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.
In order to better constrain the evolution of the Tethyan orogenic system, we conducted an integrated investigation involving U-Pb dating of igneous and detrital zircon, geochemical analysis of igneous rocks, compositional analysis of sedimentary strata, and a synthesis of existing work across the Qilian Shan, Qaidam Basin, and the Eastern Kunlun Range of central and northern Tibet. This effort reveals five stages of arc magmatism at 1005–910 Ma, 790–720 Ma, 580–500 Ma, 490–375 Ma, and 290–195 Ma, respectively. Arc activities were interrupted by repeated continent-continent collision followed by ocean opening along the older suture zones first created in the Neoproterozoic. This suggests that Wilson cycles have played a controlling role in constructing the southern Asian continent. The magmatic history and regional geologic constraints allow us to construct a coherent tectonic model that has the following key features. (1) The linked South Qilian suture in the west and North Qinling suture in the east formed the northern boundary of the coherent Kunlun–Qaidam–North Qinling Terrane in the early Paleozoic. (2) The Songpan-Ganzi Terrane has been the western part of the Yangtze craton since the Neoproterozoic. (3) Development of the wide (>700 km) Permian–Triassic arc across the Kunlun-Qaidam Terrane was induced by flat subduction and rapid slab rollback, which also caused extreme extension of the Songpan-Ganzi Terrane. (4) The formation of the Anymaqen-Kunlun-Muztagh Ocean (= the Neo–Kunlun Ocean in this study) was created within Laurasia rather than being a preexisting ocean between Gondwana and Laurasia as postulated by most early studies.
Monoclines developed in the Colorado Plateau region during the Laramide orogeny are divided into western and eastern groups by a broad NNW trending antiform through the central part of the plateau. In the western group the major monoclines verge to the east, whereas in the eastern group the major monoclines verge to the west. Paleogeographic reconstruction based on paleocurrent indicators and sedimentary facies distribution suggests that the broad antiform was developed during the Laramide orogeny and was coeval with the formation of the monoclines in the plateau. This relationship implies that the monoclines were drag folds verging towards the center of the plateau as a response to the antiformal warping of the plateau. To simulate the warping of the plateau region and the stress distribution that produced the variable trends of the monoclines, an elastic thin plate model considering in‐plane stress was developed. This model assumes that (1) sedimentation in the Laramide basins provided vertical loading along the edge of the plateau region, (2) frictional sliding was operating along the Laramide faults on the northern and eastern boundaries, and (3) the greatest regional compressive stress was oriented in the N60°E direction and was applied uniformly along the western and southwestern sides of the plateau. Buoyancy due to instantaneous isostatic adjustment of crustal thickening or magmatic addition was also considered. The result of the model suggests that the frictional strength of the Uinta thrust system on the northern side of the plateau is at least 2 times greater than that along the Park Range and Sangre de Cristo thrust systems on the eastern side of the plateau in order to explain the observed monoclinal trends and the warping pattern within the plateau during the Laramide orogeny.
Long-runout subaerial landslides (>50 km) are rare on Earth but are common features shaping Mars’ Valles Marineris troughs. In this study, we investigated the highly debated emplacement mechanisms of these Martian landslides by combining spectral and satellite-image analyses. Our results suggest that hydrated silicates played a decisive role in facilitating landslide transport by lubricating the basal sliding zone. This new understanding implies that clay minerals, generated as a result of water-rock interactions in the Noachian and Hesperian (4.1–3.3 Ga), exert a long-lasting influence on geomorphic processes that shape the surface of the planet.
The present paper summarizes the major environmental events in China during the period from January to February in the year 2014. These events are classified into five categories,i. e. pollution accidents, earthquake, landslide and debris flow, draught,as well as other disasters. Total 10,49,5,4,and 14 major events are reported with their detailed statistics on the loss, places,and the nature of the events respectively. Causes are also listed which actually led to the 82 events.
Knowledge of the magnitude of differential stress and strain rate during the formation of mylonitic shear zones in metamorphic core complexes provides constraints on the mechanical behavior of the middle continental crust during extension. We analyzed the differential flow stress during the mylonitization of quartzofeldspathic rocks in the Whipple Mountains, California, using grain‐size piezometers and kinetic laws for grain growth. Mylonitic gneisses collected from two widely separated transects have grain sizes that cluster in a range from 32 to 61 µm. Analysis of grain growth kinetics indicates that mylonitization of the gneisses continued during cooling to temperatures ≤500°C, compatible with estimates from two‐feldspar thermometry. Quartz grain‐size piezometers suggest that the mylonitization occurred under differential stresses (σ 1 –σ 3 ) of ∼40–150 MPa, or maximum shear stresses of 20–75 MPa. Extrapolation of quartzite flow laws to 500°C indicates that the mylonitization occurred at strain rates faster than 10 −14 s −1 . These estimates suggest that the mylonitic zone within the Whipple Mountains had an effective viscosity of the order of 10 18±4 −10 20±4 Pa s. These low viscosities and rapid strain rates, combined with seismic reflection data showing that continental crust is layered, suggest that more realistic physical models of extension of the continental lithosphere should treat the lithosphere as a heterogeneous distribution of high‐viscosity regions separated by low‐viscosity zones.
'/%3e%3cuse xlink:href='%23a' transform='rotate(23.036 .093 25.536)'/%3e%3cuse xlink:href='%23a' transform='rotate(45.87 1.273 16.18)'/%3e%3cuse xlink:href='%23a' transform='rotate(69.945 .996 12.078)'/%3e%3cuse xlink:href='%23a' transform='rotate(20.66 -19.689 31.932)'/%3e%3c/svg%3e)