PECENEAGA-CAMENA FAULT: GEOMAGNETIC INSIGHTS INTO ACTIVE TECTONIC CONTACT ÓÄÊ 550.389:550.838 Peceneaga-Camena Fault: Geomagnetic insights into active tectonic contact L. Besutiu 1, M. Orlyuk 2, L. Zlagnean 1, A. Romenets 2, L. Atanasiu 1, I. Makarenko 2, 2014 1Institute of Geodynamics of the Romanian Academy (IGAR), Bucharest, Romania 2 Institute of Geophysics National Academy of Sciences of Ukraine, Kiev, Ukraine Received 18 July 2013 Presented by Editorial Board Member V. I. Starostenko Highly detailed, very accurate ground magnetic investigations were jointly conducted by Ro- manian and Ukrainian researchers on a segment of the Peceneaga-Camenas Fault (PCF) in order to reveal the potential of geomagnetic method for active faults investigating. The survey succeeded to outline the PCF track in the area covered by recent sediments, and provide in- sights on the fault structure and in-depth development. 2D numerical modeling has been em- ployed for interpreting the obtained geomagnetic anomaly. Lateral variations in magnetization, as suggested by the model, reveal the complex geological architecture in the area, hidden by recent deposits. The zero magnetization outlined in the central part of the survey lines has been interpreted in geodynamic terms, as a breccias zone created along PCF track by its active dy- namics. Key words: magnetic survey, magnetization, residual geomagnetic anomaly, modeling, faults, geodynamics. Ïå÷åíåæñêî-Êàìåíñêèé ðàçëîì: ãåîìàãíèòíàÿ îöåíêà àêòèâíîãî òåêòîíè÷åñêîãî êîíòàêòà Ë. Áåøóòüþ, Ì. Îðëþê, Ë. Çëàãíåàí, À. Ðîìåíåö, Ë. Àíàñòàñüþ, È. Ìàêàðåíêî, 2014 Ñ öåëüþ îöåíêè âîçìîæíîñòåé ãåîìàãíèòíîãî ìåòîäà ïðè èçó÷åíèè àêòèâíûõ ðàçëîìîâ ñîâìåñòíî ñ ðóìûíñêèìè è óêðàèíñêèìè ó÷åíûìè áûëè âûïîëíåíû âûñîêîòî÷íûå íàçåì- íûå èññëåäîâàíèÿ Ïå÷åíåæñêî-Êàìåíñêîãî ðàçëîìà (ÏÊÐ). Ñúåìêà ïîçâîëèëà ïðîñëå- äèòü ïîëîæåíèå ÏÊÐ ïîä ñîâðåìåííûìè îñàäî÷íûìè îáðàçîâàíèÿìè è ïîëó÷èòü ïðåä- ñòàâëåíèå î åãî ãëóáèííîé ñòðóêòóðå. Èíòåðïðåòàöèÿ âûäåëåííûõ âäîëü ïðîôèëåé ìàãíèò- íûõ àíîìàëèé áûëà âûïîëíåíà ñ ïîìîùüþ äâóìåðíîãî ÷èñëåííîãî ìîäåëèðîâàíèÿ.  ñîîò- âåòñòâèè ñ ìîäåëüþ, ëàòåðàëüíûå âàðèàöèè íàìàãíè÷åííîñòè èññëåäóåìîé çîíû ñâèäå- òåëüñòâóþò î ñëîæíîì ãåîëîãè÷åñêîì ñòðîåíèè, ñêðûòîì ïîä ìîëîäûìè îñàäêàìè. Îá- ëàñòü êîðû ñ íóëåâîé íàìàãíè÷åííîñòüþ, êîòîðàÿ âûäåëåíà â öåíòðàëüíîé ÷àñòè ãåîìàã- íèòíûõ ïðîôèëåé, ïðîèíòåðïðåòèðîâàíà ñ ãåîäèíàìè÷åêèõ ïîçèöèé êàê ïîÿñ áðåê÷èðî- âàííûõ ïîðîä, îáðàçîâàííûõ âäîëü ÏÊÐ âñëåäñòâèå àêòèâíûõ ïåðåìåùåíèé ïî íåìó. Êëþ÷åâûå ñëîâà: ìàãíèòíàÿ ñúåìêà, íàìàãíè÷åííîñòü, îñòàòî÷íàÿ ãåîìàãíèòíàÿ àíî- ìàëèÿ, ìîäåëèðîâàíèå, ðàçëîìû, ãåîäèíàìèêà. Ãåîôèçè÷åñêèé æóðíàë ¹ 1, Ò. 36, 2014 133 L. BESUTIU, M. ORLYUK, L. ZLAGNEAN, A. ROMENETS, L. ATANASIU, I. MAKARENKO General consideration. The Peceneaga-Ca- 1976] has revealed its crustal nature, showing a mena Fault (PCF) represents one of the most studi- step of about 10 km at the both Conrad and Moho ed tectonic features in the Romanian territory, even discontinuities. Later on, seismic tomography ima- from the beginning of the 20th century [Mrazec, 1912; ges based on CALIXTO experiment [Martin et al., Macovei, 1912]. It generally appears (Fig. 1) as the 2006], have revealed