Subduction of the Caribbean Plate and Basement Uplifts in the Overriding South American Plate" James N

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12-1985 Reply to Comment on "Subduction of the Caribbean plate and basement uplifts in the overriding South American plate" James N. Kellogg

William E. Bonini Princeton University

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Publication Info Published in Tectonics, Volume 4, Issue 7, 1985, pages 785-790. Kellogg, J. N. & Bonini, W. E. (1985). Reply to comment on "Subduction of the Caribbean plate and basement uplifts in the vo erriding South American plate". Tectonics, 4 (7), 785-790. ©Tectonics 1985, American Geophysical Union

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REPLY

James N. Kellogg

Hawaii Institute of Geophysics, University of Hawaii, Honolulu

Wil 1 Jam E. Bonini

Department of Geological and Geophysical Sciences, Princeton University, New Jersey

Since we wrote our paper [Kellogg and our overthrust model for the M6rida Andes Bonini, 1982], a great deal of new based on the observed gravity field, which information has been published about the Schubert fails to explain. The second complex Caribbean-South American plate comment concerned displacement on the boundary. We were pleased that recent Bocon• fault zone. We do not question multichannel seismic profiles of the South Schubert's estimates of displacement on Caribbean deformed belt [Lehner et al., the fault, but his tectonic interpretation 1983; Lu and McMillen, 1983; Ladd et al., of the fault is called into question by 1984] support our interpretation that observed geological and geophysical data. Caribbean oceanic crust is actively Finally, we use velocity vector triangles underthrusting the deformed belt north of to predict the relative movement of the Colombia (Figure 1). We also learned that North Andes block. recent drilling by Intercor [International Colombia Resources Corporation] for the NORTHWESTWARD ANDEAN OVERTHRUSTING Cerrej6n Coal Project northwest of the Sierra de Perij• [Reyes and Luna, 1983] Hospers and Van Wijnen [1959], Bell confirmed the existence of the buried [1972], Jordan [1975], Shagam[1975], thrust faults that we predicted (Figure Giegengack [1984], and Kohn et al. [1984] 2). Schubert [this issue] comments on a proposed that the Venezuelan Andes were brief part of our paper concerning the uplifted by thrusting. Bell and Jordan tectonics of the Venezuelan [M•rida] Andes proposed thrusting over both the Maracaibo [Figure 2]. We presented a regional and Barihas basins, while Hospers and Van tectonic interpretation of the Caribbean- Wijnen, Shagam, Giegengack, and Kohn et South American boundary and did not intend al. observed the asymmetry of the Andes to give a detailed review of the late and concluded that the primary direction Tertiary geology of the M•rida Andes. We of thrusting was to the northwest over the would like to respond to two of Schubert's Maracaibo basin. Hospers and Van Wijnen comments, however, that have broader [1959] and Schubert [1969] also noted that tectonic implications. The first concerns the basement block uplifts of the Venezuelan Andes could be compared to the Laramide orogenic structures in the middle Copyright 1985 and southern Rocky Mountains of the United by the American Geophysical Union. States. We propose northwestward overthrusting Paper number 5T0538. of the Maracaibo basin by crystalline 0278-7407/85/005T-0538502.00 rocks of the Andes on a thrust fault [22 ø- 78 6 Ke 1 logg and Bonini: Commentary

CARIBBEAN PLATE

10" N

SOUTH AMERICAN PLATE

6.4

NAZCA PLATE

9 50,0 1090km.

;' NORTH NAZCA ß / ANDES 6,4 ./ ,•/,/,/.'"-' '""•'/ AMERICAso '- CARIBBEAN

I I 80 ø 70 ø 60øW Fig. 1. Present-day plate motions [bold arrows] relative to the North Andeanblock (stippled pattern) showing average slip rates (in centimeters per year) during the last 5-10 m.y. Plate motions are also shownin the velocity vector diagram (lower right) showingaverage slip rates (in centimeters per year) [after Minster and Jordan, 1978].

