Determining the tempo of exhumation in the eastern Himalaya: Part 1. Geometry, kinematics and predicted cooling ages. (20th September 2021)

• Record Type: Journal Article
• Authors: Braza, Mary; McQuarrie, Nadine
• Is Part Of: Basin research. Volume 34:Number 1(2022)
• Page Start: 141
• Page End: 169
• Publication Date: 2021-09-20
• Subjects: exhumation rate -- fold thrust belt -- foreland basin modelling -- thermal‐kinematic modelling; Sedimentation and deposition -- Periodicals; Sedimentary basins -- Periodicals; 551
• DOI: 10.1111/bre.12615
• Languages: English
• ISSNs: 0950-091X

Abstract

Abstract: Quantitative integration of cross‐section geometry, kinematics and cooling ages requires notably more complicated kinematic and exhumation pathways than are typically assumed with a simple in‐sequence model of cross‐section deformation. Incorporating measured basin thickness and depositional ages, determined from magnetostratigraphy or young detrital zircon fission track cooling ages, provide further constraints on the timing of fault motion, as changes in shortening rate that may not alter bedrock cooling ages can affect the depositional age of foreland basin strata. Thermokinematic models of balanced cross‐sections in Arunachal Pradesh, NE India demonstrate that the kinematic sequence and shortening rate exert the largest control over the pattern of predicted cooling ages for the region, by dictating the location and timing of rock uplift and exhumation (cooling) over ramps. The best fit to the measured bedrock cooling ages and basin constraints is achieved with a kinematic sequence involving early foreland propagation of four Lesser Himalayan faults combined with variable shortening rates. Fast rates (25–30 mm/yr) are required to accompany early foreland propagation at ca. 14–13 Ma followed by slower rates (18–20 mm/yr) until 10 Ma. Shortening rates increase to ca. 25–35 mm/yr at ca. 10 Ma until ca. 5–7 Ma. A decrease in shortening rate occurs between 7 and 5 Ma, with rates of 9–15 mm/yr until the present. Although non‐unique, the updated cross‐section geometry and kinematics highlight the components of geometry, deformation and exhumation that must be included in any valid cross‐section model for this portion of the eastern Himalaya such as the location of active ramps, and location and age of two key fault systems, the Bomdila imbricate zone and the thrust faults that form the Lumla duplex. Less unique are the specific geometries of faults, thickness of strata they carry, shortening rates, particularly between 14–8 Ma, and model parameters such as topography, heat production and flexure. Abstract : Thermokinematic models of balanced cross‐sections integrated with bedrock cooling ages and basin thickness and depositional ages are presented for Arunachal Pradesh, NE India. Model results demonstrate that the location and timing of rock uplift and exhumation (cooling) is largely controlled by the kinematic sequence and shortening rate. Measured bedrock cooling ages and basin constraints are best fit by models with a kinematic sequence involving early foreland propagation combined with variable shortening rates.