The association of Hawaiian-Emperor volcanism with a large-scale central Pacific anisotropy anomaly at ~150 km depth can be explained by tapping of shallow melt sources in a perisphere/LLAMA (layer of lateral advection of mass and anisotropy) model. The origin of the anisotropy anomaly can be traced to the formation of a phlogopite-garnet-pyroxenite assemblage in the perisphere beneath an island arc on the Stikine terrane of the North American Cordillera in the Carboniferous. The pyroxenites were formed when subduction-related melts invaded the mantle wedge at ~150–200 km depth. The enriched region inherited the thermal profile of the mantle wedge, along with a solar-like noble gas isotopic composition from earlier fluxing of hydrothermal fluids between interplanetary dust particle–bearing deep-sea sediments and ultramafic layers of the oceanic crust prior to subduction. After termination of subduction, the enriched perisphere was displaced to the northeast beneath the Farallon plate, and then to the northwest beneath the Izanagi and Pacific plates, eventually becoming distorted into the shape of the present-day central Pacific anisotropy anomaly. During the thermal equilibration time, estimated at ~170 m.y., the phlogopite-garnet-pyroxenite assemblage followed a horizontal trajectory in pressure-temperature ( P-T ) space. As the P-T path crossed the solidi for volatile-bearing pyroxenite compositions, diabatic partial melting generated carbonatitic to alkaline melts which began to ascend and metasomatize shallower levels of the perisphere, carrying with them the geochemical signature of the original pyroxenites. The present central Pacific anisotropy anomaly is the current manifestation of the metasomatized domain. The latter was tapped from the Late Cretaceous to the present, by propagating fractures induced by large-scale plate reorganizations in the northwest of the Pacific Basin, to produce the Hawaiian-Emperor volcanic chain.

Lithospheric foundering or delamination has been long recognized as an important process in the formation of the Andes, but the scale, timing, and surface uplift consequences remain controversial. We use recently completed ambient noise tomography and finite-frequency P-wave tomography results and other geologic and geophysical information to identify two ~200-km-diameter regions of piecemeal delamination in the Puna region between 21°S and 27°S. One location in the northern Puna Plateau is centered under the 11–1 Ma large-volume silicic Altiplano-Puna volcanic center, and the other in the southern Puna Plateau is centered approximately between the Arizaro Basin and 6–2 Ma Cerro Galan volcanic field. The foundering in the northern location has progressed to the point where the main thermal anomaly resides in the middle and upper crust, and the surface volcanic flare-up and mantle thermal anomalies are both in a waning stage. In the southern location, the main thermal anomaly is still in its waxing stage in the lower crust and upper mantle, and the foundering mantle material is imaged in the mantle wedge. The differing patterns of back-arc volcanism in the two foundering centers suggest different styles and timing of delamination, with the foundering process coming to completion earlier in the north than in the south. Based on plate-motion reconstructions, the NE-SW–aligned Juan Fernandez Ridge swept southward through this area starting about ca. 14 Ma in the north and ca. 10 Ma in the south. Although we do not think the passage of the Juan Fernandez Ridge initiated foundering, it played an important role in facilitating delamination by increasing interplate coupling, and weakening and perhaps hydrating the upper plate, and its passage allowed the delaminated material to sink into the expanding space of the mantle wedge. Another important factor in this evolution is the upper-plate lithospheric strength variations inherited from the different geologic basements underlying the northern and southern Puna regions. As the larger-scale delamination progressed, leaving behind thin lithosphere and a mantle wedge with a mixture of continental lithospheric fragments and hot asthenosphere, smaller secondary Rayleigh-Taylor instabilities occurred beneath the southern Puna Plateau, influencing basin development, and subsequent melting of this “drip” material was the source of the ensuing low-volume mafic volcanism.