25ø ] extendinginto the mantle and overriding the Maracaibo basin by 25 km (Figures 2 and 3) [Bonini et al., 1980; Kellogg and Bonini, 1982]. The dip of the thrust fault wouldexplain the shapeand amplitude of the gravity low associated with thick deposits of low-density sediments on the northwest flank of the Venezuelan Andes. In fact, contrary to Schubert's [this issue] assertions, there is geological evidence for thrust faulting 10o at the surface on the northwest margin of the Andes [Bellizzia et al., 1976; Bonini et al., 1977]. Along the 40-km-long trace of the Las Virtudes overthrust (Figure 2) pre-Cambrian (?), Paleozoic, and Lower Cretaceous rocks are thrust over Upper 8 ø Thrust faulting is also consistent with a bodyCretaceous, wave focalMiocene, mechanismandPliocene determination units. for a shallow earthquake on the northwest flank of the Andes [Dewey, 1972]. In our model much of the predicted thrust Fig. 2. Tectonic location map of western displacement occurs on a buried fault Venezuela and northeastern Colombia plane dipping shallowly to the southeast [after Kellogg and Bonini, 1982]. Kellogg and Bonini: Commentary 787

-100

-150

NW - Lake Mc•rc•caibo MeridoAndes LAS2,25-2.67VlRTUDES 2,60THRUST / •._..___._ /•BOCONO2,20-FAULT

E 20 2,zo 2.0 /

3,20 M 4O • • I • • • • I i i i i I . 50 100 150 200 km

Fig. 3. Northwest-southeast section from Lake Haracaibo to the Barihas Basin [after Bonini et al., 1980; Kellogg and Bonini, 1982]. No vertical exaggeration. Note the predicted buried thrust fault northwest of the Hgrida Andes. See Figure 2 for line of section.

(Figure 3) with little displacement at the tested by deep drilling and seismic surface fault traces. Burial of most of reflection studies. the fault trace would not be surprising in view of the rapid deposition of up to 6400 BOCONO FAULT ZONE m of Betijoque and Necesidad Formation conglomerates and sandstones on the In our 1982 paper we interpreted the northwest flank of the rising Andes in the limited displacement on the Bocon• fault last 12 m.y. [L•xico Estratigrifico de as intraplate deformation. To explain Venezuela, 1970; Zambrano et al., 1971]. better the present seismicity and Holocene This rapid deposition rate (6400 m/12 displacement on the fault zone, we propose m.y. = 0.5 mm/yr) is probably the result of that the Bocon• fault might be interpreted flexural loading and erosion from the as part of the eastern boundary of a North rapidly rising (0.8 mm/yr [Kohn et al., Andes block or microplate [Figure 1]. We 1984]) northwest flank of the Andes. have no objections to Schubert's [1982, Berg and Romberg [1966] inferred from a this issue] estimates of right-lateral similar gravity anomaly that crystalline offset on the fault. However, rocks of the Wind River uplift in Wyoming interpretation of the Bocon•fault as part had been thrust at least 20 km over the of the Caribbean-South American plate Green River Basin along the low-angle Wind boundary [Schubert, 1981, 1984], curiously River thrust fault. The fault trace was omitted in Schubert's [this issue] buried by sediments, but Berg and comment, encounters difficulties Romberg's low-angle thrust interpretation explaining the following geophysical and was confirmed by COCORPdeep crustal geological observations: reflection profiling in 1976 and 1977 1. Hult/.channel seismic profiles [Smithson et al., 1979; Hurich and indicate that Caribbean oceanic basement Smithson, 1982] that showed the Wind River is actively underthrusting the South thrust fault zone as a continuous Caribbean deformed belt [Lehner et al., reflector dipping30ø-38 ø to a depthof 24 1983; Lu and HcHillen, 1983; Ladd et al., kin. As we noted earlier, recent drilling 1984]. for the Cerrej6n Coal Project [Reyes and 2. Focal mechanisms for four shallow Luna, 1983] confirmed the existence of the earthquakes and 21 microearthquakes in thrust faults that we predicted would lie northern Colombia and northwestern buried northwest of the Sierra de Perij•. Venezuela indicate N49øW+ 8ø reverse We hope that our prediction of a buried fault displacement [Dewey, 1972; low-angle thrust on the northwest margin Vierbuchen, 1978; Perez and Aggarwal, of the Venezuelan Andes will also be 1980; Hutchings et al., 1981; Kellogg and 788 Kellogg and Bonini' Commentary

