Geological Society Of America Bulletin Research Articles

Fossil micrometeorites from Monte dei Corvi: Searching for dust from the Veritas asteroid family and the utility of micrometeorites as a palaeoclimate proxy

We searched late Miocene sedimentary rocks in an attempt to recover fossil micrometeorites derived from the Veritas asteroid family. This study was motivated by the previous identification of a pronounced 3He peak (4-5x above background) within marine sediments with ages between ∼8.5–6.9 Ma ago (Montanari et al., 2017. GSA Bulletin, 129:1357–1376). We processed 118.9 kg of sediment from the Monte dei Corvi beach section (Italy), the global type-section for the Tortonian epoch (11.6–7.2 Ma). Samples were collected both before and within the 3He peak. Although a small number of iron-rich (I-type) fossil micrometeorites were recovered from each horizon studied (Ntotal = 20), there is no clear difference between the pre- and intra- 3He peak samples. All micrometeorites are compositionally similar, and three out of five horizons yielded similar abundances and particle sizes. Micrometeorites extracted from sediments at the base of the 3He peak were exclusively small (ø <75 µm), while micrometeorites extracted from sediments near the highest 3He values were relatively large (ø <270 µm). The recovered fossil micrometeorites are interpreted as samples of the background dust flux derived from metal-bearing chondritic asteroids. The presence of a 3He signature combined with the absence of fossil micrometeorites or extraterrestrial spinels (Boschi et al., 2019, Spec. Pap. Geol. Soc. Am. 542:383–391) unambiguously related to the Veritas event suggests that the Veritas family is composed of highly friable materials that rarely survive on the sea floor to become preserved in the geological record. Our data supports the existing hypothesis that the Veritas asteroid family is an aqueously altered carbonaceous chondrite parent body, one that contains minimal native metal grains or refractory Cr-spinels. The low yield of fossil micrometeorites at Monte dei Corvi is attributed to loss of particles by dissolution whilst they resided on the sea floor but also due to high sedimentation rates leading to dilution of the extraterrestrial dust flux at this site. As with other fossil micrometeorite collections (e.g. Cretaceous chalk [Suttle and Genge, EPSL, 476:132–142]) the I-type spherules have been altered since deposition. In most particles, both magnetite and wüstite remain intact but have been affected by solid state geochemical exchange, characterised by partial leaching of Ni, Co and Cr and implantation of Mn, Mg, Si and Al. In some particles Mn concentrations reach up to 16.6 wt%. Conversely, in some micrometeorites wüstite has been partially dissolved, or even replaced by calcite or ankerite. Finally, we observe evidence for wüstite recrystallisation, forming a second generation of magnetite. This process is suggested to occur by oxidation during residence on the seafloor and has implications for the use of fossil I-type micrometeorites as a potential proxy for probing Earth’s upper atmospheric composition (oxidative capacity) in the geological past. However, solutions to the limitations of post-depositional recrystallisation are suggested. Fossil I-type spherules remain a potential tool for palaeo-climatic studies.

Influence Of Lithospheric Scale Basement Faults On Seismicity In The Himalayan Orogenic System

The Himalayan system is the result of a continental collision that occurred approximately 55 million years ago between the Indian and Asian tectonic plates1,2. The collision resulted in the underthrust of the Indian crust beneath Asia, and a deformed crustal wedge3,4. The Indian plate records a complex pre-Himalayan geological history that includes several basement faults that reach depths of 70 kilometres and are oriented at a high angle to the Himalayan front5. These basement faults bound topographic basement highs that are interpreted to limit the rupture of Himalayan earthquakes6. Recent research suggests the basement faults control the distribution and magnitude of seismicity along the Himalaya7. &#x0D; The Himalayan system serves as a prototype for novel three-dimensional numerical modelling to understand if and how inherited basement structures influence seismicity in orogenic settings. Models are generated using the Coreform Cubit meshing software and are run on the supercomputer platform hosted at the University of Toronto. The initial model contains three crustal blocks: the Indian crust, a deformed orogenic wedge, and the Asian crust, all cut at a high angle by a lithospheric scale basement fault. The 2015 7.9 MW Gorkha earthquake is simulated, and slip is generated along the Himalayan basal detachment. Seismograms, shear wave potential, and compressional wave potential movies are created to understand if and how the inherited basement faults influence seismicity within orogenic systems. Understanding how these regionally significant basement faults influence seismicity in the densely populated regions of northern India and Nepal is of utmost societal importance. &#x0D; References &#x0D; 1. Najman, Y., et al., (2010). Timing of India‐Asia collision: Geological, biostratigraphic, and palaeomagnetic constraints. Journal of Geophysical Research: Solid Earth, 115. &#x0D; 2. Hodges, K. V. (2000). Tectonics of the Himalaya and southern Tibet from two perspectives. Geological Society of America Bulletin, 112(3), 324-350. &#x0D; 3. Godin, L., et al., (2019). Influence of inherited Indian basement faults on the evolution of the Himalayan Orogen, in Crustal Architecture and Evolution of the Himalayan-Karakoram-Tibet Orogen, R. Sharma, I. M. Villa, and S. Kumar, Editors, Geological Society of London Special Publication, 481, 251-276. &#x0D; 4. Chung, S.-L. et al. (2005). Tibetan tectonic evolution inferred from spatial and temporal variations in post-collisional magmatism. Earth-Science Reviews 68, 173–196. &#x0D; 5. Godin, L., &amp; Harris, L. B. (2014). Tracking basement cross-strike discontinuities in the Indian crust beneath the Himalayan orogen using gravity data – relationship to upper crustal faults. Geophysical Journal International, 198, 198-215. &#x0D; 6. Gahalaut, V. K., &amp; Kundu, B. (2012). Possible influence of subducting ridges on the Himalayan arc and on the ruptures of great and major Himalayan earthquakes. Gondwana Research, 21(4), 1080-1088. &#x0D; 7. Gahalaut, V, K., &amp; Arora, B. R. (2012). Segmentation of seismicity along the Himalayan Arc due to structural heterogeneities in the under-thrusting Indian plate and overriding Himalayan wedge. Episodes Journal of International Geoscience, 35(4), 493-500.

