Himalayan-Tibetan Orogen Research Articles

Early Eocene high-flux magmatism and concurrent high-temperature metamorphism in the Gangdese belt, southern Tibet

Abstract The Himalayan-Tibetan orogen represents one of the major Cenozoic tectonic features on Earth, and yet considerable debate continues over the timing and sequence of collisional events leading to its formation. In this contribution, we present new field relations, petrology, geochemistry, geochronology, and phase equilibria modeling in the Gangdese belt of southern Tibet in an effort to address Indo-Asian collisional events in the region. These investigations reveal that the dominantly dioritic Nymo intrusive complex was formed at ca. 50–47 Ma. We establish that the Jurassic-aged Bima volcano-sedimentary sequence underwent early Eocene (50–47 Ma) high-temperature (HT) amphibolite-facies metamorphism. Petrology and phase equilibria modeling of garnet-biotite schists in the Bima rocks reveals mineral assemblages of melt + plagioclase + garnet + biotite + magnetite + ilmenite + sillimanite formed under conditions of 5.3–7.5 kbar and 700–800 °C. We contend that the early Eocene Nymo intrusive complex represents part of the ca. 50 Ma high-flux magmatic “flare-up” that triggered the HT amphibolite-facies metamorphism within the overlying plate during Indo-Asian collision. The synchroneity of high-flux magmatism and HT metamorphism in the Gangdese belt roughly coincided with the continuing Indo-Asian collisional process, implying the early Eocene closure of the Neotethys Ocean along the southern margin of the Lhasa terrane.

Kinematic evolution of a continental collision: Constraining the Himalayan-Tibetan orogen via bulk strain rates

We investigated temporal variations of the bulk strain rate across the Himalayan-Tibetan orogen, which impact the magnitudes, rates, and distribution of deformation across the orogen. The present-day strain rate estimated from geodesy is ~5-6×10-16 s-1 and estimation of past rates depends on the orogenic shortening rate and effective orogen width. Plate-circuit reconstructions provide constraints on time-varying India-Asia convergence rates, showing a marked deceleration since initial collision at ca. 58 Ma. Geologic evidence suggests that most of the Tibetan crust started deforming shortly after initial collision, which simplifies estimation of the initial orogen width. We examined several kinematic models: (1) Greater Indian and Tibetan crust started deforming immediately after collision, (2) only Tibetan crust deformed initially, (3) plate convergence was decoupled from crustal shortening, with Tibetan crust deforming slower than plate rates, or (4) a hard India-Asia collision at ca. 45 Ma following closure of the Xigaze backarc. Models 1, 3, and 4 yield early Cenozoic bulk strain rates that match present-day rates (5-6×10-16 s-1), whereas Model 2 yields faster rates (1.2×10-15 s-1) that must have decreased through time to avoid shortening exceeding total plate convergence. Using these bounds, we constrain crustal shortening across the entire orogen and along its southern and northern margins, defined by the Himalaya and Qilian Shan, respectively. Application of these models to Tibetan crustal thickening suggests that the plateau reached its present-day value (~70 km) by ca. 15 Ma, which corresponds to the onset of lateral deformation (e.g., strike-slip and normal faulting). Lateral deformation in the Himalayan-Tibetan orogen may have resulted from progressive crustal thickening and reorientation of the intermediate principal stress axis. At the thrust-belt scale, our modeling yields shortening rates and magnitudes that match geologic observations. This approach provides testable external kinematic constraints to guide future geological and geophysical investigations.

Glacial vis-à-vis tectono-provenance signals of the Plio-Pleistocene sediments of the intermontane Kashmir basin, northwestern Himalaya: Evidence from quartz micro-textures and a till deposit

