Geology: North America's broken heart
On a bright October Saturday, the trees have reached their full autumn blaze at Interstate State Park on the border between Minnesota and Wisconsin in the US heartland. Crowds of people gawking at leaves thread their way along paths that wind through bulwarks of dark basalt, leading to views of the St Croix River. Along one of the walkways, a photographer directs a young couple in coordinating grey shirts to lean against the rocks as she snaps a romantic portrait. If the two sweethearts are looking to commemorate their ever lasting love, they should have picked a different backdrop. The fractured basalt that frames their faces is part of a great gash that opened up in the middle of North America and nearly split the continent 1.1 billion years ago — hardly a symbol of a happy union. The volcanic rocks are remnants of what is called the Midcontinent Rift, and it is an enormous geological puzzle. Rifts are wounds in Earth’s outer layer that can grow to eventually form new oceans. That is how the A billion years ago, a huge rift nearly cleaved North America down the middle. And then it failed. Researchers may be getting close to finding out why.
Possible extension of the Midcontinent Rift in west Texas and eastern New Mexico
The Midcontinent Rift System forms one of the most prominent gravity features in North America. The recognized geophysical anomaly extends in an arc from southern Oklahoma to Lake Superior and then into southern Michigan. The Midcontinent Rift System was active between 1185–1010 Ma, as indicated in the Lake Superior region by age determinations on intrusive igneous rocks. We suggest that the period of formation of the Midcontinent Rift was also a time of extensive igneous activity in Texas and New Mexico. This activity is represented by intrusions beneath the Central basin platform (Texas and New Mexico), intrusions which crop out at the Pajarito Mountain in the Sacramento Mountains (New Mexico), a basaltic debris flow in the Franklin Mountains (Texas), basalt flows at Van Horn (Texas), and the Crosbyton geophysical anomaly (east of Lubbock, Texas). These bodies and other bodies located by geophysical anomalies and wells drilled into mafic Precambrian rocks may be related to the Midcontinent Rift System. ...
Analysis of the Ionospheric Effect for Time Offsets per GPS Code Measurements
This paper shows the analysis results of time offsets using P1, P2 and P3 code in GPS time transfer. The r2cggtts program has been used in GNSS Time Transfer and use the P3 ionosphere free combination of P1 and P2 code measurements. We modified the r2cggtts program in order to calculate and write all kinds of time offsets P3 as well as P1 and P2. The result of the modified r2cggtts program shows that time offsets using P1 and P2 are of wide distribution comparing to time offsets using P3. In order to Figure out the error factors for wide distributions of P1 and P2, we analyze and present the relation between the elevation angle and time offsets in this paper.