The Santiago Peak volcanics, in the northern Santa Ana Mountains, are the northernmost exposures of the Santiago Peak–Alisitos magmatic arc present along the western edge of the Peninsular Ranges batholith. Remnants of deeply eroded volcanic sequences in the Santa Ana Mountains consist of subaerial basaltic-andesite to rhyolite lavas, rare basalt, welded tuff, and pyroclastic rocks that were emplaced across deformed Middle Jurassic turbidites. Subalkaline lavas have mixed calc-alkaline and tholeiitic affinities. Relatively primitive ε Sr (−18 to +5) and ε Nd (+7.5 to +0.1) values for the lavas plot along the mantle array. Silicic lavas have higher ε Sr and ε Nd values in comparison to mafic lavas. Parental magmas were derived from hydrous melts of relatively depleted mantle wedge, followed by fractionation and the assimilation of up to 10% crustal materials. The whole-rock compositions, isotopic data, and U/Pb and 40 Ar/ 39 Ar ages (128–110 Ma) of the Early Cretaceous Santiago Peak volcanics and related Estelle Mountain volcanics overlap with emplacement ages of plutons of the western zone of the Peninsular Ranges batholith. The volcanic rocks are interpreted as the volcanic component of the arc plumbing system of the batholith. Arc rocks are in turn unconformably overlain by a forearc sequence of Upper Cretaceous through Tertiary strata that indicate deep erosion of the Santiago Peak volcanics by 95 Ma. Volcanic clasts of Turonian age within the forearc sequence yield U/Pb ages of 108–106 Ma. Age data and whole-rock geochemistry of the volcanic clasts indicate that they were eroded from supracrustal volcanic rocks located farther east within the Elsinore block.

The Kings-Kaweah ophiolite belt of the southwestern Sierra Nevada Foothills was generated in two pulses of mid-oceanic-ridge basalt (MORB) magmatism. The first was in the Early Ordovician, which resulted in the generation of a complete abyssal crust and upper mantle section. The crustal section was rendered from convecting mantle whose Nd, Sr, and Pb isotopic systematics lie at the extreme end of the sub-Pacific mantle regime in terms of time integrated depletions of large ion lithophile (LIL) elements. Semi-intact fragments of this Early Ordovician oceanic lithosphere sequence constitute the Kings River ophiolite. Following ~190 m.y. of residence in the Panthalassa abyssal realm, a second pulse of MORB magmatism invaded the Early Ordovician lithosphere sequence in conjunction with intensive ductile shearing and the development of ocean floor mélange. This Permo-Carboniferous magmatic and deformational regime produced many of the essential features observed along spreading ridge–large-offset transform fracture zones of the modern ocean basins. During this regime, Early Ordovician upper mantle–lower crustal rocks were deformed in the ductile regime along what appears to have been an oceanic metamorphic core complex, as well as along steeply dipping strike-slip ductile shear zones that broke the ophiolite into semi-intact slabs. Progressive deformation led to the development of serpentinite-matrix ophiolitic mélange within the abyssal realm. This (Kaweah) serpentinite mélange constitutes the majority of the ophiolite belt and encases fragments of both disrupted Early Ordovician oceanic lithosphere and crustal igneous-metamorphic assemblages that were deformed and disrupted as they formed by diffuse spreading along the fracture zone. An ~190 m.y. hiatus in abyssal magmatism cannot be readily accommodated in the current configuration of Earth's ocean basins, but it was possible during the mid- to late Paleozoic Panthalassa regime, when the proto-Pacific basin occupied over half of the Earth's surface. The transform history of the ophiolite belt can be directly linked to the late Paleozoic transform truncation of the SW Cordilleran passive margin. Following juxtaposition of the transform ophiolite belt with the truncated margin a change in relative plate motions led to the inception of east-dipping subduction, and the en masse accretion of the ophiolite belt to the hanging wall of the newly established subduction zone. Structural relations and isotopic data on superimposed igneous suites show that the ophiolite belt was not obducted onto the SW Cordilleran continental margin. The accreted ophiolite belt formed the proto-forearc of the newly established active margin. The ophiolite belt never saw high-pressure/temperature (P/T) metamorphic conditions. Rare small blocks of high-pressure metamorphic rocks were entrained from the young subduction zone by serpentinite diapirs and emplaced upward into the ophiolitic mélange within a