The Himalayan-Tibetan orogen has a great influence on regional and global atmospheric circulation and, hence, it is important for understanding the dynamics of global environmental change. The Kashmir valley, located in the northwestern Himalaya, provides a unique sequence of continuous sedimentary records of unconsolidated sediments of more than a km thickness, dated back to 4 Ma. There are number of studies which suggest episodic and widespread cold conditions, including glaciations, within the Kashmir valley during the Plio-Pleistocene. In order to test the hypothesis of the glacial input into the Kashmir basin, scanning electron microscopy (SEM) was applied to analyze quartz grains of the Karewa deposits stratigraphically for the evidence of their sedimentary history. The microtextures indicate the dominant presence of sustained high stress fractures on the quartz grains with little effect of weathering and dissolution from 4 to 2.1 Ma and from 1.6 to 0.4 Ma. The quartz grains are also angular and of high relief. All these features suggest that these sediments are primarily transported by glaciers and melt water streams. However, the samples ranging in age from 2.1 to 1.7 show a mixed signal (glacial and fluvial) with a dominance of fluvial signal. This transition is attributed to the source area change from the Himalayan range (NE) to the Pir Panjal range (SW) because of the uplift along the Main Boundary Thrust (MBT). Furthermore, we report the first occurrence of a till deposit within the lower part (Dubjan Member 4–3.5 Ma) of the Karewa Group of the Kashmir basin which points to ice advancement in the northwestern Himalaya during the mid-Pliocene. Since, the till occurs in the upper part of the Dubjan Member, therefore, the timing of this glaciation can be restricted to be between 3.7 and 3.5 Ma. Hence, matches well with the mid-Pliocene glaciation that occurred in the Tibetan Plateau (~3.6 Ma) and other parts of the Northern Hemisphere (3.5 Ma).

Permian plume-strengthened Tarim lithosphere controls the Cenozoic deformation pattern of the Himalayan-Tibetan orogen

AbstractThe high strength of the Tarim Basin (northwestern China) lithosphere, widely regarded as a Precambrian craton, is evidenced by its resistance to Cenozoic deformation in the Himalayan-Tibetan orogen. However, Neoproterozoic suturing and early Paleozoic shortening within the Tarim Basin suggest that its rigidity is a relatively recent phenomenon with unknown cause. We reprocessed high-resolution magnetic data that show a 300–400-km-diameter radial pattern of linear anomalies emanating from a central region characterized by mixed positive-negative anomalies. We suggest that this pattern was generated by the previously hypothesized Permian (ca. 300–270 Ma) plume beneath the Tarim Basin. Constrained by published geochemical and geochronological data from plume-related igneous rocks, we propose that the ∼30 m.y. Permian plume activity resulted in a more viscous, depleted, thicker, dehydrated, and low-density mantle lithosphere. The resulting stronger lithosphere deflected strain from the Cenozoic India-Asia convergence around Tarim Basin, including Pamir overthrusting to the northwest and Altyn Tagh left-slip displacement to the northeast, thus shaping the geometry of the Himalayan-Tibetan orogen.

Magmatic history of central Myanmar and implications for the evolution of the Burma Terrane

The Burma Terrane is a microplate at the eastern edge of the Tibetan-Himalayan orogen, the origin of which remains poorly understood. Its basement comprises metamorphic and igneous rocks forming the Wuntho-Popa Arc (WPA) and has been correlated with Tibetan, Gondwana or Transtethyan rocks. Yet, little is known about the magmatic history of the WPA. We report elemental and Sr-Nd isotopic compositions of magmatic rocks, crystallization (zircon and apatite U-Pb) and exhumation (apatite fission-track) ages from rocks and river sands, and structural measurements from the Wuntho Ranges, central Myanmar, where the WPA is best exposed. We show that the WPA in the Wuntho Ranges is characterized by two magmatic events at 108–90 Ma and 46–32 Ma. Magmatism is subduction-related for both events, characterized by depleted Nd and Sr isotopic compositions, with more enriched values with time. Apatite fission-track data suggest arc exhumation during the 39–22 Ma time interval, partly overlapping with the last magmatic event. Structural data indicate NW-SE-striking tilting, folding, and thrusting that we associate with at least two phases of deformation, in the Cretaceous and the late Paleogene. Correlating the WPA with Tibetan, Gondwana or Transtethyan rocks based on its magmatic history remains ambiguous; however, models arguing for a Transtethyan origin for the WPA are most compatible with our results combined with available Burmese geological data.

Late Cenozoic Activity of the Tashkurgan Normal Fault and Implications for the Origin of the Kongur Shan Extensional System, Eastern Pamir

In the northwest of the Himalayan-Tibetan Orogen, the ~250 km-long Kongur Shan extensional system in the eastern Pamir was formed during the convergence between the Indian and Asian plates. Tectonic activity of the Kongur Shan normal fault and the Tashkurgan normal fault can help to reveal the origin of east-west extension along the Kongur Shan extensional system. The Kongur Shan fault has been extensively studied, while the Tashkurgan fault calls for systemic research. In this study, low-temperature thermochronology including apatite fission track analysis and apatite and zircon (U-Th)/He analyses is applied to constrain the timing of activity of the Tashkurgan fault. Results indicate that the Tashkurgan fault initiated at 10-5 Ma, and most likely at 6-5 Ma. The footwall of the Tashkurgan fault has been exhumed at an average exhumation rate of 0.6-0.9 mm/a since the initiation of the Tashkurgan fault. Combined with previous research on the Kongur Shan fault, we believe that the origin of east-west extension along the Kongur Shan extensional system was driven by gravitational collapse of over-thickened Pamir crust.