PCF as a major lithospheric boundary between the Moesian Platform (MP), re- contact between East European Plate (EEP) and presented in the area by Central Dobrogea (CD), Moesian Micro-plate (MoP) reactivated during the and North Dobrogea (ND) geological units. W Black Sea opening [Besutiu, Zugravescu, 2004; During the time, PCF has been alternately con- Besutiu, 2009]. sidered as a simple reverse fault [Macovei, 1912], Geological evidence shows a PCF geodynamic or the over thrusting plan of the hypothetic Green evolution during the time with both right-lateral and Schists Nappe [Preda, 1964]. More recent research left-lateral slip episodes [Pavelescu, Nitu, 1977; San- pointed out its strike-slip nature [Sandulescu, 1980; dulescu, 1980; Gradinaru, 1984; 1988; Seghedi, Oaie, Gradinaru, 1984; Hippolyte et al., 1996; Besutiu, 1997; 1995; Banks, Robinson, 1997; Cosma et al., 2010]. Banks, Robinson, 1997]. The Baspunar Geodynamic Observatory (BGD) Geophysics brought significant evidence on the was especially designed and run by the Solid Earth PCF in-depth extent. The international deep seis- Dynamics Department at the Institute of Geody- mic soundings (DSS) line ¹ 2 [Radulescu et al., namics of the Romanian Academy in order to moni- Fig. 1. Simplified tectonic setting of PCF and location of the study area: 1 — North Dobrogea boundaries (a — cropping out, b — covered); 2 — strike—slip faults; 3 — structural axes (a — syncline, b — anticline); 4 — boundaries between North Dobrogea main units (a — cropping out; b — buried); 5 — Cirjelari-Camena Outcrop Belt (a — cropping out, b — covered); 6 — episutural post-tectonic cover; 7 — river; 8 — settlements (a — major cities; b — villages); 9 — Baspunar Geodynamic Observatory (BGD) location; PDD — Predobro- gean Depression; ND — North Dobrogea; CD — Central Dobrogea; BB — Babadag Basin. 134 Ãåîôèçè÷åñêèé æóðíàë ¹ 1, Ò. 36, 2014 PECENEAGA-CAMENA FAULT: GEOMAGNETIC INSIGHTS INTO ACTIVE TECTONIC CONTACT Fig. 2. Simplified geologic sketch of the study area (modified after [Gradinaru, 1988]): 1 — Quaternary; 2 — Babadag basin, Episutural sedimentary cover; 3—9 — CCOB (3 — Baspunar Melange; 4 — Formation Sfanta (a), Amara Formation (b), 5 — Amara Breccia; 6 — Baspunar Spilite; 7 — Baspunar Formation; 8 — Camena Rhyolite; 9 — Aiorman Formation); 10—13 — Magin unit (10 — Uspenia Formation, 11 — Cirjelari Rhyolite, 12 — Camena Formation, 13 — Lower Paleozoic (marbles, quartzites and argillites)); 14—16 — Central Dobrogea (14 — Infragrauwacke, 15 — Lower Grauwacke, 16 — Upper Grauwacke), 17 — settlement; 18 — quarry; 19 — cross-section location; 20 — BGD; 21 — magnetic survey panel; 22 — PCF track (a — exposed, b — covered). tor slip along PCF. This paper mainly deals with mena Outcrop Belt (CCOB). A thorough descripti- results of the high accuracy detailed magnetic in- on of the structure and lithostratigraphy of this unit vestigations carried out on the PCF segment loca- was provided by Gradinaru [Gradinaru 1980, 1984, ted in the neighborhood of the BGD, aimed at re- 1988], and a simplified geological sketch for the stu- vealing the path and in-depth structure of the PCF dy area is shown in Fig. 2, along with