Tectonic significance of Late Triassic post-collisional lamprophyre dykes from the Qinling Mountains (China)

2007 ◽  
Vol 144 (5) ◽  
pp. 837-848 ◽  
Author(s):  
XIAOXIA WANG ◽  
TAO WANG ◽  
BOR-MING JAHN ◽  
NENGGAO HU ◽  
WEN CHEN
Keyword(s):  
Lithospheric Mantle ◽  
Central China ◽  
Age Dating ◽  
Late Triassic ◽  
Dabie Orogen ◽  
Western Qinling ◽  
Isotopic Analyses ◽  
Mantle Sources ◽  
Peridotite Mantle ◽  
Orogenic Belts

The Qinling–Dabie orogen in central China is one of the major orogenic belts in East Asia. In the eastern Dabie–Sulu region, mafic lamprophyres show the enriched signatures of old sub-continental lithospheric mantle. However, little is known about the mafic igneous rocks and their lithospheric mantle sources in the western Qinling Range. New 40Ar–39Ar age dating, major- and trace-element data, and isotopic analyses of Qinling lamprophyres reveal their differences from the Dabie Sulu lamprophyres. Biotite 40Ar–39Ar dating yielded a plateau age of 219±2 Ma, identical to the ages of rapakivi-textured granitoids in the area. The association of lamprophyre dykes and rapakivi-textured granitoids indicates that the Qinling region was a post-collisional setting at c. 220 Ma. The Qinling lamprophyres are calc-alkaline, and rich in large ion lithophile elements (e.g. Ba, K), but depleted in Nb, Ta and Ti. They show highly fractionated REE patterns with LaN>100 and HREE <10 times chondrite abundances. εNd (219 Ma) values range from −0.5 to −3.3 and initial Sr isotope values from 0.7036 to 0.7058. These features suggest generation of the lamprophyre by partial melting of a metasomatized, garnet peridotite mantle source. The Qinling lamprophyres are distinct from the Dabie–Sulu lamprophyres in emplacement age (c. 135 Ma for Dabie–Sulu) and isotopic composition, suggesting that the nature of the lithospheric mantle and geodynamic evolution of the Qinling region contrasts with that of the Dabie–Sulu region.

Triassic calc-alkaline lamprophyre dykes from the North Qiangtang, central Tibetan Plateau: evidence for a subduction-modified lithospheric mantle

2021 ◽  
pp. 1-14
Author(s):  
Bin Liu ◽  
You-Jun Tang ◽  
Lü-Ya Xing ◽  
Yu Xu ◽  
Shao-Qing Zhao ◽  
...  
Keyword(s):  
Tibetan Plateau ◽  
Oceanic Lithosphere ◽  
Late Triassic ◽  
The North ◽  
Deep Crust ◽  
Central Tibetan Plateau ◽  
Low Degree ◽  
Peridotite Mantle ◽  
Orogenic Belts ◽  
Isotopic Variations

Abstract Primitive lamprophyres in orogenic belts can provide crucial insights into the nature of the subcontinental lithosphere and the relevant deep crust–mantle interactions. This paper reports a suite of relatively primitive lamprophyre dykes from the North Qiangtang, central Tibetan Plateau. Zircon U–Pb ages of the lamprophyre dykes range from 214 Ma to 218 Ma, with a weighted mean age of 216 ± 1 Ma. Most of the lamprophyre samples are similar in geochemical compositions to typical primitive magmas (e.g. high MgO contents, Mg no. values and Cr, with low FeOt/MgO ratios), although they might have experienced a slightly low degree of olivine crystallization, and they show arc-like trace-element patterns and enriched Sr–Nd isotopic composition ((87Sr/86Sr)i = 0.70538–0.70540, ϵNd(t) = −2.96 to −1.65). Those geochemical and isotopic variations indicate that the lamprophyre dykes originated from partial melting of a phlogopite- and spinel-bearing peridotite mantle modified by subduction-related aqueous fluids. Combining with the other regional studies, we propose that slab subduction might have occurred during Late Triassic time, and the rollback of the oceanic lithosphere induced the lamprophyre magmatism in the central Tibetan Plateau.