SHRIMP U–Pb geochronology of Mesoproterozoic basement and overlying Ocoee Supergroup, NC–TN: dating diagenetic xenotime and monazite overgrowths on detrital minerals to determine the age of sedimentary deposition

Sedimentary rocks of the Ocoee Supergroup crop out in the Appalachian Blue Ridge of western North Carolina and eastern Tennessee. This ∼12 km thick sequence of strata was mapped as nonconformably overlying Mesoproterozoic crystalline basement (about 1.20–1.02 Ga) and beneath the lower Cambrian Chilhowee Group, leading to the traditional interpretation that the Ocoee Supergroup was deposited between about 1.02 and 0.54 Ga. This interpretation was challenged by Unrug and Unrug (1990, Geology, 18: 1041–1045) and Unrug et al. (2000, Geological Society of America Bulletin. Vol. 112, pp. 982–996), who claimed that Paleozoic fossils were recovered from rocks of the Walden Creek Group (upper Ocoee), and thereby created a new tectonic model for the origin of Laurentia. To resolve the age controversy concerning the time of deposition of the Ocoee Supergroup, diagenetic xenotime overgrowths on detrital zircon and diagenetic monazite on detrital monazite were dated by the U–Pb method. Sensitive High Resolution Ion Microprobe ages of diagenetic xenotime from three samples of sandstone (Thunderhead Sandstone, Cades Sandstone, and Shields Formation) indicate that the Ocoee Supergroup was deposited in the interval of about 580–550 Ma. A sample of Sandsuck Formation (uppermost Ocoee) yielded xenotime overgrowths of about 410 Ma, probably related to post-depositional low-grade metamorphism. Various origins of xenotime overgrowths may be distinguished by trace element distributions. Ages and trace element concentrations of monazite overgrowths support the xenotime age results, although concordia systematics are complicated by high concentrations of common Pb and inheritance of ages (∼1.2 and 0.6 Ga). These age data support the observed field relations for a late Neoproterozoic depositional age of the Ocoee Supergroup.

Stratigraphy, age, and provenance of the Eocene Chumstick basin, Washington Cascades; implications for paleogeography, regional tectonics, and development of strike-slip basins: Comment

In the Pacific Northwest (North America) are a series of Paleogene basins infilled by non-marine sedimentary and volcanic rocks. Starting in the 1980s, significant efforts have been made to determine the relationships between the various basins; the underlying causes for basin formation, deposition, and basin inversion; and the histories of regional fault systems. One research group has recently produced two papers in GSA Bulletin, proposing that these sedimentary basins reflect the accretion history of the Siletzia terrane between 51.3 and 49.9 Ma, concurrent with the onset of regional dextral strike-slip faulting between 50 and 46 Ma (Eddy et al., 2016). The paper by Donaghy et al. (2021) uses this geochronology data to conduct a detailed depositional systems analysis of one of these basins, the Chumstick basin (filled by the Chumstick Formation), to clarify the sedimentary response to dextral strike-slip faulting and to validate the Eddy et al. (2016) terrane accretion model. To quote the abstract: “These data allow us to reconstruct regional Eocene paleo-drainage systems of Washington and Oregon and suggest that drainage within the Chumstick basin fed a regional river system that flowed into a forearc or marginal basin on the newly accreted Siletzia terrane.

Discovery of an Entrapped Early Permian (ca. 299 Ma) Peri-Gondwanic Sliver in the Cretaceous Shyok Suture of Northern Ladakh, India: Diverse Implications

