International Geology Review

Wang, Xinyu; Yao, Xin; Wang, Shifeng; Zhu, Xinyou; Wang, Jingbin; Wang, Chao

doi: 10.1080/00206814.2018.1531356pmid: N/A

In recent years, abundant Cenozoic potassic magmatic rocks from eastern Tibet and the Indochina Block have been studied extensively; however, until now, knowledge of Cenozoic A-type granites from the interior of the Indochina Block has been limited. U–Pb zircon ages for six samples of the Salei granite pluton within the Indochina Block range from 26 to 24 Ma. In situ Lu–Hf and Sr–Nd isotope data indicate that the Salei pluton was sourced mostly from Mesoproterozoic basement rocks of the Indochina Block, mixed with a small volume of juvenile crust derived from the underplated mantle. Whole-rock major element geochemistry indicates that the six samples are peraluminous high-K calc-alkaline granites. The trace and rare earth element patterns are typical of within-plate A-type granites. In combination with previous research, the present results suggest that the late Oligocene Salei granite formed from the convective removal of thickened lower continental lithospheric mantle. Moreover, the presence of 26–24 Ma A-type granites in the Indochina Block indicates within-plate extension in the interior of the block during the late Oligocene.

Colás, Vanessa; González-Jiménez, José María; Camprubí, Antoni; Proenza, Joaquín A.; Griffin, William L.; Fanlo, Isabel; O’Reilly, Suzanne Y.; Gervilla, Fernando; González-Partida, Eduardo

doi: 10.1080/00206814.2018.1542633pmid:

Santos, Anderson Costa; Mohriak, Webster Ueipass; Geraldes, Mauro Cesar; Santos, Werlem Holanda; Ponte-Neto, Cosme Ferreira; Stanton, Natasha

doi: 10.1080/00206814.2018.1542634pmid: N/A

This work discusses the regional geological and geophysical datasets (potential field data coupled with seismic lines) available across the Eastern Brazilian Continental Margin and addresses tectonic models that have been applied to the geological interpretation of the Vitória-Trindade Chain (VTC). New magnetic data acquired in the Trindade Island is combined with compiled petrological data and geological maps to propose a stratigraphic column with radiometric control for the volcanic sequences. The gravity and magnetic anomaly maps were integrated with regional seismic profiles extending from the continental platform towards the oceanic crust, showing the geomorphology of the Abrolhos Volcanic Complex (AVC) and the VTC. A detailed geological mapping of the Trindade Island was complemented by magnetometric profiles acquired on the island. The magmatic episodes identified in the Trindade Island within different volcano-stratigraphic sequences are, geochronologically, dated by 40Ar/39Ar method as Late Neogene to Quaternary (Pliocene/Upper Pleistocene) and indicate intrusive and extrusive igneous rocks formed on the Mesozoic (Cretaceous) oceanic crust. Models for the emplacement of these volcanic rocks on much older oceanic crust include hotspots and leaking fracture zones. The presence of flat tops as observed in the volcanic banks and seamounts along the Vitória-Trindade volcanic chain indicate abrasion of much higher volcanic edifices that now form the isolated islands in the Trindade-Martin Vaz Archipelago. Geological mapping and detailed magnetometric surveys suggest different rock properties for distinct volcanic episodes that formed the Trindade Island. The remarkable pattern of magnetic anomalies trending NE-SW in the deep-water region of the Espírito Santo Basin, eastwards of the AVC, suggests that the linear chain of volcanic edifices in the VTC may be associated with mantle anomalies caused by a hotspot or plume that was influenced by the E-W direction of leaking transform fracture zones. Abbreviation: Abrolhos Volcanic Complex (AVC); Vitória-Trindade Chain (VTC)

Amorim, José Victor Antunes de; de Pinho Guimarães, Ignez; Farias, Douglas José Silva; Lima, Jefferson Valdemiro de; Santos, Lucilene; Ribeiro, Vanessa Biondo; Brainer, Caio

doi: 10.1080/00206814.2018.1544936pmid: N/A

Ferroan granites (585–530 Ma) have been described in the Transversal subprovince of the Borborema Province (BP) and in Pan-African counterparts. They comprise two groups: Group 1 – slightly peraluminous to metaluminous, alkali-calcic rocks, with low Fe# mica and crystallized under intermediate fO2 (Aroeiras Complex and Serra Branca – Coxixola dike swarms); Group 2 metaluminous to slightly peraluminous, alkalic to alkali-calcic rocks, with high Fe# mica and crystallized under low fO2 (Queimadas and Prata intrusions). Group 1 marks transition from collision to transcurrence (ca. 585 Ma), or from transcurrence to uplift and transtension (ca. 545 Ma). Group 2 – represents granitoids intruded during extensional tectonics in transcurrent setting (ca. 550 Ma), or coeval with deposition of transtensional intracratonic basins (ca. 530 Ma). Hf and Nd model ages are older than 2.0 Ga, suggesting that the ferroan granitoids involved partial melting of Paleoproterozoic rocks. The data presented in this paper show that the ferroan magmatism was widespread in the BP and its counterparts in Africa in pre-drift reconstructions.

