H20: Pah Tempe Hot Springs S25, 26 T41S R13W (Feb/1/06):

Layman’s Arena

 This is an interesting hike, covering 2 km in two directions from the Virgin River bridge. It shows drastic changes in rock type and age within a short distance, and is entirely along the roaring river. The hike upstream along the roadway is simple and the cliffs of the Kaibab limestone loom overhead, where the change from the red sandstones to the lofty cliffs of the drab limestones is obvious. This hike displays the change from the sandstones of the Mesozoic (middle life) to the shallow sea deposits of the Paleozoic (old life) in stark detail as you cross the Hurricane fault. The highlands to the east are uplifting almost a millimeter per year, and the water flows down from the drainage area where it is heated at depth and emerges in Pah Tempe Hot spring. At the fault plane, there is a cross-canyon to the south, along which you can see the direction of the fault orientation (north to south).

 After viewing the turbid waters of the springs, as they dominate the Virgin River, one may walk west along the north side of the river, to hike in the rugged canyon with its vertical basalt walls. This is a more challenging hike, and one is advised to take a hiking stick to surmount the large boulders in the path. One kilometer to the west the basalts cover some sedimentary rocks half-way up the cliff walls to the south. These are conglomerates and sandstones, which were present when the lavas first began to flow. All of this occurred in the last million years, and the basalts may be measured for radioactive isotopes, to determine the age of vulcanism.

 Take your lunch, for a respite along the beach and cliffs, at about the one km. distance. The river water is still warm, 60-70 degrees Fahrenheit, and one can wash off the film of the day, but be prepared to smell rotten eggs (mercaptens, or hydrogen sulfide) the entire trek.

Technical analysis

 Pah Tempe facility is currently closed- due to diminishing water flow caused by losses to water wells- nevertheless, there is an obvious odor of rotten eggs wafting both upstream and down the Virgin Canyon. This H2S can be due to the chemically-reducing environment along the Hurricane fault, but can also be due to bacteria breaking down the SO4 in the groundwater. The temperature is abnormal, and indicates that the environment of its source is chemically reductive, as well as hot for its depth.

 Normally, in the CP, the temperature gradient from wells is about 1.5 degrees F/100 feet of depth (as opposed to 1.0 in basins which are not mechanically active). For this 107F spring, considering that 65F is the mean annual temperature of the ground surface, this would indicate that it originated no deeper than about 3000 feet below the ground surface. The more likely circumstance is that the water immediately arrives from a much shallower depth, and that the heat is abnormal, geothermally. In the
Gulf Coast, where geothermally-hot salt domes are frequently found, the salt (mainly NaCl and CaSO4- anhydrite) is normally encountered drilling at about 1km, where it makes right turns into a mushroom-shaped entity. The right turns are due to the ease of salt moving laterally compared to splitting the earth vertically, when Poisson¡¯s ratio causes the lifting of the overburden to be less strenuous than splitting a zero shear-strength rock. At the km depth, the SO4 is attacked by shallow bacteria (in groundwater), and converted to H2S and yellow sulphur. That this process is reductive, is proved by the fact that there is always limestone (in these silicate, sandstone, rocks) associated with the sulphur, as derived by the relation:

 

CaSO4 + H2CO3, bacteria, aqueous > CaCO3 + S + H2S (loss of oxidation, gain of electrons).

 There are several intermediate steps, involving acidity change, reductive change, and formation of unstable compounds. There is usually some gypsum, CaSO4.H2O, near the calcite, derived from the anhydrite (by hydration of the CaSO4).

 The above process is the likely one happening at thermal springs, with the earth or magmatic waters supplying the acidic waters and excess of electrons. This process is unstable, causing the air to be fetid as the H2S is either absorbed by our nostrils or by an oxidative event. All processes involving smell are caused by excessive vapor pressure, likely due to gases which are temporarily unstable (they stink).

