Geological Society of America Bulletin 1970 FEININGER 1201 16

8/13/2019 Geological Society of America Bulletin 1970 FEININGER 1201 16

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Geological Society of America Bulletin

doi: 10.1130/0016-7606(1970)81[1201:TPFC]2.0.CO;21970;81, no. 4;1201-1216Geological Society of America Bulletin

TOMAS FEININGERThe Palestina Fault, Colombia

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TOMAS FEININGER U.S.GeologicalSurvey Medellln Colombia

ThePalestina Fault Colombia

BSTR CTT h e Palestina fau l t i s an inact ive r igh t - la tera lwrench fau l t more t h an350 km long in the largelymetamorphic and igneous terrain of the northernCentral Cordillera of the Colombian Andes. Itstrikes north to north-northeast, nearly parallelto the reg ional An d ean s t ru c t u res . Much of thef a u l t is fol lowed by straight canyons 50 to 600 mdeep.Azoneofb reccia and mylomte lessthan 50 mthick marks th e fau l t . Rock i s in tensely f rac turedwithin 50 m of this b reccia zone. Defo rmat i o n a leffects of the Palestina include large fault-blocksliversof megabreccia and drag tails thatcontainsome allochthonous material. A g rav i t y profi leacross the Palestina showsno associated anomaly.Horizontal d i sp l acemen t on the Palestinaof27.7km iswell documented because the fau l t ha s offsetten u n i q u e hthologic, metamorphic, and s t r u c t u ra lfea tures that have been mapped on both blocks.

These offset f ea tures are:marble, q u a r t z i t e fe ld-spath ic and a l u m i n o u s gneiss dionte, zones ofdiorite mixed with Precambrian gneiss hornblendegabbro, Cretaceous shale, metamorphic isograds am a j o r wren ch fau l t an d several minor fau l ts .The Palestina fau l t ison lyone of several recentlyrecognized w r e n c h fau l ts in the northernCentralCordillera, and its documentation should call atten-tion to the possible importance of these f ea tures inthe t ecton ics of the area.Published analysesof wrench-fault tectonics innorthern Colombia and Venezuela assume a genet icrelat ionsh ip between al l the wrench f a u l t s : t h eyoriginatedinresponseto a singleu n c h a n g i n g reg ion-al stresssystem. A moreme a n in g fu l ana lys i s mightresul t from th e i nd i v i dua l s tudy of smal lergeo-graphic areas and considerat ion o f the r e l a t i ve agesof the wrench faul ts .INTRODUCTION

Wrench faults and their role in the struc-tural evolution of the earth's crust have beenappreciated only rece ntly, as is apparent by thepaucity of lite rat ure on these feature s prior to1950. This is largely due to the d i f f i cu l t y inrecognizing most wrench faults and in docu-menting the sense and magnitude of theirdisplacements. In the words of deSitter (1964,p. 143-144): As regards the larger wrenchfaults, it is for several reasons extremelydif f icu l t to prove anything except their strike,and relativelyfew are definitely determined aswrench faults. Of these several reasons, thefollowing are particularly important: (1) Rockalong most wrench faults is either deeplyweathered or covered by alluvial deposits(deSitter, 1964, p. 144). (2) The verticalcomponent ofmovement onsome wren chfaultsis conspicuous, and accordingly they may bemisinterpreted as normal faults (deSitter,1964, p. 144). (3) Commonly the relativepositions of homologous elements on oppositesides of a wrench fault do not allow an un-equivocal interpretation of whether the dis-placement is due to horizontal or verticalmovement or both (deSitter, 1964,p. 144).(4) The displacement on many wrench faults

isso large that geologic mapping of restrictedareas may not encounter correlative elementson the two sides of the fault.Once a wrench fault has been recognized,especially if it is a large one,opinions on themagnitude of displacement commonly varygreatly among geologists. An example is theDeath Valley-Furnace Creek fault zone ofCalifornia. Here, 50 mi of displacement ispostulated by Stewart (1967), 30 mi by McKee(1968),and 5mib yWright and Troxel (1967).Even the sense of movement on some wrenchf a u l t sisdisputed.The Boconofault,Venezuela,is interpreted by Rod (1956) as right-lateralwith33 km ofdisplacement, whereasRaasveldt(1956) interprets the same fault asleft-lateral.To date, probably only onelarge wrench fault,the Great Glen fault in Scotland, is so welldocumented (Kennedy, 1946)that nodoubtislef t as to either its senseor exact magnitude ofdisplacement.The purpose of the present paper is threefold.One is to discussin some detail a recentlydis-covered wrench fault in Colombia, that hasalmost 30 km of right-lateral displacement.Thisfault, here named th e Palestina fault,ca nbe documented with unusual precision becauseit haso f fset 10unique lithologic, metam orphic,an d structural featuresthat have been mappedGeological Society of Amer i ca Bu l l e t i n v. 81, p. 1201-1216,6 figs.,Ap r i l1970

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1202 T. FEININGER-THE PALESTINA FAULT, COLOMBIAon both sides of the fault. Restoration of thedisplacement of the fault with correspondingleft-lateral movement brings all ten featuresinto alignment across the fault trace. Anotherpurpose is to call attention to the possibleimportance of wrench faults in the tectonics ofthe north ern Ce ntral Cordillera of the Colombi-an Andes. The third purpose is to assess theregional significance of the Palestina andassociated wrench faults with respect to thetectonic frameworkof northern Colombia andVenezuela, and to discuss publishe d inte rpr eta -tions of wrench-fault tectonics in the region.Recognition and documentation of thePalestina fault is one result of the systematicregional geologic mapping program tha t is partof amineral-resources study of Colombia beingundertaken jointly by the Colombian Inven-tario Minero Nacional, Ministerio de Minasy Petroleos, and the U.S. Geological Survey.The join t study is sponsored by the ColombianGovernment and by the Agency for Interna-tional Development, U.S. Department ofState.THE P LESTIN F ULTGeologic andGeographic Setting

