Magma Genesis and Arc Evolution at the Indochina Terrane Subduction: Petrological and Geochemical Constraints From the Volcanic Rocks in Wang Nam Khiao Area, Nakhon Ratchasima, Thailand
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Volcanic rocks and associated dikes have been exposed in Wang Nam Khiao area, Nakhon Ratchasima Province, northeastern Thailand where complex tectonic setting was reported. These volcanic rocks are classified as rhyolite, dacite, and andesite while dikes are also characterized by andesitic composition. These dikes clearly cut into the volcanic rocks and Late Permian hornblende granite in the adjacent area. Rhyolite and dacite are composed of abundant plagioclase and quartz whereas andesite and andesitic dike contain mainly plagioclase and hornblende with minor quartz. The volcanic rocks typically show plagioclase and hornblende phenocrysts embedded in fine-grained quartz and glass groundmass whereas dike rocks contain less glass matrix with more albitic laths. P-T conditions of crystallization are estimated, on the basis of Al-in-hornblende geobarometry and hornblende geothermometry, at about 4.5 – 5.5 kbar, 861 – 927 oC and 4.8 – 5.5 kbar, 873 – 890 oC for the magma intrusions that fed volcanic rocks and andesitic dikes, respectively. Whole-rock geochemistry indicates that these rock suites are related to calc-alkaline hydrous magma. The enriched LILE (e.g. Rb, Sr) and depleted HFSE (e.g. Nb, Ce, Ti), with similar REE patterns indicate arc magmatism. The results of this study are comparable to the continental arc magmatism along the Loei Fold Belt as a consequence of the Late Permian Palaeo-Tethys subducted beneath Indochina Terrane.Keywords:
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The Teneme Formation is located in the Mayari-Cristal ophiolitic massif and represents one of the three Cretaceous volcanic Formations established in northeastern Cuba. Teneme volcanics are cut by small bodies of 89.70 ± 0.50 Ma quarz-diorite rocks (Rio Grande intrusive), and are overthrusted by serpentinized ultramafics. Teneme volcanic rocks are mainly basalts, basaltic andesites, andesites, and minor dacites, and their geochemical signature varies between low-Ti island arc tholeiites (IAT) with boninitic affinity (TiO2 < 0.4 %; high field strength elements << N-type MORB) and typical oceanic arc tholeiites (TiO2 = 0.5-0.8 %). Basaltic rocks exhibit low light REE/Yb ratios (La/Yb < 5), typical of intraoceanic arcs and are comparable to Maimon Formation in Dominican Republic (IAT, pre Albian) and Puerto Rican lavas of volcanic phase I (island arc tholeiites, Aptian to Early Albian). The mantle wedge signature of the Teneme Formation indicates a highly depleted MORB-type mantle source, without any contribution of E-MORB or OIB components. Our results suggest that Teneme volcanism represents a primitive oceanic island arc environment. If the Late Cretaceous age (Turonian or early Coniacian) proposed for Teneme Formation is correct, our results indicate that the Cretaceous volcanic rocks of eastern Cuba and the Dominican Republic are not segments of a single arc system, and that in Late Cretaceous (Albian-Campanian) Caribbean island arc development is not represented only by calc-alkaline (CA) volcanic rocks as has been suggested in previous works.
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Metaperidotites, cumulates, volcanic rocks and their overlying cherts in the Muztag ophiolitic melange are exposed discontinuously along the E-W-trending Muztag-Jingyuhu fault. These rocks show tectonic contact relationships. Of these, volcanic rocks consist of basalt, basaltic andesite and andesite. Field observations show that the volcanic rocks are a part of the ophiolites. However, the trace element and REE analyses of volcanic rocks indicate that they are enriched in LREE, Cs, Ba, Th and Pb and depleted in Nb, with Ba/Nb, Ce/Pb, Cs/Rb, Ba/La and Nb/Ta ratios of 18.59-102.82, 1.42-8.13, 0.10-0.49, 11.76-51.79 and 6.22-13.58 respectively and TiO2=1.64-2.09%. These features suggest that the volcanic rocks are those that formed in a relatively mature island-arc environment rather than a member of the ophiolites and also indicate that the Muztag area underwent an evolutionary process that resembles that on the margins of the Western Pacific Ocean, in which a relatively mature trench-arc-basin regime might form.
