Petrogenesis of Early Jurassic (ca. 181 Ma) dacitic–rhyolitic volcanic rocks in the Amdo ophiolite mélange, central Tibetan Plateau: Low‐pressure partial melts of Bangong–Nujiang Tethys oceanic crust?

2019 ◽  
Vol 55 (5) ◽  
pp. 3283-3296
Author(s):  
Ming‐Jian Li ◽  
Yun‐Chuan Zeng ◽  
Ji‐Feng Xu ◽  
Feng Huang ◽  
Qin Chen
Keyword(s):  
Tibetan Plateau ◽  
Oceanic Crust ◽  
Volcanic Rocks ◽  
Low Pressure ◽  
Early Jurassic ◽  
Central Tibetan Plateau ◽  
Ophiolite Mélange ◽  
Partial Melts ◽  
Ophiolite Melange

Late Eocene two-pyroxene trachydacites from the southern Qiangtang Terrane, central Tibetan Plateau: High-temperature melting of overthickened and dehydrated lower crust

2021 ◽  
Author(s):  
Yun-Chuan Zeng ◽  
Ji-Feng Xu ◽  
Ming-Jian Li ◽  
Jian-Lin Chen ◽  
Bao-Di Wang ◽  
...  
Keyword(s):  
High Temperature ◽  
Tibetan Plateau ◽  
Thermal State ◽  
Middle Eocene ◽  
Volcanic Rocks ◽  
Late Eocene ◽  
Integrated Analysis ◽  
Central Tibetan Plateau ◽  
Anhydrous Mineral ◽  
Qiangtang Terrane

Abstract Orthopyroxene-bearing granitic rock (e.g., charnockite) is relatively rare but provides an excellent opportunity to probe the thermal and tectonic evolution of deep orogenic crust because of its distinct mineral assemblage. Here we present petrological, mineralogical, elemental, and Sr–Nd–Hf–O isotopic data for late Eocene (ca. 36 Ma; zircon U–Pb ages) volcanic rocks exposed in the Ejiu region in the southern Qiangtang Terrane to investigate how the central Tibetan crust evolved to its modern thickness and thermal state. The Ejiu volcanic rocks (EVRs) are trachydacites with anhydrous mineral assemblages (i.e., two pyroxenes, sanidine, plagioclase, and ilmenite, without amphibole and biotite) and geochemical characteristics (e.g., high P2O5 and TiO2) that resemble those of charnockite-type magmatic rocks. Mineral and whole-rock thermometry and hygrometry suggests that the parent magma crystallized under hot (~1000 °C) and dry (H2O < 2 wt.%) condition. Besides, the EVRs display adakitic affinities according to their high SiO2 and Al2O3 contents, high Sr/Y, La/Yb, and Gd/Yb ratios, and low Y and Yb contents, without marked negative Eu anomalies. The calculated melts in equilibrium with pyroxenes also display adakitic compositions (e.g., high Sr/Y and La/Yb ratios), indicating that the adakitic compositions of the EVRs did not result from late-stage magmatic evolution. In addition, the melts of the EVRs were saturated in TiO2, as inferred from the high TiO2 contents of these rocks and the presence of ilmenite. An integrated analysis of the geochemical, petrological, and mineralogical data suggests that the EVRs were neither evolutional products nor partial melts of hydrous mafic materials at normal crustal pressures, but were formed by fusion of an eclogitized mafic protolith with residue containing garnet and rutile but lacking amphibole and plagioclase. The whole-rock Sr–Nd and zircon Hf isotope compositions of the EVRs [(87Sr/86Sr)i = 0.7053 to 0.7066; εNd(t) = −1.40 to −0.99; zircon εHf(t) = +1.08 to +5.31] indicate that the parental protolith was relatively juvenile in nature, but also contained some supracrustal materials given the high zircon δ18O values [zircon δ18O = +8.21‰ to +11.00‰]. The above arguments lead us to propose that of partial melting of a previously dehydrated—but chemically undepleted—mafic lower continental crust at high pressure (>1.5 GPa) and high temperature (>1000 °C) generated the EVRs. Based on a synthesis of independent geological and geophysical data, we further suggest that the southern Qiangtang Terrane crust of the central Tibetan Plateau was thick, dry, and elevated during the Late Cretaceous to early Eocene time, and that it became abnormally hot owing to the ascending asthenosphere after lithospheric foundering during the middle Eocene.

scholarly journals COMPARATIVE GEOCHEMICAL STUDY OF THE TRIASSIC TRACHYANDESITES OF GLYKOMILIA AND ALKALI BASALTS FROM THE KOZIAKAS OPHIOLITE MELANGE (W. THESSALY): IMPLICATIONS FOR THEIR ORIGIN

2004 ◽  
Vol 36 (1) ◽  
pp. 587 ◽  
Author(s):  
P. Pomonis ◽  
V. Tsikouras ◽  
K. Hatzipanagiotou
Keyword(s):  
Partial Melting ◽  
Close Association ◽  
Volcanic Rocks ◽  
Mountain Range ◽  
Alkali Basalts ◽  
Rock Fragments ◽  
Geochemical Study ◽  
Ophiolite Mélange ◽  
Discrimination Diagram ◽  
Ophiolite Melange