Late Pliocene onset of the Cona rift, eastern Himalaya, confirms eastward propagation of extension in Himalayan-Tibetan orogen

Several competing hypotheses have been proposed to explain east-west extension observed across the Himalayan orogen, based primarily on observations from the western and central Himalaya. They make predictions for the temporal and spatial patterns of deformation in the eastern Himalaya. These tectonic models include radial spreading or oroclinal bending of the Himalayan arc, oblique convergence of the Indian continent, tearing or lateral detachment of the Indian slab and eastward flow of lithosphere. Here, for the first time we constrain the activity history of the Cona rift, the only north-trending rift currently recognized in the eastern Himalaya, based on biotite and K-feldspar 40Ar/39Ar and zircon and apatite (U–Th)/He thermochronology, to evaluate these proposed rifting mechanisms. Low-temperature thermochronological results suggest that the Cona rift is the youngest rift system in the Himalayas: after a slow phase of exhumation since ∼14 Ma (∼0.2–0.13 mm/yr), normal faulting initiated here at ∼3.0–2.3 Ma with a fault slip rate of ∼3.8–1.6 mm/yr and a horizontal extension magnitude of ∼2–5 km. Analysis of rifting across the Himalayas shows that rift initiation ages young eastward, which is matched by eastward decreasing rift-extension magnitudes. Monotonically eastward younging rift development is consistent with the tectonic model involving eastward lithospheric flow driven by Indian slab dynamics and coupled asynchronous gravitational potential energy gradients.

Cenozoic tectonic rotations in different parts of the NE Pamir: implications for the evolution of the arcuate orogen

The Pamir salient, defining the NW end of the Himalayan–Tibetan orogen, is a prominent curved orogen as a response to the Indian-Eurasian collision. Its evolution history is essential for understanding intracontinental tectonic processes in the context of continental collision. In this study, we carry out systematic paleomagnetic studies on four sections in different parts of the NE Pamir to unravel the tectonic evolution of the curved orogen. Our new results from the Oytag section suggest that the clockwise (CW) rotations of the eastern Pamir salient mainly occurred in the Oligocene (~ 32–26 Ma) as a response to the northward indentation of the Pamir salient and was dominated by large-scale dextral strike-slip faults since then. Additionally, the final collision between Pamir and SW Tian Shan in the latest Miocene reactivated the dextral Talas-Ferghana Fault (TFF), thus be responsible for the counter-clockwise (CCW) rotations at Ulugqat. However, the limited tectonic rotations of the Keliyang and Sanju sections can be explained by the dominant thrust faulting in the foreland of the West Kunlun Mountains. Combined with the existing paleomagnetic data around the Pamir salient, our results support a four-stage evolution: (1) a roughly linear orogen before the early Eocene; (2) symmetric rotations on both sides until the latest Oligocene followed by (3) asymmetric geometries with continued radial thrusting on the western flank and large-scale strike-slip fault on the eastern flank; and (4) final collision between the Pamir salient and SW Tian Shan in the late Miocene.

Deciphering the evolution and forcing mechanisms of glaciation over the Himalayan-Tibetan orogen during the past 20,000 years

The evolution of past glaciations over the Himalayan-Tibetan orogen and their links with climate change remain elusive, partially owing to the immense scale of the orogen preventing the investigation of all areas. Numerical modeling aids in filling the gaps, verifying the geologic observations, and exploring forcing factors. Based on a transient climate-ice sheet simulation for the past 20 kyr, we demonstrate that the maximum extent of glaciation over the Himalayan-Tibetan orogen occurs around the last glacial maximum (LGM; defined here at ∼20 ka), with expanded ice caps and extensive valley glaciers and being equivalent to a fourfold/sixfold expansion of today's glacier area/volume. The glacier extent shrinks rapidly after the LGM and reaches the minimum around ∼8–7 ka, followed by a slight long-term advancing trend afterwards. Our results suggest a dominant role of summer temperature in controlling the overall trend of glacier response, with precipitation generally modulating the regional extent of glaciation. However, the timing and extent of glaciation in the simulations varies across the Himalayan-Tibetan orogen on millennial timescale, especially between the monsoon-influenced southern and westerly-influenced western parts, further confirming previous speculations based on glacial geologic records. Despite the uncertainties in the simulations and the discrepancy in glaciation between the simulations and the glacial geologic evidence (e.g., 10Be ages), our results provide additional clues on the relationship between climatic change and glacier response. In addition, the modeling aids in advancing our knowledge of the paleoglaciological history of the Himalayan-Tibetan orogen.

