Stern, Robert J.
Permanent URI for this collectionhttps://hdl.handle.net/10735.1/4141
Dr. Robert Stern serves as a Professor of Geosciences. His research interests include:
- Volcanism associated with convergent plate margins (subduction zones)
- How new subduction zones form
- How Earth's continental crust is generated and destroyed
- When Plate Tectonics started
- The geologic evolution of the Middle East (especially the region between Egypt and Iran)
- The formation of the Gulf of Mexico
- The geology of the Dallas- Fort Worth Metroplex.
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Browsing Stern, Robert J. by Author "0000-0002-8083-4632 (Stern, RJ)"
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Item Age, Geochemistry, and Emplacement of the ~40-Ma Baneh Granite-Appinite Complex in a Transpressional Tectonic Regime, Zagros Suture Zone, Northwest Iran(Taylor & Francis Inc, 2018-01-12) Azizi, Hossein; Hadad, Sepideh; Stern, Robert J.; Asahara, Yoshihiro; 0000-0002-8083-4632 (Stern, RJ); 284885305 (Stern, RJ); Stern, Robert J.The Baneh plutonic complex is situated in the Zagros suture zone of northwest Iran between the Arabian and Eurasian plates. This complex is divided into granite and appinite groups. Zircon U-Pb dating shows that granites crystallized 41-38 million years ago but appinites experience more protracted magmatic evolution, from at 52 to 38 Ma. Whole-rock chemical compositions show significant major and trace element variations between the two lithologies. Granitic rocks are more evolved, with high contents of SiO₂ (62.4-77.0 wt%), low contents of TiO₂ (0.25 wt%), MgO (0.05-1.57 wt%), and Fe₂O₃ (0.40-4.06 wt%) and high contents of Na₂O + K₂O (approximate to 10 wt%). In contrast, appinites have low contents of SiO₂ (51.0-57.0 wt%) and K₂O (<2.1 wt%) and high Fe₂O₃ (6.4-9.35 wt%), MgO (2.0-9.9 wt%), and Mg number (Mg# = 35-76). The concentration of rare earth elements in the appinites is higher than in granitic rocks, making it difficult to form granites solely by fractionation of appinite magma. (⁸⁷Sr/⁸⁶Sr)ᵢ and ε_{Nd(40 Ma)} in both groups are similar, from 0.7045 to 0.7061 and -1.2 to +2.6, except for a primitive gabbroic dike with ε_{Nd(40 Ma)}) = +9.9. Appinites show mainly typical I-type characteristics, but granites have some S-type characteristics. The sigmoidal shape of the Baneh pluton and its emplacement into deformed Cretaceous shales and limestone showing kink bands, asymmetric and recumbent folds in a broad contact zone, with pervasive ductile to brittle structures in both host rocks and intrusion, indicate that magma emplacement was controlled by a transpressional tectonic regime, perhaps developed during early stages in the collision of Arabia and Eurasian plates.Item Commentary on JGR-Sold Earth Paper “Deep Seismic Structure Across the Southernmost Mariana Trench: Implications for Arc Rifting and Plate Hydration” By Wan et al.(Blackwell Publishing Ltd, 2019-05-06) Stern, Robert J.; 0000-0002-8083-4632 (Stern, RJ); 284885305 (Stern, RJ); Stern, Robert J.No abstract available.Item Jurassic Igneous Rocks of the Central Sanandaj–Sirjan Zone (Iran) Mark a Propagating Continental Rift, Not a Magmatic Arc(Blackwell Publishing Ltd, 2019-04-29) Azizi, H.; Stern, Robert J.; 0000-0002-8083-4632 (Stern, RJ); 284885305 (Stern, RJ); Stern, Robert J.Jurassic igneous bodies of the Sanandaj–Sirjan zone (SaSZ) in SW Iran are generally considered as a magmatic arc but critical evaluation of modern geochronology, geochemistry and radiogenic isotopes challenges this conclusion. There is no evidence for sustained igneous activity along the ~1,200 km long SaSZ, as expected for a convergent plate margin; instead activity was brief at most sites and propagated NW at ~20 mm/a. Jurassic igneous rocks define a bimodal suite of gabbro-diorite and granite. Chemical and isotopic compositions of mafic rocks indicate subcontinental lithospheric mantle sources that mostly lacked subduction-related modifications. The arc-like features of S-type granites reflect massive involvement of Cadomian crust and younger sediments to generate felsic melts in response to mafic intrusions. We conclude that Jurassic SaSZ igneous activity occurred in a continental rift, not an arc. SaSZ igneous rocks do not indicate that subduction along the SW margin of Eurasia began in Jurassic time. © 2019 John Wiley & Sons Ltd