The evolution of Middle America and the Gulf of Mexico-Caribbean Sea region during Mesozoic time THOMAS H. ANDERSON I Department of Geology and Planetary Science, University of Pittsburgh, Pittsburgh, Pennsylvania VICTOR A. SCHMIDT | 15260 ABSTRACT Geometric constraints suggest that of Central America, the Nicaraguan Rise, probably shear initially occurred along the and southeastern Cuba) was sutured A plate-tectonic model for the evolution Mexican volcanic zone near the end of the against the Maya East plate along the of Middle America and the Gulf of Mex- Middle Jurassic. Subsequently, probably present Motagua fault and Cayman ico-Caribbean Sea region is presented. about 160 m.y. ago, displacements that Trench. The model, which is based upon the exist- total ~800 km began along the Mojave- Our model is constrained by published ence of the Mojave-Sonora megashear, Sonora megashear. Contemporaneously, geologic data, the relative positions of incorporates into the Triassic Pangea re- Yucatan and fragments of pre-Cretaceous North and South America from Atlantic construction three microplates between rocks that compose parts of central and sea-floor magnetic anomalies, and the re- North and South America, thus avoiding western Cuba migrated northward toward quirement that the major transform faults the overlap of the Bullard fit. These plates their present positions. Rotation of Yuca- be compatible with the poles of rotation are the Yaqui, bounded on the north by tan was facilitated by considerable dis- for the appropriate relative motions be- the Mojave-Sonora megashear; the east placement along the proto-Motagua zone tween North and South America. Paleo- and west Maya plates, bounded on the and along a zone that is probably coinci- magnetic data from Middle America are north by the Mexican volcanic zone and dent with the modern Salina Cruz fault. sparse but do not conflict with the pre- on the south by a predecessor of the Accumulation of widespread major salt dicted motions of some of the microplates, Motagua fault zone; and the Chortis plate units of Late Jurassic (Callovian to early especially Chortis. (parts of Guatemala and Honduras). Dur- Oxfordian) age in the Gulf Basin probably ing Late Jurassic time, as North America occurred contemporaneously with the ar- INTRODUCTION split away from Europe, Africa, and rival of these blocks at their present posi- South America, shear, with left-lateral tions. Clastic units that interfinger with The Mojave-Sonora megashear, whose sense of displacement, occurred along the some of the youngest salt units and rim existence is suggested by interruption of transform faults that bounded the micro- the Gulf of Mexico have not recorded northeasterly striking Precambrian tecton- plates. major recognized translations since their ic belts, was defined by Silver and Ander- accumulation. If ~800 km of left-lateral displacement son (1974) as a zone of major apparent along the Mojave-Sonora megashear, Clockwise rotation of South America left-lateral offset. This zone of disruption -300 km along the Mexican volcanic belt, and the Chortis plate occurred during appears to extend S50°E from the south- and ~ 1,300 km along a proto-Motagua Early Cretaceous time. This movement, ern Inyo Mountains, California, across the megashear are restored, and if Yucatan which was manifested by subduction of Mojave, Colorado, and Sonoran Deserts, and Cuba are rotated to fit against north- Jurassic ocean floor against the previously into the Sierra Madre Occidental of So- ern South America, then (1) a curvilinear rifted precursor of the island of Cuba and nora, northeast of Hermosillo (Fig. 1). belt of late Paleozoic rocks that show under parts of Hispaniola and Puerto Examination of the regional distribution lithologic as well as paleontologic similari- Rico, is recorded by circum-Caribbean of overlying late Precambrian and Paleo- ties extends across the reconstruction and orogeny. zoic rocks resulted in recognition of trun- links outcrops in Texas, eastern Mexico, Abrupt changes in the relative motions cation of depositional trends offset in a nuclear Central America, and Colombia; between North and South America during sense compatible with the megashear. (2) a Mediterranean-like sea is delineated Late Cretaceous time may have resulted in Provocative similarities between strati- that was a precursor of most of the pres- extension and outpourings of basalt upon graphic columns in the Inyo Mountains- ent Gulf of Mexico; (3) correlation is the Jurassic rocks of the ocean floor of Death Valley region and the area around implied between the distinctive quartzose the Venezuelan Basin. West of Beata Caborca, Mexico, on opposite sides of the San Cayetano Formation of Cuba and the Ridge, sea-floor spreading formed the Co- dislocation zone, suggest 700 to 800 km of Caracas and Juan Griego Groups of lombian Basin. Related subduction oc- left-lateral offset. Arguments based upon: Venezuela. curred as the Chortis plate (including part (1) the tectonic and stratigraphic history Supplementary data (Appendix) for this article are available upon request from the GSA Documents Secretary. Ask for Supplementary Data 83-13. Geological Society of America Bulletin, v. 94, p. 941-966, 18 figs., 1 table, August 1983. 