The gabbroic rocks of the Peninsular ranges batholith, Southern California: cumulate rocks associated with calc-alkalic basalts and andesites

Gabbroic rocks occur only in the west, and are the oldest intrusions in the Peninsular Ranges Cordilleran batholith. They comprise an olivine-pyroxene gabbronorite series and an amphibole gabbro series both of which contain abundant plagioclase and amphibole. They formed by crystal accumulation and in situ differentiation, in multiple intrusive complexes, and are not considered to be related by fractionation to the granitoid rocks of the batholith.Pure mineral separates of plagioclase, olivine, clinopyroxene, orthopyroxene, and amphibole were obtained by magnetic and heavy-liquid methods from a representative suite of gabbroic rocks. Their major- and trace-element contents were determined by X-ray fluorescence, and the data used to test hypotheses on the genesis and fractionation of the gabbros.The plagioclases range from An₉₈ to An₆₅ in composition, olivines, Fo₇₉ to Fo₇₀, occur in rocks where An>₃₆. All clinopyroxenes are augite with Mg #'s varying from 81.1 to 64.7. Orthopyroxene occurs where An<₉₂, and is generally inverted pigeonite or bronzite, and has Mg #'s ranging from 77.9 to 52.1. The amphiboles include tschermakite, tschermakitic hornblende, pargasite, pargasitic hornblende, ferroan pargasite, magnesio-hornblende, and magnesio-taramite, Mg #'s range from 80.4 to 62.5. Systematic chemical and mineralogical changes confirm that differentiation, controlled by mineral assemblages of plagioclase, olivine, spinel, and clinopyroxene initially, and orthopyroxene, amphibole, and magnetite later, took place between intrusive episodes and in situ.The highly clacic plagioclase coexisting with olivine and amphibole suggests that the gabbros were formed from hydrous mafic magmas. The modal mineralogy of the gabbros, and the chemistry of the minerals is very similar to that of the cumulate blocks of the Lesser Antillean volcanoes. These features confirm that the gabbros were derived from a hydrous mafic magma, with high Al₂O₃ and low TiO₂ contents, typical of orogenic environments.Cumulate minerals from the gabbros show little or no zoning and are considered to have formed in equilibrium with the evolving melts. Selected trace-element contents and distribution coefficients are used to calculate the compositions of the melts. The calculations show that the melts in equilibrium with the olivine-pyroxene gabbronorite series contain approximately 100–200 ppm Ba, 200–400 ppm Sr, 30-10 ppm Ni, 20-10 ppm Co, and 300-100 ppm V. K/Rb ratios of the melts, derived from post-cumulus and prismatic amphiboles, are generally in the range 550-250. These values are typical of calc-alkalic basalts and andesites, and it is suggested that they may have erupted at the surface to form a coeval calc-alkalic volcanic sequence.     

Geochemistry of Cenezoic volcanic rocks, Baja California, Mexico: Implications for the petrogenesis of post-subduction magmas

Late Cenozoic volcanism in Baja California records the effects of cessation of subduction at a previously convergent, plate margin. Prior to 12.5 m.y., when subduction along the margin of Baja ceased, the predominant volcanic activity had a calc-alkaline signature, ranging in composition from basalt to rhyolite. Acidic pyroclastic activity was common, and possibly represented the westermost, distal edge of the Sierra Madre Occidental province. After 12.5 m.y., however, the style and composition of the magmatic products changed dramatically. The dominant rock type within the Jaraguay and San Borja volcanic fields is a magnesian andesite, with up to 8% MgO at 57% SiO₂, low Fe/Mg ratios, and high Na/K ratios. These rocks have unusual trace-element characteristics, with high abundances of Sr (up to 3000 ppm), low contents of Rb; K/Rb ratios are very high (usually over 1000, and up to 2500), and Rb/Sr ratios are low (less than 0.01). Furthermore, La_n/Yb_n ratios are high, consistent with derivation from a mantle source with fractionated REE patterns. ⁸⁷Sr/⁸⁶Sr ratios are less than 0.7048, and usually less than 0.7040, whereas the pre-12.5 m.y. lavas have ⁸⁷Sr/⁸⁶Sr ratios between 0.7038 and 0.7063. We have previously termed these rocks bajaites, in order to distinguish them from other magnesian andesites. Bajaites also occur in southernmost Chile and the Aleutian Islands, areas which also have histories of attempted or successful ridge subduction.It is proposed that the bajaite series is produced during the unusual physico-chemical conditions operating during the subduction of young oceanic lithosphere, or subduction of a spreading centre. During normal subduction, the oceanic crust dehydrates, releasing volatiles (water, Rb and other large-ion lithophile elements) into the overlying wedge. Subduction of younger crust will result in a progressive decrease, and eventual cessation of the transfer of volatiles when subduction stops. Thermal rebound of the mantle may cause the slab to melt, perhaps under eclogitestable conditions. The resulting melt will be heavy-REE-depleted, perhaps dacitic, but will otherwise inherit MORB-like Rb/Sr and K/Rb ratios. The ascending melt will react with the mantle to form the source of the bajaitic rocks. Furthermore, any amphibole in the mantle, stabilised during the higher PH₂O conditions of earlier subduction, will break down and contribute a high-K/Rb ratio component.The implications of this study are that firstly, the subducted slab does not contribute a highly fractionated REE component in most modern arcs (i.e. the slab does not melt); secondly, Rb has a very short residence time in the mantle, and its abundance in arc rocks is a direct reflection of the input from the dehydrating slab; and thirdly, bajaitelike rocks may provide recognition of attempted or successful ridge subduction in the geologic past.     

