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Bulletin of the Geological Society of America Vol BULLETIN OF THE GEOLOGICAL SOCIETY OF AMERICA VOL. 68. PP. 1669-1682. 1 FIG. DECEMBER 1957 MAGMATIC, CONNATE, AND METAMORPHIC WATERS BY DONALD E. WHITE ABSTRACT Some major types of water of "deep" origin are believed to be recognizable from their chemical and isotopic compositions. Oil-field brines dominated by sodium and calcium chlorides differ markedly from average ocean water. In general, the brines are believed to be connate in origin ("fossil" sea water) with a negligible to high proportion of meteoric water. Many brines, particularly in pre-Tertiary rocks, are much higher in salinity than sea water and are greatly enriched in calcium as well as sodium chloride. Brines near the salinity of sea water are generally higher, relative to sea water, in bicarbonate, iodine, boron, lithium, silica, ammonium, and water-soluble organic compounds, and lower in sulfate, potassium, and magnesium. Many changes take place after sea water is entrapped in newly deposited marine sedi- ments: (1) Iodine, silicon, boron, nitrogen, and other elements have been selectively con- centrated in organisms that decompose during and after burial in sediments. Many of the elements may redissolve in the interstitial water. (2) Bacteria are active in the sediments and reduce sulfate to sulfide and produce methane, ammonia, carbon dioxide, and other products. (3) Some elements have been selectively removed from sea water by inorganic processes, such as adsorption on clays and colloidal matter. When this matter is reconsti- tuted by diagenetic and other changes, some components are redissolved. The abundance of lithium and possibly boron and other elements may be controlled to a considerable ex- tent by these inorganic processes. (4) The interstitial water may react chemically with en- closing sediments and produce dolomite, reconstituted clays, and other minerals. The high loss of magnesium relative to calcium in most connate waters is probably caused by such reactions. Volcanic hot-spring waters of different compositions have been discussed in an ac- companying paper (White, 1957). The most significant type is believed to be dominated by sodium chloride, and is best explained as originating from dense gases driven at high temperature and pressure from magma and containing much matter of low volatility that is in solution because of the solvent properties of high-density steam. This dense vapor is condensed in and greatly diluted by deeply circulating meteoric water. Most other types of volcanic water are believed to be derived from the sodium-chloride type. Volcanic sodium-chloride waters are similar in many respects to connate waters but are believed to be distinguishable by relatively high lithium, fluorine, silica, boron, sulfur, COz, arsenic, and antimony; by relatively low calcium and magnesium; and by lack of hy- drocarbons, water-soluble organic compounds, and perhaps ammonia and nitrate. Rela- tively high boron and combined COj are alone not reliable indicators of a volcanic origin. During compaction, rocks lose most of their interstitial high-chloride water; much additional water may then be lost during progressive metamorphism, and the content changes from about 5 per cent in shale to perhaps 1 per cent in gneiss. This expelled water is here called metamorphic. Because of pressure and permeability gradients, it must normally escape upward and mix with connate and meteoric water. Even though large quantities must exist, no example of metamorphic water has been positively identified. Some thermal springs in California are high in salinity and relatively low in tempera- ture and apparent associated heat flow. Some are clearly connate in origin. Other springs are characterized by very high combined carbon dioxide and boron, relative to chloride. Their compositions are considerably different from known connate and volcanic waters and are believed to be best explained by a metamorphic origin. Although some major types of deep water seem to be recognizable, there is much danger of oversimplifying the problems. Many waters are no doubt mixtures of different types, and some of high salinity result from dissolution of salts by meteoric water. 1659 Downloaded from http://pubs.geoscienceworld.org/gsa/gsabulletin/article-pdf/68/12/1659/3431726/i0016-7606-68-12-1659.pdf by guest on 01 October 2021 1660 D. E. WHITE—MAGMATIC, CONNATE, METAMORPHIC WATERS CONTENTS TEXT Page Thermal waters of mixed origin 1679 Introduction 1660 Conclusions and speculations 1679 Statement of the problem 1660 References cited 1679 Acknowledgments 1661 Definitions 1661 Terms defined elsewhere 1661 ILLUSTRATIONS Meteoric water 1661 Connate water 1661 Figure Page Metamorphic water. 