the location in the monitoring area. Research has been carried of the magnetically surveyed panels. out in the frame of the bi-lateral project INRAF (“In- On the overall, the study area is dominated by the tegrated research of some active faults located in presence of the Jurassic sedimentary and volcanic the NW inland of the Black Sea on the Romanian rocks, unconformable overlying older Palaeozoic de- and Ukrainian territories”), jointly developed by the posits of the Macin Unit and largely covered by the Institute of Geodynamics of the Romanian Acade- post-tectonic sedimentary cover of the Cretaceous my and the Institute of Geophysics of the National Babadag Basin and shallow Quaternary formations. Academy of Sciences of Ukraine. The Quaternary rocks are mainly represented The local geological background. North by shallow layers of loess deposits. Dobrogea. The area subject to geophysical inves- The Babadag Basin comprises two main Upper tigation mainly belongs to the so called Cirjelari-Ca- Cretaceous formations: Iancina and Dolosman se- Ãåîôèçè÷åñêèé æóðíàë ¹ 1, Ò. 36, 2014 135 L. BESUTIU, M. ORLYUK, L. ZLAGNEAN, A. ROMENETS, L. ATANASIU, I. MAKARENKO ries mainly consist of limestone and sandstone, rite schist), and Carboniferous, represented by Carape- with transient facia (between sandy limestone and lit Fm (conglomerates, sandstones and schist series). limy sandstones). Overall, the Upper Cretaceous do- The bimodal (acid and basic) CCOB volcanic Pz es not contain any source of geomagnetic anoma- rocks may be grouped into Camena Rhyolite ( 3) J lies, except for some residual red shale deposits, and Baspunar spilite ( 3). T locally developed within confined volumes, but able The Camena Porphyries ( 3?) crop out between to provide slight geomagnetic effects at the surfa- Cara Burun Hill (Camena) and Baspunar, and seem ce [Besutiu, Nicolescu, 1999]). to be connected to the tectonic lineament Baspu- Jurassic rocks of CCOB (Gradinaru, herein) may nar-Camena. They pierce the Proterozoic crystalli- be grouped into several main sedimentary formati- ne series, but occur as remnants in the Liassic cong- ons (Fm): lomerates. They have been described as micro-gra- Fm J – Cirjelari ( 3 ox-km) is composed of: 1) gaizes, nites accompanied by dykes [Mirauta, Mirauta, 1961], spongolites, tuffittes, 2) polimictic conglomera- tuffs, ignimbrites and lava flows [Gradinaru, 1984]. J tes, 3) (marly and silty) shales, 4) bioclastic cal- The Baspunar spilite ( 3) is mainly represented carenites and calcirudites, 5) oolitic calcareni- by pillow-lava flows interbeded in Jurassic limestone. tes. Also in the Cirjelari Fm mixtites with Green Central Dobrogea (CD). South PCF, CD de- Schist clasts, Cirjelari Rhyolite clasts, and oli- posits are mainly represented by the Upper Prote- gomictic conglomerates may occur; rozoic Green Schist Series (GSS), largely descri- Fm J – Baspunar ( 3 ox) consists of: 1) gaizes, spon- bed during the time by various authors [Mrazec, golites, tuffittes, 2) crinoidal calcarenites, marl- 1910, 1912; Macovei, 1912; Mirauta, Mirauta, 1961; stones, marly shales, 3) rhyolitic tuffs at the bottom; Mirauta, 1964, 1965, 1969; Paraschiv, Paraschiv,