Triple junction magmatism: a geochemical study of Neogene volcanic rocks in western California

Inception of volcanism at late Oligocene to Recent centers in the eastern Coast Ranges of California (ECR suite) regularly decreases in age northward and is correlated with the northward migration of the transform-transform-trench Mendocino triple junction (MTJ). Miocene volcanism in the southern California basin (SCB suite) is spatially and temporally associated with the transform-ridge-trench Rivera triple junction (RTJ). The tholeiitic to calc-alkaline rocks in both suites were erupted through older trench melange while arc magmatism was occurring several hundred kilometers to the east. Therefore they are not related to subduction zone magmatism, but instead to interactions of the MTJ and RTJ with the continental margin.The ECR rocks, dominantly intermediate to silicic in composition, have relatively high δ¹⁸O values up to 11.3, ⁸⁷Sr/⁸⁶Sr ratios up to 0.7055, as well as relatively high Th contents, suggesting that crustal anatexis played a dominant role in their generation. Coupled crystal fractionation and crustal assimilation by an initially basaltic magma cannot explain the high δ¹⁸O values and ⁸⁷Sr/⁸⁶Sr ratios because greater than 95% of the basalt would need to crystallize. In contrast, the SCB rocks, dominantly mafic to intermediate in composition, have relatively low δ¹⁸O values down to 5.2 and ⁸⁷Sr/⁸⁶Sr ratios down to 0.7025 suggesting that these rocks were derived dominantly from a mantle source.Whether crustal anatexis occurs is determined largely by the type of stress a triple junction imposes upon the continental margin. Both the MTJ and RTJ are associated with high heat flow and magma fluxes from the mantle. The transform-transform-trench MTJ is associated with locally variable mild extension to compression and therefore allows pooling of basaltic magma in the crust to initiate crustal melting. The high rates of continental extension associated with the transform-ridge-trench RTJ prevents such pooling of magma.The space created by decoupling of the subducted slab at a transform-transform-trench triple junction might promote passive upwelling of mantle material to fill it and induce melting to generate basalts. Mafic volcanic rocks of this origin may provide a unique view of the subcontinental mantle at the continental margin. ⁸⁷Sr/⁸⁶Sr ratios as low as 0.70255 for mafic volcanic rocks in the Sonoma-Tolay center associated with the MTJ contrast with high La/Sm ratios of 1.1 to 1.3 and low Zr/Nb,Hf/Ta,La/Th, and La/Ta ratios of 5.0 to 6.7, 2.6 to 3.5, 4.7 to 8.8, and 10.2 to 12.5, respectively. These data suggest that the mantle beneath parts of western California may have originally been depleted but has been enriched relatively recently. Such enrichment might have occurred by metasomatic processes associated with crustal accretion and/or juxtaposition of differing lithospheric mantle in the Mesozoic and Cenozoic.     