Bonini, 1982]. This northwestward prevented an aesthenospheric wedge and displacement is difficult to relate to volcanic arc from forming in the N55øEright-lateral strike-slip overriding plate. Compressire stresses in displacement on the Bocon• fault. the overriding plate in the last 10 m.y. 3. A zone of earthquakes suggesting a produced the basement block overthrusts of Benioff zonedips about 30ø to the the Santa Marta massif, Sierra de Perij• southeast under the Santa Marta massif and [Kellogg, 1981, 1984], and M•rida Andes. the Sierra de Perij• and terminates 200 km 2. The Panama volcanic arc terrane below the Maracaibo Basin [Dewey, 1972; began colliding with South America Pennington, 1981; Kellogg and Bonini, approximately 10 m.y. ago [Wadgeand 1982]. Burke, 1983]. The North Andes block or 4. The Sierra de Perij• and Sierra microplate [Figure 1] was subsequently Nevada de Santa Marta [the highest detached from South America along the Caribbean mountain range, about 5800 m] Bocono and East Andean frontal fault were thrust to the northwest and uplifted system [Pennington, 1981; Kellogg et al., 7-12 km in the last 10 m.y. These ranges 1983]. Subducti on of Nazca and Caribbean are 250 and 400 km, respectively, lithosphere continues beneath the North northwest of the Caribbean plate margin Andes block. If the simplifying proposed by Schubert [1981, 1984]. assumption is made that the North Andes 5. Estimates of Caribbean-North block is rigid and velocity rather than American movement can be combined with angular velocity vectors are used, the constrained estimates of relative motion South America-North Andes relative motion between North America and South America to vector (1.0 +__0.2 cm/yr, S55øW__+ 5ø ) can deduce the late Tertiary Caribbean-South be added to the Caribbean-South America American convergence as approximately 600- vector (2.2 +__0.5 cm/yr, S78øE+__ 10ø[ 1200 km in an east-southeast [Jordan, Minster and Jordan, 1978]) to obtain the 1975; Minster and Jordan, 1978; Sykes et Caribbean-North Andes vector shown in al., 1982] or eastward [Pindell and Dewey, Figure 1 (1.7 __+0.7 cm/yr, S52øE_+ 24ø). 1982; Burke et al., 1984] direction. The The magnitude and direction of the largest estimate of right-lateral offset Caribbean-North Andes vector are very along the Bocon• fault, based on an similar to our 1982 estimates for the apparent offset of the Caribbean frontal Maracaibo-Santa Marta area based on the thrust, is only 100 km [Stephan, 1977], length of the seismic zone, focal but most estimates are less than 50 km mechanisms, and structural and gravity [Gonzalez de Juana et al., 1980; Schubert, data (1.9 __+0.3 cm/yr, S50øE__+ 10ø). 1982; Giegengack, 1984]. Using block vector diagrams, Dewey and From the short-term seismicity, Pindell [1985] obtained comparable vector Aggarwal [1983] deduced a seismic slip directions for subduction beneath the rate of 1 _+ 0.2 cm/yr for the Bocono fault Maracaibo(3.2 cm/yr, S44øE)and t•e zone. Using a measured 100-m right- Cordillera Central (2.3 cm/yr, S56VE) lateral offset of glacial moraines, blocks. Schubert [1980] estimated a similar In summary, several predict ions of our average rate of strike-slip motion on the 1982 paper, a d•collement beneath the fault, 0.8 cm/yr for the last 12,000 South Caribbean deformed belt and buried years. To produce the estimated thrust faults northwest of the Sierra de displacement on the Bocono fault, a 1- Perij•, have been subsequently confirmed cm/yr slip rate could only have begun 10 by seismic surveys and drilling. We hope m.y. ago at the earliest and may have that our prediction of a buried thrust begun only 3 or 4 m.y. ago. fault northwest of the M•rida Andes will To explain better the observed be similarly tested by a seismic geological and geophysical data, we reflection survey or drilling. Schubert's propose the following speculative tectonic [1981, 1984] proposal that the Bocon• interpretation: fault is part of the Caribbean-South 1. We suggested in our 1982 paper that America plate boundary fails to explain for the last 40 m.y., Caribbean crust has Caribbean underthrusting of the deformed been underthrusting South America at the belt, regional seismicity, the formation South Caribbean deformed belt [Figure 1] of two mountain ranges, and estimated and subducting southeastward. The shallow magnitude of the relative plate motion. dip and slow rate of subduction of the We suggest that considering the Bocon• bouyant Caribbean lithosphere may have fault zone as part of the boundary between Kellogg and Bonini' Commentary 789