The Andes Mountains in Colombia formthree subparallel and geologically distinctCordilleras. The Palestina fault is on the eastflank of the Central Cordillera, near its northe rnend. Thispart of the Central Cordillera, whichlies between the Cauca and Magdalena Rivers,is composed chiefly of Paleozoic metamorphicrocks discontinuously mantled by Mesozoicsedimentary and volcanic rocks which in turnhave been intruded by enormous UpperCretaceous quartz diorite batholiths. Northof the latitude of Medellin, the CentralCordillera diminishes in alti tud e progressively,and about 300 km northeast of the city, itpasses beneath Tertiary and Holocene sedi-mentsof theLower Magdalena Basin (Fig. 1C).Th e terrain through which the Palestinafault passes ismountainous and maturely dis-sected. Level ground is restricted to sparsealluviated valleys that are generally no morethan 200m wide. Total relief isabout 700m ;altitudes range from 150 m on the Rio SamanaNortetonearly90 0 m onhillsin the northwest.Local relief is mostly 200 m or more, and inthe canyon of the Rio Samana Norte, it is asmuch as 600 m. Access is by m ule trails and therailroad. There are no roads.The climate is hot and humid. The averageannual temperature ranges from 25 to 29

C (77 to 84 F) , depending upon altitude.Seasonal variationsareabsent due to the near-equatorial location (lat. 6 30 N.), and frostsare unknown. Annual rainfall is between 300and 500 cm (120 and 200 in.) and is fairlyevenly distributed throughout the year, al-though January and February are the driestmonths (Banco de la Repiiblica, 1959, cartog.3) .Bedrock has been weathered deeply, andexposures of fresh rock are limited. Neverthe-less,outcrops are reasonablyplentiful in streamsand rivers, some of which afford nearly con-t inuous exposure of fresh rock over tens oreven hundreds of meters.Th ePalestina faultstrikes northeas t tonorth,and over much of its course, it roughly parallelsthe Magdalena River (Fig. 1C). Geologistsofthe Inventario have mapped the fault in thefield over a distance of 160 km, from the north-ern part of the Department of Caldas to nearthe town of Segovia in the Department ofAntioquia. It can be traced on aerial photo-graphs an additional 200 km to the north,where it islost to view under Holocene alluvi-um of the Magdalena River near the town ofEl Banco (Fig. 1C). The fault is known tocontinue south of the area mapped, but itsprecise course is unce rtain . The Palestina faultishere named after a station on the yard-gaugeAntioquian Railroad; this statio n is nearly a-stridethefault (Fig.1 A). It is theonly place onthe known length of the fault where it can bereachedon land by means other than mulebackor walking.Near the known limitsof the Palestina fault,satellite faults branch from it at low angles.Many of these satellite faults parallel thePalestina for considerable distances, and eachhas absorbed some of its displacement. Apartin southeastern Antioquia Department, mostof which is shown on F igure 1 A, may be theonly place where all lateral displacement oc-curred on the Palestina alone. It isd i f f i c u l t toweigh the importance of most of the satellitefaults relative toeach otheror to the Palestina.To the north thegeology ispoorly known,andto the south the trend of the rock unit s changesfrom south to south-southwest and becomesparallelwith the strikes of all the f a u l t s so thatestimates of thedisplacements on any of themare d i f f i c u l t to make. Nevertheless, meta-morphic isograds o f fset by the Jetudo fault(Fig. 1C) suggest 12 km of righ t-la ter al dis-placement, whereas the Palestina between theJetudo and El Mulato faults, based on the



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THE PALESTINA FAULT 1203offset of marble beds, has about 15 km ofright-lateral displacement. Th e total, 27 km,is very nearly the amount of displacement thatis well documented for the Palestina alone justto the north. Farther south, relationships ar eless clear. The Palestina fault just north of itsjunction with the Cocorna Su r fault may haveas little as 1 km of right-lateral displacement.Th e Cocorna Su r fault, however, appears tohave a large displacement, possibly exceeding20 km. Whether the Palestina could be recog-nized as a discrete entity far south of the map-ped area is not known. It may become lost in anetwork of wrench faults, each with smallright-lateral displacement.The part of the Palestina fault that has beenmost inte nsely studied by the In ven tario is azone 72 km long that is unaffected by satellitefaults and lies about 100 km east of Medelh n.A detailed geologic map (Fig. 1A) of a strip15 km wide and covering abo ut 1000 km 2centered on that 72-km stretch is the founda-tion of the ensuing discussions, unless statedotherwise.Gravity Data

While undertaking a gravity s urve y of north-western Colombia, Professor JamesE. Case ofTexas A. and M. University ran a gravitytraverse along the Antioquian Railroad fromMedellin to Puerto Berrio on the MagdalenaRiver. A part of that traverse centered on thePalestina fault is shown in the simple Bouguergravity profile reproduced in Figure 2. Thesmoothness of the profile across the Palestinashows that vertical displacement on the faultcannot be appreciable but is consistent withan interpretation of horizontal displacement.Field Characteristics

The most outsta nding field characteristics ofthe Palestina fault are its straightness and boldtopographic expression. Over most of itslength, the fault is marked by straight canyons50 to 600 m deep. For example, of the 72-kmstretch of the Palestina shown on Figure 1A,a length of 62 km is followed by nearly rectilin-ea r drainage that contrasts sharply with thedendritic drainage elsewhere in the area. Fromthe air, the fault trace looks like a colossaltrench, a virtually uninterrupted gash throughthe rugged mountainous terrain.The fault is marked by a narrow zone ofbreccia and mylonite that rarely crops out andis nowhere well exposed. In most streams thatflow along or across the fault, the zone is a gap

