Exhumation of the Coastal Metamorphic Belt Above the Subduction‐to‐Transform Transition, in the Southeast Caribbean Plate Corner

Abstract

Plate corners that transition from subduction to transform motion can result in complex deformation. The southeastern corner of the Caribbean plate is a site where active westward subduction of the oceanic South American plate transitions to transform motion along continental South America. The Northern Range (Trinidad) and Paria (Venezuela) metamorphic mountains are located directly above this eastward propagating plate transition zone. We examined the exhumation history of the Northern Range and eastern Paria using apatite fission track (AFT) and apatite and zircon (U‐Th)/He (AHe and ZHe, respectively) thermochronology on 21 bedrock samples. These samples yield ages of ∼43–6 Ma (ZHe: aliquots), ∼20–4 Ma (AFT: pooled) and ∼5–2 Ma (AHe: aliquots). Along strike of the mountains, our new and published samples show a gradual eastward increase in age. Thermal modeling reveals two phases of rapid cooling and inferred exhumation that post‐dates oblique collision and that migrated from west to east. We record an ∼six‐fold increase in cooling and exhumation between ∼13–9 Ma in the Paria Peninsula and western Northern Range; a deceleration followed this rapid exhumation at ∼7 and 5 Ma. Synchronous with the deceleration in the west, exhumation of the eastern Northern Range increased ∼4 Ma. These post‐collisional changes in exhumation constrain the inversion to east‐side‐up tilting of the Northern Range to ∼4 Ma. We interpret the timing and pattern of exhumation since the mid‐Miocene to be consistent with the time‐transgressive processes produced by an eastward propagating lithospheric subduction‐transform edge propagator fault.

Geothermometric constraints on the thermal architecture, metamorphism, and exhumation of the Northern Range, Trinidad

“…Thus, the activity of the Chupara Fault may be linked to the exhumation of the more deeply buried rocks in the western Northern Range that we document using RSCM data, perhaps as the STEP front migrated eastward (Figure 9c). Thermal models, erosion data, and other regional geomorphic data also indicate that differential cooling and exhumation inverted around 4.5 Ma (Arkle et al, 2017, 2021). The STEP edge at this time (c. 4.5 Ma) would have moved sufficiently far to the east, became insignificant in the Northern Range, and brought the activity along the Chupara Fault to an end (Figure 9d).…”

“…The bedrock cooling models of Arkle et al (2021) indicate that a significant amount of postcollisional cooling and exhumation occurred in the western Northern Range from c. 10–4.5 Ma, while little cooling and exhumation occurred in the east during that same time period. Arkle et al (2021) further speculate that the STEP edge passed eastward under Trinidad following the oblique collision (Figure 9c), creating a series of late‐stage, en echelon normal faults that accommodated the overall strike‐slip (transform) motion that is also pervasive throughout the Northern Range, Trinidad (Algar & Pindell, 1993; De Verteuil et al, 2005), and northeastern Venezuela (Cruz et al, 2007). We propose that the Chupara Fault may be such a postorogenic, extensional feature (Figures 2, 7a, and 9c).…”

“…Zircon fission‐track (ZFT) data from the Northern Range show a general pattern with reset ages of c. 12 Ma in the west (Figure 8b), whereas most eastern zircons are un‐reset and display ages ranging from c. 80 to 200 Ma (Algar et al, 1998; Arkle et al, 2021; Weber, Ferrill, & Roden‐Tice, 2001). Our new RSCM temperatures from both the east and west (310°C to 450°C) all exceed the ZFT closure temperature of 240°C ± 30°C (Brandon et al, 1998).…”

“…In the east, the cooling path following peak metamorphism, and possibly its timing, remains largely unconstrained due to the disparity between unreset ZFT ages and high RSCM temperatures, potentially indicating a short-lived thermal event. Dark and light grey lines are the expected cooling histories of the high and low elevation samples, respectively, with the shaded regions representing a 95% confidence interval (Arkle et al, 2021).…”

3D geodynamic-geomorphologic modelling of deformation and exhumation at curved plate boundaries: Implications for the southern Alaskan plate corner

“…Finally, it is noteworthy that the configuration of our model is applicable to plate corners where the downgoing plate subducts and collides along a concave boundary relative to the overriding plate, as in southern Alaska 18 , 33 , 34 , 43 , while a convex shape of the convergent boundary 93 , such as in the Southeast Caribbean plate corner 94 , remains outside the scope of our study.…”