Sun, Pu; Niu, Yaoling; Guo, Pengyuan; Chen, Shuo; Duan, Meng; Gong, Hongmei; Wang, Xiaohong; Xiao, Yuanyuan

doi: 10.1080/00206814.2018.1548307pmid: N/A

We analysed whole-rock major and trace elements and Sr-Nd-Pb-Hf isotopes of the late Cenozoic volcanic rocks in the Leizhou Peninsula, South China to investigate their mantle source characteristics. These volcanic rocks, collected from Jiujiang, Tianyang and Huoju areas of the Leizhou Peninsula, are characterized by incompatible element enrichment but variable isotopic depletion. The volcanic rocks from Jiujiang and Tianyang show prominent primitive-mantle-normalized positive Nb, Ta and Sr anomalies and depleted Sr-Nd-Pb-Hf isotope compositions, whereas those from Huoju show slight positive to negative Nb and Ta anomalies, a prominent positive Pb anomaly, and more enriched Sr-Nd-Pb-Hf isotope compositions. Two types of mantle metasomatism are required to explain the geochemical characteristics of these rocks. The Jiujiang and Tianyang samples were largely derived from a mantle source metasomatized recently by a low-F melt. Such low-F melt is generated within the asthenospheric mantle, which is enriched in volatiles and incompatible elements with positive Sr anomaly and depleted Sr-Nd-Pb-Hf isotope compositions. The Huoju samples were largely derived from a mantle source metasomatized by recycled upper continental crust material. These two types of mantle metasomatism beneath the Leizhou Peninsula are consistent with trace element characteristics of mantle mineralogy (e.g. clinopyroxene vs. amphibole), which reflects source evolution in space and time (e.g. tectonic setting change).

Simmonds, Vartan; Moazzen, Mohssen; Selby, David

doi: 10.1080/00206814.2018.1561334pmid: N/A

The Siah Kamar porphyry Mo deposit is the newly discovered deposit of this type in the Neo Tethys-related Urumieh–Dokhtar magmatic arc, northwest Iran. Mineralization occurs as stock-work quartz–molybdenite and mono-mineralic molybdenite veinlets within the porphyry quartz-monzonite stock and the country rocks, accompanied by locally scattered later-stage and cross-cutting quartz-chalcopyrite-pyrite veinlets in the trachy-andesite and trachy-basalt country rocks. U–Pb zircon geochronology of the porphyry stock yielded Early Oligocene dates of 32.7 ± 0.4 to 30.9 ± 0.4 Ma (at 2σ level). The Th/U ratios of the zircons range between 0.48 and 0.77, and they possess initial εHf(t) values of 3.2 to 12.1, which may suggest a dominant mantle source for the magma. Molybdenite separates yielded rhenium contents between ~10 and 41 ppm (average ~26 ppm, n = 4) and slightly younger Re–Os ages compared to the porphyry stock, ranging from 29.1 ± 0.2 to 28.1 ± 0.2 Ma (at 2σ level). The Siah Kamar porphyry Mo deposit is nearly temporally coeval with the Haft Cheshmeh porphyry Cu deposit and the vein-type Cu–Mo–Au mineralization in the Qarachilar area, corresponding to the second porphyry Cu–Mo mineralization epoch in NW Iran. However, it is younger than the majority of the porphyry Cu deposits in the southern Lesser Caucasus and only shows temporal correlation with the Paragachay and first-stage Kadjaran porphyry Cu deposits. Moreover, it is older than all the porphyry Cu–Mo systems across the central and south-eastern parts of the Urumieh–Dokhtar magmatic arc, except the Bondar Hanza deposit, which is nearly coeval with the Siah Kamar porphyry Mo deposit. All these data reveal an old to young trend along the UDMA and the porphyry Cu belt of Iran, further testifying to the diachronous and later closure of the Neo-Tethyan oceanic basin in central and SE Iran.

Aksoy, Rahmi

doi: 10.1080/00206814.2019.1581996pmid: N/A

In the Central Anatolia, the style of neotectonic regime governing the region has been a controversial issue. A tectonic study was carried out in order to contribute to this issue and better understand the neotectonic stress distribution and style of deformation in the west-southwest of the Konya region. From Middle Miocene to Recent time, Konya region was part of the Central Anatolia extensional province. The present-day topography in the west-southwestern part of Konya is characterized by alternating elongate grabens and horsts trending E-W and NW-SE. The grabens were developed upon low-grade metamorphic rocks of Palaeozoic and Mesozoic ages and ophiolite slabs of possibly Late Cretaceous age. The evolutionary history of grabens is episodic as evidenced by two graben infills; older and younger graben infills separated by an angular unconformity. The older infill consists of fluviolacustrine sequence intercalated with calc-alkaline lavas and pyroclastic rocks. This infill is folded; thrust faulted and Middle Miocene-Early Pliocene in age. The younger and undeformed basin fill comprises mainly of Plio-Quaternary conglomerates, sandstone-mudstone alternations of alluvial fan and recent basin floor deposits. Three major tectonic phases were differentiated based on the detailed mapping, morphological features and kinematic analysis. Approximately N-S trending extension began in the Middle Miocene-Early Pliocene in the region with the formation of E-W and NW-SE-trending grabens. Following NE-SW-directed compression which deformed the older basin fill deposits by folding and thrusting, a second period of ENE-WSW-trending extension began in the late Pliocene and continued to the present. The west-southwestern margin of the Konya depression is bounded by the Konya Fault Zone. It is an oblique-slip normal fault with a minor dextral strike-slip component and exhibits well-preserved fault slickensides and slickenlines. Recent seismicity and fault-related morphological features reveal that the Konya Fault Zone is an active neotectonic structure.