MAPPING BRITTLE STRUCTURES IN THE HOLYOKE BASALT OF THE HARTFORD BASIN USING LIDAR-BASED DEM DATA

Hillslope models constructed from LiDAR-based DEM data (horizontal resolution of 10 feet, and a vertical resolution of 1 foot) reveal a complex pattern of brittle structures in the Jurassic Holyoke Basalt of the Hartford Basin in central Connecticut. The basalt is exposed over vast areas by glacial scouring, and has little till cover or soil development. The brittle structures are manifested as combinations of linear depressions and/or cliff faces that extend up to 2 km in length and are interpreted to be fractures or faults; data from published geologic maps reveal fault structures that are parallel to the DEM features. On the maps, the basalt is offset by large-scale faults into discrete km-scale blocks along the N-S trend of the basin. The mapped brittle structure patterns vary significantly from fault block to fault block, and across the basin. Within some fault blocks, the structures are pervasive, with a spacing of 50m to >200m, while in other blocks, spacing is random.

Brittle structure orientations typically have a 30° to 35° conjugate angle and vary from north to south as follows. The Penwood block in Bloomfield has two well developed sets of structures that trend 355° and 025°, (So: 010°, 20°SE); while in the King Phillip Mountain block near Farmington structures trend 340° and 015°, (So: 005°, 15°SE). In the Shuttle Meadow block near New Britain, structures trend 015° and 050° (So: 000°, 15° SE) while in the Hanging Hills block north of Meriden, structures trend 020° and 055° (So: 270° to 350°, 5° to 15° NE). In the Lamentation block east of Meriden, structures trend 035° and 070° (So: 020°, 14° SE) and in the Higby block west of Middletown and to the south, only one well-developed set of structures trending 070° (So: 010°, 10° SE) is recognized.

All of the structure trends parallel previously mapped fault patterns that have been related to discrete deformation events within the Hartford Basin. However, at this point, we cannot confirm that the observed features are related to these events. The general similarity in bedding strike and dip between fault blocks suggests that the brittle structure patterns are not the result of fault block rotations. If the mapped structures are faults, the cumulative strain accommodated by these structures may be significant. Further field work will be done to confirm the origin of these features.