of no outcrop, 20 to 50 m wide, that lies be-tween exposures of intensely fractured rock.This gap is especially conspicuous in the RiosCupina, Nus, an d Samana Norte. The at t i tudeof the fault thus cannot be measured directly,but the regional straightness of the trace, eventhro ugh areas of great local relief, indicates thatit must be vertical or nearly so.Faultbreccia is exposed in 17 places along thePalestina in the 72-km stretch shown onFigure 1A, either in weathered (hydro-thermally altered?) outcrops or in residualboulders of fresh rock. Breccia is particularlywelldeveloped in marble (Fig. 3 ) and quartzite,but it has been found in all rocks cut by thePalestina. Clasts are angular and range fromless than 1 cm to 1 m across. They are set in adull-lustered cataclastic matrix, except inbrecciated marble where the matrix is chieflyrecrystallized white calcite. Clast-to-matrixratios exceed 2:1. Schistose mylonite derivedfrom a marble lens in Precambrian gneiss andcomposed entirely of extremely fine-grainedcalcite is exposed with breccia 1.2 km north ofthe RioCupina.On each side of the Palestina, lie belts ofintensely fractu red rock generallyno more than50 m wide (Fig. 4). Rock beyond these frac-ture belts shows no evidence of faulting.In a few places, the Palestina fault dividesto form a pair of nearly parallel faults that re-unite to enclose fault-block slivers of mappablesize.The largest sliver is in part followed by theRio Volcan and is 11 km long and less than 400m wide (Fig. 1A). The slivers consist of mega-breccias produced by drag along the fault.They are composed of jumbled rock masses,individually tens to perhaps hundreds ofmeters thick, that have been torn from theopposing fault blo cks during movement on thePalestina. For example, large masses ofCretaceous black shale are exposed in onefault-block sliver, 500 m south of the RioCupina. The nearest outcrops of this shalealong the fault, and the only possible sources,are 8 km to the north or 17 km to the south.Other large-scale effec t s of drag along thePalestina fault have been found. Th e mostobvious effects on the west block are the longsouthward-pointing tail of quartzite and theisolated small bodies of marble that extendsouthward from the main body of marblenearly to the railroad. The small marblebodies afford unequivocal evidence of em-placement by drag. This marble is distinctive;it is fine grained, gray, and extensively brec-



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-e- -ee- o --

r 0 MILLIGALS

2030

40

5 0

1000 METERS 50 0

10 KILOMETERS

Figure 2. ravitydata, Palestina fault. Bottom: sketch geologic map, letter symbols as on Figure 1.Light lines, contacts; heavy lines, faults. Circles are gravitystations. Middle: Geologic cross section projected from the route of the railroad onto a verticaleast-west plane. Top: Simple Bouguer gravity profile of the crosssection (gravity datagram Professor James E. Case).


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Figure3. Breccia alongthe Palestinafault. Boulder 4mlong) ofbrecciatedmarblein theRio Alicante,8 kmsouth-southeastof LaSusana.

Figure 4. Intensely fractured Precambrian feldspar-quartz gneiss adjacent to the Palestina fault on the eastblock, RioCupina.Black area at lower right is water-filledhole.



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1206 T. FEININGERTHE PALESTINA FAULT, COLOMBIAciated.The narrow elongate marble bodiesareparallel to the Palestina fault and not parallelto the regional structural trend of the adjacentrocks. Th e southernmost marble bodies areencased in feldspathic and aluminous gneissof high metamorphic rank (sillimanite grade).Nearby marbles, in beds 1 to 10m thick (toothin to show on the geologic map), that areintimately intercalated with the gneiss andclearly autochthonous are medium to coarsegrained and brilliantly white.The fine-grainedgray marble is obviously allochthonous; it wasnot metamorphosed at the site where it isactually found nor under the same conditionsas theadjacent gneiss,but instead formed else-where under conditions of low-grade regionalmetamorphism. The nearest outcrops ofmarble petrographically similar and largeenough to be a plausible source of the isolatedmarble bodies are in the RioAlicante south ofthe small stock of diorite, abou t 13 km nort hof the southernmost isolated marble body onthe west block. An analogous but smaller bodyof fine-grained brecciated marble emplacedbydragalong the Palestina fault occurson theeast block, 5 km north of the Rio SamanaNorte (Fig. 1A). Also, the south end of theCretaceous shale on the west block of thePalestina north of the Rio San Bartolomeappears to have been dragged southward insimilar fashion to the tail of quartzitementioned above. Outcrop in the area, how-ever, is scarce, and nei ther the shape nor thedetails of thisfeature are well known.Horizontal Displacement1

The drag features discussed above con-sistently indicate right-lateral displacementalong the Palestina fault. Simple inspection ofthe geologic map (Fig. 1A) suggests that thisdisplacement is nearly 30 km. The reality ofsuch a large displacement will be carefullydocumented in the following pages. To rein-force the arguments to be presented, I haveprepared a map in which the two blocks havebeen restored to the positions that they oc -cupied before movement on the Palestina

1Since the wri t ing of this paper, a grooved andslickensided vertical surface several square meters inarea has been exposed in the Palestina fault on an al-lochthonous block of marble (notshown onFig. 1 in acut along a relocation of the Antioquian Railroad about30 0m sou thwestof Palestina Station. Th e grooves an dslickensides bear N. 15 E. and are horizontal. A faintdirectio nal ro ughnes s along the grooves indicates right-lateral movement.

fault started (Fig. IB) . This map will here-after be called the reconstruction. The re-construc tion is not a geologic map of the areain pre-Palestina tim e, but rath er is a geologicmap of the present topographic surface of therestored blocks that prior to faulting was atdepth in the crust.The reconstruction was prepared in thefollowing manner. The south half of the eastblock was transferred from the geologic map(Fig. 1A) to the reconstruction (Fig. IB)with-ou t modification. Th e corresponding part ofthe west block was then traced onto the re-construction so as to be flush with the eastblock, and positioned so that the fault thatseparates marble and quartzite on each blockpassed without offset across the trace of thePalestina. This reconstruction restores 27.7 kmof righ t-latera l displacement on the Palestinafault.A fewmo difications, however, were madeon the west block. The drag featuresdiscussedearlierthe fault-block slivers, tails ofquartzite and Cretaceous shale, and isolatedmarble bodies south to the railroadwereeliminated. Furthermore, the Palestina isgently sinuous, barely evident on the geologicmap, south of the Rio Cupina. These slightcurves had to be ironed out to avoid gapsbetween or overlaps of the two blocks. Toachieve this, the west block had to be distortedlocally in the reconstruction. Nowhere didthisdisto rtion exceed 8 degrees of rotation, andmost was between only 2 and 4 degrees. AttheRioCupina, thePalestina curves northwardand within 6 km, its strike changes from N.16 E. to N. 2 E. This regional bend of thePalestina produces a gap between the blocksat the north end of the reconstruction. Th egap was left open, because it is not clear pre-cisely how it should be closed.Note,however,that restoring the small left-lateral wren chfault that hasoffset the Otiifault near the RioSan Bartolome, and restoring the poppedout wedge of quartzite bounded by wrenchfaults 5 km south of La Susana (Fig. 1A)would tend to close the gap. Thesesmall faultsmay be contemporaneous with the Palestina,in which case they should not appear in the re-construction.A similar reconstruction was made usinghigh-altitude aerial photographs. Two suchphotographs, each centered near where themarble of the metasedimentary rocks istruncated by the Palestina on the west andeast blocks, respectively, have been cut alongthe fault and placed oppositeone anotherso as