Tectonic evolution of the Grenville Orogen in the central Appalachians

Remnants of the Grenville Orogeny—a globally pervasive tectonothermal event resulting from the amalgamation of the supercontinent Rodinia between ca. 1.3 and 1.0 Ga—are exposed throughout eastern North America for ca. 3000 km from Labrador to Alabama. Although tectonic models for the development of the Grenville have historically been based on observations from the large and well-exposed Canadian Grenville Province, recent investigations suggest that initial continental collision occurred proximal to the Appalachian Blue Ridge. Mesoproterozoic rocks within this portion of the orogen are exposed within a series of allochthonous terranes that were extensively reworked during Paleozoic orogenesis. To better understand the tectonic history of this critical region, we utilized garnet and monazite geochronology to reconstruct the metamorphic history of eleven samples of ortho- and paragneiss from the Appalachian Blue Ridge Province.The resultant dates, together with new results from trace element thermobarometry, define a prolonged record of high temperature metamorphism coincident with the timing of continent–continent collision as recognized in the northern portion of the orogen. Initial garnet and monazite growth commenced between 1100 and 1065 Ma with peak granulite-facies conditions (750–900 °C, 0.55–0.85 GPa) occurring from 1050 to 1010 Ma. Burial and heating of the paragneisses progressed rapidly with peak metamorphism occurring ∼20–30 Myr after deposition of the sedimentary protoliths. Local hydrothermal alteration followed peak metamorphism and occurred at 1000–990 Ma with later cooling through ∼660 °C between 980 and 935 Ma (3 ± 2 °C/Myr). The metamorphic history outlined here, together with insights from previous studies, is consistent with formation of the Blue Ridge rocks within a continental suture zone that had an orogenic architecture comparable to that of the Himalayan-Tibetan orogen.

Cenozoic multi-phase deformation in the Qilian Shan and out-of-sequence development of the northern Tibetan Plateau

Uplift of the Tibetan Plateau and the distribution of deformation across it are the result of India-Asia collision, which bring an opportunity of understanding intracontinental tectonics in the context of continent-continent collision. The Tibetan Plateau is bound on the northern margin by the Qilian Shan thrust belt and the strike-slip Haiyuan fault. These Cenozoic fault systems play a critical role in accommodating continental convergence, yet the initiation age, deformation sequence and mechanisms of deformation are debated. In this study, integrated geologic mapping, field observations, and apatite fission track thermochronology were conducted to constrain the initiation ages of the localized thrust faults and the exhumation history of the central and northern Qilian Shan, northern Tibet. Our analyses reveal the central and northern Qilian Shan underwent rapid cooling during the Cretaceous as a result of a far-field tectonic event. In the Eocene-Oligocene, a period of thrust-related cooling occurred along the Shule Nan Shan, Tuolai Nan Shan and Tuolai Shan faults. Reactivation of the proximal thrust faults and initiation of the western segment of the Haiyuan fault occurred at ca. 16 Ma and drove final accelerated Miocene cooling and denudation to the surface. We argue that the Qilian Shan thrust belt has persisted as the stationary and internally deformed northern boundary of the Himalayan-Tibetan orogen since the early Cenozoic, involved overprinting out-of-sequence development starting by Eocene related to initiation of India-Asia collision, and the basins and ranges across the northern Tibetan Plateau have since experienced multi-phase of growth.

Phylogeny of spiny frogs Nanorana (Anura: Dicroglossidae) supports a Tibetan origin of a Himalayan species group.

