinese Altai. The features of whole-rock geochemistry and the cumulative distribution curves of the detrital zircon age spectra indicate that the Mongolian Altai sequence was probably deposited in an active continental setting during early Paleozoic. The zircon age spectra of our samples are all characterized by a main age group in the early Cambrian (peak at 541 Ma, 522 Ma, 506 Ma and 496 Ma, respectively), subdominant age populations during the Tonian, as well as rare older zircons. The nearby Lake Zone of Ikh-Mongol Arc most likely provided plenty of early Paleo zoic materials, the subdominant Neoproterozoic detrital zircons could be supplied by the felsic intrusions along the western margin of the Tuva-Mongol microcontinent, and the sparse older zircons may be derived from its basement material. The Precambrian age distribution of the AMT is quite similar to both the Tarim and Siberia cratons, but the Siberia Craton displays a closer resemblance in Hf isotopic composition with the AMT. Thus, we believe that the Siberia Craton contains a closer tectonic affinity with the AMT, and that the Tuva-Mongol microcontinent possibly rifted from the western margin of this craton after the Tonian. To the south of the AMT, recent studies indicated the Yili and Central Tianshan blocks in the Kazakhstan collage of the western CAOB likely have a closer affinity with Gondwana. Therefore, the microcontinents in the CAOB most likely derived bilaterally from both the Siberia Craton and the Gondwana supercontinent. Moreover, our Hf isotopic compositions indicate two significant continental growth events in the Tonian and early Paleozoic, respectively. [ABSTRACT FROM AUTHOR]

The tectonic setting of the southwestern Sichuan foreland basin, China, changed rapidly during the Paleogene period, and records from this period may provide crucial information about the formation and tectonic processes that affected the Sichuan Basin. To constrain the provenance and to reconstruct the paleogeography of the Paleogene successions, we conducted a detailed analysis of the petrology, geochronology, and sedimentary facies of rocks from the southwestern Sichuan foreland basin. The detrital components of the three analyzed sandstone samples indicate moderately to highly mature sediment that was primarily derived from a recycled orogen provenance. Five major age populations were identified in the UPb age spectra: Neoarchean to Siderian (2524-2469 Ma and 2019-1703 Ma), Neoproterozoic (Tonian to Cryogenian, 946-653 Ma), Ordovician to Carboniferous (Katian to lower Pennsylvanian, 448-321 Ma), and Carboniferous to Triassic (306-201 Ma). Each of these age populations corresponds to one or several potential sources around the southwestern Sichuan foreland basin. A multidimensional scaling analysis indicated that the Paleogene zircons were mainly derived from recycled sediments of the SongpanGanzi terrane and the Sichuan Basin, with minor input from the Yidun terrane, Kangdian terrane, Qinling orogenic belt, and JiangnanXuefeng orogenic belt. More specifically, the sediment supply from the SongpanGanzi terrane to the foreland basin decreased significantly from the Mingshan stage to the Lushan stage, and the Sichuan Basin simultaneously became the most important source area. In addition, there is a high correlation between the detrital zircon UPb age spectrum of the southwestern Sichuan Basin and that of the Xichang Basin, which may suggest that a wider and unified PaleoYangtze Basin existed during the Late Cretaceousearly Paleogene. [ABSTRACT FROM AUTHOR]