Fault growth by segment linkage in seismically active settings: Examples from the Southern Apennines, Italy, and the Coast Ranges, California

Most models for fault growth and scaling are based on analysis of faults which display dip-slip (i.e. reverse, normal) and strike-slip kinematics; by contrast, little information is derived from faults displaying oblique-slip kinematics. Observations on mesoscopic transpressional faults from the Salinian Block of California and transtensional faults from the Southern Apennines of Italy reveal a complex kinematic history of fault propagation. Faults initially nucleate as isolate segments, which are later kinematically and mechanically linked via development of diffuse deformation zones and/or localised oblique connecting splays. The geometry of observed mesoscopic faults is similar to that of the host, larger structures, thus suggesting that the produced fault patterns are scale independent. Moreover, the overprinting relationships among minor fault-related fabrics permit to define a relative chronology within fault arrays, thus enabling a general sequence of structural stages to be correctly established. Based on minor fabrics and their overprinting relationships, a kinematic deformation model of fault growth by segment linkage is presented, which may have a wide applicability in the field of seismic hazard evaluation.     

The petrology and geochemistry of volcanic rocks from the Northern Harşit river area, Pontid Volcanic Province, Northeast Turkey

Two volcanic cycles can be distinguished, in the Pontid magmatic arc. They comprise an Upper Cretaceous, Lower Volcanic Cycle of which only the waning stage contains abundant pyroclastic rocks. The latter show spatial association to the fault pattern and are closely related to mineralisation. The overlying, early Tertiary, Upper Volcanic Cycle shows evidence of explosive vulcanicity in the Upper Basic Series. Dacites and rhyodacites are only locally developed and again show spatial association with the faulting.Comparison of the major and minor element chemistries of the two cycles demonstrates the clear separation into a lower tholeiitic and an upper calc-alkaline cycle. The rocks show similar chemistry to volcanic suites from island arcs in other areas.The origin of the tholeiitic magma is ascribed to melting of “dry” amphibolite during early subduction of Tethyan ocean floor beneath “Pontian Land”. This resulted in low K abundances and K/Rb ratios, and some Fe enrichment in the tholeiitic basalts.The calc-alkaline magma is thought to be derived from a later stage in the subduction process when melting of amphibole was joined by melting of biotite or phlogopite. The Upper Volcanic Cycle is thus enriched in K and shows no Fe enrichment due to a probable higher water content. The higher Cr and Ni contents of the Upper Volcanic Cycle, together with K, may imply some melting of lherzolite overlying the subducted slab.     

The stratigraphic significance of fission-track ages on volcanic ashes in the marine Late Cenozoic of Southern California

Fission-track dates and planktonic microfossil datum levels provide a revised chronology for the marine Late Cenozoic of southern California. In southern California, the Pliocene/Pleistocene boundary has been placed at the first appearance of Globorotalia truncatulinoides within the Pico Formation, Balcom Canyon, Ventura County. A fission-track age on glass shards from the Bailey Ash close to this level yields a result of 1.12 ± 0.36 m.y. B.P. (millions of years before present). In tropical deep-sea cores, however, G. truncatulinoides has been shown to evolve within the Gilsa paleomagnetic event with an estimated age of 1.8 m.y. B.P. Thus, the first appearance of G. truncatulinoides in southern California is cryptogenic and probably related to the delayed migration into this region of water-mass conditions suitable for this species.Two volcanic ashes from the upper part of the Malaga Formation, Malaga Cove, Los Angeles County, yielded fission-track dates on glass shards of 4.42 ± 0.57 m.y. B.P. (lower ash) and 3.364 ± 0.69 m.y. B.P. (upper ash). These dates, in addition to inferred paleomagnetic ages of planktonic microfossil datum levels suggest that the Delmontian Stage of California ranges in age from ～6 to ～3 m.y. B.P. Therefore, the Miocene/Pliocene boundary considered by Berggren and Van Couvering to be ～5 m.y. B.P. must lie in the lower Delmontian Stage but paleontologic criteria for its recognition in California are not yet available.     

Petrology of the volcanic rocks of martinique,West Indies

Volcanological differences between the old and the recent lavas from Martinique, Lesser Antilles, are presented, showing that two volcanic series exist in this island:

Dash

a high-alumina basalt series generally mafic, line-grained, partly pillowed, with clinopyroxene-rich lavas which show iron enrichment tendancies en an A.F.M. plot;

a calc-alkaline (slightly potassic) series much more siliceous as a group, porphyric, predominantly sub-aerially erupted with orthopyroxene-rich lavas which show no iron enrichment.