Recent advances in the understanding of the evolution of the Asian continent challenge the long‐held belief of a faunal immigration into the Himalaya. Spiny frogs of the genus Nanorana are a characteristic faunal group of the Himalaya–Tibet orogen (HTO). We examine the phylogeny of these frogs to explore alternative biogeographic scenarios for their origin in the Greater Himalaya, namely, immigration, South Tibetan origin, strict vicariance. We sequenced 150 Nanorana samples from 62 localities for three mitochondrial (1,524 bp) and three nuclear markers (2,043 bp) and complemented the data with sequence data available from GenBank. We reconstructed a gene tree, phylogenetic networks, and ancestral areas. Based on the nuDNA, we also generated a time‐calibrated species tree. The results revealed two major clades (Nanorana and Quasipaa), which originated in the Lower Miocene from eastern China and subsequently spread into the HTO (Nanorana). Five well‐supported subclades are found within Nanorana: from the East, Central, and Northwest Himalaya, the Tibetan Plateau, and the southeastern Plateau margin. The latter subclade represents the most basal group (subgenus Chaparana), the Plateau group (Nanorana) represents the sister clade to all species of the Greater Himalaya (Paa). We found no evidence for an east–west range expansion of Paa along the Himalaya, nor clear support for a strict vicariance model. Diversification in each of the three Himalayan subclades has probably occurred in distinct areas. Specimens from the NW Himalaya are placed basally relative to the highly diverse Central Himalayan group, while the lineage from the Tibetan Plateau is placed within a more terminal clade. Our data indicate a Tibetan origin of Himalayan Nanorana and support a previous hypothesis, which implies that a significant part of the Himalayan biodiversity results from primary diversification of the species groups in South Tibet before this part of the HTO was uplifted to its recent heights.

Inherited terrane properties explain enigmatic post-collisional Himalayan-Tibetan evolution

AbstractObservations highlight the complex tectonic, magmatic, and geodynamic phases of the Cenozoic post-collisional evolution of the Himalayan-Tibetan orogen and show that these phases migrate erratically among terranes accreted to Asia prior to the Indian collision. This behavior contrasts sharply with the expected evolution of large, hot orogens formed by collision of lithospheres with laterally uniform properties. Motivated by this problem, we use two-dimensional numerical geodynamical model experiments to show that the enigmatic behavior of the Himalayan-Tibetan orogeny can result from crust-mantle decoupling, transport of crust relative to the mantle lithosphere, and diverse styles of lithospheric mantle delamination, which emerge self-consistently as phases in the evolution of the system. These model styles are explained by contrasting inherited mantle lithosphere properties of the Asian upper-plate accreted terranes. Deformation and lithospheric delamination preferentially localize in terranes with the most dense and weak mantle lithosphere, first in the Qiangtang and then in the Lhasa mantle lithospheres. The model results are shown to be consistent with 11 observed complexities in the evolution of the Himalayan-Tibetan orogen. The broad implication is that all large orogens containing previously accreted terranes are expected to have an idiosyncratic evolution determined by the properties of these terranes, and will be shown to deviate from predictions of uniform lithosphere models.

Crustal thickening prior to 43 Ma in the Himalaya: Evidence from lower crust‐derived adakitic magmatism in Dala, eastern Tethyan Himalaya, Tibet

The Himalayan–Tibetan orogen is the world's largest active orogen with the thickest continental crust on Earth. However, the timing of crustal thickening of this orogen remains controversial. In recent years, magmatic rocks with adakitic affinities have been widely used to constrain the crustal thickness. Here, we present zircon U–Pb ages, geochemical and Sr–Nd–Pb–Hf isotopic data for the Dala two‐mica granites (eastern Tethyan Himalaya) that may shed light on this issue. Zircon U–Pb dating shows that the Dala two‐mica granites were emplaced at ca. 43 Ma. The granites display adakitic signatures, including high SiO2, Al2O3 and Sr contents, low Y and Yb contents with high Sr/Y (27−67) and La/Yb (35−99) ratios. High K2O and Th contents, low Nb/U, Ce/Pb, Ti/Eu and Nd/Sm ratios and low MgO, Mg#, Cr and Ni contents suggest that the Dala two‐mica granites were derived from partial melting of a thickened lower crust. Low negative zircon εHf(t) values (−10.4 to −0.5) with old two‐stage Hf model ages (1.1–1.8 Ga), high (87Sr/86Sr)i (0.715861–0.717665) with low εNd(t) (−12.5 to −11.3) and high Pb isotopes [(206Pb/204Pb)i=18.783–18.861, (207Pb/204Pb)i=18.783–18.861 and (208Pb/204Pb)i=39.052–39.285], together with previous literature data, indicate that the magma source for the Eocene granites in the Yardoi area was composed of ancient lower crust consisting mainly of garnet‐amphibolite and probably subordinate metapelites of the High Himalayan Crystalline Sequence. The residual mineral assemblage of garnet + rutile + plagioclase ± amphibole in the source region demonstrates that the crust beneath the Himalaya could have been thickened to ﹥50 km in the Eocene. Combining with previous studies, we propose that the Eocene magmatic rocks in the Tethyan Himalaya (e.g. ca. 43 Ma old Dala two‐mica granites) can be best interpreted as the consequence of breakoff of the Neo‐Tethyan oceanic slab.