The tectonic affinity of the terranes and microcontinents within the Central Asian Orogenic Belt (CAOB) remains controversial. The Altai-Mongolian terrane (AMT), as a representative tectonic unit in the Mongolian collage, plays a vital role in reconstructing evolution history of the CAOB. The well-preserved early Paleozoic sedimentary sequence covering in this terrane could be considered as a fingerprint to track its provenance and tectonic affinity. Here, we present new whole-rock geochemistry, detrital zircon U-Pb dating, and Hf isotopic analysis for the metasedimentary rocks from the Mongolian Altai in order to shed new light on the tectonic affinity of the AMT. The youngest detrital zircon ages and the regional intrusions constrain the depositional time of the Mongolian Altai sequence to between Late Silurian and Early Devonian, which is consistent with the Habahe group in the western Chinese Altai. The features of whole-rock geochemistry and the cumulative distribution curves of the detrital zircon age spectra indicate that the Mongolian Altai sequence was probably deposited in an active continental setting during early Paleozoic. The zircon age spectra of our samples are all characterized by a main age group in the early Cambrian (peak at 541 Ma, 522 Ma, 506 Ma and 496 Ma, respectively), subdominant age populations during the Tonian, as well as rare older zircons. The nearby Lake Zone of Ikh-Mongol Arc most likely provided plenty of early Paleo zoic materials, the subdominant Neoproterozoic detrital zircons could be supplied by the felsic intrusions along the western margin of the Tuva-Mongol microcontinent, and the sparse older zircons may be derived from its basement material. The Precambrian age distribution of the AMT is quite similar to both the Tarim and Siberia cratons, but the Siberia Craton displays a closer resemblance in Hf isotopic composition with the AMT. Thus, we believe that the Siberia Craton contains a closer tectonic affinity with the AMT, and that the Tuva-Mongol microcontinent possibly rifted from the western margin of this craton after the Tonian. To the south of the AMT, recent studies indicated the Yili and Central Tianshan blocks in the Kazakhstan collage of the western CAOB likely have a closer affinity with Gondwana. Therefore, the microcontinents in the CAOB most likely derived bilaterally from both the Siberia Craton and the Gondwana supercontinent. Moreover, our Hf isotopic compositions indicate two significant continental growth events in the Tonian and early Paleozoic, respectively. [ABSTRACT FROM AUTHOR]

Granulite occupies the root of orogenic belts, and understanding its formation and evolution may provide critical information on orogenic processes. Previous studies have mainly focused on garnet-bearing high-pressure and medium-pressure granulites, whereas the metamorphic evolution and pressure-temperature (P-T) paths of garnet-absent, low-pressure granulites are more difficult to constrain. Here, we present zircon U-Pb ages and mineral chemistry for a suite of newly discovered two-pyroxene granulites in the North Altyn Tagh area, southeastern Tarim craton, northwestern China. Conventional geothermobarometry and phase equilibrium modeling revealed that these rocks experienced a peak granulite-facies metamorphism at T = 790-890 ²C and P = 8-11 kbar. The mineral compositions and retrograde symplectites record a clockwise cooling and exhumation path, possibly involving near-isothermal decompression followed by near-isobaric cooling. Zircon U-Pb dating yielded a ca. 1.97 Ga metamorphic age, which likely represents the initial cooling age, based on Ti-in-zircon thermometry. Combined with regional geological records, we interpret that these granulites originated from the basement rocks of a late Paleoproterozoic magmatic arc that was subsequently involved in a collisional orogen in the southern Tarim craton, presumably related to the assembly of the Columbia/Nuna supercontinent. The clockwise P-T paths of the granulites record crustal thickening and burial followed by crustal thinning and exhumation in the upper plate of the collisional orogen. Our data indicate that the initial exhumation of this orogen probably occurred no later than ca. 1.97 Ga, which is supported by widespread 1.93-1.85 Ga postorogenic magmatism in this area. [ABSTRACT FROM AUTHOR]