The high-alumina basalt series is considered as having originated from a differentiation trend by fractionation of olivine, clinopyroxene and plagioclase. Lavas range from olivine basalt to tridymite-rich dacite. The calc-alkaline series probably derives from the contamination of the first suite but the occurence of hornblende-rich cumulates indicates the process of fractionation takes place too. Lavas range from orthopyroxene andesite and hornblende andesite to quartz-hornblende dacite and quartz-biotite dacite.     

Petrology of the volcanic rocks of saba,West Indies

Saba is composed of basic and intermediate members of the calc alkaline series with a broad resemblance to volcanic rocks on other islands of the northern Lesser Antilles. The most abundant rock-type is hornblende andesite with relatively high potassium and associated elements. Notable petrographic features are the persistence of magnesian olivine into relatively siliceous whole-rock composition and the prevalence of hornblende even in the more basic rocks. Quartz xenocrysts also occur in the basalts Clinopyroxene phenocrysts are of an gite composition but groundmass grains are sometimes in the range subcalcic augite to magnesian pigeonite. Disequilibrium features in the petrography, together with anomalies in the chemical trends may be due to incorporation of xenocrysts or perhaps in extreme instances to the hybridisation of contrasting magmas.     

The composition and differentiation of the volcanic rocks of Carriacou,grenadines, West Indies

Tertiary volcanic rocks of Carriacou occupy two-thirds of the island. The volcanics include volcaniclastics, lava flows and dome lavas and range in composition from basalts to andesites. Carriacou basalts fall into two petrographic types (a) clinopyroxene-plagioclase-phyric basalts and (b) olivine microphyric basalts; the latter having higher MgO and lower Al₂O₃ than the clinopyroxene basalts. Both types are unusually rich in mafic minerals compared with Lesser Antilles basalts in general, although similar types have been reported from the nearby island of Grenada. The potash to silica ratios are relatively high and confirm the similarity between Carriacou and Grenada basalts and the differences between these basalts and basalts from other islands of the Lesser Antilles. The basaltic andesites and andesites from Carriacou correspond closely in mineralogical and chemical composition with typical andesites found elsewhere in the Lesser Antilles. The geochemistry of the volcanics shows that the olivine microphyric basalts display tholeiitic affinities whereas the clinopyroxeneplagioclase-phyric basalt, basaltic andesites and andesites are calcalkaline. The compositional gradation in both the geochemistry and mineralogy of these volcanics suggests that fractional crystallization played an important role in the derivation of the various magma.     

Magma mixing recorded in intermediate rocks associated with high-Mg andesites from the Setouchi volcanic belt, Japan: implications for Archean TTG formation

Calc-alkaline intermediate rocks are spatially and temporally associated with high-Mg andesites (HMAs, Mg#>60) in Middle Miocene Setouchi volcanic belt. The calc-alkaline rocks are characterized by higher Mg# (strongly calc-alkaline trend) than ordinary calc-alkaline rocks at equivalent silica contents. Phenocrysts in the intermediate rocks have petrographical features such as: (1) coexisting reversely and normally zoned orthopyroxene phenocrysts in single rock; (2) sieve type plagioclase in which cores are mantled by higher An%, melt inclusion-rich zone; and (3) reversely zoned amphibole phenocrysts with opacite cores. In addition, mingling textures and magmatic inclusions were observed in some rocks. These petrographic features and the mineral chemistry indicate that magma mixing was the most important process in producing the strongly calc-alkaline rocks. The core composition of normally zoned orthopyroxene phenocrysts and the mantle composition of reversely zoned orthopyroxene phenocrysts have relatively high Mg# (85–90) in maximum. Although basaltic and high-Mg andesitic magmas are candidate as possible mafic end-member magmas, basaltic magma is excluded in terms of phenocryst assemblage and bulk composition. HMA magmas are suitable mafic end-member magmas that precipitated high Mg# (90) orthopyroxene, whereas andesitic to dacitic magma are suitable felsic end-members. In contrast, it is difficult to produce the strongly calc-alkaline trend through fractional crystallization from a HMA magma, because it would require removal of plagioclase together with mafic minerals from the early stage of crystallization, whereas the precipitation of plagiolase is suppressed due to the high water content of HMA magmas. These results imply that Archean Mg#-rich TTGs (>45–55), which are an analog of the strongly calc-alkaline rocks in terms of chemistry and magma genesis, can be derived from magma mixing in which a HMA magma is the mafic end-member magma, rather than by fractional crystallization from a HMA magma.     