High-frequency Holocene glacier fluctuations in the Himalayan-Tibetan orogen

Holocene glacial chronostratigraphies in glaciated valleys spread throughout the Himalayan-Tibetan orogen, including the Himalaya, Tibet, Pamir, and Tian Shan, are developed using a landsystems approach, detailed geomorphic mapping, and new and published 10Be surface exposure dating. New studies in the Kulti valley of Lahul and the Parkachik valley of the Nun Kun massif of the Himalaya of northern India define three glacier advances at ∼14.7, 12.2, 0.5 ka, in addition to one historically dated late 19th Century advance in the Kulti valley, and one Late Holocene advance at ∼0.2 ka in the Parkachik valley. Three major climatic groups (subdivided into five climatic zones) are defined across the orogen using Cluster Analysis (CA) and Principal Component Analysis (PCA) to identify glaciated regions with comparable climatic characteristics to evaluate the timing, and extent of Holocene glacier advances across these regions. Our regional analyses across the Himalayan-Tibetan orogen suggest at least one Lateglacial (∼15.3–11.8 ka) and five Himalayan-Tibetan Holocene glacial stages (HTHS) at ∼11.5–9.5, ∼8.8–7.7, ∼7.0–3.2, ∼2.3–1.0, and <1 ka. The extent (amplitude) of glacier advances in 77 glaciated valleys is reconstructed and defined using equilibrium-line altitudes (ELAs). Modern glacier hypsometries are also assessed to help explain the intra-regional variations in glacier amplitudes during each regional glacier advance. A linear inverse glacier flow model is used to decipher the net changes in temperature (ΔT) between periods of reconstructed regional glacier advances in 66 glaciated valleys across different climatic regions throughout the orogen. The 10Be, ELAs, and ΔT data suggest enhanced monsoonal and increased precipitation during the Early Holocene, followed by relative cooling and increased aridity during the Mid- and Late Holocene that influenced glaciation. The sublimation-dominated cold-based glaciers in the northern regions of Himalayan-Tibetan orogen are more affected during these shifts in climate than the temperate glaciers in the south.

Sediment-hosted Pb–Zn deposits in the Tethyan domain from China to Iran: Characteristics, tectonic setting, and ore controls

The Tethyan domain from China to Iran hosts many important sediment-hosted Pb–Zn deposits but most have been poorly documented. This study summarizes the salient features of these deposits and discusses the type of ore, tectonic setting, and important ore controls, on the basis of new geological observations and previous publications. The Tethyan domain is characterized by the young and extensive Himalayan–Tibetan and Zagros orogens that formed through collisions between the India/Arabia and Eurasia continents since the Late Cretaceous or early Cenozoic. Abundant Mississippi Valley-type (MVT) and subordinate clastic-dominated (CD, also known as SEDEX) Pb–Zn deposits occur in this domain, including in central and eastern Himalayan–Tibetan orogen in China, the Indian passive margin in southern Pakistan, and various tectonic units of Iran. Economically important deposits contain 0.1–21 Mt Pb + Zn and have total metal resources of ∼75 Mt with ∼48% being oxidized ores. All major deposits known in this domain are MVTs (i.e., the Jinding, Huoshaoyun, Mehdiabad, and Angouran deposits).Mississippi Valley-type Pb–Zn deposits occur in continental-collision-related fold-and-thrust belts and forelands, where deposits are mostly located on the margin of the Eurasian continent, with some in the Indian and Arabian continental margins. Clastic-dominated Pb–Zn deposits occur in central Iran and southern Pakistan, hosted by deep-water siliciclastic sequences of the early Cambrian rifted continental margin of Gondwana and the Jurassic passive continental margin of India, respectively. The youngest mineralized rocks and ages constrain that some important MVT deposits (e.g., the Jinding, Chaqupacha, and Angouran deposits) were formed after a main phase of regional compression, during a regional, large-scale strike-slip or crustal-extension stage in a continental collision setting. In sense of lithologic structure, important ore controls for MVT deposits include evaporite diapir structure, carbonate/evaporite dissolution–collapse structure, pre-existing barite, and porous dolostone. Much of the primary sulfide ore in this domain has been oxidized by supergene processes. This is particularly pronounced in the newly discovered Huoshaoyun deposit, where almost all sulfides have been oxidized to smithsonite and cerussite. An understanding of tectonic setting, ore controls, and supergene processes is essential in exploring for MVT deposits in this domain.