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THE PALESTINA FAULT 1207to restore the displacement of the Palestina(Fig. 5). The areasof the two photos are out-lined on the geologic map (Fig. 1A).Offset Features

Ten unique lithologic, metamorphic, andstructural features have been offset by thePalestina fault in theareaofFigure 1A. On thefollowing pages, these features and their dis-placements willbe discussed in detail.Marble. Th e most conspicuous unit withinthe Paleozoic metasedimentary rocks is fine-grained gray marble, which forms a north-striking belt asmuchas 3 kmwide.The marbleproduces a distinctive and unique topographymarked by groups of crowded haystack hills,50 to 350 m high, that have steep toverticalwalls which support only scanty vegetation.This topography is very evident on aerialphotographs (Fig. 5). Some horizons in themarble contain rhythmic 1- to 10-cm-thickbeds of white quartzite that weather intopositive relief and give outcrops an eye-catching ribbed surface. West of the Palestinafault, these horizons are particularly abundantnear the confluence ofQuebrada Guardasolandthe Rio Alican te, whereas to the east, they areabundant in the walls of caverns between thePalestina and Otu faults north of the RfoSamanaNorte.In the reconstruction, the marble forms asingle uninterrupted belt; furthermore, thetwo areas in which thin rhythmic quartzitebeds are intercalated with the marble arecontiguous, whereas today these areas areseparated bynearly 30 km.Quartzite. The marble isbounded by dis-tinctive fine-grained and finely laminated tanquartzite. In two places, however, the Otufault ha s cut out the quartzite and put themarble directly in contact with diorite.Quartzite on the west block faces diorite andCretaceous shale across the Palestina fault, andthat on the east block faces feldspathic andaluminousgneiss.The quartzite forms a single belt in the re-construction, and the two places on the westand east blocks of the Palestina fault where ithas been cut out by the Otu fault form asingle stretch 7 km long. In addition, asmallwedge of quartzite in normal stratigraphiccontact with marble, but in fault contact withthe main body of quartzite in QuebradaAlejandria on the west block (Fig. 1A), fallsdirectly opposite (in the reconstruction) acor-responding wedge of quartzite that is today

27.7 km away on the east block in the RioSamana Norte.Feldspathic and Aluminous Gneiss. Mostof the feldspathic and aluminous gneiss ismedium to coarse grained and migmatitic; itcontains pods and lenses of granite generallya few centimeters thick that are separated bysilvery-gray laminae composed of mica andsillimanite. In the south part of the area (Fig.1A), this gneiss is found on both sides of thePalestina, and the geologic map of that partalone does not suggest the presence of a majorfault. To the north, however, thegneisson thewest block faces quartzite, marble, and dioriteon the east block.In the reconstruction, the gneiss faces onlyidentical gneiss acrossthe traceof the Palestinaand formsacontinuous unit.

Diorite. Medium-grained, mostly saus-suritized and chloritized, massive to foliated,plutonic igneous rock that ranges from dioriteto quartz diorite in composition is here col-lectively called diorite on Figure 1.Excludinga small and faulted stock southeast of LaSusana, and two stocks near the Rio SamanaNorte (Fig. 1A), all the diorite lies north andeast of the Otu fault. The two largest bodiesof diorite, one on each side of the Palestinafault, are roughly triangular on the geologicmap. Each isbounded by the Otu andPalestinafaults and Cretaceous shale (partly in faultcontact to the south). Movement along thePalestina hasplaced thediorite incontact withsuch diverse rock types asPrecambrian gneissand Paleozoic feldspathic and a luminous gneiss,quartzi te, and marble.In the reconstruction, the twolargest bodiesof diorite that today are completely separatedfrom one another are united to form a singlebody of batholithicdimensions. Also, the smallstock southeast of La Susana falls directly op-posite an even smaller stock presently in theRio Samana Norte, 27.5 km to the south. Th ediorite of the two stocks is virtually identical.It is composed of saussuritized subhedral toeuhedral plagioclase, euhedral hornblende thathas light-yellow to dark green-brown pleo-chroism and pronounced dispersion (r > v),thoroughly chloritized biotite, and anhedralstrained quartz. Accessories include apatite oftwo generations, and clear subhed ral zirconssurrounded by weak pleochroic halos inchlorite. A modal analysis of a random samplefrom each of the two parts of what clearly was asingle stock in pre-Palestina time is given inTable 1.



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Figure 5. High altitude aerial photographic reconstruction of a part of the Palestina fau l t Notehaystackhilltopography producedbymarble. Areas coveredbyphotosareindicatedonFigure1A.