Volcanic and structural history of the Hohi volcanic zone,central Kyushu,Japan

More than 5000 km³ of magmatic material was erupted in Pliocene-Pleistocene times in a volcano-tectonic depression, i. e., the Hohi volcanic zone (HVZ) in central Kyushu, Japan. The eruptive deposits consist mainly of andesite lava flows and large-scale pyroclastic-flow deposits. Their eruptions were accompanied by the formation of an EW-oriented graben (70 km × 45 km) under regional NS extensional stress. Pre-Tertiary basement rocks are absent on the surface of the graben but occur at depth, having subsided up to 3 km. Radiometric ages of volcanic rocks on the surface show zoned isochrons from 5 Ma at the margin to 0.3 Ma in the center of the HVZ. The youngest center of age zonation coincides with a 30 mgal negative Bouguer gravity anomaly. Radiometric ages of rocks from drill cores are older toward the bottom of the graben, reaching a maximum of at least 4 Ma. Volcanic activity concentrated over time toward the center of the graben and buried successively erupted material. Areas of active volcanism in the HVZ became smaller and changed in style during the 5-Ma history of activity. Volcanism of the early stage (5-2 Ma) was characterized by voluminous eruptions of andesitic lava flows that formed lava plateaus and were intruded by EW-oriented feeder dikes, perhaps related to fissure eruptions. In contrast, late-stage volcanism (2-0 Ma) resulted primarily in andesitic to dacitic lava domes with features of monogenetic volcanoes produced at low eruption rates. The HVZ shows unimodal volcanism dominated by andesitic and dacitic lavas with a small amount of rhyolite and only traces of basalt; these characteristics differ from those that typify volcanism in most other extensional areas. Erupted material in the HVZ is of the calc-alkali and high-alkali tholeiite series and shows no significant chemical changes over 5 Ma, except for an increase in K₂O after 1.6 Ma. The net horizontal displacement along normal faults indicates that the HVZ widened by about 10%–20% across the graben at an average rate of 0.1 cm/yr. I interpret the HVZ to be neither a pull-apart structure of the pre-Tertiary basement nor the result of propagation of the Okinawa Trough, but rather the earliest stage of rifting when vertical subsidence caused by normal faulting is compensated by filling with volcanic material.     

Geochemical variation with time in the Cenezoic volcanic rocks of southwest Hokkaido, Japan

Abundances of major and trace elements were determined for the Tertiary volcanic rocks from SW Hokkaido. The Late Miocene to Pliocene volcanic rocks of this region show geochemical features similar to those of the Quaternary rocks, that is, K/Si, Th/Si and LREE/HREE ratios increasing across the arc, east to west, from the Pacific to the Japan Sea side. In contrast, the Early Miocene volcanic rocks, which are geographically restricted to the Japan Sea coast, are distinct from all later volcanics and show “within-plate” characteristics — in particular, high concentrations of HFS elements. The Quaternary basalts have low Hf/Yb ratios and Hf contents, whereas the Early Miocene basalts are high in Hf/Yb and Hf, similar to Hawaiian alkali basalts. The compositional variation with time may result from the progressive depletion of incompatible HFS elements in the mantle source. Th/Yb ratios increase from Early Miocene to Quaternary, possibly reflecting increase in the LIL element contribution to the mantle source during that time.     

The geochemistry and petrogenesis of the volcanic rocks of Carriacou,Grenadine Islands,West Indies

Carriacou is small volcanic island located near the southern end of the Lesser Antillean chain. Field relationships, petrography and geochemistry of the Tertiary lavas, outcropping in the southern half of the island, are used to identify the rocks present and to determine their petrogenesis and assess their significance within the island arc.Six main volcanic units are present. From oldest to youngest, these are the clinopyroxene-phyric basalt (CPB) sequence, the amphibole-phyric andesite (APA) sequence, the clinopyroxene-megaphyric basalt (CMB) sequence, the olivine-microphyric basalt (OMB) sequence, the clinopyroxene phyric andesite (CPA) sequence, and the amphibole-megaphyric andesite (AMA) sequence. Volcaniclastic deposits are associated with the APA, CMB, and AMA sequences. The APA sequence is calcalkaline, whereas the other five sequences are tholeiitic.Sr isotope and rare earth element (REE) data suggest that these volcanic rocks were derived from partial melts of garnet-peridotite generated deep within the mantle. The OMB lavas have the highest temperature assemblages of intratelluric minerals and the least evolved chemical characteristics, and are considered to be closest in composition to a parental melt. Phenocryst assemblages and chemical variation suggest that the andesite sequences have been derived from the mafic melts by low pressure fractional crystallization of approximately 20% clinopyroxene and 20% olivine, plus smaller amounts of plagioclase and amphibole. The high concentrations of incompatible and compatible elements and the high⁸⁷Sr/⁸⁶Sr ratios may indicate that subduction is slower in the southern part of the arc, and fluids released during slab dehydration rich in Incompatible trace elements, in Radiogenic strontium, and in Silica (IRS), have modified the parental melts.     

