Detrital zircon data have recently become available from many different portions of the Tibetan–Himalayan orogen. This study uses 13,441 new or existing U‐Pb ages of zircon crystals from strata in the Lesser Himalayan, Greater Himalayan, and Tethyan sequences in the Himalaya, the Lhasa, Qiangtang, and Nan Shan–Qilian Shan–Altun Shan terranes in Tibet, and platformal strata of the Tarim craton to constrain changes in provenance through time. These constraints provide information about the paleogeographic and tectonic evolution of the Tibet–Himalaya region during Neoproterozoic to Mesozoic time. First‐order conclusions are as follows: (1) Most ages from these crustal fragments are <1.4 Ga, which suggests formation in accretionary orogens involving little pre‐mid‐Proterozoic cratonal material; (2) all fragments south of the Jinsa suture evolved along the northern margin of India as part of a circum‐Gondwana convergent margin system; (3) these Gondwana‐margin assemblages were blanketed by glaciogenic sediment during Carboniferous–Permian time; (4) terranes north of the Jinsa suture formed along the southern margin of the Tarim–North China craton; (5) the northern (Tarim–North China) terranes and Gondwana‐margin assemblages may have been juxtaposed during mid‐Paleozoic time, followed by rifting that formed the Paleo‐Tethys and Meso‐Tethys ocean basins; (6) the abundance of Permian–Triassic arc‐derived detritus in the Lhasa and Qiangtang terranes is interpreted to record their northward migration across the Paleo‐ and Meso‐Tethys ocean basins; and (7) the arrival of India juxtaposed the Tethyan assemblage on its northern margin against the Lhasa terrane, and is the latest in a long history of collisional tectonism.
Research Article| March 01, 2000 Magnetic polarity stratigraphy of the Neogene Siwalik Group at Khutia Khola, far western Nepal T. P. Ojha; T. P. Ojha 1Department of Geosciences, University of Arizona, Tucson, Arizona 85721 Search for other works by this author on: GSW Google Scholar R. F. Butler; R. F. Butler 1Department of Geosciences, University of Arizona, Tucson, Arizona 85721 Search for other works by this author on: GSW Google Scholar J. Quade; J. Quade 1Department of Geosciences, University of Arizona, Tucson, Arizona 85721 Search for other works by this author on: GSW Google Scholar P. G. DeCelles; P. G. DeCelles 1Department of Geosciences, University of Arizona, Tucson, Arizona 85721 Search for other works by this author on: GSW Google Scholar D. Richards; D. Richards 1Department of Geosciences, University of Arizona, Tucson, Arizona 85721 Search for other works by this author on: GSW Google Scholar B. N. Upreti B. N. Upreti 2Department of Geology, Tri-chandra Campus, Ghantaghar, Kathmandu, Nepal Search for other works by this author on: GSW Google Scholar GSA Bulletin (2000) 112 (3): 424–434. https://doi.org/10.1130/0016-7606(2000)112<424:MPSOTN>2.0.CO;2 Article history received: 13 Aug 1998 rev-recd: 18 Mar 1999 accepted: 26 Mar 1999 first online: 01 Jun 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation T. P. Ojha, R. F. Butler, J. Quade, P. G. DeCelles, D. Richards, B. N. Upreti; Magnetic polarity stratigraphy of the Neogene Siwalik Group at Khutia Khola, far western Nepal. GSA Bulletin 2000;; 112 (3): 424–434. doi: https://doi.org/10.1130/0016-7606(2000)112<424:MPSOTN>2.0.CO;2 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 middle Miocene–Pliocene Siwalik Group was deposited in the Himalayan foreland basin in response to uplift and erosion in the Himalayan fold-thrust belt. Results of thermal demagnetization experiments on samples from the Siwalik Group in central and western Nepal demonstrate that laminated siltstones yield paleomagnetic data useful for tectonic and magnetostratigraphic studies. Sandstones and paleosols of the Siwalik Group, however, generally display highly erratic paleomagnetic behavior during thermal demagnetization. On the basis of these observations, siltstones from a well-exposed, 2423-m-thick section of the Siwalik Group in Khutia Khola, far western Nepal, were sampled for magnetic polarity stratigraphy. The Siwalik Group is composed of informal lower, middle, and upper members. Correlation of the resulting polarity stratigraphy with the geomagnetic polarity timescale indicates that the exposed section spans 13.30 to 7.65 Ma. The lower-middle Siwalik boundary occurs at 11.05 Ma, near the beginning of chron C5n. The rate of sediment accumulation increases upsection, similar to rate changes previously observed in the Pakistan Siwalik Group, and probably in response to increasing proximity of the Himalayan thrust belt. In the Khutia Khola section, a discordant declination indicates that this region has rotated about a vertical axis 16.6° counterclockwise with respect to the Indian subcontinent. Measurements of δ13C in paleosol carbonate indicate the predominance of C3 plants until 7.65 Ma, and the clear presence of C4 plants higher in the undated portion of the section. You do not have access to this content, please speak to your institutional administrator if you feel you should have access.
