Geochronology and Geochemistry of Early Cretaceous Granitic Rocks in the Dongqiao Area, Central Tibet: Implications for Magmatic Origin and Geological Evolution

2018 ◽  
Vol 126 (2) ◽  
pp. 249-260 ◽  
Author(s):  
Hao Wu ◽  
Zhaxi Qiangba ◽  
Cai Li ◽  
Qiang Wang ◽  
Wangdui Gesang ◽  
...  
Keyword(s):  
Early Cretaceous ◽  
Granitic Rocks ◽  
Magmatic Origin ◽  
Geological Evolution ◽  
Central Tibet

scholarly journals Petrogenesis and Tectonic Setting of Early Cretaceous Intrusive Rocks in the Northern Ulanhot Area, Central and Southern Great Xing’an Range, NE China

Minerals ◽  
2021 ◽  
Vol 11 (12) ◽  
pp. 1414
Author(s):  
Baoqiang Tai ◽  
Wentian Mi ◽  
Genhou Wang ◽  
Yingjie Li ◽  
Xu Kong
Keyword(s):  
Early Cretaceous ◽  
Tectonic Setting ◽  
Granite Porphyry ◽  
Granitic Rocks ◽  
Magma Source ◽  
Isotopic Data ◽  
Quartz Porphyry ◽  
Intrusive Rocks ◽  
Quartz Monzonite ◽  
Great Xing’An Range

Abundant Early Cretaceous magmatism is conserved in the central and southern Great Xing’an Range (GXR) and has significant geodynamic implications for the study of the Late Mesozoic tectonic framework of northeast China. In this study, we provide new high-precision U–Pb zircon geochronology, whole-rock geochemistry, and zircon Hf isotopic data for representative intrusive rocks from the northern part of the Ulanhot area to illustrate the petrogenesis types and magma source of these rocks and evaluate the tectonic setting of the central-southern GXR. Laser ablation inductively coupled plasma–mass spectrometry (LA-ICP-MS) zircon U–Pb dating showed that magmatism in the Ulanhot area (monzonite porphyry: 128.07 ± 0.62 Ma, quartz monzonite porphyry: 127.47 ± 0.36, quartz porphyry: 124.85 ± 0.34, and granite porphyry: 124.15 ± 0.31 Ma) occurred during the Early Cretaceous. Geochemically, monzonite porphyry belongs to the metaluminous and alkaline series rocks and is characterized by high Al2O3 (average 17.74 wt.%) and TiO2 (average 0.88 wt.%) and low Ni (average 4.63 ppm), Cr (average 6.69 ppm), Mg# (average 31.11), Y (average 15.16 ppm), and Yb (average 1.62 ppm) content with enrichment in Ba, K, Pb, Sr, Zr, and Hf and depletion in Ti, Nb, and Ta. The granitic rocks (e.g., quartz monzonite porphyry, quartz porphyry, and granite porphyry) pertain to the category of high-K calc-alkaline rocks and are characterized by high SiO2 content (>66 wt.%) and low MgO (average 0.69 wt.%), Mg# (average 31.49 ppm), Ni (average 2.78 ppm), and Cr (average 8.10 ppm) content, showing an affinity to I-type granite accompanied by Nb, Ta, P, and Ti depletion and negative Eu anomalies (δEu = 0.57–0.96; average 0.82). The Hf isotopic data suggest that these rocks were the product of the partial melting of juvenile crustal rocks. Notably, fractionation crystallization plays a crucial role in the process of magma emplacement. Combining our study with published ones, we proposed that the Early Cretaceous intrusive rocks in the Ulanhot area were formed in an extensional tectonic background and compactly related to the subduction of the Paleo-Pacific Ocean plate.

Geochemistry, geochronology and Sr–Nd–Hf isotopes of two types of Early Cretaceous granite porphyry dykes in the Sulu orogenic belt, eastern China

2020 ◽  
Vol 57 (2) ◽  
pp. 249-266 ◽  
Author(s):  
Song-Jie Wang ◽  
Hans-Peter Schertl ◽  
Yu-Mao Pang
Keyword(s):  
Early Cretaceous ◽  
Eastern China ◽  
Orogenic Belt ◽  
Granite Porphyry ◽  
Granitic Rocks ◽  
Geodynamic Setting ◽  
Type I ◽  
Yangtze Craton ◽  
T Values ◽  
Sulu Orogenic Belt

Late Mesozoic granitic rocks are widely distributed in the Sulu orogenic belt, but the source, tectonic affinity, and associated geodynamic setting that produced the respective magmas remain controversial. To provide insights into these issues, we present field-based petrological, whole-rock major and trace element and Sr–Nd isotope geochemical, zircon U–Pb dating, and Lu–Hf isotope studies on two types of granite porphyry dykes that are newly recognized from the central Sulu belt. U–Pb dating of magmatic zircons from both types yields consistent ages that vary between 124 ± 2 and 118 ± 2 Ma, constraining the timing of intrusion as Early Cretaceous. The granitic rocks have high-K calc-alkaline peraluminous compositions with low Mg# values and are characterized by fractionated rare earth element patterns with strong depletion in high field strength elements. Compared with type I of the granite porphyry dykes, type II exhibits higher SiO2 but slightly lower Na2O and K2O abundances, contains higher Rb/Sr and 87Sr/86Sr ratios, and shows more pronounced negative Eu, Sr, and Ba anomalies. Both types I and II have high initial 87Sr/86Sr ratios of 0.709–0.711 and negative εNd(t) values of −19.8 to −18.4. The magmatic zircons possess negative εHf(t) values of −29.1 to −20.8, with mostly Neoarchean Hf model ages of 3001–2478 Ma. These features, together with the presence of Neoproterozoic inherited zircons, indicate that the two types of granite porphyries successively crystallized from a joint granite magma that derived from partial melting of the continental crust of the Yangtze Craton. Therefore, an interrelationship between the granite porphyry dykes and massive magmatic granitoids from adjacent regions in the Sulu belt may be documented, recording evidence of a joint ancient crustal reworking and recycling in a fossilized continental subduction zone during the Early Cretaceous.