proto-forearc environment. An Sm/Nd garnet-matrix age on a high-pressure garnet amphibolite block suggests subduction initiation at ca. 255 Ma. This timing corresponds well with the initiation of arc magmatism along the eastern Sierra Nevada region. In Late Triassic to Early Jurassic time proximal submarine mafic eruptions spread across and mingled with hemipelagic and distal volcaniclastic strata that were accumulating above the accreted ophiolite belt. These lavas carry boninitic to arc tholeiitic and primitive calc-alkaline geochemical signatures. By Middle Jurassic time siliciclastic turbidites derived from early Paleozoic passive margin strata and early Mesozoic arc rocks spread across the primitive forearc. In late Middle to Late Jurassic time tabular plutons and dike swarms of calc-alkaline character invaded the ophiolite belt in a transtensional setting. Deformation fabrics that developed in these intrusives, as well as cleavage that developed in the cover strata for the ophiolite belt, imparted components of superimposed finite strain on the ophiolitic mélange structure but did not contribute significantly to mélange mixing. By ca. 125 Ma, copious gabbroic to tonalitic plutonism of the western zone of the Cretaceous Sierra Nevada batholith intruded the ophiolite belt and imparted regional contact metamorphism. Such metamorphism variably disturbed U/Pb systematics in rare felsic intrusives of the ophiolite belt but did not significantly disturb whole rock Sm/Nd systematics. Age constraints gained from the Sm/Nd and U/Pb data in conjunction with Nd, Sr, and Pb isotopic and trace element data clearly define the polygenetic abyssal magmatic history of the ophiolite belt. The variation of Nd and Sr radiogenic isotopes over time from the Paleozoic abyssal assemblages, through early Mesozoic supra-subduction zone volcanism to Early Cretaceous batholithic magmatism, record the geochemical maturation of the underlying mantle wedge without the involvement of SW Cordilleran continental basement.

Major- and trace-element and Sr-Nd-Pb isotope compositions are presented for an extensive data set of samples (44) recovered along the active ridge axis of the southern Tyrrhenian backarc basin represented by the Marsili volcano (<0.7 Ma). In addition, major and trace elements are presented for the few lavas sampled from the summit area (active at 0.4–0.1 Ma) of Vavilov volcano, located in the oceanic subbasin (i.e., Vavilov Basin) formed during the first stage of the southern Tyrrhenian backarc basin formation. Overall, these data confirm that southern Tyrrhenian backarc basin magmatism is chemically heterogeneous, ranging from an island-arc basalt (IAB) type, prevalent throughout the backarc evolution, to an ocean-island basalt (OIB)–like magmatism that occurred later in the development of the basin. Since the lavas sampled from Vavilov volcano have been strongly altered, their isotope composition was not acquired in this study. Thus, our attempt to identify the mantle domains beneath the southern Tyrrhenian system was restricted to its youngest and active part, i.e., the Marsili backarc basin and the Aeolian arc. These new data together with previously published trace-element and Sr-Nd-Pb isotope data for Marsili volcano lavas reveal that two mantle domains are involved in their petrogenesis: One represents the southern Tyrrhenian ambient mantle from which the mid-ocean-ridge basalts (MORB) flooring the Vavilov backarc basin are derived, and the other has HIMU (high U/Pb) OIB-like character, resembling the mantle source of the nearby Ustica Na-alkaline lavas. Subduction-related signatures characterize both, although to a lesser extent in the OIB-like domain with respect to the MORB-like mantle. The new data provide a much needed insight into the evolution of the southern Tyrrhenian backarc basin system, confirming that the HIMU OIB-like component results from the propagation of deep northern African mantle inflow around the southern tear of the subducting Ionian slab, rather than being a component that was present in the mantle wedge prior to the Ionian subduction process. Furthermore, a comparison between the Marsili backarc and Aeolian arc lavas permits interpretation of the trajectories followed by the African OIB-like mantle inflow within the southern Tyrrhenian mantle wedge. In particular, mantle trajectories involve upward-directed flow from the slab edge beneath Ustica Island and Prometeo submarine lava field, slab-parallel flow beneath the Marsili backarc volcano, and arcward-directed flow affecting the western margin of the Aeolian arc, thus compositionally influencing the Alicudi basic lavas.

