The uppermost Carboniferous (Gzhelian)–Lower Permian (Asselian–Sakmarian) stratigraphy and smaller foraminifers of the Ozbak‐Kuh region (Tabas Block, east central Iran)

The uppermost Carboniferous (Gzhelian)–Lower Permian (Asselian to Sakmarian) Anarak Group of the Zaladou section in central Iran is more than 180‐m thick and includes thick units of shale, calcareous sandstone, fusulinid limestone, sandy limestone, and dolomite. The Zaladou and Tigh‐e‐Madanu formations of this group were dated as Gzhelian to Sakmarian. A review of the smaller foraminifers of the Zaladou section is presented. Five foraminiferal subzones grouped in three biozones are proposed in this work: The first assemblage zone (I) is Gzhelian; the second zone (II) corresponds to the Gzhelian–Asselian boundary interval, and the third biozone (III) is Asselian in age. Biozone I is subdivided informally into two subzones: the Hemigordius spirilliniformis‐Bradyina cf. samarica subzone IA (probably early Gzhelian in age) and the Raphconilia modificata and Globivalvulina spp. subzone IB (middle to late Gzhelian); biozone II is the Nodosinelloides spp. zone; biozone III is subdivided informally into two subzones: IIIA with Pseudoacutella partoazari‐Bradyina lucida and IIIB with Planoendothyra persica n. sp.‐Rectogordius sp. The studied assemblages are correlated with those from the Carnic Alps (Austria–Italy), East European Platform of Russia, the Urals (Russia), Darvas (Uzbekistan), the northern and central Pamirs (Tajikistan), northern Iran (Alborz), northern Afghanistan, and other classical regions of the Tethyan realm. The genera Raphconilia and Planoendothyra are revised, and Planoendothyra persica n. sp. is described.

Geochemistry and zircon U–Pb–Hf isotopes of the granitoids of Qianjinchang pluton in the Xi Ujimqi, Inner Mongolia: Implications for petrogenesis and geodynamic setting

We conducted zircon U–Pb dating and geochemical analyses for the Qianjinchang (QJC) pluton in the Xi Ujimqi, Northeast China, with an aim to determine their ages, petrogenesis, and sources. The QJC pluton consists of coarse/medium‐grained biotite monzogranite in the core and fine‐grained biotite granodiorite in the rim; those rocks intrude into quartz diorite but are intruded by minor intrusive phases, including small biotite syenogranite, diorite bodies, late diorite, granodiorite, granite, and pegmatite dykes. Our new laser ablation inductively coupled plasma mass spectrometry zircon U–Pb data indicate that the QJC composite pluton composed of 2 phases of magmatic activities, with the ages of 301~313 Ma for the quartz diorite, 283 ± 1 Ma for the biotite granodiorite, 280 ± 1 Ma for the biotite syenogranite, and 280 ± 2 Ma for the diorite dyke. Hf isotopic analyses for the quartz diorite sample show εHf (t) = 3.75 to 11.72, with 2‐stage Hf model age (TDM2) ranging 568–1,078 Ma. The biotite syenogranite sample also shows a depleted εHf (t) = 4.47 to 8.71, with TDM2 ranging 745–1,015 Ma, suggesting the major involvement of juvenile crustal components. The various εHf values of the QJC pluton indicate a hybrid magma source of juvenile material with old crustal component, and the TDM2 values increase from the Carboniferous to Permian, which suggests an increasing proportion of old continental material during this period. Petrological and geochemical characteristics of the biotite granodiorite and biotite monzogranite samples suggest that they are S‐type granites and derived from partial melting of the clay‐poor, plagioclase‐rich psammitic source, produced at low‐medium pressure. The biotite syenogranite sample belongs to alkaline and shoshonitic series and probably formed by a hybridization process between basaltic magma and old continental components. Combined with previous studies on the contemporaneous magma‐tectonic activities in the Xilinhot microcontinent, we suggest that the QJC pluton formed in a postcollisional setting.

Prograde Barrovian metamorphism along Darjeeling–Tista transect, Eastern Himalaya, India: constraints from textural relationship, phase equilibria and geothermobarometry

The Darjeeling–Tista transect, located in Lesser Himalaya, is a part of the North‐Eastern Himalaya. Along the transect, polyphase deformation and prograde Barrovian metamorphism have been delineated. The time relations between the phases of deformations (D1, D2 and D3) and metamorphic crystallization reveal a single major prograde metamorphic event that initiated with the D1 deformation and finally outlasted it. The earlier phase of this metamorphism is essentially regional syntectonic low grade, which may be designated (M1a). This was followed by regional static metamorphism (M1b) in the post‐tectonic phase between the D1 and D2 deformations. This M1 metamorphism is superposed by later retrogressive metamorphism (M2) during the D2 and D3 deformations. The different parageneses of pelitic rocks containing chlorite, muscovite, biotite, garnet, staurolite, kyanite, sillimanite, K‐feldspar and plagioclase show various textures that resulted from the continuous and discontinuous reactions in the different zones. The metamorphic zones and isograds delineated on the basis of specific metamorphic reactions, namely reaction isograd or isoreaction grad, and by critical mineral assemblages are as follows: (a) chlorite–biotite zone, (b) garnet–chlorite zone, (c) staurolite–biotite–chlorite zone, (d) kyanite–biotite–staurolite zone and (e) sillimanite–biotite–staurolite zone. Chemographic relations and inferred reactions for different zones are portrayed in the AKF and AFM projections. A sequence of metamorphic reactions at different isograds has been deduced through textural relations. The prograde P‐T evolution of the study area has been constrained through the use of internally consistent winTWQ programme and Perple_X software in the MnNCKFMASHTO model system. The study has the potential to instigate future researches focusing on Himalayan metamorphic evolutionary trends using modern approaches. Copyright © 2017 John Wiley & Sons, Ltd.

Late Triassic adakite‐like volcanic rocks in Moguqi area in the central Great Xing’an Range, NE China: Implications for partial melting of delaminated thickened crust

Adakite‐like volcanic rocks in the Moguqi area of the central Great Xing’an Range of NE China consist of trachyandesites and trachydacites. These rocks yield LA–ICP–MS U–Pb zircon ages of 229.5–232.6 Ma. These adakite‐like rocks are high in Sr (459–1960 ppm) and MgO (1.2–4.3%), low in Y (11.4–23.70 ppm) and Yb (0.88–2.07 ppm), and have high Sr/Y ratios (37.17–146.31) and high Mg# values (0.43–0.58). These characteristics are similar to those of rocks derived from slab melting. However, the existence of Early Triassic stable continental sedimentary rocks of the Laolongtou Formation does not favour this mode of formation. The zircon εHf(t) values of the samples range from +8.09 to +13.29, indicating the primary magmas were generated by partial melting of juvenile crust. Analysis of geophysical data, combined with the previously published history of the Hegenshan–Heihe Suture in this region and the southward subduction of Mongol–Okhotsk oceanic plate, suggests that the Late Triassic adakite‐like volcanic rocks in the Xing’an Massif formed from the partial melting of delaminated thickened crust in an extensional setting. This occurred after orogenesis involving the Xing’an Massif and the Songnen Massif and was influenced by southward subduction of the Mongol–Okhotsk oceanic plate.