The Devonian connection between the Brooks Range of Alaska, USA, with the continental margin of Arctic Canada and its subsequent Jurassic-Cretaceous counterclockwise rotation to form the Amerasian Basin, is a highly debated topic in Arctic tectonics. This resource-rich region was assembled from terranes that formed part of Laurentia or Baltica, or were juvenile oceanic arcs in the early Paleozoic that were brought together during Caledonian Orogenesis and the subsequent collision that formed Pangea (Uralide Orogeny). Elements of these orogens, as well as older ones, are predicted to occur in the Brooks Range of Arctic Alaska. This study presents the first combined zircon U-Pb and oxygen data from six Brooks Range metasedimentary units with assumed Neoproterozoic to Devonian ages. Three distinct detrital zircon patterns are identified in these units: (1) those with Neoproterozoic maximum depositional ages characteristic of the Timanide Orogen of northern Baltica and adjacent parts of Siberia, (2) an almost unimodal Siluro-Ordovician (443.5 ± 2.3 Ma) detrital zircon population consistent with the oceanic Apoon arc believed to have existed off shore of northern Laurentia and to have accreted to the North Slope subterrane during the Caledonian event, and (3) those with Middle Devonian maximum depositional ages consistent with post-accretion extension during the final (Scandian) phase of Caledonian Orogenesis. Oxygen isotopes from the same zircons reveal minor to significant crustal contamination with approximately two thirds (n = 255/405) having δ18O values >5.9‰ (above the mantle field of 5.3 ± 0.6‰). Pattern 1 units exhibit a progressive increase in δ18O values throughout the Proterozoic (5.99 to 9.29‰) indicative of increasing crustal growth and Timanide age zircons yield average δ18O values of 7.18 ± 0.64‰ (n = 26) suggestive of more crustal influence than Caledonian age zircons, possibly reflecting northern Baltica signatures. The unimodal population in Pattern 2 yields average δ18O values of 5.49 ± 0.66‰ (n = 17) and 6.02 ± 0.27‰ (n = 23) prior to and during, respectively, the main Caledonian event and suggest derivation from Devonian juvenile arc sources possibly representing the initiation of the collision between Laurentia and Baltica. Similar to Pattern 1, the δ18O values associated with Pattern 3 show a progressive increase in δ18O values throughout the Proterozoic (5.00 to 9.39‰). However, Pattern 3 also exhibits a distinct juvenile fingerprint (6.13 ± 0.24‰, n = 51) during the main Caledonian event and a slight increase to 7.12 ± 1‰ (n = 7) in post-Caledonian zircons possibly suggest correlating with a post-accretion phase in which proximally sourced zircon-bearing detritus was deposited in extension-related basins marking the joining of Laurentia and Baltica. [ABSTRACT FROM AUTHOR]

U-Pb geochronology of detrital zircon from Lower Jurassic to Lower Cretaceous strata of the southern Canadian Rocky Mountains fold-and-thrust belt documents the presence of zircon ages close to the time of sediment accumulation throughout this succession. The identification of syndepositional zircons in Lower Jurassic strata indicates proximity of Cordilleran island arcs and terranes to the Western Canada epicratonic basin, consistent with the Jurassic sudden appearance of ash layers in the basin stratigraphy. The association of syndepositional zircon grains with Paleozoic arc-related zircons and zircons in the "North American Magmatic Gap"--likely derived from the Mesoproterozoic Belt-Purcell Supergroup--hints at possible geographic connections to the west or southwest since Early Jurassic, long before the inferred Kimmeridgian initiation of the ancestral Rocky Mountain foredeep trough in the region. Paleozoic and older grains in the Jurassic strata reflect the pre-history of the basin distributive province and show an episodic pattern that includes well-defined lower Paleozoic and Grenvillian maxima, and early Neo- to Paleoproterozoic populations, which may reflect recycling of detrital zircons from older clastic formations uplifted in the Cordilleran orogen. The youngest peaks in the probability diagrams provide maximum depositional ages for several imprecisely dated stratigraphic units. Discordant data modeling suggests a Pb-loss event in the Early Cretaceous (ca. 125-115 Ma). Our provenance data and the Fernie stratigraphic record suggest initiation of Jurassic deposition either in the backbulge or the distal foredeep depozones. We propose two alternative Jurassic foreland basin evolutionary models that explain the Fernie stratigraphic record in the examined epicratonic southwestern Canada as the result of vertical stacking of migrating foreland depozones, east of the encroaching Cordilleran orogen. The two possible initial settings, backbulge or distal foredeep, require either normal cratonward migration of a forebulge or cratonward migration interrupted by a Callovian phase of orogenward retreat, respectively. Besides filling a long-standing knowledge gap, our data allow direct comparison between the southern Canada and northern United States segments of the Cordilleran foreland basin. [ABSTRACT FROM AUTHOR]