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THE PALESTINA FAULT 1209The small wedge of diorite along thePalestina f a u l t on thewest block thatcrops ou tas a southward-pointing appendage on thestock southeast of La Susana, is not matchedby a corresponding body of diorite on theeast block. This relation suggests that the

wedge is a piece torn from the contiguousstock to the north and was emplaced tec-tonically during movement on the Palestina.Although this could not beproved in the field,it is a plausible explanation and is compatiblewith thepreviously described well-documenteddrag features on the same block only a fewkilometers to the south. Accordingly, thewedge has not been included in the recon-struction.Zones of Diorite Mixed with PrecambrianGneiss. In a few places, not shown on thegeologic map, the diorite is so thoroughlymixed with the Precambrian gneiss that it isuncertainwh eth er such areas should bemappedasdioriteo rgneiss. Where diorite predomin ates,the mixture is an intrusive breccia containingdiscordant inclusions of gneiss without pre-vailing orientation. Where the two rocks aresubequal, the diorite forms countless irregulardiscordant to concordant intrusive bodies,ranging from 1 to 100macross, in the gneiss.The only extensive areasof this mixed rockare in the Rio Cupina on the west block be-tween theO tuand Palestina faults,and on theeast block along the railroad in QuebradaMalena between the Palestina and Nus faults.Today these unique exposures are 29.5 kmapart where truncated by the Palestina fault.In the reconstruction, they are separated byless than 2 km.Hornblende Gabbro. A half dozen stocksof distinctive dark-green to black coarse-grained hornblende gabbro, ranging in areafrom a few thousand square meter s to 1.5 sqkm, occur adjacent to the Palestina fault.Two of the stocks lieclose to one another onthe west block, east of La Susana; the otherfour stocks form a cluster near the railroad onthe east block. Presently the stocks arewidelyscattered, and the most distant are 30 kmapart. In the reconstruction, however, the sixstocks form a relatively compact northeast-trending group in which the most distant areonly 12 km apart.Cretaceous Shale. A narrow north-strikingbelt of crumpled Cretaceous black shale thatcontains fragmentary plant fossils has beenoffset by the Palestina fault (Fig. 1A). Theseparation of the truncated ends of the belt is

T BLE 1. MOD L ANALYSES OF TwoSAMPLES OF DIORITESampleAG-705A HG-766

QuartzPlagioclaseAmphiboleChlorite and biotiteAccessories

10.565.013.410.01.1

8.358.823.88.90.2T o t a l 100.0 100.0

AG-705A, from west block, 7 km south-southeast ofLa Susana; HG-766, from east block,RioSamanaNorte6 km nor th of the R io Nare .Analysesin volume percent based on about 1000 pointcounts, each spaced over standard thin sections.26.3 km, which is a little less than the offsetof therocks discussed above. The precise causeof thisdiscrepancy is unknown. Perhapsduringmovement on the Palestina, rocks in thenorthern part of the area (Fig. 1A) were de-formed plastically in a broad zone borderingthe fault that could not be recognized in thefield.Displacement on the fault measured bymatching offset featur es at or near the faultplane in the zone of plastic deformation wouldtherefore be less than the displacementmeasured by the use of reference points outsidethe plastically deformed zone. Conversely, inthe south, deformation caused by movementon the Palestina may have been entirelybrittle an d restricted to the narrow discon-tinuous zones on each side of the Palestina inwhich arefound the tail ofquartzite on thewest and the small bodies of brecciated marbleon both blocks (described earlier).Under theseconditions, the displacement of rocks con-tiguous to the fault, excluding the al-lochthonous products of brittle deformation,would begreaterin thesouth thanin thenorth.On the other hand, the lesser offset of theCretaceous shale relative to the other rocksmay be related to the northward bend of thePalestina fault that begins at the Rio Cupina.Duringmovement on the fault, the west blockwould have been subjected to compression bytheeast blockas it moved relatively southwardalong this bend. Such compression on the westblock would be most intense in the area nowbounded by the Rio San Bartolome and thesouthern stock of hornblende gabbro. If thecompression could produce a shortening of alittle more than 1 km on that part of thewestblock, it would account for the discrepancy.



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1210 T. FEININGER-THE PALESTINA FAULT, COLOMBIAIt may be significant that the other offsetfeatures on the west block, all of which havevirtually identical displacements (27.7 + 0.3km), are south of the bend in the Palestinaand would therefore not have beenaffected bythe proposed compression.

Metamorphic Isograds. Th e intensity ofmetamorphism of the Paleozoic metasedi-mentary rocks varies appreciably. Threemetamorphic grades have been recognized inthin-section study of mineral assemblages inpelitic beds: high-grade sillimanite-bearingrocks; middle-grade rocks containing an-dalusite or staurolite; and low-grade (green-schist facies) rocks containing only quartz,micas, and albite. Rocks of each of the threegrades on both blocks have been delimited bya pair of metamorphic isogradsthat are locatedwith an accuracy of + 500 m. In the recon-struction, the isograds fall within 250 m of aperfect match acrossthe traceof the Palestina.

t Fault. On the west block of thePalestina, a major regional fault, the Otu,joins the Palestina 6.3 km southeast of LaSusana. Near that junction, the Otu separatesmarble an d diorite. Another major fault thatseparates the same two rock units on the eastblock joins the Palestina near the Rio SamanaNorte, 27.6 km south of the junction with theOtu.In the reconstruction, these two majorfaults no t only fall opposite each other, bu tthey meet the trace of the Palestina at identicalanglesand cross it as a straight line. Clearly thetwo are the same fault (th us they have beengiven a single name) that predates and has beenoffset by the Palestina.Minor Faults. Three minor faults cu tmarble, quartzite, and diorite on the westblock of the Palestina just south of the Otiifault. Two minor faults were mapped in cor-responding positions on the east block alongthe Rio Samana Norte. It is possible that thethird fault ispresent aswell, but the extremelyrugged topography of the Samana Nortecanyon makes detailed mapping there impos-sible.VerticalD isplacement

