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Past geodynamic events can be reconstructed using the spatial and temporal patterns of geochemical variability in igneous rocks. Here we apply this principle to define the timing and geometry of breakoff of the Neo-Tethyan slab after the India-Asia collision. Two episodes of mafic magmatism (∼53 Ma and ∼ 48 Ma) are preserved in the Quxu area of the southern Lhasa terrane (SL). We present their whole-rock geochemistry, zircon U-Pb ages, and in situ zircon Hf isotope ratios. The early gabbro (∼53 Ma) exhibits typical arc basalt characteristics, including enrichment of large-ion lithophile elements (LILEs), depletion of high-field strength elements (HFSEs), and radiogenic Nd and zircon Hf isotopes, implying that they were formed by partial melting of metasomatized lithospheric mantle. In comparison to the early gabbro, the late hornblende gabbro (∼48 Ma) contains higher contents of HFSEs (e.g., Nb, Zr) and relatively less radiogenic Nd and zircon Hf isotopes, suggesting interaction between the enriched sub-continental lithospheric mantle and asthenospheric mantle. It is likely that upwelling asthenosphere reached the central SL around 50 Ma and that the Neo-Tethyan slab tore off under this area at this time. The spatial and temporal distribution of mafic rocks across the whole southern Lhasa terrane show that this geochemical transition and hence, presumably, the tearing off of the Neo-Tethyan slab, propagated eastward along the collision zone throughout Paleocene-Eocene time.

The Eastern Pontides Orogenic Belt (EPOB) in northeastern Turkey is a continental arc that is part of the Himalayan-Alpine orogeny. Late Cretaceous magmatism in this belt is dominated by high-K calc-alkaline, shoshonitic, and alkaline rocks that occur over an area of -600 km (E-W) and -200 km (N-S). We present new geochemical data (whole rock major and trace element analyses, mineral compositions, U-Pb zircon and titanite ages, zircon trace element data, and Sr-Nd-Pb isotopic analyses) for 153 samples, with compiled data for an additional 265 samples. Magmatism is diachronous across the arc. In the north, Cycle-I (92-84 Ma) commenced with tholeiitic and calc-alkaline basalts and andesites, and continued with felsic extrusive rocks. Cycle-II (84-70 Ma) includes mainly intermediate and felsic extrusive rocks. Over time, the low-K granitoids progressively give way to calc-alkaline granitoids in the north. In the south, Cycle-I (84-78 Ma) includes high-K trachyandesites, trachytes and felsic extrusive rocks. Cycle-II (78-65 Ma) comprises leucitites, trachybasalts, and other K-rich rocks. Shoshonitic granitoids in the south show ages between 80 and 65 Ma. Clinopyroxene compositions in trachyandesites and leucitites indicate initial crystallization at -38 km depth and 1120 degrees C. Amphibole joins the phase assemblage at -8 km depth and T < 950 degrees C. All samples have LILE and LREE enrichments and negative Nb, Ta, and Ti, and positive Pb anomalies, consistent with their subduction-related origin. Isotopic data indicate mixing between magmas from heterogeneous, enriched subcontinental mantle sources and those from a range of crustal sources. Mantle-derived and crustally-derived magmas are clearly separated by (Gd/Yb)N. Chemical zoning of the EPOB, from tholeiitic and calc-alkaline rocks to high-K calc-alkaline, shoshonitic, and alkaline rocks, from north to south, and the timing of magmatism younging southward, are consistent with a model of southward subduction in the Late Cretaceous. (c) 2021 International Association for Gondwana Research. Published by Elsevier B.V. All rights reserved.

Late Cretaceous to Early Paleocene hypabyssal intrusives near Bayburt in northeastern Turkey, in the Eastern Pontides Orogenic Belt (EPOB), host a variety of xenoliths, including clinopyroxenite, hornblendite, hornblende-and plagioclase-rich gabbro, quartz diorite and amphibole-rich diorite, quartz syenite, and amphibolite. We report major and trace element data for both host rocks and xenoliths, along with zircon U-Pb and amphibole 40Ar/ Ar-39 ages, zircon trace element data, mineral compositions, and Sr-Nd-Pb-Hf isotopic data. Host rock compositions range from trachyandesite to dacite and rhyodacite, but major element (e.g. Mg-number) and trace element systematics (e.g. La/YbN) indicate that they are not related by fractional crystallization. Host rocks belong to the high-K calc alkaline and calc-alkaline series, and have the signature of arc rocks (depleted Nb, Ta, Ti, and elevated Pb). Trace element data (Sr/Y and La/Yb) indicate that the dacitic rocks are adakitic. Host rock ages cluster around 70 +/- 2 Ma; one intrusion contains zircons that suggest a -62 Ma crystallization age. Hornblendite xenoliths show ages of 76, 78, and 81 Ma, whereas quartz syenites range from 66 to 70 Ma. The younger ages (62, 66, 70 Ma) fall in an apparent magmatic gap, and document the oldest adakitic magmatism in the EPOB. Mineral compositions indicate initiation of crystallization in the host rocks at -9 kb and 1250 degrees C, with progressive crystallization continuing to -2 kb and 800 degrees C. Host rocks and xenoliths have similar ranges of Sr-87/(86)Sri (0.7044-0.7062), Nd-143/(144)Ndi (-1.5 < epsilon Nd < 1.5), and Pbi (18.28 < Pb-206/Pb-204 < 18.68) compositions. The clinopyroxenite, hornblendite, and gabbro xenoliths are broadly cognate with the host rocks, and are cumulate fragments from an arc-root magma system. The quartz diorite, quartz syenite, and amphibolite xenoliths have different histories. Some of the quartz syenites are near eutectic compositions in the H2O saturated q-or-ab system at -5 kb. The host rocks and xenoliths derive from crustal magma chambers and dominantly crustal melting in the back-arc region of the EPOB. (C) 2021 Elsevier B.V. All rights reserved.