The internal metamorphic-plutonic zone of the middle Paleoproterozoic Wopmay orogen, northwestern Canadian Shield, exposes an oblique section through a prograde Buchan-type metamorphic sequence. New petrographic, petrologic, and geochronologic analyses of pelite and quartz arenite samples from the eastern margin of the internal zone quantify the evolving conditions and timing of metamorphism and enable the discriminant evaluation of competing tectonic models. Study of fabric development and mineral growth relationships indicates that prograde metamorphism occurred late within a craton-verging, crustal-shortening ("Calderian") deformation event. Phase equilibria modeling was used to calculate pressure-temperature (P-T) path segments and determine peak conditions from andalusite-muscovite grade at ~3.3 kbar and 575 °C to sillimanite-K-feldspar ± granitic leucosome grade at ~4.8-6.2 kbar and 670-745 °C. In situ monazite geochronology indicates that thermal peak metamorphic conditions were reached between 1878.6 ± 6.5 Ma and 1872 ± 9 Ma. Ages of detrital zircon within quartz arenite across the width of the metamorphic sequence document a diagnostic easterly Slave craton-Thelon tectonic zone derivation that links the metasedimentary rocks, including those previously considered to be "exotic" in a proposed tectonic klippe model for the internal zone, to the adjacent craton. Integration of these results with observations on the relatively low state of strain and the bracketing of a common (single) metamorphic field gradient for all garnet-bearing mineral zones confirm that the latter have preserved their prograde isogradic continuity from time of formation, and that the leading edge of a tectonic klippe consisting of rocks exotic to the Coronation margin does not traverse the study area. [ABSTRACT FROM AUTHOR]

The largest accretionary orogen in the world, the Central Asian orogenic belt, has evolved through the assembly of various oceanic and continental blocks. Understanding the processes associated with the development of this orogenic belt relies on precise recognition of the boundaries between various terranes. One such major suture zone, which records the collisional history of the Siberian marginal arc system (Chinese Altai) with intra-oceanic arc systems (East/West Junggar), is the Irtysh shear zone in NW China. The spatial continuity and the tectonic nature of this shear zone are still poorly understood, but its development has supposedly made a significant impact on the architecture of the western Central Asian orogenic belt and the formation of the Kazakhstan orocline. Here, we provide new insight into the evolution of this shear zone based on detrital zircon ages, Hf isotope composition, structural data and 40Ar/39Ar age constraints on the timing of deformation. Our results show a major discrepancy in detrital zircon populations and Hf model ages across the southern Chinese Altai and the northern East/West Junggar, thus allowing us to map the exact location of the tectonic boundary. Detrital zircon data constrain the initial closure of the Ob-Zaisan Ocean to the late Carboniferous (<323 Ma), and new structural and 40Ar/39Ar geochronological data shed light on the subsequent collisional processes. We propose that the collisional zone between the Chinese Altai and the East/West Junggar was initially subjected to crustal thickening at ca. 323-295 Ma, followed by orogen-parallel extension (ca. 295 Ma) and transpressional deformation (ca. 286-253 Ma). The closure of the Ob-Zaisan Ocean in NW China postdates the initial phase of oroclinal bending in the western Central Asian orogenic belt, thus indicating that oroclinal bending initiated during subduction. Based on our new constraints and other available geological data, we suggest that the early stage of oroclinal bending was likely driven by slab rollback. [ABSTRACT FROM AUTHOR]

We present a multidisciplinary study that constrains the development history of the southern part of the Central Andean Plateau, a prototypical noncollisional orogenic system. In the Antofagasta de la Sierra region of NW Argentina, data from sedimentary geology, sandstone modal composition, detrital zircon U-Pb geochronology, and apatite fission-track and (U-Th-Sm)/He thermochronology indicate that sediments accumulated in the late Eocene to early Oligocene, with a maximum depositional age of ca. 39-38 Ma provided by the youngest detrital zircon U-Pb dates. Provenance data, including paleocurrent indicators, sandstone modal composition, and detrital zircon U-Pb ages, point to prevailing western sources, including the Sierra de Quebrada Honda (a proximal source), the Ordovician to Late Cambrian Famatinian magmatic arc in western Argentina and Chile (a distal source), and the Permian-Triassic plutonic and volcanic rocks in coastal Chile (a distal source). Along the western basin margin, these strata were deformed by a basement-involved thrust fault that was active at ca. 25-20 Ma, as constrained by apatite fission-track and (U-Th-Sm)/He data. Analysis of new and existing U-Pb geochronologic data from both detrital and basement samples across the Puna suggests that the Sierra Laguna Blanca, a major mountain range in the southern Puna, remained buried during the late Eocene to early Oligocene. Our multidisciplinary data indicate that the southern Central Andean Plateau may have hosted a regional basin primarily formed by lithospheric flexure during the late Eocene to early Oligocene. Furthermore, this study refines the history of basin compartmentalization and exhumation of the major mountain ranges in the southern Puna, revealing propagation of deformation from the west to east, starting as early as the late Eocene and continuing to the mid-late Miocene. [ABSTRACT FROM AUTHOR]

