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Progressive Metamorphism of Permian Siliceous Limestone and Dolomite

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Progressive Metamorphism of Permian Siliceous Limestone and Dolomite New Mexico Geological Society Downloaded from: http://nmgs.nmt.edu/publications/guidebooks/31 Progressive metamorphism of Permian siliceous limestone and dolomite - a complete sequence around a monzonite intrusion, Marble Canyon, Diablo Plateau, west Texas Thomas E. Bridge, 1980, pp. 225-229 in: Trans Pecos Region (West Texas), Dickerson, P. W.; Hoffer, J. M.; Callender, J. F.; [eds.], New Mexico Geological Society 31st Annual Fall Field Conference Guidebook, 308 p. This is one of many related papers that were included in the 1980 NMGS Fall Field Conference Guidebook. Annual NMGS Fall Field Conference Guidebooks Every fall since 1950, the New Mexico Geological Society (NMGS) has held an annual Fall Field Conference that explores some region of New Mexico (or surrounding states). Always well attended, these conferences provide a guidebook to participants. Besides detailed road logs, the guidebooks contain many well written, edited, and peer-reviewed geoscience papers. These books have set the national standard for geologic guidebooks and are an essential geologic reference for anyone working in or around New Mexico. Free Downloads NMGS has decided to make peer-reviewed papers from our Fall Field Conference guidebooks available for free download. Non-members will have access to guidebook papers two years after publication. Members have access to all papers. This is in keeping with our mission of promoting interest, research, and cooperation regarding geology in New Mexico. However, guidebook sales represent a significant proportion of our operating budget. Therefore, only research papers are available for download. Road logs, mini-papers, maps, stratigraphic charts, and other selected content are available only in the printed guidebooks. Copyright Information Publications of the New Mexico Geological Society, printed and electronic, are protected by the copyright laws of the United States. No material from the NMGS website, or printed and electronic publications, may be reprinted or redistributed without NMGS permission. Contact us for permission to reprint portions of any of our publications. One printed copy of any materials from the NMGS website or our print and electronic publications may be made for individual use without our permission. Teachers and students may make unlimited copies for educational use. Any other use of these materials requires explicit permission. This page is intentionally left blank to maintain order of facing pages. New Mexico Geological Society Guidebook, 31st Field Conference, Trans-Pecos Region, 1980 225 PROGRESSIVE METAMORPHISM OF PERMIAN SILICEOUS LIMESTONE AND DOLOMITE-A COMPLETE SEQUENCE AROUND A MONZONITE INTRUSION, MARBLE CANYON, DIABLO PLATEAU, WEST TEXAS THOMAS E. BRIDGE Department of Physical Science Emporia State University Emporia, Kansas 66801 INTRODUCTION IGNEOUS ROCKS The Marble Canyon elliptical intrusion ranges in composition The igneous intrusion consists of a central mass of light-colored from syenite at the center to olivine-bearing monzonite with a dis- syenite surrounded by green monzonite (M,) and a gray mon- continuous biotite gabbro border phase near the contact. The zonite (M,). Felsic dikes cut the monzonites, syenite and contact contact aureole contains the complete sequence of previously rocks (fig. 1). described anhydrous mineral phases resulting from temperature The central syenite is coarser grained than are the other rocks. gradients in metamorphosed siliceous limestone and dolomite. Potassium-enriched solutions precipitated thick mantles of ortho- This is the first discovery in the United States of a complete se- clase on the previously formed plagioclase (An„) laths and also quence of minerals described by Bowen (1940) and Tilley (1923) as filled the interstices between crystals with orthoclase. Deuterically occurring with increasing temperatures in siliceous limestones and altered biotite is present as an accessory mineral. dolomites. The polymorphic forms of dicalcium silicate Ca 2SiO4, a The green monzonite surrounding the intrusion contains plagio- (bredigite), 