Th e gravity data discussed earlier (Fig. 2)and the excellent match of offset featuresachieved in the reconstruction through solelyhorizontal movement indicate that th e amountof vertical displacement on the Palestina faultmust be small. Nevertheless, evidence affordedby the marble unit suggests that some vertical

displacement may have taken place, and thatthe east block may be slightly downdroppedrelative to the westblock.Structu ral attitu des and the distribut ion ofmetamorphic isograds on the west block showthat the marble occupies a syncline. Althoughthe rocks are intensely crumpled and inplaceseven isoclinally folded, the syncline isshallow.Local topographic reliefis great enough so thatat an altitude of about 350 m in the deepcanyons of the Rios Cupina and Alicante andsome of their tributaries, the underlyingquartzite in the keelof the synclineis exposedat several places. Furthermore, the synclineisshallow enough to have allowed the marbleto beentirely eroded from the upthrown blockof a small normal fault between the RiosCupina and SanBartolome (Fig. 1A).On the east block, however, the base of themarble unit is nowhere exposed in the keelof the corresponding syncline, not even in theSamana Norte canyon at altitudes as low as150 m. These data imply that the east blockis downthrown at least 200 m relative to thewest block. Structural data are inadequate,however, to indicate the precise plunge of thesyncline, and some or evenall of the proposedverticaldisplacement may beillusory.Age

Movement on the Palestina fault cannot bedated precisely. The youngest rock offset bythe Palestina is the Cretaceous shale.2 Fossilsin the shale nearRemedios,about 30 km northof the area shown on Figure 1A, establish anAlbian-Aptian (middle Cretaceous) age. Thedisplacement of the Cretaceous shale, however,is a little less than that of the other (and older)rocks,as was pointed out ear lier. At first glance,this relation might be taken as evidence ofsome pre-Albian-Aptian movement on thePalestina. This suggestion must be rejected,however, because the same Cretaceous shaleistruncated by the Otu fault just east of the

2 In a new exposure along a relocation of the Ant io -quian Railroad 100 m southwest of Palestina Station,brecciated migmatit ic feldspathic an d a luminous gneisshas been cut by two parallel 75-cm-thick, f ine-grainedintermed iate dike s. All rock in the exposure is thoroug hlyweathered, and it is no t possible to determine preciselyth e composition of the dikes. The t ex ture an d generalaspect of the dikes, however, ar e l ike those of the young-es t dikes known in the area which ar e genet ical ly re -lated to the nearby Antioquian batholi th. If thispro-posed correlation is correct, then al l movement on thePalestina fault would be pre-Tertiary.



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REGIONAL SIGNIFICANCEOF THE PALESTINAFAULT 1211area of the geologic map (Fig. 1A). As theOtu has inturn been displaced by thePalestina,the post-Albian-Aptian age of the Palestina isfirmly established; hence, mechanisms suchasthose discussedin the sectionon theCretaceousshale, rather than pre-Albian-Aptian move-ment, must be invoked to account for theslightly lesser displacement of the Cretaceousshale relative to the other rocks.Considerable evidence indicates that thePalestinafaultis nolongeractive.No seismicityrecorded at the Geophysical Institute of thePontificia Universidad Javeriana, Bogota, canbe correlated with the trace of the Palestina orits satellite faults in Antioquia (J. RafaelGoberna, S.J., 1966, written commun.).Furthermore, such morphologic features char-acteristic of active wrench faults asscarps,sagponds, truncated spurs, and offset drainage areall wanting along the Palestina. To be sure,muchof thedrainage from thehighlands to thewest is sharply deflected by the Palestina andfollows it for considerable distances beforeresuminganeastward course to theMagdalena.Thisis partly because the breccia and myloniteof the fault zone are easily eroded, and also be-cause in most places the fault is a boundarybetween unlike rocks that have unlike re-sponses to erosion. The deflections, however,have no directional preference. The Ri'osVolcan andNusfollow the Palestina southward8.5 and 1.5 km, respectively, whereas theAlicante andSamanaNortefollowitnorthward13 and 9 km, respectively. Other drainage,such as the Rios San Bartolome and Cupina,and Quebrada Malena, cross the Palestinawithout deflection.REGIONAL SIGNIFICANCEOF THEPALESTINAFAULTNorthernCentralCordilleraofColombia

Documentation of large displacement on thePalestina fault should call attention to thepossible importance of wrench faults in thetectonic framework of the northern CentralCordillera of Colombia. In addition, recogni-tion of the field characte ristic s of the Palestinahas provided insight on nearby faults newlydiscovered by the Inventario Minero Nacionaland on faults previously known but poorlyunderstood. Four such faults are discussedbelow.Otu Fault. An important result of deci-phering the Palestina fault's displacement hasbeen thediscovery that the Otu fault does no t

terminate to thesouth at thePalestina, but hasinstead been cut and o ffse t by it. Inventariogeologists have mapped the two segments ofthe Otu throu gh a distance of 90 kmthesouth segment from where it emerges frombeneath Tertiary sediments in the MagdalenaValley (Fig. 1C) to the Palestina fault, and thenorth segment from the Palestina to a point20 km northwest of Segovia (Fig. 1C). Thenorth segment has been mapped on aerialphotographsanadditional30 kmnorthward towhere it is lost under Tertiary sediments atZaragoza.The Otiifault islike the Palestina in that ithas a narrow and inconspicuous breccia zone.Unlike the Palestina, however, the traceof theOtu is generally rather sinuous and has littletopographic expression; these charac teristicsare consistent with the known antiquity of theOtu relative to the Palestina.The Otu fault is a truly remarkable geologicboundary; it separates blocks of nearly totallydissimilar geology and lithology.This relationalone suggests that the Otu is a wrench faultwith large displacement. Only one rock, thediorite (Fig. IB ), is comm on to both sides ofthe Otii,although in very unlike distribution.Near the fault on the east block, the diorite isareally important or even dominant from theMagdalena Valley to apoint a fewkilometersnorth ofSegovia. On the west block, however,the diorite is restricted to small stocks in thesouth (Fig. IB). These stocks increase in sizeand abundance southward beyond the area ofthe geologic map (Fig. 1A). The distributionof the diorite suggests left-lateral movementon theOtii, theeast block having moved no rthrelative to the west block. Displacement mayexceed 70 km.The presence of extensive areas of Precam-brian and Ordovician rocks on the east blockof the Otu fault is significant. Such old rocksin Colombia are largely restricted to the Ser-rania de la Macarena and the Guyana Shield,both east of the Andes (Trumpy, 1943). Pre-cambrian and Ordovician rocks are known inthe Colombian Andes only in the Sierra Nevadade Santa Marta near the north coast (C. M.Tschanz, 1966, written commun.) in theGarzon Massif in the Eastern Cordillera southof Bogota (Hubach, 1957, p. 73;Radelli, 1962,p. 17), andasasmall areaof Precambriangneisson theeastflank of the Central Cordillera nearthe town ofPayande,250 km south of the areashown on Figure 1A (Dario Barrero, 1968,written commun.). The presence of old rocks



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1212 T. FEININGERTHE PALESTINA FAULT, COLOMBIAon the east block of the Otii fault could beinterpreted to mean that that block ha s beenbrought from the east, fromasitefarther with-in the continent. Th e postulated left-lateralmovement of the Otu would have resulted insuch transport.

