Petrogenesis of mid-Carboniferous volcanics and granitic intrusions from western Junggar Basin boreholes: geodynamic implications for the Central Asian Orogenic Belt in Northwest China
21
Citation
95
Reference
10
Related Paper
Citation Trend
Abstract:
The western Junggar Basin is located on the southeastern margin of the West Junggar terrane, Northwest China. Its sedimentary fill, magma petrogenesis, tectonic setting, and formation ages are important for understanding the Carboniferous tectonic evolution and continental growth of the Junggar terrane and the Central Asian Orogenic Belt. This paper documents a set of new zircon secondary ion mass spectrometry U–Pb geochronological and Hf isotopic data and whole-rock elemental and Sr–Nd isotopic analytical results for the Carboniferous strata and associated intrusions obtained from boreholes in the western Junggar Basin. The Carboniferous strata comprise basaltic andesite, andesite, and dacite with minor pyroclastic rocks, intruded by granitic intrusions with zircon secondary ion mass spectrometry U–Pb ages of 327–324 Ma. The volcanic rocks are calc-alkaline and show low high εNd(t) values (5.3–5.6) and initial 87Sr/86Sr (0.703561–0.703931), strong enrichment in LREEs, and some LILEs and depletion in Nb, Ta, and Ti. Furthermore, they also display high (La/Sm)N (1.36–1.63), Zr/Nb, and La/Yb, variable Ba/La and Ba/Th and constant Th/Yb ratios. These geochemical data, together with low Sm/Yb (1.18–1.38) and La/Sm (2.11–2.53) ratios, suggest that these volcanic rocks were derived from a 5–8% partial melting of a mainly spinel Iherzolite-depleted mantle metasomatized by slab-derived fluids and melts of some sediments in an island-arc setting. In contrast, the granitic intrusions represent typical adakite geochemical features of high Sr and low Y and Yb contents, with no significant Eu anomalies, high Mg#, and depleted εNd(t) (5.6–6.4) and εHf(t) (13.7–16.2) isotopic compositions, suggesting their derivation from partial melting of hot subducted oceanic crust. In combination with the previous work, the West Junggar terrane and adjacent western Junggar Basin are interpreted as a Mariana-type arc system driven by northwestward subduction of the Junggar Ocean, possibly with a tectonic transition from normal to ridge subduction commencing ca. at 331–327 Ma.Keywords:
Petrogenesis
Quartz monzonite
Continental arc
Dacite
Continental arc
Basaltic andesite
Metallogeny
Cite
Citations (24)
Diorite
Quartz monzonite
Geochronology
Continental arc
Petrogenesis
Volcanic arc
Cite
Citations (48)
Petrogenesis
Cite
Citations (0)
Quartz monzonite
Batholith
Continental arc
Porphyritic
continental collision
Continental Margin
Lile
Underplating
Diorite
Cite
Citations (34)
Andesites
Massif
Continental arc
Basaltic andesite
Volcanic belt
Cite
Citations (9)
The Oligocene volcanism of the Okushiri Island, situated on the northeastern border of the Japan Sea, may have taken place as the volcanic front of the Eurasian continental margin prior to the formation of the Japan Sea basin. The Oligocene volcanic rocks from the Okushiri Island consist of High-Mg andesite (HMA), High-Ti basalt to andesite (HTV), and Low-Ti andesite (LTV). The rocks of HMA have high contents of MgO, Cr and Ni, and have low Sr and high Nd isotopic ratios. The patterns of primordial mantle-normalized incompatible elements indicate that the HMA rocks are enriched in Rb, Ba, K and Sr and depleted in Nb, and show patterns which resemble those of calc-alkaline rocks from back arc side of the NE Japan arc. The HTV rocks, comparable with the high alumina basalt series, are characterized by high concentrations of both LIL and HFS elements, high Sr isotopic ratio. The primordial mantle-normalized geochemical patterns and the Sr and Nd isotopic ratios of the HTV are similar to those of an enriched island arc tholeiite in the NE Japan arc. By reference to melting experiments at high pressure, the HTV magmas were inferred to have been segregated at 50-60km depth. The LTV rocks are locally exposed, in which contamination phenomena are apparent from the petrographical and geochemical point of views. In comparison with the NE Japan arc magma, we discussed the chemical heterogeneity of the wedge mantle, the characteristics of the Oligocene frontal volcanism at the Eurasian continental margin, and the temporal variation of the Sr isotopic ratios of the Cenozoic volcanic rocks from SW Hokkaido, Japan.
Continental Margin
Island arc
Continental arc
Basaltic andesite
Cite
Citations (15)
Early Paleozoic turbiditic sedimentary rocks and submarine volcanic-arc rocks in the Mel River area have been designated, respectively as the Woodstock and Meductic groups and divided into six formations. The Woodstock Group includes interbedded Cambrian to Early Ordovician quartz wacke, sandstone, and shale of the Baskahegan Formation and overlyng Early Ordovician silty mudstone and shale of the Bright Eye Brook Formation The conformably overlying Meductic Group is divided into the Early Ordovician Porten Road Formation (mainlv rhyolite). Eel River Formation (mainly andesite) and Oak Mountain Formation (basalt), and Late Ordovician Belle Lake Formation (feldspathic wacke and shale).