Late Oligocene–early Miocene transformation of postcollisional magmatism in Tibet

Abstract Uplift of the Tibetan Plateau is thought to be one of the most important orogenic and climate forcing events of the Cenozoic Era, associated with geodynamic changes related to India-Asia collision and subsequent continental lithosphere subduction. However, the fate and scale of the subducted continental lithosphere segments remain highly controversial. Using a comprehensive compilation of the spatiotemporal distribution of postcollisional magmatic rocks across Tibet, together with new geochemical and Sr-Nd-Pb isotopic data and modeling simulations, we propose a holistic, two-stage evolutionary model to explain the link between genesis of the magmas and continental subduction. The magmatism prior to 25 Ma resulted from continuous upwelling of a carbonate-rich upper-mantle plume induced by northward underthrusting of Indian oceanic and continental lithosphere with its cover of Tethyan platform carbonate sediments, whereas magmatism after 25 Ma was related to opposing north-directed and south-directed continental subduction. Our model indicates a transformation in the distribution and nature of the magmatism in Tibet at ca. 25 Ma, which reflects a significant change in the Himalayan-Tibetan orogen and associated mantle dynamic processes in the early Miocene. Understanding this transformation could have important implications for the utility of the Himalayan-Tibetan system as a modern analogue for ancient orogens.

Mesozoic evolution of the eastern Pamir

AbstractWe present field and analytical results from the Tashkurgan and Waqia valleys in the southeastern Pamir that shed new light on the tectonic evolution and terrane architecture of the region. Field mapping of metasedimentary and igneous units along the Tashkurgan and Waqia valleys in the Southeast Pamir, integrated with metamorphic petrology, garnet-biotite thermometry, and zircon U/Pb isotopic analysis, help identify major structures and terrane boundaries in the region, as well as compare structural units across the Miocene Muztaghata gneiss dome. South of the Muztaghata dome, the gently northwest-plunging synformal Torbashi thrust klippe juxtaposes amphibolite facies Triassic Karakul-Mazar terrane schist and gneiss structurally above (1) greenschist facies Triassic Karakul-Mazar terrane metasedimentary rock in the north, and (2) lower-amphibolite facies schist in the south that are interpreted to be Gondwanan-derived crust (Central or South Pamir terrane). Farther south, the Rouluke thrust fault imbricates the Gondwanan crust, placing early Paleozoic schists over Permian marble and slate. Exposure of the Torbashi thrust sheet terminates in the southeast, and with it the surface exposure of the Triassic Karakul-Mazar terrane, leaving the Paleozoic Kunlun terrane juxtaposed directly against Gondwanan terrane crust. Based on lithologic and isotopic similarities of units north and south of the Muztaghata gneiss dome, we document the existence of a regionally extensive thrust nappe that stretched across the northern and eastern Pamir, prior to being cut by Miocene exhumation of the Muztaghata dome. The thrust nappe links the Torbashi thrust in the southeast Pamir with the Tanymas thrust in the northern Pamir, and documents regionally extensive exposure of lithologically continuous units across the northeast Pamir. While timing of emplacement of the Torbashi thrust klippe and displacement on the Rouluke fault to the south is not well constrained, we interpret shortening to be Cretaceous in age based on previously published cooling ages. However, a component of Cenozoic shortening cannot be ruled out.A key observation from our mapping results is that the surface exposures of the Karakul–Mazar–Songpan Ganzi terrane are not continuous between western Tibet and the Pamir, which indicates tectonic and/or erosional removal, likely sometime in the Mesozoic. Furthermore, our documentation of the Jinsha suture in the southeast Pamir on the eastern side of the Karakoram fault shows deflections of terranes across the Himalayan-Tibetan orogen were not primarily accommodated along discrete, large displacement faults (&gt;400 km) faults. Instead, oroclinal bending of the northern Pamir, and dextral shear along the Pamir margins, may be largely responsible for the northward deflection of terranes.