The age of the Otu fault cannot bepreciselyestablished. It iso f fset by, and thus older than,thePalestina fault.How ever, the Otu is youn g-er than the middle Cretaceous shale which itcuts near the Rio Samana Norte 10 km southofVirginiasand 3 kmeastof theare a shownonFigure 1A.Cimitarra Fault. The Cimitarra is a long,straight, northeast-striking fault that passesnear the city of Barrancabermeja on the Mag-dalena River (Fig. 1C). It hasbeen mapped asa normal fault on which the southeast block isdownthrown (Servicio Geologico Nacional eInventario MineroXacional, 1967). The traceof the Cimitarra iseasily followed to the south-west on aerial photographs and iscontinuouswith a conspicuous fault followed by the RioAlicante and mapped by Inventario geologists.It is therefore given the same name on Figure1A.Field characteristicsof the Cimitarraarelikethose of the Palestina, though breccias areeven more abund ant and the zones of fractu redrock that parallel the fault are considerablywider th an those parallelto thePalestina.Topo-graphic expressionof the Cimitarraisbold, andnortheast of the area shown on Figure 1A, thefault is marked by rectilinear canyons of theRiosSan Bartolome, Ite,and Cimitarra.The long straight trace and topographicexpression of the Cimitarra suggest that it toois a wrench fault. Its sense of movement isunknown. Its displacement may be small, asthe dioriteoccupiesbothblocks justeastof thearea of Figure 1A. The Cimitarra dies outwithin the east block of the Palestina and nocorresponding fault occurs within the westblock.The age of the Cimitarra fault is unknown.It ispre-Pliocene,as it iscoveredby and has notdisturbed PliocenesedimentswestofBarranca-bermeja (ServicioGeologicoNacional e Inven-tario Minero Nacional, 1967). The relativelywide brecciaand shatter zonesof the Cimitarrafaultsuggest it has a shallower origin and there-fore is of a possibly younger age than thePalestina.Nus Fault. The long straight trace (Fig.1A)and striking topographic expression to the

south where followed by the Rio Nus, suggestthat the Nus fault may be a wrenchfault. Thisview is reinforced by the smooth gra vity profileacross the fault (Fig. 2) , which isirreconcilablewith large vertical displacement. Docum enta-tion of either the sense or magnitude of dis-placement of the fault, however, is hamperedby poor outcrop and the general concordanceof the fault with regional structu ral trends. TheNus fault does not appreciably disrupt thedistribution of the hornblende gabbro bodieswhich suggests that either the fault has littledisplacement, or movement on it predates thegabbro.No correspondingf a u l t hasbeen recog-nized between diorite and Cretaceous shaleon the west block of the Palestina, but outcropin criticalareasisexceedinglysparse.The Nus fault cuts and is thus younger tha nthe middle Cretaceous shale but is older thanthe Otii fault, as the Otu sh arply trun cat esthe Nus at the Rio Samana Norte 3 km eastofthe area of Figure 1A seeFig. 1C).Romeral Fault. A large north- south faultwest of Medellin (Fig. 6) was mapped andnamed the Romeral fault more than 40yearsago by Grosse (1926). Recent mapping by theFacultad Nacional de Minas, Medellin, andthe Inventariohas shown that the Romeral ismore than300 kmlong.At thenorthi temergesfrom under Tertiary sediments about 200 kmnorth-northeast of Medellin. Fifty kilometersto the southwest the fault coincides with astraight 20-km stretch of the canyon of theRio Cauca. From there to a point south ofManizales, the limit ofgeologic mapping, theRomeral parallels the Cauca several kilometersto the east.The nature of the Romeral is uncertain.Grosse (1926, p. 292) interprets it as a high-angle thrust. It s long straight course, however,is like that of a wrench fault, and its fieldcharacteristicsarelikethoseof the documentedwrench faults to the east (Fig. 6) . Incompletemapping by the Inventario near the north en dof the fault suggests possible right-lateral dis-placement of several tens of kilometers. Else-where the Romeralisconcordantwith regionalstructure and consequently its displacement isobscured.The Romeral is covered by and has notfaulted Tertiary sediments in the north. South-west of Medellin, however, the Romeral faultcuts the middle of the three Tertiary units;this unit wasmapped by Grosse (1926, p.292,map 3) anddatedaslateOligocene by Van der



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Ciudad BolivarE X P L A N A T I O N

Wrench faultDashed where inferred

1) Alberding 1957)2) Barr 1958)3) ampbell 1965)4)Grosse 1926)

0

(5) Raasveldt (1956)6 ) Rod (1956)7) Rod 1958)(8) Rod (1959)

100 200

Thrust faultSawteeth on upper plate9) Colombia Servicio Geologico Nacional

and Inventario Minero Nacional 196710 Unpublished mapping by the Colombia

Inventario Minero Nacional

300 KILOMETERS

Figure 6. Large wrench f aults of northern Colombia and Venezuela.


