40Ar/39Ar age and geochemistry of the post-collisional Miocene Yamadağ volcanics in the Arapkir area (Malatya Province), eastern Anatolia, Turkey

doi:10.1016/j.jseaes.2007.12.001

Journal of Asian Earth Sciences

Volume 33, Issues 3–4, 15 July 2008, Pages 229-251

https://doi.org/10.1016/j.jseaes.2007.12.001 Get rights and content

Abstract

The Neogene Yamadağ volcanics occupy a vast area between Sivas and Malatya in eastern Anatolia, Turkey. These volcanic rocks are characterized by pyroclastics comprising agglomerates, tuffs and some small outcrops of basaltic–andesitic–dacitic rocks, overlain upward by basaltic and dacitic rocks, and finally by basaltic lava flows in the Arapkir area, northern Malatya Province. The basaltic lava flows in the Arapkir area yield a ⁴⁰Ar/³⁹Ar age of 15.8 ± 0.2 Ma, whereas the dacitic lava flows give ⁴⁰Ar/³⁹Ar ages ranging from 17.6 through 14.7 ± 0.1 to 12.2 ± 0.2 Ma, corresponding to the Middle Miocene. These volcanic rocks have subalkaline basaltic, basaltic andesitic; alkaline basaltic trachyandesitic and dacitic chemical compositions. Some special textures, such as spongy-cellular, sieve and embayed textures; oscillatory zoning and glass inclusions in plagioclase phenocrysts; ghost amphiboles and fresh biotite flakes are attributable to disequilibrium crystallization related to magma mixing between coeval magmas. The main solidification processes consist of fractional crystallization and magma mixing which were operative during the soldification of these volcanic rocks. The dacitic rocks are enriched in LILE, LREE and Th, U type HFSE relative to the basaltic rocks. The basaltic rocks also show some marked differences in terms of trace-element and REE geochemistry; namely, the alkaline basaltic trachyandesites have pronounced higher HFSE, MREE and HREE contents relative to the subalkaline basalts. Trace and REE geochemical data reveal the existence of three distinct magma sources – one subalkaline basaltic trachyandesitic, one alkaline basaltic and one dacitic – in the genesis of the Yamadağ volcanics in the Arapkir region. The subalkaline basaltic and alkaline basaltic trachyandesitic magmas were derived from an E-MORB type enriched mantle source with a relatively high- and low-degree partial melting, respectively. The magmatic melt of dacitic rocks seem to be derived from an OIB-type enriched lithospheric mantle with a low proportion of partial melting. The enriched lithospheric mantle source reflect the metasomatism induced by earlier subduction-derived fluids. All these coeval magmas were generated in a post-collisional extensional geodynamic setting in Eastern Anatolia, Turkey.

Introduction

The genesis of widespread Miocene to Plio-Quaternary post-collisional volcanism in east and southeast Anatolia, Turkey (Fig. 1, Fig. 2) (Yılmaz, 1990, Pearce et al., 1990, Ercan et al., 1990, Notsu et al., 1995, Keskin et al., 1998, Yılmaz et al., 1998) has been connected with (1) strike-slip faulting mainly controlled by convergence between the Eurasian and Arabian plates which has continued since the Late Eocene/Oligo-Miocene (Şengör and Yılmaz, 1981, Innocenti et al., 1976, Bozkurt and Mittwede, 2001); (2) post-collisional extensional tectonics resulting from slab break-off which is considered to have taken place during the Middle Miocene following the collision between the Eurasian and Arabian plates (Şengör et al., 2003, Keskin, 2003).

This paper presents some new data, consisting of a geological map covering approximately 300 km², ⁴⁰Ar/³⁹Ar geochronology, petrography and whole-rock geochemistry of the Miocene Yamadağ volcanic rocks around the Arapkir, N Malatya region, to bring some new insights into the evolution of this widespread post-collisional volcanic province in east Anatolia.

Section snippets

Regional geology

The main geologic–tectonic segments of East Anatolia, termed the East Anatolian High Plateau (EAHP) by Şengör et al. (2003), can be subdivided into (1) Pontide basement (Eurasian plate), (2) East Anatolian accretionary complex, (3) Anatolian basement (Bitlis-Pötürge massif), (4) Neogene sedimentary and volcanic rocks belonging to EAHP and Anatolian basement in eastern Turkey.

