http://www2.ess.ucla.edu/~yin/05-Publications/papers/091-Yin-2006-ESR.pdf

Cenozoic tectonic evolution of the Himalayan orogen as constrained by along-strike variation of structural geometry, exhumation history, and foreland sedimentation

High-P/T metamorphic belts were classified into types A and B according to their protoliths. The A-type (collision-type) blueschists possess passive-margin protoliths characterized by platform-type carbonates, bimodal volcanics, and peraluminous sediments. B-type (Cordilleran-type) blueschists consist of active continental-margin protoliths in an accretionary complex characterized by bedded chert, MORB and ocean-island basalts, reef limestones, and graywackes. The spatiotemporal distribution of blueschists and eclogites of the world was compiled; among 250 recognized high-P/T belts, about 20% belong to the A type and the rest to the B type. Most A-type zones lie in Europe and the Tethyan domain, include ultrahigh-pressure metamorphic terranes, and have metamorphic pressure up to 45 kbar. B-type zones occur mainly in the circum-Pacific orogenic belts and intracontinental orogens in Asia, and were recrystallized at P <12 kbar. Associated peridotites include garnet peridotite in the A type and strongly serpe...

Blueschists and Eclogites of the World and Their Exhumation

Structural, sedimentological, magnetostratigraphic, and 40Ar/39Ar thermochronological investigations were conducted in the southern Chinese Tian Shan. On the basis of our own mapping and earlier investigations in the area, the Late Cenozoic southern Tian Shan thrust belt may be divided into four segments based on their style of deformation. From west to east, they are (1) Kashi-Aksu imbricate thrust system, (2) the Baicheng-Kuche fold and thrust system, (3) the Korla right-slip transfer system, and (4) the Lop-Nor thrust system. The westernmost Kashi-Aksu system is characterized by the occurrence of evenly spaced (12–15 km) imbricate thrusts. The Baicheng-Kuche and Korla systems are expressed by a major north dipping thrust (the Kuche thrust) that changes its strike eastward to become a NW striking oblique thrust ramp (the Korla transfer zone). The Lop Nor system in the eastern-most part of the southern Chinese Tian Shan consists of widely spaced thrusts, all involved with basement rocks. Geologic mapping and cross-section construction suggest that at least 20–40 km of crustal shortening with a horizontal shortening strain of 20–30% has occurred in the southern Chinese Tian Shan during the late Cenozoic. These estimates are minimum because of both conservative extrapolation of the thrust geometries and partial coverage of the thrust belt by the cross sections. The timing of initial thrusting is best constrained in the Kuche basin where crustal shortening may have occurred at 21–24 Ma, the time of a major facies transition between lacustrine and braided-fluvial sequences constrained in general by biostratigraphy and in detail by magnetostratigraphy. This estimate represents only a minimum age, as development of thrusts in the southern Chinese Tian Shan may have propagated southward toward the foreland. Thus the sedimentary record only represents the southernmost and therefore youngest phase of thrusting. If our estimate of timing for the thrust initiation (21–24 Ma) is correct, using the estimated magnitude of shortening (20–40 km) and shortening strain (20–30%), the averaged rates of late Cenozoic horizontal slip and shortening strain are 1–1.9 mm yr−1 and 2.9–4.5 × 10−16 s−1, respectively. Our reconnaissance 40Ar/39Ar thermochronological analysis in conjunction with earlier published results of apatite fission track analysis by other workers in the Chinese Tian Shan suggests that the magnitude of Cenozoic denudation is no more than 10 km, most likely less than 5 km. We demonstrate via a simple Airy-isostasy model that when the thermal effect on changes in surface elevation is negligible, determination of the spatial distribution and temporal variation of both horizontal shortening strain and denudation becomes a key to reconstructing the elevation history of the Tian Shan. Using this simple model, the loosely constrained magnitude of crustal-shortening strain and denudation in the southern Chinese Tian Shan implies that it may have been elevated 1.0–2.0 km since the onset of Cenozoic thrusting.