Measurement and distribution of zircons in some granitic rocks of magmatic origin

1957 ◽  
Vol 31 (238) ◽  
pp. 544-564 ◽  
Author(s):  
Leonard H. Larsen ◽  
Arie Poldervaart
Keyword(s):  
Major Axis ◽  
Morphological Characters ◽  
Granitic Rocks ◽  
Careful Study ◽  
Scatter Plot ◽  
Growth Trend ◽  
Small Bodies ◽  
Magmatic Origin ◽  
Quartz Monzonite ◽  
Reduced Major Axis

SummaryMorphological characters of zircons in concentrates have been studied by measurement of length along the c-axis and breadth along the a1- or a2-axis of 200 doubly terminated crystals for each sample. The sample is represented graphically by a line fitted mathematically to a scatter plot of the measurements. This line, the reduced major axis, is visualized as a growth trend, and samples are described and compared statistically.From a careful study of zircons in a tonalite it is concluded that zircon crystallized over a short range before crystallization of the main constituent minerals.The distribution of zircon in a batholith of magmatic origin has also been studied. The batholith grades from a core of granodiorite to a mantle of tonalite, but the zircons are uniform throughout. Small bodies of granodiorite and quartz monzonite have sharp contacts against the main batholithic rocks, and zircon samples from these intrusives differ from one another and from those of the batholith. It is concluded that the batholith represents a single intrusion which differentiated after emplacement, and that the later intrusives each crystallized under different conditions.

Closure of the Bangong–Nujiang Tethyan Ocean in the central Tibet: Results from the provenance of the Duoni Formation

2019 ◽  
Vol 89 (10) ◽  
pp. 1039-1054 ◽  
Author(s):  
Zhicai Zhu ◽  
Qingguo Zhai ◽  
Peiyuan Hu ◽  
Sunlin Chung ◽  
Yue Tang ◽  
...  
Keyword(s):  
Early Cretaceous ◽  
Late Cretaceous ◽  
Suture Zone ◽  
The Tibetan Plateau ◽  
Tectonic History ◽  
Magmatic Rocks ◽  
Two Samples ◽  
Delta Sequence ◽  
History Of ◽  
Central Tibet

ABSTRACT The closure of the Bangong–Nujiang Tethyan Ocean (BNTO) and consequent Lhasa–Qiangtang collision is vital to reasonably understanding the early tectonic history of the Tibetan Plateau before the India-Eurasia collision. The timing of the Lhasa–Qiangtang collision was mainly constrained by the ophiolite and magmatic rocks in previous studies, with only limited constraints from the sedimentary rocks within and adjacent to the Bangong–Nujiang suture zone. In the middle segment of the Bangong–Nujiang suture zone, the Duoni Formation, consisting of a fluvial delta sequence with minor andesite interlayers, was originally defined as the Late Cretaceous Jingzhushan Formation and interpreted as the products of the Lhasa–Qiangtang collision during the Late Cretaceous. Our new zircon U-Pb data from two samples of andesite interlayers demonstrate that it was deposited during the latest Early Cretaceous (ca. 113 Ma) rather than Late Cretaceous. Systemic studies on the sandstone detrital model, heavy-mineral assemblage, and clasts of conglomerate demonstrate a mixed source of both Lhasa and Qiangtang terranes and ophiolite complex. Clasts of conglomerate contain abundant angular peridotite, gabbro, basalt, chert, andesite, and granite, and minor quartzite and gneiss clasts also exist. Sandstones of the Duoni Formation are dominated by feldspathic–lithic graywacke (Qt25F14L61 and Qm13F14L73), indicative of a mixture of continental-arc and recycled-orogen source origin. Detrital minerals of chromite, clinopyroxene, epidote, and hornblende in sandstone also indicate an origin of ultramafic and mafic rocks, while garnets indicate a metamorphosed source. Paleocurrent data demonstrate bidirectional (southward and northward) source origins. Thus, we suggest that the deposition of the Duoni Formation took place in the processes of the Lhasa–Qiangtang collision during the latest Early Cretaceous (∼ 113 Ma), and the BNTO had been closed by this time.

Early Cretaceous exhumation of the Qiangtang Terrane during collision with the Lhasa Terrane, Central Tibet

Terra Nova ◽  
2017 ◽  
Vol 29 (6) ◽  
pp. 382-391 ◽  
Author(s):  
Zhongbao Zhao ◽  
Paul D. Bons ◽  
Konstanze Stübner ◽  
Gen-Hou Wang ◽  
Todd A. Ehlers
Keyword(s):  
Early Cretaceous ◽  
Lhasa Terrane ◽  
Central Tibet ◽  
Qiangtang Terrane
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