GSA Logo HomeJoinGSA StoreDonateContact Toggle search Toggle navigation Sign In Toggle Search Advanced Search HomeJoinGSA StoreDonateContact AboutToggle Scientific DivisionsGeographic SectionsLeadershipCommitteesHonors & AwardsWho We AreDiversityEthicsGSA InternationalGSA Foundation MembershipToggle Join / RenewBenefits and DuesGet InvolvedCampus RepsMember RecognitionCode of Ethics PublicationsToggle JournalsGSA TodayBooksGSA StoreInfo & ServicesGeofacetsMeeting Abstracts EventsToggle Annual MeetingFuture Annual MeetingsSection MeetingsPast Meetings & AbstractsPenrose ConferencesThompson Field ForumsField ExperiencesGeoscience CalendarEvents Code of Conduct Education & CareersToggle GeoCareersGeoscience Job BoardGrants & ScholarshipsField ExperiencesNetworking/MentoringK-12 Educator SupportWebinar LibraryGeologic Time Scale Science PolicyToggle News from The HillGSA Policy RolesPosition StatementsCritical IssuesCongressional Science FellowshipScience Policy FellowshipEngage with Policymakers NewsToggle Science Communication FellowshipScience Communication InternshipNews ReleasesNewsroom (for Journalists)GSA In The NewsAnnual Meeting NewsroomSpeaking of Geoscience BlogGSA ConnectionGeoScene Newsletter Keyword Search Home » Publications » GSA Today Abstract View GSA Today Full Text | PDF Discovery of an Entrapped Early Permian (ca. 299 Ma) Peri-Gondwanic Sliver in the Cretaceous Shyok Suture of Northern Ladakh, India: Diverse Implications Rajeev Upadhyay Dept. of Geology (CAS), Kumaun University, Nainital-263001 (Uttarakhand), India, rajeevntl1@gmail.com Saurabh Gautam Birbal Sahni Institute of Palaeosciences, 53 University Road, Lucknow-226007, India Ram Awatar 7/464 A, Vikas Nagar, Lucknow-226022, India Abstract In a significant breakthrough, we report the first discovery of twenty-six genera and thirty-five species of Early Permian (Asselian–Sakmarian and Artinskian; 299 Ma to 276 Ma) Gondwanic palynomorphs from a tectonically emplaced metasedimentary sliver of Shyok Ophiolitic Mélange of the India-Asia Collision zone of Northern Ladakh, India. These palynofloral assemblages are of peri-Gondwanian (Cimmerian) origin and have a strong affinity with the Gondwana assemblage of peninsular India. Similar palynofloral assemblages are also known from Extra-Peninsular India, Salt Range, Karakoram, Antarctica, Australia, South Africa, and South America. The occurrence of Gondwanic sliver within the Shyok Suture is interpreted as a thin flake of active continental margin of peri-Gondwanic microcontinent/Kshiroda plate, which was sliced off during the subduction/collision process, between Ladakh block and Karakoram–Qiangtang-Lhasa terrane and amalgamated with obducted remnants of the accretionary prism of the nascent Shyok Suture. The Shyok Suture closed during the mid- to Late Cretaceous period. Subsequent syn- and post-collision synkinematic episodes tectonically juxtaposed the peri-Gondwanic sliver in the tectonized zone of Shyok Ophiolitic Mélange. The India-Asia collision, which took place ca. 60–50 Ma with the demise of Neo-Tethys Ocean, along the Indus Tsangpo Suture Zone, modified the geometry of accreted ophiolitic stack of the Shyok Suture. Manuscript received 16 Aug. 2020. Revised manuscript received 23 Sept. 2021. Manuscript accepted 27 Oct. 2021. Posted 19 Nov. 2021. © The Geological Society of America, 2021. CC-BY-NC. https://doi.org/10.1130/GSATG481A.1 Search Google Scholar for Rajeev Upadhyay Saurabh Gautam Ram Awatar Search GSA Today Publications Journals Geology GSA Bulletin Geosphere Lithosphere Environmental & Engineering Geoscience GSA Today Full Issue Archive Features Info for Authors Advertising Geoscience Job Board Books Special Papers Field Guides Memoirs Reviews in Engineering Geology DNAG Digital Maps Map & Chart Series Memorials GSA Store Info & Services About Our Publications Editors Author Info Manuscript Submission Data Repository Ethical Guidelines Copyright Subscriptions How to Access Publications Advertising Data Policy Open Access Geofacets Meeting Abstracts Facebook Twitter Instagram YouTube LinkedIn Wordpress HomeAdvertisingFAQsSearchPrivacy PolicyJobs at GSA © 2021 The Geological Society of America, Inc.

Quantitative analysis of hillshed geomorphology and critical zone function: Raising the hillshed to watershed status

Abstract Landscapes are frequently delineated by nested watersheds and river networks ranked via stream orders. Landscapes have only recently been delineated by their interfluves and ridge networks, and ordered based on their ridge connectivity. There are, however, few studies that have quantitatively investigated the connections between interfluve networks and landscape morphology and environmental processes. Here, we ordered hillsheds using methods complementary to traditional watersheds, via a hierarchical ordering of interfluves, and we defined hillsheds to be landscape surfaces from which soil is shed by soil creep or any type of hillslope transport. With this approach, we demonstrated that hillsheds are most useful for analyses of landscape structure and processes. We ordered interfluve networks at the Calhoun Critical Zone Observatory (CZO), a North American Piedmont landscape, and demonstrated how interfluve networks and associated hillsheds are related to landscape geomorphology and processes of land management and land-use history, accelerated agricultural gully erosion, and bedrock weathering depth (i.e., regolith depth). Interfluve networks were ordered with an approach directly analogous to that first proposed for ordering streams and rivers by Robert Horton in the GSA Bulletin in 1945. At the Calhoun CZO, low-order hillsheds are numerous and dominate most of the observatory's ~190 km2 area. Low-order hillsheds are relatively narrow with small individual areas, they have relatively steep slopes with high curvature, and they are relatively low in elevation. In contrast, high-order hillsheds are few, large in individual area, and relatively level at high elevation. Cultivation was historically abandoned by farmers on severely eroding low-order hillsheds, and in fact agriculture continues today only on high-order hillsheds. Low-order hillsheds have an order of magnitude greater intensity of gullying across the Calhoun CZO landscape than high-order hillsheds. In addition, although modeled regolith depth appears to be similar across hillshed orders on average, both maximum modeled regolith depth and spatial depth variability decrease as hillshed order increases. Land management, geomorphology, pedology, and studies of land-use change can benefit from this new approach pairing landscape structure and analyses.

Petrography, geochemistry and tectonic setting of adakitic bodies in the Tighanab area and their relationship with iron skarn mineralization (southeast of Sarbisheh-east of Iran)

Petrography, geochemistry and tectonic setting of adakitic bodies in the Tighanab area and their relationship with iron skarn mineralization (southeast of Sarbisheh-east of Iran)

Subduction Polarity in Ancient Arcs: A Call to Integrate Geology and Geophysics to Decipher the Mesozoic Tectonic History of the Northern Cordillera of North America: REPLY

Subduction Polarity in Ancient Arcs: A Call to Integrate Geology and Geophysics to Decipher the Mesozoic Tectonic History of the Northern Cordillera of North America: REPLY

Special issue of MAPS in honor of Wolf Uwe Reimold on occasion of his 65th birthday

Special issue of <i>MAPS</i> in honor of Wolf Uwe Reimold on occasion of his 65th birthday

Evolution of a rapidly slipping, active low-angle normal fault, Suckling-Dayman metamorphic core complex, SE Papua New Guinea

Evolution of a rapidly slipping, active low-angle normal fault, Suckling-Dayman metamorphic core complex, SE Papua New Guinea

Detrital zircon double-dating of forearc basin strata reveals magmatic, exhumational, and thermal history of sediment source areas