New low-temperature thermochronology and geochronology data from Upper Jurassic-Upper Cretaceous strata from the North American Cordilleran foreland basin in Utah, Colorado, Wyoming, and South Dakota document rapid exhumation rates of the adjacent Cordilleran orogenic belt to the west. Both zircon (U-Th-[Sm])/He (zircon He) and apatite fission track (AFT) thermochronology were applied to proximal and distal synorogenic deposits in order to identify a thermochronometer suitable to record source exhumation during the North America Cordilleran orogeny. AFT lag times from Upper Jurassic-Upper Cretaceous deposits are 0-5 m.y. and indicate a relatively steady-state to slightly increasing exhumation rate between 118 Ma and 66 Ma. These lag-time measurements are consistent with active shortening and rapid exhumation rates of ~0.9->1 km/m.y. of the North American Cordillera throughout the Cretaceous. Double dating of the detrital AFT samples was performed on apatites with young AFT cooling ages, in order to test whether or not the young cooling ages represent a signal related to exhumation rather than volcanic activity. Maximum depositional ages using detrital zircon U-Pb geochronology match existing ages on basin stratigraphy. This study indicates that AFT is the most effective thermochronometer to resolve source exhumation from Lower to Upper Cretaceous foreland stratigraphy in the central Cordilleran foreland, and indicates that source material was exhumed from 4 to 5 km depths but was never buried more than a few kilometers (<4 km) since Cretaceous time. Zircon He dates indicate that the orogenic hinter land could not have been exhumed from depths >8-9 km. Double dating of apatites (with AFT and U-Pb) shows that volcanic contamination is a significant issue that can, however, be addressed by double dating. [ABSTRACT FROM AUTHOR]

Recent results show that evolution of the huge Central Asian orogenic belt can be explained in terms of southwest Pacific-style accretion of arcs and microcontinents. A better understanding of the origin and evolution of arcs and microcontinents will enhance our knowledge on the evolution of the Central Asian orogenic belt. As one of the most important early Paleozoic arc systems south to the Solonker suture zone, the origin and evolution of the Bainaimiao arc belt are still not well constrained. New zircon U-Pb geochrono logical and geochemical results on magmatic rocks in the Bainaimiao arc belt indicate that the arc was active from 0.52 Ga to 0.42 Ga and can extend to east Siping in NE China. Zircon U-Pb geochronological results of metasedimentary rocks in the Bainaimiao arc belt indicate that they are early Paleozoic in age, not Precambrian as previously regarded. Detrital zircon analysis of metasedimentary rocks and Sr-Nd-Hf geochemical results of magmatic rocks indicate the existence of some Proterozoic basement rocks beneath the Bainaimiao arc, and it was built upon a Precambrian microcontinent that has a tectonic affinity to the Tarim or Yangtze cratons. The Bainaimiao arc is an ensialic island arc characterized by different evolution history and basement compositions from the northern North China craton. It was separated by a wide ocean from the northern North China craton during the Cambrian-Ordovician period. Successive northward subduction resulted in contraction of the ocean and final accretion of the Bainaimiao arc to the northern North China craton during the Late Silurian-earliest Devonian by arc-continent collision. Arc-continent collision could be an important mechanism for continental crustal growth and formation of the huge Central Asian orogenic belt. [ABSTRACT FROM AUTHOR]