scholarly journals Magmatism and related metamorphism as a response to mountain-root collapse of the Dabie orogen: Constraints from geochronology and petrogeochemistry of metadiorites

2021 ◽  
Author(s):  
Yang Yang ◽  
Yi-Can Liu ◽  
Yang Li ◽  
C. Groppo ◽  
F. Rolfo
Keyword(s):  
Rare Earth ◽  
Rare Earth Elements ◽  
Partial Melting ◽  
Central China ◽  
Ultrahigh Pressure ◽  
Ca 125 ◽  
Two Stage ◽  
Dabie Orogen ◽  
Isotopic Analyses ◽  
T Values

Post-collisional mountain-root collapse and subsequent massive partial melting occurred in the high-temperature (HT) ultrahigh-pressure (UHP) metamorphic terrane of the North Dabie complex zone (NDZ), central China. The NDZ was deeply subducted in the Triassic, producing widespread migmatites and various magmatic intrusions in the Cretaceous. Post-collisional metadiorites with distinctive large K-feldspar augen porphyroblasts, locally reported but rarely exposed in the NDZ, underwent a complex evolutional history. In this contribution, integrated studies including field investigation, petrographic observation and mineral analysis, zircon U-Pb geochronological and Hf isotopic analyses, and whole-rock elemental and Sr-Nd-Pb isotopic analyses of the metadiorites were carried out. Our results provide new constraints on the mountain-root collapse in the Dabie orogen. The metadiorites are enriched in large ion lithophile elements and light rare earth elements, whereas they are depleted in high field strength elements and heavy rare earth elements with significant Ba positive anomalies, a composition consistent with the lower continental crust. All the studied samples have moderately enriched initial 87Sr/86Sr ratios (0.707582−0.708099), low εNd(t) values (−15.3 to −20.4), and low initial Pb isotopic ratios (16.0978−16.8452, 15.3167−15.4544, and 37.1778−37.8397 for 206Pb/204Pb, 207Pb/204Pb, and 208Pb/204Pb, respectively). However, they have highly negative εHf(t) values and Paleoproterozoic two-stage Hf model ages, which are only partially consistent with data from the associated UHP metamorphic rocks. Such features suggest the metadiorites resulted from a magma produced by mixing of Triassic UHP mafic lithologies and minor amounts of mantle-derived materials. Zircon morphological analysis and U-Pb sensitive high-resolution ion microprobe dating combined with conventional thermobarometry indicate that these upwelling melts crystallized at pressure-temperature (P-T) conditions of 5.4−5.7 kbar and 750−768 °C at ca. 130 Ma and subsequently suffered HT metamorphism at ca. 125 Ma. We conclude that the metadiorites’ precursors were derived from partial melting of the Triassic subducted Neoproterozoic mafic lower-crustal rocks, with addition of minor amounts of mantle-derived materials in the Early Cretaceous, in response to mountain-root collapse of the orogen. Based on petrographic textures and mineral compositions, it is moreover inferred that formation of the distinctive K-feldspar porphyroblasts is likely related to a two-stage process, i.e., crystallization derived from biotite breakdown after the formation of the metadiorite at T = 640−703 °C and P &lt; 4.5 kbar and coarsening related to shear deformation.

Metasomatized Lithospheric Mantle beneath the Western Qinling, Central China: Insight into Carbonatite Melts in the Mantle

2012 ◽  
Vol 120 (6) ◽  
pp. 671-681 ◽  
Author(s):  
Ben-Xun Su ◽  
Hong-Fu Zhang ◽  
Ji-Feng Ying ◽  
Yan-Jie Tang ◽  
Yan Hu ◽  
...  
Keyword(s):  
Lithospheric Mantle ◽  
Central China ◽  
Western Qinling ◽  
Insight Into

scholarly journals Re–Os Pyrite Geochronological Evidence of Three Mineralization Styles within the Jinchang Gold Deposit, Yanji–Dongning Metallogenic Belt, Northeast China

Minerals ◽  
2018 ◽  
Vol 8 (10) ◽  
pp. 448 ◽  
Author(s):  
Shun-Da Li ◽  
Zhi-Gao Wang ◽  
Ke-Yong Wang ◽  
Wen-Yan Cai ◽  
Da-Wei Peng ◽  
...  
Keyword(s):  
Gold Deposit ◽  
Northeast China ◽  
Gold Mineralization ◽  
Metallogenic Belt ◽  
Isotopic Analyses ◽  
Mantle Sources ◽  
Stage 1 ◽  
Geochronological Evidence ◽  
Gold Bearing