Research Article| January 30, 2019 Detrital zircon double-dating of forearc basin strata reveals magmatic, exhumational, and thermal history of sediment source areas Eva Enkelmann; Eva Enkelmann † 1University of Calgary, Department of Geoscience, 2500 University Drive NW, Calgary, Alberta T2N 1N4, Canada †eva.enkelmann@ucalgary.ca Search for other works by this author on: GSW Google Scholar Sonia K. Sanchez Lohff; Sonia K. Sanchez Lohff 2University of Cincinnati, Department of Geology, 500 Geology Physics Building, Cincinnati, Ohio 45221-0013, USA Search for other works by this author on: GSW Google Scholar Emily S. Finzel Emily S. Finzel 3University of Iowa, Department of Earth and Environmental Science, 115 Trowbridge Hall, Iowa City, Iowa 52242, USA Search for other works by this author on: GSW Google Scholar Author and Article Information Eva Enkelmann † 1University of Calgary, Department of Geoscience, 2500 University Drive NW, Calgary, Alberta T2N 1N4, Canada Sonia K. Sanchez Lohff 2University of Cincinnati, Department of Geology, 500 Geology Physics Building, Cincinnati, Ohio 45221-0013, USA Emily S. Finzel 3University of Iowa, Department of Earth and Environmental Science, 115 Trowbridge Hall, Iowa City, Iowa 52242, USA †eva.enkelmann@ucalgary.ca Publisher: Geological Society of America Received: 22 May 2018 Revision Received: 04 Oct 2018 Accepted: 21 Nov 2018 First Online: 31 Jan 2019 Online Issn: 1943-2674 Print Issn: 0016-7606 © 2019 Geological Society of America GSA Bulletin (2019) 131 (7-8): 1364–1384. https://doi.org/10.1130/B35043.1 Article history Received: 22 May 2018 Revision Received: 04 Oct 2018 Accepted: 21 Nov 2018 First Online: 31 Jan 2019 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation Eva Enkelmann, Sonia K. Sanchez Lohff, Emily S. Finzel; Detrital zircon double-dating of forearc basin strata reveals magmatic, exhumational, and thermal history of sediment source areas. GSA Bulletin 2019;; 131 (7-8): 1364–1384. doi: https://doi.org/10.1130/B35043.1 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGSA Bulletin Search Advanced Search Abstract Subduction along the southern margin of Alaska, USA, has been ongoing since at least the Jurassic. However, the character of the subducting slab has changed through time and has included subduction of normal oceanic crust, a spreading ridge, and an oceanic plateau. The latter two resulted in a change of subduction mode by inducing a shallow subduction angle. Geologic processes and landscape evolution of the overriding plate were affected by these variations in subduction mode and are recorded in the forearc basin strata. We investigate the Cenozoic to modern sediment of the forearc Cook Inlet basin in south-central Alaska. Here we use a double-dating approach that combines fission track dating and U-Pb dating on individual detrital zircon grains. In total we analyzed more than 1700 zircons from Eocene to Pliocene strata and modern river sand that has eroded from the surrounding regions of the Cook Inlet basin. The double-dating approach combined with the existing knowledge of the regional geology allows us to discriminate between magmatic cooled grains of extrusive and shallow intrusive rocks, exhumational cooled grains, and thermal reset grains. We find that the erosion of both shallow and deep intrusive arc rocks dominate the detrital age signal, while syn-depositional extrusive grains are lacking. The erosion of rocks that have been thermally altered during the subduction of a spreading ridge dominates the fission track (FT) age signal. This pattern is particularly prominent in the accretionary prism where ages in the most inboard (older) portion have not been thermally reset, but thermal resetting is prevalent in the outboard (younger) portion located proximal to the Paleocene–Eocene near-trench intrusions. Thermal alteration is also evident in the region of the arc that was affected by the passage of the asthenospheric slab window. The erosional signal of the more inboard arc and backarc region (Alaska Range) is characterized by exhumational FT ages of deep-seated rocks, which currently provide material into the forearc basin. This age signal results from flat-slab subduction of the Yakutat microplate, which transfers stress far inboard and produces significant mountain building and deformation. This exhumational age signal, however, is not recorded in the late Cenozoic strata, suggesting that the modern landscape developed since <3 Ma. You do not have access to this content, please speak to your institutional administrator if you feel you should have access.

Coexistence of MORB- and OIB-like dolerite intrusions in the Purang ultramafic massif, SW Tibet: A paradigm of plume-influenced MOR-type magmatism prior to subduction initiation in the Neo-Tethyan lithospheric mantle

The Yarlung Zangbo Suture Zone (YZSZ) of South Tibet is divided by the ZhongbaZhada terrane into two subparallel ophiolitic belts in its western end. The peridotite massifs of the southern belt tectonically overlie the Tethyan Himalaya sequence. The Purang peridotite body in this belt is intruded by two groups of dolerite dikes, providing significant compositional, geochronological, and isotopic information about the melting history of the Neo-Tethyan mantle. U-Pb ages of zircons separated from dolerites show that peridotites of West Purang were intruded by an early generation of dikes at 138.5 +/- 2.0 Ma (Valanginian). These dolerites show ocean island basalt (OIB)-type normalized multi-elemental profiles and Sr-Nd isotopic signatures [(La/Yb)(N )= 13-16], high initial Sr-87/Sr-86 ratios (0.70598-0.70765), and low epsilon(Nd)(t) values (-2.6 to -2.3). Zircons separated from this group of dolerites have slightly radiogenic epsilon(Hf)(t) values (+2.6 to +4.6). The next generation of dolerite dikes intruded the East Purang peridotites between 124.5 +/- 2.5 Ma and 124.4 +/- 3.2 Ma (Aptian). These East Purang dolerites show normal mid-ocean ridge basalt (N-MORB)-type normalized multi-element patterns [(La/Yb)(N) = 0.6-0.9] with noticeable negative Nb and Th (+/- Ti) anomalies, and have high Sr-87/Sr-86((i)) (0.70295-0.70618) and high epsilon(Nd)(t) values (+7.7 to +9.2). Zircons separated from the East Purang dolerites show strongly radiogenic epsilon(Hf)(t) values (+3.5 to +17.0).Semiquantitative geochemical modeling demonstrates that the parental magmas of West Purang dolerites were generated from 5 %-10 % polybaric partial melting of a deep-seated juvenile asthenospheric source enriched by plume-type components. In contrast, the parental melts of East Purang dolerites were derived from more than 20% melting of a juvenile spinel-bearing MORB-type mantle source that was modified by subduction-related melts/fluids to a minor extent. A possible tectono-magmatic model for the petrogenesis of the Purang ophiolitic massif could be linked to incipient continental rifting and subsequent oceanic seafloor spreading associated with decompression upwelling of an asthenospheric source contaminated by plume-type components. This plume-proximal seafloor spreading-system was succeeded by the initiation of Neo-Tethyan intra-oceanic subduction close to the active continental margin of Eurasia during the Early Cretaceous.