 The mere fact of a geothermal spring is indicative that the zone is geochemically as well as geologically abnormal (anomalous). When this circumstance is encountered, abnormal compounds can be expected to occur in the water, and precipitation of exotic minerals results. Looking at the Virgin River at this location and downstream, one notices that there is unusual turbidity (murkiness, or super-saturation of Ca compounds) in the river water. This feature explains the unusual cementation downstream of young conglomerates, Qc, near the Sky Mountain Golf course- the river precipitates the Ca compounds as it equilibrates with loss of pressure going downstream. Qc has the strength of Pliocene due to the addition of abnormal cementing agents.  I found a similar circumstance at Pamukkale (Cotton Castle Roman ruin) in Turkey, as murky water precipitated travertine along its path toward the lower valley. The Romans made crypts of the travertine, and these are strewed about- showing the T¨¸rks¡¯ disdain for the practices of non-Muslim cultures (I could have carried one away, if my vehicle could have handled a 6¡¯x 3 x2 monstrosity).

 As for geological observations, notice that there are several features which bear on the problem of determining the crustal behavior at the Hurricane fault:

1.     There is a great slump just before encountering the Pah Tempe, exhibiting several dips at odd angles- this is Mesozoic, with gypsum (selenite) allowing us to determine that the formation is in the Triassic Moenkopi Trm, which is typically red, compared to the underlying grey Permian Kaibab Pk;

2.     The Pk dips up to the west going eastward from the Hurricane fault, which is backwards to that expected at an uplift (drag at a normal fault face would be expected to be down-wardly, with uplift of the east block, to cause the dip to be down to the west at the fault boundary);

3.     Fractures in Pk are roughly N-S, as influenced by the stress system at the fault boundary- this is not the same as exhibited by the river bends on either side of the fault (which are 30 degrees from north- NW wardly on the west side, NE wardly on the east side). Evidently the fault does not fit with either system, and I expect it to exhibit the New REGIONAL system instituted since Pliocene times;

4.     Basalts lie at various elevations, which would allow the time of emplacement to be determined- the most influential of which is the one at canyon bottom, just to the west of the Hiway 9 bridge. This indicates that there was a canyon, through which the Virgin flowed, in a cycle preceding the present one (basalt would follow river courses, since it was liquid at the time of emplacement);

5.     There is a small side canyon at the Hurricane fault, indicating the direction of faulting, to the south of the Virgin canyon. Look for the vertical beds, which are the main indication of the large fault- other dips may just show the result of slumping or gravity sliding;

6.     We saw vertical beds near the powerhouse, on the banks of the Virgin, some 4000 feet to the west. This indicates that either the fault is moving eastward with time, or that the transition zone is wide.

 

 We hiked downstream after looking at the Pah Tempe spring location, and encountered level conglomerates (two meters) below a sandstone (< a meter thick), both fairly level, conformable, and sitting atop a Mesozoic beveled basement rock, halfway up the Hurricane side of the steep canyon. Both show that the land was much higher in elevation and fairly flat with low stream gradient at the time of the sandstone deposition. These will be investigated by climbing down from the Hurricane side of the Virgin in a succeeding week, to answer the questions of orientation by imbrication and whether the stream was the ancestral Laverkin or the Virgin. Other than the two outcrops of pre-basalt sedimentary rocks, basalts were monotonously omnipresent- all the way down to the river level. The Pc conglomerate is midway up the cliffs, and unattainable from the Laverkin side of the river. This is a key outcrop, since if there is Pine Valley intrusive cobbles in the formation, this will show that there was no significant impediment between PV Mtns and this old drainage. This is probably an old Ash or Laverkin channel, which we will try to prove was the principal drainage in Pliocene (>2mybp) time. The Virgin would have captured the old drainage after breaking through the Hurricane scarp in Pleistocene time.

 I studied the analysis of the Pah Tempe spring water, to determine whether there is other information which might bear on the incipience of the Hurricane fault. From 10 water samples, I averaged the composition, to obtain cations and anions:

Pah Tempe Hot Springs ions, compared to cold springs & ocean water

 

10 sets

pH units

TDS mg/l

Na mg/l

K mg/l

Mg mg/l

Ca mg/l

Cl mg/l

HCO3 mg/l

SO4 mg/l

Ave.