https://agupubs.onlinelibrary.wiley.com/doi/pdf/10.1029/97TC03140

Late Cenozoic tectonic evolution of the southern Chinese Tian Shan

The respective tectonic effects of back arc spreading and continental collision in Asia are considered either as two independent processes or as closely interrelated. Extrusion tectonics assumes that the opening of the South China Sea and the left-lateral motion along the Red River fault are geometrically linked in a pull-apart manner. This model is not accepted by several workers because the structural link between the two processes is not clearly demonstrated. In the case of the Japan Sea, we can show without ambiguity that back arc opening was controlled by large intracontinental strike-slip faults which can be easily understood as effects of the India-Asia collision far from the indenter. The Japan Sea opened in the early Miocene in a broad pull-apart zone between two major dextral strike-slip shear zones. The first one extends from north Sakhalin to central Japan along 2000 km, it has accommodated about 400 km of finite displacement. Deformation along it varies from dextral transpression in the north to dextral transtension in the south. The second is between Korea and SW Japan and has accommodated a smaller displacement of about 200 km. The extensional domain in between lies in the back arc region of Japan. Distributed stretching of the arc crust resulted in the formation of most of the Japan Sea, while localized oceanic spreading at the southern termination of the eastern transpressional shear zone shaped the Japan Basin. The first oceanic crust was formed in a small triangle based on the eastern shear zone, and spreading propagated westward inside the pull-apart region. Timing of oceanic crust formation, of formation of the dextral shear zones and of block rotation in between, as well as the internal structure of the basins and the geometry of deformation along the master shear zones are used to reconstruct the opening history. This evolution is discussed by comparison to other manifestations of the arc and back arc activity, such as the history of sedimentation and volcanism. The paper then suggests that the collision of India can have tectonic consequences as far north as Japan and Sakhalin and describes the geometrical relation of back arc opening there and diffuse extrusion.

/pdf/japan-sea-opening-history-and-mechanism-a-synthesis-2pn9b8wlyp.pdf

Japan Sea, opening history and mechanism: A synthesis

The Siwalik formations of northern Pakistan consist of deposits of ancient rivers that existed throughout the early Miocene through the late Pliocene. The formations are highly fossil- iferous with a diverse array of terrestrial and freshwater vertebrates, which in combination with exceptional lateral exposure and good chronostratigraphic control allows a more detailed and tem- porally resolved study of the sediments and faunas than is typical in terrestrial deposits. Conse- quently the Siwaliks provide an opportunity to document temporal differences in species richness, turnover, and ecological structure in a terrestrial setting, and to investigate how such differences are related to changes in the fluvial system, vegetation, and climate. Here we focus on the interval between 10.7 and 5.7 Ma, a time of significant local tectonic and global climatic change. It is also the interval with the best temporal calibration of Siwalik faunas and most comprehensive data on species occurrences. A methodological focus of this paper is on controlling sampling biases that confound biological and ecological signals. Such biases include uneven sampling through time, differential preservation of larger animals and more durable skeletal elements, errors in age-dating imposed by uncertainties in correlation and paleomagnetic timescale calibrations, and uneven tax- onomic treatment across groups. We attempt to control for them primarily by using a relative-abun- dance model to estimate limits for the first and last appearances from the occurrence data. This model also incorporates uncertainties in age estimates. Because of sampling limitations inherent in the terrestrial fossil record, our 100-Kyr temporal resolution may approach the finest possible level of resolution for studies of vertebrate faunal changes over periods of millions of years. Approximately 40,000 specimens from surface and screenwash collections made at 555 localities form the basis of our study. Sixty percent of the localities have maximum and minimum age esti- mates differing by 100 Kyr or less, 82% by 200 Kyr or less. The fossils represent 115 mammalian species or lineages of ten orders: Insectivora, Scandentia, Primates, Tubulidentata, Proboscidea, Pholidota, Lagomorpha, Perissodactyla, Artiodactyla, and Rodentia. Important taxa omitted from this study include Carnivora, Elephantoidea, and Rhinocerotidae. Because different collecting methods were used for large and small species, they are treated separately in analyses. Small spe- cies include insectivores, tree shrews, rodents, lagomorphs, and small primates. They generally weigh less than 5 kg. The sediments of the study interval were deposited by coexisting fluvial systems, with the larger emergent Nagri system being displaced between 10.1 and 9.0 Ma by an interfan Dhok Pathan sys- tem. In comparison to Nagri floodplains, Dhok Pathan floodplains were less well drained, with smaller rivers having more seasonally variable flow and more frequent avulsions. Paleosol se- quences indicate reorganization of topography and drainage accompanying a transition to a more seasonal climate. A few paleosols may have formed under waterlogged, grassy woodlands, but most formed under drier conditions and more closed vegetation. The oxygen isotopic record also indicates significant change in the patterns of precipitation be- ginning at 9.2 Ma, in what may have been a shift to a drier and more seasonal climate. The carbon isotope record demonstrates that after 8.1 Ma significant amounts of C 4 grasses began to appear and that by 6.8 Ma floodplain habitats included extensive C4 grasslands. Plant communities with predominantly C3 plants were greatly diminished after 7.0 Ma, and those with predominantly C4 plants, which would have been open woodlands or grassy woodlands, appeared as early as 7.4 Ma. Inferred first and last appearances show a constant, low level of faunal turnover throughout the interval 10.7-5.7-Ma, with three short periods of elevated turnover at 10.3, 7.8, and 7.3-7.0 Ma. The three pulses account for nearly 44% of all turnover. Throughout the late Miocene, species richness declined steadily, and diversity and richness indices together with data on body size imply that community ecological structure changed abruptly just after 10 Ma, and then again at 7.8 Ma. Be- tween 10 and 7.8 Ma the large-mammal assemblages were strongly dominated by equids, with more balanced faunas before and after. The pattern of appearance and disappearance is selective with respect to inferred habits of the animals. Species appearing after 9.0 Ma are grazers or typical of more open habitats, whereas many species that disappear can be linked to more closed vege- tation. We presume exceptions to this pattern were animals of the mixed C