The Pontide basement rocks are represented by the Eastern Pontide arc magmatics and associated sedimentary rocks which

Geological setting

The most prominent feature of the geology of the Arapkir area is its location close to the junction of the Malatya–Ovacık fault with the NAFZ (Fig. 1, Fig. 2, Fig. 3). Basement rocks of pre-Miocene age mainly comprise the Munzur limestone (Carboniferous to Early Cretaceous) and, locally, the Divriği ophiolite (Late Cretaceous) (Fig. 3). Miocene sedimentary rocks are represented by the limestone and flyschoidal sequence of the Kemah formation (Fig. 3), which was deposited in post-collisional

Analytical techniques

A total of 60 rock samples were collected from the Yamadağ volcanic rocks in the Arapkir area. Approximately two third of these samples belong to mappable lava flows within the pyroclastics rocks (Fig. 3). Their mineralogical compositions and textures were studied using a binocular polarizing microscope. Based on these microscope studies, 15 of the freshest and most representative rock samples taken from lava flows were selected for whole-rock major-element, trace-element and REE analysis (see

Petrography

The Yamadağ volcanics in the Arapkir area (northern Malatya Province) mainly comprise pyroclastic rocks and some alkaline basaltic trachyandesitic, subalkaline basaltic/basaltic andesitic and dacitic lava intercalations in the field (Fig. 3, Fig. 4). All the rock samples collected from the distinct mappable and unmappable lava flows intercalated with pyroclastic rocks have been studied under microscope in order to get the mineralogical composition and texture. The geochemical and

⁴⁰Ar/³⁹ Ar age determination

Four fresh rock samples, without superficial or hydrothermal alteration, were selected for ⁴⁰Ar/³⁹Ar geochronology. The results of ⁴⁰Ar/³⁹Ar age determinations are given in Table 1. U-shaped age spectra are commonly associated with excess argon (the first few and final few steps often have lower radiogenic yields, thus apparent ages calculated for these steps are effected more by any excess argon present), and this is often verified by isochron analysis, which utilizes the analytical data

Whole-rock geochemistry

Results of whole rock major, trace and REE geochemical analyses are reported in Table 2. Analyzed samples from the Yamadağ volcanics in the Arapkir area show a subalkaline (Fig. 9a and b) to calc-alkaline character with a medium-K compositions (Fig. 9c); and alkaline, medium- to slightly high-K composition (Fig. 9c). The dacitic rocks are easily distinguished from the non-dacitic rocks in all the geochemical variation diagrams based on major and trace elements versus silica content (Fig. 10,

Discussion

All of the major-, trace- and REE geochemical (Fig. 10, Fig. 11, Fig. 12, Fig. 13, Fig. 14) data presented above reveal that the widespread Middle to Late Miocene Yamadağ volcanics in the Arapkir area of eastern Anatolia are composed of three different lava suites – one dacitic, one subalkaline basaltic and alkaline basaltic trachyandesitic in composition. The dacitic rocks are enriched in LILE (K, Rb, Ba, Th, U) and LREE (La, Ce, Pr, Nd), but the subalkaline basaltic and alkaline basaltic

Conclusions

The Early–Middle to Late Miocene Yamadağ volcanism comprises essentially pyroclastics intercalated with alkaline basaltic trachyandesitic and subalkaline basaltic lavas at the base, alkaline basaltic in the middle and different dacitic and alkaline trachybasaltic lava flows at the top of the sequence. The alkaline basaltic trachyandesitic lava flows from the middle part of section give an ⁴⁰Ar/³⁹Ar age of 15.8 Ma, whereas various dacitic lavas yield ⁴⁰Ar/³⁹Ar ages ranging from 17.6 through 14.7