Nd and Sr isotopes and the trace element contents, including the rare earths, were determined for fluvial sands of lithic arenite composition from the Madre de Dios foreland basin of Bolivia and Peru. On standard petrologic ternary diagrams, the sands fall in the recycled orogen provenance field and thus are similar to typical ancient foreland basin composition. The average rare earth elemental pattern of the sands is identical to the upper continental crustal average, as estimated from post-Archean composite shales of different continents. Ratios ofTh/U, Co/Th, La/Sc and Th/Sc of the fluvial sands are intermediate between an average magmatic arc and an upper crustal average compositions. The dispersion of some trace elemental patterns in the sands can be attributed to fractionation of dense minerals, including zircon, during the sedimentation process. The variations of Nd isotopes in conjunction with the petrographic parameters of lithic metamorphic (Lm) and volcanic (Lv) fragments allow a two-fold classification of the sands. These two sand types can be interpreted in terms of mixing among three different provenances: one volcanic rock-suite with less negativeεNd(O) parameter than the other volcanic suite, and a third metasedimentary source withεNd(O) value of around −12, which is considered to be similar to the average western Brazilian shield composition. Thus the overall compositions of the sands has been modeled as mechanical mixtures of two components, an Andean magmatic arc and the Brazilian shield-derived metasediments. The model is strongly supported by a plot ofεNd(O) versusεSr(O) of the sands. In this plot, the Type 1 and 2 sands define two coherent hyperbolic trends contiguous with two different portions of the Andean magmatic trend. This relationship has been interpreted to indicate that the observed Andean magmatic trend in anεSr(O)-εNd(O) diagram is the result of varying degrees of contamination of a "primitive arc-type" magma by the Precambrian continental crust of the western Brazilian Shield. The depleted mantle average Nd model age of 1.46 Ga for the fluvial sands reflects the average age of the Brazilian continental crustal source. The development of the Andean orogenic belt has been discussed schematically with the isotopic data of the sands. The model describes a trailing edge prism of sediments, derived from the Brazilian Shield during the late Paleozoic-early Mesozoic. The prism becomes part of the fold-thrust belt during the Andean orogeny in the Neogene, when the foreland basin develops with the basin fill partly derived from the fold-thrust belt. The sedimentary rocks in the fold-thrust belt are also a major source of contaminants for the Andean magmas. The contiguous nature of the Andean magmatic trend and the fluvial sand data in theεSr(O)-εNd(O) diagram suggests that the ensialic Andean magmatic arc has remained connected to its parent continent, the western Brazilian Shield, throughout the development of the Andean orogeny.