The Jinchang gold deposit is located in the eastern Yanji–Dongning Metallogenic Belt in Northeast China. The orebodies of the deposit are hosted within granite, diorite, and granodiorite, and are associated with gold-mineralized breccia pipes, disseminated gold in ores, and fault-controlled gold-bearing veins. Three paragenetic stages were identified: (1) early quartz–pyrite–arsenopyrite (stage 1); (2) quartz–pyrite–chalcopyrite (stage 2); and (3) late quartz–pyrite–galena–sphalerite (stage 3). Gold is hosted predominantly within pyrite. Pyrite separated from quartz–pyrite–arsenopyrite cement within the breccia-hosted ores (Py1) yield a Re–Os isochron age of 102.9 ± 2.7 Ma (MSWD = 0.17). Pyrite crystals from the quartz–pyrite–chalcopyrite veinlets (Py2) yield a Re–Os isochron age of 102.0 ± 3.4 Ma (MSWD = 0.2). Pyrite separated from quartz–pyrite–galena–sphalerite veins (Py3) yield a Re–Os isochron age of 100.9 ± 3.1 Ma (MSWD = 0.019). Re–Os isotopic analyses of the three types of auriferous pyrite suggest that gold mineralization in the Jinchang Deposit occurred at 105.6–97.8 Ma (includes uncertainty). The initial 187Os/188Os values of the pyrites range between 0.04 and 0.60, suggesting that Os in the pyrite crystals was derived from both crust and mantle sources.

Mineral ages and zircon Hf isotopic composition of the Andong ultramafic complex: implications for the evolution of Mesozoic subduction system and subcontinental lithospheric mantle beneath SE Korea

2013 ◽  
Vol 151 (5) ◽  
pp. 765-776 ◽  
Author(s):  
GI YOUNG JEONG ◽  
CHANG-SIK CHEONG ◽  
KEEWOOK YI ◽  
JEONGMIN KIM ◽  
NAMHOON KIM ◽  
...  
Keyword(s):  
Lithospheric Mantle ◽  
Tectonic Setting ◽  
Eastern China ◽  
Mantle Xenoliths ◽  
Late Triassic ◽  
Magmatic Differentiation ◽  
Suprasubduction Zone ◽  
Ultramafic Complex ◽  
Yeongnam Massif ◽  
Subduction System

AbstractThe Phanerozoic subduction system of the Korean peninsula is considered to have been activated by at least Middle Permian time. The geochemically arc-like Andong ultramafic complex (AUC) occurring along the border between the Precambrian Yeongnam massif and the Cretaceous Gyeongsang back-arc basin provides a rare opportunity for direct study of the pre-Cretaceous mantle wedge lying above the subduction zone. The tightly constrained SHRIMP U–Pb age of zircons extracted from orthopyroxenite specimens (222.1±1.0 Ma) is indistinguishable from the Ar/Ar age of coexisting phlogopite (220±6 Ma). These ages represent the timing of suprasubduction zone magmatism likely in response to the sinking of cold and dense oceanic lithosphere and the resultant extensional strain regime in a nascent arc environment. The nearly coeval occurrence of a syenite-gabbro-monzonite suite in the SW Yeongnam massif also suggests an extensional tectonic setting along the continental margin side during Late Triassic time. The relatively enriched ɛHf range of dated zircons (+6.2 to −0.6 at 222 Ma) is in contrast to previously reported primitive Sr–Nd–Hf isotopic features of Cenozoic mantle xenoliths from Korea and eastern China. This enrichment is not ascribed to contamination by the hypothetical Palaeozoic crust beneath SE Korea, but is instead attributable to metasomatism of the lithospheric mantle during the earlier subduction of the palaeo-Pacific plate. Most AUC zircons show a restricted core-to-rim spread of ɛHf values, but some grains testify to the operation of open-system processes during magmatic differentiation.

Sign in / Sign up

Export Citation Format

Share Document