Flat subduction of the Farallon plate beneath the western United States during the Laramide orogeny was caused by the combined effects of oceanic plateau subduction and unusually great suction in the mantle wedge, the latter of which was caused by the shallowing slab approaching the North American craton root. Once in contact with basal North America, the slab cooled and hydrated the lithosphere. Upon removal, asthenospheric contact with lithosphere resulted in magma production that was especially intense where the basal lithosphere was fertile (in what now is the Basin and Range Province), and this heating weakened the lithosphere and made it convectively unstable. Small-scale convection has since affected many areas. With slab sinking and unloading, the western United States elevated into a broad plateau, and the weak portion gravitationally collapsed. With development of a transform plate boundary, the western part of the weak zone became entrained with the Pacific plate, and deformation there is dominated by shear.

The Elder Creek ophiolite, which crops out along the South, Middle, and North Forks of Elder Creek, is the largest exposure of mid-Jurassic Coast Range ophiolite in the northern Coast Ranges of California. The Elder Creek ophiolite contains almost all of the components of a classic ophiolite (mantle tectonites, cumulate ultramafics and gabbro, dike complex, volcanics), although most of the volcanic section has been removed by erosion and redeposited in the overlying Crowfoot Point breccia. It differs from classic ophiolite stratigraphy in that it has substantial volumes (25%–30% of the complex) of felsic plutonic rocks intimately associated with the other lithologies. The felsic lithologies include hornblende diorite, quartz-diorite, tonalite, and trondhjemite, which crop out in four distinct associations: (1) as rare, small pods within the sheeted dike complex, (2) as the felsic matrix of igneous breccias (agmatites), (3) 1–25-m-thick dikes that crosscut cumulate or isotropic gabbro, and (4) sill-like plutons up to 500 m thick and 3 km long that intrude the upper part of the plutonic section. Typical phase assemblages include quartz, plagioclase, hornblende, and pyroxene, in a hypidiomorphic texture. The Elder Creek tonalite-trondhjemite-diorite (TTD) suite spans a wide range in composition: 54%–75% SiO 2 , 3.3%–14.3% FeO*, and 2.7%–6.4% MgO; all are low in K 2 O (<0.7%). The large sill-like plutons are generally higher in silica (average 69% SiO 2 ) than the dikes, pods, and agmatite matrix (average 60% SiO 2 ). Mg#’s range from 65 to 17, with Cr up to 227 ppm at 58% silica. High-Mg diorites with 4%–7% MgO at 53%–58% SiO 2 are common in the dike suite, but relatively high MgO, Mg#, and Cr values are found in the large plutons as well. The major- and trace-element characteristics are consistent with partial melting of subducted, amphibolite-facies oceanic crust at relatively low pressures (5–10 kbar) outside the garnet stability field. Melting of subducted oceanic crust at these pressures can only occur during the collision and subduction of an active spreading center. Subsequent reaction of these melts with the overlying mantle wedge has increased their refractory element concentrations. The occurrence of zircons with inherited Pb isotope characteristics implies the involvement of subducted sediments containing an ancient zircon component. Formation of the Elder Creek TTD suite was a transient event associated with ridge collision-subduction. This is consistent with previous models for the Coast Range ophiolite and other suprasubduction-zone ophiolites; it is not consistent with an ocean-ridge spreading-center origin.

The magmatic diversity of the Trans-Mexican Volcanic Belt is directly or indirectly controlled by two independent oceanic plates with differing geophysical and compositional parameters; by an extensional tectonic regime that operates with different intensities over the upper plate; by a continental basement with a diversity of ages, thick nesses, and compositions; and by a compositionally heterogeneous mantle wedge that has been modified to various extents by the slab-derived chemical agents. The convergent margin and the magmatic arc have not remained static throughout their geologic histories, but instead have shown significant changes in position, geometry, and composition. For these reasons, the Trans-Mexican Volcanic Belt is the result of one of the most complex convergent margins on the planet, the subject of more than a century of scientific investigations, and at the core of the most notorious debates on Mexican geology.