Carbonate stable and clumped isotopic evidence for late Eocene moderate to high elevation of the east-central Tibetan Plateau and its geodynamic implications

Carbonate stable and clumped isotopic evidence for late Eocene moderate to high elevation of the east-central Tibetan Plateau and its geodynamic implications

Linking high-pressure mafic granulite, TTG-like (tonalitic-trondhjemitic) leucosome and pluton, and crustal growth during continental collision

Research Article| November 09, 2018 Linking high-pressure mafic granulite, TTG-like (tonalitic-trondhjemitic) leucosome and pluton, and crustal growth during continental collision Shengyao Yu; Shengyao Yu † 1Key Laboratory of Submarine Geosciences and Prospecting Technique, MOE and College of Marine Geosciences, Ocean University of China, Qingdao 266100, China2Laboratory for Marine Geology, Qingdao National Laboratory for Marine Science and Technology, Qingdao 266061, China †yushengyao@ouc.edu.cn Search for other works by this author on: GSW Google Scholar Sanzhong Li; Sanzhong Li 1Key Laboratory of Submarine Geosciences and Prospecting Technique, MOE and College of Marine Geosciences, Ocean University of China, Qingdao 266100, China2Laboratory for Marine Geology, Qingdao National Laboratory for Marine Science and Technology, Qingdao 266061, China Search for other works by this author on: GSW Google Scholar Jianxin Zhang; Jianxin Zhang 3Institute of Geology, Chinese Academy of Geological Sciences, Beijing 100037, China Search for other works by this author on: GSW Google Scholar Deyou Sun; Deyou Sun 4College of Earth Sciences, Jilin University, Changchun 130061, China Search for other works by this author on: GSW Google Scholar Yinbiao Peng; Yinbiao Peng 1Key Laboratory of Submarine Geosciences and Prospecting Technique, MOE and College of Marine Geosciences, Ocean University of China, Qingdao 266100, China Search for other works by this author on: GSW Google Scholar Yunshuai Li Yunshuai Li 5Institute of Surface-Earth System Science, Tianjin University, Tianjin 300072, China Search for other works by this author on: GSW Google Scholar GSA Bulletin (2019) 131 (3-4): 572–586. https://doi.org/10.1130/B31822.1 Article history received: 06 Apr 2017 rev-recd: 10 Jan 2018 accepted: 14 Aug 2018 first online: 10 Nov 2018 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation Shengyao Yu, Sanzhong Li, Jianxin Zhang, Deyou Sun, Yinbiao Peng, Yunshuai Li; Linking high-pressure mafic granulite, TTG-like (tonalitic-trondhjemitic) leucosome and pluton, and crustal growth during continental collision. GSA Bulletin 2018;; 131 (3-4): 572–586. doi: https://doi.org/10.1130/B31822.1 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGSA Bulletin Search Advanced Search Abstract The early continental crust is composed predominantly of Archean tonalite-trondhjemite-granodiorite (TTG); however, the tectonic regime and melting conditions for TTG magmas have been debated. In this study, we report field and microscopic evidence for the partial melting of arc-related metagabbro and its products, including TTG-like melt, volumetrically significant plutons evolved from melt, and the associated granulitic residua during continental collision in the North Qaidam Mountains, China. Migmatite shows successive stages of initial intragranular or droplet-like melt along grain boundaries, which grew into a three-dimensional interconnected intergranular network, segregated, and accumulated in pressure shadow areas, and merged to form melt channels and sheets that finally combined to form a TTG-like tonalite pluton. Pressure-temperature (P-T) calculations indicate high-pressure granulite-facies metamorphism and the crystallization of leucosome at P = 15.5–18.5 kbar and T = 850–950 °C. Based on zircon U-Pb dating and petrological analyses, partial melting and magmatic crystallization occurred 438–430 m.y. ago, which is slightly younger or temporally overlaps with ultrahigh-pressure metamorphism in the region. The metagabbros exhibit a subduction-related arc signature with slightly positive εNd(t) values of 2.1–4.2. The felsic leucosomes and tonalite plutons are characterized by high Na, Sr, Sr/Y, and La/Yb values and low heavy rare earth element values, with εNd(t) values of 0.1–4.3, similar to typical TTGs. The geological context, geochemistry, and timing of the TTG-like melt formation observed in this study differ from the prevailing models; however, our observations and documentations demonstrate that melting of arc-like metagabbro under high-pressure granulite-facies conditions during continental collision may make important contributions to crustal growth and differentiation. You do not have access to this content, please speak to your institutional administrator if you feel you should have access.