Lag time is the difference between the closure age of a thermochronologic system and the depositional age of host strata. Lag-time analysis of sedimentary basin fill provides insight into the exhumation history of adjacent eroded orogens. In a case study of the Paleogene Floresta basin in the Eastern Cordillera fold-thrust belt of Colombia, variations in lag time reflect changes in both sediment source areas and exhumation patterns. However, near-zero lag times can be produced by either syndepositional volcanism or rapid exhumation. We applied U-Pb geochronology and (U-Th)/He (ZHe) thermochronology to individual zircon grains and identified zircons of volcanic origin as those for which the U-Pb age is within the 2δ uncertainty of their ZHe age. Consistent discrimination of young ZHe ages as the products of either rapid exhumation or volcanism reveals three stages in the history of the northern Andean hinterland. (1) Early to late Paleocene: The appearance of syndepositional and Mesozoic volcanic zircons marks the initial influx of magmatic arc detritus. (2) Middle to late Eocene: Near-zero lag times point to rapid, regionally extensive exhumation attributable to thrust-induced uplift of the Magdalena Valley basement. (3) Late Eocene to late Oligocene: Increased lag time is interpreted as recycling of shallowly buried foreland-basin strata possibly due to movement on basinbounding thrust systems. The presence of volcanic zircons with ZHe ages younger than or indistinguishable from the youngest exhumationally cooled zircons underscores the need for double dating to reliably identify volcanic influence in detrital thermochronology datasets. These data highlight the utility of double-dated ZHe results for extracting tectonic histories and reliably excluding volcanic zircons from lag-time analysis. [ABSTRACT FROM AUTHOR]

More than 1800 detrital zircon uranium-lead (U-Pb) ages collected from Franklinian Basin sedimentary strata of the Canadian Arctic Islands provide important insights into the depositional and tectonic evolution of the northern margin of Laurentia from the late Neoproterozoic to the Late Devonian. The Franklinian Basin succession is composed of strata with three distinctly different U-Pb age provenance signatures, which have implications for the tectonic and paleogeographic evolution of the entire Arctic region. Neoproterozoic and Lower Cambrian formations contain detrital zircon populations of 1750-1950 Ma and 2650-2800 Ma, which are consistent with derivation from Archean to Paleoproterozoic gneisses and granites of the west Greenland--northeast Canadian Shield. The Lower Silurian to Lower Devonian Danish River Formation contains a dominant population of 900-2150 Ma detrital zircons with scattered Archean ages. The 900-2150 Ma zircons were likely transported axially along the foreland basin of the East Greenland Caledonides (Caledonian orogen) and deposited in a deep-water basin between the Pearya terrane and northern Laurentian margin. Middle Devonian to Upper Devonian strata contain detrital zircon populations of 900-2150 Ma, similar to the Danish River Formation, but these units also contain 370-450 Ma and 500-700 Ma detrital zircons. The 900-2150 Ma zircons were likely derived from the East Greenland Caledonian Mountains, the uplifted foreland of the East Greenland Caledonides, and the Pearya terrane. The population of 370-450 Ma detrital zircons potentially comes from uplifting granites in the Caledonian Mountains and Pearya terrane. The 500-700 Ma detrital zircons were likely de derived from the continental landmass responsible for the Ellesmerian orogen. The 500-700 Ma age of the zircons suggests that the northern landmass likely had a connection to rocks of the Timanide orogens, located in the Timan Range of northwestern Russia. A dominant population of 365-450 Ma and 500-700 Ma ages in Upper Devonian strata suggests that the Pearya terrane and the northern continental landmass became the dominant source by the end of Franklinian Basin sedimentation. Because detrital zircons are often recycled from older strata into younger deposits, these data provide the basis for understanding the sedimentary provenance of younger units of the Sverdrup Basin and sedimentary wedges along the present Arctic continental margin. [ABSTRACT FROM AUTHOR]

The article discusses the correlation between episodic uranium/lead (U/Pb) age clusters and hafnium (Hf) isotopic ratios in detrital zircons with supercontinent formation, which preserves juvenile and reworked continental crust in collisions. It states that the crust preservation rate increases by capture and a paucity of zircon ages may relate with supercontinent breakup times. This may reportedly imply that a planet with plate tectonics should exhibit episodic ages in continental crust.