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Allochthonous upper Paleozoic volcanic island-arc suites of the U.S. Cordillera have previously been interpreted as parts of a single island arc. New lithologic, age, structural, biogeographic, and geochemical data indicate the presence at least of two arcs, one built on a basement with continental crustal affinities including that of the Northern Sierra terrane, and the other built on an oceanic basement including that of the Eastern Klamath terrane. In the Garfield Hills, western Nevada, the Lower Permian Black Dike Formation appears to be a remnant of the Northern Sierra Paleozoic island arc. It consists of calc-alkaline rocks with low-to-negative ratios. Volcanic rocks share similar ages, magmatic affinities, and ratios with lavas of the Goodhue Formation in the Northern Sierra terrane. Our new data suggest that these rocks are part of the Northern Sierra terrane, and we therefore infer that part of western Nevada was originally underlain by a basement with continental crustal affinities.
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The Teneme Formation is located in the Mayari-Cristal ophiolitic massif and represents one of the three Cretaceous volcanic Formations established in northeastern Cuba. Teneme volcanics are cut by small bodies of 89.70 ± 0.50 Ma quarz-diorite rocks (Rio Grande intrusive), and are overthrusted by serpentinized ultramafics. Teneme volcanic rocks are mainly basalts, basaltic andesites, andesites, and minor dacites, and their geochemical signature varies between low-Ti island arc tholeiites (IAT) with boninitic affinity (TiO2 < 0.4 %; high field strength elements << N-type MORB) and typical oceanic arc tholeiites (TiO2 = 0.5-0.8 %). Basaltic rocks exhibit low light REE/Yb ratios (La/Yb < 5), typical of intraoceanic arcs and are comparable to Maimon Formation in Dominican Republic (IAT, pre Albian) and Puerto Rican lavas of volcanic phase I (island arc tholeiites, Aptian to Early Albian). The mantle wedge signature of the Teneme Formation indicates a highly depleted MORB-type mantle source, without any contribution of E-MORB or OIB components. Our results suggest that Teneme volcanism represents a primitive oceanic island arc environment. If the Late Cretaceous age (Turonian or early Coniacian) proposed for Teneme Formation is correct, our results indicate that the Cretaceous volcanic rocks of eastern Cuba and the Dominican Republic are not segments of a single arc system, and that in Late Cretaceous (Albian-Campanian) Caribbean island arc development is not represented only by calc-alkaline (CA) volcanic rocks as has been suggested in previous works.
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The Qilian orogen involves North,Centrer and South Qilian.Lenglongling area of Menyuan,located in the eastern segment of north Qilian,is composed of volcanic rocks and few acid volcanic rocks.LA-ICP-MS U-Pb zircon weighted 238U/204Pb ages of(460.17 ±0.92)Ma dated for the ceratophyre can be interpreted as its emplacement age.These rocks have SiO2 ranging from 48.94 to 60.97 wt %,K2O/Na2O less than 1,and TFeO-K2O+Na2O-MgO diagram shows these samples belong entirely to the tholeiitic series.While the low Ti and high Al and Fe indicate that they are typically characterized as island arc volcanic rocks.These monzogranites are depleted in HFSE,such as Ta,Nb and Ti,and enriched in LILE,such as K,Th,Rb and Ba,with total REE contents ranging from 9.88 to 42.21 ppm and ∑LREE/∑HREE ratios of 0.81-5.70.The chondrite-normalized REE patterns of these volcanic rocks display weak negative Eu anomalies(δEu=0.59-1.10).Zr/Y-Zr,Ti-Zr,Y/15-La/10-Nb/8,and Hf/3-Th-Ta illustrates that these volcanic rocks could represent typical island arc volcanic rocks.
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