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REFERENCESCITED 1215of that system, but it seems less likely that thePalestina, Otii, and Cimitarra are a part of it.Will future geologists relate yet undiscoveredwrench faults farther south in the Andes to theCaribbean shears? I think not. Also, more at-tention must be given to the ages of the wrenchfaults. Few data have been published on this.Careful consideration of their relative agesmay reveal thatsomewrench faults wereactivein response to one stress field, and that this wasfollowed by later activity on other wrenchfaults oriented favorably to a different andyounger stress field. That the wrench faultsoriginated under such dynamic and changingconditions isvery compatible with the variedand complex geologic history of northernSouth America and should be kept in mindduring future investigations.ACKNOWLEDGMENTSThe accompanying geologic map (Fig. 1A)is the wo rk of 11 geologists of the Inventario

MineroNacional: A.Gomez P., H.Gomez M.,J. Gonzalez R. , G. Guarin C., Michel Her-melin, H. Lozano Q., P. Marin R., D. Mos-queraT.,O. Ramirez A., R.VeraL.,and C. J.Vesga, in addition to myself. The mapping ofmore than adozen other Inventario geologistshas been referred to, particularly in the prepa-ration ofFigure 1C.Photogeologic interpreta-tions byTaissirKassem,alsoof the Inventario,have been essential, especially in tracing thePalestina fault north of the geologic map intoareas that could not be visited in the field.Professor James E. Case, Texas A. and M.University, kindly gave permission to use thegravity data. Dr. Darfo Suesciin G. and Pro-fessor Gerardo Botero A. helped with thebibliography. Discussions on the regional geol-ogy of Colombia with my counterpart in theInventario program, Dario Barrero L., wereindispensable. Richard Goldsmith, U.S. Geo-logical Survey, offered helpful suggestions toimprove the original manuscript.

REFERENCES CITEDAlberding,Herbert, 1957,Application of principlesof w re nc h - fa u l t tectonics of Moodyand Hillto northern South Ame r i c a [and Trinidad]:Geol. Soc. Ame r i c a B u l l . ,v .68, no. 6, p. 785-790.Banco de la Republica, 1959,Atlas de economiaColombiana, primera entrega:Bogota.Barr,K. W., 19 8,The structuralframeworkof theCaribbean r:gion: 1st Caribbean Geol.Conf.,Antigua, British West Indies, 1955, Rept.,p. 33-51.Campbell, C. J., 1965,The Santa Marta wrenchf au l t of Colombia and its regional setting:4th Caribbean Geol.Conf., Trinidad,BritishWest Indies, 1965,Rept.,loose-leafpreprint.Carey,S.W ., 1958,The tectonicapproachtocon-tinental d r i f t , in Carey, S.W.,Editor Conti-nentald r i f t A symposium:Hobart, Austra l ia ,Geology Dept.,Tasmania Univ.,363 p.deSitter, L. U., 1964,Structural geology (2ded.):New York, McGraw-Hill,551 p.Grosse, Emil, 1926, El Terciario ca rbonifero deAntioquia: Berlin, Dietrich Reimer, 361 p.Hubach, Enrique, 1957, Contribucion a las un i -dades estratigraficas de Colombia: Bogota,Servicio GeologicoNacional,I n f o r m e no.1212,166 p.Kennedy, W. Q., 1946, The Great Glen fault:Geol. Soc. London Quart. lour., v. 52, p.41-72.Maxwell, J. C., and Wise, D. U., 1958,Wrench-fau l t tectonicsA discussion: Geol. Soc.America Bull.,v. 69, no. 7, p.927-928.McKee,E.H., 1968,Age andrateofmovementof

the northernpartof theDeathValley-FurnaceCreek faul tzone,California:Geol. Soc.Ameri-caBull.,v. 79, no. 4, p.509-512.Moody,J.D.,andHill,M .J.,1956,W rrench-fau l ttectonics: Geol. Soc. Ame r i c a Bull., v. 67,no. 9, p.1207-1246.Raasveldt, H. C., 1956, Fallas de rumbo en elnordeste de Colombia: Bogota, Revista delPetroleo,v. 7, no. 64, p. 19-26.Radelli, Luigi, 1962,Introduccion al estudio de lapetrografia del macizo de Garzon: Bogota,GeologiaColombiana,no. 3, p. 17-46.Rod, Emil, 1956, Strike-slip f aul t s of northernVe ne z ue la : Am. Assoc. Petroleum GeologistsBull.,v. 40, no. 3, p. 457-476.1958, Application of principles of w r e n c h -faul t tectonicsofMoodyand Hill tonorthernSouth America: Geol. Soc. America Bull.,v. 69, no. 7, p. 933-936.

1959,West end ofSerraniadel Interior,easternVenezuela: Am. Assoc. Petroleum GeologistsBull., v. 43, no. 4, p. 772-789.ServicioGeologico Nacionale Inventario MineroNacional, 1967, Geologia del cuadranguloH- l l , B a r ra nc a be rme ja [map]: Bogota, scale1:200,000.Stewart, J. H., 1967, Possiblelarge right-lateraldisplacementalongfaultandshear zonesin theDeath Valley-Las Vegas area, California andNevada:Geol. Soc.America Bull.,v. 78, no. 2,p. 131-142.Trumpy, Daniel, 1943,Pre-Cretaceous ofColom-bia: Geol. Soc. America Bull., v. 54, no. 9,p. 1281-1304.



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1216 T. FEININGERTHE PALESTINA FAULT, COLOMBIAVan derHammen,Thomas, 1958, Es tra t igraf ia del tions of right-lateral strike-slip displacement,Terciario y Maestrichtiano contmentales y Death Valley and Furnace Creek f au l t zones,tectogenes is de los AndesColombianos: Bogo- California: Geol. Soc. America B u l l . , v. 78,ta, Boletin Geologico, v. 6, p. 67-128. no. 8, p. 933-949.Wright L.A. and Troxell B.W. 1967,Limita-

MANUSCRIPT RECEIVED BY THE SOCIETY AUGUST15, 1969PUBLICATION AUTHORIZED BY THE DIRECTORS, IN -VE N T AR I O M l NERO NACIONAL COLOMBIA, ANDU.S. GEOLOGIC AL SURVEYAUTHOR S PRESENT ADDRESS: DEPARTMENT OFMINERAL SCIENCES, SMITHSONIAN INSTITU-TION, WASHINGTON,D.C.20560


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