Acknowledgements

This study was supported by the Scientific Research Unit of Fırat University, Elazığ, Turkey (FÜBAP). The Municipality of the Arapkir town is thanked for logistical support during fieldwork. Dr. Ercan ALDANMAZ (Kocaeli University, Turkey) has kindly read and corrected the manuscript. Prof. John WINCHESTER (University of Keele, England) and one anonymous reviewer are kindly thanked for their helpful comments which substantially improved the manuscript. Prof. Kevin BURKE (University of Houston,

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The third late Pliocene-Holocene volcanic association is characterized by volcanoes composed of lavas with transitional tholeiitic to alkaline mafic to felsic compositions that are mainly emplaced along NNE-SSW-trending transtensional left-lateral structures (Adamia et al., 2010; Dilek et al., 2010; Kürüm et al., 2008; Philip et al., 1989; Veliev et al., 2010; Yılmaz, 1990). Geochemical data from early Miocene-early Pliocene calc-alkaline to late Pliocene-Holocene alkaline igneous units across eastern Turkey and the Lesser Caucasus point to an increasing role of partial melting of subduction-metasomatized subcontinental mantle, and a degree of magma-crust interaction that is larger in the south than in the north (Dilek et al., 2010; Keskin, 2003; Kürüm et al., 2008). In contrast, south of the Bitlis-Zagros suture in the Arabian Platform, volcanism consists dominantly of mafic lavas that erupted along normal faults.
Exploration in the central Tethys region of Turkey, Armenia, Azerbaijan, Georgia, Iran, and western Pakistan has led to the identification of the giant Reko Diq (24 Mt Cu and 1300 t Au), Sar Cheshmeh (8.9 Mt Cu and 0.46 Mt Mo), Sungun (5.1 Mt Cu and 0.20 Mt Mo), and Kadjaran (4.6 Mt Cu, 0.94 Mt Mo, and 1100 t Au), and 10 other large (1–2 Mt Cu) porphyry deposits including Saindak, Cevizlidere, Teghout, Meiduk, and Halilağa. Continued exploration efforts have also resulted in the development of porphyry-related gold deposits such as Kişladağ (9.6 Moz Au), Çöpler (3.7 Moz Au), Aği Daği (1.7 Moz Au), and Sary Gunay (3.0 Moz Au), and in the generation of several other promising exploration projects.
The distribution in space and time of porphyry deposits in the central Tethys region was shaped by complex pre- to post-mineral tectonic, igneous, collisional, uplift and burial events. These events are represented by a partially-overlapping and variably exhumed and covered collage of twenty-six Early Jurassic to Holocene magmatic belts permissive for the occurrence of porphyry deposits (porphyry tracts and sub-tracts). Twelve tracts or sub-tracts are characterized by compressional continental arcs that formed on drifting terranes or continental margins, 10 developed in compressional to extensional intra-oceanic arc and backarc-rift settings, and 4 formed in extensional post-collisional environments over amalgamated terranes. Eight of these belts were variably affected by coeval and younger metamorphic, fold-and-thrust, and extensional faulting events.
Fifty-four porphyry Au-(Cu), Cu-Au, Cu-Mo, Mo-Cu deposits, 15 porphyry-related Au, Au-(Mo) and W-(Mo-Au) deposits, 239 porphyry prospects, and 68 other porphyry-related mineral sites were identified in the study region. Of the 376 porphyry and porphyry-related sites, about 11% formed in island arc, 42% in continental arc, 20% in backarc, and 27% in post-collisional settings. Of the 69 porphyry and porphyry-related deposits, 7% developed in intra-oceanic arc, 41% in continental arc, 27% in backarc, and 25% in post-collisional settings. The largest occur in either compressional continental arc (18 deposits including the Reko Diq and Sar Cheshmeh giants) or post-collisional (13 deposits including the Kadjaran and Sungun giants) environments. Ninety percent of the largest porphyry or porphyry-related deposits occur in only 9 of the 26 permissive porphyry tracts or sub-tracts. Moreover, 88, 90, and 77% of the identified Cu, Mo, and Au resources are contained in porphyry deposits that occur in only 4 of these 9 tracts. Of these 4 tracts, 3 outline arc settings, and one delimits a post-collisional environment.