We propose that the late Paleoproterozoic igneous and deformational history preserved in the northern midcontinent United States can be explained by a change in subduction-polarity from geon 18 south-dipping subduction during Penokean accretion to geon 17 north-dipping subduction as convergence continued after Penokean orogenesis. New U-Pb zircon ages indicate that late to post-Penokean magmatism occurred at Ca. 1800, 1775, and 1750 Ma and generally migrated southeastward across the newly accreted Penokean terrane. We suggest that geon 17 Yavapai slab rollback caused continental arc magmatism to step southeastward between 1800 and 1750 Ma. As the slab steepened, reduced compressional stresses and magma-induced thermal weakening allowed for collapse of the overthickened portions of the Penokean crust. Postcollapse crustal stabilization (the 1750–1650 Ma Baraboo interval) was followed by geon 16 Mazatzal arc accretion further south. The 1900–1600 Ma tectonic history of the north-central United States, not surprisingly, records events related to the southward growth and tectonic development of the southern Laurentian margin. New and published 40Ar/39Ar mineral ages delineate the northern and western extent of geon 16 Mazatzal deformation. Interestingly, only little exhumed crust intruded by a small volume of shallow-level Ca. 1750 Ma plutons (and associated rhyolites) was deformed significantly during geon 16. In contrast, more deeply exhumed crust and crust pervasively invaded by a large volume of post-Penokean magma (i.e., East-Central Minnesota Batholith) were largely unaffected by Mazatzal deformation and reheating. We suggest that posttectonic intrusions and crustal thinning were an important step in strengthening and stabilizing the crust in the southern Lake Superior region. [ABSTRACT FROM AUTHOR]

Siliciclastic rocks in the Transantarctic Mountains record the tectonic transformation from a Neoproterozoic rift-margin setting to a passive-margin and ultimately to an active early Paleozoic orogenic setting along the paleo-Pacific margin of East Antarctica. New U-Pb detrital-zircon ages constrain both the depositional age and sedimentary provenance of these strata. In the central Trans-antarctic Mountains, mature quartz arenites of the late Neoproterozoic Beardmore Group contain Archean and Proterozoic zircons, reflecting distal input from the adjacent East Antarctic shield, Mesoproterozoic igneous provinces, and Grenville-age parts of East Gondwana. Similarly, basal sandstones of the Lower Cambrian Shackleton Limestone (lower Byrd Group) contain zircons reflecting a dominantly cratonic shield source; the autochthonous Shackleton was deposited during early Ross orogenesis, yet its basal sandstone indicates that the inner shelf was locally quiescent. Detrital zircons from the Koettlitz Group in southern Victoria Land show a similar age signature and constrain its depositional age to be ≤670 Ma. Significant populations (up to 22%) of ca. 1.4 Ga zircons in these Neoproterozoic and Lower Cambrian sandstone deposits suggest a unique source of Mesoproterozoic igneous material in the East Antarctic craton; comparison with the trans-Laurentian igneous province of this age suggests paleogeographic linkage between East Antarctica and Laurentia prior to ca. 1.0 Ga. In strong contrast, detrital zircons from upper Byrd Group sandstones are dominated by young components derived from proximal igneous and metamorphic rocks of the emerging Ross orogen. Zircon ages restrict deposition of this syn- to late-orogenic succession to ≤520Ma (Early Cambrian or younger). Sandstone samples in the Pensacola Mountains are dominated by Grenville and Pan-African zircon ages, suggesting a source in western Dronning Maud Land equivalents of the East African orogen. When integrated with stratigraphic relationships, the detrital-zircon age patterns can be explained by a tectonic model involving Neoproterozoic rifting and development of a passive-margin platform, followed by a rapid transition in the late Early Cambrian (Botomian) to an active continental-margin arc and forearc setting. Large volumes of molassic sediment were shed to forearc marginal basins between Middle Cambrian and Ordovician time, primarily by erosion of volcanic rocks in the early Ross magmatic arc. The forearc deposits were themselves intruded by late-orogenic plutons as the locus of magmatism shifted trenchward during trench retreat. Profound syntectonic denudation, followed by Devonian peneplanation, removed the entire volcanic carapace and exposed the plutonic roots of the arc. [ABSTRACT FROM AUTHOR]