LITHOSPHERIC SCALE STRUCTURAL VARIATIONS ACROSS THE CHEYENNE BELT

Study of the lithospheric scale structure across the Cheyenne belt from the CD-ROM and Lodore/Deep Probe PASSCAL teleseismic experiments reveal changes in crustal structure and thickness that suggest the Cheyenne belt is preserved as a steeply dipping structure, while the belt's mantle signature is not preserved. The crustal observations show that the 1.7 ga collisional processes between Archean and Proterozoic lithosphere ultimately resulted in a steep suture between the crust of the two "collidors". Why a Cheyenne belt signature is preserved in the crust, and not the mantle, is most simply explained by overprinting of the mantle suture structure by subsequent orogenies (the Laramide and Late-Cenozoic heating).

The change in crustal structure across the Cheyenne belt is evidenced by the crustal images created via processing teleseismic P-wave coda to isolate converted P to S arrivals. Both our Cheyenne belt crustal transects show a break in crustal structure and thickness approximately below the surface expression of the suture: Evidence for the Cheyenne belt being a steeply dipping, crustal scale, structure. The lack of a mantle signature across the Cheyenne belt is evidenced by teleseismic P-wave images from the Deep Probe teleseismic arrays and shear wave splitting results from the Lodore/Deep Probe and CD-ROM arrays. The teleseismic P-wave residuals show no major step in upper mantle P-wave velocities across the Cheyenne belt. Likewise, the shear wave splitting results show that that no large variation in mantle anisotropy is present across the Cheyenne belt. However, it is important to note that our northernmost seismic sampling ends only 150 km north of the Cheyenne belt (at the "Geochron Front"). Thus, our sampling never crosses into northern Wyoming and hence our results do not rule out the possibility that a mantle boundary exists to the north of our sampling (North of Riverton).