We provide geochronological (zircon U-Pb) and geochemical data (whole rock major and trace elements, Sr-Nd-Pb isotopes, mineral compositions, zircon trace elements) for Late Cretaceous I- and A-type granitoids and associated gabbros from three areas (Dereli, Sebinkarahisar, Divrigi), along a north-south traverse in eastern Turkey from the northern part of the Eastern Pontides Orogenic Belt to the Anatol ide-Tauride Block, and from two locations (Sokmen and Pimalli) that are situated away from the traverse line. Our aim is to interpret the tectonic environment in which the granitoids formed. Late Cretaceous plutonic activity began similar to 90 Ma and continued uninterruptedly for about 20 my. The Dereli suite and the Asarcik intrusion at Sebinkarahisar are 1-type granitoids; the others are A-type granitoids. The A-type classification of these rocks is ambiguous; they are A-typerelative to other coeval granitoids in eastern Turkey. The Sebinkarahisar, Murmana (Divrigi), and Pirnalli granitoids evolved primarily by closed-system fractional crytallization. At Sebinkarahisar, I- and A-type intrusions are isotopically indistinguishable, and must share the same source. Open system, AFC processes affected the other granitoids. Crustal components contributed to all of the granitoids. The Dereli granitoids have an old component (1.2 < T-DM < 1.75 Ga) that is unusual among Turkish igneous rocks. No mantle component is recognizable in the A-type granitoids, but the low SiO2 content of some granitoids requires a mantle-derived component. Arc-like geochemical features may be inherited from a mid-crustal source component, in addition to contributions from the arc environment active at the time of magmatism. A petrogenetic relation cannot be demonstrated between the Divrigi gabbros and their contemporaneous granitoids. The gabbros require a subcontinental lithospheric mantle source. Trace elements in zircon track fractional crystallization paths within suites, and faithfully map the arc-related petrogenesis of the granitoids, but do not mirror trace element distributions in zircons from other A-type suites. Available data indicate that Late Cretaceous plutonic activity began at about similar to 90 Ma in both the northern part of the Eastern Pontides Orogenic Belt and the southern part of the Anatolide-Tauride Block. Magma compositions began to change at ca. 80 Ma, and transformed successively into high-K I-type and shoshonitic A-type activity, and magmatism continued until similar to 70 Ma. We interpret this 20 my interval to be the subduction-dominated, arc-construction phase in the Eastern Pontides. The distribution of I-type magmas in eastern Turkey is best explained by double-sided, initially shallow-angle subduction of Paleo- and Neo-Tethyan lithospheres, with subsequent steepening of the subducted slabs leading to an extensional regime and the generation of A-type magmas. This hypothesis also explains the origin of Late Cretaceous I- and A-type Central Anatolian granitoids. (C) 2018 Elsevier B.V. All rights reserved.

The Eastern Pontides Orogenic Belt offers critical clues on the origin of Early Cenozoic continental arc magmatism in the Alpine-Himalayan system. Systematic geological, geochemical and chronological studies indicate that there are three subgroups among the Early Cenozoic intrusions in the Eastern Pontides Oro genic Belt - Late Paleocene-Early Eocene adakitic intermediate-felsic intrusions, Eocene mafic intrusions, and Eocene non-adakitic granitoid intrusions. Here we focus on the petrology and geodynamic setting of the Eocene non-adakitic granitoid intrusions that are well exposed in a belt between the Thanetian-Ypresian adakitic intrusions in the south and the Lutetian gabbroic intrusions in the north. We also present data on enclaves and surrounding Eocene volcanics. The studied intrusions can be grouped into two main categories, based on their field and petrographical characteristics: granodiorite and monzodiorite-dominated and syenite-dominated bodies. They can be further subdivided into four groups of differing K2O content: low-K2O (cevrepinar, Kaletas, Saricicek and Uzengili), mixed (Sorkunlu, Kozluk and Tamdere), and high-K2O (Dolek, Mesebasi, cakirbag, and Arslandede) rocks are granodioritic and monzodioritic, whereas shoshonitic (Kosedak, Meydanli and Bademli) bodies are syenitic. Zircon U-Pb age determinations reveal that these granitoids were emplaced into crustal rocks of the Eastern Pontides Orogenic Belt between 47 and 42 Ma, in Lutetian time, simultaneously with the gabbroic intrusions in the north. Mineral compositions and P-T calculations are consistent with the interpretation that crustal melting or magma storage started at mid-crustal depth (similar to 25 km), with a magma system that subsequently extended to shallow levels (