1662 1. Simplified diagram illustrating the relation- Juvenile water 1662 ships of genetic types of water considered Comparison of ocean, connate, and volcanic in this paper 1662 waters 1662 Method of approach 1662 Temperature and heat flow 1663 TABLES Isotopes of the waters 1663 Total dissolved solids 1667 Table Page Halogen elements 1668 1. Analyses of oil-field brines of the chloride Alkali elements 1668 types, compared with ocean water 1664 Sulfur 1669 2. Analyses of volcanic hot springs of the Carbon dioxide 1670 sodium-chloride type, compared with Boron 1671 average igneous rocks 1665 Combined nitrogen 1671 3. Tentative criteria for recognition of major Hydrocarbons and other organic com- types of ground water of different pounds 1672 origins 1666 Silica 1672 4. Approximate ranges in chemical compo- Alkaline-earth elements 1673 nents of ocean water, oil-field brines Other elements 1673 dominated by chloride, and volcanic Nonvolcanic hot springs 1674 sodium-chloride springs 1666 Discussion 1674 5. Analyses of thermal waters believed to Hot springs with connate water 1674 contain water of connate or metamorphic Hot springs with metamorphic water 1678 origin 1676 INTRODUCTION but individual analyses (p. 630) range from 0.4 to 1.8 per cent. For comparison, average grano- Statement of the Problem diorite, which is at least in part ultrametamor- phosed or fused sedimentary rock, contains only Many thermal springs occur in areas of re- 0.65 per cent of water (Nockolds, 1954, p. cent or active volcanism, are high in tempera- 1014). The evidence is clear that very large ture and in associated total heat flow, and have quantities of connate and metamorphic water chemical characteristics that indicate a close must be driven off from sediments during com- relation to volcanism (White, 1957). Other paction, progressive metamorphism, and recon- springs have only low to moderate temperatures stitution to minerals containing little water. but are more highly mineralized than ordinary Some of this water no doubt reaches the surface ground waters. Do some of these springs also in thermal springs. contain volcanic water, or is the mineral matter Some effort has been made in the past to derived from nonvolcanic sources? This is part distinguish ocean water from oil-field brines of a broader problem: How many different ge- (Revelle, 1941; Vinogradov, 1948; Piper et al. netic types of ground water exist, and what 1953, p. 90-92). The characteristics of volcanic means are available to distinguish each from or magmatic water as compared with the waters the others? driven from sediments are much less well When fine-grained marine sediments are de- known. posited, their initial water content is commonly The writer has considered magmatic or vol- 50 per cent or more of the wet weight (Emery canic waters of different types in an associated and Rittenberg, 1952, p. 747-755). Most of this paper (White, 1957) and concluded that the water is driven off during compaction and pro- sodium-chloride type is derived directly from gressive metamorphism. Clarke (1924, p. 631) high-density vapors at considerable depth and computed the average water content for the fol- is most representative of magmatic emanations. lowing rocks: Shale, 5.0 per cent; slate, 3.8; and Other types seem to be for the most part schist, 2.0. No averages are given for gneiss, derived from the sodium-chloride type. The Downloaded from http://pubs.geoscienceworld.org/gsa/gsabulletin/article-pdf/68/12/1659/3431726/i0016-7606-68-12-1659.pdf by guest on 01 October 2021 INTRODUCTION 1661 volcanic sodium-chloride waters are here com- Fix, S. Muessig, and C. H. Sandberg, who have pared with ocean water and with other possible read the manuscript. A. H. Lachenbruch of the types of "deep" water. Geological Survey has been most helpful with This paper reviews the characteristics of considerations of heat flow of the different different kinds of "deep" water, within the types of thermal springs. Much benefit has also limitations of available data. Analyses contain- been derived from discussions and communica- ing many of the components now believed to be tions with the following members of the U. S. diagnostic are surprisingly scarce. The most Geological Survey: C. S. Howard, V. T. String- diagnostic components seem to be: all the field, H. E. LeGrand, S. K. Love, W. F. White, halogen and alkali elements; all the ionic and C. L. McGuinness, J. H. Feth, J. D. Hem, and molecular species of sulfur, carbon, boron, and F. H. Rainwater. None of these men, however, nitrogen; silica; organic compounds; and iso- should be held responsible for interpretations topes of the water. The alkaline-earth elements and conclusions. and many other metals are of considerable in- terest but are of less diagnostic value because Definitions quantities in natural solutions are so dependent
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