The compositional diversity of porphyry intrusions in these tectono-magmatic environments generally varies from island arc settings with the most restricted range (partly alkaline but mainly calc-alkaline dioritic to granodioritic-tonalitic), to continental arc (calc-alkaline dioritic-quartz dioritic, granodioritic, quartz monzonitic-granitic, and less commonly mildly alkaline), to backarc (mildly alkaline and calc-alkaline dioritic to granitic), to post-collisional settings with the most expansive range (alkaline and calc-alkaline mafic to felsic, and weakly peraluminous). Metal associations also vary broadly as a function of porphyry intrusion composition from weakly peraluminous to metaluminous felsic (Mo[±W ± Cu]; <2% of porphyry-related systems [i.e., Tyrnyauz]), to metaluminous felsic and intermediate (Cu-Mo[±Au]; 85% [i.e., Cevizlidere, Haft Cheshmeh, Kahang, Sar Cheshmeh, Sungun, Teghout, Reko Diq, Saindak]), to mildly alkaline felsic and intermediate (Cu-Au[±Mo] [i.e., Agarak, Kadjaran, Kale Kafi]) and mafic (Au-Cu; 12% [i.e., Çöpler]), and to alkaline felsic (Au-Mo; 1% of porphyry-related systems [i.e., Kişladağ).
Tectonic changes were critical in triggering the formation of large porphyry deposits in the region. Large porphyry deposits were preferentially emplaced in continental arc settings shortly before major collisional events (Dar Alu, Kahang, Meiduk, Now Chun, and the giant Sar Cheshmeh and Reko Diq deposits), or in post-subduction environments shortly after collision (Bakirçay, Güzelyayla, Haft Cheshmeh, Masjed Daghi, and the giant Kadjaran and Sungun deposits) or during periods of prominent extension (Aği Daği, Halilağa, Kişladağ, Sari Gunay, and Zarshuran porphyry-related deposits). Collision-induced uplift, erosion, and removal of coeval volcanic rocks favorably exposed the hypabyssal level of subduction-related porphyry deposits. Extensional structures that developed parallel and orthogonal to the compressional principal stress component along transtensional or transpressional strike-slip faults or in pull-apart basins commonly controlled porphyry-related deposits in post-collisional settings. The latter deposits typically exhibit shallow epithermal levels of emplacement because of preservation by burial.
Seventeen porphyry deposits and one porphyry-related deposit in the study region are reported to contain significant supergene resources. Relatively mature levels of secondary copper enrichment in dominantly granodioritic to granitic porphyry deposits occur in areas where large pyrite-rich quartz-sericite alteration zones have been preserved and exposed to surface oxidation (Güzelyayla and Ulutaş in northeastern Turkey; Agarak, Ankavan, Dastakert, Kadjaran, and Teghout in Armenia; Ali Javad in northern Iran; Kale Kafi in central Iran; Darreh Zar, Meiduk, Now Chun, and Sar Cheshmeh in southeastern Iran; and Tanjeel in southwestern Pakistan). Chalcocite blankets also developed over porphyry deposits in regions where significant post-mineral faulting has occurred (Muratdere and Sarıçayıryayla in western Turkey). Normal faulting also enhanced secondary enrichment of gold in the Halilağa porphyry and Sary Gunay porphyry-related deposits located respectively in western Turkey and northern Iran.
Evaluation of provincial as well as local controls strongly suggests that continued exploration in the region will lead to the identification of additional porphyry and porphyry-related deposits. These deposits will likely be found under younger cover formations in porphyry belts that are already known, and in association with superjacent high- and intermediate-sulfidation epithermal deposits, or increasingly peripheral skarn, carbonate-replacement, and sediment-hosted deposits. Application of suitable exploration techniques to detect concealed and/or deformed deposits in porphyry belts that remain under-explored may also prove productive.

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40Ar/39Ar age and geochemistry of the post-collisional Miocene Yamadağ volcanics in the Arapkir area (Malatya Province), eastern Anatolia, Turkey

Abstract

Introduction

Section snippets

Regional geology

Geological setting

Analytical techniques

Petrography

40Ar/39 Ar age determination

Whole-rock geochemistry

Discussion

Conclusions

Acknowledgements

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