Ignimbrites, as widespread sheets tens of meters thick, form the Central American Tertiary Ignimbrite Province. Geochemical data were collected from 99 Cenozoic marine ash layers within Caribbean Sea sediments, 76 vitrophyres, and 21 mafic lavas from Nicaragua and Honduras. Two major eruptive periods, one in the Eocene and one in the Miocene, have been broadly identified. 40 Ar/ 39 Ar laser fusion ages, determined from sanidine or plagioclase in 10 of the vitrophyre samples, have been interpreted to indicate that the bulk of the younger group of ignimbrites formed largely in the middle Miocene during a 3.5-m.y. period between 16.9 and 13.4 Ma. Modeling indicates that initial melts were from a normal mid-oceanic-ridge basalt (N-MORB)–type source, rather than the enriched mid-oceanic-ridge basalt (E-MORB)–type source postulated for the modern arc. All of the ignimbrites analyzed have 87 Sr/ 86 Sr isotope values ( 87 Sr/ 86 Sr = 0.7040–0.7069) within the range of continental crust. Trace element trends are similar to those estimated for lower continental crust. Assimilation– fractional crystallization and melt mixing models produce trends that are consistent with ignimbrite compositions. This evidence is consistent with a large influence of continental crust in the ignimbrite formation. In addition, the ignimbrite magmas, like those of the modern arc, have also been determined to have been contaminated by sediment-derived fluids. Abnormally rapid subduction of the Farallon-Cocos plate, which coincides with the formation of the ignimbrites, may have resulted in their generation. A slab gap that currently exists beneath the modern arc may be the cause of a change in source from N-MORB to E-MORB by allowing rising asthenospheric material to “recharge” the mantle wedge in trace elements that had been depleted prior to the gap formation.

The Aeolian Island arc, emplaced on continental lithosphere, is composed of seven islands and several seamounts, which have evidence of magmatic activity from 1.3 Ma (Sisifo seamounts) to present time (Vulcano, Stromboli). The rock compositions belong to different magmatic series and show a large silica range (48–76 wt%). Calc-alkaline and high-K calc-alkaline volcanics are present in all the islands, except for Vulcano. Shoshonitic rocks are only lacking at Alicudi, Filicudi, and Salina. Potassic magmas have been erupted at Vulcano and Stromboli. The different parental magmas originated in a heterogeneous mid-ocean-ridge basalt (MORB)–like mantle wedge, variously metasomatized by subduction-related components (oceanic crust + sediments, released as either fluids or sediment melts). Trace-element and Sr-Nd isotopic ratios show clear geographical west-east variations among calc-alkaline rocks. The composition of the mantle source of Stromboli is strongly influenced by the addition of a sedimentary component recycled into the mantle wedge; it shows evidence of a higher amount (∼2%) than in all the other islands (<0.5%). Furthermore, the islands from the central sector of the arc are characterized by a higher proportion of slab-derived fluids, which promotes a higher degree of melting. In this frame, the high Pb isotopic ratios (HIMU-like [high µ–like]) of the rocks of the central and western branch of the arc are explained with the high 206 Pb/ 204 Pb carried from a fluid component derived from the dehydration of the ancient subducting Ionian oceanic crust. On the contrary, the low Pb isotope signature of Stromboli magmas is dictated by the sediment input, as for Sr and Nd isotopes. Parental shoshonitic magmas of Vulcano are generated by low melting degrees of a MORB-like mantle wedge, metasomatized by crustal contaminant with high fluids/sediment values, whereas Vulcano potassic magmas are interpreted as deriving from the shoshonitic magmas by refilling, tapping, fractionation, assimilation (RTFA) processes. At Stromboli, potassic to calc-alkaline magmas are generated by increasing melting degrees of a heterogeneous veined mantle. The involvement of K-micas in the genesis of potassic magmas (during partial melting of mantle wedge and/or subducted sediments) is also suggested. U-Th disequilibria confirm the higher fluid versus melt proportion in the central than in the western islands. At Stromboli, the 238 U excesses measured in calc-alkaline volcanics suggest a consistent addition of slab-derived fluids in the source, also promoting higher degrees of melting. The shift to the consistent 230 Th excesses in shoshonitic and potassic rocks requires dynamic melting processes capable of producing in-growth of 230 Th. Quantitative modeling suggests lower melting rates for shoshonitic and potassic rocks, which are consistent with the lower melting degree proposed for these magmas.