South America and a North Andes block northern South America' Continental better explains observed data. Successful application of the finite difference tectonic interpretations will explain the method, Tectonics, 4, 71-83, 1985. geophysical as well as the geological data Dewey, J. W., Seismicity and tectonics of and regional observations as well as the western Venezuela, Bull Seismol. Soc. details of local geology. We hope that in Am., 62, 1711-1751, 1972. the coming decade, precise geodetic Giegengack, R., Late Cenozoic tectonic measurements using the Global Positioning environments of the central Venezuelan System will help resolve the complex Andes, The Caribbean-South American Plate tectonic deformation in the northern Boundary and Regional Tectonics, edited Andes. by W. E. Bonini, R. B. Hargraves, and R. Shagam, Mere. Geol. Soc,_Am., 162, Acknowledgments. We thank R. Shagam 343-364, 1984. for his helpful comments on our Gonzalez de Juana, C., J. M. Iturra]de de manuscript. Figures were prepared by J. Arozena, and X. Picard Cadillat, Geolog•a Simmons. The manuscript was reviewed by de Venezuela y de sus Cuencas R. Pujalet and typed by C. ¾asui. Petrol•feras, 1031 pp., Ed{ciones Foninves, Caracas, 1980. REFERENCES Hospers, J., and J. C. van Wijnen, The gravity field of the Venezuelan Andes and Aggarwal, Y., Seismic slip rates and adjacent basins, Verh. _K. Ned. Akad. Wet. earthquake rupture zones in the southern Afd. Natuurk., 2_•3, 95 pp., 1959. Caribbean' Implications for plate Hurich, C. A., and S. B. Smithson, Gravity motions and earthquake hazard in this interpretation of the southern Wind River region, Abstr. Caribb. Geol. C.onf.• Mountains, Wyoming, .Geophysics, 47, 1550- 10th, 16, 1983. 1561, 1982. Bell, J. S., Geotectonic evolution of the Hutchings, L., T. Turcotte, J. McBride, and southern Caribbean area, Studies in Earth H. Ochoa, Microseismicity along and near and Space Sciences, edited by R. Shagam the Dolores shear zone in Anti'6quia, et al., Mem. Geol. Soc. Am., 13.2, Colombia, report, Woodward-Clyde, 369-386, 1972. Consultants for Interconexi•n El•ctrica Bellizzia, A., N.M. Pimentel, and R. O. S. A., Medellin, 1981. Bajo, MapaGeo16gico Estructural de Jordan, T. H., The present-day motions of Venezuela, scale 1:500,000, Minist. de the Caribbean plate, J. Geo•_hysRes., 80, Minas e Hydrocarb. Venez., Caracas, 1976. 4433-4439, 1975. Berg, R. R., and F. E. Romberg, Gravity Kellogg, J. N., The Cenozoic basement profile across the Wind River Mountains, tectonics of the Sierra de Perij•, Wyoming, Geol. Soc. Am. Bull. 77, Venezuela and Colombia, Ph.D. thesis, 647-656, 1966. Princeton Univ., Princeton, N.J., 1981. Bonini, W. E., E. Pimstein de Gaete, and V. Kellogg, J. N., Cenozoic tectonic history of Graterol (Compilers) Mapade anomal•asde the Sierra de Perij• and adjacent basins, Bouguer de la parte norte de Venezuela y The Caribbean-South American Plate •reas vecinas; scale 1:1,000,000, Boundary and Regional Tectonics, edited Venezuela Minist. de Energia y Minas, by W. E. Bonini, R. B. Hargraves, and R. Caracas, 1977. Shagam, Mem. Geol. Soc. Am., 16.2, 239- Bonini, W. E., J. D. Garing, and J. N. 261, 1984. Kellogg, Late Cenozoic uplifts of the Kellogg, J. N., and W. E. Bonini, Subduct ion Maracaibo-Santa Marta Block, slow of the Caribbean plate and basement subduction of the Caribbean plate and uplifts in the overriding South American results from a gravity study, Trans. plate, Tectonics, 1, 251-276, 1982. Ca_r.i.bb. Geol. Conf., 9th, 99-105, 1980. Kellogg, J. N., V. M. Godley, C. Ropain, and Burke, K., C. Cooper, J. F. Dewey, P. Mann, A. Bermudez, Gravity anomalies and and J. L. Pindell, Caribbean tectonics tectonic evolution of northwestern South and relative plate mot ions, The America, Trans. Caribb. Geol. Conf., Caribbean-South American Plate Boundary 10th, in press, 1983. and Regional Tectonics, edited by W. E. Kohn, B. P., R. Shagam, P. O. Banks, and L. Bonini, R. B. Hargraves, and R. Shagam, A. Burkley, Mesozoic-Pleistocene fission- Mere. Geol. Soc. Am., 162, 31-63, 1984. track ages on rocks of the Venezuelan Dewey, J. F., and J. L. Pindell, Neogene Andes and their tectonic implications, block tectonics of eastern Turkey and The Caribbean-South American Plate 790 Kellogg and Bonini' Commentary

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