Drivers of earthflow motion revealed by an 80 yr record of displacement from Oak Ridge earthflow, Diablo Range, California, USA

Research Article| September 21, 2018 Drivers of earthflow motion revealed by an 80 yr record of displacement from Oak Ridge earthflow, Diablo Range, California, USA Alexander L. Nereson; Alexander L. Nereson † 1Department of Earth and Planetary Sciences, University of California–Santa Cruz, Santa Cruz, California 95060, USA †anereson@gmail.com Search for other works by this author on: GSW Google Scholar Noah J. Finnegan Noah J. Finnegan 1Department of Earth and Planetary Sciences, University of California–Santa Cruz, Santa Cruz, California 95060, USA Search for other works by this author on: GSW Google Scholar Author and Article Information Alexander L. Nereson † 1Department of Earth and Planetary Sciences, University of California–Santa Cruz, Santa Cruz, California 95060, USA Noah J. Finnegan 1Department of Earth and Planetary Sciences, University of California–Santa Cruz, Santa Cruz, California 95060, USA †anereson@gmail.com Publisher: Geological Society of America Received: 25 Jan 2018 Revision Received: 10 May 2018 Accepted: 27 Jul 2018 First Online: 21 Sep 2018 Online Issn: 1943-2674 Print Issn: 0016-7606 © 2018 Geological Society of America GSA Bulletin (2019) 131 (3-4): 389–402. https://doi.org/10.1130/B32020.1 Article history Received: 25 Jan 2018 Revision Received: 10 May 2018 Accepted: 27 Jul 2018 First Online: 21 Sep 2018 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation Alexander L. Nereson, Noah J. Finnegan; Drivers of earthflow motion revealed by an 80 yr record of displacement from Oak Ridge earthflow, Diablo Range, California, USA. GSA Bulletin 2018;; 131 (3-4): 389–402. doi: https://doi.org/10.1130/B32020.1 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGSA Bulletin Search Advanced Search Abstract Predicting the velocity of slow landslides over multidecadal time scales requires an understanding of the potential drivers of landslide motion, analytical frameworks or models that connect those drivers to kinematic response, and historical records of movement that have sufficient spatial and temporal resolution to test model predictions. Given that detailed long-term records of slow landslide movement are still relatively uncommon, we used a time series of aerial imagery to assemble an 80 yr (1937–2017) record of movement for the Oak Ridge earthflow, a slow-moving landslide in California’s northern Diablo Range. Landslide movement was unsteady and nonuniform during this period. We used this history of movement, visual evidence from imagery and the field, and a record of surface moisture balance (the Palmer Drought Severity Index) to evaluate the relative roles of possible drivers of movement. Drivers considered included: supply of mobile regolith from the landslide source zone, fluvial debuttressing from below, changes in climate forcing over time, and changes in failure plane orientation in space. Specifically, we found that spatial patterns of earthflow velocity within the transport zone, where the bulk of movement occurred, were controlled largely by the slope of the underlying failure plane, whereas temporal patterns were governed largely by climate-driven changes in surface moisture balance (PDSI) at the annual-decadal scale. Declines in sediment supply acted as a secondary control on temporal velocity variations over our study period; however, the influence of this driver likely grows at longer time scales. Evidence for transient waves of motion in response to fluvial debuttressing was limited to the toe, and continued monitoring of Oak Ridge earthflow is required to determine whether those perturbations in sediment flux will migrate further upslope. You do not have access to this content, please speak to your institutional administrator if you feel you should have access.

Passive crustal clockwise rotational deformation of the Sichuan Basin since the Miocene and its relationship with the tectonic evolution of the fault systems on the eastern edge of the Tibetan Plateau

Research Article| August 15, 2018 Passive crustal clockwise rotational deformation of the Sichuan Basin since the Miocene and its relationship with the tectonic evolution of the fault systems on the eastern edge of the Tibetan Plateau Yabo Tong; Yabo Tong † 1Institute of Geomechanics, Chinese Academy of Geological Sciences, Beijing 100081, China2Key Laboratory of Paleomagnetism and Tectonic Reconstruction, the Ministry of Land and Resources, Beijing 100081, China †tyb816@163.com Search for other works by this author on: GSW Google Scholar Yujun Sun; Yujun Sun 1Institute of Geomechanics, Chinese Academy of Geological Sciences, Beijing 100081, China Search for other works by this author on: GSW Google Scholar Zhonghai Wu; Zhonghai Wu 1Institute of Geomechanics, Chinese Academy of Geological Sciences, Beijing 100081, China Search for other works by this author on: GSW Google Scholar Changping Mao; Changping Mao 3School of Earth Sciences and Engineering, Hohai University, Nanjing 210098, China Search for other works by this author on: GSW Google Scholar Junling Pei; Junling Pei 1Institute of Geomechanics, Chinese Academy of Geological Sciences, Beijing 100081, China2Key Laboratory of Paleomagnetism and Tectonic Reconstruction, the Ministry of Land and Resources, Beijing 100081, China Search for other works by this author on: GSW Google Scholar Zhenyu Yang; Zhenyu Yang 4College of Resources, Environment and Tourism, Capital Normal University, Beijing 100048, China Search for other works by this author on: GSW Google Scholar Zongwen Pu; Zongwen Pu 1Institute of Geomechanics, Chinese Academy of Geological Sciences, Beijing 100081, China Search for other works by this author on: GSW Google Scholar Yue Zhao; Yue Zhao 1Institute of Geomechanics, Chinese Academy of Geological Sciences, Beijing 100081, China2Key Laboratory of Paleomagnetism and Tectonic Reconstruction, the Ministry of Land and Resources, Beijing 100081, China Search for other works by this author on: GSW Google Scholar Hao Xu Hao Xu 1Institute of Geomechanics, Chinese Academy of Geological Sciences, Beijing 100081, China Search for other works by this author on: GSW Google Scholar GSA Bulletin (2019) 131 (1-2): 175–190. https://doi.org/10.1130/B31965.1 Article history received: 07 Nov 2017 rev-recd: 13 Jun 2018 accepted: 15 Jul 2018 first online: 15 Aug 2018 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation Yabo Tong, Yujun Sun, Zhonghai Wu, Changping Mao, Junling Pei, Zhenyu Yang, Zongwen Pu, Yue Zhao, Hao Xu; Passive crustal clockwise rotational deformation of the Sichuan Basin since the Miocene and its relationship with the tectonic evolution of the fault systems on the eastern edge of the Tibetan Plateau. GSA Bulletin 2018;; 131 (1-2): 175–190. doi: https://doi.org/10.1130/B31965.1 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGSA Bulletin Search Advanced Search Abstract We conducted a paleomagnetic study of the Upper and Lower Cretaceous red-beds in the Yibin area, in the southern part of the Sichuan Basin. High-temperature magnetic components were isolated between 580 °C and 695 °C. An ambiguous fold test resulted in alternative interpretations of the Cretaceous primary magnetization or Oligocene-Miocene remagnetization. Nevertheless, the two different interpretations of the paleomagnetic data consistently show that the Yibin area on the southern edge of the Sichuan Basin experienced clockwise rotation, relative to the eastern edge of the South China Block and Europe. A comparison with the Cretaceous and Paleogene paleomagnetic data from the northern and western part of the Sichuan Basin indicates that, except for the southeastern corner of the Sichuan Basin, the crust of the Sichuan Basin generally experienced significant clockwise rotational deformation since the early Miocene. The northeastward escape of the Songpan-Ganzi Terrane and the counterclockwise rotation of the Yangtze Fold Belt applied a right-lateral shear stress to the region surrounding the Sichuan Basin since the Miocene, which induced the passive crustal clockwise rotational deformation of the Sichuan Basin. Subsequently, the non-synchronous crustal rotational deformation of the Sichuan Basin and its surrounding blocks controlled the tectonic evolution of their boundary tectonic belts: for example, the right-lateral strike-slip movement of the Longmenshan fault belt and the southeastward extension of the Xianshuihe strike-slip fault since the Miocene. You do not have access to this content, please speak to your institutional administrator if you feel you should have access.