941 Downloaded from http://pubs.geoscienceworld.org/gsa/gsabulletin/article-pdf/94/8/941/3419296/i0016-7606-94-8-941.pdf by guest on 29 September 2021 942 ANDERSON AND SCHMIDT along the continental margin of western complementary fractures to the south and ment are similar to the model presented North America, (2) extensive U-Fb iso- suggest an early Mesozoic configuration by Salvador and Green (1980), although topic age data from Mesozoic rocks near for the part of Pangea that includes Mid- our directions of approach to the problem the shear zone collected in large part by dle America and the Gulf of Mexico- were very different. L. T. Silver, and (3) stratigraphic relation- Caribbean Sea region. The second half of ships in eastern Mexico suggest that this this article presents a hypothetical post- DEFINITION AND CONSTRAINTS inferred structure developed during the Triassic geotectonic evolution for the same OF PROPOSED CRUSTAL BLOCKS Callovian and Oxfordian Stages about 150 area that relies upon the motions sug- m.y. ago. (Note: The assignment of abso- gested by Ladd (1976) as applied to our From the segment defined by Silver and lute ages to stages is based upon the time proposed reconstruction. We strive to Anderson (1974) in northwestern Mexico, scales published by Van Hinte, 1976a, show that the model and its subsequent the Mojave-Sonora megashear is projected 1976b). evolution are strikingly compatible with northwest as suggested by L. T. Silver At the National Meeting of the Geolog- available geologic data as summarized by (1974, personal commun.). Additionally, ical Society of America in 1974, L. T. Lopez-Ramos (1969, 1974), de Cserna an eastward extension of the megashear Silver initially pointed out that sinistral (1960, 1971a), Dengo (1975) and P. O. that occupies a zone defined by the dis- translation along the Mojave-Sonora meg- Banks (1975). turbed patterns of distribution of Precam- ashear offers an intriguing partial solution The hypothesized configuration leads to brian, Paleozoic, and Mesozoic rocks to the seemingly intractable problem of a viable model for the evolution of the across Mexico is proposed (Fig. 1). the overlap of southern Mexico across Gulf of Mexico and the Caribbean region northern South America encountered with during post-Triassic time. The timing and the Pangea reconstruction for early Meso- style of the orogenic events in this region zoic time (Bullard and others, 1965). Sil- reflect the relative motion of South Amer- Figure 1. Index map showing the ver also recognized that viable plate-tec- ica with respect to North America (Ladd, distribution of outcrops of some crys- tonic models of the evolution of the Gulf 1976). An overview of the relationship of talline and sedimentary rocks men- of Mexico would be a product of transla- plate motion to North and Central Ameri- tioned in the text, as well as other tion along the Mojave-Sonora megashear. can tectonism was initially presented by relevant places and geologic and phys- Our model, although distinct from Silver's Coney (1972), who recognized some of the iographic features. Basement con- suggested plate geometries, is a direct out- motions described by Ladd (1976) and figuration in southwestern North growth of his discussions. who emphasized their role in evolution of America based upon radiometric the North American cordillera. The timing studies by L. T. Silver (1968; Ander- OBJECTIVE and sequence of most of the major evolu- son and others, 1971; Anderson and tionary events of the formation of the Silver, 1976; Silver and Anderson, We propose the existence of an easterly Gulf of Mexico as we view its develop- 1974). Mojave-Sonora megashear is extension of the megashear as well as northwesterly trending heavy line. Probable western margin of sheets of Paleozoic rocks thrust toward the craton in the southern United States and eastern Mexico is represented by heavy solid line (Flawn and others, 1961) or inferred by heavy dashed line (de Cserna, 1971b). Horizontally ruled areas indicate regions where comparable sections of late Precam- brian and Cambrian strata are known (Eells, 1972). 1. Llano uplift. 2. Mara- thon basin. 3. Van Horn region, west Texas. 4. Sierra del Carmen. 5. Soli- tario uplift. 6. Mina Plomosas-Placer de Guadalupe.