Cenozoic strata in the central Andes of northwestern Argentina record the development and migration of a regional foreland basin system analogous to the modern Chaco‐Paraná alluvial plain. Paleocene‐lower Eocene fluvial and lacustrine deposits are overlain by middle‐upper Eocene hypermature paleosols or an erosional disconformity representing 10–15 Myr. This ‘supersol/disconformity’ zone is traceable over a 200,000 km 2 area in the Andean thrust belt, and is overlain by 2–6 km of upward coarsening, eastward thinning, upper Eocene through lower Miocene fluvial and eolian deposits. Middle Miocene‐Pliocene fluvial, lacustrine, and alluvial fan deposits occupy local depocenters with contractional growth structures. Paleocurrent and petrographic data demonstrate westerly provenance of quartzolithic and feldspatholithic sediments. Detrital zircon ages from Cenozoic sandstones cluster at 470–491, 522–544, 555–994, and 1024–1096 Ma. Proterozoic‐Mesozoic clastic and igneous rocks in the Puna and Cordillera Oriental yield similar age clusters, and served as sources of the zircons in the Cenozoic deposits. Arc‐derived zircons become prominent in Oligo‐Miocene deposits and provide new chronostratigraphic constraints. Sediment accumulation rate increased from ∼20 m/Myr during Paleocene‐Eocene time to 200–600 m/Myr during the middle to late Miocene. The new data suggest that a flexural foreland basin formed during Paleocene time and migrated at least 600 km eastward at an unsteady pace dictated by periods of abrupt eastward propagation of the orogenic strain front. Despite differences in deformation style between Bolivia and northwestern Argentina, lithosphere in these two regions flexed similarly in response to eastward encroachment of a comparable orogenic load beginning during late Paleocene time.
The model of [Robinson et al. (2003)][1] integrates structural data from western Nepal with thermochronologic data from central Nepal. [Robinson et al. (2003)][1] suggest that the thermochronologic data can be explained within the framework of a structural model that includes the growth of a large
Research Article| July 01, 1996 Long-term sediment accumulation in the Middle Jurassic–early Eocene Cordilleran retroarc foreland-basin system P. G. DeCelles; P. G. DeCelles 1Department of Geosciences, University of Arizona, Tucson, Arizona 85721 Search for other works by this author on: GSW Google Scholar B. S. Currie B. S. Currie 1Department of Geosciences, University of Arizona, Tucson, Arizona 85721 Search for other works by this author on: GSW Google Scholar Geology (1996) 24 (7): 591–594. https://doi.org/10.1130/0091-7613(1996)024<0591:LTSAIT>2.3.CO;2 Article history first online: 02 Jun 2017 Cite View This Citation Add to Citation Manager Share Icon Share MailTo Twitter LinkedIn Tools Icon Tools Get Permissions Search Site Citation P. G. DeCelles, B. S. Currie; Long-term sediment accumulation in the Middle Jurassic–early Eocene Cordilleran retroarc foreland-basin system. Geology 1996;; 24 (7): 591–594. doi: https://doi.org/10.1130/0091-7613(1996)024<0591:LTSAIT>2.3.CO;2 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 SocietyGeology Search Advanced Search Abstract The late Middle Jurassic–early Eocene (∼ 120 m.y.) sediment-accumulation history of the Cordilleran foreland basin in northern Utah exhibits a sigmoidal pattern on a rate vs. time plot, with moderate rates of accumulation during late Middle Jurassic, very low net rates during Late Jurassic–earliest Cretaceous, increasingly rapid rates during Early-middle Cretaceous, and low rates during Late Cretaceous–early Eocene time. This pattern is consistent with deposition in a prograding foreland-basin system that comprised integrated back-bulge, forebulge, foredeep, and wedge-top depozones. The upper Middle Jurassic represents the back-bulge depozone; the Upper Jurassic was deposited on the eastern flank of a flexural forebulge; the basal Cretaceous unconformity is the result of eastward migration of the forebulge; the thick, Lower-middle Cretaceous succession represents the foredeep depozone; and the Upper Cretaceous–early Eocene embodies the syndepositionally deformed wedge-top depozone. Previous models that explain Middle-Late Jurassic stratigraphic patterns in terms of foredeep subsidence (alone) and a Late Jurassic hiatus in crustal shortening in the Cordilleran orogen are shown to be neither necessary nor supported by evidence from the Cordilleran hinterland. This content is PDF only. Please click on the PDF icon to access. First Page Preview Close Modal You do not have access to this content, please speak to your institutional administrator if you feel you should have access.
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