The evolving chemistry of the Chachahuén volcanic complex provides evidence for transient entry of a subduction zone component into the mantle wedge over a late Miocene shallow subduction zone under the Neuquén Basin. The Chachahuén complex, which is in the backarc of the Andean Southern Volcanic Zone near 37°S and some 500 km east of the Chile Trench, occurs at the intersection of NE and SE fault systems that parallel regional trends. Support for a shallow subduction-zone setting at the time of eruption and during the contractional uplift of the Sierra de Chachahuén comes from K/Ar and new 40 Ar/ 39 Ar ages, mineral assemblages, major and trace element chemistry, and Nd-Sr-Pb isotopic compositions. Importantly, the chemistry of the Chachahuén rocks requires an arc-like component in the mantle that is absent in both early Miocene or Pliocene alkaline lavas erupted in the same region. The oldest Chachahuén volcanic rocks are the ca. 7.3–6.8 Ma Vizcachas group orthopyroxene-bearing andesites to rhyodacites that erupted from fissures and small centers along the NE-trending fault system. Intraplate chemical tendencies in the most silicic samples are attributed to mantle-derived basalts interacting with a lower crust that has a chemical imprint that reflects older alkaline magmatic events. Younger Chachahuén group volcanic rocks erupted at ca. 6.8–6.4 Ma from vents generally aligned along the NE-trending fault system and ca. 6.3–4.9 Ma magmas that erupted from a trap-door–type caldera and flanking stratovolcanoes along the NW-trending fault system. These high-K basaltic to dacitic rocks contain amphibole phenocrysts and show arc-like high field strength element depletions that are the strongest in basaltic andesite lavas. Parallels between Chachahuén volcanic rocks and uplift of the Sierra de Chachahuén with late Miocene Pocho volcanic rocks and uplift of the Pampean Ranges over the modern Chilean flat-slab support transient Miocene shallow subduction zone under the Neuquén Basin.

The relationship between Cenozoic igneous rocks and the geodynamic evolution of the Aegean region is synthesized. A simplified palinspastic reconstruction of the region is attempted for the last 50 m.y., on the basis of published syntheses of paleomagnetic data and estimates of amounts of extension and of shortening in nappes. Variability in magma genesis results from hydrous melting of the asthenospheric mantle wedge during subduction, thermal melting of enriched subcontinental lithospheric mantle as a result of rising asthenosphere, and decompression melting of rising asthenosphere. Break-off of a subducting slab or lithospheric delamination occurred several times during the earlier Cenozoic as a result of Late Cretaceous and Paleogene closure of several Neo-Tethyan Ocean basins, triggering the rise of hot asthenosphere. Magmas underwent assimilation and fractional crystallization during passage through subcontinental lithosphere and crust; these processes were less effective where strike-slip faults provided efficient pathways for magma rise. Available data on the trace elements and radiogenic isotopes are used to identify the magmatic affinities of Cenozoic igneous rocks. Unusual features of the Cenozoic igneous activity of the Aegean region are the wide range of rock types in “back-arc” settings and the exposure of both upper-crustal and middle-crustal rocks. This is a consequence of (1) the numerous microcontinental blocks within the Aegean area, separated by Neo-Tethyan Ocean strands that were destroyed by subduction; (2) orogen-parallel strike-slip faulting resulting from the progressive collision of Arabia with Anatolia; and (3) the extensional collapse and roll-back of the Hellenic subduction zone over subducting oceanic crust. Magmatism directly related to hydrous melting of subarc asthenosphere lay south of the present south Aegean arc in the Paleogene; it influenced the Cyclades plutons in the Miocene and then moved southward again as a result of extension and roll-back to its present position. Calc-alkaline volcanism in Rhodope may be related to the subduction of the Intra-Pontide Ocean. Lithospheric delamination or slab break-off produced thermal melting of the sub-continental lithospheric mantle inhomogeneously enriched by earlier subduction, resulting in voluminous shoshonitic volcanism in the Miocene of the northeast Aegean and the Oligocene of Rhodope. In both cases, shoshonitic volcanism was followed by minor alkaline magmatism related to the decompression melting of upwelling asthenosphere. The thermal effects of upwelling asthenosphere, coupled with increased geothermal gradient from extension, also contributed to the thermal melting of sub-continental lithospheric mantle. The plutonic rocks of the Cyclades and northern Greece resulted from crustal melting by magmas largely derived from the melting of lithospheric mantle.