13 (larnite), and y occur together in the contact zone in clase (An„) with a thin mantle of orthoclase. Relatively fresh Marble Canyon and were described by Bridge (1966a, b). biotite crystals and scattered grains of partly altered olivine and hornblende are also present as accessory minerals. LOCATION AND SETTING The gray resistant monzonite contains large, well oriented laths Marble Canyon is in the east rim of the Diablo Plateau in Culber- of plagioclase (An„) free of orthoclase mantles. Smaller crystals of son County, Trans-Pecos Texas, 30 miles north of the town of Van orthoclase are concentrated between laths of plagioclase. The Horn and two miles west of State Highway 54. The canyon was cut gray monzonite forms a resistant ridge around the intrusion and by an intermittent stream flowing eastward down the Diablo fault looks like a dike. The well oriented plagioclase laths and absence scarp, which marks the east boundary of the Diablo Plateau. The of deuteric alteration around the ferromagnesian minerals sug- mouth of the canyon is about 300 m wide, and its walls range from gests a late-stage injection as a ring dike around a previously 60 to 180 m high. The narrow part of the canyon is about 1.5 km solidified central mass. long and terminates upstream in an elongate amphitheater The last stages of activity are represented by felsite dikes that cut roughly 2 km long and 1 km wide. all older syenite, monzonite and gabbro in the Marble Canyon in- The center of the elongate amphitheater is a small igneous intru- trusion. The Cave Peak intrusion is about a mile from the Marble sion surrounded by a bleached contact zone ranging in width from Canyon intrusion and probably formed at the same time. 70 to 180 m. The exposed contact zone includes the Permian Field relationships, such as the position of the intrusion with Hueco and Bone Spring Formations. respect to the Diablo escarpment, and bleached surfaces along The Hueco Formation is 270 m thick in Marble Canyon (King, joints also indicate that, at the time of emplacement, the intrusion 1962, measured section) and unconformably overlies older Paleo- was near enough to the surface so that the vapor pressures were zoic rocks. The basal Powwow Member of the Hueco is 60 m thick low. and consists of interbedded clastics and carbonates. The clastic A discordant contact and local horizontal extensions of the mar- rocks range from coarse chert pebble conglomerate to coarse ble over the igneous body indicate that the emplacement of the arkosic sandstone. The upper 214 m of the Hueco consists of mas- intrusion was accompanied by stoping, and that the intrusive rock sive dolomitic limestone with occasional shale partings, chert did not rise much above the present floor of Marble Canyon. nodules, and fossiliferous intervals. The contact zone on the Faulting along the marble-gabbro contact in several places is indi- northeast side of the intrusion is in the Hueco, and the Hueco at cated by slickensides on the contact and by fault gouge between this locality is an almost pure dolomite. The exposed part of the the gabbro and marble. contact zone at all other localities is in the Bone Spring Formation. The Cave Peak intrusion (Warner and others, 1959), about three- The Bone Spring Formation is 742 m thick and consists of len- quarters of a mile northeast of the Marble Canyon intrusion, is ticular massive beds of dolomitic limestone interfingering with thin composed of breccias of rhyolite and trachyte porphry, nonbrec- cherty beds of fossiliferous limestone. The thin platy cherty car- ciated felsite (largely rhyolite), and a central core of granite. bonates range in composition from a dolomitic limestone to an Associated with this intrusion are several rhyolite dikes, the largest almost pure magnesian limestone. The platy limestone is locally of which cuts across the entrance to Marble Canyon and dips interbedded with thin shales. toward the Marble Canyon intrusion. 226 BRIDGE ......4F:......... /05• _...._. ti 1 --- / • • —04-Wit.0, — ----c-------;-- ,•-‘v.",i- .: - I - . ---- WPziliab WERRA Wilt TA .-.„-77r 1.■ IR pi., . .> •c"-4-: •---- ,. - -,- 5 8,Iil •iietk., -._77.,„_,, , 0,-.4— f 4. .1- Babb Ranch I 1. l‘s, --- --r-2,(,-/---ty,•.-,...--8 , . .-/••••!.. t4..,P. 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