/pdf/faunal-and-environmental-change-in-the-late-miocene-siwaliks-wtmxa1dod0.pdf

Faunal and environmental change in the late Miocene Siwaliks of northern Pakistan

Early Miocene to Quaternary sedimentary strata drilled from the distal Bengal fan in the central Indian Ocean during Leg 116 of the Ocean Drilling Program are divided into six zones by modal proportions of detrital heavy minerals. We identified the provenance of sediments in each zone on the basis of the mineral assemblage and propose a two-phase uplift of the Higher Himalayas since 17 Ma. The oldest sedimentary strata, ranging from 17.1 to 15.2 Ma, were derived mostly from the sedimentary rocks of the Lower Himalayas and the Tethys Himalayas. The zone above these strata (15.2-10.9 Ma) contains minerals derived from the Higher Himalayas. The main provenance of the zone dated between 10.9 and 7.5 Ma also appears to be the Higher Himalayas. Calcic amphibole, which indicates contribution from the Higher Himalayas, appeared at 15.2 Ma and abruptly increased at 10.9 Ma. The acme of the uplift in the first phase was between 10.9 and 7.5 Ma. From 7.5 to 6.5 Ma, the amount of elements from the Higher Himalayas abruptly decreased. It is proposed that the Higher Himalayas were eroded, and their source area became smaller. Concurrently, pumpellyite disappeared. Because this mineral is currently found only in the limited area of the upper drainage basin of the Indus River, we presume that the drainage system of the Ganges and Indus rivers changed between 7.5 and 6.5 Ma, in association with tectonic movement. The zone dated between 6.5 and 0.9 Ma is composed of two types of sedimentary units, one from the Higher Himalayas and the other from the Indian subcontinent and Sri Lanka. The provenance of the zone younger than 0.9 Ma is thought to be the Higher Himalayas, where a large peridotite body was thrust up over the Tethys Himalayas. The second main phase of uplift of the Higher Himalayas occurred after 0.9 Ma.

Two-phase uplift of Higher Himalayas since 17 Ma

Relationship between tectonics, volcanism, sedimentation and basin development, Late Cenozoic, central part of Northern Honshu, Japan

Thirteen dike swarms in Northeast Japan were dated by the K-Ar method. The K-Ar ages in this study give some crucial constraints to the volcanostratigraphy and imply that the geological situation of some dike swarms estimated in the other studies should be reexaminned while other dike swarms showed the K-Ar ages concordant with the geological ages. Available K-Ar ages of the volcanic rocks from the present and other studies indicate that the volcanic front in Northeast Japan had a temporal position about 22–23 Ma ago to the east of that in the Quaternary and that the volcanism appears to have been inactive from 17 to 21 Ma ago.

K-Ar ages of dikes in Northeast Japan.

Early Miocene to Quaternary sediments drilled from the Bengal Fan are divided into six zones by modal proportions of heavy minerals. The sediments were mostly derived from the Himalayas. Detritus from the Indian subcontinent is found sporadically in clay-rich sediments that were deposited during periods of slow sedimentation, when the deep-sea channel migrated away from the drilled sites. The oldest sediments, ranging from 17 to about 15 Ma, were derived mostly from the Precambrian and Paleozoic sedimentary rocks of the lower Himalayas. At about 15 Ma, metamorphic terrains were eroded in the source area. Further large-scale unroofing of metamorphic rocks occurred around 11 Ma. After 10 Ma, the major constituents in the drainage basin or the drainage pattern changed a few times. Between 3.5 and 0.5 Ma, a large peridotite body was unroofed by uplift and successive erosion of the central Himalayas. At this time, the single large river that had supplied detritus to the early Bengal Fan was divided into the Indus and Ganges rivers.

http://www-odp.tamu.edu/publications/116_sr/volume/chapters/sr116_06.pdf

Kazuo Amano

Papers

Two-phase uplift of Higher Himalayas since 17 Ma

Relationship between tectonics, volcanism, sedimentation and basin development, Late Cenozoic, central part of Northern Honshu, Japan

K-Ar ages of dikes in Northeast Japan.

6. mineralogy of silts from the bengal fan1

Paleomagnetic Study of Late Miocene and Early Pliocene Rocks from Southern Peru, Central Andes