Pyrovene-bearing low-silica andesite in the lower part of the Porten Road Formation is highly enriched in LREE and LESE and depleted in HESE relative to MORB. evidence of subduction in a compressional-continental arc setting. The upper part of the Porten Road Formation comprises an interlayered sequence of quartz-rich rhyolite and quartz-poor dacite likely derived from melting of continental crust. The Eel River Formation contains hornblende-bearing, high-silica andesite moderately enriched in LFSE. Calc-alkaline basalt from the overlying Oak Mountain Formation includes low- and high-alumina basalt varieties like those formed in an extensional-continental arc setting. Volcanic activity in the Meductic Group ceased in the later part of the Early Ordovician as the arc rifted and the subduction zone migrated northwestward with the opening of the tetagouche back-arc basin.
RÉSUMÉ
Des roches dun arc volcanique sous-matin et des roches sédimentaires turbiditiques du Palérozoique inférieur du secteur d'Eel River ont été désignées, respectivement groupes de Meductic ct de Woodstock et ont été subdivisées en six formations Le groupe de Woodstock comprend du schiste et du grès à wacke quartzifere interlites du Cambrien à I'Ordovicien inferiéur de la Formation de Baskahegan ainsi que du schiste et du mudslone silleux sus-jacent de I'Ordovicien inférieur de la Formation de Bright Eye Brook. Le groupe sus-jacent concordant de Meductic se subdivisc en trois formations de I'Ordovicien inférieur celle de Porten Road (essentiellement de la rhyolite) celle d'Eel River (essentiellement de I'andesile) et celle d'Oak Mountain (basalte) et une formation de l’Ordovicien supéricur. La Formation de Belle Lake (wacke feldspalhique et schiste).
L'andesite a faible teneur en silice qui renferme de la pyroxene dans la panic inféricure de la Formation de Porten Road est fortement enrichie en EERE (éléments de terres rares légers) et en EEFC (éléments à faible intensate de champ) et pauvrce en EHIC (éléments à haute intensité de champ) comparativement aux BDMO (basaltes de la dorsale médio-océanique). ce qui temoigne d’une subduction au cours de l’établissement d’un arc compressif-continental. La partie supérieur de la Formation de Porten Road comporte une séquence interstratifiée de rhyolite riche en quartz et de dacite pauvre en quartz provenant stratisemblahlement de la fusion de la croôte contineniale. La Formation d'Eel River renferme de I'andésite riche en silice à hornblende moyennement enrichie d'EEIC. Le basalte calco-alcalin de la formation sus-jacente d'Oak Mountain comprend des basaltes à faible et forte teneur en alumine comnie ceux formes lors de I'etablissemenl d’un arc d'accretion-continetital. L'activité volcanique dans le groupe de Meductic à cessé vers la tin de I'Ordovicien inférieur lorsque l’are s'est effondré et que la zone de subduction a migré vers le nord-ouest avec I'ouverture du bassin marginal de l’étagouche
Traduit par la rédaction
Continental arc
Back-arc basin
Volcanic arc
Island arc
Cite
Citations (18)
This paper analyzed the geochemical characteristics,including petrochemistry,REE and trace elements,of the Haerjiawu Formation andesite in the bentonite mine,Barkol County,Xinjiang,trying to understand magma sources,evolution,and tectonic environment of the Late Paleozoic andesite in the Barkol County bentonite mine.The results showed that the Haerjiawu Formation andesite belongs to a mafic calc-alkaline rock,depleting of Fe and Ca and enriching of Na.It enriches of Sr,Rb,Ba,Zr,Th and Hf,depletes of compatible elements(e.g.Ta,Ti and Nb),and has notable fractionations in both light and heavy rare earth elements,but exhibits no Eu anomaly.The tectonic studies showed that it formed in a subduction environment with active continental margin,and that it had undergone a contamination by oceanic crust material,however,no fractional crystallization evidence was found in this study.In summary,this study concluded that the forming environment of the Haerjiawu andesite is the active continental margin on the mainland(or mainland arc)side,with transition signs of from the island arc to mainland.
Continental arc
Island arc
Basaltic andesite
Cite
Citations (0)
Petrogenesis
Geochronology
Continental arc
Andesites
Basaltic andesite
Fractional crystallization (geology)
Cite
Citations (6)
We report zircon U–Pb age and Hf isotopic data, and whole‐rock major and trace element data for diverse volcanic rocks from the Riwanchaka region of central Qiangtang, Tibet, including andesite and dacite. Zircon U–Pb dating of andesite yielded a magmatic crystallization age of 358.5 Ma, indicating that the volcanic rocks were erupted in the early Carboniferous. The zircons from the andesite samples have εHf(t) values from +8.27 to +11.5 and single‐stage Hf model ages of 533–670 Ma. All of the samples are calc‐alkaline, enriched in Th, U, and light rare earth elements, and depleted in Nb, Ta, Ti, and P, which are geochemical features typical of arc volcanic rocks. Geochemical and isotopic data indicate that the andesites were generated by partial melting of a mantle wedge, whereas the dacites originated by fractional crystallization of coeval andesitic melt. Compared with typical arc rocks, the Riwanchaka volcanic rocks resemble those from active continental margins. Our new and previously published data enable us to correlate the subduction‐related volcanic arc rocks in the Riwanchaka area to the northward subduction of the Paleo‐Tethys oceanic lithosphere.
Continental arc
Dacite
Fractional crystallization (geology)
Island arc
Continental Margin
Andesites
Cite
Citations (5)