The Metamorphic Evolution and Tectonic Significance of the Eclogite in the Sumdo Complex, Tibet, China

AbstractAs the main tectonic component of the Himalayan–Tibetan orogen, the Lhasa terrane has received much attention as it records the entire history of the orogeny. The occurrence of high pressure eclogite in the Sumdo complex in central Lhasa terrane has a significant bearing on the understanding of the Paleo‐Tethys subduction and plate itineration processes in this area. The petrological, geochemical and geochronological data from eclogite and associated blueschist and garnet‐bearing mica schist from Sumdo, Jilang and Bailang area have been briefly review to explore the origin and metamorphic evolution of this suture. Eclogites from the Sumdo complex have experienced low temperature, high pressure to ultrahigh pressure metamorphism, revealing a fast subduction and exhumation process in a typical oceanic subduction zone. The large P‐T span between different eclogites in the literature may be affected by the big error of unappropriated using geothermobarometry and may also because of slices of subducted blocks derived from different depths juxtapose together during exhumation. By summarizing the U‐Pb, Lu‐Hf and Sm‐Nd ages of eclogites, the eclogite facies metamorphism is likely to occur in early Triassic during 245‐225 Ma, but not the previously accepted late Permian at ca. 260 Ma by the reinterpretation of the former geochronological data from literature. The opening of Paleo‐Tethys Ocean between the Lhasa terrane initiate prior to ca. 280 Ma and ultimate closure to integrate the Lhasa terrane was no earlier than 225 Ma and may triggered by the initial subduction of Bangong‐Nujiang Tethys Ocean in the north.

Geochemical evidence for thin syn-collision crust and major crustal thickening between 45 and 32 Ma at the southern margin of Tibet

Geochemical data on widely distributed igneous rocks of southern Tibet are used to reconstruct paleo-crustal thickness during the 50+ million years that have elapsed since the onset of the India-Asia collision. We use two approaches, one based on Nd isotopes and an assimilation-recharge model for granitic magma genesis and another empirical method based on trace element geochemistry (La/Yb). The focus is on granitic rocks of two age ranges in a segment of the southern Lhasa Block between approximately 89.5° and 92.5°E longitude. One age range, 45 to 62 Ma, spans the time of the onset of collision and for which we infer the geochemistry of granitic rocks reflects mainly pre-collision structure. The other age range is 21 to 9 Ma for the Nd isotopic approach, and 32 to 9 Ma for La/Yb, where the geochemistry must reflect post-collision structure. Our results suggest that the pre- and syn-collision southern margin of the Lhasa block, that portion now located within 50–60 km of the Indus-Yarlung suture (IYS) and south of 29.8°N latitude was relatively thin, about 25–35 km thick until 45 Ma. At approximately 29.8°-29.9°N latitude there was a pronounced crustal discontinuity, and north of that latitude (for a distance that we cannot constrain), the inferred crustal thickness was greater, at least 50–55 km, as indicated by latest Cretaceous and Early Tertiary granitoids and ignimbrites that have large fractions of assimilated continental crust and high La/Yb ratios. Post-collision Nd isotopic and La/Yb data from granitoids younger than 32 Ma suggest that the southern margin south of 29.8°N was thickened substantially to at least 55–60 km (based on Nd isotopes) and possibly as much as 70–75 km (based on La/Yb) by Early to mid-Miocene time. These observations require that thickening of the southern Lhasa Block margin in the period 45–32 Ma was non-uniform; the crust now within 60 km of the suture was thickened by approximately 40 km whereas the crust north of 29.9°N latitude was thickened much less, or not at all. The region currently between 29.8°N and the YTS may have been the highest elevation mountain terrane in the period from roughly 30 to 20 Ma. The amount of Miocene denudation reflects this difference, as there is evidence of substantially more denudation near the IYS than in the region north of 29.9°N. Some of the difference in thickening could be due to magmatic additions from the mantle in the region south of 29.8°N, but there is need for at least 30 km of tectonic thickening between 45 and 32 Ma. The non-uniform thickening suggests that the high elevations at the southern margin of the Himalaya-Tibet orogen propagated southward by about 200 km, from north of Lhasa to their present position, during the period from 50 to 20 Ma. Present crustal thickness requires an additional 10–15 km of more uniform post-Miocene thickening.