6.9

9800

2410

187

126

805

3440

1200

1770

Ratio

Sl.acid

Bays

.7xCl

.05xCl

.16xCa

.23xCl

1.0

.35xCl

.51xCl

 

Pah Tempe is high in Na+ and Cl, 25% that of ocean water salinity (33,500 ppm), and is high in Mg+ and bicarbonate, indicating a limestone and dolomite source (such as with Pk and diluted original seawater). It is not anomalous in K/Cl (=.02, sea), as would be the case with emergence of a major fraction of the water from hot granite or weathered deep shales and intrusives, from a deep geothermal source. The high bicarbonate suggests a limestone source also, and nothing indicates that the water is derived from the Mesozoic. The only indicator suggesting a deep geothermal influence is the slight acidity (even in the high alkalinity water, with anomalous bicarbonate). Even though the spring occurs near the Hurricane fault, it represents water flowing almost laterally from the highland to the east, from a depth of 1000 meters. The occurrence of F, B, and As was found later, to determine that all were anomalous (they must be greater than 1 ppm, or mg/l, to indicate abnormality, according to my world-wide collection).

 Fluoride averaged 2.54 mg/l, and Boron 5.1, with high silica (28 ppb) and 2.4 mg/l PO4 for Pah Tempe. These indicate a deep magma influence, causing acidic waters to be mixed with the dominant carbonated shallow groundwater. The F likely comes from hydrofluoric acid, with the Phosphorous from phosphoric acid from magmatic waters; Boron and high silica (both of which have solubility increasing with T) derive from dissolution of tourmaline or other intrusives.

 The only other anomalous feature for the spring water is the high salinity and Na+ content. For water derived from vulcanism, with HCl the dominant acid:

 

HCl + Na rocks > NaCl + H2O, with one mol of water for every mol of salt.

 

For the above relation, Na/Cl =.65 by molecular weight, = .556 in ocean water, by measurement. For Pah Tempe, it is .7, an excess of sodium ion. Usually Chloride ion is dominant, for ground waters, and this spring has encountered NaCl along its path as well as some other sodium salt. The TDS excess is probably from evaporite beds mixed with the Pk or Pt (Kaibab or Toroweep), both of which are known to have gypsum and dolomite (and probably bedded salt as well). It is suspected that salinity of ocean water has increased with time, due to the vulcanism relation shown above, and the 10,000 ppm measured may have been the salinity in Permian times. It is difficult to find an untrammeled salinity measurement from Paleozoic rocks, since dilution by meteoric waters, concentration by squeezing out water, and various osmotic, filtering, and reactions with the host rock occur with time. Presently, ocean water has about 33,500 ppm on average, but has other concentrations when occurring in closed seas (such as the Caspian and evaporating basins). For vulcanism as the dominant entity creating new water and salt, the ocean concentration would be at salt saturation (200-300,000 ppm) if the seas were not diluted by water from other mechanism. My general classification of groundwater is as follows, for large sedimentary basins:

A.   The shallowest are Meteoric, readily circulating waters from downward percolation- which are bicarbonated waters of low salinity. Normally this zone occurs no deeper than 1 km;

B.    The next deeper zone (Mineralized waters) is that of increasing mineralization, mainly Na+Cl, as T & p increase. This continues with depth until reaching a critical compaction (the base of this zone may be 2-3 km);

C.   Then Chemically-reduced waters occur, depending upon stagnancy and T (near normal boiling). A calcite cap usually signals the entry into the zone. These harbor pyrite, hydrocarbons, sulfur, and other compounds unstable at the ground surface;

D.   Finally, at high temperature (> 300F), Acidic waters are found. All of these zones are sensitive to T, p, and composition & grain size of the containing rocks. Fine grain sediments allow exotic compounds and original waters to remain longer.

 In summation, Pah Tempe spring water is predominantly from carbonate rocks, but has been concentrated by influx of acidic waters of magmatic origin. Heat increases the solubility of most salts, while decreasing that of limestone and dolomite. This helps to establish that there is still a deep magma below Hurricane, which is feeding the vulcanism and uplift. The fact that the sedimentary beds dip upwardly to the west indicates that the magma is narrow in scale relative to the depth at which it occurs (probably at the crustal base, 100 km down). It can best be described as a lengthy (>100 km) narrow (< 10 km) shaft of hot magma, exploiting a laterally-thinning crust (to the west), which has an old weakness retained from earlier tectonics. Maslov and Anokhin, in Planetary and Space Science, suggest that deceleration of the earth¡¯s ellipsoid configuration causes major faults and fractures to occur along N-S and E-W orientations, while shear, such as with the West USA, occurs on NW-SE or NE-SW linears.