Impact of glacial-lake paleofloods on valley development since glacial termination II: A conundrum of hydrology and scale for the lowstand Brahmaputra-Jamuna paleovalley system

Research Article| August 08, 2018 Impact of glacial-lake paleofloods on valley development since glacial termination II: A conundrum of hydrology and scale for the lowstand Brahmaputra-Jamuna paleovalley system J.L. Pickering; J.L. Pickering † 1Department of Earth and Environmental Science, Vanderbilt University, Nashville, Tennessee 37235, USA †Present address: Shell International Exploration and Production, Inc., Houston, Texas 77082, USA; jennifer.pickering@shell.com. Search for other works by this author on: GSW Google Scholar M.S. Diamond; M.S. Diamond 1Department of Earth and Environmental Science, Vanderbilt University, Nashville, Tennessee 37235, USA Search for other works by this author on: GSW Google Scholar S.L. Goodbred; S.L. Goodbred 1Department of Earth and Environmental Science, Vanderbilt University, Nashville, Tennessee 37235, USA Search for other works by this author on: GSW Google Scholar C. Grall; C. Grall 2Lamont-Doherty Earth Observatory, Columbia University, Palisades, New York 10964, USA Search for other works by this author on: GSW Google Scholar J.M. Martin; J.M. Martin 3Shell International Exploration and Production, Inc., Houston, Texas 77082, USA Search for other works by this author on: GSW Google Scholar L. Palamenghi; L. Palamenghi 4Faculty of Geosciences, University of Bremen, Bremen 28359, Germany Search for other works by this author on: GSW Google Scholar C. Paola; C. Paola 5Department of Earth Sciences and St. Anthony Falls Laboratory, University of Minnesota, Minneapolis, Minnesota 55455, USA Search for other works by this author on: GSW Google Scholar T. Schwenk; T. Schwenk 4Faculty of Geosciences, University of Bremen, Bremen 28359, Germany Search for other works by this author on: GSW Google Scholar R.S. Sincavage; R.S. Sincavage 1Department of Earth and Environmental Science, Vanderbilt University, Nashville, Tennessee 37235, USA Search for other works by this author on: GSW Google Scholar V. Spieß V. Spieß 4Faculty of Geosciences, University of Bremen, Bremen 28359, Germany Search for other works by this author on: GSW Google Scholar GSA Bulletin (2019) 131 (1-2): 58–70. https://doi.org/10.1130/B31941.1 Article history received: 08 Oct 2017 rev-recd: 02 Mar 2018 accepted: 15 Jun 2018 first online: 08 Aug 2018 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn Email Tools Icon Tools Get Permissions Search Site Citation J.L. Pickering, M.S. Diamond, S.L. Goodbred, C. Grall, J.M. Martin, L. Palamenghi, C. Paola, T. Schwenk, R.S. Sincavage, V. Spieß; Impact of glacial-lake paleofloods on valley development since glacial termination II: A conundrum of hydrology and scale for the lowstand Brahmaputra-Jamuna paleovalley system. GSA Bulletin 2018;; 131 (1-2): 58–70. doi: https://doi.org/10.1130/B31941.1 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search nav search search input Search input auto suggest search filter All ContentBy SocietyGSA Bulletin Search Advanced Search Abstract To better define the base of the Brahmaputra River paleovalley, we analyzed an extensive borehole data set from the subaerial Bengal delta and a 255-km-long multichannel seismic survey along the modern river. The data reveal that the paleovalley floor is defined by a gravel unit containing boulder-sized clasts up to 30 cm in diameter, deposited after ca. 30 ka but before ca. 9 ka. Paleohydrology during that time and the previous glacial maximum was characterized by a weak monsoon and reduced river discharge, both of which are inconsistent with large valley formation. However, our work indicates that glacial-lake outburst floods sourced from the Tibetan reaches of the Brahmaputra were routed through the lowstand valley, producing megaflood-scale discharge capable of transporting gravel and cannibalizing the valley margins. The timing of these glacial-lake outburst flood–driven discharge events was coincident with valley development and explains the anomalously large width of the valley and basal gravel surface. Despite the underfit scale of Brahmaputra discharge following the last glacial period, a strengthening monsoon and high sediment discharge in the early Holocene subsequently contributed to the efficient infilling of the massive paleovalley by the mid-Holocene. In a sequence stratigraphic context, this work provides an example of a major unconformity that developed late in the eustatic cycle (i.e., during early transgression rather than an earlier, protracted response to sea-level lowering) and in response to a perturbation originating in the catchment instead of changing accommodation in the basin. As such, it represents a geologically instantaneous time surface that can be used as a marker for stratigraphic correlation but one that is not in phase with eustatic sea-level fall. You do not currently have access to this article.