The Triassic Glykomilia trachyandesites of the Koziakas mountain range (western Thessaly) are parts of the oldest volcanic series in continental central Greece. Rock fragments and blocks of pillowed alkali basalts, which are dispersed into the Koziakas ophiolite mélange, display similar subparallel chondrite-norme'ized trace and rare earth element patterns to the trachyandesites, suggesting cogenetic origin. However, the Glykomilia trachyandesites are more differentiated than the Koziakas alkali basalts, which display a different petrogenetic evolution from the basalts occurring in the Koziakas Ophiolite Unit. REE patterns and discrimination diagram plots reveal significant similarities to Triassic volcanic rocks from the Hellenides, suggesting also a VAB signature for the Glykomilia trachyandesites and a WPB affinity for the alkali basalts. Partial melting of a LILEenriched hydrous mantle under spreading conditions is suggested to give rise to Glykomilia trachyandesites. This partial melting episode was probably induced by the uplift of an OIB-type mantle plume, which subsequently produced the WPB alkali basalts of the Koziakas ophiolite mélange. The close association cf both the Glykomilia trachyandesites and the Koziakas alkali basalts with cherts lead to the hypothesis of eruption in a deep rift basin.

scholarly journals Indian Monsoon Low-Pressure Systems Feed Up-and-Over Moisture Transport to the Southwestern Tibetan Plateau

2017 ◽  
Vol 122 (22) ◽  
pp. 12,140-12,151 ◽  
Author(s):  
Wenhao Dong ◽  
Yanluan Lin ◽  
Jonathon S. Wright ◽  
Yuanyu Xie ◽  
Fanghua Xu ◽  
...  
Keyword(s):  
Tibetan Plateau ◽  
Moisture Transport ◽  
Indian Monsoon ◽  
Low Pressure ◽  
Low Pressure Systems

Three stages of arc migration in the Carboniferous-Triassic in northern Qiangtang, central Tibet, China: Ridge subduction and asynchronous slab rollback of the Jinsha Paleotethys

2021 ◽  
Author(s):  
Yin Liu ◽  
Wenjiao Xiao ◽  
Brian F. Windley ◽  
Kefa Zhou ◽  
Rongshe Li ◽  
...  
Keyword(s):  
Tibetan Plateau ◽  
Volcanic Rocks ◽  
Late Triassic ◽  
Geochemical Data ◽  
The Tibetan Plateau ◽  
Ridge Subduction ◽  
Temporal Relationships ◽  
Slab Rollback ◽  
Geodynamic Processes ◽  
Central Tibet

Carboniferous-Triassic magmatism in northern Qiangtang, central Tibet, China, played a key role in the evolution of the Tibetan Plateau yet remains a subject of intense debate. New geochronological and geochemical data from adakitic, Nb-enriched, and normal arc magmatic rocks, integrated with results from previous studies, enable us to determine the Carboniferous-Triassic (312−205 Ma), arc-related, plutonic-volcanic rocks in northern Qiangtang. Spatial-temporal relationships reveal three periods of younging including southward (312−252 Ma), rapid northward (249−237 Ma), and normal northward (234−205 Ma) migrations that correspond to distinct slab geodynamic processes including continentward slab shallowing, rapid trenchward slab rollback, and normal trenchward rollback of the Jinsha Paleotethys rather than the Longmuco-Shuanghu Paleotethys, respectively. Moreover, varying degrees of coexistence of adakites/High-Mg andesites (HMAs)/Nb-enriched basalt-andesites (NEBs) and intraplate basalts in the above-mentioned stages is consistent with the magmatic effects of slab window triggered by ridge subduction, which probably started since the Late Carboniferous and continued into the Late Triassic. The Carboniferous-Triassic multiple magmatic migrations and ridge-subduction scenarios provide new insight into the geodynamic processes of the Jinsha Paleotethys and the growth mechanism of the Tibetan Plateau.

scholarly journals Facilitation stabilizes moisture-controlled alpine juniper shrublines in the central Tibetan Plateau

2015 ◽  
Vol 132 ◽  
pp. 20-30 ◽  
Author(s):  
Yafeng Wang ◽  
Eryuan Liang ◽  
Aaron M. Ellison ◽  
Xiaoming Lu ◽  
J. Julio Camarero
Keyword(s):  
Tibetan Plateau ◽  
Central Tibetan Plateau

scholarly journals Luminescence dating of lacustrine sediments from CUOE Lake on the central Tibetan Plateau

2020 ◽  
Vol 0 (0) ◽  
Author(s):  
Yandong Hou ◽  
Hao Long ◽  
Lei Gao ◽  
Ji Shen
Keyword(s):  
Tibetan Plateau ◽  
Lacustrine Sediments ◽  
Water Reservoir ◽  
Hard Water ◽  
Luminescence Dating ◽  
Coarse Grained ◽  
The Tibetan Plateau ◽  
Sediment Layer ◽  
Central Tibetan Plateau ◽  
Dating Method

AbstractLuminescence dating technology has been used for chronological constraints on lacustrine sediments due to the ubiquitous materials (e.g., quartz and feldspar) as dosimeters, and a relatively long dating range, compared with the commonly used radiocarbon dating method. However, quartz dating on the Tibetan Plateau may suffer from dim and unstable luminescence signals. In the current study, we investigate a lake-related outcrop from the shore of Cuoe Lake on the central Tibetan Plateau. Both coarse-grained quartz and K-feldspar fractions were extracted, and OSL and post-IR IRSL signals were measured from these fractions, respectively. Combining the stratigraphy analysis and dating results, this study shows that: (1) quartz appears to be unsuitable for dating because of very dim natural signals and even anomalous fading (average g-value: 4.30 ± 2.51 %/decade). The suitability of the applied pIRIR protocol measured at 150°C (pIRIR150) for K-feldspar samples was confirmed by a set of luminescence tests; (2) compared with the luminescence-based chronology, the 14C age of shells from the same sediment layer yielded older age by ~7 ka, which is likely attributed to hard water reservoir effect in Cuoe Lake; (3) the lake level reached its peak and maintained high-stand during the early Holocene (~9.4–7.1 ka). This study highlights the applicability of K-feldspar luminescence dating when the counterpart quartz OSL is insensitive and encounters anomalous fading.

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