This article summarizes the geological setting, spatial-temporal distribution, and major-element, trace-element, and Nd-Sr-Pb isotopic compositional variation of rocks representative of Tibetan postcollisional magmatic activity. The implications of petrogenesis and spatial-temporal distribution are discussed in relation to lithospheric mantle heterogeneity and a possible role for collision-induced asthenospheric mantle flow. Rocks indicative of postcollisional volcanism are widely distributed across the terranes making up the Tibetan plateau. Three stages of activity are recognized (ca. 45–25, 25–5, and 5–0 Ma), mostly conforming to potassic to ultrapotassic shoshonitic and high-potassium calc-alkaline types. These show strong relative enrichments in large-ion lithophile elements (LILE), U, Th, and light rare earth elements (LREE); depletions in high field strength elements (HFSE) and heavy rare earth elements (HREE)—with (La/Yb) N ratios ranging from 4.3 to 699, mainly 40–50; ∑REE and abundances of 50–2560 ppm, mainly 300–500 ppm—in most cases lacking significant negative Eu anomalies. However, the element distributions for kamafugite and carbonatite show ocean island basalt–like nondepleted or even slightly enriched HFSE patterns. The plots of ϵNd versus 87 Sr/ 86 Sr define a mixing array between Neo-Tethyan mid-ocean ridge basalts (MORB) and High Himalayan crustal compositions, with ϵNd(t) varying from +5.95 to −17.42 and 87 Sr/ 86 Sr (i) 0.702059 to 0.746320. The range of Nd and Sr isotopic compositions in the northern parts of the plateau, Sanjiang, and west Qinling is relatively small compared to that from Gangdese to the south, where 87 Sr/ 86 Sr ratios range from 0.703785 to 0.746320 and 143 Nd/ 144 Nd from 0.511737 to 512710. The variation of Pb isotopic ratios is somewhat less, with 206 Pb/ 204 Pb ranging from 18.149 to 19.345, 207 Pb/ 204 Pb from 15.476 to 15.803, and 208 Pb/ 204 Pb from 37.613 to 40.168. In general, magmatic isotopic compositions indicate the regional-scale presence of DUPAL-like mantle, reflecting additions of the “enriched mantle” components (EM1, EM2) to an ambient MORB-HIMU (high μ, i.e., high U/Pb mantle) asthenospheric hybrid. The observed geochemical, isotopic, and mineral phase compositional variations of primitive magmatic products and their entrained mantle xenoliths clearly suggest LILE-enriched and HFSE-depleted phlogopite/amphibole–bearing mantle wedge sources contaminated by (presumably subduction-related) hydrous fluids or smallfraction H 2 O-CO 2 –rich melts. Tibetan lithospheric mantle appears to reflect the presence of and interaction between at least three compositional end-members. The overall spatial-temporal pattern of Tibetan collisional and postcollisional activity is consistent with the hypothesis that the Neo-Tethyan asthenospheric mantle was laterally displaced along discrete northeast- and southwestward flow channels in response to the IndiaAsia collision.