Pattern and mechanism of volcanic activity at the Santiaguito Volcanic Dome,Guatemala

Santiaguito volcano has shown a continuous slow extrusion of dacite lava since 1922. In the 50 years of activity there have been four periods of abnormally high extrusion rates, interspersed by periods of little magma production. The type of activity shown by the volcano has been varied and crudely cyclic. Dome extrusion periods are accompanied by pyroclastic activity and followed by lava flows. There are now 16 time stratigraphic units delineated on the dome. Activity since 1967 has been especially closely observed. Dome extrusion at the west end of the complex has been accompanied by pyroclastic cruptions and plug dome extrusion at the east end. The eurrent extrusion rate has remained essentially constant since 1967 at about 5×10⁶ m³/yr, far below Santiaguito’s 1922–71 average of 14×10⁶ m³/yr. The active vent at the east end of the volcano (Caliente vent) has been the principal vent of the volcano since the creation of the explosion crater in 1902. After its initial period of dome extrusion (1922–25), the Caliente vent has chiefly produced pyroclastic eruptions as well as at least 95% of the dome’s lumarolic activity, while lateral vents have continued to give rise to lavas. Lava flows at Santiaguito have effective viscosity values of about 10⁶ poises, while dome lavas are significantly more viscous. The differences in viscosity are in part related to volatile content of the lava when it reaches the surface. During dome extrusion, lavas lose their volatiles through pyroclastic activity before they reach the surface. Lava flows at Santiaguito occur when lava reaches the surface with higher volatile content. Obstruction of either the central (pyroclastic) vent or the lateral (dome extrusion) vent or both vents has an important influence on succeeding activity. In June 1972, at the time of this writing, the outbreak of new lava flows at both the Caliente and lateral El Brujo vents has just occurred, resulting from obstruction of pyroclastic activity by a large plug dome at the Caliente vent.     

Geochemistry of Cenozoic volcanic rocks in Tengchong,SW China: relationship with the uplift of the Tibetan Plateau

There are wide spread Cenozoic volcanic rocks in Tengchong (CVRT), Yunnan province, SW China. These rocks comprise three rock types: basalt, andesite (dominant type) and dacite. Most samples are sub‐alkaline, and among the sub‐alkaline rocks, most are high‐K calc‐alkaline. These rocks have a SiO₂ range of 49.1 wt.% to 66.9 wt.%. TiO₂ contents are not high and have a variation of 0.7 wt.%–1.6 wt.%. Trace element concentrations and element ratios (such as Nb/U, Ce/Pb, Nb/La, etc.) of these rocks have a large variation. ⁸⁷Sr/⁸⁶Sr values fall in the range of 0.7057–0.7093 and ¹⁴³Nd/¹⁴⁴Nd values change from 0.5120 to 0.5125. ²⁰⁶Pb/²⁰⁴Pb, ²⁰⁷Pb/²⁰⁴Pb, and ²⁰⁸Pb/²⁰⁴Pb ratios are in the range of 17.936–19.039, 15.614–15.810, and 38.894–39.735, respectively. These geochemical characteristics of CVRT make them resemble island‐arc volcanic rocks. We suggest that the magmas were generated in the lithospheric mantle that had already been metasomatized by previous subduction processes. By the study of the uplift history of the Tibetan Plateau, we found that the beginning of the geotectonic processes to the eruption of CVRT was coeval with one uplift event. Therefore, we propose that the uplift of the Tibetan Plateau caused collapse of the collisional orogeny in Tengchong, which further triggered the generation and eruption of the CVRT magmas.