Response of larger benthic foraminifera to the Paleocene-Eocene thermal maximum and the position of the Paleocene/Eocene boundary in the Tethyan shallow benthic zones: Evidence from south Tibet

Research Article| August 01, 2018 Response of larger benthic foraminifera to the Paleocene-Eocene thermal maximum and the position of the Paleocene/Eocene boundary in the Tethyan shallow benthic zones: Evidence from south Tibet Qinghai Zhang; Qinghai Zhang † 1Key Laboratory of Continental Collision and Plateau Uplift, Institute of Tibetan Plateau Research, and CAS Centre for Excellence in Tibetan Plateau Earth Sciences, Lincui Road 16-3, 100101 Beijing, China2Department of Geosciences, University of Bremen, Klagenfurter Straße 4, 28359 Bremen, Germany †zhang@itpcas.ac.cn Search for other works by this author on: GSW Google Scholar Helmut Willems; Helmut Willems 2Department of Geosciences, University of Bremen, Klagenfurter Straße 4, 28359 Bremen, Germany3Nanjing Institute of Geology and Palaeontology, Chinese Academy of Sciences, East Beijing Road 39, 210008 Nanjing, China Search for other works by this author on: GSW Google Scholar Lin Ding; Lin Ding 1Key Laboratory of Continental Collision and Plateau Uplift, Institute of Tibetan Plateau Research, and CAS Centre for Excellence in Tibetan Plateau Earth Sciences, Lincui Road 16-3, 100101 Beijing, China Search for other works by this author on: GSW Google Scholar Xiaoxia Xu Xiaoxia Xu 2Department of Geosciences, University of Bremen, Klagenfurter Straße 4, 28359 Bremen, Germany Search for other works by this author on: GSW Google Scholar GSA Bulletin (2019) 131 (1-2): 84–98. https://doi.org/10.1130/B31813.1 Article history received: 24 Mar 2017 rev-recd: 21 May 2018 accepted: 19 Jun 2018 first online: 01 Aug 2018 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn Email Tools Icon Tools Get Permissions Search Site Citation Qinghai Zhang, Helmut Willems, Lin Ding, Xiaoxia Xu; Response of larger benthic foraminifera to the Paleocene-Eocene thermal maximum and the position of the Paleocene/Eocene boundary in the Tethyan shallow benthic zones: Evidence from south Tibet. GSA Bulletin 2018;; 131 (1-2): 84–98. doi: https://doi.org/10.1130/B31813.1 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search nav search search input Search input auto suggest search filter All ContentBy SocietyGSA Bulletin Search Advanced Search Abstract The Paleocene-Eocene thermal maximum (PETM) is one of the most pronounced global warming events in the Cenozoic. This event was associated with a large negative carbon isotope excursion (CIE) and with major changes in the atmosphere, hydrosphere, and biosphere. However, how the larger benthic foraminifera (LBFs) in the shallow Tethyan Ocean responded to the PETM remains controversial. In this study, we investigate two shallow-marine, LBF-rich carbonate sections from south Tibet, aiming to locate the position of the Paleocene/Eocene (P/E) boundary in the Tethyan shallow benthic zones (SBZs) and to examine the response of the LBFs to the PETM. Carbon isotope compositions of bulk carbonate were measured to constrain the stratigraphic position of the CIE onset marking the P/E boundary in the sections, and the LBFs were studied in rock thin sections in order to assess their biostratigraphy and to construct the SBZs. The combination of the carbon isotope data and constructed SBZs shows that the P/E boundary is located within SBZ5, not at the SBZ4/SBZ5 transition as proposed in the Western Tethyan domain. At the P/E boundary, no evident compositional change in LBF assemblages can be observed. However, a major compositional change in LBF assemblages occurs in the CIE recovery, characterized by the sudden disappearance of Miscellanea, Ranikothalia, Setia, Orbitosiphon, and the initial dominance of porcellaneous-walled Alveolina and Orbitolites together with small miliolids and rotaliids. We tentatively speculate that this compositional change in LBF assemblages may be related to a eutrophication event, likely resulting from intensified continental weathering during the CIE recovery of the PETM. You do not currently have access to this article.

Petrology, geochemistry, and Sr, Nd isotopes of mantle xenolith in Nghia Dan alkaline basalt (West Nghe An): implications for lithospheric mantle characteristics beneath the region

Petrology, geochemistry, and Sr, Nd isotopes of mantle xenolith in Nghia Dan alkaline basalt (West Nghe An): implications for lithospheric mantle characteristics beneath the region

Provenance, U-Pb detrital zircon geochronology, Hf isotopic analyses, and Cr-spinel geochemistry of the northeast Yukon-Koyukuk Basin: Implications for interior basin development and sedimentation in Alaska

The Yukon-Koyukuk Basin is a large depression that covers ∼118,000 km2 in western interior Alaska and is divided into two subbasins by a volcanic arc assemblage. Interpretations of the depositional ...